KR101225879B1 - Polar material of lithium secondary battery for a large output and lithium secondary battery comprising thereof - Google Patents

Abstract

The present invention relates to a lithium secondary battery composite electrode for improving the output and a lithium secondary battery comprising the same, the particle size is such that the size of the active material particles to be mixed in the composite electrode mixed with two or more active materials to have a uniform size The present invention provides a lithium secondary battery composite electrode having a high output characteristic by improving electrical conductivity by agglomerating a small active material and granulating the secondary active material in a secondary electrode, thereby providing a lithium secondary battery having the same.
In the composite electrode according to the present invention, the conductive material is evenly distributed in the compound by alleviating the particle size difference of each component to be mixed, and thus the electrical conductivity of the electrode active material is greatly improved even without adding an excessive conductive material to the electrode. Accordingly, it is possible to provide a lithium secondary battery having a wide SOC area that can be used by lowering the electrical resistance of the lithium secondary battery and having high output characteristics. In particular, when used as a medium-large battery used as a power source for electric vehicles, it provides a medium-large lithium secondary battery that can satisfactorily satisfy the conditions such as the required output characteristics, capacity, safety.

Description

Active material for lithium secondary battery composite electrode to improve output, and lithium secondary battery comprising same {POLAR MATERIAL OF LITHIUM SECONDARY BATTERY FOR A LARGE OUTPUT AND LITHIUM SECONDARY Battery Battery

The present invention relates to an active material for a lithium secondary battery composite electrode for improving the output and a lithium secondary battery comprising the same, and more specifically, the size of the active material particles to be mixed in a composite electrode of two or more active materials mixed uniformly It is to provide a lithium secondary battery electrode and a lithium secondary battery comprising the same by aggregating the active material having a small particle size and secondary particles to form a composite electrode to form a composite electrode so that the electrical conductivity is improved.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self discharge rate are commercially used. In addition, as interest in environmental problems increases, researches on electric vehicles and hybrid electric vehicles, which can replace fossil fuel-based vehicles such as gasoline and diesel vehicles, which are one of the main causes of air pollution, are being conducted. . Recently, researches using lithium secondary batteries having high energy density and discharge voltage have been actively conducted as power sources of such electric vehicles and hybrid electric vehicles, and some commercialization stages are in progress.

In particular, the development of cathode materials for large-capacity lithium secondary batteries for electric vehicles has been conducted to replace LiMn ₂ O ₄ , which is currently used, and recently, LiNi _x Mn _y Co _{1 -x- y} O has been developed to develop high capacity batteries. There have been many studies on the use of two-component layered oxides of _two .

However, in the case of the three-component layered oxide, there is a problem about stability during overcharging. In order to solve the problem, the lithium metal phosphate LiMPO ₄ (M) having an olivin structure without O ₂ emission during overcharging with the three-component layered oxide is solved. = Fe, Mn, Co, Ni), in particular, research on the composite electrode using the FeFe LiFePO ₄ for the positive electrode active material is active, such a composite electrode has a higher capacity than the single-component electrode, life characteristics and overcharge safety In view of the above, it is preferable to provide a lithium secondary battery used as a power source for medium and large devices.

However, in the case of the composite electrode including LiFePO ₄ as described above, there is a problem that the electrical conductivity is not good, so that a technique for producing an electrode by increasing the content of the conductive material is known. However, in the case of the electrode manufactured by the above method, a large electrical resistance is expressed during discharge of the lithium secondary battery, so that it is difficult to improve the output characteristics of the lithium secondary battery.

Therefore, the problem of improving the electrical conductivity of the electrode has become an important issue in the study of lithium secondary batteries, especially in the case of lithium secondary batteries used as a power source for medium and large devices, the required output characteristics are high and to prevent the sudden drop in output It is urgently required to introduce a technology for solving the above problems.

In order to improve the conductivity of the electrode composed of two or more composite materials as described above, attempts have been made to add a larger amount of conductive material to the electrode.

