KR20220079430A - Positive active material and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a positive electrode active material and a lithium secondary battery including the same, and more specifically, to a lithium-manganese-based oxide in excess of lithium, which is a solid solution of a phase belonging to the C2/m space group and a phase belonging to the R3-m space group, Stability caused by excess lithium and manganese in the lithium manganese oxide by the existence of a region in which an abundance ratio of a phase belonging to the C2/m space group and a phase belonging to the R3-m space group is different in the lithium manganese oxide It relates to a positive electrode active material in which deterioration is alleviated and/or prevented, and a lithium secondary battery including the same.

Description

A cathode active material and a lithium secondary battery comprising the same

The present invention relates to a positive electrode active material and a lithium secondary battery including the same, and more specifically, to a lithium-manganese-based oxide in excess of lithium, which is a solid solution of a phase belonging to the C2/m space group and a phase belonging to the R3-m space group, Stability caused by excess lithium and manganese in the lithium manganese oxide by the existence of a region in which an abundance ratio of a phase belonging to the C2/m space group and a phase belonging to the R3-m space group is different in the lithium manganese oxide It relates to a positive electrode active material in which deterioration is alleviated and/or prevented, and a lithium secondary battery including the same.

A battery stores electric power by using a material capable of electrochemical reaction between the anode and the cathode. A representative example of such a battery is a lithium secondary battery that stores electrical energy by a difference in chemical potential when lithium ions are intercalated/deintercalated in a positive electrode and a negative electrode.

The lithium secondary battery is manufactured by using a material capable of reversible intercalation/deintercalation of lithium ions as a positive electrode and a negative electrode active material, and filling an organic electrolyte solution or a polymer electrolyte solution between the positive electrode and the negative electrode.

A lithium composite oxide is used as a cathode active material for a lithium secondary battery, for example, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiMnO ₂ or Korean Patent Application Laid-Open No. 10-2015-0069334 (published on June 23, 2015) ), complex oxides in which Ni, Co, Mn, or Al are complexed are being studied.

Among the cathode active materials, LiCoO ₂ is used the most because of its excellent lifespan characteristics and charge/discharge efficiency, but it is expensive due to the resource limitation of cobalt used as a raw material, so it has a limitation in price competitiveness.

LiMnO ₂ , LiMn ₂ O ₄ Lithium manganese oxide has advantages of excellent thermal stability and low price, but has problems in that it has a small capacity and poor high temperature characteristics. In addition, although the LiNiO ₂ -based positive electrode active material exhibits high discharge capacity battery characteristics, it is difficult to synthesize due to a cation mixing problem between Li and a transition metal, and thus has a large problem in rate characteristics.

In addition, a large amount of Li by-products are generated according to the degree of intensification of the cation mixing, and most of these Li by-products are composed of LiOH and Li ₂ CO ₃ compounds. It causes gas generation due to charging and discharging after manufacturing. Residual Li ₂ CO ₃ increases cell swelling, which not only reduces the cycle, but also causes the battery to swell.

Various candidate materials are being discussed to compensate for the shortcomings of the existing cathode active materials.

As an example, research is being conducted to use a lithium manganese-based oxide in excess of lithium in excess of the sum of the transition metal content and Mn content in the transition metal as a positive electrode active material for a lithium secondary battery. This lithium-rich lithium manganese-based oxide is also referred to as a lithium-overlithiated layered oxide (OLO).

Although the OLO has the advantage that it can theoretically exhibit a high capacity under a high voltage operating environment, in fact, it has relatively low electrical conductivity due to the excessive amount of Mn in the oxide. It has the disadvantage of low capability rate). As such, when the rate characteristic is low, there is a problem in that the charge/discharge capacity and lifespan efficiency (cycle capacity retention rate; capacity retentio) of the lithium secondary battery are deteriorated during cycling.

In addition, reduction in charge/discharge capacity or voltage decay during cycling of a lithium secondary battery using OLO may be induced by a phase transition according to movement of a transition metal among lithium manganese oxides. For example, when a transition metal among lithium manganese oxides having a layered crystal structure moves in an unintended direction to induce a phase transition, a spinel or similar crystal structure may occur entirely and/or partially in the lithium manganese oxide. .

In order to solve the above-mentioned problems, there are attempts to improve the problems of OLO through structural improvement and surface modification of particles, such as adjusting the particle size of OLO or coating the surface of OLO, but it does not reach the level of commercialization. .

Korean Patent Publication No. 10-2015-0069334 (published on June 23, 2015)

In the lithium secondary battery market, while the growth of lithium secondary batteries for electric vehicles is playing a leading role in the market, the demand for positive electrode active materials used in lithium secondary batteries is also constantly changing.

For example, in the prior art, lithium secondary batteries using LFP have been mainly used from the viewpoint of securing safety, etc., but recently, the use of nickel-based lithium composite oxides having a large energy capacity per weight compared to LFP has been expanding.

In addition, most nickel-based lithium composite oxides recently used as positive electrode active materials for high-capacity lithium secondary batteries include ternary metal elements such as nickel, cobalt and manganese or nickel, cobalt, and aluminum. Among them, cobalt Due to the unstable supply and demand and excessively expensive compared to other raw materials, there is a need for a cathode active material with a new composition capable of reducing the cobalt content or excluding cobalt.

From this point of view, lithium manganese oxide in excess of lithium can meet the market expectations described above, but the electrochemical properties or stability of lithium manganese oxide are insufficient to replace the commercially available NCM or NCA type positive electrode active material. can do

However, when compared to other commercially available positive electrode active materials, the lithium manganese oxide in excess of lithium has disadvantages in terms of electrochemical properties and/or stability. If possible, it was confirmed by the present inventors that lithium manganese-based oxide in excess of lithium can also exhibit electrochemical properties and stability at a level that can be commercialized.

Accordingly, the present invention provides a positive electrode active material comprising an excess lithium-manganese oxide as a solid solution of a phase belonging to the C2/m space group and a phase belonging to the R3-m space group, and among the lithium manganese oxides, the C2/m space group A positive active material in which stability degradation caused by excess lithium and manganese in the lithium manganese oxide is alleviated and/or prevented by the presence of a region in which the ratio of the abundance of the phase belonging to the phase and the phase belonging to the R3-m space group is different intended to provide

In addition, the present invention is a positive electrode active material comprising an excess lithium manganese oxide, which is a solid solution of a phase belonging to the C2/m space group and a phase belonging to the R3-m space group, in the region where the phase belonging to the R3-m space group exists. An object of the present invention is to provide a positive electrode active material capable of improving the low discharge capacity and rate characteristics of the existing lithium-manganese oxide in excess of lithium by allowing the concentration of Ni to exist within a predetermined range.

