KR20140009928A - Bimodal type-anode active material and lithium secondary battery comprising the same - Google Patents

Abstract

Provided is an anode active material comprising chemical formula 1, the chemical formula 1 comprises first and second particles. The first and second particles comprise in a ratio of 5:95~50:50 wt%. In the chemical formula 1, M is one which is selected from a group comprising Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr, or a mixture comprising at least two from the group; x,y and z are decided by the oxidation number of M. According to an embodiment of the present invention specification, by using an anode active material comprising the well balanced first and second particles, high-density of electrode can be realized and adhesive properties and peak factor of the electrode can be improved at the same time. [Reference numerals] (AA) First particles; (BB) Second particles

Description

Bimodal type anode active material and lithium secondary battery comprising the same {Bimodal type-anode active material and lithium secondary battery comprising the same}

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

A lithium ion secondary battery is a kind of secondary battery that operates on the principle of generating a battery while moving a positive electrode and a negative electrode. Components of a lithium ion secondary battery can be roughly divided into a positive electrode, a negative electrode, a separator and an electrolyte. Among 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 and detached into the active material, and charge and discharge are performed by a reversible reaction.

Conventionally, lithium metal is used as a negative electrode active material of a lithium battery. However, when lithium metal is used, a short circuit occurs due to the formation of dendrite, causing a risk of explosion, and a carbon-based material is used as a negative electrode active material instead of lithium metal.

The carbonaceous material includes crystalline carbon such as graphite and artificial graphite, and amorphous carbon such as soft carbon and hard carbon. However, although the amorphous carbon has a large capacity, there is a problem that irreversibility is large in the charging and discharging process. Graphite is typically used as the crystalline carbon, which has a high theoretical limit capacity. However, even though the crystalline carbon or amorphous carbon has a rather high theoretical capacity, it is only about 380 mAh / g. Therefore, it is difficult to use such a negative electrode when developing a high capacity lithium battery.

Therefore, in recent years, researches are being actively conducted to apply lithium titanium oxide (LTO) as a negative electrode active material as a metal oxide having a spinel structure for the purpose of developing a lithium ion secondary battery having high-speed charge and discharge and long life battery performance.

LTO does not produce SEI (Solid Electrolyte Interface) film produced by incidental reaction between graphite negative electrode active material and electrolyte, which is generally used in Li-ion secondary battery, and has excellent reversible charge and discharge in comparison with graphite. The cycle also has excellent reversibility for insertion and desorption of lithium ions. It is also a promising material that is structurally very stable and can express the long life performance of a secondary battery.

On the other hand, lithium titanium oxide is divided into two forms made of secondary particles by agglomerating the primary particles and the case consisting of only primary particles. In the case of the primary particles, there is no problem of electrode adhesion at an appropriate particle size, but high-speed charging and discharging is inferior. Therefore, when the particle size is manufactured to 300 nm or less in order to compensate for these disadvantages and to improve the rate capability, process problems in slurry production due to the increase in specific surface area appear. In addition, when the secondary particles to improve the problem of the nano-primary particles, the problem is improved, but still a large amount of binder is required to maintain the electrode adhesion. Since the binder acts as an electrical resistance element of the electrode, there is a problem that ultimately worsens the overall energy density of the battery.

In addition, as the function of a device using a battery is improved, a battery having a high energy density is required. In order to satisfy this, a technology for increasing energy per unit volume is required. In order to improve the energy per unit volume, it is possible to construct a high-density electrode by increasing the amount of electrode material coated per unit volume to construct a battery having high energy.

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

The present invention is to provide a negative electrode active material capable of securing high-rate characteristics of the battery and high density of the electrode, as well as adhesion to the electrode.

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

By using the negative electrode active material in which the first primary particles and the secondary particles are mixed in an appropriate ratio, not only an electrode of high density can be realized, but also the adhesion and high rate characteristics of the electrode can be simultaneously improved.

1 illustrates a schematic diagram of a negative electrode active material in which first primary particles are mixed with secondary particles in an appropriate amount according to an embodiment of the present invention.
2 is a schematic view showing a schematic diagram of a negative electrode active material in which first primary particles are mixed with secondary particles in a large amount.
3 is a graph showing the electrode density according to the first primary particle mixing ratio used for the negative electrode of Examples 7 to 12 according to an embodiment of the present invention.

