JP2014527267A - Bimodal type negative electrode active material and lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to a negative electrode active material comprising a compound of the following formula (1) that can embody a high-density electrode and can simultaneously improve the adhesion and high-rate characteristics of the electrode. The compound includes first primary particles and secondary particles, wherein the ratio of the first primary particles: secondary particles is 5:95 to 50:50 weight ratio: Li _x M _y O _z (1) In the formula (1), M is independently any one selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al, and Zr, or 2 of these. A mixture of species and more; x, y and z are determined according to the oxidation number of M.
[Selection] Figure 1

Description

  The present invention relates to a bimodal type negative electrode active material and a lithium secondary battery including the same, wherein a negative electrode active material is a mixture of primary particles and secondary particles. The present invention relates to a negative electrode including lithium and a lithium secondary battery.

  A lithium ion secondary battery is a type of secondary battery that operates on the principle of generating a battery while moving a positive electrode and a negative electrode relative to each other. The components of the lithium ion secondary battery can be roughly divided into a positive electrode, a negative electrode, a separation membrane, and an electrolyte. Of these components, the positive electrode active material and the negative electrode active material have a structure in which lithium in an ionic state can be inserted into and removed from the active material, and charging and discharging are performed by a reversible reaction.

  Lithium metal was used as the negative electrode active material of conventional lithium batteries, but when lithium metal is used, there is a risk of explosion due to the short circuit of the battery due to the formation of dendrites. Many materials are used as negative electrode active materials.

  Examples of the carbonaceous material include crystalline carbon such as graphite and artificial graphite, and amorphous carbon such as soft carbon and hard carbon. However, the amorphous carbon has a large capacity, but has a problem that it has a large irreversibility in the charge / discharge process. Graphite is typically used for crystalline carbon, which has a high theoretical limit capacity. However, since such crystalline carbon and amorphous carbon are only about 380 mAh / g even if the theoretical capacity is somewhat high, it is difficult to use such a negative electrode when developing a high capacity lithium battery. It is.

  Therefore, recently, with the aim of developing lithium-ion secondary batteries with high-speed charge and discharge and long-life battery performance, research to apply lithium titanium oxide (LTO) as a spinel metal oxide to the negative electrode active material Is being actively promoted.

  LTO does not generate an SEI (Solid Electrolyte Interface) film produced by the incidental reaction between the graphite-based negative electrode active material and the electrolyte that is generally used in lithium-ion secondary batteries at present, so it has an irreversible capacity compared to graphite. It is excellent in terms of generation, and has excellent reversibility with respect to insertion and desorption of lithium ions even in repeated charge / discharge cycles. Furthermore, since it is structurally very stable, it is a promising material that can exhibit the long-life performance of the secondary battery.

  On the other hand, lithium titanium oxide can be divided into two forms: a case where it consists only of primary particles, and a case where primary particles are aggregated into secondary particles. Among these, when composed of primary particles, there is no problem of electrode adhesion force with an appropriate particle size, but there is a characteristic that high-speed charge / discharge is deteriorated. Therefore, when the particle size is manufactured to 300 nm or less in order to compensate for such disadvantages and improve the rate capability, a process problem at the time of slurry production due to an increase in specific surface area appears. Further, when secondary particles are used to improve the problem of nano-primary particles, the problem is improved, but a large amount of binder is still necessary to maintain electrode adhesion. Since the binder acts as an electrical resistance element of the electrode, there is a problem that it ultimately deteriorates the total energy density of the battery.

  In addition, as a function of a device using a battery is improved, a battery having a high energy density is demanded, and a technique capable of increasing energy per unit volume is required to satisfy this. In order to improve the energy per unit volume, the amount of the electrode material coated per unit volume is increased to form a high-density electrode, and a battery having high energy can be configured.

  Accordingly, there is a need for an active material that can reduce the amount of binder used and improve the electrode density.

  The present invention aims to provide a negative electrode active material capable of ensuring not only adhesive strength with an electrode but also high-rate characteristics of a battery and high density of the electrode.