In addition, an object of the present invention is to provide a lithium secondary battery having improved low rate characteristics of the existing OLO by using a positive electrode including a positive electrode active material as defined herein.

According to one aspect of the present invention for solving the above-described technical problem, as a positive active material comprising an excess lithium lithium manganese oxide containing at least lithium, nickel and manganese, C2 / m space group of the lithium manganese oxide A positive active material in which a phase belonging to and a phase belonging to the R3-m space group coexist, and a region in which the abundance ratio of a phase belonging to the C2/m space group and a phase belonging to the R3-m space group of the lithium manganese oxide is different. provided

In one embodiment, the concentration of the metal element in the lithium manganese oxide may satisfy Equation 1 below.

positive electrode active material.

[Equation 1]

0.24 ≤ M ² /M ¹ ≤ 0.55

here,

M ¹ is the number of moles of all metal elements (excluding lithium) in the lithium manganese oxide,

M ² is the number of moles of nickel based on all metal elements (excluding lithium) among the lithium manganese oxide.

As the content of nickel in the metal element (excluding lithium) in the lithium manganese oxide satisfies Equation 1, the discharge capacity and rate characteristics lowered by the excess Mn in the lithium manganese oxide are at a commercially available level It is possible to improve with

The lithium manganese oxide may be a core-shell particle including a core and a shell covering at least a portion of a surface of the core. In this case, the core and the shell are distinguished only to refer to regions in which the abundance ratio of the phase belonging to the C2/m space group and the phase belonging to the R3-m space group of the lithium manganese oxide is different. That is, even when the lithium manganese oxide is a core-shell particle, it should be understood that the core and the shell form a single solid solution.

When the lithium manganese oxide is a core-shell particle, the phase belonging to the C2/m space group and the phase belonging to the R3-m space group coexist in the core, and the phase belonging to the C2/m space group in the shell The ratio of the phases belonging to the R3-m space group to the phases may be greater than the ratio of the phases belonging to the R3-m space group to the phases belonging to the C2/m space group in the core.

In this case, the concentration of the metal element in the shell may satisfy Equation 3 below.

[Equation 3]

0.24 ≤ M ⁴ /M ³ ≤ 0.75

here,

M ³ is the number of moles of all metal elements (excluding lithium) in the shell,

M ⁴ is the number of moles of nickel based on all metallic elements (excluding lithium) in the shell.

At this time, the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2/m space group among the lithium manganese oxide has a gradient that increases from the core to the shell, so that in the lithium manganese oxide It is possible to prevent damage to particles during charging and discharging by reducing abrupt changes in the crystal structure.

The lithium manganese oxide may be represented by Formula 1 below.

[Formula 1]

rLi ₂ MnO ₃ ·(1-r)Li _a Ni _x Co _y Mn _z M1 _1-(x+y+z) O ₂

here,

M1 is Mo, Nb, Fe, Cr, V, Cu, Zn, Sn, Mg, Ru, Al, Ti, Zr, B, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si and at least one selected from Bi,

0<r≤0.8, 0<a≤1, 0 < x≤1, 0≤y<1, 0 < z<1, and 0<x+y+z≤1.

As shown in Formula 1, the lithium manganese oxide as defined herein is a solid solution in which a phase belonging to the C2/m space group and a phase belonging to the R3-m space group coexist in a single particle.

In this case, a single particle means "a particle of a non-agglomerated form including a single primary particle", "a particle formed by agglomeration of a relatively small number of primary particles" or "a plurality of (tens to hundreds or more) It may mean "particles formed by agglomeration of primary particles".

The phase belonging to the C2/m space group in the solid solution represented by Formula 1 is caused by Li ₂ MnO ₃ , and the phase belonging to the R3-m space group is Li _a Ni _x Co _y Mn _z M1 _{1-(x+y+z )} is caused by O ₂ .

In addition, according to another aspect of the present invention, a positive electrode including the above-described positive electrode active material is provided.

In addition, according to another aspect of the present invention, a lithium secondary battery using the above-described positive electrode is provided.

According to the present invention, it is possible to improve the limitations of the existing lithium-excess lithium manganese-based oxide, which has several disadvantages in terms of electrochemical properties and/or stability when compared with other commercially available positive electrode active materials.

First, the lithium manganese oxide contained in the positive electrode active material according to the present invention is a lithium manganese oxide in excess of lithium, which is a solid solution of a phase belonging to the C2/m space group and a phase belonging to the R3-m space group.

As described above, the lithium manganese-based oxide containing lithium and manganese in excess may exhibit a high capacity under a high voltage operating environment. However, such lithium manganese oxide has a disadvantage in that the discharge capacity and rate characteristics are low due to excess lithium and manganese among oxides, but, like the positive electrode active material according to the present invention, it belongs to the C2/m space group. When the proportion of the phase belonging to the R3-m space group is varied for each region, the effect of improving the discharge capacity and rate characteristics is exhibited.

In particular, when the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2/m space group in the surface portion (which may be referred to as a core) of the lithium manganese oxide is large, (mainly the C2/m space group) The low electrical conductivity of lithium manganese oxide is improved by alleviating the charge-transfer and/or diffusion of Li ions on the particle surface (which is highly likely to be caused by a phase belonging to the It is possible to improve with

In addition to the above-described effects, the specific effects of the present invention will be described together while describing specific details for carrying out the invention below.

1 shows the TEM analysis result of the lithium manganese-based oxide contained in the positive electrode active material according to Example 4. Referring to FIG. 1 shows a 50 nm-scale TEM image and a 5 nm-scale TEM image of an enlarged area indicated in the 50 nm-scale TEM image, and the crystal structure confirmed through FFT conversion for the A and B regions of the 5 nm-scale TEM image. was shown.
2 is a line scanning the EDX mapping result of the cross-sectional TEM image of the lithium manganese oxide included in the positive active material according to Example 4 to confirm the change in the concentration (at%) of nickel from the core to the shell of the lithium manganese oxide. It is a sum spectrum. Region A indicated in the line sum spectrum of FIG. 2 corresponds to region A of FIG. 1 .

