WO2016108382A1 - Cathode active material for lithium secondary battery, method for preparing same, and lithium secondary battery including same - Google Patents

Abstract

The present invention relates to a cathode active material for a lithium secondary battery wherein the cathode active material comprises a nickel-based lithium transition metal oxide having a layered structure represented by the formula Li_aNi_bCo_cMn_dO₂ (wherein 1 < a < 1.14, b > c, b > d, 0.4 ≤ b ≤ 0.9, 0 < c < 0.4, and 0 ≤ d < 0.4), and wherein the highest peak among the peaks presented within a scattering angle 2θ ranging from 20° to 25° is shown between 21.8° and 22.5° when measured using X-ray diffraction analysis; a method for preparing the same; and a lithium secondary battery including the same. According to the present invention, the mobility of a lithium-adjacent nickel within a nickel-based lithium transition metal oxide is reduced, thereby inhibiting the generation of nickel oxide related heterogeneous phase which can degrade the performance of an active material, and as a result, the present invention can provide a lithium secondary battery which exhibits excellent initial efficiency, capacity and life characteristics.

Description

Cathode active material for lithium secondary battery, manufacturing method thereof and lithium secondary battery including same

The present invention relates to a cathode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same. More specifically, the initial efficiency, capacity, and lifespan of a battery are included by including a nickel-based lithium transition metal oxide having reduced nickel mobility. The present invention relates to a cathode active material for a lithium secondary battery capable of improving characteristics, a method of manufacturing the same, and a lithium secondary battery including the same.

The electronics and telecommunications industry is rapidly developing through the portable, miniaturized, lightweight, and high performance electronic devices, and the demand for lithium secondary batteries that can realize high capacity and high performance as a power source for these electronic devices is rapidly increasing. Further, as electric vehicles (EVs) and hybrid electric vehicles (HEVs) are put into practical use, research on lithium secondary batteries having high capacity and output and excellent stability is being actively conducted.

Lithium secondary batteries are manufactured by using a material capable of intercalation and disintercalation of lithium ions as a negative electrode and a positive electrode, and filling an organic or polymer electrolyte between a negative electrode and a positive electrode, and lithium ions are inserted in the positive and negative electrodes. And electrical energy is generated by the oxidation reaction and the reduction reaction at the time of detachment.

Among the components of the lithium secondary battery, the cathode material plays an important role in determining the capacity and performance of the battery in the battery.

Lithium cobalt oxide (LiCoO ₂ ) is the first commercially available cathode material, which is still widely used as a cathode material due to its relatively good structural stability and ease of mass production compared to other lithium transition metal oxides. Due to its limitations, the price is expensive and harmful to the human body.

Accordingly, various studies have been made on cathode materials that can replace lithium cobalt oxide. In particular, nickel-rich (Ni-rich) -based positive electrode active material containing a lot of nickel (Ni) of the lithium metal oxide having a layered structure exhibits a high capacity of more than 200mAh / g is considered as the next-generation electric vehicle and power storage cathode material have. In addition, nickel (Ni) has been researched in a lot of interest because it is less toxic to human body and cheaper than cobalt (Co) (Non-Patent Document 1).

However, since nickel tends to prefer divalent rather than trivalent valence, it is an empty space of a lithium layer in which lithium deficiency occurs due to volatilization of a raw material lithium salt at high temperature firing, and nickel having a divalent valence similar in lithium ion to an ion radius. ions (Ni ^{+ 2)} results in the incorporation, there is a problem that a non-stoichiometric lithium nickel oxide of the following composition are prepared. Non-chemical lithium nickel oxide of stoichiometric composition, the Ni ^{2 +} incorporated into the lithium layers, as well as interfere with the diffusion of lithium ions, there is a problem of reducing the reversible capacity to significantly increase non-reversible.

The phenomenon is Li ⁺ (0.76Å) and Ni ^{2 +} (0.69Å) with each other is similar ionic radius as described above In other forming crystals of the seat to each other refers to as mixed cation (Cation mixing). As a conventional method for solving such a problem, Patent Document 1 (Korean Patent Application Laid-Open No. 2013-0084361) discloses a metal cation having an ion radius larger than that of the Ni cation to prevent Ni cation mixing in the Li layer. Is disclosed in the positive electrode active material contained in the Li cation site or the empty space in the crystal lattice. According to this method, the movement path of Ni ²⁺ may be partially blocked, but the metal cations may interfere with the diffusion of lithium ions (Li ⁺ ), thereby lowering the electrochemical properties of the cathode active material.

