KR20210118644A - Positive electrode active material for lithium secondary battery, preparing method of the same, positive electrode and lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery to increase lifespan characteristics and to a manufacturing method thereof. According to the present invention, the positive electrode active material comprises: a lithium transition metal oxide of a core-shell structure including a core portion containing a first lithium transition metal oxide and a shell portion formed on the core portion and containing a second lithium transition metal oxide having a composition different from that of the first lithium transition metal oxide; and a coating layer formed on the surface of the lithium transition metal oxide of the core-shell structure and including at least one coating element selected from a group consisting of Al, B, W, Nb, and Co. The shell portion includes a surface doping portion in which a coating element is mixed and the surface doping portion exists in a region at a distance of 30 nm or less from the outermost surface of the positive electrode active material.

Description

Positive electrode active material for lithium secondary battery, manufacturing method thereof, positive electrode for lithium secondary battery including same, and lithium secondary battery

The present invention relates to a cathode active material for a lithium secondary battery, a method for manufacturing the cathode active material, a cathode for a lithium secondary battery including the cathode active material, and a lithium secondary battery.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, a lithium secondary battery having a high energy density and voltage, a long cycle life, and a low self-discharge rate has been commercialized and widely used.

A lithium transition metal composite oxide is used as a cathode active material for a lithium secondary battery, and among them, a lithium cobalt composite metal oxide such as _{LiCoO 2 having a high operating voltage and excellent capacity characteristics is mainly used.} However, LiCoO ₂ has very poor thermal properties due to the destabilization of the crystal structure due to delithiation. In addition, since the LiCoO ₂ is expensive, there is a limit to its mass use as a power source in fields such as electric vehicles.

As a material for replacing the LiCoO ₂ , a lithium manganese composite metal oxide (LiMnO ₂ or LiMn ₂ O _4, etc.), a lithium iron phosphate compound (LiFePO ₄ etc.) or a lithium nickel composite metal oxide (LiNiO ₂ etc.) has been developed. . Among them, research and development on lithium-nickel composite metal oxide, which has a high reversible capacity of about 200 mAh/g, and is easy to implement in a large-capacity battery, is being actively studied. However, the LiNiO ₂ has _{inferior thermal stability compared to LiCoO 2 ,} and when an internal short circuit occurs due to external pressure in a charged state, the positive electrode active material itself is decomposed, resulting in rupture and ignition of the battery. Accordingly, as a method for improving low thermal stability while maintaining excellent reversible capacity of the LiNiO ₂ , lithium nickel cobalt manganese oxide in which a part of Ni is substituted with Mn and Co has been developed.

Recently, high-nickel lithium nickel cobalt manganese oxide having a high nickel content has been developed in order to increase the capacity of the positive electrode active material. However, when the content of nickel in lithium nickel cobalt manganese oxide is increased, the amount of oxidation of nickel increases in the same voltage band due to the high nickel content, so that the amount of lithium ion movement increases, thereby reducing the stability of the positive electrode, and the capacity of the secondary battery There was also a problem that the retention rate was lowered.

In order to solve the above problems, a concentration gradient positive active material with improved structural stability on the surface of the positive active material has been developed by gradually changing the concentration of the transition metal in the positive active material so that the nickel content decreases from the center of the positive active material toward the surface. became However, in the case of a positive active material in which the concentration of nickel is gradually changed as described above, there is a problem in that the content of nickel included in the entire positive active material is reduced and thus the capacity is decreased, and the effect of improving structural stability is not sufficient, so there is a limit to improving the high temperature cycle characteristics there was

Therefore, there is a demand for the development of a positive electrode active material capable of improving lifespan characteristics while exhibiting high capacity characteristics.

In order to solve the above problems, a first technical object of the present invention is to provide a positive electrode active material with improved structural stability.

A second technical object of the present invention is to provide a method of manufacturing the positive active material.

A third technical object of the present invention is to provide a positive electrode for a lithium secondary battery including the positive electrode active material.

A fourth technical object of the present invention is to provide a lithium secondary battery including the positive electrode for a lithium secondary battery.

The present invention, a core portion comprising a first lithium transition metal oxide; and a shell portion formed on the core portion and including a second lithium transition metal oxide having a composition different from that of the first lithium transition metal oxide; and a core-shell structure lithium transition metal oxide comprising a, and the core-shell structure It provides a positive electrode active material comprising a coating layer formed on the surface of the lithium transition metal oxide of Al, B, W, Nb and at least one coating element selected from the group consisting of Co.

In this case, the first lithium transition metal oxide and the second lithium transition metal oxide each independently have a composition represented by the following [Formula 1].

[Formula 1]

Li _1+a Ni _x Co _y M ¹ _z M ² _w O ₂

In Formula 1,

M ¹ is at least one of Mn and Al,

M ² is at least one selected from the group consisting of Al, B, W, Nb and Co,

0≤a≤0.3, 0.5≤x<1, 0<y<0.5, 0<z<0.5, 0≤w≤0.1.

In addition, the shell part includes a surface doped part in which the coating element is mixed, and the surface doped part is present in a region at a distance of 30 nm or less from the outermost surface of the positive electrode active material.

In addition, the present invention, a core portion comprising a first lithium transition metal oxide; and a shell portion formed on the core portion and including a second lithium transition metal oxide having a composition different from that of the first lithium transition metal oxide; and mixing the lithium transition metal oxide and a coating raw material containing at least one coating element selected from the group consisting of Al, B, W, Nb, and Co, and heat-treating it. .

In this case, the first lithium transition metal oxide and the second lithium transition metal oxide each independently have a composition represented by the above [Formula 1], and the coating element is diffused into the shell part by the heat treatment so that the coating element is mixed. A surface doped portion is formed, and the surface doped portion is present in a region at a distance of 30 nm or less from the outermost surface of the positive electrode active material.

In addition, the present invention provides a positive electrode for a lithium secondary battery comprising the positive active material.