The present invention relates to a negative electrode active material including a compound of Formula 1, wherein the compound of Formula 1 includes first primary particles and secondary particles, and the ratio of the first primary particles: secondary particles is 5:95 to 50. It provides a negative electrode active material, characterized in that: 50% by weight:

[Formula 1]

Li _x M _y O _z

In 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 a mixture of two or more thereof; x, y and z are determined according to the oxidation number of M.

According to an embodiment of the present invention, by using the negative electrode active material in which the first primary particles and the secondary particles are mixed in an appropriate ratio, not only an electrode of high density can be realized but also the adhesion and high rate characteristics of the electrode can be simultaneously improved. .

1 is a schematic diagram 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. 2 is a schematic view of a negative electrode active material in which first primary particles are mixed with secondary particles in a large amount.

As shown in FIG. 1 and FIG. 2, in the case where the first primary particles are mixed in a proper amount and in a large amount, the first primary particles may fill the voids between the secondary particles. However, in order to satisfy not only the electrode density but also the optimum performance at the same time in the adhesive force and the high rate characteristic, as shown in FIG.

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

If the average particle diameter of the first primary particles is less than 10 nm, there may be a substantial difficulty in the manufacturing process, if the average particle diameter of more than 3 ㎛ the size of the first primary particles is too large to improve the high rate characteristics due to the first primary particles Difficult to expect

When the lithium metal oxide particles are composed of only the first primary particles and used as the negative electrode active material of the lithium secondary battery, there is no problem of electrode adhesion, but the high-speed charge and discharge characteristics are inferior. In order to overcome these disadvantages, the first primary particles may be manufactured to a smaller size, but in this case, due to the increase in specific surface area, problems in the manufacturing process of the negative electrode slurry, for example, product cost due to the use of excess binder Problems such as increase, lowering of electrical conductivity may occur.

Therefore, in order to solve the problem of using only the first primary particles, according to an embodiment of the present invention by mixing the first primary particles and secondary particles of the lithium metal oxide in an appropriate ratio to use as a negative electrode active material, In addition to implementing a high-density electrode, it is possible to improve the adhesiveness and high rate characteristics of the electrode at the same time.

According to one embodiment of the invention, the mixing ratio of the first primary particles and secondary particles is preferably a weight ratio of 5:95 to 50:50, preferably a weight ratio of 5:95 to 40:60.

When the amount of the first primary particles is greater than the above range, the electrode density may increase, but the adhesion of the electrode and the high rate characteristic of the secondary battery may be reduced. In addition, when the amount of the first primary particles is less than the above range it is difficult to fill the voids between the secondary particles with the first primary particles is difficult to achieve the desired effect of the present invention.

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

According to an embodiment of the present invention, when two or more second primary particles are aggregated to form a secondary particle, the specific surface area is relatively small compared to the case where the second primary particles are not aggregated and exist individually, in terms of electrode adhesion. Can be excellent.

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

When the internal porosity of the secondary particles is less than 3%, there may be substantial difficulties in terms of manufacturing process in that the secondary particles are formed by the aggregation of the second primary particles, and when the internal porosity exceeds 15%, The amount of binder required to maintain proper electrode adhesion can be increased, resulting in lowered conductivity and reduced capacity.

According to one embodiment of the invention, the internal porosity of the secondary particles can be defined as follows:

Internal porosity = pore volume per unit mass / (specific volume + pore volume per unit mass)

The measurement of the internal porosity is not particularly limited, and according to an embodiment of the present invention, for example, it may be measured using BELSORP (BET equipment) of BEL JAPAN using an adsorbent gas such as nitrogen.

In a similar manner, 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 the secondary particles can be measured by the Brunauer-Emmett-Teller (BET) method. For example, it can be measured by a BET 6-point method by a nitrogen gas adsorption / distribution method using a porosimetry analyzer (Bell Japan Inc, Belsorp-II mini).