  The present invention provides a bimodal type negative electrode active material, in which particles forming the negative electrode active material are present as a mixture of first primary particles and secondary particles, a negative electrode including the same, and a lithium secondary battery To do.

  By using a negative electrode active material in which primary primary particles and secondary particles are mixed in an appropriate ratio, it is possible not only to realize a high-density electrode, but also to improve the adhesion and high-rate characteristics of the electrode at the same time. be able to.

FIG. 3 is a schematic view of a negative electrode active material in which first primary particles are mixed with secondary particles in an appropriate amount based on an embodiment of the present invention. It is a schematic diagram of the negative electrode active material in which a large amount of first primary particles are mixed with secondary particles. It is the graph which showed the electrode density with the ratio of the mixing of the 1st primary particle used for the negative electrode of Examples 7-12 based on one Example of this invention.

The present invention relates to a negative electrode active material containing a compound of the following formula (1), wherein the compound of the following formula (1) contains first primary particles and secondary particles, and the ratio of the first primary particles: secondary particles Provides a negative electrode active material characterized in that the weight ratio is 5:95 to 50:50:
[Formula 1]
Li _x M _y O _z (1)
In the formula (1), each M is independently selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al, and Zr, or two or more of these. A mixture; x, y and z are determined according to the oxidation number of M.

  According to an embodiment of the present invention, a high-density electrode can be realized by using a negative electrode active material in which the first primary particles and secondary particles are mixed in an appropriate ratio. It is possible to simultaneously improve the adhesiveness and the high rate characteristics.

  FIG. 1 is a schematic view of a negative electrode active material according to an embodiment of the present invention in which first primary particles are mixed with secondary particles in an appropriate amount, and FIG. It is a schematic diagram of the negative electrode active material mixed with secondary particles.

  As shown in FIGS. 1 and 2, the first primary particles fill the voids between the secondary particles in all cases where the first primary particles are mixed in an appropriate amount and in a large amount. can do. However, in order to satisfy not only the electrode density but also the optimum performance with adhesive strength and high rate characteristics at the same time, as shown in FIG. 1, when the first primary particles and secondary particles are properly mixed, Is possible.

According to an embodiment of the present invention, the average particle diameter (D ₅₀ ) of the first primary particles and the like is in the range of 10 nm to 3 μm, preferably 100 nm to 1 μm, more preferably 100 nm to 700 nm.

  When the average particle size of the first primary particles is less than 10 nm, there may be a substantial difficulty in terms of the manufacturing process. When the average particle size exceeds 3 μm, the size of the first primary particles is large. Therefore, it is difficult to expect the effect of improving the high rate characteristics by the first primary particles.

  When the lithium metal oxide particles are composed only of the first primary particles and are used as a negative electrode active material of a lithium secondary battery, there is no problem of electrode adhesion, but there is a drawback that high-speed charge / discharge characteristics deteriorate. . In order to overcome these disadvantages, the first primary particles can be produced in a smaller size. In this case, however, the specific surface area is increased to cause problems during the production process of the negative electrode slurry, for example, an excessive amount of binder. Problems such as increased product costs and reduced electrical conductivity due to use may occur.

  Therefore, in order to solve the problem in the case of using only such first primary particles, according to one embodiment of the present invention, the first primary particles and the secondary particles of the lithium metal oxide are appropriately mixed. By using the mixture as a negative electrode active material, it is possible not only to realize a high-density electrode, but also to improve the adhesion and high-rate characteristics of the electrode at the same time.

  According to an embodiment of the present invention, the mixing ratio of the first primary particles and the secondary particles is 5:95 to 50:50, preferably 5:95 to 40:60. Is preferred.

  If the amount of the first primary particles is larger than the above range, the electrode density can be increased, but the electrode adhesion and the high-rate characteristics of the secondary battery can be decreased. Furthermore, if the amount of the first primary particles is less than the above range, the voids between the secondary particles cannot be filled with the first primary particles, so that it is difficult to achieve the intended effect of the present invention. It is.

  The lithium metal oxide particles according to an embodiment of the present invention may be secondary particles in which two or more second primary particles are aggregated, and may be porous particles.