However, in order to form an electrode, a binder must be added together to bond the active material particles or interpose the active material on the electrode current collector. As the content of the conductive material included in the electrode increases, the content of the binder that is not electrically conductive also increases. Accordingly, when a large amount of the conductive material and the binder are included in the electrode, not only the thickness of the electrode is increased but also the amount of the active material in the electrode is relatively decreased, thereby greatly reducing the energy density of the electrode, There is a problem that the electrical conductivity falls as much as the content.

Therefore, in the prior art, despite the addition of a large amount of conductive material, the effect of improving the electrical conductivity of the electrode active material is inadequate, but rather, the capacity of the secondary battery and the output characteristics are deteriorated.

The present invention is to solve the problems and technical problems of the prior art as described above, the inventors of the present application after an in-depth study and various experiments, in an electrode made of a composite material mixed with two or more compounds as described above The cause of low electrical conductivity was identified.

This is a result of the difference in particle size between components having different electrical conductivity, that is, when the size difference of particles between two or more materials to be mixed is large, the surface area difference becomes large, and the absolute amount of the conductive material included in the electrode has a large surface area. This is because it is biased with either compound.

In other words, when the conductive material is biased to one active material having a large surface area, the absolute amount of the conductive material distributed on the surface of the other active material becomes smaller, which is less than the absolute amount of the conductive material than when used as a single component and is rather high. Resistance will appear.

As a result, the electrical conductivity of the entire electrode is reduced, and the above-described problem is repeated even if the amount of the conductive material is continuously increased.

Accordingly, the present invention minimizes the particle size difference between two or more active materials constituting the electrode in order to solve the above problems, so that the conductive material can be evenly distributed in the composite electrode consisting of two or more active materials, accordingly the composite electrode An object of the present invention is to provide a composite electrode for a lithium secondary battery in which the electrical conductivity is greatly improved even if the conductive material is not added in an excessive amount.

It is another object of the present invention to provide a lithium secondary battery having a high capacity, including the electrode, in which output characteristics are greatly improved.

The present invention is a composite electrode containing two or more active materials in order to solve the above problems,

The active material (small particle active material) having a relatively small particle size among the active materials to be mixed is secondary to the particles so that the particles (primary particles) of the small particle active material can be aggregated to be similar to the particle size of other active materials composited. It provides a composite electrode, characterized in that it comprises a (secondary particles).

The present invention is also characterized in that the primary particles of the small particle active material are composed of nano particles of primary particles.

Furthermore, the nano-sized primary particles are characterized in that 5nm to 200nm. In addition, the small particle active material is characterized in that it comprises 10 to 60% by weight based on the total amount of the composite electrode.

In addition, the secondary particles included in the small particle active material is characterized in that it is contained in 30% by weight to 100% by weight of the total amount of the small particle active material.

In addition, the secondary particles of the small particle active material is characterized in that the primary particles and the conductive material is produced by agglomeration.

In addition, the conductive material is characterized in that it comprises 0.5% by weight to 5% by weight based on the total amount of secondary particles.

In addition, the conductive material is one selected from carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black carbon black or a group consisting of a material containing graphene or graphite crystal structure Or more characterized in that the mixed material.

In addition, the composite electrode is characterized in that the anode.

In addition, the small particle active material is characterized in that the active material of the olivine structure that can be represented by the following [Formula 1].

[Formula 1] LiMPO ₄ (M is at least one element selected from Co, Ni, Mn and Fe)

Further, the small particle active material is characterized in that LiFePO ₄ .

In addition, the composite electrode active material is characterized in that it further comprises a three-component lithium-containing metal oxide represented by the following [Formula 2] in addition to LiFePO ₄ .

LiNi _x Mn _y Co _{1 -x- y} O ₂ , 0 <x <0.5, 0 <y <0.5

Further, the three-component system lithium-containing metal oxide is characterized in that _{LiM 1/3 Ni 1/3} Co 1/3 O.