Meanwhile, the average particle diameter (D ₅₀ ) of the secondary particles may be 5 μm to 30 μm, preferably 5 μm to 12 μm, and the average particle diameter (D ₅₀ ) of the second primary particles constituting the secondary particles may be 100 nm to 1 μm. Μm, preferably 100 nm to 700 nm.

In the present invention, the average particle size (D ₅₀ ) can be defined as the particle size at 50% of the particle size distribution. The average particle diameter (D ₅₀ ) of the first and second primary particles and the secondary particles according to an embodiment of the present invention may be measured using, for example, a laser diffraction method. The laser diffraction method generally enables measurement of a particle diameter of several millimeters from a submicron region, resulting in high reproducibility and high degradability.

In general, lithium metal oxides have a low conductivity, so a small average particle diameter is advantageous for application to a fast charging cell. However, in this case, as described above, a large amount of binder is required to maintain proper electrode adhesion due to an increase in specific surface area. Need.

That is, when the average particle diameter of the secondary particles is less than 5 μm, the amount of the binder for maintaining the desired electrode adhesive force increases due to an increase in the specific surface area of the negative electrode active material, which may cause problems such as a decrease in electrode conductivity. have. On the other hand, when the average particle diameter of secondary particle | grains exceeds 30 micrometers, there exists a problem that a fast filling characteristic falls.

Therefore, the high-density negative electrode active material according to the embodiment of the present invention can reduce the amount of the binder for maintaining the electrode adhesion when the secondary particles having an average particle diameter in the range of 5 μm to 30 μm, as well as directly with Li ions. The responsive area is increased to improve the fast charging properties.

On the other hand, when the average particle diameter of the second primary particles is less than 100 nm, there may be difficulties in terms of the manufacturing process in the production of the average particle diameter of less than 100 nm, of the secondary particles formed by the aggregation of the second primary particles In addition to decreasing the porosity, it is difficult to penetrate lithium ions into the secondary particles, making it difficult for the second primary particles inside the secondary particles to participate in the charge / discharge reaction. On the other hand, when the average particle diameter of the said 2nd primary particle is more than 1 micrometer, the moldability of a secondary particle may fall and the problem which it is difficult to control granulation may arise.

According to an embodiment of the present invention, the compound of Formula 1 is Li ₄ Ti ₅ O ₁₂ , Li ₂ TiO ₃ , Li ₂ Ti ₃ O ₇ And may include one or more lithium titanium oxide selected from the group consisting of:

(2)

Li _{x '} Ti _y' O ₄

In Formula 2, 0.5 ≦ x ′ ≦ 3; 1≤y'≤2.5.

In addition, the compound of Formula 2 is preferably LiTi ₂ O ₄ .

In the method of manufacturing a negative electrode active material according to an embodiment of the present invention, the first primary particles of the lithium metal oxide are first prepared by a conventional method, and the secondary particles of the lithium metal oxide particles are prepared after the second primary particles. Although it may be formed by a separate granulation process, the secondary particles may be manufactured by a method of generating the second primary particles and agglomerating the second primary particles through one process. Then, the negative electrode active material according to the present invention may be prepared by uniformly mixing the prepared first and second secondary particles.

In the method of preparing a negative electrode active material according to an embodiment of the present invention, the first primary particles may be obtained by adding lithium salt and metal oxide to a volatile solvent, stirring, calcining, and then pulverizing and sieving. .

More specifically, the first primary particles are dissolved in a lithium salt in the volatile solvent, the titanium oxide as a metal oxide is added while stirring, and then calcined at about 500 ℃ to 1000 ℃ for about 1 hour to 15 hours, and then pulverized And sieved.

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

In addition, 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.

In addition, in the method for preparing a negative electrode active material according to an embodiment of the present invention, the method for preparing secondary particles includes adding a lithium salt and a metal oxide to a volatile solvent to prepare a precursor solution, and spraying the precursor solution. Supplying into the chamber of the drying equipment, spraying the precursor solution in the chamber may comprise the step of drying.

In this case, the lithium salt, the metal oxide and the volatile solvent may be selected and used the same material as the material used to prepare the first primary particles.

According to one embodiment of the present invention, the secondary particles of the lithium metal oxide particles may be formed by a separate granulation process after preparing the second primary particles, but typically, the second primary particles through one process It may be prepared by a method of agglomeration with the second primary particles while producing a.

