WO2017164650A1 - Anode active material for secondary battery, and secondary battery comprising same - Google Patents

Abstract

The present invention provides an anode active material for a secondary battery, and a secondary battery comprising the same, the anode active material comprising: a core containing lithium titanium oxide; and a surface treatment layer located on the surface of the core, wherein the surface treatment layer comprises boron-containing lithium oxide in an amount such that a boron content becomes a molar ratio of 0.002 to 0.02 per 1 mole of lithium titanium oxide, and upon titrating 2 g of the anode active material with 0.1 M HCl at a pH of 5 or less, a titration amount is 0.9 to 1.5 ml. The anode active material may exhibit an excellent capacity recovery rate and output characteristics when applied to a battery, and can prevent the decomposition of an electrolyte, thereby reducing gas generation.

Description

Anode active material for secondary battery and secondary battery comprising same

Citation with Related Applications

This application claims the benefit of priority based on Korean Patent Application No. 2016-0034164 dated March 22, 2016 and 2017-0036235 dated March 22, 2017, and all contents disclosed in the literature of the Korean Patent Application are It is included as part of the specification.

Technical Field

The present invention relates to a negative electrode active material for a secondary battery and a lithium secondary battery including the same, which exhibits an output characteristic together with an excellent capacity recovery rate when applied to a battery, can prevent the decomposition of an electrolyte and reduce gas generation.

As technology development and demand for mobile devices increase, the demand for secondary batteries as a source of energy is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self discharge rate have been commercialized and widely used. In particular, as the market expands from small lithium secondary batteries used in portable devices to large secondary batteries used in automobiles, high capacity and high output technology of negative electrode active materials is required.

In the negative electrode of the conventional lithium secondary battery, a carbon-based material, especially graphite, which is capable of reversible intercalation and desorption of lithium ions while maintaining structural and electrical properties, is mainly used as a negative electrode active material, but in recent years, there is a demand for a high capacity battery. Increasingly, researches on lithium oxide-based negative electrode materials, such as a lithium alloy (alloy) anode material using silicon (Si), tin (Sn), and lithium titanium oxide, which have a larger theoretical capacity than graphite, have been conducted.

Among them, lithium titanium oxide is a zero-strain material having extremely low structural changes during charging and discharging. The lithium titanium oxide has excellent life characteristics, forms a relatively high voltage band, and does not generate dendrite. The safety and stability are very good.

However, lithium titanium oxide does not form a solid electrolyte interface (SEI) layer because the operating voltage is higher than the electrolyte decomposition voltage. Therefore, in the case of a lithium secondary battery to which lithium titanium oxide is applied, electrolyte decomposition is continuously generated as charging and discharging proceeds, which causes a problem of depletion of electrolyte and deterioration of life characteristics. In addition, in the case of a lithium secondary battery to which lithium titanium oxide is applied, a large amount of gas is generated when left at a high temperature.

SUMMARY OF THE INVENTION The first technical problem to be solved by the present invention is to provide an anode active material for a secondary battery and a method of manufacturing the same, which exhibit an output characteristic with excellent capacity recovery rate when applied to a battery, and can prevent the decomposition of electrolyte and reduce the generation of gas. .

In addition, a second technical problem to be solved by the present invention is to provide a secondary battery negative electrode, a lithium secondary battery, a battery module and a battery pack including the negative electrode active material.

According to an embodiment of the present invention to solve the above problems, in the negative electrode active material comprising a core comprising a lithium titanium oxide, and a surface treatment layer located on the surface of the core, the surface treatment layer is boron-containing Lithium oxide is contained in an amount such that the boron content is in a molar ratio of 0.002 to 0.02 per 1 mol of lithium titanium oxide, and a titration amount of 0.9 to 1.5 ml when titrating 2 g of the negative electrode active material to pH 5 or less using 0.1 M HCl A negative electrode active material for phosphorus secondary batteries is provided.

According to another embodiment of the present invention, after the surface treatment of the precursor of the boron-containing lithium oxide to the core containing the lithium titanium oxide, heat treatment at 350 ℃ to 450 ℃, the boron-containing lithium oxide on the surface of the core Provided is a method for producing a negative electrode active material for a secondary battery, comprising the step of forming a surface treatment layer comprising an amount such that the boron content is a molar ratio of 0.002 to 0.02 with respect to 1 mol of lithium titanium oxide.

According to another embodiment of the present invention, a negative electrode for a secondary battery and a lithium secondary battery including the negative electrode active material are provided.

Other specific details of the embodiments of the present invention are included in the following detailed description.

The negative electrode active material for a secondary battery according to the present invention may exhibit excellent capacity recovery. In addition, the negative electrode active material can improve the output characteristics by preventing a decrease in resistance caused by lithium by-products generated in the manufacturing process of the core, the surface treatment layer can reduce the generation of gas by preventing the decomposition of the electrolyte, in particular low SOC In the state of charge, electrolyte decomposition and gas generation due to elution of titanium ions (Ti ^{4 +} ) may be reduced.

The following drawings, which are attached to this specification, illustrate preferred embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical spirit of the present invention, the present invention is limited to the matters described in such drawings. It should not be construed as limited.

1 is a schematic diagram schematically showing a mechanism of generating a lithium ion mobile energy barrier.

FIG. 2 is a schematic diagram schematically showing a migration path of lithium ions in the crystal structure of Li ₂ B ₄ O _7. FIG.

3 is a schematic diagram schematically showing a migration path of lithium ions in the crystal structure of Al ₂ O ₃ .

Figure 4 is a photograph of the negative electrode active material prepared in Example 1 observed with a scanning electron microscope.

5 is a photograph of a negative electrode active material prepared in Comparative Example 2 observed with a scanning electron microscope.

6 is a graph comparing reduction amounts of lithium impurities in the negative electrode active materials of Examples 1 and 3 and Comparative Examples 1 and 5-8.

7 is a graph measuring the initial discharge capacity at 0.2C for the negative electrode active materials of Example 1 and Comparative Example 1.

8 is a graph measuring the discharge capacity at 10C for the negative electrode active materials of Example 1 and Comparative Example 1.

9 is a graph measuring the amount of gas generated in the lithium secondary battery including the negative electrode active material of Example 1 and Comparative Example 1, respectively.

10 is a graph measuring the amount of gas generation in a lithium secondary battery including the negative electrode active materials of Example 4, Comparative Examples 9 and 10.

11 is a graph showing the normal capacity of the lithium secondary battery including the negative electrode active material of Example 1 and Comparative Example 11.

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention.

The terms or words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

In the negative electrode active material having the surface treatment layer, the electrical conductivity in the surface treatment layer is related to the surface resistance of the negative electrode active material and the side reactivity with the electrolyte solution. Specifically, when the electrical conductivity in the surface treatment layer is low, the surface resistance is increased while the side reaction with the electrolyte may be reduced. Boron (B) usually has a low electrical conductivity as an insulator. Accordingly, it is preferable to appropriately control the content of boron included in the surface treatment layer in order to reduce the surface resistance of the negative electrode active material and thereby improve output characteristics and to prevent side reactions with the electrolyte.

