KR20170068130A - Rechargeable lithium battery - Google Patents

Abstract

1. A lithium secondary battery comprising a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte solution, wherein the positive electrode active material comprises a lithium metal compound and activated carbon, the negative electrode active material comprises a titanium- (D50) of the average particle diameter (D50) of the secondary particles, and the average particle diameter (D50) of the ground particles is in the range of 0.01% to 50% A lithium secondary battery is provided.

Description

[0002] Lithium secondary batteries {RECHARGEABLE LITHIUM BATTERY}

To a lithium secondary battery.

The low voltage system (LVS) is a system that will be widely used before the commercialization of electric vehicles in the future. When used as a dual system using lead-acid batteries, it helps improve the fuel efficiency and extend the life of the lead-acid batteries by assisting the lead battery.

Such an LVS system is a total collection of battery technology for achieving low resistance characteristics of a lithium ion battery. Lithium-ion batteries store electricity through a chemical redox reaction, which causes low rate-of-life characteristics and lifetime characteristics. This low rate-limiting characteristic is limited by the application of applications requiring high input / output.

As a negative electrode active material used in a lithium ion battery, lithium titanium oxide exhibits electrochemical activity against lithium similar to lithium metal oxide such as LiCoO ₂ used as a positive electrode active material. In addition, since lithium titanium oxide has little difference in crystal gap before and after charging / discharging, it may exhibit stable lifetime characteristics. In addition, since the operating potential is 1.5V, which is somewhat higher than that of carbon, it shows high safety because byproducts due to the decomposition reaction of the electrolyte are not produced. However, because of low conductivity and low diffusion rate of lithium ion, capacity and high rate characteristics are limited.

One embodiment is to provide a lithium secondary battery having excellent electric conductivity and high capacity and high rate characteristics.

One embodiment includes a positive electrode comprising a positive electrode active material; A negative electrode comprising a negative electrode active material; And an electrolyte solution, wherein the cathode active material comprises a lithium metal compound and activated carbon, and the anode active material comprises a titanium-containing oxide, wherein the titanium-containing oxide comprises secondary particles formed by agglomeration of primary particles, Wherein the average particle size (D50) of the ground particles is 0.01% to 50% of the average particle size (D50) of the secondary particles.

The pulverized particles may have a size of 0.01% to 20% of the average particle diameter (D50) of the secondary particles.

The average particle diameter (D50) of the secondary particles may be 5 [mu] m to 15 [mu] m.

The titanium-containing oxide may contain the secondary particles and the pulverized particles in a weight ratio of 9: 1 to 4: 6.

The titanium-containing oxide may include TiO ₂ , LiTiO ₂ , LiTi ₂ O ₄ , Li ₄ Ti ₅ O _12, or a combination thereof.

The lithium metal compound may include lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel phosphate or a combination thereof.

The specific surface area of the activated carbon may be 1500 m ² / g to 1800 m ² / g.

The activated carbon may be contained in an amount of 0.1 to 20% by weight based on the total amount of the lithium metal compound and the activated carbon.

The details of other embodiments are included in the detailed description below.

A lithium secondary battery having excellent electric conductivity and high capacity and high rate characteristics can be realized.

1 is a schematic view showing a lithium secondary battery according to one embodiment.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

Hereinafter, a lithium secondary battery according to one embodiment will be described with reference to FIG.

1 is a schematic view showing a lithium secondary battery according to one embodiment.

Referring to FIG. 1, a lithium secondary battery 100 according to an embodiment includes an electrode assembly 110, a battery container 120 containing the electrode assembly 110, and a current generated from the electrode assembly 110 And an electrode tab 130 serving as an electrical path for guiding the electrode tabs to the outside. The two surfaces of the battery container 120 are sealed by overlapping surfaces facing each other. Also, the electrolyte solution is injected into the battery container 120 containing the electrode assembly 110. The electrode assembly 110 includes a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode.

Of course, the lithium secondary battery according to one embodiment is not limited to the embodiment shown in FIG. 1, but may include any type such as cylindrical, square, or coin type, as long as it includes a cathode for a lithium secondary battery according to an embodiment and can operate as a battery. Of course.

The negative electrode may include a current collector and a negative electrode active material layer formed on the current collector.

The negative electrode active material layer may include a negative electrode active material.

The negative electrode active material may include a titanium-containing oxide.