In addition, the composite electrode may include lithium cobalt oxide, lithium nickel oxide, lithium cobalt-nickel oxide, lithium cobalt-manganese oxide, lithium manganese-nickel oxide, lithium cobalt-nickel-manganese oxide, lithium-containing olivine-type phosphate, and other elements thereof. (S) further comprises any one or a mixture of two or more selected from the substituted or doped oxide, wherein the ellipsoid (s) is selected from the group consisting of Al, Mg, Mn, Ni, Co, Cr, V, Fe It is characterized by any one or two or more elements.

In addition, the present invention is a composite electrode; It provides a composite electrode further comprising a binder and a conductive material of 10% by weight or less based on the total amount of the composite electrode.

In addition, the present invention provides a lithium secondary battery including the composite electrode.

The lithium secondary battery may be used as a unit cell of a battery module that is a power source of a medium and large device. The medium and large device may be a power tool, an electric vehicle, or a hybrid electric vehicle. Electric vehicles including Electric Vehicles (HEV), and Plug-in Hybrid Electric Vehicles (PHEVs); Electric motorcycles including electric bicycles (E-bikes) and electric scooters (E-scooters); Electric golf carts; Electric trucks; It is characterized in that the electric commercial vehicle or a system for power storage.

In the composite electrode including the electrode active material according to the present invention, since the conductive material is evenly distributed in the compound by alleviating the particle size difference of each component to be mixed, the electrical conductivity of the electrode is greatly improved even without adding an excessive conductive material. Accordingly, it is possible to provide a lithium secondary battery having a wide SOC area that can be used by lowering the electrical resistance of the lithium secondary battery and having high output characteristics.

In particular, when used as a medium-large battery used as a power source for electric vehicles, it provides a medium-large lithium secondary battery that can satisfactorily satisfy the conditions such as the required output characteristics, capacity, safety.

1 is a graph showing a change in resistance and output according to SOC of a rechargeable lithium battery according to Examples and Comparative Examples of the present invention.

In order to solve the problems and technical problems of the prior art as described above, in order to alleviate the particle size difference between the active materials in the composite electrode including two or more active materials, an active material having a relatively small particle size (hereinafter, Agglomerated particles (hereinafter referred to as 'primary particles') of 'small particle active materials', and secondarily granulated (hereinafter referred to as 'secondary particles') to a size equivalent to the particle size of other active materials to be mixed. It characterized in that the composite electrode to include).

In particular, the small particle active material is preferred that the size of the primary particles is nano (nano) size.

Hereinafter, the present invention will be described in detail.

In the composite electrode including two or more active materials, when there is a difference in particle size between the active materials to be mixed, the primary particles of the active material (small particle active material) consisting of particles of a relatively small size are aggregated and dried. Secondary granulation.

When the primary particle size difference between the two or more active materials constituting the composite electrode is large, the electrical conductivity of the electrode and the output characteristics are degraded as described above.

Accordingly, the present invention aggregates the primary particles of the small particle active material to make the second active particles into a particle size and a uniform size by agglomerating the primary particles of the small particle active material so that the particle size difference between two or more active materials included in the composite electrode is different. It is characterized by almost no. Therefore, the composite electrode according to the present invention can alleviate the phenomenon in which the conductive material is biased to any one active material having a large specific surface area, thereby increasing the electrical conductivity of the composite electrode including the two or more active materials.

In particular, the size of the primary particles of the small particle active material is preferred when it has a nano (nm) size. More preferably, the active material may be composed of primary particles having a size of 5 nm to 200 nm.

If the primary particles are of the same size as above, it is advantageous to agglomerate them into secondary particles, and if the secondary particles are included in the composite electrode as described above, the effect expected by the present invention can be further maximized. .

According to the present invention, the method of agglomerating the secondary particles by agglomerating the primary particles of the small particle active material is not particularly limited, and it is satisfied if the primary particles can be aggregated and granulated using a known method.

Specifically, for example, after the primary particles of the small particle active material is added to the stirrer together with water and stirred to prepare a mixture, the secondary particles may be prepared by aggregating them by a rotary spray drying method, followed by drying and pressing.

