KR102478973B1 - Composite positive electrode active material with strong superstructure, preparing method for the same, positive electrtode including the same, and lithium ion battery including the same - Google Patents

Abstract

The positive electrode active material according to the present invention can obtain a higher discharge capacity than conventional positive electrode active materials with excess lithium, has a composition containing excess lithium represented by the following [Formula 1], and has a layered structure in the crystal structure, In X-ray diffraction analysis, I (20 )/I(18) is 0.1 or more, and I(22)/ is the ratio of the peak intensity at 22.y° (y = 1 to 9.9) to the peak intensity at 20.x° It is characterized in that I (20) is 0.78 or more.
[Formula 1]
x(Li ₂ MO ₃ ) + (1-x)LiMeO ₂
(Where 0<x<1, M or Me is one of 3d, 4d, 5d transition metals or non-transition metals including Al, Mg, Mn, Ni, Co, Cr, V, Fe, Ir, and Mo above, and M and Me may be the same or different from each other)

Description

Composite positive electrode active material with strong superstructure, preparing method for the same, positive electrode including the same, and lithium ion battery including the same}

The present invention relates to a composite cathode active material having an enhanced superlattice peak, a method for manufacturing the active material, a cathode containing the active material, and a lithium ion battery including the cathode.

Recently, as the size of the electric vehicle market has exploded, research on lithium ion batteries having high capacity characteristics has been actively conducted in relation to lithium-based energy storage devices used in electric vehicles.

A lithium transition metal oxide having a layered structure is mainly used as a cathode active material used in such a lithium ion battery. Lithium transition metal oxides having such a layered structure have not yet reached a satisfactory level of energy capacity for use in electric vehicles, and improvement thereof is required.

Recently, a so-called lithium-excessive layered composite active material containing an excess of lithium as a cathode active material for obtaining a high capacity has attracted attention. As the material contains an excessive amount of lithium, a relatively lithium-rich region and a relatively low-lithium (Li-dilute) region exist. In this way, in the layered structure composite active material having an excess of lithium, the region with more lithium in the layered structure is a composite of Li ₂ MO ₃ and the region with less lithium is LiMeO ₂ .

On the other hand, for high capacity, it is essential to increase the amount of electrons as well as the amount of usable lithium. However, in the case of a lithium-excessive layered composite active material, not only cations but also anions are used for electron supply and emission. Oxygen reaction by Li-O-Li bonding can occur in Li ₂ MO ₃ with relatively much lithium, and in general, the Li ₂ MO ₃ phase has a stacking fault, which causes a super-lattice (super-lattice). structure) is changed, and it is known that this affects the electrochemical activity of the Li ₂ MO ₃ phase.

In addition, in the case of lithium-excessive layered composite active materials, it is known that oxygen generation by Li ₂ MO ₃ is essential at the first charging high voltage (about 4.5V), and a large amount of irreversible capacity occurs due to severe structural changes according to oxygen generation There is a problem with

Therefore, in order to increase the capacity of a cathode material used in a lithium ion battery, an irreversible capacity must be reduced, and a cathode material that is structurally stable even when oxygen is generated is required.

Korean Patent Publication No. 2011-0118225

An object of the present invention is to maximize the anion reaction by suppressing the oxygen release reaction at a high voltage (about 4.5V) during charging, compared to the conventional cathode active material composed of an excess lithium composite oxide, thereby obtaining a high discharge capacity. It is to provide a composite cathode active material, a cathode containing the composite cathode active material, and a lithium ion battery containing the cathode.

Another object of the present invention is to provide a method capable of producing a composite cathode active material having a high degree of regularly arranged stacking between a lithium layer and a transition metal layer at low cost, compared to a conventional cathode active material composed of an excess lithium composite oxide. .

The first aspect of the present invention for solving the above problems has a composition containing excess lithium represented by the following [Formula 1], has a layered structure in the crystal structure, and upon X-ray diffraction analysis, 18.y ° The ratio of the peak intensity appearing at 20.x° (x = 1 ~ 9.9) to the peak intensity appearing at (y = 1 ~ 9.9), I(20) / I(18), is 0.1 or more , I(22)/I(20), which is the ratio of the peak intensity at 22.y° (y = 1 to 9.9) to the peak intensity at 20.x° (x = 1 to 9.9) ) is 0.78 or more, to provide a positive electrode active material.