In addition, the present invention provides a lithium secondary battery including the positive electrode for the lithium secondary battery.

The positive electrode active material of the present invention does not gradually change the transition metal concentration, but forms the composition of the core portion and the shell portion completely different so that the composition changes rapidly at the boundary between the core portion and the shell portion, thereby improving the structural stability of the positive electrode active material while improving the positive electrode active material It was made possible to realize high capacity characteristics by preventing the overall nickel content in the active material from being reduced.

In addition, the positive active material according to the present invention includes a coating layer on the surface of the shell part to stabilize the surface, and to form a surface doping part in which some of the coating elements forming the coating layer are inserted into the shell part, so that when the nickel content of the shell part is high excellent structural stability can also be realized.

Therefore, when the positive electrode active material of the present invention is used, excellent lifespan characteristics can be realized even at high temperatures while maintaining high capacity characteristics.

1 is a TEM photograph of a cross section of a coating layer and a shell part of a cathode active material prepared in Example 1, (b) is a 10 times magnification of (a).
2 is a TEM photograph showing the component distribution in the coating layer and the shell part of the positive active material prepared in Example 1, (d) is to show the distribution of the coating element B in the box region shown in (c), ( e) shows the distribution of Ni in the box area shown in (c).
3 is a graph showing the capacity retention rate of the secondary batteries prepared in Example 1 and Comparative Examples 1 to 3;

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

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

As a result of repeated research to develop a cathode active material having high capacity and excellent structural stability at high temperatures, the inventors of the present inventors formed completely different compositions of transition metals in the core and shell, and applied a coating layer to the surface of the cathode active material having a core-shell structure. However, it was found that structural stability of the positive electrode active material can be dramatically improved by allowing some of the coating elements included in the coating layer to be inserted from the surface of the shell part to a specific region, and the present invention has been completed.

cathode active material

First, the cathode active material of the present invention will be described.

The cathode active material according to the present invention includes a lithium transition metal oxide having a core-shell structure including a core portion and a shell portion having different transition metal compositions, and a coating layer formed on the surface of the lithium transition metal oxide, and a coating element of the coating layer includes a surface doped portion formed by being inserted into the shell portion.

Specifically, the lithium transition metal oxide having the core-shell structure includes a core portion and a shell portion, the core portion includes a first lithium transition metal oxide, and the shell portion has a composition different from that of the first lithium transition metal oxide. and a second lithium transition metal oxide. In this case, 'composition is different' means that the types of transition metals included in the lithium transition metal oxide are different, or the content of each transition metal component is different even though the types of transition metals are the same.

On the other hand, in the present invention, it is preferable that the first lithium transition metal oxide and the second lithium transition metal oxide maintain a constant concentration of the transition metal and do not have a concentration gradient. As such, when the composition of the core part and the shell part are configured differently without a concentration gradient of the transition metal, a rapid composition change occurs at the boundary between the core part and the shell part, and the nickel content decrease according to the concentration gradient is suppressed while the shell part is relatively stable. It can be formed with this high composition, and the structural stability of the positive electrode active material can be improved.

Specifically, the first lithium transition metal oxide and the second lithium transition metal oxide may each independently have a composition represented by the following [Formula 1].

[Formula 1]

Li _1+a Ni _x Co _y M ¹ _z M ² _w O ₂

In Formula 1, M ¹ may be at least one of Mn and Al, and M ² may be at least one selected from the group consisting of Al, B, W, Nb, and Co.

1+a represents the atomic ratio of lithium in the lithium transition metal oxide, and may be 0≤a≤0.3, 0≤a≤0.2, or 0≤a≤0.15.

The x represents the atomic ratio of nickel among the total transition metals in the lithium transition metal oxide, and may be 0.5≤x<1, 0.6≤x<1, 0.8≤x<1, or 0.85≤x<1.

The y represents the atomic ratio of cobalt among the total transition metals in the lithium transition metal oxide, and may be 0<y<0.5, 0<y<0.4, 0<y<0.2, or 0<y<0.15.

^{The z represents the atomic ratio of M 1} among the total transition metals in the lithium transition metal oxide, and may be 0<z<0.5, 0<z<0.4, 0<z<0.2, or 0<z<0.15.

^{The w represents the atomic ratio of M 2} among the total transition metals in the lithium transition metal oxide, and may be 0≤w≤0.1, 0≤w≤0.05, or 0≤w≤0.02.

According to one embodiment, the first lithium transition metal oxide may have a composition represented by the following [Formula 1-1].

[Formula 1-1]

Li _1+a1 Ni _x1 Co _y1 M ¹ _z1 M ² _w1 O ₂

In Formula 1-1, M ¹ may be at least one of Mn and Al, and M ² may be at least one selected from the group consisting of Al, B, W, Nb, and Co.

1+a1 represents the atomic ratio of lithium in the lithium transition metal oxide, and may be 0≤a1≤0.3, 0≤a1≤0.2, or 0≤a1≤0.15.

The x1 represents the atomic ratio of nickel among the total transition metals in the lithium transition metal oxide, and may be 0.8≤x1<1, 0.85≤x1<1, or 0.87≤x1<1. When a lithium transition metal oxide having a high nickel atomic ratio as described above is used for the core portion, high capacity characteristics can be realized while minimizing structural stability degradation.

The y1 represents the atomic ratio of cobalt among the total transition metals in the lithium transition metal oxide, and may be 0<y1<0.2, 0<y1<0.15, or 0<y1<0.13.

^{The z1 represents the atomic ratio of M 1} among the total transition metals in the lithium transition metal oxide, and may be 0<z1<0.2, 0<z1<0.15, or 0<z1<0.13.

^{The w1 represents the atomic ratio of M 2} among the total transition metals in the lithium transition metal oxide, and may be 0≤w1≤0.1, 0≤w1≤0.05, or 0≤w1≤0.02.

