JP5731276B2 - Positive electrode active material for lithium secondary battery, method for producing the same, and lithium secondary battery - Google Patents

Description

  The present invention relates to a positive electrode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery.

  Lithium secondary batteries that have been in the limelight as a power source for recent portable small electronic devices have a discharge voltage that is more than twice as high as that of batteries using existing alkaline aqueous solutions by using organic electrolytes. As a result, the battery has a high energy density.

  Such a lithium secondary battery includes a positive electrode including a positive electrode active material capable of intercalating and deintercalating lithium, and a negative electrode including a negative electrode active material capable of inserting and desorbing lithium. It is used by injecting an electrolyte into the battery cell.

JP 2004-273451 A

As the positive electrode active material, LiCoO ₂ is widely used. However, due to the scarcity of cobalt (Co), problems of increase in manufacturing cost and stable supply are emerging. For this reason, development of a positive electrode active material using inexpensive Ni (nickel) or Mn (manganese) is in progress.

  On the other hand, a positive electrode active material using Ni (nickel) is suitable for use in a battery for high capacity and high voltage, but its structure is unstable and capacity deterioration occurs, and heat due to reaction with the electrolytic solution. There is a problem that stability is weak.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a lithium secondary battery having a high capacity and excellent thermal stability with an electrolytic solution, a method for producing the same, and lithium. It is to provide a secondary battery.

  In order to solve the above problems, a first aspect of the present invention provides a positive electrode active material for a lithium secondary battery including voids having an average diameter of 10 to 60 nm and a porosity of 0.5 to 20%.

  The voids may have an average diameter of 20-40 nm.

  The positive electrode active material may include a lithium metal oxide represented by the following chemical formula (1), and specifically may include a lithium metal oxide represented by the following chemical formula (2) or chemical formula (3). .

(In the chemical formula (1), M is Al, Mg, Ti, Zr, or a combination thereof, and 0.95 ≦ a ≦ 1.2, 0.45 ≦ x ≦ 0.65, 0.15 ≦ y. ≦ 0.25, 0.15 <z ≦ 0.35, 0 ≦ k ≦ 0.1, and x + y + z + k = 1.)

(In the chemical formula (2), 0.95 ≦ a ≦ 1.10, 0.55 ≦ x ≦ 0.65, 0.15 ≦ y ≦ 0.25, 0.15 <z ≦ 0.25, x + y + z = 1)

(In the chemical formula (3), 0.95 ≦ a ≦ 1.10, 0.45 ≦ x ≦ 0.55, 0.15 ≦ y ≦ 0.25, 0.25 <z ≦ 0.35, x + y + z = 1)

The second aspect of the present invention is a coprecipitation reaction of each metal source material containing nickel (Ni), cobalt (Co) and manganese (Mn), and ammonium hydroxide (NH ₄ OH) or sodium hydroxide (NaOH). Producing a precipitate, mixing the precipitate with a lithium raw material to obtain a mixture, and heat-treating the mixture at a temperature of 800 to 950 ° C. for 8 to 10 hours, Provided is a method for producing a positive electrode active material for a lithium secondary battery that includes a void of 60 nm and has a porosity of 0.5 to 20%.

  The positive electrode active material may include a lithium metal oxide represented by the chemical formula (1).

  The heat treatment may be performed at a temperature of 800 to less than 900 ° C.

  The coprecipitation reaction may be performed at a reaction rate of 600 to 800 rpm, may be performed at a pH of 10 to 12, may be performed for 8 to 10 hours, or may be performed at a temperature of 35 to 40 ° C.

  The precipitate and the lithium source material may be mixed in a weight ratio of 1: 1 to 1: 1.1.

  The third aspect of the present invention provides a lithium secondary battery including a positive electrode including the positive electrode active material, a negative electrode, and an electrolytic solution.

  The lithium secondary battery may have a discharge capacity of 170 to 190 mAh / g.

  In addition, the specific matters of the aspects of the present invention are included in the following detailed description.

  As described above, the positive electrode active material according to the present invention has high particle strength, prevents cracking after rolling, has excellent thermal stability with the electrolyte, and can realize a high-capacity lithium secondary battery.