[Formula 1]

x(Li ₂ MO ₃ ) + (1-x)LiMeO ₂

(Where 0<x<1, M or Me is one of 3d, 4d, 5d transition metals or non-transition metals including Al, Mg, Mn, Ni, Co, Cr, V, Fe, Ir, and Mo above, and M and Me may be the same or different from each other)

A second aspect of the present invention for solving the above problems is to provide a positive electrode including a current collector and an active material layer formed on the current collector and including the positive electrode active material.

A third aspect of the present invention for solving the above problems is a lithium, comprising a positive electrode including the positive electrode active material, a negative electrode disposed at a predetermined distance from the positive electrode, and an electrolyte interposed between the positive electrode and the negative electrode. It is to provide an ion battery.

A fourth aspect of the present invention for solving the above other problems is to prepare a transition metal precursor composed of secondary particles forming a spherical shape by aggregating plate-shaped or spherical primary particles, the transition metal precursor and the lithium precursor Mixing to prepare a mixture, heat treatment in an air atmosphere by putting the mixture into a heat treatment furnace, and rapid cooling (quenching) of the heat-treated material, the material produced through the steps, the following [ It has a composition containing excess lithium represented by Formula 1], has a layered structure in the crystal structure, and in X-ray diffraction analysis, for the peak intensity appearing at 18.y ° (y = 1 ~ 9.9) I(20)/I(18), the ratio of the peak intensity appearing at 20.x° (x = 1 to 9.9), is 0.1 or more, and the peak appears at 20.x° (x = 1 to 9.9) ( To provide a method for producing a composite cathode active material in which I(22)/I(20), which is the ratio of peak intensity appearing at 22.y ° (y = 1 to 9.9) to peak) intensity, is 0.78 or more.

[Formula 1]

x(Li ₂ MO ₃ ) + (1-x)LiMeO ₂

(Where 0<x<1, M or Me is one of 3d, 4d, 5d transition metals or non-transition metals including Al, Mg, Mn, Ni, Co, Cr, V, Fe, Ir, and Mo above, and M and Me may be the same or different from each other)

In the case of a conventional lithium-excessive layered composite active material, the first cycle is called an activation process by Li ₂ MnO ₃ , and at this time, high irreversible capacity is exhibited due to the release of a large amount of oxygen. When the activation process in the first cycle is completed, anion redox can occur reversibly from the second cycle without additional oxygen release. That is, the capacity excluding the irreversible capacity due to oxygen release in the first cycle can be reversibly obtained from the second cycle. Therefore, reducing the irreversible capacity in the first cycle is important to obtain a high charge/discharge capacity as the cycle progresses and to further improve the energy capacity of the positive electrode active material.

In the cathode active material according to the present invention, the regularity of the stacking between the lithium layer and the transition metal layer is higher than that of a conventional cathode active material composed of a composite oxide having an excess of lithium. Accordingly, the lithium ion battery having a positive electrode including the positive electrode active material according to the present invention can maximize the anion reaction by suppressing the oxygen release reaction at a high voltage (about 4.5V) during charging, compared to conventional materials. Even with the same charging capacity, high discharge capacity can be obtained by reducing the irreversible capacity.

According to the method according to the present invention, it is possible to easily obtain a positive electrode active material having a high degree of regularly arranged stacking between a lithium layer and a transition metal layer at low cost, compared to a conventional positive electrode active material composed of a lithium-excessive composite oxide.

1 is a flowchart illustrating a method for synthesizing a lithium-excess layered composite active material according to an embodiment of the present invention.
2 is a flowchart illustrating a method for synthesizing a lithium-excess layered composite active material according to a comparative example.
3 shows a transition metal precursor (plate shape) prepared according to an embodiment of the present invention.
Figure 4 shows a transition metal precursor (spherical) prepared according to a comparative example.
Figure 5 shows the X-ray diffraction pattern (XRD) of the layered structure composite active material with lithium and prepared according to Examples and Comparative Examples.
6 is a first charge/discharge graph and a graph of a voltage/capacity curve (dQ/dV plot) thereof, which are electrochemical characteristics of the lithium-furnace layered composite active material prepared according to Examples and Comparative Examples.

Hereinafter, the configuration and operation of embodiments of the present invention will be described with reference to the accompanying drawings.

In describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted. In addition, when a part "includes" a certain component, it means that it may further include other components without excluding other components unless otherwise stated.