According to another embodiment, the first lithium transition metal oxide and / or the second lithium transition metal oxide is, each independently, a lithium nickel-cobalt-manganese-aluminum oxide having a composition represented by the following [Formula 1-2] can

[Formula 1-2]

Li _1+a2 Ni _x2 Co _y2 Mn _z2 Al _w2 O ₂

In Formula 1-2,

1+a2 represents an atomic ratio of lithium in the lithium nickel-cobalt-manganese-aluminum oxide, and may be 0≤a2≤0.3, 0≤a2≤0.2, or 0≤a2≤0.15.

x2 represents the atomic ratio of nickel among the total transition metals in the lithium nickel-cobalt-manganese-aluminum oxide, 0.5≤x2<1, 0.6≤x2<1, 0.8≤x2<1, or 0.85≤x2<1 can be

y2 represents the atomic ratio of cobalt among the total transition metals in the lithium nickel-cobalt-manganese-aluminum oxide, 0<y2<0.5, 0<y2<0.4, 0<y2<0.2, or 0<y2<0.15 can be

Wherein z2 represents the atomic ratio of manganese among the total transition metals in the lithium nickel-cobalt-manganese-aluminum oxide, 0<z2<0.5, 0<z2<0.4, 0<z2<0.2, or 0<z2<0.15 can be

The w2 represents the atomic ratio of aluminum among the total transition metals in the lithium nickel-cobalt-manganese-aluminum oxide, and may be 0<w2≤0.1, 0<w2≤0.05, or 0<w2≤0.02.

According to another embodiment, the lithium transition metal oxide of the core-shell structure includes a core portion including a first lithium transition metal oxide represented by the following [Formula 1-3], and the following [Formula 1-4] It may include a shell portion including a second lithium transition metal oxide. When the composition of each of the core part and the shell part satisfies the following [Formula 1-3] and [Formula 1-4], high-temperature lifespan characteristics are particularly excellent.

[Formula 1-3]

Li _1+a3 Ni _x3 Co _y3 Mn _z3 O ₂

In Formula 1-3, 1+a3 represents the atomic ratio of lithium in the lithium transition metal oxide, and may be 0≤a3≤0.3, 0≤a3≤0.2, or 0≤a3≤0.15.

The x3 represents the atomic ratio of nickel among the total transition metals in the lithium transition metal oxide, and may be 0.8≤x3<1, 0.85≤x3<1, or 0.87≤x3<1. When a lithium transition metal oxide having a high nickel atomic ratio as described above is used for the core portion, high capacity characteristics can be realized while minimizing structural stability degradation.

The y3 represents the atomic ratio of cobalt among the total transition metals in the lithium transition metal oxide, and may be 0<y3<0.2, 0<y3<0.15, or 0<y3<0.13.

The z3 represents the atomic ratio of manganese among the total transition metals in the lithium transition metal oxide, and may be 0<z3<0.2, 0<z3<0.15, or 0<z3<0.13.

[Formula 1-4]

Li _1+a4 Ni _x4 Co _y4 Mn _z4 Al _w4 O ₂

In Formula 1-4, 1+a4 represents the atomic ratio of lithium in the lithium transition metal oxide, and may be 0≤a4≤0.3, 0≤a4≤0.2, or 0≤a4≤0.15.

The x4 represents the atomic ratio of nickel among the total transition metals in the lithium transition metal oxide, and may be 0.8≤x4<1, 0.85≤x4<1, or 0.87≤x4<1.

The y4 represents the atomic ratio of cobalt among the total transition metals in the lithium transition metal oxide, and may be 0<y4<0.2, 0<y4<0.15, or 0<y4<0.13.

The z4 represents the atomic ratio of manganese among the total transition metals in the lithium transition metal oxide, and may be 0<z4<0.2, 0<z4<0.15, or 0<z4<0.13.

The w4 represents the atomic ratio of aluminum among the total transition metals in the lithium transition metal oxide, and may be 0<w4≤0.1, 0<w4≤0.05, or 0<w4≤0.02.

Meanwhile, the cathode active material of the present invention includes a coating layer on the surface of the lithium transition metal oxide having the core-shell structure.

Specifically, the coating layer is formed on the surface of the shell portion, and includes at least one coating element selected from the group consisting of Al, B, W, Nb and Co. When the coating layer including the coating element as described above is formed on the surface of the shell part, it is possible to obtain an effect that the surface structure of the positive electrode active material is further stabilized by the coating layer.

Meanwhile, the coating element is preferably included in an amount of 0.01 to 2 parts by weight, preferably 0.01 to 1 parts by weight, based on 100 parts by weight of the lithium transition metal oxide having the core-shell structure. When the content of the coating element is too small, the surface stabilizing effect of the positive electrode active material is insignificant, and when the content of the coating element is too large, the capacity characteristics may be deteriorated.

On the other hand, the coating layer may be formed on the entire surface of the shell portion, may be formed partially. Specifically, when the coating layer is partially formed on the surface of the shell part, 20% or more to less than 100% of the total area of the shell part may be formed. When the area of the coating layer is less than 20%, the surface stabilization effect according to the formation of the coating layer may be insignificant.

The coating layer may have a thickness of 1 to 30 nm, preferably 1 to 15 nm, and more preferably 1 to 10 nm. When the thickness of the coating layer satisfies the above range, it is possible to obtain an effect of improving the lifespan characteristics according to the surface stabilization.

In addition, the positive active material according to the present invention includes a surface doping portion in which a coating element is mixed in the shell portion. The surface doping part is formed by allowing the coating element to diffuse into the shell part and inserted, and may be formed by appropriately adjusting heat treatment conditions (temperature/time) when forming the coating layer.