  According to one embodiment of the present invention, when two or more second primary particles are aggregated to form a secondary particle, the second primary particles are not agglomerated and are present individually. In particular, since the specific surface area is small, it can be excellent in terms of electrode adhesion.

In the present invention, the secondary particles have an internal porosity of 3% to 15%, an average particle diameter (D ₅₀ ) of 5 μm to 30 μm, and a specific surface area (BET) of 1 m ² / g to 15 m ² / g. possible.

  When the internal porosity of the secondary particles is less than 3%, there is a possibility that there is a substantial difficulty in terms of the manufacturing process in that the secondary particles are formed by aggregation of the second primary particles. When the internal porosity exceeds 15%, the amount of the necessary binder may be increased to reduce the conductivity and the capacity may be decreased in order to maintain an appropriate electrode adhesion.

According to one embodiment of the present invention, the internal porosity of the secondary particles can be defined as follows:
Internal porosity = void volume per unit mass / (specific volume + void volume per unit mass)

  The measurement of the internal porosity is not particularly limited, and can be measured based on one embodiment of the present invention, for example, using BELSORP (BET equipment) manufactured by BEL JAPAN using an adsorbed gas such as nitrogen.

For a similar purpose, the specific surface area (BET) of the secondary particles is preferably 1 m ² / g to 15 m ² / g.

  In the present invention, the specific surface area of the first primary particles and secondary particles can be measured by a BET (Brunauer-Emmett-Teller; BET) method. For example, the BET 6-point method can be measured by a nitrogen gas adsorption flow method using a pore distribution analyzer (Bell Japan Inc, Belsorp-II mini).

On the other hand, the average particle size (D ₅₀ ) of the secondary particles may be 5 μm to 30 μm, preferably 5 μm to 12 μm. The average particle size (D ₅₀ ) of the second primary particles constituting the secondary particles is from 100 nm. It may be 1 μm, preferably 100 nm to 700 nm.

In the present invention, the average particle size (D ₅₀ ) can be defined as a particle size based on 50% of the particle size distribution. The average particle diameter (D ₅₀ ) of the first and second primary particles and secondary particles according to an embodiment of the present invention can be measured using, for example, a laser diffraction method. it can. In general, the laser diffraction method can measure a particle diameter of about several millimeters from a submicron region, and can obtain high reproducibility and high resolution results.

  In general, lithium metal oxide has low conductivity, so that it is advantageous for the average particle size to be small for application to a cell for fast charging. Large amounts of binder are required to maintain adequate electrode adhesion by increasing the surface area.

  That is, when the average particle size of the secondary particles is less than 5 μm, the amount of the binder for maintaining the desired electrode adhesion increases due to the increase in the specific surface area of the negative electrode active material, thereby reducing the electrode conductivity. Such a problem may occur. On the other hand, when the average particle size of the secondary particles exceeds 30 μm, there is a problem that the fast charge characteristics are deteriorated.

  Therefore, when the high-density negative electrode active material according to an embodiment of the present invention is a secondary particle having an average particle diameter in the range of 5 μm to 30 μm, the amount of the binder for maintaining the electrode adhesive force is reduced. In addition, since the area capable of directly reacting with Li ions is increased, both the fast charge characteristics can be improved.

  On the other hand, when the average particle size of the second primary particles is less than 100 nm, there may be a difficulty in the production process in producing the average particle size less than 100 nm. In addition to reducing the porosity of the secondary particles formed by the secondary particles, it is difficult for lithium ions to penetrate into the secondary particles, making it difficult for the second primary particles inside the secondary particles to participate in the charge / discharge reaction. possible. On the other hand, when the average particle size of the second primary particles is more than 1 μm, the formability of the secondary particles is lowered, and there is a problem that it is difficult to control the assembly.

According to one embodiment of the present invention, the compound of the formula (1) is one selected from the group consisting of Li ₄ Ti ₅ O ₁₂ , Li ₂ TiO ₃ , Li ₂ Ti ₃ O ₇ and the following formula (2). The following lithium titanium oxide can be included:
[Chemical 2]
Li _{x '} Ti _y' O ₄ (2)
In the formula (2), 0.5 ≦ x ′ ≦ 3; 1 ≦ y ′ ≦ 2.5.