The size of the secondary particles is preferably made to be the same as the particle size of the other active material included in the composite electrode together with the small particle active material, but the particle size and uniformity of the other active material included in consideration of the manufacturing process error In addition to the secondary particles, secondary particles of smaller size may be further included. The size of the particles may vary depending on the manufacturing process.

The size of the secondary particles produced by agglomerating the primary particles of the small particle active material is not limited numerically, and is satisfied to be made to be uniform with the particle size of other active materials included in the electrode together with the small particle active material.

According to the present invention, when the composite electrode including two or more active materials having different particle sizes includes all (100%) secondary particles of the small particle active material and includes the composite electrode in the composite electrode, the particle size with other active materials to be mixed Since it becomes almost uniform, it is most preferable, but the effect anticipated by this invention can be expressed even if it contains secondary particle | grains 30% or more of the total amount of a small particle active material.

However, when the secondary particles are included in less than 30% of the small particle active material, it is difficult to obtain the desirable effect expected by the present invention due to insufficient electrical conductivity synergistic effect of the active material.

Meanwhile, the small particle active material included in the composite electrode may further include particles of different sizes in addition to the primary particles and the secondary particles as described above.

That is, in addition to the original particles (primary particles) of the small particle active material, secondary particles prepared by agglomeration thereof may further include particles of other sizes.

This is because the secondary particles are broken or deformed in the process of being prepared as secondary particles and then mixed with other active materials to be compressed into a composite, thereby forming particles of various sizes.

In addition, when preparing the secondary particles, it is preferable to add conductive materials. That is, when manufacturing secondary particles, the conductive material may be mixed with the primary particles to form secondary particles.

As such, when manufacturing the secondary particles including the conductive material, not only the surface of the secondary particles, but also the electrical conductivity inside the secondary particles is improved, so that the conductive path is sufficiently formed between the two or more kinds of the electrode active materials mixed, thereby forming the electrode. The electrical conductivity of the can be further increased to significantly lower the resistance of the lithium secondary battery.

The conductive material included in the secondary particles may be mixed with the primary particles in 0.5% by weight to 5% by weight based on the total weight of the primary particles to prepare the secondary particles.

When the amount of the conductive material included is less than 0.5% by weight, it is difficult to form a sufficient conductive path between particles and improve electrical conductivity. When the content of the conductive material exceeds 5% by weight, the amount of the active material is relatively small. There is a problem that can be lowered and the energy density is lowered.

The conductive material included in the secondary particles is not particularly limited as long as it has excellent electrical conductivity and has conductivity without causing side reactions in the internal environment of the secondary battery or causing chemical change in the battery.

Specifically, the graphite does not limit natural graphite or artificial graphite, and the conductive carbon is particularly preferably a carbon-based material having high conductivity, and specifically, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black And carbon black such as summer black, or a substance in which the crystal structure contains graphene or graphite.

On the other hand, the composite electrode including the secondary particles provides a more preferable effect when the positive electrode.

In particular, when the primary particles of the small particle active material is a nano-size as described above, the effect expected by the present invention can be maximized, and in the case of a positive electrode, LiMPO ₄ (M is Co, Ni, The active material represented by one or more elements selected from Mn and Fe is composed of primary particles of nano size (50 nm to 200 nm), and is preferable as a small particle compound.

More preferably, among the LiMPO ₄ (M is at least one element selected from Co, Ni, Mn, and Fe), LiFePO ₄ (hereinafter referred to as 'olivin') having a relatively inexpensive, high capacity and stable olivine structure Can be used.

The olivine has a theoretical capacity of 170 mAh / g and a standard reduction potential of 3.4 V. The olivine can maintain an energy density without causing the reaction voltage to be high enough to cause side reactions such as decomposition of the electrolyte. It is advantageous to secure the discharge output at the stage.

On the other hand, when the olivine is included in the positive electrode active material, it is preferable to include 10 to 60% by weight based on the total amount of the positive electrode active material.

When the olivine is contained in less than 10% by weight, there is a problem in the safety of the secondary battery, and when it is included in excess of 60% by weight because of the low capacity of the olivine there is a limit to the high capacity of the entire positive electrode.