It is the schematic which showed the lithium secondary battery which concerns on 1st Embodiment. It is the graph which showed distribution of the space | gap average size (diameter) of the positive electrode active material which concerns on Example 1 measured by BET method. It is the graph which showed distribution of the space | gap average size (diameter) of the positive electrode active material which concerns on Example 1 measured by the mercury intrusion method. 2 is a FIB analysis photograph of the positive electrode active material according to Example 1. 5 is a FIB analysis photograph of a positive electrode active material according to Comparative Example 1. 3 is a particle size analysis graph of a positive electrode active material according to Example 1. 3 is a particle size analysis graph of a positive electrode active material according to Comparative Example 1. 2 is a DSC graph of each positive electrode active material according to Example 1 and Comparative Example 1.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  Hereinafter, the positive electrode active material according to the first embodiment will be described.

  The positive electrode active material includes fine voids, and the size of the voids may have an average diameter of 10 to 60 nm, specifically, an average diameter of 20 to 40 nm. When the gap has a size in the above range, cracks after rolling can be prevented as the particle strength of the positive electrode active material increases, and the thermal stability with the electrolyte can be improved. Here, the average diameter is, for example, an arithmetic average value of sphere equivalent diameters (diameters) of the respective voids. The porosity is a ratio of the total volume of the voids to the total volume of the positive electrode active material.

  The positive electrode active material may have a porosity of 0.5 to 20%, and specifically may have a porosity of 1 to 5%. When the porosity is within the above range, cracking after rolling can be prevented as the particle strength of the positive electrode active material increases, and the thermal stability with the electrolyte can be improved.

  The size (average diameter) and porosity of the voids are values obtained as a result of measurement by the BET method.

  As the positive electrode active material having the voids, a lithium metal oxide represented by the following chemical formula (1) may be used.

(In the chemical formula (1), M is Al, Mg, Ti, Zr or a combination thereof, and 0.95 ≦ a ≦ 1.2, 0.45 ≦ x ≦ 0.65, 0.15 ≦ y ≦. 0.25, 0.15 <z ≦ 0.35, 0 ≦ k ≦ 0.1, x + y + z + k = 1.)

  Specifically, a lithium metal oxide represented by the following chemical formula (2) or chemical formula (3) may be used as the positive electrode active material.

(In the chemical formula (2), 0.95 ≦ a ≦ 1.10, 0.55 ≦ x ≦ 0.65, 0.15 ≦ y ≦ 0.25, 0.15 <z ≦ 0.25, x + y + z = 1)

(In the chemical formula (3), 0.95 ≦ a ≦ 1.10, 0.45 ≦ x ≦ 0.55, 0.15 ≦ y ≦ 0.25, 0.25 <z ≦ 0.35, x + y + z = 1)

  The lithium metal oxide can realize a high-capacity lithium secondary battery when the nickel (Ni) content is included in the above range.

  The lithium metal oxide may be manufactured by a solid phase method in which a lithium source material and a metal source material such as nickel (Ni), cobalt (Co), manganese (Mn), etc. are mixed in a powder state and heat-treated.

The lithium metal oxide is prepared by mixing a metal raw material such as nickel (Ni), cobalt (Co), manganese (Mn) or the like in a solvent, and adding it to ammonium hydroxide (NH ₄ OH) or sodium hydroxide ( It may be manufactured by a coprecipitation method in which (NaOH) is added and continuously mixed in a coprecipator to form a precipitate, and then lithium raw material is mixed and heat-treated.

  At this time, the coprecipitation reaction may be performed under conditions of pH 10 to 12, reaction time 8 to 10 hours, reaction temperature 35 to 40 ° C., and reaction rate 600 to 800 rpm. As described above, the coprecipitation reaction is performed at a somewhat low reaction rate in order to generate fine voids. However, when the reaction rate is extremely low, the particles become too large, and thus the reaction rate depends on the composition of the positive electrode active material. The range must be adjusted. When carried out in the condition range of the coprecipitation reaction, it becomes easy to produce a positive electrode active material having a specific range of void average size and porosity according to the first embodiment, and thereby a positive electrode active material having high particle strength. Is obtained.

  The precipitate and the lithium source material may be mixed at a weight ratio of 1: 1 to 1: 1.1. When mixing in the said range, a positive electrode active material with high particle strength is obtained.

  Among such production methods, the production is preferably performed by the coprecipitation method. In the case of producing by a coprecipitation method, the metal raw material and the lithium raw material are further mixed, and the formation of fine voids is further advantageous.

