KR20150106203A - electrode active material comprising reduced titanium oxide and electrochemical device using the same - Google Patents

Abstract

The present invention provides an electrode active material comprising a lithium composite oxide capable of inserting and discharging lithium, and TiO_x, wherein x is greater than or equal to 1 and less than 2. The electrode active material used as a positive electrode active material of a lithium secondary battery can provide a lithium secondary battery with improved output and excellent cycle properties.

Description

[0001] The present invention relates to a reduced titanium oxide-containing electrode active material and an electrochemical device using the reduced titanium oxide and an electrochemical device using the same.

The present invention relates to an electrode active material containing a lithium complex oxide capable of lithium intercalation / deintercalation and TiO _x (1? _X <2); An electrode containing the electrode active material; And an electrochemical device containing the electrode active material on a positive electrode.

2. Description of the Related Art Recently, with the trend toward downsizing and thinning of portable devices such as cellular phones and notebooks, there is a demand for high capacity of lithium secondary batteries used as energy sources for these portable devices.

In general, lithium-cobalt-based metal oxide is used as a cathode active material and carbon is used as a negative electrode active material. The lithium-cobalt-based metal oxide is comparatively easy to synthesize, has excellent stability and cycle characteristics, but has limitations in application to a high-capacity battery technology.

Due to these problems, lithium-manganese-based metal oxides, lithium-nickel-based metal oxides, and the like have recently been attracting attention as cathode active materials. Among these, the lithium-manganese-based metal oxide having a layered structure has an advantage over the lithium-cobalt-based metal oxide in terms of capacity but it is known that the structure is unstable and the cycle characteristics are poor. The spinel lithium-manganese-based metal oxide is excellent in thermal stability, but has a disadvantage in that it is lower in capacity than the lithium-cobalt-based metal oxide. Further, the lithium-nickel-based metal oxide can exhibit a high capacity, but has a poor cycle characteristic and a complicated manufacturing method.

Accordingly, many attempts have been made to improve the thermal stability, capacity, and cycle characteristics by partially replacing the dissimilar metal with the cathode active material, or coating the surface of the cathode active material with a dissimilar metal oxide or the like, but the degree of improvement is insufficient .

On the other hand, other materials have poorer high-temperature characteristics and low-temperature characteristics due to low electronic conductivity than LiCoO ₂ , and the energy density of the battery is not improved despite the high capacity due to low tap density. In particular, the _{Li [Ni 1/2 Mn 1} /2] is difficult to put to practical use a very low electronic conductivity for O _2. In particular, the high output characteristics of these materials as a hybrid power source for electric vehicles are inferior to those of LiCoO ₂ and LiMn ₂ O ₄ . In order to solve such a problem, JP-A-2003-59491 proposes a method of treating conductive carbon black on the surface, but many improvements have not been reported yet.

As a result of intensive efforts to improve the performance of the cathode active material, the present inventors have found that the performance of the cathode active material is improved when TiO _x (1? _X <2) is added or coated on the cathode active material.

An object of the present invention is to provide a method for modifying an electrode active material which can improve the output and cycle characteristics by increasing the electronic conductivity of an electrode active material of an electrochemical device such as a lithium secondary battery.

A first aspect of the present invention provides an electrode active material containing a lithium composite oxide capable of lithium insertion / discharge and TiO _x (1? _X <2).

A second aspect of the present invention provides an electrode containing an electrode active material, a conductive agent and a binder according to the first aspect of the present invention.

A third aspect of the present invention provides an electrochemical device comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode contains the electrode active material according to the first aspect of the present invention.

Hereinafter, the present invention will be described in detail.

The lithium secondary battery is a battery in which lithium ions existing in an ion state move from an anode to a cathode when discharging and move from a cathode to an anode when charging to generate electricity. The performance of the lithium secondary battery is dependent on the lithium ion activation capability of the cathode material and the presence of sufficient space for inserting lithium ions in the cathode material. Particularly, since lithium is contained in the positive electrode active material, the positive electrode active material substantially determines the performance of the lithium secondary battery.

The cathode active material is generally composed of a transition metal oxide, because a change in the oxidation number is necessary to satisfy the charge neutral condition during lithium deintercalation. The properties required for the cathode active material should be considered high operating voltage, small polarization during charging and discharging, high capacity and efficiency, life characteristics, and stability with electrolyte.