On the other hand, in the present invention, the surface doped portion is formed to exist in a region at a distance of 30 nm or less from the outermost surface of the positive electrode active material. According to the research of the present inventors, when the coating element is present only in the coating layer without being inserted into the shell portion, the effect of stabilizing the surface structure of the positive electrode active material is insignificant, and the surface doping portion is formed from the outermost surface of the positive electrode active material to a region exceeding 30 nm. There is also a problem in that the internal structural stability of the cathode active material is deteriorated, so that high temperature characteristics are lowered, and the capacity characteristics of the cathode active material are also lowered. More preferably, it is preferably formed in a region at a distance of 5 nm to 30 nm from the outermost surface of the surface positive electrode active material.

On the other hand, the shell portion, based on the total number of atoms of the transition metal contained in the shell portion 0.1atm% to 5atm%, preferably 0.5atm% to 4atm%, more preferably 1atm% to 4atm% of content may be included. When the content of the coating element inserted into the shell part satisfies the above range, it is possible to achieve the effect of structurally stabilizing the surface and the inside of the shell part at the same time.

Method for manufacturing a cathode active material

Next, a method for manufacturing the positive electrode active material of the present invention will be described.

A method of manufacturing a cathode active material according to the present invention comprises: (1) a core part comprising a first lithium transition metal oxide; and a shell portion formed on the core portion and including a second lithium transition metal oxide having a composition different from that of the first lithium transition metal oxide; and (2) mixing the lithium transition metal oxide and a coating raw material containing at least one coating element selected from the group consisting of Al, B, W, Nb and Co, and performing heat treatment.

In this case, the first lithium transition metal oxide and the second lithium transition metal oxide are the same as described above. That is, the first lithium transition metal oxide and the second lithium transition metal oxide may each independently have a composition represented by the above [Formula 1].

The step of (1) preparing the lithium transition metal oxide having a core-shell structure may be performed by mixing a precursor of a core-shell structure having a core and a shell having different transition metal compositions and a lithium raw material and then sintering. have.

In this case, the precursor having a core-shell structure having a core and a shell having a different transition metal composition may be used by purchasing a commercially available product, or two transition metal-containing solutions having different compositions may be introduced into the reactor at different input times. It can also be prepared by a method of co-precipitation reaction by adding it.

Specifically, the precursor of the core-shell structure is (1-1) preparing a first transition metal-containing solution and a second transition metal-containing solution having different transition metal compositions, (1-2) the first transition metal-containing solution in a reactor Forming a precursor core by adding a transition metal-containing solution, an ammonium cation complex forming agent, and a basic compound and performing a co-precipitation reaction, (1-3) the second transition metal-containing solution, ammonium cations in a reactor including the precursor core A complex forming agent and a basic compound are added, and a shell is formed on the precursor core by co-precipitation to prepare a precursor having a core-shell structure.

In this case, the first transition metal-containing solution and the second transition metal-containing solution may be prepared by dissolving a nickel-containing raw material, a cobalt-containing raw material, and an M ¹ metal (Al and/or Mn)-containing raw material in water. . In addition, in ^{the case of preparing a lithium transition metal oxide containing M 2 element, if necessary, the M 2} metal-containing raw material may be further included in the first transition metal-containing solution and/or the second transition metal-containing solution. can

The nickel-containing raw material may be, for example, nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and specifically, Ni(OH) ₂ , NiO, NiOOH, NiCO _{3 .} 2Ni(OH) ₂ ·4H ₂ O, NiC ₂ O ₂ ·2H ₂ O, Ni(NO ₃ ) ₂ ·6H ₂ O, NiSO ₄ , NiSO ₄ ·6H ₂ O, fatty acid nickel salt, nickel halide or these It may be a combination, but is not limited thereto.

The cobalt-containing raw material may be cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and specifically, Co(OH) ₂ , CoSO _{4 ,} CoOOH, Co(OCOCH ₃ ) ₂ ㆍ 4H ₂ O, Co(NO ₃ ) ₂ ㆍ6H ₂ O, CoSO ₄ ㆍ7H ₂ O, or a combination thereof, but is not limited thereto.

In the M ¹ containing raw material, M ¹ may be at least one of aluminum and manganese, and the M ¹ containing raw material is an acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxy compound containing ^{M 1 element.} hydroxide or the like. Specifically, the M ¹ containing raw material may include manganese oxide such as _{Mn 2} O ₃ , MnO ₂ , Mn ₃ O _{4 ;} manganese salts such as MnCO ₃ , Mn(NO ₃ ) ₂ , MnSO ₄ , manganese acetate, dicarboxylic acid manganese salt, manganese citrate, fatty acid manganese salt; manganese oxyhydroxide, manganese chloride; Al ₂ O ₃ , AlSO ₄ , AlCl ₃ , Al-isopropoxide (Al-isopropoxide), AlNO ₃ , or a combination thereof may be, but is not limited thereto.

A first transition metal-containing solution and a second transition metal-containing solution are prepared by adding the transition metal raw material as described above to water, respectively, but the first transition metal-containing solution and the second transition metal-containing solution are the types of transition metals and / or prepared so that the content of the transition metal is different.

When the first transition metal-containing solution and the second transition metal-containing solution are prepared, the first transition metal-containing solution, an ammonium cation complex former, and a basic compound are added to the reactor to perform a co-precipitation reaction to form a precursor core. When the co-precipitation reaction proceeds, precursor particles (cores) are formed inside the reactor. When the precursor particles (core) grow to a desired size, the input of the first transition metal-containing solution is stopped, the second transition metal-containing solution, an ammonium cation complex former, and a basic compound are added and a co-precipitation reaction is performed on the precursor core By forming the shell in the core-shell structure precursor can be obtained.

In this case, the ammonium cation complexing agent is at least one selected from the group consisting of _{NH 4} OH, (NH ₄ ) ₂ SO ₄ , NH ₄ NO ₃ , NH ₄ Cl, CH ₃ COONH ₄ , and NH ₄ CO _{3 .} and may be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. In this case, as the solvent, water or a mixture of water and an organic solvent that can be uniformly mixed with water (specifically, alcohol, etc.) and water may be used.