  Examples of the lithium raw material include lithium carbonate, lithium acetate, and lithium hydroxide. Examples of the metal raw material include metal-containing acetate, metal-containing nitrate, metal-containing hydroxide, metal-containing oxide, Examples thereof include, but are not limited to, metal-containing sulfates. Of the metal source materials, a metal-containing sulfate may be used. As the solvent, water, ethanol, methanol, acetone or the like may be used.

  The heat treatment may be performed at a temperature range of 800 to 950 ° C., specifically 800 to less than 900 ° C. during the heat treatment after the solid phase method and the coprecipitation method, or may be performed for 8 to 10 hours. Good. As described above, the heat treatment is performed at a slightly lower temperature in order to generate fine voids. However, when the heat treatment temperature is extremely low, unreacted substances increase. Therefore, the temperature range is adjusted according to the positive electrode active material composition. Must. When the heat treatment is performed within the range of the temperature and time, the grain shape of the positive electrode active material is excellent, the surface is smooth, and the thermal stability with the electrolyte can be improved. A lithium secondary battery having a high capacity and excellent efficiency can be obtained.

  Hereinafter, a lithium secondary battery including the positive electrode active material will be described with reference to FIG.

  FIG. 1 is a schematic view showing a lithium secondary battery according to the first embodiment.

  Referring to FIG. 1, a lithium secondary battery 100 according to the first embodiment includes a positive electrode 114, a negative electrode 112 facing the positive electrode 114, a separator 113 disposed between the positive electrode 114 and the negative electrode 112, and a positive electrode 114, The battery cell includes an electrolyte solution (not shown) impregnating the negative electrode 112 and the separator 113, the battery container 120 including the battery cell, and the sealing member 140 that seals the battery container 120.

  The positive electrode 114 includes a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer includes a positive electrode active material, a binder, and optionally a conductive material.

  Al may be used as the current collector, but is not limited thereto.

  As the positive electrode active material, a lithium metal oxide containing voids as described above may be used. When the lithium metal oxide is used as a positive electrode active material, a high-capacity lithium secondary battery can be realized, and cracking after rolling is prevented as the particle strength of the positive electrode active material increases, so that the electrolyte solution And thermal stability can be improved.

  The binder plays a role of adhering a plurality of positive electrode active material particles to each other and also adhering the positive electrode active material to a current collector, for example, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride. , Carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber , Epoxy resin, nylon and the like, but are not limited thereto.

  The conductive material is used for imparting conductivity to the electrode. In the battery that is configured, any material may be used as long as it is an electron conductive material without causing a chemical change. Natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, copper, nickel, aluminum, silver and other metal powders, metal fibers, etc. may be used, or conductive materials such as polyphenylene derivatives May be used alone or in combination.

  The negative electrode 112 includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector.

  The negative electrode current collector may use copper foil.

  The negative active material layer includes a negative active material, a binder, and optionally a conductive material.

  The negative active material includes a material capable of reversibly inserting / extracting lithium ions, a lithium metal, a lithium metal alloy, a material capable of doping and dedoping lithium, or a transition metal oxide.

  The material capable of reversibly inserting / extracting lithium ions is a carbon material, and any carbon-based negative electrode active material generally used in lithium secondary batteries may be used. Carbonaceous, amorphous carbon, or these may be used together. Examples of the crystalline carbon include amorphous, plate-like, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon. Examples thereof include carbon (soft carbon), hard carbon, meso-face pitch carbide, and calcined coke.

  Examples of the lithium metal alloy include lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn. More selected metal alloys may be used.

Examples of the material capable of doping and dedoping lithium include Si, SiO _x (0 <x <2), Si—Y alloy (where Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a transition metal, An element selected from the group consisting of rare earth elements and combinations thereof, not Si), Sn, SnO ₂ , Sn—Y (where Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition) These are elements selected from the group consisting of metals, rare earth elements and combinations thereof, and are not Sn), and at least one of these may be used in combination with SiO ₂ . As the element Y, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, It may be selected from the group consisting of S, Se, Te, Po, and combinations thereof.

  Examples of the transition metal oxide include vanadium oxide and lithium vanadium oxide.

  The binder plays a role of adhering a plurality of negative electrode active material particles to each other well and adhering the negative electrode active material to a current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose. , Polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated Examples include, but are not limited to, styrene-butadiene rubber, epoxy resin, and nylon.

