KR101577180B1 - Positive electrode active material with improved energy density - Google Patents

Abstract

The present invention relates to a mixed cathode active material, and more particularly, to a mixed cathode active material exhibiting a high energy density.
The mixed cathode active material according to the present invention exhibits high energy density and high stability by mixing a cathode active material having a concentration gradient with a high energy density and a layered lithium nickel cobalt manganese composite oxide having a relatively high stability while controlling the particle size .

Description

{Positive electrode active material with improved energy density}

The present invention relates to a mixed cathode active material, and more particularly, to a mixed cathode active material exhibiting a high energy density.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, a lithium secondary battery having a high energy density and voltage, a long cycle life, and a low self-discharge rate has been commercialized and widely used. In addition, as the interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, . In recent years, studies on the use of lithium secondary batteries having high energy density and discharge voltage as power sources for electric vehicles and hybrid electric vehicles have been actively conducted, and some of them are in the commercialization stage.

In the case of LiCoO ₂ , which is a typical anode material, the energy density and output characteristics reach practical limits. Especially, when used for high energy density applications, due to the structural instability, Thereby generating an exothermic reaction with the electrolyte in the cell, thereby causing the explosion of the battery. In order to improve the instability of LiCoO ₂ , the use of lithium-containing manganese oxide such as LiMnO _{2 having} a layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure and lithium-containing nickel oxide (LiNiO ₂ ) has been considered. Mn, and Co have been continuously studied.

The most representative Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ among the above three-component layered oxides changes to Ni ³⁺ or Ni ⁴⁺ according to the depth of filling in Ni ²⁺ upon charging. However, unlike stable Ni ²⁺ , Ni ³⁺ or Ni ⁴⁺ lose the lattice oxygen due to instability and are reduced to Ni ²⁺ . This lattice oxygen reacts with the electrolyte to change the surface properties of the electrode, transfer impedance to decrease capacity and high-rate characteristics, resulting in low energy density.

In general, these materials are uniform in the composition of the metal on the particle surface and in the bulk. In order to have good anodic performance, the function of the inside and the surface of the anode powder particle must be different from each other. In other words, the composition in the particle should be structurally stable with a lot of lithium intercalation sites, but the reaction with the electrolyte should be minimized on the surface.

For this purpose, Korean Patent Laid-Open Publication No. 2005-0083869 proposes a lithium transition metal oxide having a concentration gradient of a metal composition. This method is a method of synthesizing an internal material and then forming a double layer by applying a material having a different composition to the outside, followed by heat treatment by mixing with a lithium salt. In this method, the metal composition of the inner layer and the outer layer can be differently synthesized at the time of synthesis, but the metal composition of the produced cathode active material does not change continuously. That is, although the gradual gradation of the metal composition can be achieved through the heat treatment process, at a high heat treatment temperature of 850 ° C or more, the concentration gradient of the metal ions hardly occurs due to thermal diffusion of the metal ions. Also, since the powder synthesized by the present invention does not use ammonia as a chelating agent, the powder has a low tap density and is not suitable for use as a cathode active material for a lithium secondary battery. When a lithium transition metal oxide is used as an internal material, And the reproducibility is low.

In order to solve this problem, Korean Patent Laid-Open Publication No. 2007-0097923 proposes a cathode active material having internal bulk portions and external bulk portions, and metal components in the external bulk portion have a continuous concentration distribution depending on positions.

On the other hand, according to Japanese Patent Application No. 2002-001724, a high-stability composite oxide, Li 2 O 2 _.2 Ni _0.65 Mn _0.35 , which is excellent in lifetime characteristics and thermal stability but has a low conductivity and discharge capacity in order to improve the thermal stability and life- O ₂ and a cathode active material mixed with Li _1.02 Ni _0.7 Co _0.3 O ₂ having a high conductivity and discharge capacity characteristics but a poor life characteristic and thermal stability have been reported.

However, as the mixing ratio of the high - stability composite oxide increased, the life characteristics of the mixed cathode active material were improved. As the mixing ratio of the high - conductivity composite oxide increased, the high - rate characteristics were excellent. That is, it was impossible to obtain a cathode active material having both a high rate and a long life characteristic.

