KR20160097407A - Lithium secondary battery comprising lithium titanium oxide, battery pack and vehicle including the same - Google Patents

Abstract

The present invention relates to a lithium secondary battery comprising lithium-titanium oxide, a battery pack and a vehicle comprising the same. The lithium secondary battery comprises: lithium-titanium oxide (LTO) as a negative electrode active material; and nickel-cobalt-aluminum (NCA) as a positive electrode active material. The secondary battery has excellent cycle properties while being capable of rapidly charging and discharging.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery including lithium-titanium oxide, a battery pack including the lithium secondary battery,

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery including lithium-titanium oxide (LTO) as a negative electrode active material and lithium-nickel-cobalt- The present invention relates to a secondary battery.

As the electric, electronic, communication and computer industries rapidly develop, the demand for high performance and high stability secondary batteries is gradually increasing. Especially, due to the thin and simple miniaturization and portability of precision electric appliances, The battery is also required to be thinned and miniaturized.

In response to this demand, a lithium secondary battery is one of the most popular batteries in recent years.

The lithium secondary battery generally includes a positive electrode, an organic electrolyte, a separator, and a negative electrode. These materials are selected in consideration of battery life, charge / discharge capacity, temperature characteristics, stability and the like.

Accordingly, the anode uses a lithium metal oxide, and the separation membrane uses a solvent-free polymer electrolyte or a plasticized polymer electrolyte.

In recent years, lithium secondary batteries using lithium-titanium oxide (LTO), which has a higher Li intercalation desorption potential than carbonaceous materials, as an anode active material, have been used in recent years as cathode materials such as graphite or cokes. Has been put to practical use.

Korean Patent Publication No. 2010-0136805 discloses a lithium secondary battery using lithium titanium oxide as an anode active material.

Lithium titanium oxide is excellent in cycle characteristics as compared with a carbonaceous material because the volume change due to charging and discharging is small. Lithium titanium oxide is advantageous in that it does not precipitate metal lithium in principle and exhibits rapid charging and low-temperature performance at the lithium insertion elimination potential. Among them, spinel type lithium titanate is mainly used.

On the other hand, electric vehicles include an electric vehicle (Full Electric Vehicle) that only runs on electric motors without using fossil fuel at all, and a hybrid vehicle that provides driving power in addition to the internal combustion engine.

In the case of electric vehicles, due to the fact that the price of the vehicle is increased due to the use of the expensive secondary battery, the lifetime of the secondary battery is not sufficiently guaranteed, and the mileage is not long, It is difficult. Therefore, a hybrid vehicle having an electric motor added to the internal combustion engine is more commonly used.

The hybrid vehicle combines an electric motor with an internal combustion engine such as gasoline or diesel to operate in a region where the two power sources can exhibit the respective characteristics, thereby achieving high energy efficiency, thereby reducing fuel consumption and improving vehicle exhaust gas. Here, the output of the electric motor used in optimizing or adjusting the fuel consumption and the capacity of the secondary battery sufficient to support its output must be considered.

Regenerative braking of a secondary battery mounted on a hybrid vehicle is a braking technique in which kinetic energy of an automobile recovers a back electromotive force generated by driving a generator (a rotation axis of a wheel) to a battery and performs braking. Rotation force is needed to rotate the generator, and the required torque is the braking force (decelerating wheel rotation axis) that was conventionally wasted. At this time, the kinetic energy is converted into electric energy, stored (recharged) in the secondary battery, and then the motor can be driven and energy can be reused at the time of oscillation, acceleration, and back-up.

The present invention provides a lithium secondary battery having improved permissible charging output, a battery pack including the lithium secondary battery, and an automobile including the lithium secondary battery.

However, the problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

According to a first aspect of the present invention, there is provided a lithium secondary battery comprising a positive electrode, a negative electrode and an organic electrolyte, wherein the positive electrode includes nickel-cobalt-aluminum (NCA) as a positive electrode active material, Lithium secondary batteries, including lithium-titanium oxide (LTO).

