KR20150030364A - Cathode Active Material Comprising the double Surface Treatment layer for Secondary Battery and Method of Preparing the Same - Google Patents

Abstract

The purpose of the present invention is to inhibit interfacial side reaction between a cathode active material and an electrolyte and adjust the surface reforming effect of the cathode active material by adjusting the relative thickness of surface treatment layers, thereby effectively improving the performance of a desired battery. The present invention relates to the cathode active material for a secondary battery comprising double surface treatment layers and to a manufacturing method thereof. More particularly, the cathode active material for a secondary battery comprises: lithium transition metal oxide particles; a first surface treatment layer formed on the surface of the lithium transition metal oxide particles; and a second surface treatment layer formed by surface-reforming the whole or part of the first surface treatment layer.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode active material for a secondary battery including a dual surface treatment layer and a method for manufacturing the cathode active material,

The present invention relates to a cathode active material for a secondary battery including a dual surface treatment layer and a method for producing the cathode active material, and more particularly, to a lithium transition metal oxide particle; A primary surface treatment layer formed on a surface of the lithium transition metal oxide particle; And a secondary surface treatment layer formed by surface-modifying all or a part of the primary surface treatment layer; A cathode active material for a secondary battery, and a method of manufacturing the same.

Lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as the positive electrode active material of the lithium secondary battery, and a lithium-containing manganese oxide such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure, The use of oxides (LiNiO ₂ ) is also used.

Among them, LiCoO ₂ is superior in properties such as excellent cycle characteristics and is widely used at present. However, LiCoO ₂ is relatively expensive, has a charge and discharge current as low as about 150 mAh / g, has a crystal structure unstable at a voltage of 4.3 V or higher, And there is a risk of ignition.

Lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have the advantage of using manganese which is abundant in resources and environmentally friendly as a raw material and thus attracts much attention as a cathode active material capable of replacing LiCoO ₂ , The oxide has a disadvantage in that it has a small capacity and poor cycle characteristics.

Lithium nickel oxide such as LiNiO ₂ has a lower discharge capacity than that of the cobalt oxide when it is charged at 4.3 V and the reversible capacity of the doped LiNiO ₂ is about 165 mAh / g of LiCoO ₂ ) ≪ / RTI > to about 200 mAh / g. However, the LiNiO ₂ based oxide has a problem in that a rapid phase transition of the crystal structure occurs depending on the volume change accompanied by the charge-discharge cycle, and an excessive amount of gas is generated during the cycle.

On the other hand, lithium secondary batteries using the above-mentioned positive electrode active material generally have a problem in that their lifespan rapidly decreases due to repeated charging and discharging. This problem is especially serious at high temperatures. This is because the electrolyte is decomposed or deteriorated due to moisture or other influences inside the battery, and the interface resistance between the electrode including the active material and the electrolyte is increased.

In order to solve these problems and improve the performance of the battery, studies are being made on a technique of surface-modifying the cathode active materials with metal and non-metal or metal-non-metal materials.

Korean Patent Publication No. 277796 discloses a technique of coating metal oxide such as Mg, Al, Co, K, Na, Ca on the surface of a cathode active material and heat-treating the metal oxide in an oxidizing atmosphere. In addition, TiO ₂ is added to LiCoO ₂ to improve energy density and high-rate characteristics (Electrochemical and Solid-State Letters, 4 (6) A65-A67 2001). Recently, a method of modifying the surface of a cathode active material with a lithium metal phosphate compound (Korean Patent Publication No. 2007-0119929) or a technique including sulfur or phosphorus near the surface of a cathode active material (Japanese Patent Application Laid-Open No. 2007-335331) .

However, the problem of structural transition at the surface of the cathode active material due to the reaction between the electrolyte and the cathode active material or the attack of hydrofluoric acid (HF) has not been solved yet.

In addition, the phenomenon that the active material is dissolved by the acid generated by the oxidation of the electrolyte during charging has been introduced as a cause of the capacity reduction of the battery (Journal of Electrochemical Society, 143, 2204 1996). Various methods have been studied to suppress the reactivity between the electrolyte and the cathode active material.