In order to better understand the present invention, certain terms are defined herein for convenience. Unless defined otherwise herein, scientific and technical terms used herein shall have the meanings commonly understood by one of ordinary skill in the art. Also, unless the context specifically dictates otherwise, it is to be understood that a term in the singular includes its plural form as well, and a term in the plural form also includes its singular form.

Hereinafter, the positive electrode active material including at least lithium, nickel, manganese, and an excess lithium manganese-based oxide containing at least lithium, nickel, manganese, and a doping metal and a lithium secondary battery including the positive electrode active material according to the present invention will be described in more detail.

cathode active material

According to one aspect of the present invention, there is provided a positive electrode active material including at least lithium, nickel, manganese, and a lithium manganese-based oxide in excess of lithium including a doping metal. The lithium manganese oxide is a composite metal oxide capable of intercalation and deintercalation of lithium ions.

The lithium manganese-based oxide included in the positive active material as defined herein may be a secondary particle including at least one primary particle.

Here, "secondary particles including at least one primary particle" is intended to include both "particles formed by agglomeration of a plurality of primary particles" or "non-agglomerated particles including a single primary particle". will have to be interpreted.

The primary particle and the secondary particle may each independently have a rod shape, an oval shape, and/or an irregular shape.

When the average long axis length is used as an index indicating the sizes of the primary particles and the secondary particles, the average long axis length of the primary particles constituting the lithium manganese oxide may be 0.1 μm to 5 μm, and the secondary The average long axis length of the particles may be 1 μm to 30 μm. The average long axis length of the secondary particles may vary depending on the number of the primary particles constituting the secondary particles, and particles having various average long axis lengths may be included in the positive active material.

When the lithium manganese oxide is "a particle in a non-agglomerated form including a single primary particle" or "a particle formed by agglomeration of a relatively small number of primary particles," "Ratio including a single primary particle" The size (average particle diameter) of primary particles included in “aggregated particles” or “particles formed by agglomeration of a relatively small number of primary particles” is “secondary particles formed by agglomeration of dozens to hundreds or more primary particles” It may be larger than the primary particles (average particle diameter) included in "particles".

As such, lithium manganese oxide, which is “a particle in a non-agglomerated form including a single primary particle” or “a particle formed by agglomeration of a relatively small number of primary particles,” is generally “tens to hundreds or more. It requires stronger heat treatment conditions (high heat treatment temperature/long time heat treatment) compared to the case of manufacturing "secondary particles formed by agglomeration of primary particles." For example, it is known that, when heat treatment is performed at a relatively high temperature (800° C. or higher) for a long time, particle growth (crystal growth) is promoted to obtain a cathode active material having a single particle size and a low aggregation degree at the same time.

For example, when the lithium manganese oxide is "particles in a non-agglomerated form including a single primary particle" or "particles formed by agglomeration of a relatively small number of primary particles," the average of the primary particles The major axis length may be in the range of 0.5 μm to 20 μm. On the other hand, when the lithium manganese oxide is "particles formed by aggregation of a plurality of (tens to hundreds or more) primary particles," the average long axis length of the primary particles may be in the range of 0.1 μm to 5 μm. have.

In addition, the primary particles may include at least one crystallite (crystallite). That is, the primary particle may be formed as a single crystallite or may exist as a particle including a plurality of crystallites.

The lithium manganese oxide as defined herein is a composite metal oxide containing lithium and manganese in excess, and a phase belonging to the C2/m space group and a phase belonging to the R3-m space group coexist in the lithium manganese oxide. That is, the lithium manganese oxide is a solid solution of a phase belonging to the C2/m space group and a phase belonging to the R3-m space group.

Herein, the solid solution means that the phase belonging to the C2/m space group and the phase belonging to the R3-m space group exist as single particles in the lithium manganese oxide.

In this case, a single particle means "a particle of a non-agglomerated form including a single primary particle", "a particle formed by agglomeration of a relatively small number of primary particles" or "a plurality of (tens to hundreds or more) It may mean "particles formed by agglomeration of primary particles".

Herein, the solid solution does not mean a state in which the phase belonging to the C2/m space group and the phase belonging to the R3-m space group present in the lithium manganese oxide are physically and/or chemically bonded or attached to each other.

For example, by mixing a metal oxide having a phase belonging to the C2/m space group and a metal oxide having a phase belonging to the R3-m space group, C2 coated with a metal oxide having a phase belonging to the R3-m space group Metal oxides with phases belonging to the /m space group do not correspond to solid solutions.

Meanwhile, in the lithium manganese oxide, a phase belonging to the C2/m space group and a phase belonging to the R3-m space group coexist, but in the lithium manganese oxide, a phase belonging to the C2/m space group and the R3-m space group Regions with different proportions of the phases to which they belong may exist.

As such, when the ratio of the presence of the phase belonging to the C2/m space group and the phase belonging to the R3-m space group among the lithium manganese oxide is different for each region, the discharge capacity and rate characteristics of the cathode active material including the lithium manganese oxide This improving effect can be exhibited.

In addition, the concentration of the metal element in the lithium manganese oxide may satisfy Equation 1 below.

positive electrode active material.

[Equation 1]

0.24 ≤ M ² /M ¹ ≤ 0.55

here,

M ¹ is the number of moles of all metal elements (excluding lithium) in the lithium manganese oxide,

M ² is the number of moles of nickel based on all metal elements (excluding lithium) among the lithium manganese oxide.

When M ² /M ¹ in Equation 1 exceeds 0.55, the content of Ni in the lithium manganese oxide is excessively increased, so that cation mixing with Li may occur, and the lithium manganese oxide is OLO It can be difficult to show the characteristics as

As described above, since the lithium manganese oxide according to the present application contains an excess of lithium, when the content of Ni in the lithium manganese oxide increases, cation mixing becomes severe and LiOH and Li ₂ CO in the lithium manganese oxide The amount of lithium impurities such as ₃ and the like may be increased. The lithium impurity is a major cause of gelation of the paste when manufacturing the positive electrode paste using the positive electrode active material or the swelling of the cell during charging and discharging after the positive electrode is manufactured.