A second aspect of the present invention provides a battery pack comprising at least one lithium secondary battery according to the first aspect of the present invention.

A third aspect of the present invention provides an automobile including the battery pack according to the second aspect of the present invention.

The lithium secondary battery according to the present invention includes lithium-titanium oxide (LTO) as a negative electrode active material and nickel-cobalt-aluminum (NCA) as a positive electrode active material.

Also, it is possible to provide a secondary battery which can be charged / discharged at a high speed and excellent in cycle characteristics by coating the lithium-titanium oxide (LTO) and the nickel-cobalt-aluminum (NCA) with carbon having excellent electrical conductivity.

The effects of the present invention are not limited to those described above and include all possible effects that can be directly or indirectly derived in accordance with the detailed contents for carrying out the invention described below.

FIG. 1 is a graph illustrating the output characteristics of a lithium secondary battery according to an embodiment of the present invention measured by a hybrid pulse power characterization (HPPC) method.
2 shows the results of measurement of the output characteristics of the lithium secondary battery according to the comparative example according to the HPPC method.
3 shows the results of measurement of the output characteristics of the lithium secondary battery according to the comparative example according to the HPPC method.
4 is a graph showing current application amount when measuring the power capability in a specific charged state using a hybrid pulse power characterization (HPPC) method.

Hereinafter, embodiments and examples of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains.

It should be understood, however, that the present invention may be embodied in many different forms and is not limited to the embodiments and examples described herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout this specification, when a part is referred to as being "connected" to another part, it is not limited to a case where it is "directly connected" but also includes the case where it is "electrically connected" do.

Throughout this specification, when a member is "on " another member, it includes not only when the member is in contact with the other member, but also when there is another member between the two members.

Throughout this specification, when an element is referred to as "including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise.

As used herein, the terms "about," " substantially, "and the like are used herein to refer to or approximate the numerical value of manufacturing and material tolerances inherent in the stated sense, Accurate or absolute numbers are used to prevent unauthorized exploitation by unauthorized intruders of the mentioned disclosure. Also, throughout the present specification, the phrase " step "or" step "does not mean" step for.

Throughout this specification, the term "combination thereof" included in the expression of the machine form means one or more combinations or combinations selected from the group consisting of the constituents described in the expression of the machine form, And the like.

Throughout this specification, the description of "A and / or B" means "A, B, or A and B".

Hereinafter, the lithium secondary battery of the present invention will be described in detail with reference to embodiments, examples, and drawings. However, the present invention is not limited to these embodiments and examples and drawings.

According to a first aspect of the present invention, there is provided a lithium secondary battery comprising a positive electrode, a negative electrode and an organic electrolyte, wherein the positive electrode includes nickel-cobalt-aluminum (NCA) as a positive electrode active material, Lithium secondary batteries, including lithium-titanium oxide (LTO).

In one embodiment of the present invention, the lithium-titanium oxide (LTO) has a ramsdellite structure and may be represented by the formula Li ₂ Ti ₃ O ₇ .

Li ₂ Ti ₃ O ₇ having a rhamstellite structure Are arranged in hexagonally close packed (HCP). And a space group of Pnma, and the framework possesses rhamstellite (γ-MnO ₂ ). At this time, the lithium ion is crystallographically divided into three types. Li1 (8d) and Li2 (4c) are located inside the tunnel, and reversible migration is possible. Li3 (4c) is formed at the ratio of 86% Ti and 14% Li at the cation position of the framework, and forms an octahedral together with oxygen ions.

The Lammeralite type LTO has a one-dimensional tunnel structure unlike the spinel type LTO having a three-dimensional channel structure. Due to these structural features, they have different slope shapes in the 1.4 V to 2.0 V range during charging and discharging, but they have a higher reversible capacity (198 mAh / g) than the spinel type LTO (reversible capacity: 175 mAh / g). In addition, it exhibits excellent structural stability even in a long cycle life. Due to such structural stability, it is expected as a material satisfying high capacity, high output, high safety and durability required as an anode active material of a future medium and large sized battery.