Furthermore, the compound of the formula (2) is preferably LiTi ₂ O ₄ .

  The negative active material manufacturing method according to an embodiment of the present invention includes first manufacturing the first primary particles of the lithium metal oxide by a normal method, and the secondary particles of the lithium metal oxide particles are second Can be formed by a separate assembling process after the primary particles are manufactured, but the secondary particles are usually formed by a method of aggregating the second primary particles and aggregating the second primary particles through one process. Can be manufactured. Thereafter, the manufactured first primary particles and second secondary particles can be uniformly mixed to manufacture the negative electrode active material according to the present invention.

  In the method for manufacturing a negative electrode active material according to an embodiment of the present invention, the first primary particles are prepared by adding a lithium salt and a metal oxide to a volatile solvent, stirring, firing, and then grinding and sieving. ) Can be obtained.

  More specifically, the first primary particles are obtained by dissolving a lithium salt in the volatile solvent, adding titanium oxide, which is a metal oxide, with stirring, and then at about 500 ° C. to 1000 ° C. for about 1 hour to 15 ° C. It can be manufactured by calcination and sieving after firing for a period of time.

  Here, the volatile solvent may be, for example, water, acetone or alcohol.

  Furthermore, the lithium salt may be any one selected from the group consisting of lithium hydroxide, lithium oxide, and lithium carbonate, or a mixture of two or more thereof.

  Furthermore, in the method for manufacturing a negative electrode active material according to an embodiment of the present invention, the method for manufacturing the secondary particles includes the step of manufacturing a precursor solution by adding and stirring a lithium salt and a metal oxide to a volatile solvent. And supplying the precursor solution into a chamber of a spray drying equipment, and spraying and drying the precursor solution in the chamber.

  At this time, the lithium salt, the metal oxide, and the volatile solvent can be selected from the same materials as those used in the production of the first primary particles.

  According to an embodiment of the present invention, the secondary particles of the lithium metal oxide particles can be formed by a separate assembly process after the second primary particles are manufactured, but usually through one process. The second primary particles can be produced and produced by a method of aggregating the second primary particles.

  An example of such a method is a spray drying method. Below, the manufacturing method of the secondary particle which concerns on one Example of this invention is demonstrated taking a spray drying method as an example.

  Meanwhile, the manufacturing method according to an embodiment of the present invention may include a step of supplying the precursor solution to a chamber provided in the spray drying equipment.

  As the spray drying equipment, a commonly used spray drying equipment can be used, for example, an ultrasonic spray drying device, an air nozzle spray drying device, an ultrasonic nozzle spray drying device, a filter expansion droplet generator, or an electrostatic spray. Although a drying apparatus etc. may be used, it is not limited to this.

  According to an embodiment of the present invention, the supply rate of the precursor solution into the chamber may be 10 ml / min to 1000 ml / min. If the feed rate is less than 10 ml / min, the average particle size of the agglomerated second primary particles becomes small, making it difficult to form high-density secondary particles, and the feed rate is 1000 ml / min. If it exceeds, the average particle size of the secondary particles becomes coarse, so that it may be difficult to realize a desired high-rate characteristic.

  Furthermore, the method for producing secondary particles according to an embodiment of the present invention may include a step of spraying and drying the precursor solution in the chamber.

  The precursor solution can be sprayed through a disk that rotates at a high speed in the chamber, and spraying and drying can be performed in the same chamber.

  Furthermore, for the realization of the average particle size and the internal porosity of the present invention, it may be possible to control the spray drying conditions such as the flow rate of the carrier gas, the residence time in the reactor and the internal pressure.

  According to an embodiment of the present invention, the internal porosity of the secondary particles can be controlled through adjustment of the drying temperature, and the drying can be performed at a temperature of 20 ° C. to 300 ° C. It is advantageous to proceed at the lowest possible temperature for the conversion.