The cathode active material according to the present invention has a composition containing excess lithium represented by the following [Chemical Formula 1], forms a layered structure in crystal structure, and upon X-ray diffraction analysis, 18.y ° (y = 1 to 9.9 ), the ratio of the peak intensity appearing at 20.x ° (x = 1 ~ 9.9) to the peak intensity appearing at I (20) / I (18) is 0.1 or more, and 20.x ° ( Characterized in that I(22)/I(20), the ratio of the peak intensity appearing at 22.y° (y=1-9.9) to the peak intensity appearing at x=1-9.9, is 0.78 or more to be

[Formula 1]

x(Li ₂ MO ₃ ) + (1-x)LiMeO ₂

(Where 0<x<1, M or Me is one of 3d, 4d, 5d transition metals or non-transition metals including Al, Mg, Mn, Ni, Co, Cr, V, Fe, Ir, and Mo above, and M and Me may be the same or different from each other)

As in the present invention, while having a layered structure and performing X-ray diffraction analysis, the ratio of I (20) / I (18) and the ratio of I (22) / I (20) simultaneously satisfy the above numerical range , This means that the regular arrangement of the lithium layer and the transition metal layer is higher than that of the conventional lithium-excessive layered composite oxide.

On the other hand, 'peak appearing at 18.y° (y = 1 ~ 9.9)' means the peak where 2θ is located between 18.1° and 18.99°, and the peak appearing at 20.x° (x = 1 ~ 9.9) 2θ means a peak located between 20.1 ° and 20.99 °, and a peak appearing at 22.y ° (y = 1 to 9.9) means a peak with 2θ located between 22.1 ° and 22.99 °.

In this way, there are many regularly arranged stacks in the crystal structure, and the stability of the oxidation/reduction reaction of oxygen is increased, so that a larger amount of lithium is stored in the cathode material despite the same amount of desorbed lithium (charging capacity). Since it can be inserted, it is possible to obtain a high discharge capacity by reducing the irreversible capacity even with the same charging capacity compared to the conventional lithium-excessive composite oxide.

In addition, in the cathode active material, 2θ obtained by X-ray diffraction analysis is the full width at half-maximum of the first (020) peak, which is the maximum peak of the superlattice at 20 ° to 22 ° ; FWHM) may be 0.13 ° to 0.18 °, and the full width at half maximum of the second peak may be 0.13 ° to 0.18 °.

The positive electrode according to the present invention may include a current collector and the positive electrode active material layer formed on the current collector.

The current collector may be a metal current collector having good conductivity, for example, an aluminum foil may be used, but is not necessarily limited thereto.

The cathode active material layer is prepared and molded from a composition in which a cathode active material powder having the above composition, a conductive material, a binder, and a solvent are mixed, and then laminated on the metal current collector or coated on the metal current collector. A positive electrode can be manufactured in the form of However, it is not limited to the above-listed methods, and forms other than the above methods may be used.

Carbon black, graphite fine particles, etc. may be used as the conductive material, but are not limited thereto, and any material that can be used as a conductive material in the art may be used. For example, graphite, such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, farnes black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as aluminum and nickel powder; conductive whiskers made of zinc oxide, potassium titanate, and the like; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

Examples of the binder include vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene and mixtures thereof, or styrene butadiene rubber-based polymers. This may be used, but is not limited thereto, and any that can be used as a binder in the art may be used.

N-methylpyrrolidone, acetone, or water may be used as the solvent, but it is not limited thereto, and any solvent that can be used in the art may be used. The contents of the positive electrode active material, conductive agent, binder, and solvent may be adjusted according to characteristics required for a lithium ion battery, and if necessary, one or more may not be used.

The present invention provides a lithium ion battery comprising the positive electrode, a negative electrode disposed at a predetermined distance from the positive electrode, and an electrolyte interposed between the positive electrode and the negative electrode.

The negative electrode may include a current collector and a negative active material layer formed on the current collector.

The anode active material layer is prepared by mixing anode active material powder, a conductive material, a binder, and a solvent, and then directly coated on a metal current collector and dried, or the anode active material composition is cast on a separate substrate and then separated from the substrate to form a metal It may be manufactured by a method of lamination on a current collector.