In the present invention, in the preparation of the negative electrode active material, a surface treatment layer of boron-containing lithium oxide is formed on the core surface containing lithium titanium oxide, but in consideration of the electrical conductivity in the surface treatment layer and the suppression of side reaction with the electrolyte solution. By controlling the content based on the total weight of the lithium titanium composite oxide constituting the core, it is possible to improve the balance of the lithium ion conductivity and electrical conductivity in the surface treatment layer.

Specifically, the negative electrode active material for a secondary battery according to an embodiment of the present invention, the core including a lithium titanium oxide, and a surface treatment layer located on the surface of the core, the surface treatment layer is boron-containing lithium oxide To 1 mol of lithium titanium oxide, the boron content is contained in an amount such that the molar ratio of 0.002 to 0.02, the titration amount is 0.9 to 1.5ml when titrating 2g of the negative electrode active material to pH 5 or less using 0.1M HCl.

The surface treatment layer including the boron-containing lithium oxide is formed through reaction with a lithium impurity in which a precursor of boron-containing lithium oxide such as boric acid is present on the core surface, and a lithium raw material additionally added in the manufacturing process, By forming the surface treatment layer, the content of lithium impurities in the core may be reduced, and at the same time, the lithium ion conductivity and the electrical conductivity in the surface treatment layer may be improved by optimizing the boron content. In addition, due to the formation of the surface treatment layer having the above-described configuration, electrolyte decomposition may be prevented from the core surface including lithium titanium oxide, thereby exhibiting excellent capacity recovery. In addition, the decomposition of the electrolyte may be prevented by the surface treatment layer, so that the amount of gas generated may be reduced, and in particular, electrolyte decomposition and gas generation due to the dissolution of titanium ions (Ti ^{4 +} ) may be reduced at low SOC (state of charge). . In addition, the surface treatment layer uniformly covers the entire surface of the core without recrystallization, thereby preventing a decrease in resistance caused by lithium by-products generated in the manufacturing process of the core, thereby improving output characteristics.

In the present invention, the capacity recovery rate means the average discharge capacity during two and three cycles except for the initial discharge capacity when the battery is stored for one week at 80 ° C. after full charge, discharged, and charged and discharged under the same charge and discharge conditions. do.

Specifically, in the negative electrode active material according to an embodiment of the present invention, the surface treatment layer containing boron-containing lithium oxide is an amount such that the boron content is a molar ratio of 0.002 to 0.02 with respect to 1 mol of lithium titanium oxide constituting the core. It may include a boron-containing lithium oxide as described above. If the content of boron is less than 0.002 molar ratio compared to lithium titanium oxide, the improvement effect due to the formation of the surface treatment layer is insignificant. If the content of boron exceeds 0.02 molar ratio, the surface resistance is increased due to the decrease in the electrical conductivity in the surface treatment layer and the output characteristics of the battery. May cause degradation. More specifically, the surface treatment layer may include boron-containing lithium oxide in an amount of 5000 to 7000 ppm with respect to the total weight of lithium titanium oxide.

In the present invention, the content of boron included in the surface treatment layer may be analyzed using an inductively coupled plasma optical emission spectrometer (ICP).

In addition, the lithium ion migration energy barrier (E _barrier ) can be predicted from the diffusion path of lithium ions in the material forming the surface treatment layer.

FIG. 1 is a schematic diagram showing a mechanism of generating a lithium ion mobile energy barrier, and FIGS. 2 and 3 are schematic diagrams showing crystal structures of Li ₂ B ₄ O ₇ and Al ₂ O ₃ , respectively. 1 to 3 are only examples for describing the present invention, but the present invention is not limited thereto.

As shown in FIG. 1, the lower the lithium ion mobility energy barrier value, the easier the movement of lithium ions, and the better the lithium ion conductivity. On the other hand, both boron and aluminum have low electrical conductivity as an insulator, and as a result, side reaction with the electrolyte solution can be suppressed, and the resistance at the negative electrode interface can be increased to improve the safety of the active material, thereby providing a surface treatment agent for the active material. Mainly used. However, as shown in FIGS. 2 and 3, Li ₂ B ₄ O ₇ is a representative example of the boron-containing lithium oxide, and the movement path of lithium ions in the crystal structure is lower than that of Al ₂ O ₃ , which is usually used for forming a surface treatment layer. long. Accordingly, relatively large lithium ion is Al ₂ O ₃ the movement of lithium ions between the crystal and easier than, as a result, can exhibit a lower lithium ion migration barrier energy values and more excellent lithium ion conductivity.

In addition, the E _barrier value of boron-containing lithium oxide is usually about 0.05 eV to 0.45 eV. The value of the E _barrier of the boron-containing lithium oxide is due to the difference in the lithium ion migration path in the crystal structure, which can be controlled according to the heat treatment temperature during manufacture. In this case, when the heat treatment temperature is too high and the E _barrier value is too large, the gas reduction effect and the output characteristic improvement effect may be reduced due to the decrease in the surface coverage ratio due to the recrystallization of the boron-containing lithium oxide. In particular, the E _barrier value is increased as the heat treatment is performed at a high temperature when forming the surface treatment layer. At this time, the recrystallization occurs, and as a result, the surface coverage is decreased, thereby decreasing the output characteristics and reducing the gas generation effect.

In the negative electrode active material according to an embodiment of the present invention, the surface treatment layer may be made of a single boron-containing lithium oxide, or may be made of a mixture of two or more boron-containing lithium oxides. In the present invention, by controlling the type or mixing ratio of the boron-containing lithium oxide forming the surface treatment layer under the conditions that satisfy the above content range of boron in the surface treatment layer, it is possible to improve the lithium ion conductivity in the surface treatment layer. .

Specifically, in the negative electrode active material according to an embodiment of the present invention, the surface treatment layer may have an E _barrier value of 0.05 eV to 0.3 eV, more specifically 0.05 eV to 0.2 eV. If the E _barrier value in the surface treatment layer is less than 0.05 eV, it is difficult to manufacture itself, and if it exceeds 0.3 eV, gas reduction effect and output characteristic improvement effect may be deteriorated due to the decrease of the surface coverage due to the recrystallization of boron-containing lithium oxide. have.

In the present invention, the E _barrier value can be obtained through first principle calculation using the VIenna Ab initio simulation package (VASP) program.

Specifically, the boron-containing lithium oxide constituting the surface treatment layer may be a compound of Formula 1 below:

[Formula 1]

Li _a B _b O _{(a + 3b) / 2}

In Formula 1, 1 ≦ a ≦ 4 and 1 ≦ b ≦ 8.

Specific examples include Li ₂ B ₄ O ₇ , LiB ₃ O ₅ , LiB ₈ O ₁₃ , Li ₄ B ₂ O ₅ , Li ₃ BO ₃ , Li ₂ B ₂ O ₄ , or Li ₂ B ₆ O ₁₀ . And any one or a mixture of two or more thereof.