Recently, Korean Patent Publication No. 2007-0120842 discloses a method for preserving a high temperature of a battery using benzoate, phthalate, maleate, succinate, and citrate, which are electrolyte additives that reduce the concentration of hydrofluoric acid present in a battery, There have been reported a technique for improving lifetime characteristics of a cathode active material at a high temperature by coating zinc oxide (ZnO), which generates a compound well by reacting with hydrofluoric acid, on the surface of the cathode active material Al, Co, K, Na, Ca, Si, Ti, Al, and the like are coated on the surface of the cathode active material in Korean Patent Application Publication No. 2003-32363, Oxide, hydroxide, oxycarbonate, hydroxycarbonate salt containing metal of Sn, V, Ge, Ga, B, As, and Zr.

However, these techniques also fail to address the problem of lifetime reduction at high voltages of the cathode active material.

The surface modification of the cathode active material proceeds using an aqueous or organic material as a solvent. In the case of the step of carrying out the surface modification using the above-mentioned solvent, it is easy to confirm the excellent property improvement in a small amount of the surface modification step, but when it is used in a large amount of production, the cost of the process design becomes very high, It is hard to do.

Therefore, there is a great need for a technique capable of easily and economically manufacturing a cathode active material capable of simultaneously suppressing interfacial reaction between a cathode active material and an electrolyte to prevent decrease in battery capacity, and simultaneously improving various performance of a battery. It is true.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments and have found that a lithium transition metal oxide including a primary surface treatment layer and a secondary surface treatment layer formed by surface modification of all or a part of the primary surface treatment layer When used as an active material, it is possible not only to suppress the interface side reaction between the positive electrode active material and the electrolyte, but also to combine the effect of surface modification of the positive electrode active material by controlling the relative thickness of the surface treatment layers, And thus the present invention has been accomplished.

Therefore, the positive electrode active material according to the present invention,

Lithium transition metal oxide particles;

A primary surface treatment layer formed on a surface of the lithium transition metal oxide particle; And

A secondary surface treatment layer formed by surface-modifying all or a part of the primary surface treatment layer;

And a control unit.

FIG. 1 is a schematic view of a secondary surface modification process of a cathode active material, and a formation process of a secondary surface treatment layer can be confirmed.

1, on the surface of the lithium transition metal oxide particle 100 before the secondary surface modification, only the primary surface treatment layer 200 is formed to a predetermined thickness, and the lithium transition metal oxide particles after the secondary surface modification 110, a primary surface treatment layer 210 and a secondary surface treatment layer 310, in which a part of the primary surface treatment layer is changed, are formed to have predetermined thicknesses, respectively.

At this time, the thickness of the primary surface treatment layer 200 formed on the surface of the lithium transition metal oxide particle 100 before the secondary surface modification is not particularly limited, and the thickness of the primary surface treatment layer 200 formed on the surface of the lithium transition metal oxide particle after the secondary surface modification (210) and the secondary surface treatment layer (310).

 This shows that the second surface treatment layer 310 is not newly formed on the first surface treatment layer 200 but a part of the first surface treatment layer 200 is a transition.

In one specific example, the primary surface treatment layer may be composed of a metal or a metal oxide, which is specifically composed of Al, Ba, Ca, Mg, Si, Ti, Zr, Zn, And the metal oxide may be at least one selected from the group consisting of Al ₂ O ₃ , ZnO, TiO ₂ , SiO ₂ , MgO, SnO ₂ , and ZrO ₂ .

In one specific example, the primary surface treatment layer may be formed on part or all of the surface of the lithium transition metal oxide particle, and more specifically, it may be formed on the entire surface.

At this time, the formation of the primary surface treatment layer can be performed by either a dry method or a wet method, and the dry method is a method in which the surface treatment material precursor is mixed with the lithium transition metal oxide particles and subjected to a mixing process, The wet method is a surface treatment by a sol-gel method or a coprecipitation method in an aqueous solution state or a non-aqueous solution state in which a surface treatment substance precursor and a lithium transition metal oxide particle are mixed with each other .