The negative electrode active material is not particularly limited as long as it is used in a lithium ion battery and is capable of reversibly intercalating/deintercalating lithium ions, and examples thereof include lithium metal, lithium alloys, and carbon-based materials. The material capable of reversibly intercalating and deintercalating lithium ions is a carbon-based material, and any carbon-based negative electrode active material generally used in a conventional lithium ion battery may be used. For example, crystalline carbon, amorphous carbon or mixtures thereof. The crystalline carbon may be, for example, natural graphite in amorphous, platy, flake, spherical or fibrous form; or artificial graphite, and the amorphous carbon may be, for example, soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, or the like. The contents of the negative electrode active material, conductive material, binder, and solvent may be adjusted according to the use and configuration of the lithium ion battery, or some components may be omitted.

The separator preferably has low resistance to the movement of ions included in the electrolyte and has good moisture absorption characteristics of the electrolyte solution. Such a separator is, for example, selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in the form of a non-woven fabric or a woven fabric, and may be used for lithium ion batteries. There may be polyethylene, polypropylene, etc., which are widely used in

The electrolyte is a non-aqueous electrolyte and may preferably be made of an organic material, and a lithium salt may be dissolved in an organic solvent in the organic material.

The organic solvent may be used as long as it can be used as an organic solvent in this technical field. For example, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate , benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide , dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, or mixtures thereof.

In addition, the electrolyte may be a solid electrolyte such as an organic solid electrolyte or an inorganic solid electrolyte. When a solid electrolyte is used, the solid electrolyte may also serve as a separator.

The positive electrode, the negative electrode, the separator, and the electrolyte are accommodated in a case, which is a general manufacturing method of a lithium ion battery, and finally made into a battery. At this time, the positive electrode, the negative electrode, and the separator are manufactured by a method of stacking, winding, or folding in multiple layers to accommodate them in a case, and then injecting electrolyte into the case to seal them. The material of the case may be made of various materials such as metal and plastic, and the shape of the case may also be made in various forms such as a cylindrical shape, an angular shape, and a pouch shape.

As shown in FIG. 1, the method for producing a cathode active material according to the present invention includes preparing a transition metal precursor (step 1) and mixing the transition metal precursor and a lithium precursor to prepare a mixture (step 2). ), preparing the composition of [Formula 1], including the step of charging the mixture into a heat treatment furnace and heat-treating it in an air atmosphere (step 3), and rapidly cooling the heat-treated material (step 4) It is characterized by doing.

The method according to the present invention is characterized in that, in particular, in step 1, through control of the shape of the transition metal precursor, the regularity of the stacked arrangement of the lithium layer and the transition metal layer is increased in the final composite oxide.

In addition, the transition metal precursor may preferably include secondary particles having a substantially spherical shape by aggregating a plurality of primary particles having a plate-like shape.

In the step of preparing the transition metal precursor, a hydroxide containing at least one transition metal is prepared. At this time, a process including the following steps may be performed in order to prepare a hydroxide having a uniform array of transition metals.

Injecting distilled water, ammonia water, and sodium hydroxide into the reactor and mixing them by injecting gas (step 1-1), and introducing an aqueous solution containing a transition metal and a solution for adjusting the pH in the reactor into the reactor and reacting the mixture (step 1-2) and filtering the precipitate produced by the reaction (step 1-3).

The shape of the transition metal precursor formed may vary depending on the gas injected in step 1-1. For example, a plate-like shape is formed when nitrogen is used, and a sphere-like shape is formed when air is used. can be formed.

Step 2 is a step of preparing a mixture by mixing the transition metal precursor and the lithium precursor prepared in the above process.

To this end, first, for example, a step (step 2-1) of adding a lithium precursor and a transition metal precursor to an acetone solvent and then mixing them using a mixing process such as a ball mill (step 2-1) may be performed. For example, when a ball mill process is applied, it is preferable to perform it for 4 hours to 24 hours because a homogeneous mixture can be obtained. On the other hand, the solvent used for the mixing is not particularly limited as long as it can properly dissolve each precursor and prepare a uniform mixture, and if a homogeneous precursor mixture can be formed through simple mixing, the ball mill process A simple stirring process may be applied without using it.

Next, the step of removing the solvent by heating the mixture solution using a hot plate (step 2-2) may be performed. The heating temperature is preferably heated to, for example, about 100 ° C., but heating to a higher temperature is not preferable because a phase may be generated in the precursor mixture in addition to removing the solvent.

Subsequently, a step (step 2-3) of pelletizing the mixture from which the solvent is removed may be performed. The pelletization step is to ensure that gases such as carbon dioxide and oxygen are easily released in the heat treatment step performed thereafter, so that the synthesis of phase formation is facilitated. In this step, pellets having a diameter of about 1 cm can be produced using pelletizing equipment such as a press, but the diameter of the pellets is not particularly limited as long as the heat treatment step can be performed smoothly.