Korea Patent Publication No. 2005-0083869 Korea Patent Publication No. 2007-0097923 Japanese Patent Laid-Open No. 2002-001724

It is an object of the present invention to provide a novel mixed cathode active material having improved both high energy density characteristics and safety life characteristics.

The present invention has been made to solve the above problems

A core portion represented by the following Chemical Formula 1;

A shell part represented by the following formula (2); And

A first lithium composite oxide including a concentration gradient portion between the core portion and the shell portion, the concentration of the metal ions gradually changing from the composition of the core portion to the composition of the shell portion; And

???????? Li _x1 [Ni _1-y1-z1-w1 Co _y1 Mn _z1 M _w1 ] O ₂

Wherein M is at least one element selected from the group consisting of Mg, Ba, Zn, Ca (where x is at least one element selected from the group consisting of Mg, Ba, Zn, , At least one metal selected from the group consisting of Sr, Cu, Zr, P, Fe, Al, Ga, In, Cr,

???????? Li _{x 2} [Ni _{1-y 2-z 2 -w 2} Co _{y 2} Mn _{z 2} M _{w 2} ] O ₂

0.5, 0? W2? 0.1, 0.3? 1-y2-z2-w2 <0.7, M is at least one element selected from the group consisting of Mg, Ba, At least one metal selected from the group consisting of Zn, Ca, Sr, Cu, Zr, P, Fe, Al, Ga, In, Cr, Ge,

A second lithium composite oxide having a constant metal ion concentration throughout the particle and represented by the following Chemical Formula 3;

And a high-energy density mixed cathode active material.

???????? Li _{x 3} Ni _{y 3} Mn _{z 3} Co _{1 -y 3 -z 3} M _s O ₂

M, Mg, Ti, Ba, Ca, B, Al, Cr, F, Mo, P (where 0 &amp;le; , Sr, and Zr)

In the high energy density mixed cathode active material according to the present invention, the mixed cathode active material is mixed in a ratio of 0.001 to 50 parts by weight of the second lithium composite oxide per 100 parts by weight of the first lithium composite oxide.

In the high energy density mixed cathode active material according to the present invention, the first lithium composite oxide has a particle diameter R1 of 10 to 15 mu m.

In the high energy density mixed cathode active material according to the present invention, the second lithium composite oxide has a particle diameter R 2 of 1 to 6 탆.

In the high energy density mixed cathode active material according to the present invention, the ratio of the particle diameter of the first lithium composite oxide to the particle diameter of the second lithium composite oxide is 2 to 15.

In the high energy density positive electrode active material mixture according to the invention, the second lithium composite oxide is _{Li [Ni 1/3 Mn 1/3 Co 1/3} ] O 2, Li [Ni 0.5 Mn 0.2 Co 0.3] O 2, Or Li [Ni _0.6 Mn _0.2 Co _0.2 ] O ₂ .

The present invention also provides a positive electrode comprising the mixed cathode active material according to the present invention.

The present invention also provides a lithium secondary battery comprising a positive electrode according to the present invention.

The present invention also provides a middle- or large-sized device characterized by comprising a lithium secondary battery according to the present invention.

In the present invention, the middle- or large-sized device may be a power tool, an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle , PHEV); Electric motorcycle including E-bike, E-scooter; Electric golf cart; Electric truck; An electric commercial vehicle or a system for electric power storage.

The mixed cathode active material according to the present invention exhibits high energy density and high stability by mixing a cathode active material having a concentration gradient with a high energy density and a layered lithium nickel cobalt manganese composite oxide having a relatively high stability while controlling the particle size .

1 and 2 show the results of measuring the pellet density and the energy density of the active material prepared in Examples and Comparative Examples of the present invention.
FIGS. 3 and 4 are measurement results of life characteristics and energy characteristics of a battery including the active material prepared in Examples and Comparative Examples of the present invention.

Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited by the following examples.