As such a method, the spray drying method is mentioned, for example. Hereinafter, a method of manufacturing secondary particles according to an embodiment of the present invention will be described taking a spray drying method as an example.

On the other hand, the manufacturing method according to an embodiment of the present invention may include supplying the precursor solution to the chamber provided in the spray drying equipment.

The spray drying equipment may be used spray drying equipment commonly used, for example, ultrasonic spray drying device, air nozzle spray drying device, ultrasonic nozzle spray drying device, filter expansion droplet generator or electrostatic spray drying device May be used, but is not limited thereto.

According to one embodiment of the invention, the feed rate of the precursor solution into the chamber may be from 10 ml / min to 1000 ml / min. If the feed rate is less than 10 ml / min, the average particle diameter of the aggregated second primary particles is small, there is a difficulty in forming a high density secondary particles, if the feed rate exceeds 1000 ml / min, the average of the secondary particles Since the grain size becomes coarse, it may be difficult to achieve the desired high rate characteristics.

Furthermore, the method of manufacturing the secondary particles according to an embodiment of the present invention may include the step of spraying the precursor solution in the chamber to dry.

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

Furthermore, in order to implement the average particle diameter and the internal porosity of the present invention, it may be possible to control the spray drying conditions, for example, the flow rate of the carrier gas, the residence time in the reactor and the internal pressure.

According to one embodiment of the present invention it is possible to control the internal porosity of the secondary particles by controlling the drying temperature, the drying can be carried out at a temperature of 20 ℃ to 300 ℃ but for the densification of the secondary particles to proceed at a low temperature as possible It is advantageous.

According to an 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 in a weight ratio of 5:95 to 40:60, and thus not only the adhesive force to the electrode The negative electrode active material in which the high rate characteristic of a battery and the high density of an electrode are ensured can be manufactured. In this case, in order to mix the first primary particles with the particles as best as possible, the mixing may be performed uniformly using a conventional 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% based on the weight of the entire negative electrode active material. When the content of the lithium metal oxide is 100% by weight based on the total weight of the negative electrode active material, it means a case in which 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 is any one selected from the group consisting of carbon-based materials, transition metal oxides, Si-based, and Sn-based materials commonly used in the negative electrode active material in addition to the lithium metal oxide. It may further include two or more active materials, but is not limited to these kinds.

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

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

The negative electrode may be prepared by mixing the negative electrode active material composition including the negative electrode active material with a solvent such as NMP (N-methyl pyrrolidone) and coating the 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 causing chemical change in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver and the like, aluminum-cadmium alloy and the like can be used. The negative electrode current collector may form fine concavities and convexities on the surface to reinforce the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

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

The binder is polyvinylidene fluoride (PVdF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, Polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluorine rubber, various copolymers and the like.

On the other hand, the positive electrode included in the lithium secondary battery of the present invention, for example, is prepared by applying a positive electrode slurry containing a positive electrode active material on a positive electrode current collector and then drying, the positive electrode slurry, if necessary, Ingredients as described may be included.

In particular, the lithium secondary battery includes a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals as a positive electrode active material; Formula _{Li 1 + x Mn 2 - x} O 4 ( where, x is from 0 to 0.33), LiMnO _3, the lithium manganese oxide such as LiMn ₂ O _3, LiMnO _2; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Ni-site type lithium nickel oxide represented by the formula LiNi _{1 - x} M _x O ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3; Formula LiMn _{2 - x} M _x O ₂ (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO _{4) 3,} or the like, but may preferably be used _{LiNi x Mn 2-x O 4} (0.01 = x = 0.6), more preferably LiNi _{0 .5} Mn _{1 .5} O ₄ or LiNi _0.4 Mn _1.6 O ₄ can be used. That is, in the present invention, it is preferable to use a spinel lithium manganese composite oxide having 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 as the positive electrode active material. .

The present invention also provides a battery module including the lithium secondary battery as a unit cell and a battery pack including the battery module.

The battery case used in the present invention may be of any type that is commonly used in the art, and is not limited in its external shape depending on the use of the battery. For example, a cylindrical case, a square type, a pouch type, (coin) type or the like.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells. Preferable examples of the above medium and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric power storage systems, and the like.