The lithium precursor of Chemical Formula 1 may include Li ₂ CO ₃ , LiOH, LiNO ₃ , etc., and the transition metal precursor may mix one or more respective transition metal precursors together with a lithium precursor, or one or more transition metal precursors may be used. The mixed transition metal precursor and lithium precursor may be mixed together by separately mixing, heat-treating, and drying.

Step 3 is a step of heat-treating the mixture to cause a solid phase synthesis reaction. In the heat treatment process, by heating at a temperature of about 800 to 900° C., carbonate and nitrate attached to the metal precursor are removed to form a phase of only the metal component of the mixture. If the temperature of the heat treatment process is less than 800 ° C, even if the rapid cooling is performed in step 4, the degree of reaction between the Li ₂ MnO ₃ phase and the LiNi _0.5 Mn _0.5 O ₂ phase is weak, and if the temperature exceeds 900 ° C, Li loss occurs. It is desirable to maintain the temperature range.

In addition, if the heat treatment time (firing time) is less than 1 hour, it is difficult to sufficiently synthesize, and if it exceeds 10 hours, the formed particle size increases and the initial activation process may not occur well. It is desirable to do

Step 4 is a step of rapidly cooling (quenching) at a cooling rate equal to or higher than a certain level so that the state of the material synthesized at a high temperature through the heat treatment can be maintained at room temperature.

Rapid cooling is performed to maintain the state in which the interaction (increased solubility of elements and high electrochemical activity of oxygen ions) of each component of the composite synthesized through the sintering process of the heat treatment proceeds. At this time, if the cooling rate is slow, a material that does not have high element solubility and high anion electrochemical activity may be obtained, and thus the electrochemical activity may decrease. Since the purpose of the rapid cooling process is to obtain a stable phase at a high temperature while being maintained at room temperature, the rapid cooling method is not limited as long as the cooling rate can be set to a certain level or higher. At this time, the cooling rate is preferably higher than that of water-quenching.

[Example]

1 is a manufacturing process diagram of a composite oxide according to an embodiment of the present invention.

The composition of the lithium-excessive cathode active material prepared in the embodiment of the present invention is Li _1.2 Ni _0.2 Mn _0.6O2 composition, and in [Formula 1], x = 0.5, M = Mn, Me = Ni, Mn Manufacturing method of FIG. 1 Through this, 0.5Li ₂ MnO ₃ +0.5LiNi _0.5 Mn _0.5O2 was synthesized.

First, a 20L co-precipitation reactor was used to prepare the transition metal precursor. Inside the reactor, NH ₄ OH and NaOH were added at a ratio of 15:1 by weight, and 2.5 L of distilled water was added and nitrogen (N ₂ ) was injected while stirring for about 10 minutes. Separated tanks 1 and 2 in the reactor were prepared as follows. In tank 1, NiSO ₄ ·6H ₂ O and MnSO ₄ ·H ₂ O were prepared at a ratio of 1:3 mol%, and about 10 L of distilled water was added and mixed while maintaining a temperature of 45 °C. In tank 2, NaOH and NH ₄ OH (24% aqueous solution) were prepared at a ratio of 3:1 by weight, and about 2.5 L of distilled water was added and mixed while maintaining at 10 ° C. Through a pump, tank 1 and tank 2 were injected in a metered amount into the reactor at a rate of 680 g/h and 432 g/h, respectively, for reaction. The final mixed solution was naturally dried using filter paper, and when the moisture content was less than 0.5%, the precipitate (coprecipitation) was filtered out. Through this, approximately plate-like Ni _0.25 Mn _0.75 (OH) ₂ was prepared, and the average size of the transition metal precursor was 3 to 5 μm.

As a precursor for the solid phase reaction, Li ₂ CO ₃ (Junsei, purity 99% or more) as a lithium precursor and Ni _0.25 Mn _0.75 (OH) ₂ (plate shape) as a transition metal precursor were prepared as follows. Here, the difference from the comparative example is that the morphology of the transition metal precursor is plate-like, unlike the spherical shape in the comparative example.

4/7 Ni _0.25 Mn _0.75 (OH) ₂ + 3/7 Li ₂ CO ₃

The ball mill was performed with the total weight fixed at 1.6 g, where Li ₂ CO ₃ was 0.6102 g and Ni _0.25 Mn _0.75 (OH) ₂ was 0.9898 g.