Accordingly, the present inventors have a diffraction peak in the region where the diffraction angle 2θ is 20 ° to 25 ° in the X-ray diffraction analysis using a Cu target, and the peak peak is located between 21.8 ° and 22.5 °. In the case of the nickel-based transition metal oxide, the present invention was completed by confirming that the mobility of nickel around lithium is reduced and the generation of nickel oxide-related heterogeneous phases, which may degrade the performance of the active material, is suppressed.

[Preceding technical literature]

[Patent Documents]

(Patent Document 1) KR2013-0084361 A

[Non-Patent Documents]

(Non-Patent Document 1) Sang-Yoon Lee, Study on Substitution and Surface Modification of Heterogeneous Elements for Structural Stability Improvement of Ni-rich Cathode Active Materials for Lithium Secondary Batteries, Master's Thesis, Graduate School of Korea University (2013.2)

The problem to be solved by the present invention, the diffraction peak is present in the region where the diffraction angle 2θ is 20 ° ~ 25 ° in the X-ray diffraction analysis using a Cu target, the peak peak is 22.5 ° to 22.5 By including a nickel-based lithium transition metal oxide located between ° to reduce the mobility of nickel around the lithium has excellent conductivity, to provide a positive electrode active material that can improve the initial efficiency, capacity and life characteristics of the battery.

Another object of the present invention is to provide a lithium secondary battery including the cathode active material.

In order to solve the above problems, the present invention includes a nickel-based lithium transition metal oxide having a layered structure represented by the following formula (1), X-ray diffraction using a copper target (Cu Target) of the lithium transition metal oxide The present invention provides a cathode active material for a lithium secondary battery, characterized in that a diffraction peak exists in a region having a diffraction angle 2θ of 20 ° to 25 °, and the peak of the peak is located between 21.8 ° and 22.5 °.

[Formula 1]

Li _a Ni _b Co _c Mn _d O ₂

In Formula 1, 1 <a <1.14, b> c, b> d, 0.4 <b <0.9, 0 <c <0.4, 0 <d <0.4.

Preferably, in Formula 1, 1 <a <1.1, and 0.9 ≦ b + c + d ≦ 1.

In the X-ray diffraction analysis of the nickel-based lithium transition metal oxide, a peak does not appear in a region having a diffraction angle 2θ of 20 ° to 21.8 °, and a peak height appearing between 21.8 ° and 22.5 ° is the lithium transition metal oxide. In the X-ray diffraction analysis, it is preferably in the range of 0.05% to 2% of the peak height appearing near the diffraction angle 2θ 18 °.

In addition, the present invention provides a method for producing the cathode active material and a lithium secondary battery comprising the cathode active material.

The method for preparing the cathode active material may include mixing a precursor represented by Chemical Formula 2 and a lithium source in an equivalent ratio satisfying the condition of Equation 1 below; And heat-treating the mixture at 800 to 1000 ° C.

[Formula 2]

Ni _x Co _y Mn _z (OH) ₂

In Formula 2, x> z, x> y, 0.4 <x <0.9, 0 <y <0.4, 0 <z <0.4.

 [Equation 1]

1.00 <Li moles / M <1.14

In Equation 1, M is the x + y + z value of the formula (2).

According to the present invention, by reducing the mobility of lithium surrounding nickel in the nickel-based lithium transition metal oxide, it is possible to suppress the occurrence of nickel oxide-related heterogeneous phases, which may reduce the performance of the active material, and provide additional mobile sites to the lithium to provide It can improve conductivity and improve structural stability during overcharging.

Therefore, by using the cathode active material containing the nickel-based lithium transition metal oxide, it is possible to provide a lithium secondary battery having excellent initial efficiency, capacity, and lifespan.

Figure 1 shows a comparison of the X-ray diffraction spectrum of the positive electrode active material prepared according to Example 1 and Comparative Example 1.

Figure 2 shows a comparison of the X-ray diffraction spectrum of the positive electrode active material prepared according to Examples 1 and 2.

Figure 3 shows a comparison of the X-ray diffraction spectrum of the positive electrode active material prepared according to Example 1 and Comparative Example 2.

Figure 4 is a graph showing the charge and discharge test results of the lithium secondary battery prepared using the positive electrode active material of Example 1 and Comparative Example 1.