On the other hand, when M ² /M ¹ in Equation 1 is less than 0.24, the charge-transfer and/or diffusion of Li ions lowered by excess manganese as the content of Ni in the lithium manganese-based oxide is insufficient is improved. it can be difficult

That is, as the content of nickel in the lithium manganese oxide satisfies Equation 1, it is possible to improve the discharge capacity and rate characteristics, etc., which are lowered by the excess Mn in the lithium manganese oxide, to a commercially available level.

In addition, since nickel in the lithium manganese oxide is present in the phase belonging to the R3-m space group and does not exist in the phase belonging to the C2/m space group, the content of nickel in the lithium manganese oxide is as the following formula 2 can be expressed

[Equation 2]

0.40 ≤ M ^2' /M ^1' ≤ 0.70

Here, M ^1' is the number of moles of all metal elements (excluding lithium) in the phase belonging to the R3-m space group,

M ^2' is the number of moles of nickel based on all metal elements (excluding lithium) in the phase belonging to the R3-m space group.

In Equation 2, when M ^2' /M ^1' exceeds 0.70, the content of Ni in the phase belonging to the R3-m space group is excessively increased, and cation mixing with Li may occur. In Equation 1, when M ^2' /M ^1' is less than 0.40, the content of Ni in the phase belonging to the R3-m space group becomes insufficient, and as manganese is excessively present, charge-transfer and/or diffusion of Li ions becomes difficult. may be lowered.

The lithium manganese oxide may be a core-shell particle including a core and a shell covering at least a portion of a surface of the core.

In this case, the core and the shell are distinguished only to refer to regions in which the abundance ratio of the phase belonging to the C2/m space group and the phase belonging to the R3-m space group of the lithium manganese oxide is different. That is, even when the lithium manganese oxide is a core-shell particle, it should be understood that the core and the shell form a single solid solution.

At this time, the shell (or surface part) and the core (or central part) of the particle are distinguished by the concentration of any metal element present in the corresponding region, or the ratio of the phase (crystal structure) present in the corresponding region as will be described later. can be distinguished as

The shell may occupy at least a portion of the surface of the core. That is, the shell may exist partially on the surface of the core, or may occupy the entire surface of the core. On the other hand, when the radius of the core-shell particle is r, the thickness of the shell may be 0.001r to 0.9r, but is not limited thereto, and as described above, the core and the shell are any metal element. It will be distinguished by the concentration of , or as the proportion of phases (crystal structures) present in the region, as will be described later.

In an embodiment, a region in which a phase belonging to the R3-m space group among the lithium manganese oxide is predominantly present may exist. That is, the abundance ratio of the phase belonging to the R3-m space group in the region where the phase belonging to the C2/m space group and the phase belonging to the R3-m space group coexist in the lithium manganese oxide is C2/m in the lithium manganese oxide When it is greater than the proportion of the phase belonging to the space group, the region may be defined as a region in which the phase belonging to the R3-m space group predominantly exists.

For example, when the lithium manganese oxide is a core-shell particle, a phase belonging to the C2/m space group and a phase belonging to the R3-m space group coexist in the core and the shell, but the shell in the core The ratio of the phase belonging to the R3-m space group to the phase belonging to the C2/m space group within the shell may be different from the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2/m space group in the shell. have. In this case, a phase belonging to the R3-m space group may predominantly exist in any one region of the core and the shell.

In addition, when the phase belonging to the C2/m space group and the phase belonging to the R3-m space group coexist in the core and the shell of the lithium manganese oxide, compared to the phase belonging to the C2/m space group in the shell Preferably, the ratio of the phases belonging to the R3-m space group is greater than the ratio of the phases belonging to the R3-m space group to the phases belonging to the C2/m space group in the core. The ratio of the phase belonging to the R3-m space group to the phase belonging to the C2/m space group in the core and the shell may be confirmed through the content of Ni in the core and the shell.

In another embodiment, when the lithium manganese oxide is a core-shell particle, a phase belonging to the C2/m space group and a phase belonging to the R3-m space group coexist in the core, but in the shell, the Only phases belonging to the R3-m space group can exist.

In the core-shell particles according to various embodiments described above, the concentration of the metal element in the shell may satisfy Equation 3 below.

[Equation 3]

0.24 ≤ M ⁴ /M ³ ≤ 0.75

here,

M ³ is the number of moles of all metal elements (excluding lithium) in the shell,

M ⁴ is the number of moles of nickel based on all metallic elements (excluding lithium) in the shell.

In addition, since nickel in the lithium manganese oxide exists in a phase belonging to the R3-m space group and does not exist in a phase belonging to the C2/m space group, the content of nickel in the shell can be expressed as Equation 4 below have.

[Equation 4]

0.40 ≤ M ^4' /M ^3' ≤ 0.75

where M ^3' is the number of moles of all metal elements (excluding lithium) in the phase belonging to the R3-m space group in the shell,

M ^4' is the number of moles of nickel based on all metallic elements (excluding lithium) in the phase belonging to the R3-m space group in the shell.

In Equation 3, when M ⁴ /M ³ or M ^4' /M ^3' exceeds 0.75, the content of Ni in the phase belonging to the R3-m space group is excessively increased, resulting in cation mixing with Li may occur, and when M ⁴ /M ³ in Equation 3 is less than 0.24 or M ^{4 '} /M ^3' in Equation 4 is less than 0.40, the content of Ni in the phase belonging to the R3-m space group is insufficient, and as manganese is excessively present, charge-transfer and/or diffusion of Li ions may be reduced.

In the case of the core-shell particles according to the various embodiments described above, as the phase belonging to the C2/m space group and the phase belonging to the R3-m space group coexist in the core of the lithium manganese oxide, the C2/m space group A phase belonging to the R3-m space group may partially offset the instability of the phase belonging to

In addition, since the phase belonging to the R3-m space group is predominantly present in the shell of the lithium manganese oxide, the particle surface with a high possibility of being mainly caused by a phase belonging to the C2/m space group unlike the conventional lithium manganese oxide It is possible to relax the charge-transfer and/or diffusion of Li ions in

In addition, it is well known that in the case of a lithium-excess lithium manganese-based oxide containing an excess of Mn, the electrical conductivity is lower than that of NCM or NCA containing an excess of LCO or Ni. In addition, in general NCM, there is a problem in that the higher the Mn content, the lower the electrical conductivity.