The precursors prepared according to the weight were added to an acetone solvent (purity of 99.7%) and ball milled for about 5 hours and 20 minutes to reduce the particle size and prepare a uniformly mixed mixture. The zirconia balls used for ball milling are 1 mm in diameter.

The ball-milled mixture with the solvent was dried at 100° C. or less in air using a hot plate to remove the solvent, and the dried mixture was made into pellets using a disc-shaped mold.

The prepared pellets were put into an alumina crucible, subjected to heat treatment at 900 ° C. for 10 hours in an air atmosphere of a box furnace, and then taken out of the furnace and rapidly quenched in the air.

[Comparative Example]

2 is a manufacturing process diagram of a composite oxide according to a comparative example.

In Comparative Example, a lithium excess layered oxide of a known Li1 _.2 Ni _0.2 Mn _0.6O2 composition, x = 0.5, M = Mn, Me = Ni, Mn in [Formula 1], through the manufacturing method of FIG. 2, 0.5 Li ₂ Mn0 ₃ +0.5LiNi _0.5 Mn _0.5 O ₂ was synthesized.

First, a 20L co-precipitation reactor was used to prepare the transition metal precursor. NH ₄ OH and NaOH were added to the reactor at a ratio of 15:1 by weight, and 2.5 L of distilled water was added thereto, followed by stirring for about 10 minutes while injecting air. Separated tanks 1 and 2 in the reactor were prepared as follows. In tank 1, NiSO ₄ ·6H ₂ O and MnSO ₄ ·H ₂ O were prepared at a ratio of 1:3 mol%, and about 10 L of distilled water was added and mixed while maintaining a temperature of 45 °C. In tank 2, NaOH and NH ₄ OH (24% aqueous solution) were prepared at a ratio of 3:1 by weight, and about 2.5 L of distilled water was added and mixed while maintaining at 10 ° C. Through a pump, tank 1 and tank 2 were injected in a metered amount into the reactor at a rate of 680 g/h and 432 g/h, respectively, and reacted. The final mixed solution was naturally dried using filter paper, and when the moisture content was less than 0.5%, the precipitate (coprecipitation) was filtered out. Through this, approximately sphere-like Ni _0.25 Mn _0.75 (OH) ₂ was prepared, and the average size of the transition metal precursor was 5 to 7 μm.

After preparing L _i2 CO ₃ (Junsei, purity of 99% or higher) as a lithium precursor as a precursor for the solid phase reaction, the spherical transition metal precursor, Ni _0.25 Mn _0.75 (OH) ₂ , was prepared in the following ratio.

4/7 Ni _0.25 Mn _0.75 (OH) ₂ + 3/7 Li ₂ CO ₃ (4:3 mol %)

The ball mill was performed with the total weight fixed at 1.6 g, where Li ₂ CO ₃ was 0.6102 g and Ni _0.25 Mn _0.75 (OH) ₂ was 0.9898 g.

The precursors prepared according to the weight were added to an acetone solvent (purity 99%.7%) and ball milled for about 5 hours and 20 minutes to reduce the particle size and prepare a uniformly mixed mixture. The zirconia balls used for ball milling are 1 mm in diameter.

The ball-milled mixture with the solvent was dried at 100° C. or lower in air using a hot plate to remove the solvent, and the dried mixture was made into approximately spherical pellets using a disc-shaped mold.

The prepared pellets were placed in an alumina crucible, subjected to heat treatment at 900 ° C. for 10 hours in an air atmosphere, and then taken out of the furnace and rapidly quenched in the air.

[Shape comparison analysis: SEM analysis]

The results of analyzing the transition metal precursors prepared in step 1 of Examples and Comparative Examples by SEM are shown in FIGS. 3 and 4, respectively.

As confirmed in FIG. 3 , it can be seen that in the transition metal precursor prepared according to the embodiment, plate-like primary particles form substantially spherical secondary particles. In contrast, as shown in FIG. 4 , in the transition metal precursor prepared according to Comparative Example, sphere-like primary particles form approximately spherical secondary particles.

The difference in the shape of the transition metal precursor affects the characteristics of the finally synthesized lithium-excessive layered composite active material.

[Composition analysis result: ICP analysis]

The composition of the composite active material prepared according to Examples and Comparative Examples was analyzed by ICP. Comparative Examples and Examples were synthesized by setting the target composition to Li _1.2 Ni _0.2 Mn _0.6 O ₂ , respectively.