At this time, 30% by weight to 100% by weight of the total amount of the olivine contained in the positive electrode active material is prepared to be included as secondary particles.

This is because the secondary particles should be at least 30% by weight or more, so there is no shortage in solving problems caused by the size difference between the particles of the two or more active materials forming the composite electrode.

Furthermore, it is most preferable to make the whole olivine (100%) into secondary particles and to include it in the anode.

The present invention is characterized in that it comprises the secondary particles of the small particle active material included in the composite electrode, the other components included in the composite electrode is not particularly limited, but preferably represented by the following [Formula 1] It may be a three-component lithium-containing metal oxide (hereinafter referred to as 'three-component').

LiNi _x Mn _y Co _{1 -x- y} O ₂ , 0 <x <0.5, 0 <y <0.5

Three-component represented by the above Formula 1 may preferably be a Ni, Co, Mn is identically configured _{Li [Ni 1/3 Co 1} /3 Mn 1/3] O 2.

The three-component compound can express a relatively high capacity, and is suitable for manufacturing a high capacity / high power secondary battery.

According to the present invention, the secondary particles of the small particle active material included in the composite electrode should be prepared to have the same size as other active material particles. When the three-component active material is included in the composite electrode, the particle size of the three-component system is included. Similar to (5um-20um), the small particle active material should be secondary granulated to a size of 5um to 20um.

As a most preferred embodiment according to the present invention, the composite electrode may be a positive electrode, two or more active materials included in the positive electrode is a three-component lithium-containing metal oxide represented by Formula 1, the small particle active material may be olivine. .

At this time, the olivine is preferably contained in 10 to 60% by weight relative to the total amount of the positive electrode. If it is included in less than 10% by weight, there is a problem in the safety of the secondary battery, if it exceeds 60% by weight because of the low capacity of the LiFePO ₄ of the olivine structure is limited because of the high capacity of the entire positive electrode.

Since the olivine is composed of primary particles having a size of 50 nm to 200 nm, it is preferable to secondary granulate to a size of 5 μm to 20 μm to be similar to the particle size of the tricomponent lithium-containing metal oxide.

The olivine secondary particles prepared as described above are to be included in at least 30% by weight or more of the total amount of olivine included in the positive electrode. If the content is less than 30%, the conductive material is biased only toward the olivine due to the significant difference between the particles of the three-component system, and thus it is difficult to improve the low electrical conductivity of the positive electrode.

On the other hand, the olivine included in the positive electrode, in addition to the secondary particles having a size similar to the primary particles and the three-component particles may further include particles of other sizes generated by breaking or deforming the secondary particles during the production of the positive electrode. As such, even if the particles further include particles of different sizes, it is a matter of course that the electrical conductivity of the anode is improved rather than the case where the olivine is composed of only the primary particles.

On the other hand, the positive electrode according to the present invention, in addition to the secondary particles and the three-component lithium-containing metal oxide of the above [Formula 1] may further include the following lithium-containing metal oxide.

That is, the lithium-containing metal oxides are various active materials known in the art, and include lithium cobalt oxide, lithium nickel oxide, lithium cobalt-nickel oxide, lithium cobalt-manganese oxide, lithium manganese-nickel oxide, lithium cobalt-nickel-manganese Oxides, lithium-containing olivine-type phosphates, and oxides substituted or doped with ellipsoid (s), and the ellipsoid (s) may be Al, Mg, Mn, Ni, Co, Cr, V, It may be any one or two or more elements selected from the group consisting of Fe.

The present invention may further include a conductive material, a binder, a filler, and the like, selectively in the composite electrode as described above.

If the amount of the conductive material and the binder included is too small, it is difficult to expect a desired effect, on the contrary, if the amount of the conductive material and the binder is too small, the amount of the active material may be reduced due to the relatively small amount of the active material. It is preferably included to be 10% by weight or less, more preferably 3 to 10% by weight.

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

The conductive material included in the composite electrode according to the present invention may be evenly distributed without biasing any one of two or more active materials in the composite electrode, thereby significantly improving the conductivity of the electrode even with a small amount. .

