KR20150069338A - Method for preparing Cathode active material, cathode active material prepared by using the same, and lithium secondary batteries comprising the same - Google Patents

Abstract

The present invention relates to a method for preparing a positive electrode active material, comprising the steps of: mixing fluoride source to lithium metal composite oxide particles and primarily treating the same by heat, and forming a first engraving coating layer from surfaces of the lithium metal composite oxide particles to the inside; and mixing Li_α(NH_4)_βPO_4(α+β=3) to the lithium metal composite oxide particles in which the first engraving coating layer is formed and secondarily treating the same by heat, and forming a second engraving coating layer from surfaces of the lithium metal composite oxide particles in which the first engraving coating layer is formed to the inside, and to the positive electrode active material prepared by the method. According to the present invention, a lithium secondary battery using the positive electrode active material expresses high capacity due to a lithium metal phosphorus oxide having strong binding force with oxygen, and can highly improve lifespan properties since oxygen gas occurs less.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method of preparing a cathode active material, a cathode active material produced by the method, and a lithium secondary battery comprising the cathode active material,

The present invention relates to a cathode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the lithium secondary battery. More particularly, the present invention relates to a lithium secondary battery comprising a lithium secondary battery, A positive electrode active material for a battery, and a method of manufacturing the same.

BACKGROUND ART [0002] A lithium secondary battery is a secondary battery having excellent performance such as a high capacity, a high output and a long life, and is widely used in small electronic products such as electronic devices, portable computers and mobile phones. Especially, as the interest in environmental problems grows, it is one of the main causes of air pollution. As a driving source of electric vehicles that can replace fossil fuel vehicles such as gasoline vehicles and diesel vehicles, lithium Research on secondary batteries is actively under way.

Lithium transition metal oxides containing lithium are mainly used as the positive electrode active material used in lithium secondary batteries, and layered lithium transition metal oxides such as cobalt based, nickel based, and cobalt-nickel- Of the total.

However, the layered lithium transition metal oxide, which is conventionally used as a cathode active material, has a limit in the energy density because the reversible capacity that can be used is 200 mAh / g or less. Therefore, as a means for solving the problem of the lithium secondary battery due to the limitation of the reversible capacity of the anode, a study on a lithium-excess layered oxide (OLO) containing an excess of lithium instead of the general layered lithium transition metal oxide .

The positive electrode active material containing a lithium-excess layered oxide has a structure in which a Li ₂ MnO ₃ phase is mixed with a layered lithium-transition metal oxide such as conventional LiMO ₂ (M is at least one selected from Co, Ni and Mn) When the battery is initially charged at 4.6 V, oxygen is desorbed from Li ₂ MnO ₃ , and lithium is extracted, thereby exhibiting a high capacity.

However, due to the decomposition of the electrolytic solution at high voltage and the generation of self-oxygen, the crystal structure is physically and chemically deformed at the time of repeated charging and discharging, and the rate characteristic is lowered, thereby deteriorating the performance and life characteristics of the battery.

In order to solve such a problem, Patent Document 1 discloses a method of modifying the surface of a lithium-excess metal composite oxide, specifically, a method of modifying the surface of a lithium-excess metal composite oxide, specifically Li _w Ni _x Co _y Mn _1- xy _z M _z O ₂ Mg, Fe, Cu, Zn, Cr, Ag, Ca, Na, K, In, Ga, Ge, V, Mo, Nb, Si, At least one metal selected from the group consisting of Ti and Zr); And a coating layer containing a fluorine compound on the lithium-metal composite oxide core, and a cathode active material for a lithium secondary battery.

Patent Document 2 discloses a lithium _secondary battery in which the core portion of the cathode active material is composed of XLi ₂ MnO _3. (1-X) LiMO ₂ having a high capacity property and the shell portion of the cathode active material is Li _δ [Ni _x Mn _{(1- x + y))} M ' _y ] O ₂ , wherein X is more than 0 and less than 0.9, and M is at least one element selected from the group consisting of nickel, Iron, manganese, cobalt or aluminum, 隆 is not less than 1.0 and not more than 1.5, x is not less than 0.01 and not more than 0.05, and M 'is cobalt, iron or aluminum.

