KR20150081936A - A cathode active material secondary particle and lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to a cathode active material secondary particle and a lithium secondary battery including the same and, more specifically, to a cathode active material secondary particle formed by aggregating a cathode active primary particle including nickel-manganese-cobalt (NMC) acid lithium, and a lithium secondary battery including the same wherein the cathode active material primary particle has an average particle diameter equal to or less than 1 μm, the cathode active material secondary particle has particle size distribution based on the volume D50 of 2-20 μm, and the cathode active material secondary particle regularly forms pores with size of 5-50 nm in the inside. An embodiment of the present invention forms the regular pores having the size in a regular range within the cathode active material secondary particle formed by aggregating the cathode active material primary particle to make an electrolyte uniformly come in contact with the cathode active material primary particle, thereby being capable of fast charging a high capacity and high output lithium secondary battery used in an electric vehicle or the like.

Description

[0001] The present invention relates to a cathode active material secondary particle and a lithium secondary battery including the cathode active material secondary particle,

The present invention relates to a cathode active material secondary particle and a lithium secondary battery comprising the cathode active material secondary particle and more particularly to a cathode active material secondary particle having uniform pores The present invention relates to a distributed secondary battery of a cathode active material and a lithium secondary battery including the same.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs and even electric vehicles are expanding, efforts for research and development of electrochemical devices are becoming more and more specified. The electrochemical device has received the most attention in this respect. Of these, the development of a rechargeable secondary battery has become a focus of attention. Recently, in developing such a battery, Research and development on the design of electrodes and batteries are underway.

Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has advantages such as higher operating voltage and higher energy density than conventional batteries such as Ni-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous electrolyte solution .

Generally, a lithium secondary battery uses a material capable of intercalating and deintercalating or alloying and dealloying lithium ions as a cathode and an anode, and a separator between a cathode and an anode And an organic electrolyte solution or a polymer electrolyte solution is charged into the lithium secondary battery in which the electrode assembly is embedded. Here, the lithium secondary battery generates electrical energy by the oxidation / reduction reaction when lithium ions are inserted and removed from the positive electrode and the negative electrode.

On the other hand, lithium secondary batteries used in electric vehicles and the like must be able to be used for more than 10 years under severe conditions in which charging / discharging by a large current is repeated in a short time, in addition to high energy density and characteristics capable of exhibiting large output in a short time, It is inevitably required to have safety and long-term life characteristics far superior to those of a small lithium secondary battery.

Particularly, since the positive electrode active material used in such a high output lithium secondary battery needs to supply ions quickly and uniformly, it is necessary that a large area of the positive electrode active material is in contact with the electrolyte solution.

However, conventionally available cathode active materials have relatively large pores inside thereof, and the pores are not uniformly formed, and thus there is a problem that the contact between the cathode active material particles and the electrolytic solution is not uniform.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a positive electrode active material secondary particle in which primary particles of a positive electrode active material primary particle are uniformly contacted with an electrolyte solution, Thereby enabling rapid charging and discharging of the battery, and a lithium secondary battery including the secondary particle.

According to an aspect of the present invention, there is provided a positive electrode active material secondary particle formed by aggregating primary particles of a positive electrode active material containing lithium nickel-manganese-cobalt (NMC) Wherein the cathode active material secondary particles have a volume-based particle size distribution D50 of 2 占 퐉 to 20 占 퐉 and pore sizes of 5 nm to 50 nm are formed inside the cathode active material secondary particles And the cathode active material secondary particles are uniformly formed.

According to another aspect of the present invention, there is provided a lithium secondary battery including a cathode including a cathode active material, a cathode including a cathode active material, and a separator interposed between the cathode and the cathode, There is provided a lithium secondary battery comprising the cathode active material secondary particles of the present invention.

Here, the negative electrode active material is a negative electrode active material secondary particle formed by agglomerating negative electrode active material primary particles containing lithium titanate (Li ₄ Ti ₅ O ₁₂ ), wherein the average primary particle diameter of the negative electrode active material is 1 μm or less And the particle size distribution D50 of the negative electrode active material secondary particles may be in the range of 2 탆 to 20 탆.

At this time, the particle size of the lithium titanate may be 0.1 탆 to 1 탆.