In more detail, the boron-containing lithium oxide may have an E _barrier value of 0.05 eV to 0.3 eV, and more specifically, may satisfy the above E _barrier value and at the same time, a band gap of 8.5 eV to 10.5 eV. . As such, by satisfying the conditions of the E _barrier value and the band gap value, a surface treatment layer having excellent balance of ion conductivity and electric conductivity can be formed with a higher coverage. More specifically, the band gap may be 8.9 eV to 10.1 eV.

In the present invention, the band gap of the boron-containing lithium oxide can be measured using cyclic voltammetry.

In addition, the surface treatment layer is preferably formed to an appropriate thickness in consideration of the particle diameter of the core for determining the capacity of the negative electrode active material. Specifically, it may be formed in an average thickness ratio of 0.01 to 0.1 with respect to the radius of the core under the conditions satisfying the boron content. If the thickness ratio of the surface treatment layer is less than 0.01, the thickness of the surface treatment layer may be too thin, so that the effect of suppressing side reactions between the negative electrode active material and the electrolyte during charging and discharging may be insignificant. If the thickness ratio of the surface treatment layer exceeds 0.1, the surface treatment layer may be too thick. Due to this, there is a risk of deterioration of output characteristics due to an increase in resistance.

In the present invention, the particle diameter of the core and the thickness of the surface treatment layer can be measured through particle cross-sectional analysis using a focused ion beam (fib).

In addition, the surface treatment layer may be formed on the entire surface of the core, or may be partially formed. More specifically, the surface treatment layer may be formed at least 80% of the total surface area of the core under the conditions satisfying the above-described boron content range, and more specifically, the surface treatment when considering the effect of preventing electrolyte decomposition at the core surface The layer can be formed over 100% of the total surface area of the core, ie over the core surface.

Meanwhile, in the negative electrode active material for a secondary battery according to an embodiment of the present invention, the core includes lithium titanium oxide.

Specifically, the lithium titanium oxide may be a compound of Formula 2 below:

[Formula 2]

Li _x Ti _y M _w O _{12 - z} A _z

In Chemical Formula 2,

0.5≤x≤4, 1≤y≤5, 0≤w≤0.17, 0≤z≤0.17,

M includes at least one element selected from the group consisting of metals of Groups 2 to 13 on the periodic table, specifically, Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg and May be one or more selected from the group consisting of Mo,

A is a nonmetallic element having a -monovalent oxidation number, and specifically, may be at least one selected from the group consisting of F, Cl, Br, and I.

The composition of lithium titanium oxide of Formula 2 is the average composition of the entire core.

More specifically, the lithium titanium oxide is Li ₄ Ti ₅ O ₁₂ , Li _{0 . 8} Ti _{2 . 2} O ₄ , Li _2.67 Ti _1.33 O ₄ , LiTi ₂ O ₄ , Li _{1 . 33} Ti _{1 . 67} O ₄ or Li _{1 . 14} Ti _{1 . 71} O ₄ , and any one or a mixture of two or more thereof may be used.

In addition, the lithium titanium oxide may be a single particle having an average particle diameter (D ₅₀ ) of 0.1 μm to 5 μm, or fine primary particles having an average particle diameter of 200 nm to 1000 nm are aggregated, and an average particle diameter (D ₅₀ ) The secondary particles may be 3 µm to 20 µm. In the case where the lithium titanium oxide is a single particle, if the average particle diameter is less than 0.1 μm, there is a fear of lowering structural stability and capacity characteristics. If the average particle diameter exceeds 5 μm, output characteristics of the secondary battery may be reduced. .

In the present invention, the average particle diameter (D ₅₀ ) of the core particles can be defined as the particle size at 50% of the particle size distribution. The average particle diameter (D ₅₀ ) of the core particles can be measured using, for example, a laser diffraction method. More specifically, when measured by the laser diffraction method, the core particles were dispersed in a solvent, and then introduced into a commercially available laser diffraction particle size measuring apparatus (for example, Microtrac MT 3000) to irradiate an ultrasonic wave of about 28 kHz at an output of 60 W. after that, it is possible to calculate the average particle diameter (D ₅₀₎ of from 50% based on the particle size distribution of the measuring device.

In addition, the core is from the surface side of the particle, specifically the interface in contact with the surface treatment layer, and from the interface in contact with the surface treatment layer from more than 0% to less than 100% with respect to the core particle radius in the direction of the core particle center. Some boron (B) elements of the boron-containing lithium oxide may be doped in an area corresponding to a distance of 0% to 30%. In addition, the content of the B element may have a concentration gradient that decreases from the surface of the core toward the core center.

The negative electrode active material according to an embodiment of the present invention having the structure and configuration as described above is much lower than the prior art due to the decrease in the lithium impurity content, such as lithium carbonate, lithium hydroxide, and the increase of boron content on the surface of the active material Initial pH value is shown. As a result, side reactions between the negative electrode active material and the electrolyte can be suppressed, and at the same time, the lithium ion conductivity and the electrical conductivity in the surface treatment layer can be improved with good balance.

 Specifically, the negative electrode active material has an initial pH value of 9 to 10, more specifically, 9.3 to 9.7, and the appropriate amount when titrating 2 g of the negative electrode active material to pH 5 or less, specifically pH 5 using 0.1M HCl, is 0.9 To 1.5 ml, and more specifically 0.9 to 1.4 ml. As the titration amount is smaller, side reactions between the negative electrode active material and the electrolyte are suppressed, and at the same time, an effect of improving the balance of the lithium ion conductivity and the electrical conductivity in the surface treatment layer can be achieved.

In the present invention, the pH of the negative electrode active material may be measured by mixing 2 g of the negative electrode active material in 100 ml of distilled water, stirring for 5 to 10 minutes, filtration, and titrating to pH 5 or less with an acid such as HCl. At this time, by-products such as lithium carbonate and lithium hydroxide included in the active material may be repeatedly soaked and decanted to be included in distilled water. At this time, it is not particularly affected by variables such as time to add the negative electrode active material to distilled water.

In addition, the negative electrode active material may be one having a BET specific surface area of 0.5m ² / g to 10.0m ² / g.

If the BET specific surface area of the negative electrode active material exceeds 10.0 m ² / g, the dispersibility of the negative electrode active material in the active material layer and the resistance in the electrode may increase due to aggregation between the negative electrode active materials, and the BET specific surface area is 0.5 m ² / g. When less than this, there exists a possibility of the dispersibility fall of a negative electrode active material itself, and a capacity fall. In addition, the negative electrode active material according to an embodiment of the present invention may exhibit excellent capacity and charge / discharge characteristics by accelerating the BET specific surface conditions. More specifically, the negative electrode active material may have a BET specific surface area of 3.0m ² / g to 6.0m ² / g.

In the present invention, the specific surface area of the negative electrode active material is measured by the Brunauer-Emmett-Teller (BET) method, specifically, nitrogen gas at liquid nitrogen temperature (77K) using BELSORP-mino II manufactured by BEL Japan It can calculate from adsorption amount.