  The conductive material is used for imparting conductivity to the electrode. In the battery that is configured, any material may be used as long as it is an electron conductive material without causing a chemical change. Conductive properties such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon materials such as carbon fiber, metal powders such as copper, nickel, aluminum and silver or metal materials such as metal fiber, polyphenylene derivatives, etc. Conductive materials including polymers or mixtures thereof may be used.

  The negative electrode 112 and the positive electrode 114 are each manufactured by mixing an active material, a conductive material, and a binder in a solvent to produce an active material composition, and applying the composition to a current collector.

  Since such an electrode manufacturing method is widely known in the field, detailed description is omitted in this specification. N-methylpyrrolidone or the like may be used as the solvent, but is not limited thereto.

  The electrolytic solution includes a non-aqueous organic solvent and a lithium salt.

  The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. The non-aqueous organic solvent may be selected from carbonate-based, ester-based, ether-based, ketone-based, alcohol-based and non-protonic solvents.

  Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (MPC), and the like. ethyl propylene carbonate (EPC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (pr pylene carbonate, PC), butylene carbonate (butylene carbonate, BC) and the like may be used.

  In particular, a mixture of a chain carbonate compound and a cyclic carbonate compound is desirable because it can be produced as a solvent having a high viscosity and a low viscosity. In this case, the cyclic carbonate compound and the chain carbonate compound may be mixed and used at a volume ratio of about 1: 1 to 1: 9.

  Examples of the ester solvent include n-methyl acetate, n-ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, and valerolactone. Mevalonolactone, caprolactone, etc. may be used. As the ether solvent, for example, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran or the like may be used, and as the ketone solvent, cyclohexanone or the like may be used. In addition, as the alcohol solvent, ethyl alcohol, isopropyl alcohol, or the like may be used.

  The non-aqueous organic solvents may be used singly or as a mixture of one or more, and the mixing ratio when used in a mixture of one or more may be appropriately adjusted according to the intended battery performance.

  The non-aqueous electrolyte may further include an additive such as an overcharge inhibitor such as ethylene carbonate or pyrocarbonate.

  The lithium salt is dissolved in an organic solvent and acts as a source of lithium ions in the battery to enable basic lithium secondary battery operation and promote the movement of lithium ions between the positive electrode and the negative electrode It is a substance that fulfills

Specific examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN (SO ₃ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural numbers), LiCl, LiI, LiB (C ₂ O ₄ ) ₂ (lithium bisoxalate borate ( lithiumbis (oxalato) borate, LiBOB), or a combination thereof.

  The concentration of the lithium salt should be in the range of about 0.1M to about 2.0M. When the concentration of the lithium salt is within the above range, the electrolytic solution has appropriate conductivity and viscosity, so that it has excellent electrolytic solution performance, and lithium ions can effectively move.

  The separator 113 may be a single film or a multilayer film, and may be formed of, for example, polyethylene, polypropylene, polyvinylidene fluoride, or a combination thereof.

  The lithium secondary battery has a discharge capacity of 170 to 190 mAh / g under a discharge condition of 4.3 V, CC / CV mode and 0.1 C rate, specifically, a discharge capacity of 175 to 185 mAh / g. May be. As a result, it is possible to improve the thermal stability and at the same time realize a high-capacity lithium secondary battery.

  Hereinafter, specific examples of the present invention will be presented. However, the examples described below are merely for illustrating and explaining the present invention, and the present invention is not limited thereto.

Further, since the contents not described here can be sufficiently technically estimated by those skilled in the art, description thereof will be omitted.
(Production of positive electrode active material)

NiSO ₄ , CoSO ₄ and MnSO ₄ aqueous solutions each having a concentration of about 3M were mixed at a molar ratio of 6: 2: 2, respectively, and about 7M NaOH aqueous solution and about 1M NH ₄ OH aqueous solution were added to the solution. Mix continuously in a sink. The mixture was coprecipitated at pH 11 with a reaction time of 8 hours, a reaction temperature of 40 ° C., and a reaction rate of about 800 rpm to obtain a (NiCoMn) OH ₂ precursor. The precursor was washed with water and dried in an oven at 120 ° C., and then the precursor and Li ₂ CO ₃ were mixed using a simple mixer so that the weight ratio was about 1: 1.03. The mixture obtained from this was put in a firing container and fired at a rate of 2 ° C./min at a temperature of 860 ° C. for about 10 hours to produce a lithium metal oxide LiNi _0.6 Co _0.2 Mn _0.2 O ₂ . .