5 is a graph showing the life characteristics of the lithium secondary battery prepared using the positive electrode active material of Example 1 and Comparative Example 1.

Figure 6 is a graph showing the comparison of the conductivity according to the pressure of the positive electrode active material prepared according to Example 1 and Comparative Example 1.

The present invention includes a nickel-based lithium transition metal oxide having a layered structure represented by Formula 1 below, and the diffraction angle 2θ is 20 ° to X-ray diffraction analysis of the lithium transition metal oxide using a copper target (Cu Target). The diffraction peak exists in the area | region which is 25 degrees, and the highest point of the peak provides the positive electrode active material for lithium secondary batteries which is located between 21.8 degrees and 22.5 degrees.

[Formula 1]

Li _a Ni _b Co _c Mn _d O ₂

In Formula 1, 1 <a <1.14, b> c, b> d, 0.4 <b <0.9, 0 <c <0.4, 0 <d <0.4.

Preferably, in Formula 1, 1 <a <1.1, and 0.9 ≦ b + c + d ≦ 1.

The lithium transition metal oxide according to the present invention is a nickel-rich (Ni-rich) lithium transition metal oxide containing nickel (Ni) more than cobalt (Co) and manganese (Mn). These Ni-rich (Ni-rich) type lithium transition metal oxide was having difficulty in commercialization due to the structural instability which it is possible to express a high capacity although the spotlight as materials for the next generation of electrodes storage, essentially Ni ^{3 +} is present .

However, since the nickel-based lithium transition metal oxide according to the present invention has a structure in which a part of lithium is arranged in a layered structure, the structural stability of nickel can be achieved.

The present inventors found that the nickel-based lithium transition metal oxide having the above structure has the highest peak among the peaks present in the region where the diffraction angle 2θ is 20 ° to 25 ° in the X-ray diffraction analysis, between 21.8 ° and 22.5 °. appears, which resulted in the completion of the in this case the present invention to determine the lithium surrounding nickel that the mobility of the drop being the generation (the Ni ^{2 +} incorporated in, for example, Li layer) nickel oxide-related yijongsang that can degrade the active material performance suppressed because of . As such, when the occurrence of nickel oxide-related heterophages is suppressed, it is possible to provide a lithium secondary battery having improved initial conductivity, battery capacity, and lifespan by providing additional moving sites to lithium, thereby improving conductivity. have.

The peak height appearing between 21.8 ° and 22.5 ° is preferably in the range of 0.05% to 2% of the peak height of the diffraction angle 2θ at around 18 ° in the X-ray diffraction analysis of the nickel-based lithium transition metal oxide. When the peak height appearing in the region of the diffraction angle 2θ is in the range of 21.8 ° ~ 22.5 ° falls within the above range it is preferable because the effect of reducing the mobility of nickel is the most excellent and the effect of improving the conductivity of the active material to the maximum.

Conventionally, LiMO ₂ (M = Co, Ni, Mn) is composed of a single phase of LiMO ₂ (M = Co, Ni, Mn) as a layered lithium transition metal oxide, or the LiMO ₂ (M = Co, Ni, Mn) layered crystal structure There is known a configuration in which crystals of lithium manganese oxide (Li ₂ MnO ₃ ) are mixed in. In the case of the lithium manganese oxide, lithium is surrounded by a metal element having a tetravalent valence such as manganese.

However, although the lithium transition metal oxide of the layer structure according to the present invention is prepared by adding an excessive amount of lithium, metal elements around lithium have a trivalent valence on average. That is, even if lithium is introduced at a ratio greater than the total amount of transition metals (Ni, Co, and Mn) in the manufacturing step, a heterogeneous Li ₂ MnO ₃ formed of lithium and manganese is not formed, but part of lithium is partially added to the layered structure. Because of the structure that exists in the arrangement, the metallic elements around lithium have an average valence of trivalent rather than tetravalent.

Specifically, referring to FIGS. 1 and 3, when the X-ray diffraction analysis of the nickel-based lithium transition metal oxide prepared according to Example 1 of the present invention, a peak does not appear in a region having a diffraction angle 2θ of 20 ° to 21.8 °. You can check it. The 20 ° to 21.8 ° region is a section in which diffraction peaks originating from the Li ₂ MnO ₃ phase appear, and in the presence of the Li ₂ MnO ₃ phase, a strong peak near 21 ° and a shoulder peak between 21 ° and 21.8 ° are observed. . For example, the peak of the lithium transition metal oxide of Comparative Example 2 including the Li ₂ MnO ₃ phase was found in the 20 ° ~ 21.8 ° region.

