KR102296218B1 - A positive electrode active material for lithium secondary battery, method of preparing the positive electrode active material, and lithium secondary battery including the positive electrode active material - Google Patents

Abstract

The present invention relates to a positive electrode active material having improved high energy density and improved long-life characteristics, a method of preparing the same, and a lithium secondary battery including the same. The positive electrode active material includes a plurality of primary particles, at least one secondary particle including an aggregate of a plurality of primary particles, or a combination thereof. The primary particles have an α-NaFeO_2 type crystal structure and include a lithium transition metal oxide including at least one of Ni, Co, Mn and Al. A part of the transition metal site in the crystal lattice of the crystal structure is substituted with the doping element M. A part of oxygen element sites in the crystal lattice is replaced with sulfur (S) element. M includes Mg, Ti, Zr, W, Si, Ca, B, V, or a combination thereof. Among the lithium transition metal oxides, M is included at an amount of 1,000 to 4,000 ppm. Among the lithium transition metal oxides, S is included at an amount of 1,100 ppm or less.

Description

A positive electrode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery comprising the same

It relates to a cathode active material for a lithium secondary battery of a novel composition, a method for manufacturing the same, and a lithium secondary battery comprising the same.

Since lithium secondary batteries were commercialized by Sony in 1991, demand has been rapidly increasing in various fields from small home appliances such as mobile IT products to medium and large electric vehicles and energy storage systems. In particular, low-cost, high-energy cathode materials are essential for mid- to large-sized electric vehicles and energy storage systems. Cobalt, which is the main raw _{material for single-crystal LiCoO 2 (LCO), a commercially available cathode active material, is expensive.}

_{So, LiNi x} Co _y Mn _z O ₂ (NCM, x+y+z=1) and LiNi _x Co _y Al _z O in which a part of Co is substituted with other transition metals instead of LCO as a cathode active material for a medium or large-sized secondary battery. _{A Ni-based positive electrode active material represented by 2} (NCA, x+y+z=1) is used, and these NCM and NCA-based positive electrode active materials have the advantage of having a low price of nickel as a raw material and a high reversible capacity. In particular, NCM and NCA in which the molar ratio of Ni is 50 mol% or more in terms of high capacity is attracting attention. In general, such a Ni-based positive electrode active material is prepared by mixing a transition metal compound precursor synthesized by a co-precipitation method with a lithium source and then synthesizing it in a solid phase. However, the Ni-based cathode material synthesized in this way exists in the form of secondary particles in which small primary particles are agglomerated, and there is a problem that micro-cracks are generated inside the secondary particles during a long-term charge/discharge process. Microcracks cause a side reaction between the new interface of the positive electrode active material and the electrolyte, and as a result, deterioration of battery performance such as stability deterioration due to gas generation and deterioration of battery performance due to electrolyte depletion is induced. In addition, it is necessary to increase the electrode density (>3.3 g/cc) to realize high energy density, which causes the collapse of secondary particles and depletion of the electrolyte due to side reactions with the electrolyte, leading to a sharp decline in the initial lifespan. After all, it means that the Ni-based positive electrode active material in the form of secondary particles synthesized by the conventional co-precipitation method cannot realize high energy density.

In order to solve the problems of the above-mentioned secondary particle type Ni-based positive electrode active material, research on single-particle type Ni-based positive electrode active material has been recently made. Single-crystal Ni-based positive electrode active material can realize excellent electrochemical performance because particle disintegration does not occur when electrode density is increased (> 3.3 g/cc) to realize high energy density. However, such a single-crystal Ni-based positive electrode active material has a problem that battery stability is deteriorated due to structural and/or thermal instability due to ^{unstable Ni 3+} and Ni ^{4+ ions during electrochemical evaluation.} Therefore, for the development of a high-energy lithium secondary battery, there is still a need for a technique for stabilizing the unstable Ni ions of the single-crystal Ni-based positive electrode active material.

According to one aspect, there is no breakage at high electrode density, and at the same time, it is to provide a positive electrode active material with improved high energy density and long life characteristics.

According to one aspect, it comprises a plurality of primary particles, an aggregate of a plurality of primary particles, or a combination thereof,

The primary particle has _{a crystal structure of α-NaFeO 2} type, includes a lithium transition metal oxide containing Ni and a doping element (M), and a part of the oxygen element site in the crystal lattice of the crystal structure is sulfur (S) replaced by an element,

M includes Mg, Zr, W, Sr, Y, La, Mo, Ba, Si, Ca, B, V, or a combination thereof,

Among the lithium transition metal oxide, the M is included in an amount of 4,000 ppm to 7,000 ppm,

In the lithium transition metal oxide, the S is included in an amount of 1,100 ppm or less, a positive electrode active material is provided.

According to another aspect, there is provided a method comprising: mixing a Li element-containing compound, a Ni-containing transition metal compound, a sulfur (S) element-containing compound, and an M element-containing compound to obtain a lithium transition metal oxide precursor;

A method of producing a positive electrode active material comprising; obtaining the above-described positive electrode active material including a plurality of primary particles, at least one secondary particle including an aggregate of a plurality of primary particles, or a combination thereof by heat-treating the precursor Offered:

According to another aspect, a positive electrode including the positive electrode active material is provided.

According to another aspect, the positive electrode; cathode; And a lithium secondary battery comprising an electrolyte is provided.

The positive electrode active material comprising a lithium transition metal oxide provided according to an aspect of the present invention includes single crystals and single particles, aggregates of such single particles, or a combination thereof, and includes Ni, and Mg, Zr, W, Sr, Y , La, Mo, Ba, Si, Ca, B, V, or a doping element (M) containing a combination thereof, and a part of oxygen is substituted with S, wherein M is included in 4,000 ppm to 7,000 ppm and, by including the S at 1,100 ppm or less, unstable Ni ions present in the high-Ni-based lithium transition metal oxide are stabilized, and deterioration is prevented between charging and discharging, thereby increasing capacity per volume and improving lifespan stability.

1 is an SEM photograph of the lithium transition metal oxides of Examples 1 to 3 and Comparative Examples 1 to 7;
2 is a graph showing capacity retention rates according to cycles for Examples 6 to 8 and Comparative Examples 10 to 15;
3 is a graph showing the capacity retention rate according to the cycle for Example 9 and Comparative Example 17.
4 is a graph of capacity retention according to cycles for Example 10 and Comparative Example 18;
5 is a schematic diagram of a lithium battery according to an exemplary embodiment.
<Explanation of symbols for main parts of the drawing>
1: Lithium battery 2: Anode
3: positive electrode 4: separator
5: Battery case 6: Cap assembly

The present inventive concept described below can apply various transformations and can have various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present inventive concept to a specific embodiment, and it should be understood to include all transformations, equivalents, or substitutes included in the technical scope of the present inventive concept.

Terms used below are only used to describe specific embodiments, and are not intended to limit the present inventive concept. The singular expression includes the plural expression unless the context clearly dictates otherwise. Hereinafter, terms such as “comprises” or “have” are intended to indicate that a feature, number, step, action, component, part, component, material, or combination thereof described in the specification is present, but one or the It should be understood that the above does not preclude the possibility of the presence or addition of other features, numbers, steps, operations, components, parts, components, materials, or combinations thereof. "/" used below may be interpreted as "and" or "or" depending on the situation.