Typically, TiO ₂ is an insulator. However, TiO _x (1? _X &lt; 2) added to a lithium composite oxide capable of lithium insertion and release by using the fact that TiO _x (1? _X <2) in which TiO ₂ is partially or wholly reduced has a significantly high electric conductivity. As a result of using the heat-treated electrode active material as an anode of a lithium secondary battery, it was found that not only output and cycle characteristics were improved but also high output characteristics were good. The present invention is based on this.

TiO _x (1? _X <2) can be prepared by partially or wholly reducing TiO ₂ in a reducing atmosphere, for example, an atmosphere containing hydrogen gas.

The electrode active material according to the present invention can be prepared by mixing a lithium complex oxide capable of lithium intercalation / deintercalation and TiO _x (1? _X <2), followed by drying and heat treatment.

At this time, the heat treatment temperature is preferably 100 ° C to 500 ° C.

In order to remove the moisture in advance for the efficiency of heat treatment, it is preferable to mix and dry.

The reduced titanium oxide (TiO _x , 1? _X <2) may be mixed with the lithium composite oxide homogeneously or may be coated with a lithium composite oxide particle.

The lithium complex oxide is _{LiCoO 2, LiNiO 2, Li 1} + x Mn 2 - x O 4 (0≤x≤0.33), Li 2 CuO 2, LiV 3 O 8, LiFe 3 O 4, LiNi 1 - x M x O ₂ (M is Co, Mn, Al, Cu, Fe, and Mg, B or _{Ga; 0.01≤x≤0.3), LiMn 2 -} x M x O 2 (M is Co, Ni, Fe, Cr, Zn or Ta, 0.01? _X ? 0.1), Li ₂ Mn ₃ MO ₈ (M is Fe, Co, Ni, Cu or Zn), Li (Ni _{1 -x- y} Co _x M _y ) O ₂ 0.33, 0? Y? 0.33, and M is Mn, Al, Mg or Fe) or a mixture thereof.

It is preferable that the reduced titanium oxide is contained in an amount of 0.1 to 10 parts by weight, preferably 5 to 10 parts by weight based on 100 parts by weight of the electrode active material. If the amount is less than 0.1 wt%, the effect of the reduced titanium oxide is insufficient, and when the amount is more than 10 wt%, the lithium composite oxide is excessively coated.

The size of the titanium oxide (TiO _x , 1? _X <2) particles is preferably 1 μm or less.

The electrode according to the present invention contains the electrode active material, the conductive agent and the binder according to the present invention.

Non-limiting examples of the conductive agent include acetylene black or carbon blacks. At this time, the content of the conductive agent used in the electrode is preferably 0.5 to 10% by weight in the case of the anode and 10% by weight or less in the case of the cathode.

Non-limiting examples of the binder used in the present invention include polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyacrylonitrile, nitrile rubber, polybutadiene, polystyrene, styrene butadiene rubber, polysulfide rubber, butyl rubber, Hydrogenated styrene-butadiene rubber, nitrocellulose, and carboxymethylcellulose. The content of the binder is preferably 0.1 to 15% by weight.

The electrochemical device according to the present invention includes a cathode, an anode, and an electrolyte containing the electrode active material according to the present invention.

The electrode active material according to the present invention exerts its effect in a lithium secondary battery of an electrochemical device.

Generally, a lithium secondary battery includes a positive electrode capable of adsorbing and desorbing lithium ions, a negative electrode capable of adsorbing and releasing lithium ions, a nonaqueous electrolyte, and a separator.

The cathode may be formed by binding the cathode active material according to the present invention to a foil produced by a cathode current collector, that is, aluminum, nickel, or a combination thereof. The content of the cathode active material is preferably 80 to 99% by weight.

The negative electrode active material for constituting the negative electrode may be lithium metal or lithium alloy and lithium adsorbent such as carbon, petroleum coke, activated carbon, graphite, Materials can be used as the main component. The negative electrode is formed by binding the negative electrode active material with a negative electrode current collector, that is, a foil produced by copper, gold, nickel or a copper alloy or a combination thereof. The content of the negative electrode active material is preferably 80 to 99% by weight.

The separation membrane may be made of polyethylene, polypropylene, or a combination of these films, or a polyvinylidene fluoride, a polyethylene oxide, or the like, having a microporous structure. A polyacrylonitrile or a polyvinylidene fluoride hexafluoropropylene copolymer, or a polymer film for a gel polymer electrolyte or the like is used.