According to an embodiment of the present invention, the negative electrode is formed by suspending a conductive agent and a binder in a suitable solvent in a mixture of the lithium-titanium oxide (LTO) and a lithium precipitation reaction inhibitor, Dried, and pressed to form strip-shaped electrodes. As the conductive agent, it is preferable to use carbon black or graphite. Examples of the binder include vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetra It is preferable to use fluoroethylene or a mixture thereof. At this time, the content of the negative electrode active material, the conductive agent, the binder and the solvent is a level commonly used in a lithium secondary battery.

According to one embodiment of the present invention, the lithium-titanium oxide (LTO) may be either lithium-titanium oxide or lithium-titanium-containing oxide phase in which a part of the lithium-titanium oxide is replaced with a hetero-element. For example, the lithium-titanium oxide (LTO) may be selected from the group consisting of C, Al, Ga, Co, Fe, Ni, Mg, Mn, V, Zr, Zn, Cu, Mo, Si, Nb, and Cr. It is preferable that the lithium-titanium oxide (LTO) phase is mainly constituted to obtain excellent high current characteristics and cycle characteristics.

According to one embodiment of the present invention, the lithium-titanium oxide (LTO) may be carbon-coated. When the lithium-titanium oxide (LTO) is coated with carbon having excellent electrical conductivity, it is possible to provide a negative active material which is capable of high-speed charge-discharge and excellent cycle characteristics, and a secondary battery comprising the negative active material.

The carbon may be coated in an amount of about 0.01 wt.% To about 10 wt.% Based on the total weight of the lithium-titanium oxide (LTO), for example, about 0.1 wt.% To about 10 wt. From about 1% to about 10%, from about 5% to about 10%, from about 0.1% to about 5%, from about 0.1% to about 1% But is not limited to, from 0.01% by weight to about 1% by weight or from about 0.01% by weight to about 0.1% by weight.

According to one embodiment of the invention, the lithium-titanium oxide (LTO) may have a tap density ranging from about 0.5 g / ml to about 2.0 g / ml. The working density was measured by placing the sample in a 100 ml container and tapping it about 500 to about 1000 times using a tapper and calculating the density.

According to one embodiment of the present disclosure, the lithium-titanium oxide (LTO) may have an average particle size in the range of about 0.05 [mu] m to about 20 [mu] m. The average particle size can be measured by a frequency distribution method of particle size distribution (PSD).

According to an embodiment of the present invention, the average particle size of the lithium-titanium oxide (LTO) is uniformed, the lithium-titanium oxide (LTO) is coated with carbon to improve the electrical conductivity, It is possible to improve the allowable charge output by adjusting the working density. Preferably, by coating the lithium-titanium oxide (LTO) having an average particle size of less than about 1 占 퐉 and a working density of less than or equal to about 1.5 g / ml with less than about 5 weight percent of carbon, Can be improved.

According to one embodiment of the present invention, the positive electrode is formed by, for example, suspending a positive electrode active material, a positive electrode conductive agent and a binder in a suitable solvent, applying the slurry prepared by suspending the positive electrode current collector to a positive electrode current collector, And then pressing it. As the conductive agent, it is preferable to use carbon black. Examples of the binder include polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyacrylonitrile, nitrile rubber, polybutadiene, polystyrene, styrene butadiene rubber, Rubber, butyl rubber, hydrogenated styrene-butadiene rubber, nitrocellulose, carboxymethylcellulose or a mixture thereof is preferably used. At this time, the content of the cathode active material, the conductive agent, the binder and the solvent is a level commonly used in a lithium secondary battery.

According to one embodiment of the invention, the nickel-cobalt-aluminum (NCA) comprises nickel in the range of about 30 wt% to about 70 wt% and cobalt in the range of about 5 wt% to about 50 wt% And aluminum in an amount ranging from about 4 wt% to about 15 wt%, but is not limited thereto.

According to one embodiment of the invention, the nickel-cobalt-aluminum (NCA) may be carbon coated. When the nickel-cobalt-aluminum (NCA) is coated with carbon, it is possible to achieve an effect of providing a negative active material having a high cycle characteristic and a secondary battery including the negative active material capable of high-speed charging and discharging.