In order to clearly express the various layers and regions in the drawings, the thickness is enlarged or reduced. Throughout the specification, like reference numerals are assigned to similar parts. Throughout the specification, when a part, such as a layer, film, region, plate, etc., is referred to as “on” or “on” another part, this includes not only the case where it is directly on the other part, but also the case where there is another part in the middle. . Throughout the specification, terms such as first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

Hereinafter, a lithium secondary battery including a positive electrode active material, a manufacturing method thereof, and a positive electrode including the same according to exemplary embodiments will be described in more detail.

The positive electrode active material according to an embodiment includes a plurality of primary particles, an aggregate of a plurality of primary particles, or a combination thereof, wherein the primary particles have an α-NaFeO ₂ type crystal structure, Ni and a doping element (M ), including a lithium transition metal oxide containing , Ba, Si, Ca, B, V, or a combination thereof, wherein the M in the lithium transition metal oxide is included in an amount of 4,000 ppm to 7,000 ppm, and the S in the lithium transition metal oxide is 1,100 ppm or less. may be included.

The positive electrode active material according to an exemplary embodiment may include the doping element (M) in the lithium transition metal oxide, but may contain a very small amount of the Mg element.

Herein, the term “agglomerate of primary particles” means that the surfaces of one or more primary particles are arranged so that they are in contact with each other during the heat treatment of the primary particles. In addition, the term "agglomerate of primary particles" means that when a coating layer is present on the surface of the primary particles, the surfaces of a plurality of individually coated primary particles are arranged to contact each other.

In the positive electrode active material according to an embodiment of the present invention, a part of the transition metal is substituted with a doping element M, and a part of O is substituted with S, wherein M is included at 4,000 ppm to 7,000 ppm, and S is 1,100 By being contained in ppm or less, crystal stability is improved and it has a long lifespan characteristic. When the S exceeds 1,100 ppm, the initial discharge capacity is lowered, and when the total amount of the doping element does not satisfy the above range, life characteristics are deteriorated. Accordingly, when the doping element content ratio and the S element content ratio are satisfied, a long lifespan characteristic can be achieved.

According to one embodiment, the lithium transition metal oxide may include Ni, and 80 mol% or more of nickel in the lithium transition metal oxide may be included.

For example, nickel in the lithium transition metal oxide is 81 mol% or more, 82 mol% or more, 83 mol% or more, 84 mol% or more, 85 mol% or more, 86 mol% or more, 87 mol% or more, 88 mol% or more, 89 mol% or more, or 90 mol% or more.

According to one embodiment, the M in the lithium transition metal oxide may be included in an amount of 4,200 ppm to 7,000 ppm. For example, M may be included in an amount of 4,200 ppm to 6,800 ppm.

According to one embodiment, the lithium transition metal oxide may include W, and the W may be included in an amount of 1,500 ppm to 3,000 ppm.

According to one embodiment, the lithium transition metal oxide may include Y, and the Y may be included in an amount of 1,000 ppm to 4,000 ppm in the lithium transition metal oxide.

According to an embodiment, the doping element may include W, Sr, Y, La, Mo, Ba, Si, Ca, V, or a combination thereof. For example, the doping elements may be Mg, W and Y. For example, the doping elements may be W and Y. For example, the doping elements may include W and Y, and Mg may further include less than W.

According to one embodiment, some of the lithium element sites in the crystal lattice of the lithium transition metal oxide may be substituted with one or more alkali metal elements other than lithium.

For example, the alkali metal element may include Na, K, or a combination thereof.

According to one embodiment, the alkali metal element in the lithium transition metal oxide may be included in an amount of 100 ppm to 250 ppm. For example, the alkali metal element may be included in an amount of 120 ppm to 230 ppm, 130 ppm to 220 ppm, or 140 ppm to 210 ppm.

According to one embodiment, the lithium transition metal oxide may have a molar ratio of Li/molar ratio of transition metal less than 1. This is distinguished from the perlithium-based positive electrode active material in which Li has a molar ratio greater than 1, and although the molar ratio of Li is less than 1, Ni ( III) Not only can the deterioration of the active material due to the side reaction of ions be prevented, but also crystal collapse is prevented even when lithium is desorbed during charging, so that it has high capacity and long life.

According to one embodiment, the lithium transition metal oxide may be represented by the following Chemical Formula 1:

<Formula 1>

Li _1-x A _x M1 _1-y M2 _y O _2-z S _z

In Formula 1,

A is sodium (Na) or potassium (K),

M1 includes Ni, Co, Mn, Al or a combination thereof,

M2 comprises Mg, Zr, W, Sr, Y, La, Mo, Ba, Si, Ca, B, V, or a combination thereof,

0<x≤0.05, 0<y<0.1, 0<z<0.01.

For example, A may be Na. For example, y may be 0<y≤0.05, 0<y≤0.04, 0<y≤0.03, 0<y≤0.02, or 0<y≤0.01.

According to one embodiment, the lithium transition metal oxide may be represented by the following Chemical Formula 2:

<Formula 2>

Li _1-x A _x M1 _1-α-β W _α Y _β O _2-z S _z

In Formula 2,

A is sodium (Na) or potassium (K),

M1 includes Ni, Co, Mn, Al or a combination thereof,

0<x≤0.05, 0<α≤0.002, 0<β≤0.004, 0<z<0.01.

As W is included as 0<α≤0.002, the structural stability of the lithium transition metal oxide is improved. When the substitution molar ratio of W exceeds 0.002, structural stability may be deteriorated due to distortion of the crystal structure, and WO ₃ may be formed as an impurity, resulting in deterioration of electrochemical properties.

As the Y is included as 0<β≤0.004, the structural stability of the lithium transition metal oxide is improved. In particular, when the substitution molar ratio of Y exceeds 0.004, structural stability may be deteriorated due to distortion of the crystal structure, and capacity may be reduced due to the formation of an irreversible crystalline phase during operation.

According to one embodiment, the lithium transition metal oxide represented by Chemical Formula 2 may further contain Mg as an impurity element in a trace amount in some cases.

In this case, Chemical Formula 2 may be represented by the following Chemical Formula 2-1:

<Formula 2-1>

Li _1-x A _x M1 _1-α-β W _α Y _β Mg _γ O _2-z S _z

For details on each of A, M1, x, z, α and β in Formula 2-1, refer to the description of the present specification, and γ is 0≤γ≤0.0005, for example, 0≤γ≤0.0004, 0≤ γ≤0.0003, 0≤γ≤0.0002, or 0≤γ≤0.0001.

According to one embodiment, A in Formula 2 may be Na. When Na is substituted in the lattice space where Li is located, the expansion of the crystal structure due to the repulsive force between oxygen atoms in the lithium transition metal oxide is suppressed when lithium is desorbed from the charged state by the intervention of Na, which has a larger ionic radius than that of lithium, As a result, structural stability of the lithium transition metal oxide is achieved even during repeated charging. In addition, high-efficiency charge/discharge characteristics may be improved by reducing lithium migration resistance due to an increase in interstitial spacing caused by Na intervention.

According to one embodiment, in Formula 2, β /α≥1. When the molar ratio of Y and W satisfies β /α≥1, a uniform and dense crystal structure can be formed by increasing the transition metal ion diffusion rate during crystal formation, thereby improving structural crystallinity, and as a result, repeatable Crystal collapse is remarkably suppressed even during phosphorus charging and discharging, and lifespan characteristics are improved.

According to one embodiment, the molar ratio of W and Y in Formula 2 may satisfy 1≤β /α≤5. As W and Y are doped in such a ratio, charge balance in the transition metal may be achieved, and crystal structure stability may be improved, thereby improving the long life characteristics of the secondary battery.