The negative electrode active material according to the embodiment of the present invention having the structure as described above, after the surface treatment of the precursor of the boron-containing lithium oxide to the core containing lithium titanium oxide, heat treatment at 350 ℃ to 450 ℃, the core It can be prepared by a manufacturing method comprising the step of forming a surface treatment layer comprising a boron-containing lithium oxide on the surface of the amount of boron content relative to 1 mol of lithium titanium oxide in a molar ratio of 0.002 to 0.02. Accordingly, according to another embodiment of the present invention is provided a method for producing the negative electrode active material.

Specifically, in the manufacturing method, the core including the lithium titanium oxide is the same as described above, and may be manufactured according to a conventional manufacturing method.

In addition, the precursor of the boron-containing lithium oxide may be a material capable of forming boron-containing lithium oxide by reacting by boron-containing lithium oxide or a subsequent heat treatment process.

Specifically, the precursor of the boron-containing lithium oxide is boric acid of H ₃ BO ₃ ; Boron oxides such as B ₂ O ₃ or B ₂ O ₅ ; _{LiBO 3, Li 2 B 4 O} 7, LiB 3 O 5, LiB 8 O 13, Li 4 B 2 O 5, Li 3 BO 3, Li 2 B 2 O 4, or Li ₂ lithium borate such as B ₆ O ₁₀ And boron-containing lithium oxides such as salts. Any one or a mixture of two or more thereof may be used.

In the above manufacturing method, the surface treatment step for the lithium titanium oxide may be a dry mixing of the core containing the lithium titanium oxide and the precursor of the boron-containing lithium oxide, or the boron-containing lithium to the core containing the lithium titanium oxide. The composition for forming a surface treatment layer including a precursor of an oxide may be performed according to a conventional surface treatment process such as spraying, coating, or dipping.

For example, when the surface treatment is performed by a spraying process, a precursor of boron-containing lithium oxide is dissolved or dispersed in a solvent to prepare a composition for forming a surface treatment layer, and then includes lithium titanium oxide using a conventional spraying apparatus. By spraying on the core. In this case, a polar solvent may be used as the solvent, and specifically, water or an alcohol having 1 to 8 carbon atoms (for example, methanol, ethanol, or isopropyl alcohol), or dimethyl sulfoxide (DMSO), N- Polar organic solvents such as methylpyrrolidone (NMP), acetone, and the like, and any one or a mixture of two or more thereof may be used. In addition, the solvent may be included in an amount that can exhibit a suitable coating property when the surface treatment of the composition, and can be easily removed during the subsequent heat treatment.

In addition, in the surface treatment process, the mixing ratio of the core containing the lithium titanium oxide and the precursor of the boron-containing lithium oxide, the execution time of the surface treatment process, and the like, the content of boron in the final negative electrode active material It can be mutually adjusted as appropriate within the range to satisfy the range.

In addition, a lithium raw material capable of reacting with the precursor of the boron-containing lithium oxide in the surface treatment process to form a boron-containing lithium oxide may optionally be further used.

The lithium raw material is specifically lithium hydroxide such as LiOH; Carbonates such as Li ₂ CO ₃ , etc., and any one or a mixture of two or more thereof may be used. In addition, the lithium raw material may be used so that the boron-containing lithium oxide in the surface treatment layer is formed in an amount such that the boron content is a molar ratio of 0.002 to 0.02 with respect to 1 mol of lithium titanium oxide.

In addition, a heat treatment process is performed at 350 ° C to 450 ° C for the cores surface-treated by the surface treatment process.

The E _barrier value of the boron-containing lithium oxide forming the surface treatment layer may be controlled by the heat treatment temperature for the surface-treated core. When the heat treatment is performed within the above temperature range, boron-containing lithium oxide that satisfies the above E _barrier value condition may be formed, and at the same time, the coverage of the core surface may be improved. If the temperature during the heat treatment is less than 350 ℃, the formation of boron-containing lithium oxide that satisfies the above E _barrier value conditions and the control of the E _barrier value is not easy, and the side reaction occurs due to the unreacted precursor material and the residual solvent component There is a fear of deterioration of the characteristics of the active material and battery characteristics. In addition, if the temperature during the heat treatment exceeds 450 ° C., the coverage of the surface treatment layer with respect to the core particles may be reduced due to the recrystallization of the produced boron-containing lithium oxide, and the effect of preventing the decomposition of the electrolyte solution may be lowered. There is a risk of occurrence. More specifically, the heat treatment process may be performed at 400 ℃ to 450 ℃.

In addition, the heat treatment process may be carried out in a multi-step within the above temperature range, in this case it may be carried out by increasing the temperature according to the progress of each step.

In addition, the heat treatment process may be performed in an air atmosphere or an oxygen atmosphere (for example, O ₂ ), and more specifically, may be performed in an oxygen atmosphere having an oxygen partial pressure of 20% by volume or more. In addition, the heat treatment process may be performed for 5 hours to 48 hours, or 10 hours to 20 hours under the above conditions.

By the heat treatment process, a surface treatment layer including boron-containing lithium oxide satisfying the above E _barrier value range is formed on the core including lithium titanium oxide in an optimal content. The prepared negative electrode active material may exhibit excellent capacity recovery due to its unique structure and constituent characteristics. In addition, the negative electrode active material can improve the output characteristics by preventing a decrease in resistance caused by lithium by-products generated in the manufacturing process of the core, and can also reduce the generation of gas by preventing the decomposition of the electrolyte solution by the surface treatment layer, especially low In the SOC (state of charge), it is possible to reduce electrolyte decomposition and gas generation due to elution of titanium ions Ti ⁴⁺ .

Accordingly, according to another embodiment of the present invention provides a negative electrode and a lithium secondary battery including the negative electrode active material.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

In the negative electrode, 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, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like on the surface of the steel, aluminum-cadmium alloy and the like can be used. In addition, the negative electrode current collector may have a thickness of about 3 to 500 μm, and like the positive electrode current collector, fine concavities and convexities may be formed on the surface of the current collector to enhance the bonding force of the negative electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

In addition, in the negative electrode, the negative electrode active material layer may further include a binder and a conductive material optionally together with the negative electrode active material, and may be prepared according to a conventional negative electrode manufacturing method except using the negative electrode active material. Can be.

Specifically, the negative electrode is coated with a negative electrode active material, and optionally a composition for forming a negative electrode comprising a binder and a conductive material on the negative electrode current collector and dried, or casting the negative electrode forming composition on a separate support, The film obtained by peeling from this support may be produced by laminating on a negative electrode current collector.

In this case, the conductive material is used to impart conductivity to the electrode. In the battery constituted, the conductive material may be used without particular limitation as long as it has electronic conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers such as polyphenylene derivatives, and the like, or a mixture of two or more kinds thereof may be used. The conductive material may be included in an amount of 1 to 30% by weight based on the total weight of the negative electrode active material layer.