In the lithium secondary battery using the titanium-containing oxide as the negative electrode active material, the oxidation / reduction potential of the negative electrode is relatively high at about 1.5 V relative to the potential of Li / Li ⁺ , so that decomposition of the electrolyte hardly occurs, Excellent cycle characteristics.

The titanium-containing oxide may comprise secondary particles and ground particles ground from the secondary particles. By using the titanium-containing oxide including the secondary particles and the ground particles as the negative electrode active material, a lithium secondary battery having improved electrical conductivity and excellent capacity characteristics and rate characteristics can be realized.

The secondary particles may be particles formed by agglomeration of primary particles which are a plurality of fine particles.

The average particle diameter (D50) of the primary particles may be 10 nm or more and less than 1 占 퐉, and may be, for example, 50 nm to 900 nm. Further, the average particle diameter (D50) of the secondary particles may be 5 占 퐉 to 15 占 퐉, and may be, for example, 6 占 퐉 to 10 占 퐉. When secondary particles having a size within the above range are used as the particles formed by agglomeration of the primary particles, the processability such as dispersibility in the slurry, coating property, and the like can be excellent at the time of formation of the negative electrode and high mixing density can be obtained, Properties and high-rate characteristics can be improved.

The average particle diameter (D50) means the diameter of particles having a cumulative volume of 50 vol% in the particle size distribution.

The pulverized particles can be obtained by pulverization from the secondary particles. The secondary particles may have a strength to be crushed without using a special device or a large external force, and the crushed particles may be used as the terms crushed particles, broken particles, and the like.

Since the pulverized particles are obtained by pulverizing the secondary particles, they may have a smaller size than the secondary particles. The pulverized particles are distinguished from the primary particles having a size smaller than that of the secondary particles, and they are the pulverized products of the secondary particles in which the primary particles are aggregated. In addition, since the ground particles have a large specific surface area and a large number of reaction sites, when used together with the secondary particles, a lithium secondary battery having excellent electric conductivity and high capacity and high rate characteristics can be realized.

Specifically, the average particle diameter (D50) of the pulverized particles may be 0.01% to 50% or less, for example, 0.01% to 20% of the average particle diameter (D50) %. ≪ / RTI > When the size of the pulverized particles is within the above range with respect to the size of the secondary particles, the capacity and rate characteristics of the battery are improved.

The titanium-containing oxide may include the secondary particles and the pulverized particles at a weight ratio of 9: 1 to 4: 6, and may be contained at a weight ratio of, for example, 7: 3 to 5: 5. When the secondary particles and the pulverized particles are mixed in the weight ratio range, the specific surface area of the active material in the electrode is enlarged due to the pulverized particles, so that the secondary particles and the pulverized particles act favorably on the rate characteristics of the battery.

The titanium-containing oxide may include titanium oxide, lithium titanium oxide, or a combination thereof. The titanium oxide may include TiO ₂ and the like, and the lithium titanium oxide may include LiTiO ₂ , LiTi ₂ O ₄ , Li ₄ Ti ₅ O _12, or a combination thereof, for example, Li ₄ Ti ₅ O ₁₂ can be used.

The negative electrode active material layer may include at least one of a conductive material and a binder in addition to the negative electrode active material.

The conductive material is used for imparting conductivity to the negative electrode. Any conductive material can be used without causing any chemical change in the battery. Examples thereof include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black and carbon fiber; Metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers; Conductive polymers such as polyphenylene derivatives; Or a mixture thereof may be used.

The binder serves to adhere the anode active material particles to each other and to adhere the anode active material to the current collector. Examples of the binder include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, polyvinyl chloride, carboxylated But are not limited to, polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene- Butadiene rubber, epoxy resin, nylon, and the like, but not limited thereto.

The negative electrode active material layer may be formed on the current collector. The current collector may include, but is not limited to, copper.

The negative electrode may be prepared by mixing the negative electrode active material, the conductive material and the binder with a solvent to prepare a negative electrode composition, and then applying the negative electrode composition to the current collector, followed by rolling and drying. As the solvent, N-methylpyrrolidone, water and the like can be used, but it is not limited thereto.

The positive electrode includes a current collector and a positive electrode active material layer formed on the current collector.

The cathode active material layer may include a cathode active material.

According to one embodiment, the cathode active material may include a lithium metal compound and activated carbon.