The carbon may be coated in an amount of about 0.01 wt% to about 10 wt%, for example, about 0.1 wt% to about 10 wt%, based on the total weight of the nickel-cobalt-aluminum (NCA) From about 1% to about 10%, from about 5% to about 10%, from about 0.1% to about 5%, from about 0.1% to about 1% But is not limited to, from about 0.01 wt% to about 1 wt% or from about 0.01 wt% to about 0.1 wt%.

According to one embodiment of the invention, the nickel-cobalt-aluminum (NCA) may have a tap density ranging from about 2.0 g / ml to about 3.0 g / ml.

The content of nickel in the nickel-cobalt-aluminum (NCA) can be adjusted to improve the capacity and safety of the lithium secondary battery, and the content of cobalt can be controlled to improve the allowable charging power. The conductivity can be improved. Preferably, the content of nickel in nickel-cobalt-aluminum (NCA) is controlled to 60% by weight or less, the content of cobalt is controlled to 5% by weight or more and the carbon is coated in 0.01% .

According to one embodiment of the present invention, the organic electrolyte may include, but is not limited to, an organic solvent and a lithium salt.

The solvent may be a material known in the art and may be one having a high permittivity (polarity) and a low viscosity and a low reactivity with lithium metal in order to increase the degree of dissociation of ions and smooth the conduction of ions And may be, for example, a mixture of chain-like hydrocarbons and cyclic hydrocarbons. The chain hydrocarbon may be, for example, polyethylene carbonate, ethylene carbonate, or propylene carbonate, and the cyclic hydrocarbon may be, for example, dimethyl carbonate or diethyl carbonate, but is not limited thereto

As the lithium salt, materials known in the art can be used, and it is preferable to use one having good lattice energy and high dissociation degree, excellent ion conductivity, and good thermal safety and oxidation resistance. The lithium salt may be, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , LiC (CF ₃ SO ₃ ) ₃ , LiAsF ₆ , But are not limited thereto.

A second aspect of the present invention provides a battery pack comprising at least one lithium secondary battery according to the first aspect of the present invention.

A third aspect of the present invention provides an automobile including the battery pack according to the second aspect of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[ Example ]

[Preparation of NCA-LTO lithium secondary battery (Example 1)] [

≪ Preparation of negative electrode &

(PVdF) was mixed with NMP (N-methyl-2-pyrrolidone) as a solvent at a weight ratio of 90: 5: 5 to prepare a slurry Was prepared and applied to an aluminum foil to prepare a negative electrode.

≪ Preparation of positive electrode &

A slurry was prepared by mixing a cathode active material, a conductive agent and a binder (PVdF) using a lithium nickel-cobalt-aluminum (NCA) oxide in a weight ratio of 90: 5: 5, respectively, to a solvent NMP to form an anode Respectively.

≪ Preparation of Secondary Battery &

An electrode assembly was prepared by inserting a separation membrane between the anode and the cathode, and an aluminum casing was fabricated. A lithium carbonate battery was prepared by injecting and sealing a mixture of a carbonate-based solvent having LiPF ₆ salt dissolved therein and an electrolyte

[Production of LMO-LTO lithium secondary battery (Comparative Example 1)] [

The cathode and lithium manganese oxide (LMO) prepared in Example 1 were used as a cathode active material, and a conductive agent and a binder (PVdF) were mixed in NMP as a solvent at a weight ratio of 90: 5: 5, To prepare a positive electrode. The prepared positive electrode and negative electrode were prepared in the same manner as in Example 1 to prepare a secondary battery.

[Production of NCM-LTO lithium secondary battery (Comparative Example 2)] [

Using the negative electrode prepared in Example 1 and lithium nickel cobalt manganese oxide (LMO) as a positive electrode active material, a conductive agent and a binder (PVdF) were mixed in NMP as a solvent at a weight ratio of 90: 5: 5 respectively to prepare a slurry Was applied to an aluminum foil to prepare a positive electrode. The prepared positive electrode and negative electrode were prepared in the same manner as in Example 1 to prepare a secondary battery.