The binder is a component that assists in bonding the active material and the conductive material to the current collector, and examples of the binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, and hydroxide. Oxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, And various copolymers.

In addition, the filler is optionally used as a component for inhibiting the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes in the battery, for example, olefin polymers such as polyethylene, polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

In addition, the composite electrode may be dried, for example, by applying a slurry prepared by mixing a positive electrode mixture such as a positive electrode active material, a conductive material, a binder, and a filler to a solvent such as NMP on a positive electrode current collector on a positive electrode current collector. It can be produced by rolling.

The current collector is generally made to a thickness of 3 to 500 nm. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the positive electrode current collector is not limited to the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. The surface-treated with carbon, nickel, titanium, silver, etc. can be used. The current collector may form fine irregularities on its surface to increase the adhesion of the active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foaming agent, and a nonwoven fabric.

The negative electrode current collector is also not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, carbon on the surface of copper or stainless steel, Surface-treated with nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. 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.

The present invention also provides a lithium secondary battery comprising the composite electrode, the separator, and a lithium salt-containing nonaqueous electrolyte.

The separator is interposed between the cathode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The said lithium salt containing non-aqueous electrolyte solution consists of a nonaqueous electrolyte solution and a lithium salt. As the nonaqueous electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, and 1,2-dime Methoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxoron, acetonitrile, nitromethane, methyl formate, Methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, pyrion An aprotic organic solvent such as methyl acid or ethyl propionate can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, and the like can be used.

As the inorganic solid electrolyte, for example, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates, and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., the non-aqueous electrolyte solution includes, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, and hexaphosphate triamide. Nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. It may be.

In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

Such a secondary battery according to the present invention can be used not only for the battery cell used as a power source of the small device, but also preferably used as a unit battery in a medium-large battery module including a plurality of battery cells.

Preferred examples of the above medium and large-sized devices include a power tool; Electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); Electric golf carts; Electric trucks; Although an electric commercial vehicle or the system for electric power storage is mentioned, It is not limited only to these.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example

Preparation of Secondary Particles

LiFePO ₄ of olivine structure The powder was mixed with water into a stirrer to make a slurry, and then, agglomerated and dried by a rotary spray drying method, thereby preparing secondary particles having a size of 10 μm.

Manufacture of anode

LiFePO ₄ prepared by the above method Secondary particles and general LiFePO ₄ for a material of 20% by weight of _{Li [Ni 1/3 Co 1} /3 Mn 1/3] O 2 60% by weight mixed with 50-50, graphite 7% by weight, dengka Black 7% by weight And 6 wt% of PVDF was prepared. Specifically, the content ratio of Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ and LiFePO ₄ After grinding and sieving graphite and denca black, 6 wt% PVDF was coated with a binder to prepare a positive electrode mixture. The positive electrode mixture was applied to a positive electrode current collector, rolled, and dried to prepare a positive electrode for a secondary battery.

Fabrication of Lithium Secondary Battery

Including a positive electrode prepared as described above, a porous lithium separator between the porous membrane based on graphite, a lithium electrolyte was injected to prepare a polymer type lithium secondary battery.

The polymer-type lithium secondary battery was formed at 4.2V, and then output was measured according to SOC while charging and discharging between 4.2V and 2.5V. (C-rate = 1C).

Example  2

A polymer lithium secondary battery was manufactured in the same manner as in Example 1, except that LiFePO ₄ was 100% secondary particles and included in the cathode active material.

Comparative example

A polymer lithium secondary battery was manufactured in the same manner as in Example 1, except that LiFePO _{4 was not added} to the secondary particles but included in the cathode active material.

For the full-cell lithium secondary batteries produced by the above Examples and Comparative Examples, the output change according to SOC was measured at a voltage range of 4.2 V to 3 V, respectively, and the results are shown in FIG. 1 below.

The data shown in FIG. 1 is just one example, and detailed power values according to SOC will vary depending on the specification of the cell. Therefore, the trend of the graph is more important than the detailed values.