In one specific example, the surface modification for the formation of the secondary surface treatment layer is carried out in the presence of a compound selected from the group consisting of halides (X ₂ ), hydrogen halides, ammonium halides, halogenated ethylamines, halogenated acetamides, and halogenated acetic acid compounds Or by solid-phase synthesis method using the above-described method. In this case, the halogen may be F or Cl.

The surface modification method using the vapor phase high-temperature replacement technique may be carried out as follows. Specifically, one or more compounds selected from the group consisting of the compounds containing F or Cl, together with the lithium-transition metal oxide particles having the primary surface- , The oxide of the first surface treatment layer is replaced by halide from the outermost layer or lithium or metal reacts with the halogen to form a halide to form a second surface A treatment layer is formed.

In the case of the solid phase synthesis method, the lithium transition metal oxide particles in which the primary surface treatment layer is formed are mixed with one or more powders selected from the group consisting of F or Cl-containing compounds through a process such as ball milling process; And a step of reacting at a high temperature, whereby a secondary surface treatment layer is formed by diffusion of ions in the solid.

Other basic matters of the vapor-phase high-temperature substitution technique and the solid-phase synthesis method are well known in the art, and therefore, the description thereof is omitted herein.

In one specific example, the secondary surface treatment layer formed by the above method may be at least one selected from the group consisting of a metal halide, a lithium metal halide, and a lithium halide, Or a halide, wherein the halide may be a fluoride or a chloride.

The material constituting the secondary surface treatment layer may be varied depending on whether the primary surface treatment layer is formed on all or part of the surface of the lithium transition metal oxide particle.

Specifically, when the primary surface treatment layer is formed on the entire surface of the lithium transition metal oxide particle, the secondary surface treatment layer is composed of a metal halide only, and when formed on a part of the surface, the metal halide, lithium metal halide and lithium And a halide. This is because lithium can not diffuse from the lithium transition metal oxide particles when the first surface treatment layer is formed on the entire surface of the lithium transition metal oxide particle.

In one specific example, the sum of the thicknesses of the primary surface treatment layer and the secondary surface treatment layer may be from 0.1 nm to 50 nm

Among them, the thickness of the secondary surface treatment layer may be in the range of 1 to 95% of the entire thickness, specifically in the range of 15 to 75%.

In one specific example, the lithium transition metal oxide particle may be a compound represented by the following formula (1).

Li _x M _y Mn _{2 - y} O _{4 - z z} (1)

Wherein 0.9? X? 1.2; 0 < y? 0.5; 0 < z &lt;0.2; M is a transition metal cation having an oxidation number of +2 valency; A is an anion of oxidation number-1 or -2.

The compound represented by the formula (1) is a lithium manganese oxide having a spinel structure, in which a part of manganese (Mn) is substituted with transition metal cations having oxidation number of +2, And may be one or more elements selected from the group consisting of Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Specifically, it may be Ni. In this case, the compound represented by Formula 1 may be LiNi _0.5 Mn _1.5 O _{4 in} detail

In the above formula 1, the oxygen element may be partially substituted with an anion such as an oxidation-1 or a -2-valent anion, and A is a halogen such as F, Cl, Br or I, or a group selected from the group consisting of S and N Or more. It goes without saying that the content (z) of A varies depending on the oxidation number of A.

The substitution of these anions is intended to improve the bonding force with the transition metal and to prevent the structural transition of the compound to improve the lifetime of the battery. On the other hand, if the substitution amount of the anion A is too large (z? 0.2), the life characteristic is deteriorated due to the incomplete crystal structure, which is not preferable.

The inventors of the present application found that when the dual surface treatment layer of the present invention is applied to a lithium transition metal oxide particle containing a high Mn content like the compound of the above formula 1, Respectively.

The present invention also provides a method for producing the cathode active material for the secondary battery.