The basic compound may be at least one selected from the group consisting of NaOH, KOH, and Ca(OH) ₂ , and may be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. In this case, as the solvent, water or a mixture of water and an organic solvent that can be uniformly mixed with water (specifically, alcohol, etc.) and water may be used.

Meanwhile, the co-precipitation reaction may be performed at a temperature of 40° C. to 70° C. under an inert atmosphere such as nitrogen or argon. In addition, in order to increase the reaction rate during the reaction, a stirring process may be optionally performed, in which case the stirring rate may be 100 rpm to 2000 rpm.

Next, the precursor of the core-shell structure is mixed with a lithium raw material and then fired to prepare a cathode active material having a core-shell structure.

Examples of the lithium raw material include lithium-containing carbonates (eg, lithium carbonate), hydrates (eg, lithium hydroxide hydrate (LiOH·H ₂ O), etc.), hydroxides (eg, lithium hydroxide, etc.) ), nitrates (eg, lithium nitrate (LiNO ₃ ), etc.), chlorides (eg, lithium chloride (LiCl), etc.), and the like, and one type alone or a mixture of two or more types thereof may be used. .

On the other hand, mixing the precursor of the core-shell structure and the lithium raw material may be performed by solid-phase mixing such as jet milling, and the mixing ratio of the precursor and the lithium raw material is the atomic fraction of each component in the finally manufactured positive active material. It can be determined within a satisfactory range. For example, the precursor of the core-shell structure and the lithium raw material may be mixed in an amount such that a molar ratio of transition metal:Li is 1:0.9 to 1:1.2, preferably 1:0.98 to 1:1.1. . When the precursor and the lithium raw material are mixed within the above range, a positive electrode active material exhibiting excellent capacity characteristics may be prepared.

Meanwhile, although not essential, raw materials for doping some of the transition metals of the positive electrode active material in addition to the precursor and the lithium raw material may be additionally included during the mixing. For example, during the mixing, the above-described M ¹ containing raw material and/or M ² containing raw material may be additionally mixed.

The firing may be carried out at 600° C. to 1000° C., preferably at 700 to 900° C., and the firing time may be 5 to 30 hours, preferably 8 to 15 hours, but is not limited thereto.

Next, the lithium transition metal oxide prepared above and the raw material containing the coating element are mixed, and a coating layer is formed on the surface of the lithium transition metal oxide by heat treatment.

The coating element-containing raw material may be an oxide, hydroxide, oxyhydroxide, sulfate, carbonate, halide, sulfide, acetate, carboxylate, or a combination thereof containing a coating element, but is not limited thereto.

The method for forming the coating layer may be used without any particular limitation as long as it is a conventional method for forming a coating layer. For example, the method for forming the coating layer is heat-treated by solid-phase mixing of lithium transition metal oxide and a raw material containing a coating element, or a coating element. A coating layer may be formed by dispersing in a solvent to prepare a composition for forming a coating layer, and then surface-treating the surface of the lithium transition metal oxide by applying, immersing, or spraying the composition for forming a coating layer, followed by heat treatment. For example, in order to prepare the composition for forming the coating layer, a solvent capable of dispersing the coating element is water, an alcohol having 1 to 8 carbon atoms, dimethyl sulfoxide (DMSO), N-methylpyrrolidone, acetone, and One or a mixture of two or more selected from the group consisting of combinations thereof may be used. In addition, the solvent may exhibit appropriate applicability and may be included in an amount that can be easily removed during subsequent heat treatment.

On the other hand, the heat treatment is performed by controlling the heat treatment conditions so that the coating element can be doped on the surface of the shell part of the lithium transition metal oxide having a core-shell structure. Specifically, the coating element is 30 nm or less from the outermost surface of the positive electrode active material. It is performed by controlling the heat treatment temperature and/or heat treatment time so that it can diffuse into the region at a distance of .

An appropriate heat treatment temperature may vary depending on the composition of the lithium transition metal oxide, the type of coating element, etc., but for example, it is preferably carried out at about 250°C to 500°C, preferably about 260°C to 400°C. If the heat treatment temperature is too high, the coating element diffuses into the lithium transition metal oxide and may adversely affect the internal structure of the positive electrode active material. If the heat treatment temperature is too low, the coating element does not diffuse into the lithium transition metal oxide and exists only in the coating layer. The effect of improving structural stability may be reduced.

The coating element is diffused into the shell portion of the lithium transition metal oxide by the heat treatment to form a surface doped portion in which the coating element is mixed, and the surface doped portion is present in a region within a distance of 30 nm from the outermost surface of the positive electrode active material. is formed

anode

In addition, there is provided a positive electrode for a lithium secondary battery comprising the positive electrode active material according to the present invention. Specifically, the positive electrode for a secondary battery includes a positive electrode current collector, a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material according to the present invention. It provides a positive electrode for a lithium secondary battery.

At this time, since the positive active material is the same as described above, a detailed description will be omitted, and only the remaining components will be described in detail below.

The positive electrode current collector may include a metal having high conductivity, and the positive electrode active material layer is easily adhered, but is not particularly limited as long as it is not reactive in the voltage range of the battery. The positive electrode current collector may be, for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface treated aluminum or stainless steel surface with carbon, nickel, titanium, silver, or the like. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body, and the like.

The positive active material layer may optionally include a conductive material, a binder, and a dispersing agent together with the positive active material, if necessary.

In this case, the positive active material may be included in an amount of 80 to 99% by weight, more specifically, 85 to 98.5% by weight based on the total weight of the positive active material layer. When included in the above content range, it can exhibit excellent capacity characteristics.

The conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it has electronic conductivity without causing chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one type alone or a mixture of two or more types thereof may be used. The conductive material may be included in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

The binder serves to improve adhesion between the positive active material particles and the adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylalcohol, polyacrylonitrile, polymethyl meth acrylate (polymethymethaxrylate), carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene Polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogen is substituted with Li, Na, or Ca, or various copolymers thereof and the like, and any one of them or a mixture of two or more thereof may be used. The binder may be included in an amount of 0.1 to 15% by weight based on the total weight of the positive active material layer.