However, as a result of ICP analysis, in the case of the comparative example, Li _1.200 Ni _0.209 Mn _0.6 O ₂ was obtained, and in the case of the example, Li _1.203 i _0.205 Mn _0.6 O ₂ was obtained. It became.

[Structure comparative analysis: XRD analysis]

Crystal structures of compositions prepared according to Examples and Comparative Examples were compared with Li _1.2 Ni _0.2 Mn _0.6 O ₂ , which is a known composition.

As confirmed in FIG. 5, the difference between the XRD analysis results of Examples and Comparative Examples is in the superlattice peak due to Li ₂ MnO ₃ appearing at 2θ of 20 to 23°. In particular, a large difference appears in the second peak ((110) peak). In general, if the order of stacking the lithium layer and the transition metal layer is arranged in a certain order without stacking faults, the first peak is strong. Both the intensity of the second peak ((110) peak) as well as the ((020) peak) are high.

That is, compared to the lithium-excess layered oxide synthesized according to the comparative example, the lithium-excess layered oxide synthesized according to the embodiment of the present invention has a long-range rule in which the lithium layer and the transition metal layer are regularly arranged (well-ordered) It can be seen that

In this way, when the lithium layer and the transition metal layer are arranged in a long-range order, when a large amount of lithium is desorbed from the cathode material, it is structurally more stable, especially in the oxygen plateau, More lithium can be reinserted.

Table 1 below shows a comparison of peak intensities and full width at half-maximum (FWHM) of the X-ray diffraction patterns of FIG. 5 .

I(20.y°)/I(18.x°) I(22.y°)/I(20.x°) FWHM (20.y°) FWHM (22.y°) comparative example 0.130 0.733 0.197 0.394 Example 0.108 0.793 0.157 0.157

In Table 1, I (20.y°) is the intensity of the maximum peak among the peaks representing the superlattice, and '20.y°' means that 2θ appears around 20°, and y is a value between 1 and 9.9. I(18.x°) is the intensity of the reference peak where 2θ appears around 18°, and '18.x°' means that 2θ appears around 18°, and x is a range between 1 and 9.9. is the value I(22.y°) is the intensity of the second peak among the peaks representing the superlattice. '22.y°' means that 2θ appears around 22°, and y is from 1 to It is a value between 9.9 and 9.9.

As confirmed in Table 1, the comparative examples and examples have a relatively high ratio of I(20.y°)/I(18.x°) of 0.10 or more in common. However, in the case of the ratio of I (22.y °) / I (20.x °), the Example is higher than the Comparative Example, and in the case of the Comparative Example, almost no (110) peak is confirmed. In other words, the intensity of the (110) peak of the composite oxide according to the embodiment of the present invention is relatively high.

[Results of evaluation of charge/discharge characteristics]

6 shows evaluation results of charge and discharge characteristics of Li _1.2 Ni _0.2 Mn _0.6 O ₂ prepared according to Examples and Comparative Examples.

In order to evaluate the electrochemical characteristics, an electrochemical test was performed by making an electrode with the cathode material Li _1.2 Ni _0.2 Mn _0.6 O ₂ prepared according to Examples and Comparative Examples.

The active materials of the electrode were 70% by weight of Li _1.2 Ni _0.2 Mn _0.6O2 , 25% by weight of super P corresponding to carbon powder, and 5% by weight of PVDF. They were put into a mortar and mixed for about 10 to 20 minutes, and NMP was added. After stirring for about 20 minutes, it was coated on aluminum foil and dried in a vacuum chamber for about 12 hours to prepare an electrode. Afterwards, the cathode material was pierced with a 13mm punch in a glove box under an argon atmosphere to manufacture a cathode of 1 ~ 2mg, and the cell was assembled using this anode. 1M LiPF6 in a 1:1 volume mixed solution of carbonate/diethylcarbonate, and the separator is Celgard 2400 polypropylene punched with a 19 mm punch.

The electrochemical test of the cell thus prepared was conducted at room temperature. A maccor series 4000 was used as the measuring equipment, and the cut-off voltage at the time of measurement was 2.5 ~ 4.7V, starting from charging, and the current was measured by applying a C/30 rate and a size of 280/30mA/g.