Specifically,

(i) a step of forming a primary surface treatment layer made of a metal or a metal oxide on the surface of the lithium transition metal oxide particle to modify the primary surface thereof; And

(ii) converting part or all of the first surface-treated layer into a second surface-treated layer composed of at least one selected from the group consisting of a metal halide, a lithium metal halide, and a lithium halide, process;

It includes

In one specific example, the secondary surface modification in the above process (ii) may include at least one compound selected from the group consisting of halogen (X ₂ ), hydrogen halide, ammonium halide, halogenated ethylamine, halogenated acetamide, and halogenated acetic acid compound , Or by solid phase synthesis, wherein the halogen may be F or Cl, and thus the halide may be fluoride or chloride.

In one specific example, the step (ii) may be carried out by adjusting the thicknesses of the primary surface treatment layer and the secondary surface treatment layer.

Specifically, the secondary surface modification using the vapor phase high-temperature substitution method or the solid phase synthesis method forms a secondary surface treatment layer through substitution or diffusion from the outermost surface of the primary surface treatment layer, so that the reaction time, It is possible to control the thickness of the car and the secondary surface treatment layer.

The inventors of the present application have found that, when the secondary surface treatment layer is formed by converting all the primary surface treatment layers through the above-described method, the secondary surface treatment layer can be uniformly coated as compared with the case where the metal halide is coated by the wet method In the case of forming a secondary surface treatment layer by converting part of the primary surface treatment layer, the ratio of the thickness of each surface treatment layer can be controlled according to the desired surface modification effect, All of which can be demonstrated.

The present invention also provides a lithium secondary battery including the positive electrode including the positive electrode active material and the positive electrode.

The positive electrode is prepared, for example, by coating a mixture of the positive electrode active material, the conductive material and the binder on the positive electrode current collector, and drying the mixture. Optionally, a filler may be further added to the mixture.

Specifically, the cathode active material may include a compound represented by Formula 1, but not limited thereto, and may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ) A compound substituted with the above transition metal; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide expressed by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); Formula _{LiMn 2-x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); A lithium manganese composite oxide having a spinel structure represented by LiNi _x Mn _2-x O ₄ ; LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel A surface treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component which assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The lithium secondary battery generally comprises a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt in addition to the positive electrode, and other components of the lithium secondary battery according to the present invention will be described below.

The negative electrode is prepared, for example, by coating an anode active material on an anode current collector, followed by drying and rolling. Optionally, the conductive material, binder, filler, and the like as described above may be further included.

The negative electrode active material may include, for example, carbon such as non-graphitized carbon or graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 &lt; x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing nonaqueous electrolyte is composed of a nonaqueous electrolyte and lithium. Nonaqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, and the like are used as the nonaqueous electrolyte, but the present invention is 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, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may 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 and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble 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.

For the purpose of improving charge / discharge characteristics, flame retardancy, etc., non-aqueous electrolytes may be used in the form of, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like are added It is possible. In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

As described above, the cathode active material according to the present invention includes the lithium-transition metal oxide having the primary surface treatment layer and the secondary surface treatment layer formed by surface-modifying all or a part of the primary surface treatment layer, It is possible not only to suppress the interfacial reaction in the system but also to manifest various surface modification properties at the same time as well as to control the thickness of the surface treatment layer and effectively improve the desired cell performance.

Further, the present invention can form the surface treatment layer uniformly by using the vapor phase high-temperature substitution technique or the solid phase synthesis method to form the secondary surface treatment layer, and suppress the deterioration of the active material in the liquid phase Therefore, it is possible to economically manufacture a high-quality cathode active material.

1 is a schematic diagram of a secondary surface modification process of a cathode active material according to an embodiment of the present invention;
2 is a SEM photograph of a cathode active material according to one embodiment of the present invention.

Hereinafter, the present invention will be described with reference to Examples. However, the following Examples are intended to illustrate the present invention, and the scope of the present invention is not limited thereto.