In the case of the secondary battery manufactured using the cathode active material manufactured by the above prior art documents, the initial discharge capacity was 220 mAh / g The lithium transition metal oxide of the present invention has been improved as compared with the cathode active material using the conventional layered lithium transition metal oxide. However, there is a continuing need for research on a cathode active material for a lithium secondary battery having a higher discharge capacity and a longer lifetime.

KR 2013-0033155 A KR 2013-0080565 A

In the present invention, in order to solve the problems of the prior art as described above, the length of the c-axis in the crystal structure on the surface of the lithium-excess layered lithium metal composite oxide capable of high- Which is capable of exhibiting a high capacity, and having an improved life characteristic, by double coating a lithium metal oxide having a strong binding force with fluorine and oxygen which improves the rate characteristics.

Another object of the present invention is to provide a simple method of manufacturing the above-mentioned cathode active material and a secondary battery including the same.

According to an aspect of the present invention, there is provided a lithium-metal composite oxide particle represented by the following Chemical Formula 1, wherein a fluorine source is mixed with a lithium metal complex oxide particle represented by the following Chemical Formula 1, Forming a first engraved coating layer represented by the following formula (1); And a lithium metal composite oxide particle is first engraved coating layer _{Li α (NH 4) β PO} 4 (α + β = 3) heat-treating the second then a solution of the lithium metal composite oxide of the first intaglio coating layer And forming a second intaglio coating layer represented by the following formula (3) inward from the surface of the particles.

Formula 1

Li _{1 + x} Ni _a Co _b Mn _c O _{2 + d}

(Where 0 <x <0.33, 0 <a <0.4, 0 <b <0.4, 0.4 <c <0.9, -0.5 <d <0.5, x + a + b + c = 1)

(2)

Li _{1 + x} Ni _a Co _b Mn _c O _{2 + d} F _z

0.4, 0 <b <0.4, 0.4 <c <0.9, -0.5 <d <0.5, x + a + b + c = 0.1, One)

(3)

Li _{1 + y} Ni _a Co _b Mn _c PO _{4 + ez} F _z

0 <a <0.4, 0 <b <0.4, 0.4 <c <0.9, -0.5 <e <0.5)

The first and second heat treatment temperatures are preferably 500 to 700 ° C.

In the first heat treatment step, the fluorine source is preferably mixed so that the molar ratio of Li: F contained in the cathode active material is 1: 0.01 to 0.05. And, as the fluorine source LiF, NaF, KF, CsF, RbF, TiF, AgF, AgF₂, BaF _2, CaF _2, CuF _2, CdF _2, FeF _2, HgF _2, Hg ₂ F _2, MnF _2, MgF _{2 , NiF 2, PbF 2, SnF} 2, SrF 2, XeF 2, ZnF 2, AlF 3, BF 3, BiF 3, CeF 3, CrF 3, DyF 3, EuF 3, GaF 3, GdF 3, FeF 3, HoF _{3, InF 3, LaF 3,} LuF 3, MnF 3, NdF 3, VOF 3, PrF 3, SbF 3, ScF 3, SmF 3, TbF 3, TiF 3, TmF 3, YF 3, YbF 3, TIF 3, _{CeF 4, GeF 4, HfF 4} , SiF 4, SnF 4, TiF 4, VF 4, ZrF 4, NbF 5, SbF 5, TaF 5, BiF 5, MoF 6, ReF 6, SF 6 , and the group consisting of WF ₆ May be used.

In the secondary heat treatment step is preferably the Li _α (NH _{4) β} of _{PO 4 (α + β = 3} ) Amount of the lithium amount is 1 to 10 mol%, based on the contained in the positive electrode active material.