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 into various other forms, and the scope of the present invention is not limited to the above-described embodiments.

Example

Preparation Example 1 Preparation of First Primary Particles

LiOHH ₂ O and TiO ₂ (Anatase) was mixed at 4: 5 (molar ratio), the mixture was dissolved in pure water, stirred, calcined at 750 ° C. for about 3 hours, pulverized and sieved to obtain an average particle diameter (D ₅₀ ). A first primary particle of 700 nm was prepared.

Preparation Example 2 Preparation of Secondary Particles

LiOHH ₂ O and TiO ₂ (Anatase) was mixed at 4: 5 (molar ratio) 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 solids contained in the solution to the total weight of the solution, and stirred at 30% to prepare a precursor solution. The precursor solution was fed into a chamber of a spray drying equipment (EinSystems) and sprayed and dried in the chamber. In this case, the spray drying conditions are carried out at a drying temperature of 130 ℃ internal pressure -20 mbar, feed rate 30 ml / min and then fired at 800 ℃ in the precursor obtained in the air to an average particle diameter of 5.4 ㎛, the internal porosity 3.5% Li ₄ Ti ₅ O ₁₂ Secondary particles were prepared.

Example 1

The first primary particles and the secondary particles prepared in Preparation Examples 1 and 2 were mixed using a planetary mill in a weight ratio of 5: 95 to prepare a negative electrode active material.

Example 2

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

Example 3

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

Example 4

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

Example 5

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

Example 6

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

Comparative Example 1

Using only 100% of the first primary particles obtained in Preparation Example 1 to prepare a negative electrode active material.

Comparative Example 2

Using only the secondary particles obtained in Preparation Example 2 100% to prepare a negative electrode active material in the same manner as in Example 1.

Comparative Example 3

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

Comparative Example 4

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

Example 7

<Production of Cathode>

As the negative electrode active material, the negative electrode active material of Example 1, carbon black (Super P) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed in a weight ratio of 84: 6: 10, and these were used as a solvent, N-methyl- A slurry was prepared by mixing in 2-pyrrolidone. The prepared slurry was coated on one side of the copper current collector to a thickness of 65 μm, dried and rolled, and then punched to a predetermined size to prepare a negative electrode.

&Lt; Production of lithium secondary battery >

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 1 M LiPF ₆ non-aqueous electrolyte.

Also, a lithium metal foil was used as a counter electrode, that is, a positive electrode, a polyolefin separator was interposed between both electrodes, and the electrolyte was injected to prepare a coin-type half cell.

Example  8 to 12 and Comparative Example  5 to 8

Using the negative electrode active material obtained in Examples 2 to 6 and Comparative Examples 1 to 4, a negative electrode was prepared in the composition of Table 1 below.

division Cathode composition
(Negative electrode active material: conductive material: binder) (weight ratio) Example 7 84 (First Primary Particle 5: Secondary Particle 95): 6:10 Example 8 84 (First Primary Particle 10: Secondary Particle 90): 6:10 Example 9 84 (First Primary Particle 20: Secondary Particles 80): 6:10 Example 10 84 (First Primary Particle 30: Secondary Particles 70): 6:10 Example 11 84 (1st primary particle 40: secondary particle 60): 6:10 Example 12 84 (First Primary Particle 50: Secondary Particles 50): 6:10 Comparative Example 5 84 (only as for the first primary particle): 6:10 Comparative Example 6 84 (secondary particles only): 6:10 Comparative Example 7 84 (1st primary particle 60: secondary particle 40): 6:10 Comparative Example 8 84 (first primary particle 3: secondary particles 97): 6:10

Experimental Example  One

<Adhesion measurement>

The adhesion to the negative electrode was measured using the negative electrode prepared during the manufacturing process of the lithium secondary battery of Examples 7 to 12 and Comparative Examples 5 to 8. Adhesion was measured by a commonly known 180 ^o 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, charge and discharge densities were respectively 0.1, 0.2, 0.5, 1, 0.2, 2, 0.2, 5, 0.2, and 10C. It proceeded sequentially. At this time, the charge end voltage was set to 1.0V, and the discharge end voltage was set to 2.5V. The high rate characteristic is expressed as a percentage value of the capacity at 0.1C by measuring the capacity at 10C.