The electrolyte is A ⁺ B ^- and may be a salt of such a structure, A ⁺ is Li ^+, Na ^+,, and comprising an alkali metal cation or an ion composed of a combination thereof, such as K ⁺ B ^- is PF ₆ ^{- _{, BF 4 -, Cl -,}} Br -, I -, ClO 4 -, ASF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO 2 ) _{3 &lt;} ^- &gt; or an ion consisting of a combination of these. Specific examples of the lithium salt include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone Is dissolved and dissolved in an organic solvent composed of N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma-butyrolactone or a mixture thereof.

Non-limiting examples of the method for producing an electrochemical device according to the present invention include: a) an electrode active material particle; Ii) conductive agent particles; And iii) preparing a slurry in which the binder is dispersed in a solvent; b) coating the slurry with a current collector, drying and pressing the slurry to produce an electrode; And c) assembling the electrochemical device having the electrode and injecting the non-aqueous electrolyte.

The solvent used for the slurry is not particularly limited. In general, N-methyl-2-pyrrolidone (NMP) can be used for both the positive electrode and the negative electrode, and distilled water can be used for the aqueous negative electrode.

When the electrodes are well dispersed by mixing during the production of the electrodes, the conductive agent particles are arranged so as to connect the electrode active material particles separated after the electrode coating.

If necessary, heat treatment may be performed to evaporate the solvent during the production of the electrode.

When the electrode active material according to the present invention is used as a positive electrode active material of a lithium secondary battery, improved output and excellent cycle characteristics can be imparted to the lithium secondary battery.

1 is a scanning electron micrograph of a cathode active material according to Example 1. Fig.
FIG. 2 is a scanning electron microscope photograph of the cathode active material according to Example 2. FIG.
Fig. 3 shows the XRD analysis results of the cathode active materials according to Examples 1 and 2. Fig.
4 shows the output characteristics of the lithium secondary battery according to one embodiment of the present invention.
5 shows evaluation of cycle characteristics of a battery according to one embodiment of the present invention.

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

Example  One

To 0.12 g of the TiO _x (1≤x <2) was added 3.88 g of _{LiNi 0 .6 Mn 0 .2 Co 0} .2 O 2 and stirred for 3 hours. After the end of stirring, the recovered powder after the drying at 80 ℃ for 6 hours, 3 hours and heat-treated for a 3% by weight on the surface of the TiO _x (1≤x <2) under an inert atmosphere at 200 ℃ coated anode To prepare an active material.

Example  2

To 0.24 g of the TiO _x (1≤x <2) was added 2.76 g of _{LiNi 0 .6 Mn 0 .2 Co 0} .2 O 2 and stirred for 3 hours. After completion of the stirring, the recovered powder was dried at 60 DEG C for 6 hours and then heat-treated at 200 DEG C for 3 hours in an inert atmosphere to obtain a positive electrode coated with 8 wt% TiOx (1 &lt; _x &lt; 2) To prepare an active material.

Comparative Example  One

LiNi _{0 .6} Mn _{0 .2} used a composite oxide particles that are not coated with the Co _{0 .2} O ₂ composition in the comparative example.

Manufacturing example  One

A coin cell comprising the cathode active material prepared in Example 1 was prepared.

Concretely, the cathode active material prepared in Example 1, polyvinylidene fluoride (PVDF) as a binder and carbon black (manufactured by Timcal) as a conductive agent were mixed at a weight ratio of 95: 2: 3, After that, it was dried and rolled to produce a positive electrode. A coin cell including lithium metal and an electrolyte (1M LiPF ₆ EC / DMC) was fabricated as the positive and negative electrodes.

Manufacturing example  2 to Manufacturing example  3

Except that each of the cathode active materials according to Example 2 (Production Example 2) and Comparative Example 1 (Production Example 3) was used in place of the cathode active material according to Example 1, Coin cells of Example 3 were prepared.

Experimental Example  1: Particle surface observation using scanning electron microscope

For each of the cathode active materials prepared in Example 1 and Example 2, particle surfaces were observed using a scanning electron microscope (JEOL), and the results are shown in FIGS. 1 and 2, respectively. It can be seen from the figure that TiO _x (1? _X <2) particles are partially coated on the surface of the lithium composite oxide particle.