According to one embodiment, in Formula 2, z may be 0<z≤0.01. Here, z denotes a molar ratio of substitution of S to element O in the lithium transition metal oxide represented by the formula (2).

As a part of the oxygen element is substituted with S, the bonding strength with the transition metal increases, so that the crystal structure transition of the lithium transition metal oxide is suppressed, and as a result, the structural stability of the lithium transition metal oxide is improved.

On the other hand, when the substitution molar ratio of S exceeds 0.01, the crystal structure becomes unstable due to the repulsive force of the S anion, and thus the lifespan characteristics are deteriorated. .

According to one embodiment, the lithium transition metal oxide may be represented by the following Chemical Formulas 3 to 5:

<Formula 3>

Li _1-x1 Na _x1 Ni _{1-a1- b1-} α1-β1 Co _a1 Al b1 W _α1 Y _β1 O _2-z1 S _z1

<Formula 4>

Li _1-x2 Na _x2 Ni _{1-a2-b2- α2-β2} Co _a2 Mn _b2 W _α2 Y _β2 O _2-z2 S _z2

<Formula 5>

Li _1-x3 Na _x3 Ni _{1-a3-b3-c3-α3-β3} Co _a3 Mn _b3 Al _c3 W _α3 Y _β3 O _2-z3 S _z3

In Formulas 3 to 5,

0<x1≤0.001, 0<a1<0.1, 0<b1<0.05, 0<α1≤0.002, 0<β1≤0.004, 0<z1<0.01,

0<x2≤0.001, 0<a2<0.1, 0<b2<0.05, 0<α2≤0.002, 0<β2≤0.004, 0<z2<0.01,

0<x3≤0.001, 0<a3<0.1, 0<b3<0.05, 0<c3<0.05, 0<α3≤0.002, 0<β3≤0.004, 0<z3<0.01.

In addition, the lithium transition metal oxide represented by Chemical Formulas 3 to 5 may include a trace amount of Mg as an impurity. For example, Mg may be included in an amount that does not substantially affect the composition ratio of the lithium transition metal oxide represented by Chemical Formulas 3 to 5, for example, 0.05% or less or 0.01% or less by molar ratio. The content of these impurities is an amount that does not substantially affect the crystal structure and lifespan characteristics of the lithium transition metal oxide according to an embodiment of the present invention.

When the Na, W, Y, and S are substituted for the lithium transition metal oxide in the above molar ratio, structural expansion of the crystal due to the electrostatic repulsive force between oxygens in the lithium transition metal oxide is suppressed even during lithium desorption in the charged state. , the structural stability is improved, and the lifespan characteristics are improved.

According to one embodiment, when the molar ratio of W and Y satisfies the above range, structural stability of the lithium transition metal oxide is ensured, and when it is out of the above range, an impurity phase is formed, which not only acts as a resistance during lithium desorption, but also , it may cause the collapse of the crystal structure upon repeated charging.

According to one embodiment, the lithium transition metal oxide may be a single particle. A single particle is a concept distinct from secondary particles formed by aggregating a plurality of particles or particles formed by aggregating a plurality of particles and coating the periphery of the aggregate. Since the lithium transition metal oxide has the form of single particles, it is possible to prevent the particles from breaking even at a high electrode density. Accordingly, it is possible to realize a high energy density of the positive electrode active material including the lithium transition metal oxide. In addition, compared to secondary particles in which a plurality of single particles are aggregated, breakage is suppressed during rolling, so that high energy density can be realized, and deterioration of lifespan due to breakage of particles can be prevented.

According to one embodiment, the lithium transition metal oxide may have a single crystal. A single crystal has a concept distinct from a single particle. A single particle refers to a particle formed of one particle regardless of the type and number of crystals therein, and a single crystal means having only one crystal in the particle. This single-crystal lithium transition metal oxide has very high structural stability, and is easier to conduct lithium ions compared to polycrystals, and thus has superior fast charging characteristics compared to polycrystals of active materials.

According to one embodiment, the positive electrode active material is a single crystal and a single particle. By forming a single crystal and single particles, it is possible to realize a structurally stable and high-density electrode, so that a lithium secondary battery including the same can have improved lifespan characteristics and high energy density at the same time.

The lithium transition metal oxide satisfying the above composition may stabilize unstable Ni ions therein, and may have high energy density and long life stability.

In the case of a positive electrode active material containing a general high-nickel lithium nickel cobalt manganese oxide, stabilization of unstable Ni ions is essential. By introducing W and Y into some of the transition metal sites in the crystal, the positive electrode active material can achieve overall charge balance. to inhibit oxidation from Ni(II) ions to unstable Ni(III) or Ni(IV) ions, and unstable Ni(III) or Ni(IV) can be reduced to Ni(II). In addition, by introducing the Y element instead of Ti, which is known as an element that provides structural stability of the crystal of the positive electrode active material, diffusion of the raw material transition metal element is accelerated during the formation of the crystal of the positive electrode active material, so that uniform crystal formation is possible, and A coating layer containing a very small amount of lithium yttrium oxide is additionally formed to prevent deterioration of lifespan due to suppression of side reactions between the positive electrode active material and the electrolyte. In addition, the loss of conductivity due to substituting a part of the transition metal with different elements W and Y was compensated for by substituting a part of O with S, and by substituting a part of Li with Na, the structural deformation during charging and discharging was reduced. By suppressing the decrease in the conductivity of Li, a positive electrode active material having a high capacity and a long lifespan, which is structurally stable in a single crystal, was obtained.

According to one embodiment, the average particle diameter (D ₅₀ ) of the lithium transition metal oxide may be 0.1㎛ to 20㎛. For example, the average particle diameter (D ₅₀ ) is 0.1 μm to 15 μm, 0.1 μm to 10 μm, 1 μm to 20 μm, 5 μm to 20 μm, 1 μm to 15 μm, 1 μm to 10 μm, 5 μm to 15 μm, or 5 μm to 10 μm. When the average particle diameter of the lithium transition metal oxide falls within the above range, a desired energy density per volume may be realized. When the average particle diameter of the lithium transition metal oxide exceeds 20 μm, a rapid decrease in charge/discharge capacity occurs, and when it is 0.1 μm or less, it is difficult to obtain a desired energy density per volume.

Aha, a method of manufacturing a cathode active material according to an aspect will be described in detail.

The method for preparing a cathode active material according to an embodiment includes mixing a Li element-containing compound, a Ni-containing transition metal compound, a sulfur (S) element-containing compound, and an M element-containing compound to obtain a lithium transition metal oxide precursor. ;

A step of heat-treating the precursor to obtain a positive electrode active material including a plurality of primary particles, at least one secondary particle including an aggregate of a plurality of primary particles, or a combination thereof, wherein the primary particles are α-NaFeO ₂ crystals It has a structure and contains a lithium transition metal compound containing Ni and a doping element (M), wherein a part of the oxygen element site in the crystal lattice of the crystal structure is substituted with a sulfur (S) element,

M includes Mg, Zr, W, Sr, Y, La, Mo, Ba, Si, Ca, B, V, or a combination thereof,

Among the lithium transition metal compound, the M is included in an amount of 4,000 ppm to 7,000 ppm,

In the lithium transition metal compound, the S content of 1,100 ppm or less is provided, a method for producing a positive electrode active material is provided.

In general, for single particle material synthesis, transition metal precursor/lithium precursor is dry mixed and ^{synthesized through heat treatment at high temperature (>1,000 o} C), but highly reversible due to structural change in the cathode active material due to the reduction of nickel ions during high temperature firing It is difficult to realize capacity, and excessive residual lithium exists on the surface of the active material, causing stability problems.