The dispersant may include an aqueous dispersant or an organic dispersant such as N-methyl-2-pyrrolidone.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the above positive electrode active material. Specifically, the cathode active material and, if necessary, a composition for forming a cathode active material layer prepared by dissolving or dispersing a binder, a conductive material, and a dispersing agent in a solvent is coated on a cathode current collector, followed by drying and rolling. can do.

The solvent may be a solvent generally used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), dimethylformamide (dimethyl formamide, DMF), acetone, or water may be mentioned, and one type alone or a mixture of two or more types thereof may be used. The amount of the solvent used is to dissolve or disperse the positive electrode active material, the conductive material, the binder, and the dispersant in consideration of the application thickness of the slurry and the production yield, and then to have a viscosity that can exhibit excellent thickness uniformity when applied for the production of the positive electrode That's enough.

Also, as another method, the positive electrode may be prepared by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating a film obtained by peeling from the support on the positive electrode current collector.

(secondary battery)

In addition, the present invention can manufacture an electrochemical device including the positive electrode. The electrochemical device may specifically be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is the same as described above, so detailed description is omitted, Hereinafter, only the remaining components will be described in detail.

In addition, the lithium secondary battery may optionally further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

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

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. Carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 3 μm to 500 μm, and similarly to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam body, a nonwoven body, and the like.

The anode active material layer optionally includes a binder and a conductive material together with the anode active material.

As the anode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO _{2 , vanadium oxide, and lithium vanadium oxide;} Alternatively, a composite including the above-mentioned metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and high crystalline carbon includes natural or artificial graphite in amorphous, plate-like, flaky, spherical or fibrous shape, and Kish graphite (Kish). graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.

The anode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the anode active material layer.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1 wt% to 10 wt% based on the total weight of the anode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro roethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

The conductive material is a component for further improving the conductivity of the anode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the anode active material layer. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; A conductive material such as a polyphenylene derivative may be used.

For example, the anode active material layer is prepared by applying and drying a composition for forming an anode active material layer prepared by dissolving or dispersing a cathode active material, and optionally a binder and a conductive material in a solvent, on the anode current collector and drying, or the anode active material layer It can be prepared by casting the composition for forming an active material layer on a separate support, and then laminating a film obtained by peeling it off from the support on a negative electrode current collector.

The anode active material layer is, as an example, a composition for forming an anode active material layer prepared by dissolving or dispersing an anode active material, and optionally a binder and a conductive material in a solvent on an anode current collector and drying, or for forming the anode active material layer It can also be prepared by casting the composition onto a separate support and then laminating a film obtained by peeling it from the support onto a negative electrode current collector.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move, and as long as it is used as a separator in a lithium secondary battery, it can be used without any particular limitation, especially for the movement of ions in the electrolyte It is preferable to have a low resistance to and excellent electrolyte moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and may optionally be used in a single-layer or multi-layer structure.

In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries, and are limited to these. it's not going to be

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

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, carbonate-based solvents such as PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Or sulfolanes and the like may be used. Among them, a carbonate-based solvent is preferable, and a cyclic carbonate (eg, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of increasing the charge/discharge performance of the battery, and a low-viscosity linear carbonate-based compound ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the electrolyte may exhibit excellent performance.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, as an anion of the lithium salt ^{, F -} , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- may be at least one selected from the group consisting of, The lithium salt is, LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) _2. LiCl, LiI, or LiB(C ₂ O ₄ ) _{2 ,} etc. may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, the electrolyte may exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions may move effectively.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as jolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

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

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

The battery module or battery pack is a power tool (Power Tool); electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for any one or more medium and large-sized devices in a system for power storage.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape using a can, a prismatic shape, a pouch type, or a coin type.

The lithium secondary battery according to the present invention may not only be used in a battery cell used as a power source for a small device, but may also be preferably used as a unit cell in a medium or large-sized battery module including a plurality of battery cells.

Examples of the medium-large device include, but are not limited to, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

Hereinafter, examples will be given to specifically describe the present invention. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Example

Example 1

NiSO ₄ , CoSO ₄ , and MnSO ₄ were mixed in distilled water in an amount such that a molar ratio of nickel:cobalt:manganese was 90:5:5 to prepare a solution containing a first transition metal having a concentration of 1.5M.

In addition, NiSO ₄ , CoSO ₄ , MnSO ₄ and Al ₂ O ₃ was mixed in distilled water in an amount such that a molar ratio of nickel:cobalt:manganese:aluminum was 88: 5: 5: 2 to prepare a solution containing a second transition metal having a concentration of 1.5M.

The container containing the first transition metal-containing solution and the container containing the second transition metal-containing solution were respectively connected to a 150L reactor set at 45°C. In addition, 3.0M NaOH solution and 28% NH ₄ OH aqueous solution were prepared and connected to the reactor, respectively.

Then, after adding deionized water to the reactor, nitrogen gas was purged into the reactor at a rate of 0.05 L/min to remove dissolved oxygen in the water and to create a non-oxidizing atmosphere in the reactor. After 3.0M NaOH was added, the mixture was stirred at a stirring speed of 500 rpm, and the pH in the reactor was maintained at pH 12.

Thereafter, the first transition metal-containing solution was introduced into the reactor at a rate of 180 _{mL/hr, and an aqueous NaOH solution was added at a rate of 360 mL/hr and an NH 4} OH aqueous solution was added at a rate of 30 mL/hr, respectively, and the co-precipitation reaction was performed for 15 hours. A core portion represented by _0.9 Co _0.05 Mn _0.05 (OH) _{2 was formed.}

Thereafter, the input of the first transition metal-containing solution is stopped, the second transition metal-containing solution is added at a rate of 180 _{mL/hr, and NaOH aqueous solution is added at a rate of 360 mL/hr and NH 4} OH aqueous solution is added at a rate of 30 mL/hr, respectively. A cathode active material precursor having a core-shell structure was prepared by growing a compound represented by _{Ni 0.88} Co _0.05 Mn _0.05 Al _0.02 (OH) ₂ on the surface of the core part by co-precipitation reaction for 0.5 hours.