In addition, the present invention provides a method for producing a cathode active material including the nickel-based lithium transition metal oxide. Specifically, the method of manufacturing the positive electrode active material comprises the steps of mixing the precursor represented by the formula (2) and the lithium source in an equivalent ratio that satisfies the conditions of the following formula (1); And heat-treating the mixture at 800 to 1000 ° C.

[Formula 2]

Ni _x Co _y Mn _z (OH) ₂

In Formula 2, x> z, x> y, 0.4 <x <0.9, 0 <y <0.4, 0 <z <0.4.

 [Equation 1]

1.00 <Li moles / M <1.14

 In Equation 1, M is the x + y + z value of the formula (2).

More preferably, the number of moles of Li / M may be 1.01 to 1.05.

When the ratio of the number of mol of lithium to M calculated according to Equation 1 (Li number of mol / M) is 1 or less, LiMO ₂ (M = Co, where no peak exists in a region having a diffraction angle 2θ of 20 ° to 25 °) Ni, Mn) a single phase positive electrode active material may be formed, whereas when the ratio is 1.14 or more, a positive electrode active material including a Li ₂ MnO ₃ phase having peaks in a region having a diffraction angle 2θ of 20 ° to 21.8 ° may be formed. Can be.

In addition, when the heat treatment temperature is less than 800 ° C, a positive electrode active material including a Li ₂ MnO ₃ phase having a peak in a region where 2θ is 20 ° to 21.8 ° may be formed. Particle size may increase too much and battery characteristics may decrease.

In addition, the present invention provides a lithium secondary battery including the cathode active material. The lithium secondary battery may include a cathode including the cathode active material, a cathode including an anode active material, a separator, and a nonaqueous electrolyte. The structure and manufacturing method of the lithium secondary battery are known in the technical field of the present invention, and may be appropriately selected without departing from the scope of the present invention.

For example, the positive electrode is manufactured by applying a composition for forming a positive electrode active material including the positive electrode active material and the binder according to the present invention to a positive electrode current collector, and then drying and rolling.

The binder serves to fix the bonding between the positive electrode active material and the current collector, and any binder used in the art may be used without limitation, and preferably, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl It may be at least one selected from chloride, polyvinylpyrrolidone, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyethylene, polypropylene, styrene butyrene rubber, fluorine rubber.

The composition for forming the positive electrode active material may include a solvent such as N-Methyl-2-pyrrolidone (NMP) and an olefinic polymer such as polyethylene and polypropylene, optionally for the positive electrode active material and the binder; It may be prepared by further adding a filler made of a fibrous material such as glass fiber, carbon fiber and the like. In addition, it may further include a conductive agent known in the art, such as hard carbon, graphite and carbon fiber.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, calcined carbon; Surface-treated with carbon, nickel, titanium, silver or the like on the surface of copper and stainless steel; Aluminum-cadmium alloys, and the like, and various forms such as films, sheets, foils, nets, porous bodies, foaming agents, and nonwoven fabrics are also possible.

The negative electrode may be prepared by coating a composition for forming a negative electrode active material including a negative electrode active material on a negative electrode current collector and then drying and rolling it, or lithium metal. The negative electrode active material composition may further include the binder and the conductive material.

The negative electrode active material may be a carbonaceous material such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, lithium and silicon (Si), aluminum (Al), tin (Sn), lead (Pb), zinc (Zn), Alloyable metal compounds such as bismuth (Bi), indium (In), manganese (Mg), gallium (Ga), cadmium (Cd), silicon alloys, tin alloys, aluminum alloys, and the like and carbonaceous materials It may be a composite including a.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, calcined carbon; Surface-treated with carbon, nickel, titanium, silver or the like on the surface of copper and stainless steel; Aluminum-cadmium alloys, and the like, and various forms such as films, sheets, foils, nets, porous bodies, foaming agents, and nonwoven fabrics are also possible.

The separator is disposed between the negative electrode and the positive electrode, and conventional porous polymer films used as conventional separators, such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate Porous polymer films made of polyolefin-based polymers such as copolymers may be used alone or in a stack of these. It is also possible to use conventional porous nonwoven fabrics such as nonwoven fabrics of high melting point glass fibers, polyethylene terephthalate fibers and the like.