The average crystallite size of the primary particles of the negative electrode active material may be 800 ANGSTROM to 1,300 ANGSTROM.

The pore volume per weight of the secondary particles of the negative electrode active material may be 0.01 to 0.02 cm ³ / g.

The negative electrode active material secondary particles may further contain lithium carbonate in an amount of 0.1% by weight or less based on the total weight of the negative electrode active material secondary particles.

Meanwhile, the separator may be formed of a polyolefin porous film or a porous polymer nonwoven fabric.

According to an embodiment of the present invention, uniform pores of a predetermined size range are formed inside the secondary particles of the cathode active material formed by agglomeration of the primary particles of the cathode active material, so that the electrolyte is uniformly in contact with the primary particles of the cathode active material This makes it possible to quickly charge a high capacity, high output lithium secondary battery used in electric vehicles and the like.

Hereinafter, the present invention will be described in detail. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The cathode active material secondary particles according to the present invention are cathode active material secondary particles formed by agglomerating cathode active material primary particles containing nickel-manganese-cobalt (NMC) lithium, wherein the average particle diameter of the cathode active material primary particles is And 1 μm or less, and the cathode active material secondary particles have a volume-based particle size distribution D 50 of 2 μm to 20 μm, and pores having a size of 5 nm to 50 nm are uniformly formed in the cathode active material secondary particles .

Since the primary active material primary particles of the present invention contain lithium nickel-manganese-cobalt oxide, it is possible to improve the output through nickel, improve stability through manganese, and improve capacity through cobalt.

The cathode active material tends to form a single combination of the respective oxide units depending on the setting conditions of the production process, and such aggregated combination exhibits the active material property itself.

In the present invention, a plurality of primary particles of 1 m or less coagulate to form one secondary particle, and the secondary particle of the cathode active material formed at this time has a volume-based particle size distribution D50 of 2 to 20 mu m. Such a cathode active material secondary particle has a limitation in increasing the particle size in the manufacturing process thereof, and when the particle size is too large, the efficiency of the battery relative to the weight is lowered.

Further, in the present invention, pores with a relatively uniform size range of 5 nm to 50 nm are uniformly formed in the inside of the secondary particles of the cathode active material, so that the electrolytic solution can uniformly contact with the primary particles of the cathode active material, A high-capacity, high-output lithium secondary battery used in automobiles, etc. can be rapidly charged.

On the other hand, the lithium secondary battery of the present invention includes a cathode including a cathode active material, a cathode including a cathode active material, and a separator interposed between the cathode and the cathode, And includes the cathode active material secondary particles of the present invention.

Furthermore, the cathode active material primary particles may include a general cathode active material in addition to the lithium nickel manganese-cobalt (NMC) lithium salt described above. The cathode active material may include a lithium-containing oxide, Metal oxides can be preferably used. For example, Li _x CoO ₂ (0.5 <x <1.3), Li _x NiO ₂ (0.5 <x <1.3), Li _x MnO ₂ (0.5 <x <1.3), Li _x Mn ₂ O ₄ 1.3), Li _x Ni _{1- y} Co _y O ₂ (0.5 <x <1.3, 0 <y <1), Li _x Co _{1 -y} Mn _y O _{2 , Li x Ni 1 -y Mn y} O 2 (0.5 <x <1.3, O≤y <1), Li x Mn 2 -z Ni z O 4 (0.5 <x <1.3, 0 <z <2), Li _x Mn _{2 -z} Co _z O ₄ (0.5 <x <1.3, 0 <z <2), Li _x CoPO ₄ (0.5 <x <1.3) and Li _x FePO ₄ Or a mixture of two or more of them may be used. The lithium-containing transition metal oxide may be coated with a metal such as aluminum (Al) or a metal oxide. In addition to the lithium-containing transition metal oxide, sulfide, selenide and halide may also be used.

At this time, the anode is prepared by applying a mixture of a cathode active material, a conductive material and a binder on a cathode current collector, followed by drying and pressing, and if necessary, a filler may be further added to the mixture. At this time, if the pores in the secondary particles of the positive electrode active material are unevenly formed during the pressing, the structure of the secondary particles may collapse due to a larger pressure of the portions having no pores. However, There is little fear that a uniform pressure is applied to the inside of the pores to collapse.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel A surface treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The conductive material may be typically added in an amount of 1 to 50 wt% based on the total weight of the mixture including the cathode active material.

Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component which assists in bonding of the positive electrode active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50% by weight based on the total weight of the mixture containing the positive electrode active material. Examples of such binders include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, poly Polytetrafluoroethylene, polypropylene, polyacrylic acid, and polytetrafluoroethylene (PTFE) may be used alone or in combination of two or more selected from the group consisting of polyvinyl pyrrolidone, polyethylene, tetrafluoroethylene, polytetrafluoroethylene, polytetrafluoroethylene and polytetrafluoroethylene.

The filler is not particularly limited as long as it is a fibrous material that is used selectively as a component for suppressing the expansion of the anode and does not cause chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fiber, carbon fiber and the like can be used.

On the other hand, the negative electrode active material is a negative electrode active material secondary particle formed by agglomerating negative electrode active material primary particles containing lithium titanate (Li ₄ Ti ₅ O ₁₂ ), wherein the average primary particle diameter of the negative electrode active material is 1 μm or less And the negative electrode active material secondary particles having a volume-based particle size distribution D50 of 2 mu m to 20 mu m can be used.

At this time, the particle diameter of the lithium titanate may be 0.1 탆 to 1 탆, preferably 0.2 탆 to 0.8 탆. If it is out of the above range, secondary particles of the negative electrode active material may not be formed smoothly.

The average crystallite size of the primary particles of the negative electrode active material can be measured using an X-ray diffractometer, and the average crystallite size is preferably 800 ANGSTROM to 1,300 ANGSTROM.

The pore volume per weight of the secondary particles of the negative electrode active material may be 0.01 to 0.02 cm ³ / g.

The negative electrode active material secondary particles may further contain lithium carbonate in an amount of 0.1% by weight or less based on the total weight of the negative electrode active material secondary particles.

On the other hand, the negative electrode is manufactured by applying, drying and pressing an anode active material on an anode current collector, and may optionally further include a conductive material, a binder, a filler, and the like as described above.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples of the anode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

Meanwhile, the separator used in the present invention can be any porous polymer substrate commonly used in the art. For example, a polyolefin porous membrane or a porous polymer nonwoven fabric may be used, but the separator is particularly limited thereto It is not.

Examples of the polyolefin-based porous film include polyolefin-based polymers such as polyethylene, polypropylene, polybutylene, and polypentene, such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene and ultra-high molecular weight polyethylene, One membrane can be mentioned.

Examples of the porous polymer nonwoven fabric include polyolefin-based nonwoven fabrics such as polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyolefins such as polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide and polyethylenenaphthalene, which are used alone or in combination, Or a nonwoven fabric formed of a polymer mixed with these. The structure of the nonwoven fabric may be a spun bond nonwoven fabric or a meltblown nonwoven fabric composed of long fibers.

The thickness of the porous polymer base material is not particularly limited but may be in the range of 5 탆 to 50 탆. The pore size and porosity present in the porous polymer base material are also not particularly limited, but may be 0.01 탆 to 50 탆 and 10-95% have.

In order to improve the mechanical strength of the separator and to improve the safety of the lithium secondary battery, the porous polymer substrate may further include a porous coating layer including inorganic particles and a polymeric binder on at least one surface of the porous polymer substrate.

Here, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles usable in the present invention are not particularly limited as long as the oxidation and / or reduction reaction does not occur in the operating voltage range of the applied lithium secondary battery (for example, 0 to 5 V based on Li / Li ⁺ ). Particularly, when inorganic particles having a high dielectric constant are used as the inorganic particles, the dissociation of the electrolyte salt, for example, the lithium salt in the liquid electrolyte, can be increased, and the ion conductivity of the electrolyte can be improved.

The polymer binder may be at least one selected from the group consisting of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-co chlorotrifluoroethylene, polyvinylidene fluoride-co-trichlorethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinyl But are not limited to, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene, polyethylene oxide, polyarylate, cellulose acetate cellulose acetate, cellulose acetate butyrate, Cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan (which may be referred to as cellulose acetate propionate), cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, pullulan, and carboxyl methyl cellulose, or a mixture of two or more thereof, but is not limited thereto.