NiSO ₄ , CoSO ₄ and MnSO ₄ aqueous solutions each having a concentration of about 3M were mixed at a molar ratio of 6: 2: 2, respectively, and about 7M NaOH aqueous solution and about 1M NH ₄ OH aqueous solution were added to the solution. Mix continuously in a sink. The mixture was coprecipitated at pH 11 with a reaction time of 8 hours, a reaction temperature of 40 ° C., and a reaction rate of about 800 rpm to obtain a (NiCoMn) OH ₂ precursor. The precursor was washed with water and dried in an oven at 120 ° C., and then the precursor and Li ₂ CO ₃ were mixed using a simple mixer so that the weight ratio was about 1: 1.03. The mixture obtained from this was put in a firing container and fired at a rate of 2 ° C./min at a temperature of 900 ° C. for about 10 hours to produce a lithium metal oxide LiNi _0.6 Co _0.2 Mn _0.2 O ₂ . .

NiSO ₄ , CoSO ₄ and MnSO ₄ aqueous solutions each having a concentration of about 3M are mixed at a molar ratio of 5: 2: 3, respectively, and about 7M NaOH aqueous solution and about 1M NH ₄ OH aqueous solution are added to the solution. Mix continuously in a sink. The mixture was coprecipitated at pH 11 with a reaction time of 8 hours, a reaction temperature of 40 ° C., and a reaction rate of about 800 rpm to obtain a (NiCoMn) OH ₂ precursor. The precursor was washed with water and dried in an oven at 120 ° C., and then the precursor and Li ₂ CO ₃ were mixed using a simple mixer so that the weight ratio was about 1: 1.03. The mixture obtained from this was put into a firing container and fired at a rate of 2 ° C./minute for about 10 hours at a temperature of 860 ° C. to produce a lithium metal oxide LiNi _0.5 Co _0.2 Mn _0.3 O ₂ . .

NiSO ₄ , CoSO ₄ and MnSO ₄ aqueous solutions each having a concentration of about 3M are mixed at a molar ratio of 5: 2: 3, respectively, and about 7M NaOH aqueous solution and about 1M NH ₄ OH aqueous solution are added to the solution. Mix continuously in a sink. The mixture was coprecipitated at pH 11 with a reaction time of 8 hours, a reaction temperature of 40 ° C., and a reaction rate of about 800 rpm to obtain a (NiCoMn) OH ₂ precursor. The precursor was washed with water and dried in an oven at 120 ° C., and then the precursor and Li ₂ CO ₃ were mixed using a simple mixer so that the weight ratio was about 1: 1.03. The mixture obtained from this was put into a firing container and fired at a rate of 2 ° C./minute at a temperature of 900 ° C. for about 10 hours to produce a lithium metal oxide LiNi _0.5 Co _0.2 Mn _0.3 O ₂ . .

[Comparative Example 1]
NiSO ₄ , CoSO ₄ and MnSO ₄ aqueous solutions each having a concentration of about 3M are mixed at a molar ratio of 5: 2: 3, respectively, and about 7M NaOH aqueous solution and about 1M NH ₄ OH aqueous solution are added to the solution. Mix continuously in a sink. The mixture was coprecipitated at pH 11 with a reaction time of 8 hours, a reaction temperature of 40 ° C., and a reaction rate of about 1000 rpm to obtain a (NiCoMn) OH ₂ precursor. The precursor was washed with water and dried in an oven at 120 ° C., and then the precursor and Li ₂ CO ₃ were mixed using a simple mixer so that the weight ratio was about 1: 1.03. The mixture obtained from this was put into a baking container and baked at a temperature of 970 ° C. for about 15 hours at a rate of 2 ° C./min to produce a lithium metal oxide LiNi _0.5 Co _0.2 Mn _0.3 O ₂ . .