When activated carbon is added to a lithium metal compound as a cathode active material for a lithium secondary battery, cell resistance can be reduced by providing absorption and desorption and insertion and desorption of anions which interfere with the movement of lithium ions in the cathode and the anode. Also, the activated carbon added to the anode can physically adsorb lithium ions by forming a capacitor structure, and rapidly transfer the adsorbed lithium ions to the lithium metal compound, thereby improving the high-rate characteristics. Also, by adding activated carbon, activated carbon is uniformly distributed between the active material and the active material to form a uniform electrode, thereby preventing deterioration of a part of the electrode due to repetitive charging and discharging, thereby ensuring excellent lifetime characteristics.

The lithium metal compound may specifically include a lithium nickel compound. The lithium nickel compound may include lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel phosphate, or a combination thereof.

The specific surface area of the activated carbon may be 1500 m ² / g to 1800 m ² / g, for example, 1600 m ² / g to 1700 m ² / g. When activated carbon having a specific surface area within the above range is used, dispersibility is excellent, and high-rate characteristics and life characteristics can be improved.

The average particle diameter (D50) of the activated carbon may be 1 to 30 m, and may be, for example, 1 to 20 m. The average particle diameter (D50) means the diameter of particles having a cumulative volume of 50 vol% in the particle size distribution. When the size of the activated carbon is within the above range, the aggregation of the particles does not occur and the localization of the particles to a specific region can be prevented, so that the high-rate characteristics can be improved.

The pH of the activated carbon may be 7 to 10, and may be, for example, 7 to 9. The activated carbon may contain not more than 3% by weight of water, and may contain, for example, 0.5 to 2% by weight of water. The activated carbon may also contain less than 1% by weight of ash. When such activated carbon is used, high-rate characteristics and life characteristics of the lithium secondary battery can be obtained due to the effect that lithium ions are adsorbed on the surface of the electrode plate.

The activated carbon may be contained in an amount of 0.1% by weight to 20% by weight, for example, 1% by weight to 10% by weight based on the total amount of the lithium metal compound and the activated carbon. When the activated carbon is contained in the above content range, excellent high-rate characteristics and life characteristics can be secured.

The cathode active material layer may include at least one of a conductive material and a binder in addition to the cathode active material.

The conductive material is used for imparting conductivity to the anode, and any material can be used as long as it does not cause any chemical change in the battery constituted and is an electron conductive material. Examples thereof include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black and carbon fiber; Metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers; Conductive polymers such as polyphenylene derivatives; Or a mixture thereof may be used.

The binder serves to adhere the positive electrode active materials to each other well and adhere the positive electrode active material to the current collector well. Examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated But are not limited to, polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene- Butadiene rubber, epoxy resin, nylon, and the like, but not limited thereto.

The cathode active material layer may be formed on the current collector. The current collector may include, but is not limited to, aluminum.

The anode may be prepared by mixing the cathode active material, the conductive material and the binder with a solvent to prepare a cathode composition, and then applying the cathode composition to the collector, followed by rolling and drying. As the solvent, N-methylpyrrolidone, water and the like can be used, but it is not limited thereto. The method of manufacturing the electrode is well known in the art, and therefore, a detailed description thereof will be omitted herein.

The electrolytic solution includes a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. The non-aqueous organic solvent may be selected from carbonate, ester, ether, ketone, alcohol and aprotic solvents.

Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethyl propyl carbonate ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC)

In particular, when a mixture of a chain carbonate compound and a cyclic carbonate compound is used, the solvent may be prepared from a solvent having a high viscosity and a high dielectric constant. In this case, the cyclic carbonate compound and the chain carbonate compound may be mixed in a volume ratio of about 1: 1 to 1: 9.

Examples of the ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, methyl propionate, ethyl propionate,? -Butyrolactone, decanolide, valerolactone, mevalonolactone mevalonolactone, caprolactone, and the like may be used. As the ether solvent, for example, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran and the like can be used. As the ketone solvent, cyclohexanone and the like can be used have. As the alcoholic solvent, ethyl alcohol, isopropyl alcohol, etc. may be used.

The non-aqueous organic solvent may be used alone or in combination of two or more thereof. If one or more of the non-aqueous organic solvents is used in combination, the mixing ratio may be appropriately adjusted according to the desired cell performance.