In addition, the binder serves to improve adhesion between the negative electrode active material particles and the adhesion between the negative electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC). ), Starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubbers, or various copolymers thereof, and the like, and one or a mixture of two or more thereof may be used. The binder may be included in an amount of 1 to 30% by weight based on the total weight of the negative electrode active material layer.

In addition, the solvent usable in the preparation of the negative electrode composition may include a solvent generally used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol, N- Methyl pyrrolidone (NMP), acetone (acetone) or water, and the like, and one of these alone or a mixture of two or more thereof may be used. The amount of the solvent is sufficient to dissolve or disperse the negative electrode active material, the conductive material and the binder in consideration of the coating thickness and the production yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity during the coating for the negative electrode production. Do.

In addition, the coating of the composition for forming a negative electrode on the negative electrode current collector may be performed by a conventional slurry coating method. Specifically, the slurry coating method may include bar coating, spin coating, roll coating, slot die coating, or spray coating, and any one or two or more of these methods may be mixed. In addition, when applying the composition for forming the negative electrode, it may be preferable to apply the composition for forming the negative electrode to an appropriate thickness in consideration of the loading amount and the thickness of the active material in the negative electrode active material layer to be finally prepared.

The drying process for the coating film of the composition for forming a negative electrode formed on the negative electrode current collector carried out after the coating process, as well as the evaporation of the solvent in the composition for forming a negative electrode to remove the moisture contained in the negative electrode to the maximum, and at the same time can increase the binding strength of the binder It may be carried out by a method such as heat treatment at a temperature, hot air injection and the like. Specifically, the drying process may be carried out at a temperature below the boiling point of the solvent or less than the melting point of the binder, more specifically, may be carried out at 100 ℃ to 150 ℃. More preferably, it may be carried out for 1 to 50 hours at a temperature of 100 ℃ to 120 ℃ and a pressure of 10torr or less.

And the rolling process performed after the drying process may be performed according to a conventional method.

The negative electrode as described above may exhibit excellent output characteristics by including the negative electrode active material in the negative electrode active material layer, and gas generation may be reduced by preventing decomposition of the electrolyte.

According to another embodiment of the present invention, an electrochemical device including the cathode is provided. The electrochemical device may be specifically a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the negative electrode is as described above. The lithium secondary battery may further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

Specifically, the positive electrode is formed on the positive electrode current collector and the positive electrode current collector, and includes a positive electrode active material layer containing the positive electrode active material.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, carbon, nickel, titanium on a surface of aluminum or stainless steel Surface treated with silver, silver or the like can be used. In addition, the positive electrode current collector may have a thickness of about 3 to 500 μm, and may form fine irregularities on the surface of the current collector to increase adhesion of the positive electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

In the cathode active material layer, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) may be used as the cathode active material.

Specifically, it may be a lithium transition metal oxide including lithium and a transition metal such as cobalt, manganese, nickel or aluminum. In addition, the lithium transition metal oxide is specifically a lithium-manganese oxide (eg, LiMnO ₂ , LiMn ₂ O Etc.), lithium-cobalt-based oxides (e.g., LiCoO _2, etc.), lithium-nickel-based oxides (e.g., LiNiO _2, etc.), lithium-nickel-manganese-based oxides (e.g., LiNi _{1 - Y} Mn _Y O ₂ (where, 0 <Y <1), LiMn _2-z Ni _z O ₄ (where, 0 <Z <2) and the like), lithium-nickel-cobalt-based oxide (for example, LiNi _{1 - Y} Co _Y O ₂ (where, 0 <Y <1) and the like), lithium-manganese-cobalt oxide (e.g., LiCo _1-Y Mn _Y O ₂ (where, 0 <Y <1), LiMn _{2 - z} Co _z O ₄ (here, 0 <Z <2) and the like, lithium-nickel-manganese-cobalt-based oxides (eg, Li (Ni _P Co _Q Mn _R ) O ₂ (here, 0 <P <1, 0 <Q <1, 0 <R <1, P + Q + R = 1) or Li (Ni _P Co _Q Mn _R ) O ₄ (where 0 <P <2, 0 <Q <2, 0 <R <2, P + Q + R = 2) or the like, or lithium-nickel-cobalt-transition metal (M) oxide (for example, Li (Ni _P Co _Q Mn _R M _S ) O ₂ (here, M is a source of Al, Fe, V, Cr, Ti, Ta, is selected from the group consisting of Mg, Mo, P, Q, R and S are each independently selected from the elements As a fraction, it may be 0 <P <1, 0 <Q <1, 0 <R <1, 0 <S <1, P + Q + R + S = 1), and these lithium transition metal oxides may be tungsten ( W) or niobium (Nb) More specifically, the lithium transition metal oxide is LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , lithium nickel manganese cobalt oxide ( For example, Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ , LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2} O ₂ , or LiNi _0.8 Mn _0.1 Co _0.1 O ₂ , or the like, or lithium nickel cobalt aluminum oxide (eg, LiNi _0.8 Co _0.15 Al _0.05 O _2, etc.), and any one or a mixture of two or more thereof may be used. Can be used.

The positive electrode as described above may be manufactured according to a conventional positive electrode manufacturing method. Specifically, the composition for forming a cathode prepared by dissolving a conductive material and a binder in a solvent together with the cathode active material may be coated on a cathode current collector, followed by drying and rolling.

On the other hand, in the lithium secondary battery, the separator is to separate the negative electrode and the positive electrode and to provide a passage for the movement of lithium ions, if it is usually used as a separator in a lithium secondary battery can be used without particular limitation, in particular for ion transfer of the electrolyte It is desirable to have a low resistance against the electrolyte and excellent electrolytic solution-moisture capability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer or the like Laminate structures of two or more layers may be used. In addition, conventional porous nonwoven fabrics such as nonwoven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be optionally used as a single layer or a multilayer structure.

In addition, examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. It doesn't happen.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolanes may be used. Of these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can improve the charge and discharge performance of a battery, and low viscosity linear carbonate compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate and the like is more preferable. In this case, the cyclic carbonate and the chain carbonate may be mixed and used in a volume ratio of about 1: 1 to about 1: 9, so that the performance of the electrolyte may be excellent.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB (C ₂ O ₄ ) ₂ and the like can be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, tri, etc. for the purpose of improving battery life characteristics, reducing battery capacity, and improving discharge capacity of the battery. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be included. In this case, the additive may be included in 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful for electric vehicle fields such as hybrid electric vehicle (HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

[ Example  One: Of cathode active material  Produce]

Li ₂ B ₄ O ₇ isopropyl alcohol for Li ₄ Ti ₅ O ₁₂ (primary particle average particle diameter (D ₅₀ ): 500 nm, secondary particle average particle diameter (D ₅₀ ): 8 μm) on secondary particles. Surface treatment using a composition prepared by mixing in, and heat treatment was performed for 5 hours at 400 ℃ under an atmosphere (wherein Li ₂ B ₄ O ₇ is Li ₄ Ti ₅ O ₁₂ Used in such a way that the molar ratio of B per mole is 0.005). By the above method, a negative electrode active material having a surface treatment layer including LiBO ₂ and Li ₂ B ₄ O ₇ formed on the surface of Li ₄ Ti ₅ O ₁₂ was prepared.