The results are shown in Table 2 below.

division Electrode Configuration
(Active material: conductive material: binder) Adhesion
[gf] High rate characteristic
[%, 10C / 0.1C capacity] Example 7 84 (First Primary Particle 5: Secondary Particle 95): 6:10 36 66.5 Example 8 84 (First Primary Particle 10: Secondary Particle 90): 6:10 35.5 69 Example 9 84 (First Primary Particle 20: Secondary Particles 80): 6:10 34.4 73 Example 10 84 (First Primary Particle 30: Secondary Particles 70): 6:10 33 82 Example 11 84 (1st primary particle 40: secondary particle 60): 6:10 30 79 Example 12 84 (First Primary Particle 50: Secondary Particles 50): 6:10 21 70 Comparative Example 5 84 (only as for the first primary particle): 6:10 7.6 73 Comparative Example 6 84 (secondary particles only): 6:10 35.9 65 Comparative Example 7 84 (1st primary particle 60: secondary particle 40): 6:10 12 63.5 Comparative Example 8 84 (first primary particle 3: secondary particles 97): 6:10 35 64

As can be seen in Table 2, when the lithium titanium oxide formed by mixing the first primary particles and the secondary particle size as shown in Examples 7 to 12 was applied to the negative electrode, it was confirmed that the adhesive strength and high rate characteristics are improved at the same time .

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

On the other hand, when applying the lithium titanium oxide consisting of only the first primary particles as an active material as in Comparative Example 5, it was confirmed that the adhesion is significantly reduced, when applying the lithium titanium oxide consisting of only secondary particles as in Comparative Example 6 to the negative electrode It was confirmed that the high rate characteristic was lowered.

On the other hand, as a result of Experimental Examples 1 and 2, it can be guessed that the first primary particles are associated with high rate characteristic expression because the accessibility of lithium titanium oxide and lithium ions on the electrolyte solution is higher than the secondary particles when the high rate characteristic is expressed. In addition, the secondary particles may have a lower specific surface area than lithium titanium oxide composed of only the first primary particles, and thus may be correlated with electrode adhesion.

Experimental Example  3

<Electrode density>

The electrode density of the negative electrode was measured using the negative electrode prepared during the manufacturing process of the lithium secondary battery 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 for the ratio of the mixed first primary particles is shown in FIG. 1.

division Electrode Configuration
(Active material: conductive material: binder) Electrode density
[g / cc] Example 7 84 (First Primary Particle 5: Secondary Particle 95): 6:10 1.89 Example 8 84 (First Primary Particle 10: Secondary Particle 90): 6:10 1.91 Example 9 84 (First Primary Particle 20: Secondary Particles 80): 6:10 1.93 Example 10 84 (First Primary Particle 30: Secondary Particles 70): 6:10 1.94 Example 11 84 (1st primary particle 40: secondary particle 60): 6:10 1.95 Example 12 84 (First Primary Particle 50: Secondary Particles 50): 6:10 1.95 Comparative Example 5 84 (only as for the first primary particle): 6:10 2.1 Comparative Example 6 84 (only the 1st secondary particle): 6:10 1.8 Comparative Example 7 84 (1st primary particle 60: secondary particle 40): 6:10 1.96 Comparative Example 8 84 (first primary particle 3: secondary particles 97): 6:10 1.8

 As shown in Table 3, the electrode density when the lithium titanium oxide mixed with the first primary particles and secondary particles at a specific mixing ratio as applied to the negative electrode as shown in Examples 7 to 12 is significantly improved compared to Comparative Examples 6 and 8 can confirm.

In addition, as shown in FIG. 1, based on the electrode densities of the negative electrode having the first primary particle 0% as in Comparative Example 6 and the negative electrode having the first primary particle 100% as in Comparative Example 5 (dashed line in the graph of FIG. 1: When the mixed electrode density calculated value), Examples 7 to 12 can confirm that the electrode density is sharply increased compared to the mixed electrode density calculated value.