The electrolytic solution may further contain additives such as an overcharge inhibitor such as ethylene carbonate, pyrocarbonate and the like.

The lithium salt is dissolved in the non-aqueous organic solvent to act as a source of lithium ions in the battery to enable operation of a basic lithium secondary battery, and a material capable of promoting the movement of lithium ions between the positive electrode and the negative electrode to be.

The lithium salt Specific examples include _{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, LiN (SO 3 C 2 F 5) 2, LiC 4 F 9 SO 3, LiClO 4, LiAlO 2, LiAlCl 4, LiN (C x F _{2 x 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) wherein x and y are natural numbers, LiCl, LiI, LiB (C ₂ O ₄ ) ₂ (lithium bis (oxalato ) borate (LiBOB), or a combination thereof.

The concentration of the lithium salt is preferably within the range of about 0.1M to about 2.0M. When the concentration of the lithium salt is within the above range, the electrolytic solution has an appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance, and lithium ions can effectively move.

The separator separates the negative electrode and the positive electrode and provides a passage for lithium ion. Any separator commonly used in a lithium battery can be used. That is, it is possible to use an electrolyte having a low resistance to ion movement and an excellent ability to impregnate an electrolyte. For example, selected from glass fibers, polyester, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be nonwoven fabric or woven fabric. For example, a polyolefin-based polymeric separator such as polyethylene, polypropylene and the like is mainly used, and a separator coated with a ceramic component or a polymeric material may be used to secure heat resistance or mechanical strength, and may be selectively used as a single layer or a multilayer structure.

Hereinafter, preferred embodiments and comparative examples of the present invention will be described. However, the following embodiment is only one preferred embodiment of the present invention, and the present invention is not limited to the following embodiments.

(Production of lithium secondary battery)

Example  One

LiNi ₁ having an average particle diameter (D50) of _{5㎛ / 3 Co 1/3 Mn} 1/3 O 2, has a mean particle size (D50) of 6.8㎛ activated carbon having a specific surface area of 1600 m ² / g (Kuraray Co., YP50F), carbon black (denka black) and polyvinylidene fluoride were mixed with N-methylpyrrolidone at a weight ratio of 85: 5: 4: 6 to prepare a slurry. The prepared slurry was applied to an aluminum foil having a thickness of 15 탆, dried and rolled to prepare a positive electrode.

Li ₄ Ti ₅ O ₁₂ having an average particle diameter (D50) of 7 mu m as secondary particles, a crushed particle obtained by grinding the secondary particles by a method of increasing the shear rate of the mixer during slurry mixing, It was prepared N- methyl pyrrolidone and mixed to the slurry in a weight ratio of 6: D50) having a Li ₄ Ti ₅ O _12, the carbon black (Denka black), and polyvinylidene fluoride to 89: 5. The prepared slurry was applied to an aluminum foil having a thickness of 15 탆, dried and rolled to produce a negative electrode.

An electrode assembly was formed using the positive and negative electrodes and the separator made of polyethylene prepared above, and then an electrolyte was injected into the electrode assembly to prepare a 50 mAh pouch type lithium secondary battery. The electrolyte solution was prepared by adding 1.15 M LiPF ₆ to a mixed solvent of ethylene carbonate (PC), ethyl methyl carbonate (DMC) and diethyl carbonate (DEC) in a volume ratio of 2: 6: 2 Respectively.

Example  2

A lithium secondary battery was produced in the same manner as in Example 1, except that Li ₄ Ti ₅ O ₁₂ having an average particle diameter (D50) of 100 nm was used as the ground particles in Example 1 to prepare a negative electrode.

Example  3

Except that secondary particles, ground particles, carbon black and polyvinylidene fluoride were mixed in a weight ratio of 50: 39: 5: 6 in Example 1 to prepare a negative electrode. A battery was produced.

Comparative Example  One

Except that Li ₄ Ti ₅ O ₁₂ having an average particle diameter (D50) of 7 μm as secondary particles, carbon black (denka black) and polyvinylidene fluoride were mixed at a weight ratio of 89: 5: 6 to prepare a negative electrode , A lithium secondary battery was fabricated in the same manner as in Example 1.