Various reactions may occur on the surface of the cathode active material. As the content of Mn in the cathode active material increases, the charge-transfer and/or diffusion of Li ions on the surface is hindered, and this phenomenon is reduced in surface kinetic or reaction kinetic of the surface. can be referred to as

In addition, a ratio of the phase belonging to the R3-m space group to the phase belonging to the C2/m space group among the lithium manganese oxide may have a gradient that increases from the core toward the shell.

As a gradient is formed in which the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2/m space group increases from the core toward the shell, a sharp change in the crystal structure between the core and the shell can be reduced. and a phase belonging to the C2/m space group and a phase belonging to the R3-m space group among the lithium manganese oxide may stably form a solid solution.

If there is an abrupt change in the phase belonging to the C2/m space group and the phase belonging to the R3-m space group among the lithium manganese oxide, the transition metal in the lithium manganese oxide moves in an unintended direction during cycling Phase transitions (changes in crystal structure) may occur.

As described above, the surface kinetics of the lithium manganese oxide can be improved by ensuring that the region in which the phase belonging to the R3-m space group exists in the core and the concentration of the metal element in the shell satisfy Equations 1 to 4 described above. can

The lithium manganese-based oxide as defined herein may be represented by Formula 1 below.

[Formula 1]

rLi ₂ MnO ₃ ·(1-r)Li _a Ni _x Co _y Mn _z M1 _1-(x+y+z) O ₂

here,

M1 is Mo, Nb, Fe, Cr, V, Cu, Zn, Sn, Mg, Ru, Al, Ti, Zr, B, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si and at least one selected from Bi,

0<r≤0.8, 0<a≤1, 0 < x≤1, 0≤y<1, 0 < z<1 and 0<x+y+z≤1.

The lithium manganese-based oxide represented by Formula 1 may optionally include cobalt. In addition, when the lithium manganese-based oxide contains cobalt, a ratio of the number of moles of cobalt to the number of moles of all metal elements in the lithium manganese-based oxide may be 10% or less.

The lithium manganese oxide represented by Formula 1 is an oxide of C2/m phase represented as Li ₂ MnO ₃ and R3-m represented as Li _a Ni _x Co _y Mn _z M1 _1-(x+y+z) O ₂ It is a complex oxide in which the oxides of the phase coexist. At this time, the oxide of the C2/m phase and the oxide of the R3-m phase exist in a solid solution state.

In addition, in the lithium manganese oxide represented by Formula 1, when r exceeds 0.8, the ratio of Li ₂ MnO ₃ , which is an oxide of the C2/m phase among the lithium manganese oxides, is excessively increased, so that the cathode active material is discharged. There is a possibility that the capacity may decrease.

lithium secondary battery

According to another aspect of the present invention, a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector may be provided. Here, the positive electrode active material layer may include the lithium manganese oxide according to various embodiments of the present invention described above as a positive electrode active material.

Therefore, a detailed description of the lithium manganese oxide will be omitted, and only the remaining components not described above will be described below. In addition, hereinafter, for convenience, the above-described lithium manganese oxide will be referred to as a positive electrode active material.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon, nickel, titanium on the surface of aluminum or stainless steel. , silver or the like surface-treated may be used. 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.

The positive electrode active material layer may be prepared by applying a positive electrode slurry composition including a conductive material and optionally a binder along with the positive electrode active material to the positive electrode current collector.

In this case, the positive active material may be included in an amount of 80 to 99 wt%, more specifically 85 to 98.5 wt%, based on the total weight of the positive active material layer. It may exhibit excellent capacity characteristics when included in the above content range, but is not necessarily limited thereto.

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, summer black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or a conductive polymer such as a polyphenylene derivative, and the like, and one or a mixture of two or more thereof may be used. The conductive material may be included in an amount of 0.1 to 15 wt% based on the total weight of the positive 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), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC) ), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, 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 wt% based on the total weight of the positive active material layer.

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 positive electrode active material and, optionally, the positive electrode slurry composition prepared by dissolving or dispersing the binder and the conductive material in a solvent may be coated on the positive electrode current collector, and then dried and rolled.

The solvent may be a solvent generally used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone) or water, and the like, and any one of them or a mixture of two or more thereof may be used. The amount of the solvent used is enough to dissolve or disperse the positive electrode active material, the conductive material and the binder in consideration of the application thickness of the slurry and the production yield, and to have a viscosity capable of exhibiting excellent thickness uniformity when applied for the production of the positive electrode thereafter. do.

Further, in another embodiment, the positive electrode may be prepared by casting the positive electrode slurry composition on a separate support and then laminating a film obtained by peeling it from the support on the positive electrode current collector.

In addition, according to another aspect of the present invention, an electrochemical device including the above-described positive electrode may be provided. The electrochemical device may specifically be a battery, a capacitor, or the like, and more specifically, may be a lithium secondary battery.

Specifically, the lithium secondary battery may include a positive electrode, a negative electrode positioned opposite to the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the 　 anode is the same as described above, a detailed description will be omitted for convenience, and only the remaining components not described above will be described in detail below.

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

The negative electrode may include a negative electrode current collector and an anode 　 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, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface. 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, a nonwoven body.

The negative electrode active material layer may be prepared by applying a negative electrode slurry composition including a conductive material and optionally a binder along with the negative electrode active material to the negative electrode current collector.

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 SiO _β (0 < β < 2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Alternatively, a composite including the 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 as high crystalline carbon, amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, 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 negative active material may be included in an amount of 80 to 99 wt% based on the total weight of the negative electrode and the active material layer.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and may be typically added in an amount of 0.1 to 10 wt% based on the total weight of the negative electrode and the active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro and 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 negative electrode 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 negative electrode 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 whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

In one embodiment, the negative electrode 　 active material layer is prepared by applying and drying a negative electrode 　 slurry composition prepared by dissolving or dispersing the negative electrode 　 active material, and optionally a binder and a conductive material in a solvent on the negative electrode current collector and drying, or the negative electrode 　 slurry It can be prepared by casting the composition on a separate support and then laminating a film obtained by peeling it from the support on a negative electrode current collector.

In addition, in another embodiment, the negative electrode 　 active material layer is coated with a negative electrode 　 slurry composition prepared by dissolving or dispersing the negative electrode 　 active material, and optionally a binder and a conductive material in a solvent on the negative electrode current collector and drying, or the negative electrode 　 slurry It can also be prepared by casting the composition on a separate support and then laminating the film obtained by peeling it off from the support on the negative electrode current collector.