  According to one embodiment of the present invention, the first primary particles and the secondary particles are mixed in a weight ratio of 5:95 to 50:50, preferably 5:95 to 40:60. In addition, it is possible to manufacture a negative electrode active material in which not only the adhesive strength with the electrode but also the high rate characteristics of the battery and the high density of the electrode are ensured. At this time, in order to mix the first primary particles with the particles and the like as much as possible, they can be uniformly mixed preferably using a normal milling method such as a planetary mill.

  The lithium metal oxide including the first primary particles and the secondary particles according to an embodiment of the present invention may be included in an amount of 50 wt% to 100 wt% with respect to the total weight of the negative electrode active material. When the content of the lithium metal oxide is 100% by weight relative to the weight of the whole negative electrode active material, it means that the negative electrode active material is composed of only the lithium metal oxide.

  In the secondary battery according to an embodiment of the present invention, the negative electrode active material includes a carbon-based material, a transition metal oxide, a Si-based material, and a Sn-based material that are commonly used for the negative electrode active material in addition to the lithium metal oxide. Any one selected or two or more active materials among them may be further included, and the present invention is not limited to these types.

  The present invention further provides a negative electrode active material composition comprising the negative electrode active material, a conductive material and a binder, wherein the negative electrode active material: conductive material: binder is in a weight ratio of 80 to 90: 3 to 9: 7 to 13. Preferably included.

  The present invention further provides a negative electrode including the negative electrode active material composition and a lithium secondary battery including the negative electrode.

  The negative electrode can be manufactured by mixing a negative electrode active material composition containing the negative electrode active material in a solvent such as NMP (N-methylpyrrolidone) and applying the mixture onto a negative electrode current collector, followed by drying and rolling.

  The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing a chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel A steel surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. The negative electrode current collector can also form fine irregularities on the surface to strengthen the binding force of the negative electrode active material, and can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics. Can be used.

  The conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black, acetylene black, ketjen black, Carbon black such as channel black, furnace black, lamp black and summer black; conductive fiber such as carbon fiber and metal fiber; metal powder such as carbon fluoride, aluminum and nickel powder; conductivity such as zinc oxide and potassium titanate Whisker; conductive metal oxide such as titanium oxide; conductive material such as polyphenylene derivative can be used.

  The binder is polyvinylidene fluoride (PVdF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-dieneterpolymer (EPDM). Sulfonated EPDM, styrene butadiene rubber, fluoro rubber, various copolymers, and the like.

  On the other hand, the positive electrode included in the lithium secondary battery according to the present invention is manufactured by, for example, applying a positive electrode slurry containing a positive electrode active material on a positive electrode current collector and then drying the positive electrode slurry. Depending on the above, components as described above may be included.

In particular, the lithium secondary battery includes a layered compound such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ) as a positive electrode active material, or a compound replaced with one or more transition metals; Li _{1 + x} Mn _2−x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and other lithium manganese oxides; lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ ; chemical formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al , Cu, Fe, Mg, B, or Ga, where x = 0.01 to 0.3); Ni-site type lithium nickel oxide represented by the chemical formula LiMn _2−x M _x O ₂ (where, M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, Ni, Cu or Zn) LiMn ₂ O ₄ in which a part of Li in the chemical formula is replaced with an alkaline earth metal ion; a disulfide compound; Fe ₂ (MoO ₄ ) _{3 and the} like can be used. LiNi _x Mn _2-x O ₄ (0.01 = x = 0.6) can be preferably used, and LiNi _0.5 Mn _1.5 O ₄ or LiNi _0.4 Mn _1.6 is more preferable. O ₄ can be used. That is, in the present invention, spinel lithium manganese composite oxide of LiNi _x Mn _2−x O ₄ (x = 0.01−0.6) having a relatively high potential due to the high potential of the negative electrode active material is used as the positive electrode. It is preferable to use it as an active material.

  The present invention further provides a battery module including the lithium secondary battery in a unit battery, and a battery pack including the battery module.

  As the battery case used in the present invention, those commonly used in the art can be adopted, and there is no limitation on the outer shape accompanying the use of the battery. For example, a cylindrical shape using a can, a square, a pouch shape, It can be a coin shape.