On the other hand, the present inventors induced crystal growth at a low temperature of less than ^{1,000 o} C after mixing a crystal growth aid together with a synthetic raw material for synthesizing a single-particulate material capable of realizing a high reversible capacity. In this case, the crystal growth aid has a melting point that can be melted at the sintering temperature of the positive electrode active material. Such a synthesis method has a lower heat treatment temperature compared to a dry-type high-temperature heat treatment of a transition metal precursor/lithium precursor, so the structural change of the positive electrode active material is small, so high reversible capacity can be realized, and it is possible to synthesize a material with less surface residual lithium.

In addition, since the crystal growth aid is melted at the sintering temperature of the cathode active material to promote uniform mixing and crystal growth of synthetic raw materials, it is possible to shorten the overall process time, thereby reducing manufacturing costs.

According to one embodiment, the crystal growth aid may include an alkali metal salt containing element S, for example, a lithium salt. When the crystal growth aid includes the element S, the element S permeates into the cathode active material crystal during sintering, so that the element S may be substituted in some of the oxygen lattice positions in the crystal. At this time, the S element is preferably substituted at 1,100 ppm or less relative to the total positive electrode active material, and when it exceeds 1,100 ppm, the capacity is reduced. This is thought to be because the excess element S acts as a resistance layer that prevents movement of lithium ions during charging and discharging of the lithium secondary battery.

The mixing step includes mechanically mixing the specific element-containing compounds. The mechanical mixing is carried out dry. The mechanical mixing is to apply a mechanical force to pulverize and mix materials to be mixed to form a uniform mixture. Mechanical mixing is, for example, a mixing device such as a ball mill using chemically inert beads, a planetary mill, a stirred ball mill, a vibrating mill, and the like. can be performed using At this time, in order to maximize the mixing effect, alcohol such as ethanol and higher fatty acids such as stearic acid may be selectively added in small amounts.

The mechanical mixing is performed in an oxidizing atmosphere, which prevents reduction of the transition metal in a transition metal source (eg, a Ni compound) to implement structural stability of the active material.

The lithium element-containing compound may include, but is not limited to, lithium hydroxide, oxide, nitride, carbonate, or a combination thereof. For example, the lithium precursor may be LiOH or Li ₂ CO ₃ .

The transition metal compound may include, but is not limited to, hydroxide, oxide, nitride, carbonate, or a combination thereof of a transition metal including Ni. For example, it may be Ni _0.91 Co _0.08 Al _0.01 (OH) ₂ , Ni _0.94 Co _0.05 Mn _0.01 (OH) ₂ , Ni _0.91 Co _0.08 Mn _0.005 Al _0.005 (OH) _{2 ,} and the like.

The sulfur (S) element-containing compound may be, for example, lithium sulfate as a crystal growth aid. For example, it may be _{Li 2} SO _{4 .} The crystal growth aid contributes to the formation of single crystals and single particles, and if it is not included, a cathode active material in the form of secondary particles is synthesized. The formed agglomerates may be formed.

The M element-containing compound is a hydroxide, oxide, nitride, carbonate, or oxide of an element comprising Mg, Zr, W, Sr, Y, La, Mo, Ba, Si, Ca, B, V, or a combination thereof, or combinations thereof, for example, W(OH) ₆ , WO ₃ , Mg(OH) ₂ , MgCO ₃ , Y ₂ O ₃ , Y(OH) _{3 ,} and the like.

According to an embodiment, the Li element-containing compound may include hydroxide, oxide, nitride, carbonate, or a combination thereof of lithium, and the S element-containing compound may include lithium sulfate. For example, the Li-element-containing compound may include hydroxide of lithium, and the S element-containing compound may include lithium sulfur oxide. Accordingly, the element S may be substituted for the oxygen position in the crystal during the heat treatment process.

According to an embodiment, the Li-containing compound and the S-element-containing compound may be mixed in a molar ratio of 99:1 to 99.9:0.1.

When the ratio of the Li-containing compound and the S-element-containing compound exceeds 99:1, for example, when it becomes 98:2, a decrease in the initial discharge capacity due to a resistance increase due to the introduction of an excess S element Occurs.

In addition, the lithium transition metal oxide precursor may further include a Na element-containing compound.

The Na element-containing compound may include, but is not limited to, a hydroxide, oxide, nitride, carbonate, or combination thereof of Na. For example, it _{may be NaOH, Na 2} CO _{3 ,} or a combination thereof.

After the mixing step, the step of heat treatment may be included. The heat treatment step may include a first heat treatment step and a second heat treatment step. The first heat treatment step and the second heat treatment step may be continuously performed or may have a rest period after the first heat treatment step. Also, the first heat treatment step and the second heat treatment step may be performed in the same chamber or in different chambers.

The heat treatment temperature in the first heat treatment step may be higher than the heat treatment temperature in the second heat treatment step.

The first heat treatment step may be performed at a heat treatment temperature of 800 °C to 1200 °C. The heat treatment temperature may be, for example, 850 °C to 1200 °C, 860 °C to 1200 °C, 870 °C to 1200 °C, 880 °C to 1200 °C, 890 °C to 1200 °C, or 900 °C to 1200 °C, but limited thereto , and includes all ranges constructed by selecting any two points within the range.

The second heat treatment step may be performed at a heat treatment temperature of 700 °C to 800 °C. The heat treatment temperature is 710 °C to 800 °C, 720 °C to 800 °C, 730 °C to 800 °C, 740 °C to 800 °C, 750 °C to 800 °C, 700 °C to 780 °C, 700 °C to 760 °C, 700 °C to 750 °C It may be ℃, or 700 ℃ to 730 ℃, but is not limited thereto, and includes all ranges configured by selecting any two points within the above range.

According to one embodiment, the heat treatment time in the first heat treatment step may be shorter than the heat treatment time in the second heat treatment step.

For example, the heat treatment time in the first heat treatment step may be 3 hours to 5 hours, 4 hours to 5 hours, or 3 hours to 4 hours, but is not limited thereto, and any two points within the range are selected. to include all of the configured ranges.

For example, the heat treatment time in the second heat treatment step may be 10 hours to 20 hours, 10 hours to 15 hours, but is not limited thereto, and includes all ranges configured by selecting any two points within the range. .

The first heat treatment step may include heat treatment at a heat treatment temperature of 800° C. to 1200° C. for 3 to 5 hours.

The second heat treatment step may include heat treatment at a heat treatment temperature of 700° C. to 800° C. for 10 to 20 hours.

In the first heat treatment step, the lithium transition metal oxide forms a layered positive electrode active material and at the same time induces particle growth, so that a single crystal shape can be achieved. In the first heat treatment step, each of the primary particles in the lithium transition metal oxide in the form of secondary particles grows rapidly and cannot withstand the inter-particle stress, so the inside of the primary particles is exposed and fused to each other, so that the single-crystal positive electrode active material for secondary batteries is produced is thought to be formed. The second heat treatment step increases the crystallinity of the layered structure generated in the first heat treatment step by performing the heat treatment for a long time at a lower temperature than in the first heat treatment step. A single-phase, single-crystal, and single-particle high-nickel-based positive electrode active material may be obtained through the first and second heat treatment steps.

According to one embodiment, the lithium transition metal oxide prepared by the manufacturing method may be a single crystal or a single particle, and the single crystal may have a layered structure. In addition, the average particle diameter of the lithium transition metal oxide may be 0.1㎛ to 20㎛.

In addition, for the content related to the content of the lithium transition metal oxide, refer to the above bar.