However, as the ratio of the mixed first primary particles increases, the increase in electrode density decreases, and when the ratio of the first primary particles approaches 50%, the electrode of the negative electrode using lithium titanium oxide mixed with the first primary particles and the secondary particles as a negative electrode active material It was confirmed that the density was similar to the average of the electrode density values of the first primary particles 100% and the secondary particles 100%.

That is, when using the lithium titanium oxide which mixed the 1st primary particle and the secondary particle as a negative electrode active material, even if mixing a small amount of 1st primary particle, the effect of electrode density improvement was acquired.

As such, in the case of the negative electrodes of Examples 7 to 12 using the lithium titanium oxide mixed with the first primary particles and the secondary particle size as the negative electrode active material, an increase in electrode density may occur when only the secondary particles are used as the active material to configure the electrode. It can be predicted that the electrode density can be increased by filling the pores between the secondary particles with lithium titanium oxide of the first primary particle structure.

That is, when the electrodes and the secondary batteries of Examples 7 to 12, in which the first primary particles and the secondary particles are mixed, are compared with the electrodes and the secondary batteries of Comparative Examples 7 and 8, the first and second batteries have the best performance in adhesion and high rate characteristics. It can be seen that the primary and secondary particles should be mixed in the proper ratios.

Claims (18)

A negative active material including a compound of Formula 1, wherein the compound of Formula 1 includes first primary particles and secondary particles, and the ratio of the first primary particles: secondary particles is 5:95 to 50:50 by weight. A negative electrode active material characterized by:
[Chemical Formula 1]
Li _x M _y O _z
In 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 a mixture of two or more thereof; x, y and z are determined according to the oxidation number of M.
The method of claim 1,
The ratio of the first primary particles: secondary particles is 5:95 to 40:60 weight ratio of the negative electrode active material.
The method of claim 1,
The average particle diameter (D ₅₀ ) of the first primary particles is a negative electrode active material, characterized in that the range of 10 nm to 3 ㎛.
4. The method of claim 3,
The average particle diameter (D ₅₀ ) of the first primary particles is a negative electrode active material, characterized in that the range of 100 nm to 1 ㎛.
The method of claim 1,
The secondary particles are anode active material, characterized in that the at least two secondary particles are aggregated.
The method of claim 5, wherein
The negative electrode active material, characterized in that the average particle diameter (D ₅₀ ) of the second primary particles is 100 nm to 1 ㎛.
The method of claim 1,
The average particle diameter (D ₅₀ ) of the secondary particles is a negative electrode active material, characterized in that in the range of 5 ㎛ to 30 ㎛.
The method of claim 7,
The average particle diameter (D ₅₀ ) of the secondary particles is a negative electrode active material, characterized in that in the range of 5 ㎛ to 12 ㎛.
The method of claim 1,
The compound of Formula 1 is Li ₄ Ti ₅ O ₁₂ , Li ₂ TiO ₃ , An anode active material comprising Li ₂ Ti ₃ O ₇ and at least one lithium titanium oxide selected from the group consisting of:
(2)
Li _{x '} Ti _y' O ₄
In Formula 2, 0.5 ≦ x ′ ≦ 3; 1≤y'≤2.5.
The method of claim 9,
The compound of formula 2 is a negative electrode active material, characterized in that LiTi ₂ O ₄ .
A negative electrode active material composition comprising the negative electrode active material, the conductive material and the binder of any one of claims 1 to 10.
The method of claim 11,
The negative electrode active material: conductive material: the binder is a negative electrode active material composition, characterized in that it comprises a weight ratio of 80-90: 3-9: 7-13.
The method of claim 11,
The conductive material is graphite; Carbon black; Conductive fibers; Metal powder; Conductive whiskey; A negative electrode active material composition, characterized in that at least one selected from the group consisting of a conductive metal oxide and a polyphenylene derivative.
The method of claim 11,
The binder is polyvinylidene fluoride (PVdF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, At least one selected from the group consisting of polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber and fluorine rubber.
A negative electrode comprising the negative electrode active material composition of claim 11.
A lithium secondary battery comprising the negative electrode of claim 15.
A battery module comprising the lithium secondary battery of claim 16 as a unit cell.
A battery pack comprising the battery module of claim 17.

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