  The lithium secondary battery according to the present invention can be used not only for a battery cell used as a power source for a small device, but also for a unit battery in a medium-sized or large-sized battery module including a large number of battery cells. Preferred examples of the medium-sized device include, but are not limited to, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

[Best Mode for Carrying Out the Invention]
Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified in various other forms, and the scope of the present invention is not limited to the embodiments described in detail below.

[Example]
Production Example 1: Production of first primary particles
LiOH.H ₂ O and TiO ₂ (anatase) were mixed at a ratio of 4: 5 (molar ratio), this mixture was dissolved in pure water, stirred, calcined at 750 ° C. for about 3 hours, ground and sieved Sieving was performed to produce first primary particles having an average particle size (D ₅₀ ) of 700 nm.

Production Example 2: Production of secondary particles
LiOH.H ₂ O and TiO ₂ (anatase) were mixed at a molar ratio of 4: 5, and the mixture was dissolved in pure water and stirred. At this time, the ratio of the total solid material was defined as the weight of the total solid powder contained in the solution with respect to the total weight of the solution, and the precursor solution was manufactured by stirring to 30%. The precursor solution was supplied into a chamber of a spray drying equipment (Ein system product) and sprayed and dried in the chamber. At this time, the spray drying conditions were as follows: the precursor obtained after proceeding at a drying temperature of 130 ° C., an internal pressure of −20 mbar, and a supply rate of 30 ml / min was calcined in air at 800 ° C., and the average particle size was 5.4 μm. Thus, Li ₄ Ti ₅ O ₁₂ secondary particles having an internal porosity of 3.5% were produced.

Example 1
The first primary particles and secondary particles produced in Production Examples 1 and 2 were mixed at a 5:95 weight ratio using a planetary mill to produce a negative electrode active material.

Example 2
A negative electrode active material was produced in the same manner as in Example 1 except that the first primary particles and secondary particles were mixed at a weight ratio of 10:90.

Example 3
A negative electrode active material was produced in the same manner as in Example 1 except that the first primary particles and secondary particles were mixed in a 20:80 weight ratio.

Example 4
A negative electrode active material was produced in the same manner as in Example 1 except that the first primary particles and secondary particles were mixed at a 30:70 weight ratio.

Example 5
A negative electrode active material was produced in the same manner as in Example 1 except that the first primary particles and secondary particles were mixed at a weight ratio of 40:60.

Example 6
A negative electrode active material was produced in the same manner as in Example 1 except that the first primary particles and secondary particles were mixed in a 50:50 weight ratio.

Comparative Example 1
A negative electrode active material was manufactured using only 100% of the first primary particles obtained in Preparation Example 1.

Comparative Example 2
A negative electrode active material was produced in the same manner as in Example 1 using only 100% of the secondary particles obtained in Production Example 2.

Comparative Example 3
A negative electrode active material was produced in the same manner as in Example 1 except that the first primary particles and secondary particles were mixed at a weight ratio of 60:40.

Comparative Example 4
A negative electrode active material was produced in the same manner as in Example 1 except that the first primary particles and secondary particles were mixed at a weight ratio of 3:97.

Example 7
<Manufacture of negative electrode>
The negative electrode active material of Example 1 as a negative electrode active material, carbon black (Super P) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are mixed in a weight ratio of 84: 6: 10, and these are solvents. A slurry was prepared by mixing with N-methyl-2-pyrrolidone. The prepared slurry was coated on one surface of a copper current collector to a thickness of 65 μm, dried and rolled, and then punched to a certain size to manufacture a negative electrode.

<Manufacture of lithium secondary batteries>
Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 30:70, and LiPF ₆ was added to the non-aqueous electrolyte solvent to prepare a 1M LiPF ₆ non-aqueous electrolyte.

  Further, a lithium metal foil was used as a relative electrode, that is, a positive electrode, a polyolefin separation membrane was interposed between both electrodes, and then the electrolyte was injected to manufacture a coin-type half battery.

Examples 8 to 12 and Comparative Examples 5 to 8
Using the negative electrode active materials obtained in Examples 2 to 6 and Comparative Examples 1 to 4, negative electrodes were produced with the compositions shown in Table 1 below.