Comparative Example  2

Primary particles having an average particle diameter (D50) of 300nm as _{Li 4 Ti 5 O 12, Li} 4 Ti having an average particle diameter (D50) of secondary particles as 7㎛ ₅ O _12, the carbon black (Denka black) and a polyvinyl Lithium secondary battery was prepared in the same manner as in Example 1, except that a negative electrode was prepared by mixing lithium fluoride in a weight ratio of 89: 5: 6.

Comparative Example  3

A lithium secondary battery was fabricated in the same manner as in Example 1, except that Li4Ti5O12 having an average particle diameter (D50) of 4 mu m was used as the ground particles in Example 1 to prepare a negative electrode.

Comparative Example  4

An embodiment in LiNi 1 having an average particle diameter (D50) of _{5㎛ 1/3 Co 1/3} Mn 1/3 O 2, carbon black (Denka Black), and polyvinylidene fluoride of 90: in a weight ratio of 6: 4 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the positive electrode was prepared by mixing.

Evaluation 1: Electrical Conductivity

The electrical conductivities of the lithium secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were measured using an LCR meter (model: 4263B). The results are shown in Table 1 below.

Evaluation 2: High-rate characteristics of lithium secondary battery

The lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 4 were evaluated for high-speed charge / discharge characteristics as follows. The results are shown in Table 1 below.

The capacity at the time when the battery was charged at a constant current of 50 C and the battery voltage was 2.8 V and the battery was discharged at a current of 1 C to 1.5 V was measured and determined as a fast charge characteristic.

Further, the capacity at the time of constant current charging at a current of 1 C, charging was terminated at a battery voltage of 2.8 V, and the battery was discharged at a current of 1.5 V at a current of 50 C, was measured.

In the following Table 1, the filling rate (%) is calculated as a percentage of the charging capacity at 50C versus the charging capacity at 1C, and the discharge rate (%) is calculated as a percentage of the discharging capacity at 50C versus the discharging capacity at 1C.

Electrical Conductivity (S / m) Capacity characteristics 50C / 1C Charging rate (%) 50C / 1C discharge rate (%) Example 1 0.01 145 77 79 Example 2 0.007 143 75 77 Example 3 0.008 143 75 78 Comparative Example 1 0.003 143 63 63 Comparative Example 2 0.002 142 59 62 Comparative Example 3 0.003 143 58 61 Comparative Example 4 0.001 142 47 58

Referring to Table 2, a mixture of secondary particles and crushed particles of a titanium-containing oxide is used as a negative electrode active material, and the size ratio of the secondary particles and the crushed particles is adjusted to an appropriate range. And the activated carbon were used as the cathode active material, the lithium secondary batteries of Examples 1 to 3 had higher electric conductivity and higher capacity and higher-rate characteristics than Comparative Examples 1 to 4.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, And it goes without saying that the invention belongs to the scope of the invention.

100: Lithium secondary battery
110: electrode assembly
120: Battery container
130: electrode tab

Claims (8)

A cathode comprising a cathode active material;
A negative electrode comprising a negative electrode active material; And
Comprising an electrolytic solution,
Wherein the cathode active material comprises a lithium metal compound and activated carbon,
Wherein the negative electrode active material comprises a titanium-containing oxide,
Wherein the titanium-containing oxide comprises secondary particles formed by aggregation of primary particles, and ground particles ground from the secondary particles,
Wherein an average particle diameter (D50) of the pulverized particles is 0.01% to 50% of an average particle diameter (D50) of the secondary particles. The method of claim 1,
Wherein the pulverized particles have a size of 0.01% to 20% of an average particle size (D50) of the secondary particles. The method of claim 1,
Wherein an average particle diameter (D50) of the secondary particles is 5 占 퐉 to 15 占 퐉. The method of claim 1,
Wherein the titanium-containing oxide contains the secondary particles and the ground particles in a weight ratio of 9: 1 to 4: 6. The method of claim 1,
Wherein the titanium-containing oxide comprises TiO ₂ , LiTiO ₂ , LiTi ₂ O ₄ , Li ₄ Ti ₅ O _12, or a combination thereof. The method of claim 1,
Wherein the lithium metal compound comprises lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel phosphate or a combination thereof. The method of claim 1,
And the specific surface area of the activated carbon is 1500 m ² / g to 1800 m ² / g. The method of claim 1,
Wherein the activated carbon is contained in an amount of 0.1% by weight to 20% by weight based on the total amount of the lithium metal compound and the activated carbon.

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