In addition, in the lithium transition metal oxide prepared by the method for preparing the cathode active material, W and Y elements are substituted for the positions of transition metal elements in the structure, S elements are substituted for O positions, and Na elements are substituted for Li positions. By substitution, ^{not only the oxidation of Ni 2+} is suppressed, but also reduction of the existing unstable Ni ³⁺ ions to Ni ²⁺ ions is induced, thereby obtaining structural stability and high density lithium transition metal oxide. In addition, since the reduced Ni ²⁺ ions and Li ⁺ ions have similar ionic radii, Li/Ni disordering is promoted, and Ni ions fill the vacant lattice during Li detachment, thereby achieving structural stability of the crystal.

According to another aspect, a positive electrode including the above-described positive electrode active material is provided.

According to another aspect, the positive electrode; cathode; and an electrolyte; a lithium secondary battery comprising a.

The lithium secondary battery has a capacity retention rate of 88% or more after being charged and discharged 50 times by including the above-described positive electrode active material including the lithium transition metal oxide.

The lithium secondary battery has an initial discharge capacity of 204 mAh/g or more.

The positive electrode and the lithium secondary battery including the same may be manufactured by the following method.

First, an anode is prepared.

For example, a positive electrode active material composition in which the above-described positive electrode active material, conductive material, binder and solvent are mixed is prepared. The positive electrode active material composition is directly coated on a metal current collector to manufacture a positive electrode plate. Alternatively, the positive electrode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to manufacture a positive electrode plate. The positive electrode is not limited to the above-listed shapes and may be in a shape other than the above-mentioned shapes.

Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black; conductive tubes such as carbon nanotubes; conductive whiskers such as fluorocarbon, zinc oxide, and potassium titanate; conductive metal oxides such as titanium oxide; and the like may be used, but are not limited thereto, and any material that can be used as a conductive material in the art may be used.

Examples of the binder include vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polytetrafluoroethylene, mixtures thereof, metal salts, or styrene butadiene. A rubber-based polymer or the like may be used, but it is not limited thereto, and any binder that can be used as a binder in the art may be used. As another example of the binder, lithium salt, sodium salt, calcium salt or Na salt of the above-mentioned polymer may be used.

As the solvent, N-methylpyrrolidone, acetone, or water may be used, but the solvent is not limited thereto and any solvent that can be used in the art may be used.

The content of the positive electrode active material, the conductive material, the binder, and the solvent is a level commonly used in a lithium battery. At least one of the conductive material, the binder, and the solvent may be omitted depending on the use and configuration of the lithium battery.

Next, the cathode is prepared.

For example, the negative electrode active material composition is prepared by mixing the negative electrode active material, the conductive material, the binder, and the solvent. The negative electrode active material composition is directly coated and dried on a metal current collector having a thickness of 3 μm to 500 μm to prepare a negative electrode plate. Alternatively, the negative electrode active material composition may be cast on a separate support, and then the film peeled from the support may be laminated on a metal current collector to manufacture a negative electrode plate.

The anode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, copper, nickel, or a copper surface treated with carbon may be used.

The negative active material may be any material that can be used as an anode active material for a lithium battery in the art. For example, it may include one or more selected from the group consisting of lithium metal, a metal alloyable with lithium, a transition metal oxide, a non-transition metal oxide, and a carbon-based material.

For example, the metal alloyable with lithium is Si, Sn, Al, Ge, Pb, Bi, Sb Si-Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a transition metal, a rare earth) an element or a combination element thereof, not Si), Sn-Y alloy (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, or a combination element thereof, and not Sn ) and so on. The element Y includes Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, or Te.

For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, or the like.

For example, the non-transition metal oxide may be SnO ₂ , SiO _x (0<x<2), or the like.

The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be amorphous, plate-like, flake-like, spherical or fibrous graphite, such as natural graphite or artificial graphite, and the amorphous carbon is soft carbon (low-temperature calcined carbon) or hard carbon (hard carbon). carbon), mesophase pitch carbide, calcined coke, and the like.

In the negative electrode active material composition, the same conductive material, binder and solvent may be used as in the positive electrode active material composition.

The content of the negative electrode active material, the conductive material, the binder, and the solvent is a level commonly used in a lithium battery. At least one of the conductive material, the binder, and the solvent may be omitted depending on the use and configuration of the lithium battery.

Next, a separator to be inserted between the positive electrode and the negative electrode is prepared.

Any of the separators may be used as long as they are commonly used in lithium batteries. Those having low resistance to ion movement of the electrolyte and excellent in the electrolyte moisture content may be used. The separator may be a single film or a multilayer film, for example, selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), or a combination thereof. , may be in the form of a nonwoven fabric or a woven fabric. Also, a mixed multilayer film such as a polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, a polypropylene/polyethylene/polypropylene three-layer separator and the like can be used. For example, a separator that can be wound up such as polyethylene or polypropylene is used for a lithium ion battery, and a separator having an excellent organic electrolyte impregnation ability may be used for a lithium ion polymer battery. For example, the separator may be manufactured according to the following method.

A separator composition is prepared by mixing a polymer resin, a filler, and a solvent. The separator composition may be directly coated on the electrode and dried to form a separator. Alternatively, after the separator composition is cast and dried on a support, a separator film peeled from the support is laminated on an electrode to form a separator.

The polymer resin used for manufacturing the separator is not particularly limited, and all materials used for the bonding material of the electrode plate may be used. For example, vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, or mixtures thereof may be used.

Next, the electrolyte is prepared.

For example, the electrolyte may be an organic electrolyte. In addition, the electrolyte may be a solid. For example, it may be boron oxide, lithium oxynitride, etc., but is not limited thereto, and any solid electrolyte that can be used as a solid electrolyte in the art may be used. The solid electrolyte may be formed on the negative electrode by a method such as sputtering.

For example, the organic electrolyte may be prepared by dissolving a lithium salt in an organic solvent.

The organic solvent may be used as long as it can be used as an organic solvent in the art. For example, Cyclic carbonates, such as a propylene carbonate, ethylene carbonate, a fluoroethylene carbonate, a butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, and dibutyl carbonate; esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, and 2-methyltetrahydrofuran; nitriles such as acetonitrile; and amides such as dimethylformamide. These can be used individually or in combination of two or more. For example, a solvent in which a cyclic carbonate and a chain carbonate are mixed can be used.

In addition, a gel polymer electrolyte obtained by impregnating an electrolyte solution in a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, LiI, Li ₃ N, Li _x Ge _y P _z S _α , Li _x Ge _y P _z S _α X _δ ( Inorganic solid electrolytes, such as X=F, Cl, Br), can be used.

The lithium salt may also be used as long as it can be used as a lithium salt in the art. For example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (where x and y are natural numbers), LiCl, LiI, or a mixture thereof.

As shown in FIG. 5 , the lithium battery 1 includes a positive electrode 3 , a negative electrode 2 , and a separator 4 . The positive electrode 3 , the negative electrode 2 and the separator 4 described above are wound or folded and accommodated in the battery case 5 . Then, an organic electrolyte is injected into the battery case 5 and sealed with a cap assembly 6 to complete the lithium battery 1 . The battery case 5 may have a cylindrical shape, a square shape, a pouch shape, a coin shape, or a thin film shape. For example, the lithium battery 1 may be a thin film battery. The lithium battery 1 may be a lithium ion battery.

A separator may be disposed between the positive electrode and the negative electrode to form a battery structure. After the battery structure is laminated in a bi-cell structure, impregnated with an organic electrolyte, and the obtained result is accommodated and sealed in a pouch, a lithium ion polymer battery is completed.