Experimental example 1
<Measurement of adhesive strength>
Using the negative electrodes manufactured during the manufacturing process of the lithium secondary batteries of Examples 7 to 12 and Comparative Examples 5 to 8, the adhesion strength to the negative electrode was measured. Adhesion was measured by a commonly known 180 ° peel test. The results are shown in Table 2 below.

Experimental example 2
<High rate characteristic analysis>
In order to analyze the high rate characteristics of the lithium secondary batteries of Examples 7 to 12 and Comparative Examples 5 to 8 of the present invention, the charge / discharge densities were 0.1, 0.2, 0.5, 1, 0.2, respectively. The process proceeded sequentially at 2, 0.2, 5, 0.2 and 10C. At this time, the end-of-charge voltage was set to 1.0V, and the end-of-discharge voltage was set to 2.5V. The high-rate characteristic is obtained by measuring a capacity at 10 C and expressing it as a percentage value of capacity at 0.1 C.

The results are shown in Table 2 below.

  As shown in Table 2, when lithium titanium oxide formed by mixing first primary particles and secondary particles as in Examples 7 to 12 is applied to the negative electrode, the adhesive force and the high rate are obtained. It was confirmed that the characteristics were improved at the same time.

  However, even if a negative electrode active material in which the first primary particles and secondary particles are mixed as in Comparative Examples 7 and 8, when the first primary particles are used in an excessive amount or an extremely small amount, the present invention is used. It can be confirmed that the adhesive strength and the high rate characteristic of the level as in Examples 7 to 12 cannot be satisfied at the same time.

  On the other hand, when lithium titanium oxide consisting only of the first primary particles as in Comparative Example 5 was applied to the active material, it was confirmed that the adhesive force was significantly reduced, and only from the secondary particles as in Comparative Example 6. It was confirmed that when the lithium titanium oxide to be applied was applied to the negative electrode, the high rate characteristic was lowered.

  On the other hand, as a result of the experimental examples 1 and 2, the first primary particles have higher rate characteristics because the accessibility of the lithium titanium oxide and the lithium ions on the electrolyte is higher than the secondary particles when the high rate characteristics are exhibited. It can be inferred that there is a relationship with expression. And since the specific surface area of the secondary particles is smaller than that of the lithium titanium oxide consisting only of the first primary particles, it can be assumed that there is a correlation with the electrode adhesive force.

Experimental example 3
<Electrode density>
The electrode density with respect to the negative electrode was measured using the negative electrode manufactured during the manufacturing process of the lithium secondary batteries of Examples 7 to 12 and Comparative Examples 5 to 8. The results for the electrode density are shown in Table 3 below, and the electrode density with respect to the ratio of the mixed first primary particles is shown in FIG.

  As shown in Table 3, the electrode density in the case where lithium titanium oxide mixed with the first primary particles and secondary particles at a specific mixing ratio as in Examples 7 to 12 is applied to the negative electrode. Can be confirmed to be exceptionally improved as compared with Comparative Examples 6 and 8.

  Further, as shown in FIG. 1, the electrode density of the negative electrode that is 0% of the first primary particles as in Comparative Example 6 and the negative electrode that is 100% of the first primary particles as in Comparative Example 5 (see FIG. 1). In the graph of 1, dotted lines (calculated values of mixed electrode density), Examples 7 to 12 confirm that the electrode density increases rapidly compared to the calculated value of mixed electrode density. it can.

  However, as the proportion of the mixed primary primary particles increases, the increase in the electrode density decreases. Therefore, if the proportion of the primary primary particles approaches 50%, the primary primary particles and the secondary particles It was confirmed that the electrode density of the negative electrode in which lithium titanium oxide mixed with was applied to the negative electrode active material approximated the average of the electrode density values of the first primary particle 100% and the secondary particle 100%.

  That is, when lithium titanium oxide in which the first primary particles and secondary particles are mixed is used as the negative electrode active material, the effect of improving the electrode density can be obtained even if a small amount of the first primary particles are mixed.