On the other hand, in the lithium secondary battery, the separator separates the anode and the anode 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 respect and an excellent electrolyte moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer and ethylene/methacrylate copolymer, or 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, a coated separator including a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, 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 is not going to be

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

The organic solvent may be used without any 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 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 sulfolane may be used. Among these, 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 performance of the electrolyte may be excellent.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) _2. LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ , etc. may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is included in the above range, since the electrolyte has appropriate conductivity and viscosity, excellent electrolyte performance may be exhibited, and lithium ions may move effectively.

In the electrolyte, in addition to the electrolyte components, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, 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-methoxyethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

As described above, since the lithium secondary battery containing 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 and HEV).

The external shape of the lithium secondary battery according to 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. In addition, the lithium secondary battery may be used not only 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 battery module including a plurality of battery cells.

According to another aspect of the present invention, a battery module including the lithium secondary battery as a unit cell and/or a battery pack including the same may be provided.

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

Preparation Example 1. Preparation of positive electrode active material

Example 1.

(a) precursor preparation

In the reactor, NiSO ₄ ·6H ₂ O and MnSO ₄ ·H ₂ O were mixed aqueous solution in a molar ratio of 25:75, and stirred while adding NaOH and NH ₄ OH. The temperature in the reactor was maintained at 45° C., and the precursor synthesis reaction was performed while N ₂ gas was introduced into the reactor. After completion of the reaction, washing and dehydration were performed to obtain a Ni _0.25 Mn _0.75 (OH) ₂ precursor.

(b) first heat treatment

O ₂ The temperature of the kiln in the atmosphere was raised at a rate of 2°C/min, and then the precursor obtained in step (a) was heat-treated for 5 hours while maintaining 550°C, followed by furnace cooling.

(c) second heat treatment

A mixture was prepared by mixing the oxide-state precursor obtained in step (b) and LiOH (Li/(metal except Li) mol ratio = 1.55) as a lithium compound.

Then, the temperature of the kiln in the O ₂ atmosphere is raised at a rate of 2° C./min and then maintained at 900° C., and the mixture is heat-treated for 8 hours and then furnace cooled to a positive electrode containing excess lithium manganese oxide. An active material was obtained.

As a result of ICP analysis, it was confirmed that the positive active material according to Example 1 had a composition of 0.54Li ₂ MnO ₃ ·0.46 LiNi _0.538 Mn _0.462 O ₂ .

Example 2

Ni _0.40 Mn _0.60 (OH) ₂ A precursor was used, and the cathode active material was the same as in Example 1, except that LiOH was mixed in a molar ratio of 1.25 before the second heat treatment (Li/(metal except Li) mol ratio = 1.25). was prepared.

As a result of ICP analysis, it was confirmed that the positive active material according to Example 2 had a composition of 0.23Li ₂ MnO ₃ ·0.77 LiNi _0.523 Mn _0.477 O ₂ .

Example 3

Ni _0.45 Mn _0.55 (OH) ₂ precursor was used, and the cathode active material was the same as in Example 1, except that LiOH was mixed in a molar ratio of 1.20 (Li/(metal except Li) mol ratio = 1.20) before the second heat treatment. was prepared.

As a result of ICP analysis, it was confirmed that the positive active material according to Example 3 had a composition of 0.19Li ₂ MnO ₃ ·0.81 LiNi _0.557 Mn _0.443 O ₂ .

Example 4

(a) precursor preparation

In the reactor, NiSO ₄ ·6H ₂ O and MnSO ₄ ·H ₂ O were mixed aqueous solution in a molar ratio of 40:60, while NaOH and NH ₄ OH were added and stirred. The temperature in the reactor was maintained at 45° C., and the precursor synthesis reaction was performed while N ₂ gas was introduced into the reactor. After completion of the reaction, washing and dehydration were performed to obtain a Ni _0.40 Mn _0.60 (OH) ₂ precursor.

(b) precursor coating

CoSO ₄ ·7H ₂ O aqueous solution, NaOH and NH ₄ OH were added to the reactor in which the precursor obtained in step (a) was stirred. At this time, CoSO ₄ ·7H ₂ O was added after weighing so as to be 10 mol%. After completion of the reaction, washed and dehydrated, and then dried at 150° C. for 14 hours to obtain a coated precursor.

(c) first heat treatment

O ₂ The temperature of the kiln in the atmosphere was raised at a rate of 2°C/min, and then the precursor obtained in step (b) was heat-treated for 5 hours while maintaining 550°C, followed by furnace cooling.

(d) second heat treatment

A mixture was prepared by mixing the oxide-state precursor obtained in step (c) and LiOH (Li/(metal except Li) mol ratio = 1.25) as a lithium compound.

Subsequently, the temperature of the kiln in an O ₂ atmosphere is raised at a rate of 2° C./min, and then maintained at 850° C., and the mixture is heat-treated for 8 hours and then furnace cooled to a positive electrode containing excess lithium manganese oxide. An active material was obtained.

As a result of ICP analysis, it was confirmed that the positive active material according to Example 3 had a composition of 0.23Li ₂ MnO ₃ ·0.77 LiNi _0.467 Co _0.127 Mn _0.405 O ₂ .

Comparative Example 1

A positive electrode active material was prepared in the same manner as in Example 1, except that LiOH was mixed in a molar ratio of 1.35 (Li/(metal except Li) mol ratio = 1.35) before the second heat treatment.

As a result of ICP analysis, it was confirmed that the positive active material according to Comparative Example 3 had a composition of 0.36Li ₂ MnO ₃ ·0.64LiNi _0.389 Mn _0.611 O ₂ .

Comparative Example 2

A positive active material was prepared in the same manner as in Example 2, except that LiOH was mixed at a molar ratio of 1.50 (Li/(metal except Li) mol ratio = 1.50) before the second heat treatment.

As a result of ICP analysis, it was confirmed that the positive active material according to Comparative Example 3 had a composition of 0.49Li ₂ MnO ₃ ·0.51LiNi _0.793 Mn _0.207 O ₂ .