In addition, a plurality of the battery structure is stacked to form a battery pack, and the battery pack may be used in any device requiring high capacity and high output. For example, it can be used in a laptop, a smartphone, an electric vehicle, and the like.

In addition, since the lithium battery has excellent lifespan characteristics and high rate characteristics, it can be used in an electric vehicle (EV). For example, it may be used in a hybrid vehicle such as a plug-in hybrid electric vehicle (PHEV). In addition, it can be used in fields requiring a large amount of power storage. For example, it can be used in electric bicycles, power tools, systems for power storage, and the like.

The present invention will be described in more detail through the following Preparation Examples, Examples and Comparative Examples. However, the examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

(Manufacture of positive electrode active material)

Example 1

150 g of Ni _0.91 Co _0.08 Al _0.01 (OH) ₂ and 70 g of LiOH·H ₂ O, 0.75 g of (NH ₄ ) ₂ S, 0.05 g of NaOH, 0.75 g of WO ₃ , 0.37 _{g of Y 2} O ₃ Mix mechanically for about 15 minutes. Lithium transition metal oxide having the composition shown in Table 1 below was synthesized by calcining the mixed powder at 960 ^o C for 4 hours and 700 ^{o C for 10 hours.}

Example 2

150 g of Ni _0.91 Co _0.08 Al _0.01 (OH) ₂ and 70 g of LiOH·H ₂ O, 0.75 g of (NH ₄ ) ₂ S, 0.05 g of NaOH, 0.75 g of WO ₃ , 0.8 g of Y ₂ O ₃ Mix mechanically for about 15 minutes. Lithium transition metal oxide having the composition shown in Table 1 below was synthesized by calcining the mixed powder at 960 ^o C for 4 hours and 700 ^{o C for 10 hours.}

Example 3

150 g Ni _0.91 Co _0.08 Al _0.01 (OH) ₂ and 70 g LiOH·H ₂ O, 0.75 g (NH ₄ ) ₂ S, 0.05 g NaOH, 0.75 g WO ₃ , 1 g Y ₂ O ₃ approx. Mix mechanically for 15 minutes. Lithium transition metal oxide having the composition shown in Table 1 below was synthesized by calcining the mixed powder at 960 ^o C for 4 hours and 700 ^{o C for 10 hours.}

Example 4

150 g of Ni _0.94 Co _0.05 Mn _0.01 (OH) ₂ and 70 g of LiOH·H ₂ O, 0.75 g of (NH ₄ ) ₂ S, 0.05 g of NaOH, 0.75 g of WO ₃ , 0.8 g of Y ₂ O ₃ Mix mechanically for about 15 minutes. Lithium transition metal oxide having the composition shown in Table 1 below was synthesized by calcining the mixed powder at 960 ^o C for 4 hours and 700 ^{o C for 10 hours.}

Example 5

150 g Ni _0.91 Co _0.08 Mn _0.005 Al _0.005 (OH) ₂ with 70 g LiOH·H ₂ O, 0.75 g (NH ₄ ) ₂ S, 0.05 g NaOH, 0.75 g WO ₃ , 0.8 g Y ₂ O ₃ is mechanically mixed for about 15 minutes. Lithium transition metal oxide having the composition shown in Table 1 below was synthesized by calcining the mixed powder at 960 ^o C for 4 hours and 700 ^{o C for 10 hours.}

Comparative Example 1

150 g of Ni _0.91 Co _0.08 Al _0.01 (OH) ₂ , 70 g of LiOH·H ₂ O, 0.75 g of (NH ₄ ) ₂ S, and 0.05 g of NaOH are mechanically mixed for about 15 minutes. Lithium transition metal oxide having the composition shown in Table 1 below was synthesized by calcining the mixed powder at 960 ^o C for 4 hours and 700 ^{o C for 10 hours.}

Comparative Example 2

Mechanically mix 150 g of Ni _0.91 Co _0.08 Al _0.01 (OH) ₂ with 70 g of LiOH·H ₂ O, 0.75 g of (NH ₄ ) ₂ S, 0.05 g of NaOH and 0.8 g of Y ₂ O ₃ for about 15 minutes. do. Lithium transition metal oxide having the composition shown in Table 1 below was synthesized by calcining the mixed powder at 960 ^o C for 4 hours and 700 ^{o C for 10 hours.}

Comparative Example 3

150 g of Ni _0.91 Co _0.08 Al _0.01 (OH) ₂ with 70 g of LiOH·H ₂ O, 0.75 g of (NH ₄ ) ₂ S, 0.05 g of NaOH and 0.75 g of WO ₃ are mechanically mixed for about 15 minutes. Lithium transition metal oxide having the composition shown in Table 1 below was synthesized by calcining the mixed powder at 960 ^o C for 4 hours and 700 ^{o C for 10 hours.}

Comparative Example 4

150 g of Ni _0.91 Co _0.08 Al _0.01 (OH) ₂ and 70 g of LiOH·H ₂ O, 0.75 g of (NH ₄ ) ₂ S, 0.05 g of NaOH, 0.8 g of Y ₂ O ₃ and 0.27 g of MgCO ₃ Mix mechanically for about 15 minutes. Lithium transition metal oxide having the composition shown in Table 1 below was synthesized by calcining the mixed powder at 960 ^o C for 4 hours and 700 ^{o C for 10 hours.}

Comparative Example 5

150 g of Ni _0.91 Co _0.08 Al _0.01 (OH) ₂ and 70 g of LiOH•H ₂ O, 0.75 g of (NH ₄ ) ₂ S, 0.05 g of NaOH, 0.8 g of Y ₂ O ₃ and 0.24 g of TiO ₃ Mix mechanically for about 15 minutes. Lithium transition metal oxide having the composition shown in Table 1 below was synthesized by calcining the mixed powder at 960 ^o C for 4 hours and 700 ^{o C for 10 hours.}

Comparative Example 6

150 g of Ni _0.91 Co _0.08 Al _0.01 (OH) ₂ and 70 g of LiOH·H ₂ O, 0.75 g of (NH ₄ ) ₂ S, 0.05 g of NaOH, 0.75 g of WO ₃ , and 0.25 g of Y ₂ O ₃ Mix mechanically for about 15 minutes. Lithium transition metal oxide having the composition shown in Table 1 below was synthesized by calcining the mixed powder at 960 ^o C for 4 hours and 700 ^{o C for 10 hours.}

Comparative Example 7

150 g of Ni _0.91 Co _0.08 Al _0.01 (OH) ₂ and 70 g of LiOH·H ₂ O, 0.75 g of (NH ₄ ) ₂ S, 0.05 g of NaOH, 0.75 g of WO ₃ , and 1.2 g of Y ₂ O ₃ Mix mechanically for about 15 minutes. Lithium transition metal oxide having the composition shown in Table 1 below was synthesized by calcining the mixed powder at 960 ^o C for 4 hours and 700 ^{o C for 10 hours.}

Comparative Example 8

150 g of Ni _0.94 Co _0.05 Mn _0.01 (OH) ₂ , 70 g of LiOH·H ₂ O, 0.75 g of (NH ₄ ) ₂ S, and 0.05 g of NaOH are mechanically mixed for about 15 minutes. Lithium transition metal oxide having the composition shown in Table 1 below was synthesized by calcining the mixed powder at 960 ^o C for 4 hours and 700 ^{o C for 10 hours.}