&Lt; Example 1 >

Preparation of cathode active material

LiNi _0.30 Mn _0.55 Co _0.15 O _{2 in} which an Al ₂ O ₃ coating layer having a thickness of about 4 nm to 5 nm was formed was heat-treated for 6 hours in a temperature range of 150 to 600 ° C under an F ₂ atmosphere to form an Al ₂ O ₃ coating layer To obtain LiNi _0.30 Mn _0.55 Co _0.15 O ₂ in which an AlF ₃ coating layer was formed to about 2 nm to 3 nm. SEM photographs of the prepared cathode active material are shown in FIG.

Manufacture of batteries

A positive electrode mixture of 90 wt% of the positive electrode active material prepared above, 5 wt% of Super-C (conductive material) and 5 wt% of PVDF (binder) was added to NMP (N-methyl-2-pyrrolidone) A slurry was prepared and then coated on an aluminum current collector to prepare a positive electrode.

A negative electrode mixture of 95 weight% of artificial graphite, 1.5 weight% of Super-P (conductive agent), 2.5 weight% of SBR (binder) and 1.0 weight% of CMC (thickener) was added to NMP as a solvent to prepare an anode slurry, And then coated on the copper collector to prepare a negative electrode.

A lithium secondary battery was prepared using an electrolyte solution of 1M LiPF6 EC / DMC / EMC = 3/4/3 (vol%) with a porous separator interposed between the positive electrode and the negative electrode.

&Lt; Example 2 >

In Example 1, about 8 nm to 9 nm Al₂O₃ LiNi with the coating layer formed_0.30Mn_0.55Co_0.15O₂AlF₃ The procedure of Example 1 was repeated except that the coating layer was formed A cathode material, a cathode material and a lithium secondary battery.

&Lt; Example 3 >

In Example 1, about 4 nm to 5 nm AlF₃ LiNi with the coating layer formed_0.30Mn_0.55Co_0.15O₂Was prepared in the same manner as in Example 1 A cathode material, a cathode material and a lithium secondary battery.

&Lt; Comparative Example 1 &

In Example 1, AlF₃ The same procedure as in Example 1 was carried out except that no coating layer was formed A cathode material, a cathode material and a lithium secondary battery.

&Lt; Comparative Example 2 &

In Example 2,₃ The same procedure as in Example 2 was carried out except that no coating layer was formed A cathode material, a cathode material and a lithium secondary battery.

&Lt; Comparative Example 3 &

In Example 1, about 4 nm to 5 nm Al₂O₃ LiNi with the coating layer formed_0.30Mn_0.55Co_0.15O₂To AlF₃The dispersed coating solution was slowly impregnated to form Al₂O₃ Coating layer and AlF₃ LiNi &lt; / RTI &gt; forming the coating layer_0.30Mn_0.55Co_0.15O₂Was used in place of &lt; RTI ID = 0.0 &gt; A cathode material, a cathode material and a lithium secondary battery.

<Experimental Example 1>

In order to confirm the effect of the double surface treatment, the elemental analysis results of the cathode active material prepared in Example 1 and a sample obtained by directly fluorinating LiNi _0.30 Mn _0.55 Co _0.15 O ₂ without Al ₂ O ₃ coating are shown in Table 1 Respectively.

element Na Ni Co F Mn O C Al F ₂ treatment ref. 9.7 0.5 0.5 59.8 3.6 23.2 2.7 - Al ₂ O ₃ / AlF ₃ bilayer 9.8 0.6 0.5 42.4 3.0 33.7 2.4 7.6

Referring to Table 1, LiNi _0.30 Mn _0.55 Co _0.15 O _2, the two of the surface-treated, i.e., a primary coating layer of the element with the content after the conversion the part of the Al ₂ O ₃ as AlF _3, Al ₂ O ₃ coating , The effect of the double surface treatment can be confirmed by comparing the element contents of the sample subjected to the fluorination treatment with LiNi _0.30 Mn _0.55 Co _0.15 O ₂ immediately (F ₂ treatment ref.).

Specifically, even when LiNi _0.30 Mn _0.55 Co _0.15 O ₂ not coated with Al ₂ O ₃ is fluorinated, a large amount of fluorine is measured because the content of oxygen is decreased. As a result, the oxygen in the active material structure and the substitution reaction or the active material , Which results in a decrease in the capacity of the active material.