Preparation Example 2. Preparation of lithium secondary battery

A positive electrode slurry was prepared by dispersing 90 wt% of each of the positive active material prepared according to Preparation Example 1, 5.5 wt% of carbon black, and 4.5 wt% of PVDF binder in 30 g of N-methyl-2 pyrrolidone (NMP). The positive electrode slurry was uniformly applied to an aluminum thin film having a thickness of 15 μm and vacuum dried at 135° C. to prepare a positive electrode for a lithium secondary battery.

For the positive electrode, lithium foil as a counter electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as a separator, and LiPF in a solvent in which ethylene carbonate and ethylmethyl carbonate were mixed in a volume ratio of 3:7 A coin battery was prepared using an electrolyte in which ₆ was present at a concentration of 1.15M.

Experimental Example 1. TEM analysis of lithium manganese oxide

After screening the lithium manganese-based oxides contained in each positive active material prepared in Preparation Example 1, cross-section polisher (accelerated voltage 5.0 kV, milling for 4 hours) cross-section, and then cross-sectional TEM photograph with a transmission electron microscope got Then, the TEM image was made into a diffraction pattern by FFT (Fast Fourier Transform), and then indexed to confirm the crystal structure in the core region and the shell region of the lithium manganese oxide.

1 shows the TEM analysis result of the lithium manganese-based oxide contained in the positive electrode active material according to Example 4. Referring to FIG. 1 shows a 50 nm scale TEM image and a 5 nm scale TEM image of an enlarged area indicated in the 50 nm scale TEM image, and a crystal structure confirmed through FFT conversion for the A and B regions of the 5 nm scale TEM image. was shown.

At this time, the crystal structure in the shell region was confirmed in a region where the distance from the outermost of the lithium manganese oxide was 0 to 0.03 μm, and the crystal structure in the core region was 0.12 from the outermost of the lithium manganese oxide. to 0.15 μm.

The analysis results are shown in Table 1 below.

division core area shell area Example 1 C2/m + R3-m C2/m + R3-m Example 2 C2/m + R3-m C2/m + R3-m Example 3 C2/m + R3-m C2/m + R3-m Example 4 C2/m + R3-m R3-m Comparative Example 1 C2/m + R3-m C2/m + R3-m Comparative Example 2 C2/m + R3-m C2/m + R3-m

In addition, EDX mapping was performed on the cross-sectional TEM image of the lithium manganese oxide contained in each positive active material prepared according to Preparation Example 1, and the EDX mapping result was line scanning the nickel from the shell to the core of the lithium manganese oxide. Concentration (at%) change was confirmed.

At this time, the concentration of nickel in the shell region is the average concentration (at%) of nickel based on the lithium manganese oxide (bulk) measured from a region where the distance from the outermost of the lithium manganese oxide is 0 to 0.03 μm. ) and the average concentration (at%) of nickel converted based on the R3-m phase in the lithium manganese oxide.

In addition, the concentration of nickel in the core region is the average concentration of nickel based on the lithium manganese oxide (bulk) measured from a region where the distance from the outermost of the lithium manganese oxide is 0.12 to 0.15 μm (at%) and the average concentration (at%) of nickel converted based on the R3-m phase among the lithium manganese oxides.

In addition, the concentration of nickel in the intermediate region is the average concentration of nickel based on the lithium manganese oxide (bulk) measured from the region where the distance from the outermost of the lithium manganese oxide is 0.075 to 0.1 μm (at%) and the average concentration (at%) of nickel converted based on the R3-m phase among the lithium manganese oxides.

2 is a line scanning the EDX mapping result of the cross-sectional TEM image of the lithium manganese oxide included in the positive active material according to Example 4 to confirm the change in the concentration (at%) of nickel from the core to the shell of the lithium manganese oxide. It is a sum spectrum. Region A indicated in the line sum spectrum of FIG. 2 corresponds to region A of FIG. 1 .

The analysis results are shown in Table 2 below.

division core area middle area shell area bulk R3-m bulk R3-m bulk R3-m Example 1 24 52 25 54 27 58 Example 2 39 51 41 52 43 56 Example 3 44 55 46 57 47 59 Example 4 40 51 46 60 63 63 Comparative Example 1 25 39 25 39 25 39 Comparative Example 2 40 79 40 79 40 79

Referring to the results of Table 1, the lithium manganese-based oxides included in each positive active material prepared according to Preparation Example 1 are all different from the phase belonging to the C2/m space group and the phase belonging to the R3-m space group within a single particle. coexistence can be observed. That is, the lithium manganese oxide contained in each positive active material prepared according to Preparation Example 1 is a solid solution represented by the following Chemical Formula 1,

rLi ₂ MnO ₃ ·(1-r)Li _a Ni _x Co _y Mn _z M1 _1-(x+y+z) O ₂

In the solid solution, the phase belonging to the C2/m space group is caused by Li ₂ MnO ₃ , and the phase belonging to the R3-m space group is caused by Li _a Ni _x Co _y Mn _z M1 _1-(x+y+z) O ₂ can be expected to be attributed. In addition, it can be confirmed that among the lithium manganese oxides included in the positive electrode active materials according to Examples 1 to 3, there is a region in which the abundance ratio of the phase belonging to the C2/m space group and the phase belonging to the R3-m space group are different. have.

Meanwhile, referring to the results of Tables 1 and 2, in the core region and the shell region of the lithium manganese oxide included in the positive electrode active materials according to Examples 1 to 3, the phase belonging to the R3-m space group and the C2/ It can be seen that the phases belonging to the m space group coexist, but a plurality of regions in the lithium manganese-based oxide having different abundance ratios of the phase belonging to the C2/m space group and the phase belonging to the R3-m space group exist.

In addition, referring to the results in Table 2 and FIG. 2 , in the core region of the lithium manganese oxide included in the positive active material according to Example 4, a phase belonging to the C2/m space group and a phase belonging to the R3-m space group coexist, but , it can be seen that only phases belonging to the R3-m space group exist in the shell region, and the concentration of nickel in the lithium manganese oxide has a gradient that increases from the core to the shell.

Considering that the phase in which nickel exists among the phases belonging to the R3-m space group and the phases belonging to the C2/m space group constituting the lithium manganese oxide is the phase belonging to the R3-m space group, the result is the lithium manganese-based oxide. This means that the proportion of phases belonging to the R3-m space group increases from the core to the shell of the oxide. Accordingly, the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2/m space group among the lithium manganese oxide will have a gradient that increases from the core to the shell.