PREPARATION EXAMPLE 1 Synthesis of first lithium composite oxide having a concentration gradient

A mixed metal solution of 2.5 M nickel sulfate hexahydrate (NiSO ₄ .6H ₂ O) and cobalt sulfate heptahydrate (CoSO ₄ .7H ₂ O) was prepared so that the molar ratio of Ni: Co: Mn was 80: 20: A continuous reactor having a volume of 90 L filled with ammonia solution was used. The pH of the initial solution was in the range of 11 to 12. The prepared 2.5 M nickel / cobalt mixed metal solution, 28% ammonia water, and 25% sodium hydroxide solution were continuously and continuously injected at a rate of 300 to 600 rpm using a metering pump while stirring.

When the particle size of the composite metal hydroxide reaches a steady state, the aqueous solution for forming the surface and the aqueous metal solution for forming the core are mixed and supplied so that the concentration of the transition metal exhibits a continuous concentration gradient Respectively. That is, the reaction was continued using the aqueous metal solution while changing the concentration until the molar ratio of nickel sulfate, cobalt sulfate and manganese sulfate aqueous solution was changed from 80: 20: 0 to 33.3: 33.3: 33.3. When the molar ratio of the metal aqueous solution reached 33.3: 33.3: 33.3, the reaction was continued until the steady state was reached while maintaining the molar ratio. Thus, spherical nickel manganese cobalt complex hydroxide having a concentration gradient was obtained.

The metal complex hydroxide was filtered and washed with water, dried in a hot air drier at 110 ° C for 15 hours, and then mixed with lithium hydroxide (LiOH) to obtain a molar ratio of Li to transition metal ion of 0.95 to 1.05 And calcined at ~ 1000 ° C for 4 to 20 hours to obtain a cathode active material powder including a shell portion exhibiting a concentration gradient.

PREPARATION EXAMPLE 2 Synthesis of second lithium composite oxide

A 2.5 M aqueous solution of metal at a molar ratio of 0.333: 0.333: 0.333 of nickel sulfate, cobalt sulfate and manganese sulfate in a ratio of 2.5 L / hr, an aqueous ammonia solution to the reactor [concentration of ammonia solution / concentration of aqueous metal solution] of 0.5 RTI ID = 0.0 &gt; 1.0. &Lt; / RTI &gt; The pH was adjusted to 11-12 by supplying a 25% aqueous solution of sodium hydroxide to adjust the pH. The average residence time of the solution was adjusted to 10 ~ 15 hours and the average temperature of the reaction tank was 40 ~ 60 ℃ Respectively.

To the obtained complex hydroxide was added caustic soda until pH 12.5 was reached to remove unreacted metal salt, followed by filtration and washing with water, followed by drying in a hot air drier at 100-150 ° C for 10-20 hours to obtain a complex hydroxide type precursor. (Li ₂ CO ₃ ) to a concentration of the metal salt of 0.95 to 1.2, heating at a heating rate of 1 to 20 ° C / min, and calcining at 700 to 1000 ° C for 4 to 20 hours, To obtain a positive electrode active material powder represented by Li [Ni _1/3 Mn _1/3 Co _1/3 ] O ₂ .

Represented by Li [Ni _0.5 Mn _0.2 Co _0.3 ] O ₂ , Li [Ni _0.6 Mn _0.2 Co _0.2 ] O _2, was prepared in the same manner as above except that the molar ratio of nickel sulfate, nickel sulfate, cobalt sulfate and manganese sulfate was controlled. To obtain a composite oxide powder.

<Examples> Preparation of mixed cathode active material

The mixing ratio of the first lithium composite oxide and the second lithium composite oxide prepared in Preparation Example 1 and Preparation Example 2 was as shown in Table 1 below to prepare a mixed cathode active material.

<Experimental Example> Measurement of particle characteristics

The pellet density and the energy density of the mixed cathode active materials prepared as shown in Table 1 were measured and shown in FIG. 1, FIG. 2, and Table 2 below.

1, 2, and Table 2, it can be seen that as the mixing ratio of the second lithium composite oxide having a constant metal ion concentration in the particles increases, the pellet density and energy density increase and decrease.