[ Example  2: Of cathode active material  Produce]

A surface including LiBO ₂ and LiB ₃ O ₅ on the surface of Li ₄ Ti ₅ O _{12 by} the same method as in Example 1 except for using LiB ₃ O ₅ instead of Li ₂ B ₄ O ₇ An anode active material having a treatment layer was prepared.

[ Example  3: Of cathode active material  Produce]

Li ₄ Ti ₅ O ₁₂ was carried out in the same manner as in Example 1, except that Li ₂ B ₄ O ₇ was used in an amount such that the molar ratio of B was 0.01 with respect to 1 mol of Li ₄ Ti ₅ O _12. A negative electrode active material having a surface treatment layer including LiBO ₂ and Li ₂ B ₄ O ₇ formed on its surface was prepared.

[ Example  4: Of cathode active material  Produce]

Li ₂ B ₄ O ₇ 5000 ppm isotropic to Li ₄ Ti ₅ O ₁₂ (primary particle average particle diameter (D ₅₀ ): 500 nm, secondary particle average particle diameter (D ₅₀ ): 8 μm) on secondary particles. Surface treatment was carried out using a composition prepared by mixing in propyl alcohol, and heat treatment was performed at 400 ° C. for 5 hours under an atmospheric atmosphere. By the above method, a negative electrode active material including 5,000 ppm of B was added to the total weight of Li ₄ Ti ₅ O _{12 on} the surface of Li ₄ Ti ₅ O ₁₂ .

[ Comparative example  One: Of cathode active material  Produce]

Li ₄ Ti ₅ O ₁₂ (primary particle average particle diameter (D ₅₀ ): 500 nm, secondary particle average particle diameter (D ₅₀ ): 8 μm) on secondary particles without surface treatment was used as a negative electrode active material.

[ Comparative example  2: Of cathode active material  Produce]

The _{Li 2 B 4 O Al 2 O} 3 to ₇ instead of the Li ₄ Ti ₅ O ₁₂ A surface treatment layer including Al ₂ O ₃ on the surface of Li ₄ Ti ₅ O _{12 by} the same method as in Example 1, except that the molar ratio of Al to 0.005 was used per 1 mole. This formed negative electrode active material was prepared.

[ Comparative example  3: Of cathode active material  Produce]

AlF ₃ is Li ₄ Ti ₅ O ₁₂ instead of Li ₂ B ₄ O ₇ A surface treatment layer including AlF ₃ was formed on the surface of Li ₄ Ti ₅ O _{12 in} the same manner as in Example 1 except that the molar ratio of Al was set to 0.005 per 1 mole. A negative electrode active material was prepared.

[ Comparative example  4: Of cathode active material  Produce]

Except for using LiBO ₂ instead of Li ₂ B ₄ O _{7 It} was carried out in the same manner as in Example 1 to provide a cathode active material having a surface treatment layer containing LiBO ₂ on the surface of Li ₄ Ti ₅ O ₁₂ Prepared.

 [ Comparative example  5: Of cathode active material  Produce]

Li ₂ B ₄ O ₇ to Li ₄ Ti ₅ O ₁₂ LiBO ₂ and Li ₂ B ₄ O ₇ were applied to the surface of Li ₄ Ti ₅ O _{12 in} the same manner as in Example 1, except that the molar ratio of B to 0.001 per mole was used. A negative electrode active material including a surface treatment layer was prepared.

[ Comparative example  6: Of cathode active material  Produce]

The _{Li 2 B 4 O Al 2 O} 3 to ₇ instead of the Li ₄ Ti ₅ O ₁₂ A surface treatment layer including Al ₂ O ₃ on the surface of Li ₄ Ti ₅ O ₁₂ by performing the same method as in Example 1 except that the molar ratio of Al was set to 0.003 per 1 mole. This formed negative electrode active material was prepared.

[ Comparative example  7: Of cathode active material  Produce]

The _{Li 2 B 4 O Al 2 O} 3 to ₇ instead of the Li ₄ Ti ₅ O ₁₂ A surface treatment layer including Al ₂ O ₃ on the surface of Li ₄ Ti ₅ O _{12 by} the same method as in Example 1, except that the molar ratio of Al was set to 0.004 per 1 mole. This formed negative electrode active material was prepared.

[ Comparative example  8: Of cathode active material  Produce]

The negative electrode active material prepared in Comparative Example 1 was put into 100 ml of water, washed by stirring for 5 minutes, and used as a negative electrode active material.

[ Comparative example  9: Of cathode active material  Produce]

Li ₂ B ₄ O ₇ for Li ₄ Ti ₅ O ₁₂ (primary particle average particle diameter (D ₅₀ ): 500 nm, secondary particle average particle diameter (D ₅₀ ): 8 μm) on secondary particles. Surface treatment was carried out using a composition prepared by mixing 300 ppm in isopropyl alcohol, and heat treatment was performed at 400 ° C. for 5 hours under an atmospheric atmosphere. Was prepared LiBO ₂ and Li ₂ B ₄ O ₇ cathode active material having a surface treated layer containing the surface of the Li ₄ Ti ₅ O ₁₂ by the method described above, Li ₄ Ti ₅ O ₁₂ of 300 ppm based on the total weight B To prepare a negative electrode active material comprising a.

[ Comparative example  10: Of cathode active material  Produce]

Li ₂ B ₄ O ₇ for Li ₄ Ti ₅ O ₁₂ (primary particle average particle diameter (D ₅₀ ): 500 nm, secondary particle average particle diameter (D ₅₀ ): 8 μm) on secondary particles. The surface treatment was carried out using a composition prepared by adding 500 ppm of the mixture to isopropyl alcohol and performing heat treatment at 400 ° C. for 5 hours under an atmospheric atmosphere. The negative electrode active material having a surface treatment layer including LiBO ₂ and Li ₂ B ₄ O ₇ was formed on the surface of Li ₄ Ti ₅ O ₁₂ by the above method, and 500 ppm of B was added based on the total weight of Li ₄ Ti ₅ O _12. To prepare a negative electrode active material comprising a.

[ Comparative example  11: Of cathode active material  Produce]

Li _{0. In the} same manner as in Example 1 except that the heat treatment was performed at 500 ° C. for 5 hours _{. 8} Ti _{2 . An} anode active material having a surface treatment layer including LiBO ₂ and LiB ₄ O ₇ formed on the surface of ₂ O ₄ was prepared.

 [ Production Example : Fabrication of Lithium Secondary Battery]

A lithium secondary battery was prepared using the negative electrode active materials prepared in Examples 1 to 4, respectively.

In detail, the negative electrode active material, the carbon black conductive material, and the PVdF binder prepared in Examples 1 to 4 were mixed in a ratio of 85: 10: 5 by weight in an N-methylpyrrolidone solvent in a composition for forming a negative electrode. (Viscosity: 5000 mPa · s) was prepared, coated on Cu foil with a loading amount of 2.6 mAh / cm ³ , dried by heat treatment at 120 ° C., and rolled to prepare a negative electrode.