On the other hand, in both the core and the shell of the lithium manganese-based oxide contained in the positive electrode active material according to Comparative Examples 1 and 2, a phase belonging to the C2/m space group and a phase belonging to the R3-m space group coexist, while the nickel in the shell is It can be seen that there is no significant difference between the average concentration and the average concentration of nickel in the core.

That is, in the lithium manganese-based oxide included in the positive electrode active material according to Comparative Examples 1 and 2, a plurality of regions having different abundance ratios of a phase belonging to the C2/m space group and a phase belonging to the R3-m space group do not exist. can confirm. The above result means that the phase belonging to the C2/m space group and the phase belonging to the R3-m space group of the lithium manganese oxide exist in a uniformly dissolved state.

Experimental Example 2. Evaluation of electrochemical properties of lithium secondary batteries

For the lithium secondary battery (coin cell) manufactured in Preparation Example 2, using an electrochemical analyzer (Toyo, Toscat-3100), a discharge rate of 25°C, voltage range 2.0V to 4.6V, 0.1C to 5.0C was applied. The initial charge capacity, the initial discharge capacity, the initial reversible efficiency and the discharge capacity ratio were measured through the discharge experiment.

The measurement results are shown in Tables 3 and 4 below.

division initial charge capacity
(0.1C-rate) Initial discharge capacity
(0.1C-rate) Initial reversible efficiency
unit mAh/g mAh/g % Example 1 270.3 218.9 81.0 Example 2 254.5 221.1 86.9 Example 3 219.7 193.7 88.1 Example 4 254.5 224.8 88.3 Comparative Example 1 103.5 96.9 93.7 Comparative Example 2 235.4 177.6 75.5

division Discharge capacity ratio
(2C/0.1C) Discharge capacity ratio
(5C/0.1C) unit % % Example 1 65 54 Example 2 73 62 Example 3 66 49 Example 4 82 72 Comparative Example 1 34 12 Comparative Example 2 64 49

Referring to the results of Tables 3 and 4, in the lithium manganese oxide, there is a region in which the abundance ratio of the phase belonging to the C2/m space group and the phase belonging to the R3-m space group is different from that of the lithium manganese oxide, and in the R3-m space group When the number of moles of nickel based on all metallic elements (excluding lithium) among the phases belonging to the R3-m space group relative to all metallic elements (excluding lithium) in the region where the phase to which it belongs is predominantly exists within a predetermined range , it can be seen that the discharge capacity and rate characteristics are improved as the stability degradation caused by lithium and manganese in excess of the lithium manganese oxide is alleviated and/or prevented.

As mentioned above, although embodiments of the present invention have been described, those of ordinary skill in the art may add, change, delete or add components within the scope that does not depart from the spirit of the present invention described in the claims. Various modifications and changes of the present invention will be possible by this, and this will also be included within the scope of the present invention.

Claims (11)

A positive electrode active material comprising at least lithium, nickel, and lithium excess lithium manganese oxide including manganese,
A phase belonging to the C2/m space group and a phase belonging to the R3-m space group coexist in the lithium manganese oxide,
In the lithium manganese oxide, a region having a different abundance ratio of a phase belonging to the C2/m space group and a phase belonging to the R3-m space group exists.
positive electrode active material.
The method of claim 1,
The concentration of the metal element in the lithium manganese oxide satisfies Equation 1 below,
positive electrode active material.
[Equation 1]
0.24 ≤ M ² /M ¹ ≤ 0.55
here,
M ¹ is the number of moles of all metal elements (excluding lithium) in the lithium manganese oxide,
M ² is the number of moles of nickel based on all metal elements (excluding lithium) in the lithium manganese oxide.
The method of claim 1,
The concentration of the metal element in the lithium manganese oxide satisfies the following Equation 2,
positive electrode active material.
[Equation 2]
0.40 ≤ M ^2' /M ^1' ≤ 0.70
Here, M ^1' is the total number of moles of metal elements (excluding lithium) in the phase belonging to the R3-m space group,
M ^2' is the number of moles of nickel based on all metal elements (excluding lithium) in the phase belonging to the R3-m space group.
According to claim 1,
The lithium manganese oxide is a core-shell particle including a core and a shell covering at least a portion of the surface of the core,
A phase belonging to the C2/m space group and a phase belonging to the R3-m space group coexist in the core,
The ratio of the phases belonging to the R3-m space group to the phases belonging to the C2/m space group in the shell is greater than the ratio of the phases belonging to the R3-m space group to the phases belonging to the C2/m space group in the core,
positive electrode active material.
5. The method of claim 4,
The concentration of the metal element in the shell satisfies the following Equation 3,
positive electrode active material.
[Equation 3]
0.24 ≤ M ⁴ /M ³ ≤ 0.75
here,
M ³ is the number of moles of all metal elements (excluding lithium) in the shell,
M ⁴ is the number of moles of nickel based on all metallic elements (excluding lithium) in the shell.
5. The method of claim 4,
The concentration of the metal element in the shell satisfies Equation 4 below,
positive electrode active material.
[Equation 4]
0.40 ≤ M ^4' /M ^3' ≤ 0.75
where M ^3' is the total number of moles of metal elements (excluding lithium) in the phase belonging to the R3-m space group in the shell,
M ^4' is the number of moles of nickel based on all metallic elements (excluding lithium) in the phase belonging to the R3-m space group in the shell.
5. The method of claim 4,
The ratio of the phase belonging to the R3-m space group to the phase belonging to the C2/m space group among the lithium manganese oxide has a gradient that increases from the core toward the shell,
positive electrode active material.
5. The method of claim 4,
In the shell, only phases belonging to the R3-m space group exist,
positive electrode active material.
The method of claim 1,
The lithium manganese oxide is represented by the following formula (1),
positive electrode active material.
[Formula 1]
rLi ₂ MnO ₃ ·(1-r)Li _a Ni _x Co _y Mn _z M1 _1-(x+y+z) O ₂
here,
M1 is Mo, Nb, Fe, Cr, V, Cu, Zn, Sn, Mg, Ru, Al, Ti, Zr, B, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si and at least one selected from Bi,
0<r≤0.8, 0<a≤1, 0 < x≤1, 0≤y<1, 0 < z<1 and 0<x+y+z≤1.
A positive electrode comprising the positive electrode active material according to any one of claims 1 to 9.
A lithium secondary battery using the positive electrode according to claim 10.

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