The non-aqueous electrolyte solution is composed of an electrolyte solution and a lithium salt, but the non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used as the electrolyte solution, but are not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and gamma Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxorone, formamide, dimethylformamide, dioxolon , Acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbo Aprotic organic solvents such as nate derivatives, tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

Examples of the organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, Polymerizers containing ionic dissociating groups and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium salt is a good material to be dissolved in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.

The secondary battery may be divided into a coin type, a square shape, a cylindrical shape, a pouch type, and the like. Since the structure and manufacturing method of these batteries are known in the art, detailed description thereof will be omitted.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

Example  One

Ni _{0 . 6} Co _{0 . 2} Mn _{0 .2} (OH) 1 ₂ precursor and LiOH: then a solution of an equivalent ratio (Li mole number / M = 1.01) of 1.01, and heat treated at a temperature of 850 ℃ LiNi _{0. 6} Co _{0 . 2} Mn _{0 . A} cathode active material having a composition of ₂ O ₂ was prepared.

Example  2

Ni _{0 . 5} Co _{0 . 2} Mn _{0 .3} (OH) 1 ₂ precursor and LiOH: then a solution of an equivalent ratio (Li mole number / M = 1.02) of 1.02, and heat treated at a temperature of 850 ℃ LiNi _{0. 5} Co _{0 . 2} Mn _{0 . A} cathode active material having a composition of ₃ O ₂ was prepared.

Comparative example  One

Ni _{0 . 6} Co _{0 . 2} Mn _{0 .2} (OH) ₂ precursor and LiOH to 1 equivalent ratio of 1 was mixed with (Li mole number / M = 1.00), heat treated at a temperature of 850 ℃ LiNi _{0. 6} Co _{0 . 2} Mn _{0 . A} cathode active material having a composition of ₂ O ₂ was prepared.

Comparative example  2

Ni _{0 . 2} Co _{0 . 2} Mn _{0 .6} (OH) ₂ precursor and LiOH 1: After mixing in 1.4 equivalent ratio (Li mole number / M = 1.40), the heat-treated at a temperature of 700 ℃ Li _{1. 17} Ni _{0 . 17} Co _{0 . 17} Mn _{0 . A} cathode active material having a ₅ O ₂ composition was prepared.

<X-ray diffraction peak analysis of the positive electrode active material>

Referring to FIG. 1, which compares the X-ray diffraction spectra of the cathode active materials prepared according to Example 1 and Comparative Example 1, the diffraction peaks in the region where the diffraction angle 2θ is 20 ° to 25 ° for the cathode active material of Example 1 Is present, the peak of the peak is located between 21.8 ° to 22.5 °, whereas the positive electrode active material of Comparative Example 1 has the same composition as the positive electrode active material of Example 1 but the peak or peak of the peak is not located in the region Do not.

In addition, referring to FIG. 2, which compares the X-ray diffraction spectrums of the cathode active materials prepared according to Examples 1 and 2, as the nickel content is increased, the peaks appearing in the region where the diffraction angle 2θ is 21.8 ° to 22.5 °. As the size increases, the peak is different from the peak appearing in the cathode active material of Comparative Example 2 and the relative size is different.

That is, referring to FIG. 3, which compares the X-ray diffraction spectra of the cathode active materials prepared according to Example 1 and Comparative Example 2, in the X-ray diffraction spectrum of the cathode active material according to Comparative Example 2, a strong peak near 21 °. And a shoulder peak between 21 ° and 21.8 ° is observed, whereas in the X-ray diffraction spectrum of Example 1, there is no peak at 20 ° to 21.8 °. This demonstrates that the positive electrode active material of Comparative Example 2 as a peak derived from the Li ₂ MnO ₃ is a does not include the cathode active material of Example 1 while containing Li ₂ MnO ₃ is a.

<Performance Evaluation of Lithium Secondary Battery>

1. Manufacturing of Lithium Secondary Battery

The aluminum foil was prepared by mixing the positive electrode active material prepared in Example 1 and Comparative Example 1, the conductive agent DenkaBlack, and the binder polyvinylidene fluoride (PVDF) at a ratio of 92: 4: 4 (w / w). Coating over to produce a positive electrode plate. A coin cell was prepared using lithium metal as a negative electrode and 1.3 M LiPF ₆ EC / DMC / EC = 3: 4: 3 solution as an electrolyte.