[Comparative Example 2]
NiSO ₄ , CoSO ₄ and MnSO ₄ aqueous solutions each having a concentration of about 3M are mixed at a molar ratio of 5: 2: 3, respectively, and about 7M NaOH aqueous solution and about 1M NH ₄ OH aqueous solution are added to the solution. Mix continuously in a sink. The mixture was coprecipitated at pH 11 with a reaction time of 8 hours, a reaction temperature of 40 ° C., and a reaction rate of about 1000 rpm to obtain a (NiCoMn) OH ₂ precursor. The precursor was washed with water and dried in an oven at 120 ° C., and then the precursor and Li ₂ CO ₃ were mixed using a simple mixer so that the weight ratio was about 1: 1.03. The mixture obtained from this was put in a firing container and fired at a rate of 2 ° C./min at a temperature of 1050 ° C. for about 15 hours to produce a lithium metal oxide LiNi _0.5 Co _0.2 Mn _0.3 O ₂ . .

[Comparative Example 3]
NiSO ₄ , CoSO ₄ and MnSO ₄ aqueous solutions each having a concentration of about 3M are mixed at a molar ratio of 5: 2: 3, respectively, and about 7M NaOH aqueous solution and about 1M NH ₄ OH aqueous solution are added to the solution. Mix continuously in a sink. The mixture was coprecipitated at pH 11 with a reaction time of 8 hours, a reaction temperature of 40 ° C., and a reaction rate of about 1000 rpm to obtain a (NiCoMn) OH ₂ precursor. The precursor was washed with water and dried in an oven at 120 ° C., and then the precursor and Li ₂ CO ₃ were mixed using a simple mixer so that the weight ratio was about 1: 1.03. The mixture obtained from this was put into a baking container and baked at a temperature of 750 ° C. for about 15 hours at a rate of 2 ° C./min to produce a lithium metal oxide LiNi _0.5 Co _0.2 Mn _0.3 O ₂ . .

[Comparative Example 4]
NiSO ₄ , CoSO ₄ and MnSO ₄ aqueous solutions each having a concentration of about 3M were mixed at a molar ratio of 6: 2: 2, respectively, and about 7M NaOH aqueous solution and about 1M NH ₄ OH aqueous solution were added thereto to Mix continuously in a sink. The mixture was coprecipitated at pH 11 with a reaction time of 8 hours, a reaction temperature of 40 ° C., and a reaction rate of about 1000 rpm to obtain a (NiCoMn) OH ₂ precursor. The precursor was washed with water and dried in an oven at 120 ° C., and then the precursor and Li ₂ CO ₃ were mixed using a simple mixer so that the weight ratio was about 1: 1.03. The mixture obtained from this was put into a firing container and fired at a rate of 2 ° C./min at a temperature of 970 ° C. for about 15 hours to produce a lithium metal oxide LiNi _0.6 Co _0.2 Mn _0.2 O ₂ . .

[Comparative Example 5]
NiSO ₄ , CoSO ₄ and MnSO ₄ aqueous solutions each having a concentration of about 3M were mixed at a molar ratio of 6: 2: 2, respectively, and about 7M NaOH aqueous solution and about 1M NH ₄ OH aqueous solution were added thereto to Mix continuously in a sink. The mixture was coprecipitated at pH 11 with a reaction time of 8 hours, a reaction temperature of 40 ° C., and a reaction rate of about 1000 rpm to obtain a (NiCoMn) OH ₂ precursor. The precursor was washed with water and dried in an oven at 120 ° C., and then the precursor and Li ₂ CO ₃ were mixed using a simple mixer so that the weight ratio was about 1: 1.03. The mixture obtained from this was put into a firing container and fired at a rate of 2 ° C./min at a temperature of 750 ° C. for about 15 hours to produce a lithium metal oxide LiNi _0.6 Co _0.2 Mn _0.2 O ₂ . .

Experimental Example 1: Evaluation of Void Size and Porosity of Positive Electrode Active Material A BET apparatus for measuring the size and porosity of the positive electrode active materials manufactured in Examples 1 to 4 and Comparative Examples 1 to 5, respectively. The results are shown in FIG. 2 and Table 1 below using Micrometrics (ASAP2020).

  The measurement range of the void size of the BET device is 1.7 to 300 nm.

  FIG. 2 is a graph showing the distribution of void size (diameter) of the positive electrode active material according to Example 1 measured by the BET method. That is, FIG. 2 is a graph showing a correspondence relationship between the average diameter of the voids and the amount of each void (gap amount). Referring to FIG. 2, it can be seen that the positive electrode active material according to Example 1 has a void average diameter of 20 to 46 nm and a porosity of 2.53%.