The cathode active material precursor and LiOH were mixed so that the molar ratio of Li:transition metal was 1.05:1, and _{calcined at 700° C. for 10 hours in an O 2} atmosphere to prepare a lithium transition metal oxide having a core-shell structure.

Then, 0.5 parts by weight of boric acid, a coating raw material, is mixed with respect to 100 parts by weight of the lithium transition metal oxide having the core-shell structure, and then heat-treated at 280° C. for 5 hours to form a core-shell structure with a coating layer on the surface of the positive electrode active material was prepared.

Example 2

A cathode active material was prepared in the same manner as in Example 1, except that the core-shell structured cathode active material was mixed with boric acid, a coating raw material, and then heat-treated at 350° C. for 5 hours.

Comparative Example 1

A cathode active material was prepared in the same manner as in Example 1, except that a separate coating layer was not formed on the surface of the cathode active material having a core-shell structure prepared in Example 1.

Comparative Example 2

A cathode active material was prepared in the same manner as in Example 1, except that the core-shell structured cathode active material was mixed with boric acid, a coating raw material, and then heat-treated at 200° C. for 5 hours.

Comparative Example 3

A cathode active material was prepared in the same manner as in Example 1, except that the core-shell structured cathode active material was mixed with boric acid, which is a coating raw material, and then heat-treated at 430° C. for 5 hours.

Experimental Example 1: Analysis of the content of coating elements in the shell of the cathode active material

The positive active material prepared in Examples 1-2 and Comparative Examples 2-3 through a depth profile using X-ray photoelectron spectroscopy (XPS) (Thermo Scientific) of the positive active material The doping content of the coating element in the shell part of the was confirmed, and it is shown in Table 1 below.

Specifically, after introducing the positive active material particles prepared in Examples 1 to 2 and Comparative Examples 2 to 3 into the chamber in a vacuum state, the positive electrode active material particles are etched using an Ar beam, and the positive electrode according to the etching time The content of the coating element B doped to the shell part of the active material was confirmed, and it is shown in Table 1 below. At this time, the surface of the cathode active material particles was etched by 1 nm per 10 seconds of etching time.

Etching time (s) Coating element content (at%) Example 1 Example 2 Comparative Example 2 Comparative Example 3 0 4.1 3.7 4.8 2.2 50 2.5 2.8 1.1 1.8 100 1.4 2.2 0 2.7 300 0.2 1.6 0 2.2 500 0 0 0 1.5 700 0 0 0 0 900 0 0 0 0 1,000 0 0 0 0

From [Table 1], in the case of Examples 1 and 2, it can be confirmed that the coating element is present from the outermost surface of the positive electrode active material to a depth within 30 nm. On the other hand, in Comparative Example 2, the coating element was present only from the outermost surface of the cathode active material corresponding to the coating layer to about 5 nm, and the coating element was not detected in the lithium transition metal oxide, and in Comparative Example 3, from the outermost surface Coating elements were detected even at depths greater than 30 nm.

Experimental Example 2: Surface analysis of positive electrode active material

The cross-section of the positive active material prepared in Example 1 was cut and the cross-sectional shape was observed using TEM (FE-STEM, TITAN G2 80-100 ChemiSTEM), and the positive electrode through a small angle diffraction pattern (SADP) A crystalline phase was confirmed in the cross section of the active material.

1 and 2 are cross-sectional TEM images of the positive active material of Example 1 is shown. Specifically, FIG. 1 is a TEM photograph of a cross section of the coating layer and the shell part of the cathode active material prepared in Example 1, (b) is a 10 times magnification of (a), and FIG. 2 is Example 1 As a TEM photograph showing the component distribution in the coating layer and the shell part of the cathode active material prepared by It shows the distribution of Ni in the indicated box area.

As shown in FIG. 1 , it can be seen that the cathode active material of Example 1 had a coating layer having a thickness of 4 to 5 nm formed on the surface, and some of the coating element B was doped into the lithium transition metal oxide.

In addition, it can be confirmed that the coating element B is doped to a depth of 20 to 25 nm from the outermost surface of the positive electrode active material through FIG. It can be confirmed that it is formed in a region at a distance of 30 nm or less from the outermost surface.

Experimental Example 3: Evaluation of lifespan characteristics

The positive electrode active material prepared in Examples 1 to 2 and Comparative Examples 1 to 3, respectively, and a conductive material and a binder were mixed in a N-methyl-2-pyrrolidone (NMP) solvent in a weight ratio of 95: 2: 3 to obtain a positive electrode. A slurry was prepared. The positive electrode slurry was applied to one surface of an aluminum current collector, dried and rolled to prepare a positive electrode.

Then, the negative electrode active material (graphite), the conductive material and the binder were _{mixed in water (H 2} O) in a weight ratio of 95:1:4 to prepare a negative electrode slurry. The negative electrode slurry was applied to one surface of a copper current collector, dried and rolled to prepare a negative electrode.

An electrode assembly was prepared by interposing a separator between the positive electrode and the negative electrode, and then placed inside a battery case, and then an electrolyte was injected to prepare a lithium secondary battery. At this time, as the electrolyte, an electrolyte in which 2 wt% of vinylene carbonate (VC) and 1M of LiPF ₆ were dissolved in an organic solvent in which ethylene carbonate: ethylmethyl carbonate: diethyl carbonate was mixed in a volume ratio of 3:3:4 was used.