2. Cell Formation

After allowing the prepared coin cell to stand at a constant temperature of 25 ℃ for 24 hours, using a lithium secondary battery charger (Toyo-System Co., LTD, TOSCAT-3600), the conditions to constant current up to 4.3V at 0.1C and 0.05 and 0.05 The cell formation process was completed by charging C under constant voltage condition with the termination current and discharging under 0.1 C at constant current condition. Initial efficiency was calculated according to Equation (1) below in the formation process.

The initial efficiency (%) = (discharge capacity / charge capacity at 1 ^st cycle of the 1 ^st cycle)

              × 100.. (One)

3. Life characteristics evaluation

The formed cell was charged and discharged with a current of 1.0 C, and repeated 50 cycles. The capacity retention ratio was calculated according to Equation (2) below, and evaluated as life characteristics. The results are shown in Table 1 below.

Capacity retention rate (%) = (discharge capacity at 50 ^th cycle / discharge capacity at 1 ^st cycle)

                × 100.. (2)

4. Conductivity measurement

Electronic conductivity was measured while adjusting the pressure applied to the powder using a powder resistance measuring instrument (LORESTA-GP, MITSHBISHI CHEMICAL ANALYTECH) equipped with a 4-pin probe for the cathode active material prepared according to Example 1 and Comparative Example 1. The results are shown in FIG.

	1 st charging capacity (mAh / g)	1 st discharge capacity (mAh / g)	Initial Efficiency (%)	50 cycle capacity retention rate (%)
Example 1	200.8	187.3	93.3	96.3
Comparative Example 1	202.2	178.5	88.3	91.0

Looking at the Table 1, the lithium secondary battery manufactured using the positive electrode active material of Example 1, the initial charge and discharge capacity, initial efficiency and life characteristics compared to the lithium secondary battery manufactured using the positive electrode active material of Comparative Example 1 It can be confirmed that it is excellent. In addition, looking at Figure 6, in the case of the positive electrode active material prepared according to Example 1, it can be confirmed that the conductivity is improved compared to the positive electrode active material of Comparative Example 1.

As described above, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to explain the protection scope of the present invention, which should be interpreted by the following claims, and all technical ideas within the equivalent scope thereof. Should be construed as being included in the scope of the present invention.

Claims (7)

1. It includes a nickel-based lithium transition metal oxide of a layer structure represented by the formula (1)

   In the X-ray diffraction analysis of the lithium transition metal oxide using a copper target (Cu Target), a diffraction peak exists in a region having a diffraction angle 2θ of 20 ° to 25 °, and the peak peak is between 21.8 ° to 22.5 °. A cathode active material for a lithium secondary battery, characterized in that:

   [Formula 1]

   Li _a Ni _b Co _c Mn _d O ₂

   In Formula 1, 1 <a <1.14, b> c, b> d, 0.4 <b <0.9, 0 <c <0.4, 0 <d <0.4.
2. The method of claim 1,

   In Formula 1, 1 <a <1.1, wherein 0.9 ≤ b + c + d ≤ 1, the positive electrode active material for a lithium secondary battery.
3. The method of claim 1,

   A cathode active material for a lithium secondary battery, characterized in that a peak does not appear in a region where the diffraction angle 2θ is 20 ° to 21.8 ° when the lithium transition metal oxide is analyzed using a copper target (Cu Target).
4. The method of claim 1

   The peak height appearing between 21.8 ° to 22.5 ° for X-ray diffraction analysis of the lithium transition metal oxide is characterized in that the diffraction angle 2θ falls within the range of 0.05% ~ 2% of the peak height appearing near 18 ° Cathode active material.
5. As a method for producing a cathode active material according to any one of claims 1 to 4,

   Mixing a precursor represented by Formula 2 with a lithium source in an equivalent ratio satisfying the condition of Equation 1 below; And

   Method for producing a positive electrode active material comprising the step of heat-treating the mixture at 800 to 1000 ℃:

    [Formula 2]

   Ni _x Co _y Mn _z (OH) ₂

   In Formula 2, x> z, x> y, 0.4 <x <0.9, 0 <y <0.4, 0 <z <0.4.

   [Equation 1]

   1.00 <Li moles / M <1.14

   In Equation 1, M is the x + y + z value of the formula (2).
6. The method of claim 5,

   The number of moles of Li / M is a method of producing a positive electrode active material, characterized in that 1.01 ~ 1.05.
7. A lithium secondary battery comprising the cathode active material for a lithium secondary battery according to any one of claims 1 to 4.

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