  FIG. 3 is a graph showing the distribution of pore size (diameter) of the positive electrode active material according to Example 1 measured by mercury porosimetry. That is, FIG. 3 is a graph showing a correspondence relationship between the average diameter of the voids and the amount of each void (gap amount). Referring to FIG. 3, it can be confirmed that the positive electrode active material according to Example 1 has a void size distribution similar to the graph of FIG. 2 measured by the BET method.

Experimental example 2: Focused ion beam (FIB) analysis photograph evaluation of positive electrode active material The internal structure of each of the positive electrode active materials manufactured in Example 1 and Comparative Example 1 was determined as an FIB apparatus (DBEI, manufactured by FEI). The results are shown in FIGS. 4 and 5, respectively.

  4 is a FIB analysis photograph of the positive electrode active material according to Example 1, and FIG. 5 is a FIB analysis photograph of the positive electrode active material according to Comparative Example 1. From FIG. 4, the size of the voids and the porosity of the positive electrode active material according to the first embodiment can be confirmed in cross section. Referring to FIG. 5, it can be confirmed that the positive electrode active material has a large void size and porosity.

Experimental Example 3: Evaluation of Particle Size Analysis Graph of Positive Electrode Active Material A particle size analyzer (manufactured by Beckman Coulter, LSI3) was used to analyze the crack prevention effect after rolling of the positive electrode active material produced in Example 1 and Comparative Example 1, respectively. 320) and the results are shown in FIGS.

  The measurement conditions of the particle size analyzer are as shown in Table 2 below.

  6 is a particle size analysis graph of the positive electrode active material according to Example 1, and FIG. 7 is a particle size analysis graph of the positive electrode active material according to Comparative Example 1. That is, FIG. 6 is a graph showing the correspondence between the particle size of the hole active material according to Example 1 and the abundance ratio of each hole active material particle. FIG. 7 is a graph showing a correspondence relationship between the particle size of the hole active material according to Comparative Example 1 and the abundance ratio of each hole active material particle. Here, the particle size is, for example, an average diameter. The definition of the average diameter is the same as the average diameter of the voids. The abundance ratio of each hole active material is, for example, the ratio of the number of each hole active material to the total number of hole active material particles. Referring to FIG. 6, according to the first embodiment, in the case of a positive electrode active material having a specific range of void size and porosity, it is confirmed that the effect of preventing cracking is large because the change in particle size distribution after rolling is not large. Thus, it can be seen that the positive electrode active material according to the first embodiment has a high particle strength. Although it can be confirmed from FIG. 7 that the change in the particle size distribution after rolling is large, the particle strength in the case of the positive electrode active material that deviates all from the void size range and the porosity range according to the first embodiment. Is low and cracks occur, and for this reason, the stability decreases due to the reaction with the electrolytic solution.

Experimental Example 4: Evaluation of DSC graph of positive electrode active material The thermal stability of the positive electrode active material produced in Example 1 and Comparative Example 1 was measured using a DSC measuring instrument (TASC, Inc., DSC Q20). The measurement results are shown in FIG.

  FIG. 8 is a DSC graph of each positive electrode active material according to Example 1 and Comparative Example 1. That is, FIG. 8 is a graph showing the correspondence between temperature and heat flow rate for each of Example 1 and Comparative Example 1.

  Referring to FIG. 8, according to the first embodiment, in the case of the positive electrode active material having a specific range of void size and porosity, compared to the case of the positive electrode active material that deviates from the void size and porosity range. It can be confirmed that the main peak moves to a higher temperature, which indicates that the thermal stability is more excellent.

<Production of lithium secondary battery>
After mixing 96% by weight of the positive electrode active materials prepared in Examples 1 to 4 and Comparative Examples 1 to 5, 2% by weight of polyvinylidene fluoride (PVDF), and 2% by weight of acetylene black, N-methyl- A slurry was prepared by dispersing in 2-pyrrolidone. Next, the slurry was applied on a glass plate to produce a positive electrode active material layer. Next, the positive electrode active material layer was applied on an aluminum foil having a thickness of 60 μm, dried at 135 ° C. for 3 hours or more, and then rolled to produce a positive electrode.

As a counter electrode of the positive electrode, a coin-type half battery was manufactured using metallic lithium. As an electrolytic solution at this time, a solution in which 1.3 M concentration of LiPF ₆ was dissolved in a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) having a mixing volume ratio of 3: 7 was used.