[Measurement of allowable charge output]

The hybrid power technique (HPPC) method, which is mainly used in the evaluation of hybrid vehicles, was used to measure the power capability in a specific charged state. Specifically, as shown in Fig. 4, a pulse discharge current (normally 75% of the maximum allowable current) is applied for 10 seconds, and when no current is applied for 40 seconds, 75% The resistance was calculated from the voltage change during discharging and charging.

The HPPC experiment is performed by varying the depth of discharge (DOD) or the state of charge (SOC), and the resistance according to each DOD is measured, and the discharge pulse power capability is measured using the resistance value. And a regen (pulse power capability) were measured to measure the allowable power change of the lithium secondary battery.

FIG. 1 is a graph showing a change in the allowable charge output according to the DOD change in the first embodiment, and FIGS. 2 and 3 are graphs showing changes in the allowable charge output according to the DOD changes in Comparative Example 1 and Comparative Example 2, respectively.

In the case of the allowable charge power, it is confirmed that the DOD of 50% is 1,153 W / kg in Comparative Example 1, 2,139 W / kg in Comparative Example 2 and 5,081 W / kg in Example 1 . The case of the discharge pulse power capability which is a measure of the instantaneous acceleration capacity when applied to a vehicle is also 1,898 W / kg in the case of the comparative example 1 and 644 W / kg in the case of the comparative example 2, In case of 2,506 W / kg, it is also improved and it can be seen that the improvement of accelerating ability is also improved.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents are to be construed as being included within the scope of the present invention do.

Claims (17)

An anode, a cathode, and an organic electrolyte,
The positive electrode includes nickel-cobalt-aluminum (NCA) as a positive electrode active material,
Wherein the negative electrode comprises lithium-titanium oxide (LTO) as a negative electrode active material.
The method according to claim 1,
Wherein the lithium-titanium oxide (LTO) has a ramsdellite-type structure and is represented by the formula Li ₂ Ti ₃ O ₇ .
The method according to claim 1,
Wherein the lithium-titanium oxide (LTO) is carbon-coated.
The method of claim 3,
Wherein the carbon is coated in an amount of 0.01 wt% to 10 wt% based on the total weight of the lithium-titanium oxide (LTO).
The method according to claim 1,
Wherein the lithium-titanium oxide (LTO) has a working density in the range of 0.5 g / ml to 2.0 g / ml.
The method according to claim 1,
Wherein the lithium-titanium oxide (LTO) has an average particle size in the range of 0.05 mu m to 20 mu m.
The method according to claim 1,
Wherein the nickel-cobalt-aluminum (NCA) comprises nickel in an amount of 30 wt% to 70 wt%.
The method according to claim 1,
Wherein the nickel-cobalt-aluminum (NCA) comprises cobalt in a range of 5 wt% to 50 wt%.
The method according to claim 1,
Wherein the nickel-cobalt-aluminum (NCA) comprises aluminum in a range of 4 wt% to 15 wt%.
The method according to claim 1,
Wherein the nickel-cobalt-aluminum (NCA) is carbon-coated.
11. The method of claim 10,
Wherein the carbon is coated in an amount of 0.01 wt% to 10 wt% based on the total weight of the nickel-cobalt-aluminum (NCA).
The method according to claim 1,
Wherein the nickel-cobalt-aluminum (NCA) has a working density in the range of 2.0 g / ml to 3.0 g / ml.
The method according to claim 1,
Wherein the organic electrolyte comprises an organic solvent and a lithium salt.
14. The method of claim 13,
Wherein the organic solvent includes one selected from the group consisting of polyethylene carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and combinations thereof.
14. The method of claim 13,
Wherein the lithium salt is selected from the group consisting of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , LiC (CF ₃ SO ₃ ) ₃ , LiAsF ₆ , , Lithium secondary battery.
A battery pack comprising at least one lithium secondary battery according to any one of claims 1 to 15.
An automobile comprising the battery pack according to claim 16.

Images