On the other hand, when the LiNi _0.30 Mn _0.55 Co _0.15 O ₂ primary coating with Al ₂ O ₃ was fluorinated, the decrease of the oxygen content hardly occurred. As a result, oxygen in the active material structure or in the active material It can be seen that the reaction with Li ions is effective in blocking the Al ₂ O ₃ primary coating layer.

<Experimental Example 2>

In order to examine the lifespan characteristics of the batteries of Examples 1 to 3 and Comparative Examples 1 to 3, using the charge / discharge device (model number: Toscat 3000U, Toyo Co., Japan) as an electrochemical analyzer, The positive and negative electrodes were charged and discharged once at a rate of 0.1 C-rate from 2.0 to 4.65 V at 25 캜. The measured charge capacity, discharge capacity and efficiency of charge vs. discharge capacity are shown in Table 2 below.

Charging capacity (mAh / g) (0.1 C) Discharge capacity (mAh / g) (0.1 C) efficiency(%) Example 1 259 248 96 Example 2 283 238 84 Example 3 257 245 95 Comparative Example 1 289 253 88 Comparative Example 2 265 205 77 Comparative Example 3 272 232 85

Referring to Table 2, it can be seen that the cells of Examples 1 and 3 were significantly improved in charge-discharge efficiency characteristics than the cells of Comparative Example 1, This is because AlF _{3, which} is a secondary surface treatment layer, improves ion conductivity and reduces resistance.

In addition, in the case of Comparative Example 3 in which the secondary surface treatment layer was formed by the wet method, the discharge capacity of the battery was decreased and the efficiency was remarkably reduced as compared with the case of Example 1. [ This is because when the secondary surface treatment layer is formed by the wet method, AlF _{3, which} is not uniform in particle size, is present on the surface of the cathode active material, and the resistance is rather increased to decrease the characteristics.

<Experimental Example 3>

In order to examine the resistance and life characteristics of the batteries of Examples 1 to 3 and Comparative Examples 1 to 3, the battery was charged and discharged once at a rate of 0.1 C-rate from 2.5 to 4.6 V at 25 ° C, And a charge-discharge cycle test was conducted 200 times at a rate of 0.5 C at a rate of 2.5 to 4.35 V at 45 ° C to obtain a life characteristic percentage of the 200th cycle versus a discharge capacity (0.5C-rate) of the first cycle Are shown in Table 3 below.

Resistance (Ohm) Life characteristics (capacity retention rate,%) Example 1 1.65 87 Example 2 1.7 85 Example 3 1.6 88 Comparative Example 1 1.7 85 Comparative Example 2 1.8 82 Comparative Example 3 2.1 70

Referring to Table 3, the batteries of Examples 1 and 3 exhibited lower resistance values than those of Comparative Example 1, and the batteries of Example 2 had lower resistance values than the batteries of Comparative Example 2, It can be seen that it is improved.

It can also be seen that the batteries of Examples 1 and 3 have significantly improved lifetime characteristics than the batteries of Comparative Example 1,

<Experimental Example 4>

In order to evaluate the high-rate characteristics of the batteries of Examples 1 to 3 and Comparative Examples 1 to 3, the batteries were charged at a rate of 0.1 C-rate up to 4.6 V, discharged to 2.5 V at a rate of 0.1 C-rate, , Charge to 0.1C-rate 2.5V, charge to 4.35V at 0.5C-rate 0.5C-rate discharge to 2.5V, charge to 4.35V at 0.5C-rate, discharge to 1.0C-rate 2.5V, 0.5C -rate was charged to 4.35 V and discharged at 2.0 C-rate to 2.5 V. The discharging capacity percentage at each C-rate based on the discharging capacity at the time of 0.1 C-rate discharge is shown in Table 4 below.