In addition, Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ A positive electrode active material, a carbon black conductive material, and a PVdF binder were mixed in an N-methylpyrrolidone solvent in a weight ratio of 90: 5: 5 to prepare a composition for forming a positive electrode (viscosity: 5000 cps), which was applied to an aluminum current collector. After that, dry rolling was performed to prepare a positive electrode.

An electrode assembly was manufactured by interposing a separator of porous polyethylene between the positive electrode and the negative electrode prepared as described above, the electrode assembly was placed in a case, and an electrolyte solution was injected into the case to prepare a lithium secondary battery. At this time, the electrolyte is prepared by dissolving 1.0M concentration of lithium hexafluorophosphate (LiPF ₆ ) in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixing volume ratio of EC / DMC / EMC = 3/4/3). It was.

The negative electrode active material of Comparative Examples 1 to 11 was carried out in the same manner as above to prepare a negative electrode and a lithium secondary battery including the same.

[ Experimental Example  One: Cathode active material  analysis]

E _barrier values and band gaps of the surface treatment layer forming material and the E _barrier and the forming metal elements of the surface treatment layer for the negative electrode active materials prepared in Examples 1, 2 and Comparative Examples 2 to 5 and 11 ( The content of B or Al) was measured respectively.

In detail, the E _barrier value was obtained by first principle calculation using The vienna Ab initio simulation package (VASP) program.

The band gap was measured using cyclic voltammetry.

The content of element B contained in the surface treatment layer of the negative electrode active material was analyzed by the ICP-AES method (Inductively Coupled Plasma-Atomic Emission Spectroscophy).

Specifically, 0.1 g of the negative electrode active material to be measured was taken, and 2 ml of distilled water and 3 ml of concentrated nitric acid were added thereto, the lid was closed, and the sample was dissolved. Thereafter, when the sample was completely dissolved, 50 ml of ultrapure water was added and diluted. Thereafter, the diluted solution was diluted 10 times again and analyzed by ICPAES (Inductively Coupled Plasma-Atomic Emission Spectroscometer). ICP-AES (ICP 5300DV, Perkinelemer) was operated under the following conditions:

Forward Power 1300 W; Torch Height 15 mm; Plasma gas flow 15.00 L / min; Sample gas flow 0.8 L / min; Assist gas flow 0.20 L / min and pump speed 1.5 mL / min.

The results are shown in Tables 1 and 2 below.

	E barrier value (eV)	Band gap (eV)
Li 2 B 4 O 7	0.15	8.9-10.1
LiB 3 O 5	0.05	-
Al 2 O 3	5.44	~ 8.8
AlF 3	0.34	~ 10.8
LiBO 2	0.45	-
Li 2 B 4 O 7	0.15	8.9-10.1

	Surface treatment layer forming material	E barrier value (eV)	B content (molar ratio to 1 mole of LTO)
Example 1	LiBO 2 , Li 2 B 4 O 7	0.30	0.005
Example 2	LiBO 2 , LiB 3 O 5	0.25	0.005
Comparative Example 2	Al 2 O 3	5.44	0.005
Comparative Example 3	AlF 3	0.34	0.005
Comparative Example 4	LiBO 2	0.45	0.005
Comparative Example 5	Li 2 B 4 O 7	0.15	0.001
Comparative Example 11	LiBO 2 , Li 2 B 4 O 7	0.40	0.005

As a result, the surface treatment layer of the cathode active materials of Examples 1 and 2 had a significantly lower E _barrier value than the surface treatment layers of Comparative Examples 2 to 5 and 11, and from this it was confirmed that it has a better lithium ion conductivity. Can be.

[ Experimental Example  2: Of cathode active material  Structure observation]

The negative electrode active materials prepared in Example 1 and Comparative Example 2 were processed using ion milling, and then observed by scanning electron microscopy (SEM). The results are shown in FIGS. 4 and 5, respectively.

As a result, in the case of the negative electrode active material prepared in Example 1, the surface treatment layer containing B was uniformly formed on the core surface, whereas in the negative electrode active material prepared in Comparative Example 2, the Al-containing coating layer was partially formed on the core surface. It can be confirmed that the formed.

[ Experimental Example  3: pH titration experiment]

In the preparation of the anode active material including the surface treatment layer according to the present invention, pH titration was performed to determine the change in the amount of lithium impurities according to the amount of B contained in the surface treatment layer.

Specifically, the pH meter (metrohm 794) for 2g of the negative electrode active material of Examples 1 and 3 varying in the molar ratio of B contained in the surface treatment layer with respect to 1 mol of Li ₄ Ti ₅ O ₁₂ was 0.005 and 0.01, respectively. 0.1M HCl was titrated in 0.02ml increments and the pH change was recorded. At this time, the pH was recorded by performing the same method for the negative active material of Comparative Examples 1 and 5-8 for comparison. The results are shown in FIG.

6 is a graph comparing reduction amounts of lithium impurities with respect to the negative electrode active materials of Examples 1 and 3 and Comparative Examples 1 and 5-8, respectively.

As a result of the experiment, the negative electrode active materials of Examples 1 and 3 had a pH of 9 to 10, and the initial pH was lower than that of Comparative Examples 1 and 5-8.

[ Experimental Example  4: Of cathode active material  Electrochemical properties evaluation]

The coin cell (using a negative electrode of Li metal) prepared using the negative electrode active material prepared in Example 1 was charged at 25 ° C. until a constant current (CC) of 4.25V was reached, followed by a constant voltage of 4.25V (CV). ), And the first charge was performed until the charging current became 0.05 mAh. After 20 minutes, the battery was discharged to a constant current of 0.2C until 3.0V, and the initial discharge capacity of the first cycle was measured. After that, the charge and discharge capacity, charge and discharge efficiency and rate characteristics were evaluated by varying the discharge conditions at 10C. The results are shown in Table 3 below and FIGS. 7 and 8.

	First charge and discharge	Second charge and discharge
	Initial discharge capacity (mAh / g, 0.2C)	efficiency (%)	10C / 0.2C (%)
Example 1	174	98.5	87.9
Comparative Example 1	168	98.5	76.3

As a result of the experiment, the negative electrode active material of Example 1 having a surface treatment layer of boron-containing lithium oxide was better in initial discharge capacity and rate characteristics than Comparative Example 1, which is a negative electrode active material of lithium titanium oxide having no surface treatment layer. The effect was shown.

[ Experimental Example  5: Measurement of Gas Generation of Lithium Secondary Battery]

After impregnating the negative electrode active material in Example 1 and Comparative Example 1 with the electrolyte, the resultant was stored at 80 ° C. for 1 week to measure the type of gas and the amount of gas generated. At this time, the electrolyte is prepared by dissolving 1.0M concentration of lithium hexafluorophosphate (LiPF ₆ ) in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixing volume ratio of EC / DMC / EMC = 3/4/3). It was. The results are shown in FIG. 9.