Then, each of the secondary batteries was charged to 4.2V at a constant current of 0.3C at 45°C. Then, discharge was performed to 2.5V with a constant current of 0.3C. After the charging and discharging behavior was 1 cycle, this cycle was repeated 100 times, and then the lifespan characteristics of the lithium secondary batteries according to Examples 1 and 2 and Comparative Examples 1 to 3 were measured. shown in

Capacity retention rate (%) Example 1 92 Example 2 90 Comparative Example 1 49 Comparative Example 2 77 Comparative Example 3 87

As shown in Tables 2 and 3, the secondary batteries including the positive electrode active materials of Examples 1 and 2 have excellent lifespan characteristics at high temperatures compared to the secondary batteries of Comparative Examples 1 to 3.

Claims (12)

A core portion comprising a first lithium transition metal oxide; And a core-shell structure lithium transition metal oxide comprising a; and a shell portion formed on the core portion and comprising a second lithium transition metal oxide having a composition different from that of the first lithium transition metal oxide;
A cathode active material comprising a coating layer formed on the surface of the lithium transition metal oxide having the core-shell structure and comprising at least one coating element selected from the group consisting of Al, B, W, Nb and Co,
The first lithium transition metal oxide and the second lithium transition metal oxide each independently have a composition represented by the following [Formula 1],
The shell part includes a surface doping part in which the coating element is mixed,
The positive electrode active material that the surface doping portion is present in a region at a distance of 30 nm or less from the outermost surface of the positive electrode active material.
[Formula 1]
Li _1+a Ni _x Co _y M ¹ _z M ² _w O ₂
In Formula 1,
M ¹ is at least one of Mn and Al,
M ² is at least one selected from the group consisting of Al, B, W, Nb and Co,
0≤a≤0.3, 0.5≤x<1, 0<y<0.5, 0<z<0.5, 0≤w≤0.1.
According to claim 1,
The first lithium transition metal oxide is a cathode active material having a composition represented by the following [Formula 1-1].
[Formula 1-1]
Li _1+a1 Ni _x1 Co _y1 M ¹ _z1 M ² _w1 O ₂
In Formula 1-1,
Wherein M ¹ is at least one of Mn and Al,
M ² is at least one selected from the group consisting of Al, B, W, Nb and Co,
0≤a1≤0.3, 0.8≤x1<1, 0<y1<0.2, 0<z1<0.2, 0≤w1≤0.1.
According to claim 1,
At least one of the first lithium transition metal oxide and the second lithium transition metal oxide is a cathode active material having a composition represented by the following [Formula 1-2].
[Formula 1-2]
Li _1+a2 Ni _x2 Co _y2 Mn _z2 Al _w2 O ₂
In Formula 1-2,
0≤a2≤0.3, 0.5≤x2<1, 0<y2<0.5, 0<z2<0.5, 0<w2≤0.1.
According to claim 1,
The first lithium transition metal oxide has a composition represented by the following [Formula 1-3],
The second lithium transition metal oxide is a cathode active material having a composition represented by the following [Formula 1-4].
[Formula 1-3]
Li _1+a3 Ni _x3 Co _y3 Mn _z3 O ₂
In Formula 1-3,
0≤a3≤0.3, 0.8≤x3<1, 0<y3<0.2, 0<z3<0.2.

[Formula 1-4]
Li _1+a4 Ni _x4 Co _y4 Mn _z4 Al _w4 O ₂
In Formula 1-4,
0≤a4≤0.3, 0.8≤x4<1, 0<y4<0.2, 0<z4<0.2, 0<w4≤0.1.
According to claim 1,
The coating element is a cathode active material that is included in an amount of 0.01 to 2 parts by weight based on 100 parts by weight of the lithium transition metal oxide having the core-shell structure.
According to claim 1,
The thickness of the coating layer is 1 nm to 30 nm of the cathode active material.
According to claim 1,
The shell portion, the cathode active material comprising the coating element in an amount of 0.1 atm% to 5 atm% based on the total number of transition metal atoms included in the shell portion.
A core portion comprising a first lithium transition metal oxide; and a shell portion formed on the core portion and including a second lithium transition metal oxide having a composition different from that of the first lithium transition metal oxide; and
Mixing the lithium transition metal oxide and a coating raw material containing at least one coating element selected from the group consisting of Al, B, W, Nb and Co, and heat-treating a method for producing a cathode active material,
The first lithium transition metal oxide and the second lithium transition metal oxide each independently have a composition represented by the following [Formula 1],
The coating element is diffused into the shell portion by the heat treatment to form a surface doped portion in which the coating element is mixed, and the surface doped portion is present in a region at a distance of 30 nm or less from the outermost surface of the positive electrode active material. manufacturing method.
[Formula 1]
Li _1+a Ni _x Co _y M ¹ _z M ² _w O ₂
In Formula 1,
M ¹ is at least one of Mn and Al,
M ² is at least one selected from the group consisting of Al, B, W, Nb and Co,
0≤a≤0.3, 0.5≤x<1, 0<y<0.5, 0<z<0.5, 0≤w≤0.1.
9. The method of claim 8,
Preparing the lithium transition metal oxide of the core-shell structure,
preparing a first transition metal-containing solution and a second transition metal-containing solution having different transition metal compositions;
forming a precursor core by adding the first transition metal-containing solution, an ammonium cation complex forming agent, and a basic compound to a reactor and performing a co-precipitation reaction;
Preparing a core-shell structure precursor by introducing the second transition metal-containing solution, an ammonium cation complex forming agent, and a basic compound into a reactor including the precursor core and performing a co-precipitation reaction to form a shell on the precursor core ; and
The method of manufacturing a cathode active material comprising the step of mixing the precursor of the core-shell structure and the lithium raw material and then sintering.
9. The method of claim 8,
The heat treatment is a method of manufacturing a cathode active material that is performed at a temperature of 260 °C to 400 °C.
A positive electrode for a lithium secondary battery comprising the positive active material according to any one of claims 1 to 7.
A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 11 .

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