Comparative Example 9

150 g of Ni _0.91 Co _0.08 Mn _0.005 Al _0.005 (OH) ₂ with 70 g of LiOH·H ₂ O, 0.75 g of (NH ₄ ) ₂ S and 0.05 g of NaOH are mechanically mixed for about 15 minutes. Lithium transition metal oxide having the composition shown in Table 1 below was synthesized by calcining the mixed powder at 960 ^o C for 4 hours and 700 ^{o C for 10 hours.}

Cho Sung-sik Comparative Example 1 Li _0.9999 Na _0.0001 Ni _0.916 Co _0.074 Al _0.01 O _1.999 S _0.001 Comparative Example 2 Li _0.9999 Na _0.0001 Ni _0.914 Co _0.074 Al _0.009 Y _0.003 O _1.999 S _0.001 Comparative Example 3 Li _0.9999 Na _0.0001 Ni _0.9138 Co _0.075 Al _0.01 W _0.0012 O _1.999 S _0.001 Comparative Example 4 Li _0.9999 Na _0.0001 Ni _0.9139 Co _0.076 Al _0.008 W _0.0013 Mg _0.0008 O _1.999 S _0.001 Comparative Example 5 Li _0.9999 Na _0.0001 Ni _0.9122 Co _0.076 Al _0.01 W _0.0011 Ti _0.0007 O _1.999 S _0.001 Comparative Example 6 Li _0.9999 Na _0.0001 Ni _0.9141 Co _0.076 Al _0.008 W _0.0011 Y _0.0008 O _1.999 S _0.001 Comparative Example 7 Li _0.9999 Na _0.0001 Ni _0.9088 Co _0.076 Al _0.01 W _0.0011 Y _0.0041 O _1.999 S _0.001 Comparative Example 8 Li _0.9999 Na _0.0001 Ni _0.94 Co _0.05 Mn _0.01 O _1.999 S _0.001 Comparative Example 9 Li _0.9999 Na _0.0001 Ni _0.94 Co _0.05 Al _0.005 Mn _0.005 O _1.999 S _0.001 Example 1 Li _0.9999 Na _0.0001 Ni _0.9136 Co _0.075 Al _0.009 W _0.0011 Y _0.0013 O _1.999 S _0.001 Example 2 Li _0.9999 Na _0.0001 Ni _0.9112 Co _0.076 Al _0.009 W _0.0011 Y _0.0027 O _1.999 S _0.001 Example 3 Li _0.9999 Na _0.0001 Ni _0.9062 Co _0.079 Al _0.01 W _0.0011 Y _0.0037 O _1.999 S _0.001 Example 4 Li _0.9999 Na _0.0001 Ni _0.9363 Co _0.05 Mn _0.01 W _0.0011 Y _0.0026 O _1.999 S _0.001 Example 5 Li _0.9999 Na _0.0001 Ni _0.9361 Co _0.05 Al _0.005 Mn _0.005 W _0.0011 Y _0.0028 O _1.999 S _0.001

(Manufacture of half cell)

Example 6

A slurry was prepared by mixing the lithium transition metal oxide:conductive material:binder synthesized in Example 1 in a weight ratio of 96:2:2. Here, carbon black (Super-P) was used as the conductive material, and polyvinylidene fluoride (PVdF) was dissolved in N-methyl-2-pyrrolidone solvent as the binder.

The slurry was uniformly applied to an Al current collector and dried at 110° C. for 2 hours to prepare a positive electrode. The loading level of the electrode plate was 11.0 mg/cm ² , and the electrode density was 3.6 g/cc.

_{The prepared positive electrode was used as a working electrode, lithium foil was used as a counter electrode, and LiPF 6} was added as a lithium salt to a mixed solvent in which EC/EMC/DEC was mixed in a volume ratio of 3/4/3 at a concentration of 1.3M. A CR2032 half cell was manufactured according to a commonly known process using the liquid electrolyte added as much as possible.

Examples 7 to 10

A CR2032 half cell was manufactured in the same manner as in Example 6, except that the lithium transition metal oxide synthesized in Examples 2 to 5 was used instead of the lithium transition metal oxide synthesized in Example 1, respectively.

Comparative Examples 10 to 18

A CR2032 half cell was manufactured in the same manner as in Example 6, except that the lithium transition metal oxide synthesized in Comparative Examples 1 to 9 was used instead of the lithium transition metal oxide synthesized in Example 1, respectively.

Evaluation Example 1: SEM analysis

SEM pictures were taken of the lithium transition metal oxides synthesized in Examples 1 to 3 and Comparative Examples 1 to 7, and the results are shown in FIG. 1 .

Referring to FIG. 1 , it can be seen that the lithium transition metal oxides prepared in Examples 1 to 3 and Comparative Examples 1 to 7 did not show a significant difference in particle size and appearance.

Evaluation Example 2: Elemental Analysis

By performing ICP spectroscopic analysis on the lithium transition metal oxide synthesized in Examples 1 to 5 and Comparative Examples 1 to 9, the content of Na, S, W, Mg, Ti and Y elements contained in the lithium transition metal oxide was analyzed did. The results are shown in Table 2 below.

Na (ppm) S (ppm) W (ppm) Mg (ppm) Ti (ppm) Y (ppm) Comparative Example 1 188 974 - - - - Comparative Example 2 194 986 - - - 2,840 Comparative Example 3 189 958 2,420 - - - Comparative Example 4 195 991 - 240 - 2,740 Comparative Example 5 181 984 - - 235 2,580 Comparative Example 6 202 963 2,460 - - 870 Comparative Example 7 199 971 2,540 - - 4,360 Comparative Example 8 203 1,061 - - - - Comparative Example 9 211 1,055 - - - - Example 1 184 981 2,670 - - 1,450 Example 2 194 967 2,460 - - 2,860 Example 3 201 992 2,530 - - 3,950 Example 4 188 1,021 2,610 - - 2,750 Example 5 194 1,078 2,580 - - 2,940

Referring to Table 2, it can be seen that the lithium transition metal oxides synthesized in Examples 1 to 5 contain Na, S, W, and Y in specific amounts.

Evaluation Example 3: Life Evaluation (1)

After resting the half-cells prepared in Examples 6 to 8 and Comparative Examples 10 to 16 for 10 hours, it was charged in CC mode at 0.2C to 4.25V, and then charged in CV mode to a current corresponding to 0.05C. . Next, the formation process was completed by discharging in CC mode at 0.2C to 3.0V.

Subsequently, after charging in CC mode to 4.25V at 0.5C at room temperature (25°C), charging was performed in CV mode up to a current corresponding to 0.05C. Next, discharging was performed in CC mode at 1C to 3.0V, and this process was repeated a total of 50 times, and the capacity retention rate according to the cycle is shown in FIGS. 2 and 3 . In addition, the initial discharge capacity and initial efficiency were measured and shown in Table 4 below.

Capacity retention (%) after 50 cycles Comparative Example 10 52.9 Comparative Example 11 64.7 Comparative Example 12 63.8 Comparative Example 13 76.9 Comparative Example 14 80.0 Comparative Example 15 85.3 Example 6 88.5 Example 7 90.3 Example 8 90.7

Initial discharge capacity
(mAh/g) initial efficiency
(%) Comparative Example 10 210.3 88 Comparative Example 11 209.7 88 Comparative Example 12 210.5 88 Comparative Example 13 210.8 88 Comparative Example 14 210.7 88 Comparative Example 15 211.1 88 Comparative Example 16 206.6 86 Example 6 209.9 88 Example 7 210.3 88 Example 8 209.8 88

Referring to FIG. 2 and Tables 3 and 4, there was no difference in the initial efficiency when W and Y were included as doping elements. A 38% difference in capacity retention was confirmed. In addition, the cells of Examples 6 to 7 containing W and Y simultaneously showed a difference in capacity retention rate of up to about 14% compared to Comparative Examples 13 and 14 containing Mg and Ti elements, which are known to affect structural stability. . In addition, according to Comparative Example 15 containing less than 1000 ppm of Y element, a difference in capacity retention rate of up to about 5% was confirmed. These results prove that the lifespan characteristics of cells can be improved by including W and Y as doping elements for transition metals, but containing Y element at 1000 ppm or more.