As a result, the negative electrode active material of Example 1 compared with the negative electrode active material of Comparative Example 1 having no surface treatment layer, the amount of gas generated in the case of H ₂ , CH ₄ , while CO, CO ₂ and C ₂ H _In the case of ₄ , gas generation was significantly reduced.

On the other hand, the lithium secondary battery containing the negative electrode active material of Example 4 and Comparative Examples 9, 10 was also impregnated with the electrolyte in the same manner as described above, and stored for one week at 80 ℃ to measure the type of gas and the amount of gas generated. The results are shown in FIG.

As a result of the experiment, the negative electrode active material of Example 4 is less than 10 to 20 times the content of boron in comparison with the negative electrode active material of Comparative Examples 9, 10, CH ₄ and C ₂ H ₄ showed the same level of gas generation, while H ₂ , In the case of CO and CO ₂ , the amount of gas generated was significantly reduced.

In the case of Comparative Examples 9 and 10, the B content is 300 ppm and 500 ppm, respectively, with respect to the total weight of the negative electrode active material, so that the content of B is less than the total weight of the negative electrode active material, and lithium is formed according to the formation of the surface treatment layer including B. It is considered that the effect of preventing the decomposition of the electrolyte on the surface of the titanium oxide has not been achieved.

[ Experimental Example  6: capacity of lithium secondary battery Recovery rate  evaluation]

After charging the lithium secondary battery each containing the negative electrode active material in Example 1 and Comparative Example 1 to 2.5V at a constant current of 0.1C, and stored at 80 ℃ for 21 days, two and three cycles excluding the initial discharge capacity The average discharge capacity of the first was measured. The results are shown in Table 4 below.

	Capacity recovery rate (%)
Example 1	95
Comparative Example 1	88

As a result, the negative electrode active material of Example 1 having a surface treatment layer of boron-containing lithium oxide showed a significantly better capacity recovery than Comparative Example 1.

[ Experimental Example  7: Evaluation of normal capacity of lithium secondary battery]

Normal capacity according to C-rate of the negative electrode active materials in Example 1 and Comparative Example 11 was observed, and the results are shown in FIG. 11.

C-rate of Figure 11 shows the amount of current required when charging and discharging for 1 hour at 1C conditions, it was confirmed that the resistance is also increased as the current amount is increased, and as a result, the normal capacity is also lowered.

Referring to FIG. 11, based on the capacity during charging and discharging at 0.2C of the lithium secondary batteries manufactured in Example 1 and Comparative Example 11, the capacity decreases as the C-rate increases, and the gap widens to charge at 20C. The lithium secondary battery containing the negative electrode active material prepared in Example 1 during discharge showed a capacity of 85% or more, and the lithium secondary battery containing the negative electrode active material prepared in Comparative Example 11 showed a capacity of less than 80%. Could.

This, in the case of the lithium secondary battery including the negative electrode active material of Example 1, the boron source includes LiBO ₂ and Li ₂ B ₄ O ₇ generated by reacting with lithium by-products such as Li ₂ CO ₃ , LiOH at 400 ℃ E _barrier value of the surface treatment layer is adjusted to about 0.3 eV, Li ₄ Ti ₅ O ₁₂ The conductivity of Li ions at the surface is improved, resulting in improved output characteristics. On the other hand, in Comparative Example 11, the heat treatment at 500 ℃ Li ₄ Ti ₅ O ₁₂ The higher the E _barrier value for Li ion transport of the LiBO ₂ and LiB ₄ O ₇ surface treatment layers formed on the surface, the lower the Li ion conductivity and the higher the resistance. . In addition, due to the heat treatment at a high temperature, it is difficult to cover the entire surface of Li ₄ Ti ₅ O ₁₂ due to the recrystallization of the boron-containing lithium oxide, thereby increasing the amount of gas generated.

Claims (11)

1. A core comprising lithium titanium oxide, and a surface treatment layer located on the surface of the core,

   The surface treatment layer includes a boron-containing lithium oxide in an amount such that the boron content is a molar ratio of 0.002 to 0.02 with respect to 1 mol of lithium titanium oxide,

   When the titration of 2g of the negative electrode active material to pH 5 or less using 0.1M HCl, the appropriate amount of the negative electrode active material for secondary batteries.
2. The method of claim 1,

   The surface treatment layer is a negative electrode active material for a secondary battery comprising a boron-containing lithium oxide to 5000 to 7000 ppm relative to the total weight of lithium titanium oxide.
3. The method of claim 1,

   The surface treatment layer has a lithium ion mobile energy barrier value of 0.05eV to 0.3eV secondary battery anode active material.
4. The method of claim 1,

   The boron-containing lithium oxide has a band gap value of 8.5eV to 10.5eV secondary battery anode active material.
5. The method of claim 1,

   The boron-containing lithium oxide is Li ₂ B ₄ O ₇ , LiB ₃ O ₅ , LiB ₈ O ₁₃ , Li ₄ B ₂ O ₅ , Li ₃ BO ₃ , Li ₂ B ₂ O ₄ , and Li ₂ B ₆ O ₁₀ A negative active material for a secondary battery comprising any one or two selected from the group consisting of.
6. The method of claim 1,

   The surface treatment layer is a negative electrode active material for secondary battery is formed more than 80 area% of the total surface area of the core.
7. The method of claim 1,

   The lithium titanium oxide is a negative electrode active material for a secondary battery comprising a compound of formula 2:

   [Formula 2]

   Li _x Ti _y M _w O _{12 - z} A _z

   In Chemical Formula 2,

   0.5≤x≤4, 1≤y≤5, 0≤w≤0.17, 0≤z≤0.17,

   M comprises one or more elements selected from the group consisting of metals of Groups 2 to 13 on the periodic table,

   A is a nonmetallic element having a -monovalent oxidation number.
8. The method of claim 1,

   The lithium titanium oxide is Li ₄ Ti ₅ O ₁₂ , Li _{0 . 8} Ti _{2 . 2} O ₄ , Li _{2 . 67} Ti _{1 . 33} O ₄ , LiTi ₂ O ₄ , Li _1.33 Ti _1.67 O ₄ and Li _{1 . 14} Ti _{1 . A} negative electrode active material for a secondary battery comprising any one or two selected from the group consisting of ₇₁ O ₄ .
9. For the core containing lithium titanium oxide, the precursor of the boron-containing lithium oxide was surface treated, followed by heat treatment at 350 ° C. to 450 ° C., so that the boron-containing lithium oxide on the surface of the core was reduced to 1 mol of lithium titanium oxide. A method for producing a negative electrode active material for a secondary battery according to claim 1, comprising the step of forming a surface treatment layer comprising an amount such that the molar ratio of 0.002 to 0.02.
10. A negative electrode for a secondary battery comprising the negative electrode active material according to any one of claims 1 to 8.
11. Lithium secondary battery comprising a negative electrode according to claim 10.

Images