<Production Example>

Acetylene black as a conductive material and polyvinylidene fluoride (solef 6020, a product name: solef6020) as a binder were mixed at a weight ratio of 90: 5: 5 to prepare a cathode active material for a lithium secondary battery manufactured according to each of the above Examples and Comparative Examples, . The slurry was uniformly coated on an aluminum foil having a thickness of 20 占 퐉 and vacuum-dried at 130 占 폚 to prepare a positive electrode for a lithium secondary battery.

An electrolytic solution obtained by dissolving LiPF ₆ at a concentration of 1 M in a solvent mixed with ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3: 7 was used as a separator, using the above anode and lithium foil as counter electrodes and a porous polyethylene film having a thickness of 25 탆 as a separator. A coin cell was produced by a conventional method.

&Lt; Experimental Example >

The life characteristics and the energy density of the coin battery manufactured using the cathode active materials of the above Examples and Comparative Examples were evaluated and shown in Tables 2, 3 and 4.

As shown in Table 2, FIG. 3, and FIG. 4, when the first lithium composite oxide and the second lithium composite oxide were mixed according to the embodiment of the present invention, energy compared to the second lithium composite oxide only Comparative Example 6 and Comparative Example 7 And the density was improved by about 30%.

Claims (10)

A core portion represented by the following Chemical Formula 1;
A shell part represented by the following formula (2); And
A first lithium composite oxide including a concentration gradient portion between the core portion and the shell portion, the concentration of the metal ions gradually changing from the composition of the core portion to the composition of the shell portion; And
???????? Li _x1 [Ni _1-y1-z1-w1 Co _y1 Mn _z1 M _w1 ] O ₂
Wherein M is at least one element selected from the group consisting of Mg, Ba, Zn, Ca (where x is at least one element selected from the group consisting of Mg, Ba, Zn, , At least one metal selected from the group consisting of Sr, Cu, Zr, P, Fe, Al, Ga, In, Cr,
???????? Li _{x 2} [Ni _{1-y 2-z 2 -w 2} Co _{y 2} Mn _{z 2} M _{w 2} ] O ₂
0.5, 0? W2? 0.1, 0.3? 1-y2-z2-w2 <0.7, M is at least one element selected from the group consisting of Mg, Ba, At least one metal selected from the group consisting of Zn, Ca, Sr, Cu, Zr, P, Fe, Al, Ga, In, Cr, Ge,
A second lithium composite oxide having a constant metal ion concentration throughout the particle and represented by the following Chemical Formula 3;
And a high-energy-density mixed cathode active material.
???????? Li _{x 3} Ni _{y 3} Mn _{z 3} Co _{1 -y 3 -z 3} M _s O ₂
M, Mg, Ti, Ba, Ca, B, Al, Cr, F, Mo, P (where 0 &amp;le; , Sr, and Zr)
The method according to claim 1,
Wherein the mixed cathode active material is mixed in a ratio of 0.001 to 50 parts by weight of the second lithium composite oxide per 100 parts by weight of the first lithium composite oxide.
The method according to claim 1,
Wherein the first lithium composite oxide has a particle diameter R1 of 10 to 15 占 퐉.
The method according to claim 1,
And the second lithium composite oxide has a particle size R 2 of 1 to 6 탆.
The method according to claim 1,
Wherein a ratio R1 / R2 of a particle diameter of the first lithium composite oxide to a particle diameter of the second lithium composite oxide is 2-15.
The method according to claim 1,
The second lithium composite oxide may be Li [Ni _1/3 Mn _1/3 Co _1/3 ] O ₂ , Li [Ni _0.5 Mn _0.2 Co _0.3 ] O ₂ , or Li [Ni _0.6 Mn _0.2 Co _0.2 ] O ₂ Lt; RTI ID = 0.0 &gt; 1, &lt; / RTI &gt;
An anode comprising the mixed cathode active material according to any one of claims 1 to 6.
A lithium secondary battery comprising the positive electrode according to claim 7.
A medium- or large-sized device characterized by comprising the lithium secondary battery according to claim 8.
10. The method of claim 9,
The middle- to large-sized devices include a power tool, an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV) Electric cars; Electric motorcycle including E-bike, E-scooter; Electric golf cart; Electric truck; An electric commercial vehicle or a system for power storage.

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