0.1 C 0.5 C 1.0 C 2.0C Example 1 100 92 87 82 Example 2 100 89 83 76 Example 3 100 93 88 82 Comparative Example 1 100 88 81 72 Comparative Example 2 100 86 77 68 Comparative Example 3 100 86 76 67

Referring to Table 4 above, the cells of Examples 1 and 3 showed better performance than the cells of Comparative Example 1, and the cells of Example 2 showed better performance than the cells of Comparative Example 2, Able to know. In addition, in the case of Comparative Example 3 in which the secondary surface treatment layer was formed by the wet method, the resistance was increased due to the uneven coating layer, and the rate characteristic was remarkably decreased.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (18)

Lithium transition metal oxide particles;
A primary surface treatment layer formed on a surface of the lithium transition metal oxide particle; And
A secondary surface treatment layer formed by surface-modifying all or a part of the primary surface treatment layer;
And a positive electrode active material for a secondary battery. The cathode active material for a secondary battery according to claim 1, wherein the lithium transition metal oxide particles are represented by the following formula (1)
Li _x M _y Mn _{2 - y} O _{4 - z z} (1)
Wherein 0.9? X? 1.2; 0 < y? 0.5; 0 < z &lt;0.2; M is a transition metal cation having an oxidation number of +2 valency; A is an anion of oxidation number-1 or -2. The cathode active material for a secondary battery according to claim 1, wherein the primary surface treatment layer is made of a metal or a metal oxide. 4. The method of claim 3 wherein the metal is Al, Ba, Ca, Mg, Si, Ti, Zr, Zn, and a is at least one selected from the group consisting of Sr, the metal oxide is Al ₂ O _3, ZnO, TiO _{2 , SiO 2, MgO, SnO 2} , and a secondary battery positive electrode active material, characterized in that at least one selected from the group consisting of ZrO _2. The positive electrode active material for a secondary battery according to claim 1, wherein the primary surface treatment layer is formed on part or all of the surface of the lithium transition metal oxide particle. The positive electrode active material for a secondary battery according to claim 1, wherein the surface modification for forming the secondary surface treatment layer is performed by a vapor phase high temperature replacement technique or a solid phase synthesis method. 2. The method of claim 1, wherein the surface modification for formation of the secondary surface treatment layer is carried out by using one selected from the group consisting of halogen (X ₂ ), hydrogen halide, ammonium halide, halogenated ethylamine, halogenated acetamide, and halogenated acetic acid compound Or more, and the halogen is F or Cl. The positive electrode active material for a secondary battery according to claim 1, wherein the secondary surface treatment layer comprises at least one selected from the group consisting of a metal halide, a lithium metal halide, and a lithium halide. The positive electrode active material for a secondary battery according to claim 8, wherein the secondary surface treatment layer comprises a metal halide. The positive electrode active material for a secondary battery according to claim 8, wherein the halide is a fluoride or a chloride. The positive electrode active material for a secondary battery according to claim 1, wherein the sum of the thicknesses of the first surface treatment layer and the second surface treatment layer is 0.1 nm to 50 nm. A method for producing a cathode active material for a secondary battery according to claim 1,
(i) a step of forming a primary surface treatment layer made of a metal or a metal oxide on the surface of the lithium transition metal oxide particle to modify the primary surface thereof; And
(ii) converting part or all of the first surface-treated layer into a second surface-treated layer composed of at least one selected from the group consisting of a metal halide, a lithium metal halide, and a lithium halide, process;
Wherein the positive electrode active material is a positive electrode active material. 13. The method of claim 12, wherein the secondary surface modification in step (ii) is performed by a vapor phase high temperature replacement technique or a solid phase synthesis method. The method according to claim 12, wherein in the step (ii), the secondary surface modification comprises at least one compound selected from the group consisting of halogen (X ₂ ), hydrogen halide, ammonium halide, halogenated ethylamine, halogenated acetamide, and halogenated acetic acid compound Wherein the halogen is F or Cl. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; 13. The method of claim 12, wherein the halide in step (ii) is a fluoride or a chloride. 13. The method of claim 12, wherein the step (ii) is performed by adjusting the thicknesses of the first surface treatment layer and the second surface treatment layer. An anode comprising the cathode active material according to claim 1. A lithium secondary battery comprising the positive electrode according to claim 17.

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