Referring to FIG. 1 in this regard, it can be seen that the lithium secondary battery according to Example 1 of the present invention exhibits a much higher level of output over the entire SOC section than the lithium secondary battery according to the comparative example. . In the case of Example 2, as the resistance increased in the region where the SOC was low, the output amount appeared to be lower than that of the comparative example, but in all other sections, it was confirmed that the output amount was higher than that of the comparative example.

This can be said to be the result of improving the electrical conductivity of the active material by the conductive material is evenly distributed in the composite electrode by the difference between the particles between the two or more active materials included in the composite electrode according to the present invention.

According to the present invention, it is possible to provide a lithium secondary battery in which an SOC region that can be used with improved output characteristics is also expanded.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. The scope of the present invention should be interpreted based on the scope of the following claims and all technical ideas within the scope of equivalents thereof are to be construed as being included in the scope of the present invention. It is to be understood that the invention is not limited thereto.

Claims (17)

As a composite electrode containing two or more active materials,
Among the two or more active material includes a secondary particle agglomerated primary particles of a small particle active material,
The secondary particle is a composite electrode, characterized in that the particle size and uniform size of the other active material to be mixed. The method of claim 1,
The primary particle of the small particle active material comprises a particle having a size of 5nm to 200nm. The method of claim 1,
The small particle active material is a composite electrode, characterized in that contained in 10 to 60% by weight based on the total amount of the composite electrode. The method of claim 1,
Secondary particles of the small particle active material is a composite electrode, characterized in that contained in more than 30% by weight to less than 100% by weight of the total amount of the small particle active material. The method of claim 1,
The secondary particles of the small particle active material further comprise a conductive material in addition to the primary particles. The method of claim 5,
The conductive material is a composite electrode, characterized in that contained 0.5% by weight to 5% by weight based on the total amount of secondary particles. The method of claim 5,
The conductive material is one selected from the group consisting of carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black, or a material whose crystal structure includes graphene or graphite. The composite electrode characterized by the above-mentioned mixed material. The method of claim 1,
The composite electrode is a composite electrode, characterized in that the anode. The method of claim 1,
The small particle active material is a composite electrode, characterized in that the lithium-containing phosphate of the olivine structure that can be represented by the following [Formula 1].
[Formula 1] LiMPO ₄ (M is at least one element selected from Co, Ni, Mn and Fe) The method of claim 1,
The small particle active material is a composite electrode, characterized in that LiFePO ₄ . The method of claim 10,
The composite electrode further comprises a tri-component lithium-containing metal oxide represented by the following [Formula 2] in addition to LiFePO ₄ .
LiNi _x Mn _y Co _{1 -x- y} O ₂ , 0 <x <0.5, 0 <y <0.5 The method of claim 11,
The three-component system lithium-containing metal oxide composite electrode, characterized in that _{LiM 1/3 Ni 1/3} Co 1/3 O. The method of claim 12,
The composite electrode may include lithium cobalt oxide, lithium nickel oxide, lithium cobalt-nickel oxide, lithium cobalt-manganese oxide, lithium manganese-nickel oxide, lithium cobalt-nickel-manganese oxide, lithium-containing olivine-type phosphate, and other element (s) ) Further comprises any one or a mixture of two or more selected from the substituted or doped oxide, wherein the ellipsoid (s) is any one selected from the group consisting of Al, Mg, Mn, Ni, Co, Cr, V, Fe Or two or more elements. The method of claim 1,
The composite electrode comprises a binder and a conductive material of 10% by weight or less based on the total amount of the composite electrode. A lithium secondary battery comprising the composite electrode according to any one of claims 1 to 14. 16. The method of claim 15,
The lithium secondary battery is a lithium secondary battery, characterized in that used as a unit cell of the battery module that is the power source of the medium and large devices. 17. The method of claim 16,
The medium and large devices include a power tool, an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV). Electric car to do; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); Electric golf carts; Electric trucks; Lithium secondary battery, characterized in that the electric commercial vehicle or power storage system.

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