In the porous coating layer, the polymeric binder is coated on a part or the entire surface of the inorganic particles, and the inorganic particles are connected and fixed to each other by the polymeric binder in an adhered state, and an interstitial volume an interstitial volume between the inorganic particles is formed, and an interstitial volume between the inorganic particles becomes an empty space to form pores. This void space becomes the pores of the porous coating layer, and it is preferable that these pores are equal to or smaller than the average particle diameter of the inorganic particles.

Meanwhile, the electrolyte salt included in the nonaqueous electrolyte solution which can be used in the present invention is a lithium salt. The lithium salt can be used without limitation as those conventionally used in an electrolyte for a lithium secondary battery. For example is the above lithium salt anion ^{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 ^- .

Examples of the organic solvent included in the above-mentioned non-aqueous electrolyte include those conventionally used for an electrolyte for a lithium secondary battery, such as an ether, an ester, an amide, a linear carbonate and a cyclic carbonate, Can be mixed and used.

Among them, a carbonate compound which is typically a cyclic carbonate, a linear carbonate, or a mixture thereof may be included.

Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, Propylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or a mixture of two or more thereof. Examples of such halides include, but are not limited to, fluoroethylene carbonate (FEC) and the like.

Specific examples of the linear carbonate compound include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate And mixtures of two or more of them may be used as typical examples, but the present invention is not limited thereto.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates in the carbonate-based organic solvent, are high-viscosity organic solvents having a high dielectric constant and can dissociate the lithium salt in the electrolyte more easily. In addition, such cyclic carbonates can be used as dimethyl carbonate and diethyl carbonate When a low viscosity, low dielectric constant linear carbonate is mixed in an appropriate ratio, an electrolyte having a higher electric conductivity can be produced.

As the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether or a mixture of two or more thereof may be used , But is not limited thereto.

Examples of the ester in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate,? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone, ε-caprolactone, or a mixture of two or more thereof, but the present invention is not limited thereto.

The injection of the non-aqueous electrolyte may be performed at an appropriate stage of the production process of the lithium secondary battery, depending on the manufacturing process and required properties of the final product. That is, it can be applied before assembling the lithium secondary battery or at the final stage of assembling the lithium secondary battery.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Claims (8)

Cathode-Active Material Containing Lithium Nickel-Manganese-Cobalt (NMC) As a cathode active material secondary particle formed by aggregation of primary particles,
The average primary particle diameter of the positive electrode active material is 1 占 퐉 or less,
The cathode active material secondary particles have a volume-based particle size distribution D50 of 2 占 퐉 to 20 占 퐉,
Wherein a pore size of 5 nm to 50 nm is uniformly formed in the inside of the cathode active material secondary particles. 1. A lithium secondary battery comprising a positive electrode comprising a positive electrode active material, a negative electrode including a negative electrode active material, and a separator interposed between the positive electrode and the negative electrode,
Wherein the positive electrode active material comprises the positive electrode active material secondary particles of claim 1. 3. The method of claim 2,
The negative electrode active material is a negative electrode active material secondary particle formed by aggregating primary particles of a negative electrode active material containing lithium titanate (Li ₄ Ti ₅ O ₁₂ )
The average primary particle size of the negative electrode active material is 1 mu m or less,
Wherein the negative electrode active material secondary particles have a particle size distribution D50 of 2 占 퐉 to 20 占 퐉 on a volume basis. The method of claim 3,
Wherein a particle diameter of the lithium titanate is 0.1 mu m to 1 mu m. The method of claim 3,
Wherein an average crystallite size of the primary particles of the negative electrode active material is 800 ANGSTROM to 1,300 ANGSTROM. The method of claim 3,
Wherein the pore volume of the secondary active material secondary particles is 0.01 to 0.02 cm &lt; ³ &gt; / g. The method of claim 3,
Wherein the negative electrode active material secondary particles further include lithium carbonate in an amount of 0.1% by weight or less based on the total weight of the negative electrode active material secondary particles. 3. The method of claim 2,
Wherein the separator is formed of a polyolefin porous film or a porous polymer nonwoven fabric.