Evaluation Example 4: Life Evaluation (2)

After resting the half-cells prepared in Example 9 and Comparative Example 17 for 10 hours, the cells were charged in CC mode at 0.2C to 4.25V, and then charged in CV mode to a current corresponding to 0.05C. Next, the formation process was completed by discharging in CC mode at 0.2C to 3.0V.

Subsequently, after charging in CC mode to 4.25V at 0.5C at room temperature (25°C), charging was performed in CV mode up to a current corresponding to 0.05C. Next, discharging was performed in CC mode at 1C to 3.0V, and this process was repeated a total of 50 times, and the capacity retention rate according to the cycle is shown in FIGS. 3 and 5, and the initial discharge capacity and initial efficiency were measured and the following table 6 is shown.

Capacity retention (%) after 50 cycles Comparative Example 17 69.1 Example 9 88.6

Initial discharge capacity
(mAh/g) initial efficiency
(%) Comparative Example 17 213.1 88 Example 9 213.5 88

Referring to FIG. 3 and Tables 5 and 6, when the content of Y in the doping element exceeds 4000 ppm (Comparative Example 17), it was confirmed that the capacity retention rate was significantly reduced with repeated cycles. Without being bound by theory, it is believed that this is due to the collapse of the crystal structure due to impurity precipitation due to the inclusion of an excess of Y element.

Evaluation Example 5: Life Evaluation (3)

After resting the half-cells prepared in Example 10 and Comparative Example 18 for 10 hours, charging was performed in CC mode at 0.2C to 4.25V, and then charging was performed in CV mode to a current corresponding to 0.05C. Next, the formation process was completed by discharging in CC mode at 0.2C to 3.0V.

Subsequently, after charging in CC mode to 4.25V at 0.5C at room temperature (25°C), charging was performed in CV mode up to a current corresponding to 0.05C. Next, discharging was carried out in CC mode at 1C to 3.0V, and this process was repeated a total of 50 times, and the capacity retention rate according to the cycle is shown in FIGS. 4 and 7, and the initial discharge capacity and the initial efficiency were measured and the following table 8 is shown. all.

Capacity retention (%) after 50 cycles Comparative Example 18 55.6 Example 10 89.9

Initial discharge capacity
(mAh/g) initial efficiency
(%) Comparative Example 18 206.7 87 Example 10 207.1 87

Referring to FIG. 4 and Tables 7 and 8, it was confirmed that the capacity retention rate was severely reduced in the case where a doping element substituting a part of the transition metal was not included (Comparative Example 18). This suggests that the substitution of some of the transition metals with W and Y greatly affects the lifespan characteristics of the cell.

In the above, the preferred embodiments according to the present invention have been described with reference to the drawings and examples, but these are merely exemplary, and various modifications and equivalent other embodiments are possible by those skilled in the art. will be able to understand Accordingly, the protection scope of the present invention should be defined by the appended claims.

Claims (20)

a plurality of primary particles, an aggregate of a plurality of primary particles, or a combination thereof;
The primary particles have _{a crystal structure of α-NaFeO 2} type, and include a lithium transition metal oxide represented by the following Chemical Formula 2, a cathode active material:
<Formula 2>
Li _1-x A _x M1 _1-α-β W _α Y _β O _2-z S _z
In Formula 2,
A is sodium (Na) or potassium (K),
M1 includes Ni, Co, Mn, Al, or a combination thereof;
0<x≤0.05, 0<α≤0.002, 0<β≤0.004, 0<z<0.01. delete delete delete delete delete According to claim 1,
Of the lithium transition metal oxide, nickel is contained in an amount of 80 mol% or more, a positive electrode active material. delete delete According to claim 1,
In Formula 2, A is Na, the positive electrode active material. According to claim 1,
In Formula 2, β/α≥1, the positive electrode active material. According to claim 1,
The lithium transition metal oxide is represented by any one of the following Chemical Formulas 3 to 5, the positive electrode active material:
<Formula 3>
Li _1-x1 Na _x1 Ni _{1-a1- b1-} α1-β1 Co _a1 Al b1 W _α1 Y _β1 O _2-z1 S _z1
<Formula 4>
Li _1-x2 Na _x2 Ni _{1-a2-b2- α2-β2} Co _a2 Mn _b2 W _α2 Y _β2 O _2-z2 S _z2
<Formula 5>
Li _1-x3 Na _x3 Ni _{1-a3-b3-c3-α3-β3} Co _a3 Mn _b3 Al _c3 W _α3 Y _β3 O _2-z3 S _z3
In Formulas 3 to 5,
0<x1≤0.001, 0<a1<0.1, 0<b1<0.05, 0<α1≤0.002, 0<β1≤0.004, 0<z1<0.01,
0<x2≤0.001, 0<a2<0.1, 0<b2<0.05, 0<α2≤0.002, 0<β2≤0.004, 0<z2<0.01,
0<x3≤0.001, 0<a3<0.1, 0<b3<0.05, 0<c3<0.05, 0<α3≤0.002, 0<β3≤0.004, 0<z3<0.01. delete According to claim 1,
The average particle diameter (D ₅₀ ) of the primary particles is 1㎛ to 20㎛, the positive electrode active material. mixing a Li element-containing compound, a Ni-containing transition metal compound, a sulfur (S) element-containing compound, and an M element-containing compound to obtain a lithium transition metal oxide precursor;
and heat-treating the precursor to obtain a cathode active material including a plurality of primary particles, an aggregate of a plurality of primary particles, or a combination thereof;
The primary particles have _{a crystal structure of α-NaFeO 2} type, and include a lithium transition metal compound represented by the following Chemical Formula 2, a method of manufacturing a cathode active material:
<Formula 2>
Li _1-x A _x M1 _1-α-β W _α Y _β O _2-z S _z
In Formula 2,
A is sodium (Na) or potassium (K),
M1 includes Ni, Co, Mn, Al or a combination thereof,
0<x≤0.05, 0<α≤0.002, 0<β≤0.004, 0<z<0.01. 16. The method of claim 15,
The Li element-containing compound includes a hydroxide, oxide, nitride, carbonate, or a combination thereof of lithium,
The S element-containing compound comprises lithium sulfur oxide, a method for producing a positive electrode active material. 16. The method of claim 15,
The Li-containing compound and the S-element-containing compound are mixed in a molar ratio of 99:1 to 99.9:0.1, a method for producing a cathode active material. 16. The method of claim 15,
The heat treatment includes a first heat treatment step and a second heat treatment step,
The heat treatment temperature in the first heat treatment step is higher than the heat treatment temperature in the second heat treatment step, a method of manufacturing a cathode active material. A positive electrode comprising the positive electrode active material according to any one of claims 1, 7, 10 to 12, and 14. A positive electrode comprising the positive electrode active material according to any one of claims 1, 7, 10 to 12, and claim 14;
cathode; and
Lithium secondary battery comprising; electrolyte.

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