Experimental Example 5: Evaluation of charge / discharge characteristics of lithium secondary battery Charge / discharge characteristics of each lithium secondary battery manufactured using the positive electrode active materials manufactured in Examples 1-4 and Comparative Examples 1-5, respectively. Was measured by the following method, and the results are shown in Table 3 below.

  After charging at 0.1 C rate, discharge at 0.1 C rate after resting for 10 minutes. Thereafter, 0.2 Crate, 0.5 C rate, and 1.0 C rate are charged and discharged by the same method. Charging and discharging were performed at 4.3 V in CC / CV mode, respectively, and the following results show the initial capacity at 0.1 C rate. Efficiency (%) is a percentage value of the initial discharge capacity with respect to the initial charge capacity at 0.1 C rate.

  According to Table 3, according to the first embodiment, in the case of a positive electrode active material having a specific range of void sizes and void ratios, it can be confirmed that a high-capacity lithium secondary battery can be realized and battery efficiency is excellent. .

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

100 Lithium secondary battery 112 Negative electrode 113 Separator 114 Positive electrode 120 Battery container 140 Sealing member

Claims (10)

Including a lithium metal oxide represented by the following chemical formula (2 ) ,
The particle size of the lithium metal oxide is 4-50 μm,
Including voids with an average diameter of 20-40 nm,
A positive electrode active material for a lithium secondary battery, wherein the porosity is 1 to 5%.
(In the chemical formula (2), 0.95 ≦ a ≦ 1.10, 0.55 ≦ x ≦ 0.65, 0.15 ≦ y ≦ 0.25, 0.15 <z ≦ 0.25, x + y + z = 1 ) A step of producing a precipitate by coprecipitation reaction of each metal source material including nickel (Ni), cobalt (Co) and manganese (Mn), and ammonium hydroxide (NH ₄ OH) and sodium hydroxide (NaOH). ,
Mixing the precipitate and the lithium source material to obtain a mixture, and heat-treating the mixture at a temperature of 800 to 950 ° C. for 8 to 10 hours,
A lithium metal oxide represented by the following chemical formula (2 ) is included, the particle size of the lithium metal oxide is 4 to 50 μm, includes voids having an average diameter of 20 to 40 nm, and the porosity is 1 to 5%. The manufacturing method of the positive electrode active material for lithium secondary batteries characterized by the above-mentioned.
(In the chemical formula (2), 0.95 ≦ a ≦ 1.10, 0.55 ≦ x ≦ 0.65, 0.15 ≦ y ≦ 0.25, 0.15 <z ≦ 0.25, x + y + z = 1 )   The method for producing a positive electrode active material for a lithium secondary battery according to claim 2, wherein the heat treatment is performed at a temperature of 800 to 900 ° C.   The method for producing a positive electrode active material for a lithium secondary battery according to claim 2, wherein the coprecipitation reaction is performed at a reaction rate of 600 to 800 rpm.   The method for producing a positive electrode active material for a lithium secondary battery according to claim 2, wherein the coprecipitation reaction is performed at a pH of 10 to 12.   The method for producing a positive electrode active material for a lithium secondary battery according to claim 2, wherein the coprecipitation reaction is performed for 8 to 10 hours.   The method for producing a positive electrode active material for a lithium secondary battery according to claim 2, wherein the coprecipitation reaction is performed at a temperature of 35 to 40C.   The method according to claim 2, wherein the precipitate and the lithium source material are mixed in a weight ratio of 1: 1 to 1: 1.1. A positive electrode having a lithium metal oxide represented by the following chemical formula (2 ), a particle size of the lithium metal oxide of 4 to 50 μm, a void having an average diameter of 20 to 40 nm, and a porosity of 1 to 5%. A positive electrode produced by rolling an active material,
A lithium secondary battery comprising a negative electrode and an electrolytic solution.
(In the chemical formula (2), 0.95 ≦ a ≦ 1.10, 0.55 ≦ x ≦ 0.65, 0.15 ≦ y ≦ 0.25, 0.15 <z ≦ 0.25, x + y + z = 1 )   The lithium secondary battery according to claim 9, wherein the lithium secondary battery has a discharge capacity of 170 to 190 mAh / g per mass of the positive electrode active material.