  Thus, in the case of the negative electrodes of Examples 7 to 12 using the lithium titanium oxide in which the first primary particles and the secondary particles are mixed as the negative electrode active material, the increase in the electrode density is only the secondary particles. Predicts the fact that the electrode density can be increased by filling the voids between the secondary particles that can occur when applied to the active material with lithium titanium oxide of the first primary particle structure can do.

  That is, when the electrodes and secondary batteries of Examples 7 to 12 in which the first primary particles and secondary particles were mixed were compared with the electrodes and secondary batteries of Comparative Examples 7 and 8, the adhesive strength and the high rate characteristics were obtained. It can be confirmed that the first primary particles and the secondary particles must be mixed at an appropriate ratio in order to have optimum performance.

  By using a negative electrode active material in which primary primary particles and secondary particles are mixed in an appropriate ratio, not only can a high-density electrode be realized, but also the adhesion and high-rate characteristics of the electrode can be improved at the same time. Therefore, it can be effectively used for a lithium secondary battery.

Claims (18)

A negative electrode active material comprising a compound of the following formula (1), wherein the compound of the following formula (1) comprises first primary particles and secondary particles, and the ratio of the first primary particles: secondary particles is A negative electrode active material having a weight ratio of 5:95 to 50:50.
[Formula 1]
Li _x M _y O _z (1)
In the formula (1), each M is independently selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al, and Zr, or two or more of these. A mixture; x, y and z are determined according to the oxidation number of M.   2. The negative electrode active material according to claim 1, wherein the ratio of the first primary particles to the secondary particles is a weight ratio of 5:95 to 40:60. 3. The negative electrode active material according to claim 1, wherein an average particle diameter (D ₅₀ ) of the first primary particles is in a range of 10 nm to 3 μm. 4. The negative electrode active material according to claim 3, wherein an average particle diameter (D ₅₀ ) of the first primary particles is in a range of 100 nm to 1 μm.   5. The negative electrode active material according to claim 1, wherein two or more second primary particles are aggregated in the secondary particles. 6. 6. The negative electrode active material according to claim 5, wherein an average particle diameter (D ₅₀ ) of the second primary particles is in the range of 100 nm to 1 μm. 2. The negative electrode active material according to claim 1, wherein an average particle diameter (D ₅₀ ) of the secondary particles is in a range of 5 μm to 30 μm. The negative active material according to claim 7, wherein the secondary particles have an average particle size (D ₅₀ ) in the range of 5 μm to 12 μm. The compound of the formula (1) includes one or more lithium titanium oxides selected from the group consisting of Li ₄ Ti ₅ O ₁₂ , Li ₂ TiO ₃ , Li ₂ Ti ₃ O ₇ and the following formula (2). The negative electrode active material according to claim 1, wherein:
[Chemical 2]
Li _{x '} Ti _y' O ₄ (2)
In the formula (2), 0.5 ≦ x ′ ≦ 3; 1 ≦ y ′ ≦ 2.5. The negative electrode active material according to claim 9, wherein the compound of the formula (2) is LiTi ₂ O ₄ .   A negative electrode active material composition comprising the negative electrode active material according to any one of claims 1 to 10, a conductive material, and a binder.   The negative electrode active material composition according to claim 11, wherein the negative electrode active material: the conductive material: the binder is included in a weight ratio of 80 to 90: 3 to 9: 7 to 13.   13. The conductive material according to claim 11 or 12, wherein the conductive material is at least one selected from the group consisting of graphite, carbon black, conductive fiber, metal powder, conductive whisker, conductive metal oxide, and polyphenylene derivative. The negative electrode active material composition as described.   The binder is polyvinylidene fluoride (PVdF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-dieneterpolymer (EPDM). 14. The negative electrode active material composition according to claim 11, wherein the negative electrode active material composition is at least one selected from the group consisting of sulfonated EPDM, styrene butadiene rubber, and fluorine rubber.   A negative electrode comprising the negative electrode active material composition according to claim 11.   A lithium secondary battery comprising the negative electrode according to claim 15.   A battery module comprising the lithium secondary battery according to claim 16 as a unit battery.   A battery pack comprising the battery module according to claim 17.

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