In FIG. 6, the red solid line represents the positive electrode material prepared according to the comparative example, and the blue solid line represents the electrochemical property test of the battery using the positive electrode material prepared according to the example, and all were conducted in the same manner at C/30 rate. Compared to the red solid line, it can be seen that the blue solid line has a significantly large difference in discharge capacity of about 30 mAh/g and an improved discharge voltage even though the same charging capacity (the amount of desorbed lithium is the same).

Looking at the dQ/dV graph of FIG. 6, which shows the degree of reaction at a specific voltage, the peak of the blue solid line compared to the red solid line at 3.4 to 3.5 V, which is generally known as the oxygen ion reaction in the discharge graph of the lithium excess layer structure, is It can be seen that it is much larger. The superstructure peak on the XRD of the lithium-excessive layered oxide appears when the Li-TM-TM (lithium-transition metal-transition metal) arrangement in the transition metal layer has a long range order. As a result, the intensity of the superlattice peak is greatly affected by the degree of long-range order of Li-TM-TM. In particular, the second peak (110 peak) is the intensity of the superlattice peak when the lithium layer and the transition metal layer are regularly arranged. will rise That is, the intensity of the (110) peak among the superlattice peaks of FIG. 5 may be significantly higher than that of the comparative example.

In conclusion, in the case of the lithium-excessive layered oxide according to the embodiment of the present invention, it can be said that the long-range order of Li/Mn/Mn in the transition metal layer is high. In this way, when the stack of the lithium layer and the transition metal layer are regularly arranged without defects, the stability of the oxidation/reduction reaction of oxygen is high, so even if the same amount of lithium is desorbed from the cathode material, a much larger amount of lithium can be inserted. know that it can.

Claims (6)

Having a composition containing an excess of lithium represented by the following [Formula 1],
It forms a layered structure in the crystal structure,
In X-ray diffraction analysis, I (20 ) / I (18) is 0.1 or more, and the peak intensity at 22.y ° (y = 1 to 9.9) for the peak intensity at 20.x ° (x = 1 to 9.9) The ratio I(22)/I(20) is 0.78 or more,
In the X-ray diffraction analysis, the full width at half-maximum (FWHM) of the first (020) peak, which is the maximum peak of the superlattice at 2θ of 20 ° to 22 °, is 0.13 ° to 0.18 ° And, the half width of the second (110) peak is 0.13 ° ~ 0.18 °, a cathode active material.
[Formula 1]
x(Li ₂ MO ₃ ) + (1-x)LiMeO ₂
(Where 0<x<1, M or Me is one of 3d, 4d, 5d transition metals or non-transition metals including Al, Mg, Mn, Ni, Co, Cr, V, Fe, Ir, and Mo above, and M and Me may be the same or different from each other) delete A positive electrode comprising a current collector and an active material layer formed on the current collector and containing the positive electrode active material according to claim 1 . The positive electrode according to claim 3;
A cathode disposed at a predetermined distance from the anode;
A lithium ion battery comprising an electrolyte interposed between the positive electrode and the negative electrode. Preparing a transition metal precursor composed of secondary particles forming a spherical shape by aggregating plate-shaped primary particles;
Preparing a mixture by mixing the transition metal precursor and the lithium precursor;
Putting the mixture into a heat treatment furnace and heat-treating it in an air atmosphere;
Including the step of rapidly cooling (quenching) the heat-treated material,
The material prepared through the above steps has a composition containing excess lithium represented by the following [Chemical Formula 1], forms a layered structure in crystal structure, and upon X-ray diffraction analysis, 18.y ° (y = 1 ~ 9.9), the ratio of the peak intensity appearing at 20.x° (x = 1 to 9.9), I(20)/I(18), is 0.1 or more, and 20.x° The ratio of the peak intensity appearing at 22.y ° (y = 1 ~ 9.9) to the peak intensity appearing at (x = 1 ~ 9.9), I(22) / I(20), is 0.78 or more ,
In the X-ray diffraction analysis, the full width at half-maximum (FWHM) of the first (020) peak, which is the maximum peak of the superlattice at 2θ of 20 ° to 22 °, is 0.13 ° to 0.18 ° And, the half width of the second (110) peak is 0.13 ° ~ 0.18 °, a method for producing a composite cathode active material.
[Formula 1]
x(Li ₂ MO ₃ ) + (1-x)LiMeO ₂
(Where 0<x<1, M or Me is one of 3d, 4d, 5d transition metals or non-transition metals including Al, Mg, Mn, Ni, Co, Cr, V, Fe, Ir, and Mo above, and M and Me may be the same or different from each other) delete

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