Experimental Example  2: X-ray diffraction  analysis

XRD analysis (manufacturer: PANalytical, model name: X'Pert pro MPD) was performed on each of the cathode active materials prepared in Examples 1 and 2 and Comparative Example 1, and the results are shown in FIG. At this time, the X-ray diffraction analysis was performed using Cu-K? Ray under the condition that the 2? Values ranged from 10 to 80, the sampling width was 0.01, and the scan rate was 4 占 min.

Experimental Example  3: Evaluation of battery output characteristics

The coin cell of Production Example 1 (including the positive electrode active material of Example 1), Production Example 2 (including the positive electrode active material of Example 2), and Production Example 3 (including the positive electrode active material of Comparative Example 1) At a rate of C / 5, followed by discharging at a rate of C / 2, 1C, and 2C, respectively. The results of the above experiment are shown in Fig.

As shown in Fig. 4, a cathode active material was prepared in the same manner as in Production Example 1 (including a cathode active material coated with 3 wt% of TiO _x (1 _x <2) on its surface) and 2 wt% of TiO _x Coin cells including <2) is coated with a positive electrode active material) is, compared with the coin cells of Production example 3 (the surface of TiO _x (including 1≤x <2) the positive electrode active material non-coated), the capacity maintenance rate and the C-rate It was confirmed that the other output characteristics were improved to be equal or higher.

Experimental Example  4: Evaluation of cycle characteristics of battery

The coin cells prepared in Production Examples 1 to 3 were subjected to charging and discharging once at a speed of C / 5 in the range of 3.0 V to 4.5 V, and then charged and discharged at a speed of 1 C, And the results are shown in Fig.

, Preparation 2 of the coin cell (of 8% by weight on the surface TiO _x (including 1≤x <2) is coated with a positive electrode active material) was prepared in Example 1 (3% by weight of TiO _x on the surface as shown in Figure 5 ( (Including the positive electrode active material coated with 1 &_lt; = _x &lt; 2) and the positive electrode active material of Production Example 3 (including the positive electrode active material not coated with TiO _x (1? _X <2) on the surface) there was.

Claims (11)

An electrode active material containing a lithium composite oxide capable of lithium insertion and release and a titanium oxide (TiO _x , 1? _X <2). The electrode active material according to claim 1, wherein the TiO _x is coated with a lithium composite oxide particle capable of lithium ion deintercalation. The electrode active material according to claim 1, wherein the TiO _x is contained in an amount of 5 to 10 parts by weight based on 100 parts by weight of the electrode active material. 2. The lithium _secondary battery according to claim 1, wherein the lithium composite oxide is selected from the group consisting of LiCoO ₂ , LiNiO ₂ , Li _{1 + x} Mn _{2 - x} O ₄ (0 _{? X?} 0.33), Li ₂ CuO _{2 ,} LiV ₃ O ₈ , LiFe ₃ O ₄ , LiNi _{1 - x} MxO ₂ (M is Co, Mn, Al, Cu, Fe, Mg, B or Ga, _{and; 0.01≤x≤0.3), LiMn 2 - x} MxO 2 (M is Co, Ni, Fe, Cr, Zn, or Ta; 0.01? X? 0.1), Li ₂ Mn ₃ MO ₈ (M is Fe, Co, Ni, Cu, or Zn), and Li (Ni _{1 -x- y} Co _x M _y ) O ₂ 0.33, 0? Y? 0.33, and M is selected from the group consisting of Mn, Al, Mg, and Fe). The electrode active material according to claim 1, wherein the size of TiO _x (1? _X <2) particles is 1 μm or less. The electrode active material according to claim 1, which is prepared by mixing a lithium complex oxide capable of lithium intercalation / deintercalation and TiO _x (1? _X <2), followed by drying and heat treatment. The method according to claim 6,
Wherein the heat treatment temperature is 100 ° C to 500 ° C. The electrode active material according to any one of claims 1 to 8, wherein the electrode active material is a cathode active material for a lithium secondary battery. An electrode containing the electrode active material, the conductive agent and the binder according to any one of claims 1 to 8. 1. An electrochemical device comprising an anode, a cathode, and an electrolyte,
Wherein the positive electrode contains the electrode active material according to any one of claims 1 to 8. The electrochemical device according to claim 10, wherein the electrochemical device is a lithium secondary battery.

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