Meanwhile, the lithium metal composite oxide may be prepared by: synthesizing a transition metal compound precursor; And a step of mixing the precursor of the transition metal compound and a source of Li and then heat-treating the precursor at 600 to 1000 ° C. The lithium source may be Li ₂ CO ₃ , LiOH, LiNO ₃ and LiCH ₃ COO At least one selected may be used.

The present invention also provides a lithium-metal composite oxide particle having a layered structure represented by Formula 1; A first intaglio coating layer represented by Formula 2 formed inside the surface of the lithium metal composite oxide particle; And a second intaglio coating layer represented by Formula 3 formed inside the surface of the lithium metal composite oxide particle having the first intaglio coating layer formed thereon.

The present invention also provides a positive electrode comprising the positive electrode active material; A negative electrode comprising a negative electrode active material; And an electrolyte existing between the positive electrode and the negative electrode.

The lithium secondary battery using the cathode active material according to the present invention is a lithium metal phosphate having a strong binding force with fluorine and oxygen to improve the rate characteristic by increasing the length of the c- The generation of oxygen gas on the surface of the positive electrode active material can be suppressed and the life characteristic can be greatly improved.

In addition, according to the method for producing a cathode active material according to the present invention, the fluorine and lithium metal phosphorus oxides can be coated on the surface of the cathode active material by a simple process.

1 is a schematic view of a cathode active material in which fluorine and lithium metal phosphorous are double intaglio coated.

&Lt; Method for producing positive electrode active material &

The method for producing a cathode active material according to the present invention is characterized by mixing a fluorine source to a lithium metal complex oxide particle expressed by the following Chemical Formula 1 and then subjecting it to a first heat treatment to form a lithium metal complex oxide particle represented by the following Chemical Formula 2 Forming a first intaglio coating layer on the first anticorrosive coating layer; And a lithium metal composite oxide particle is first engraved coating layer _{Li α (NH 4) β PO} 4 (α + β = 3) heat-treating the second then a solution of the lithium metal composite oxide of the first intaglio coating layer And forming a second engraved coating layer represented by the following formula (3) inward from the surface of the particles.

Formula 1

Li _{1 + x} Ni _a Co _b Mn _c O _{2 + d}

(Where 0 <x <0.33, 0 <a <0.4, 0 <b <0.4, 0.4 <c <0.9, -0.5 <d <0.5, x + a + b + c = 1)

(2)

Li _{1 + x} Ni _a Co _b Mn _c O _{2 + d} F _z

0.4, 0 <b <0.4, 0.4 <c <0.9, -0.5 <d <0.5, x + a + b + c = 0.1, One)

(3)

Li _{1 + y} Ni _a Co _b Mn _c PO _{4 + ez} F _z

0.1 <y <0.33, 0.01 <z <0.05, 0 <a <0.4, 0 <b <0.4, 0.4 <c <0.9, -0.5 <e <0.5).

Here, the expression "intaglio coating" means that, in a state in which only some of the raw materials forming the coating layer (lithium source, phosphorus source or fluorine compound) are additionally supplied, these additional supplied raw materials are lithium metal complex oxide Which is formed by forming a lithium metal phosphate coating layer on the surface of a base material. In this specification, the term " surface coating " &Quot; intaglio coating "is used to clearly distinguish it from &quot; intaglio coating &quot;. Therefore, the cathode active material according to the present invention does not change the particle size due to the formation of the coating layer unlike the conventional surface coating.

It is preferable that the first and second heat treatments are performed at a temperature of 500 to 700 ° C. for 1 to 10 hours. When the temperature is lower than 500 ° C., the transition metal and the fluorine source or Li _α (NH ₄ ) _β PO the reaction between ₄ does not easily achieved may be difficult to form an engraved coating layer, whereas if it exceeds 700 ℃ there is a fear that a phosphate to the inside center of the lithium metal composite oxide.

In the first heat treatment step, fluorine diffuses from the surface of the lithium-metal composite oxide particle to the transition metal in the lithium-metal composite oxide to form a first intaglio coating layer represented by Formula 2.

At this time, it is preferable that the fluorine source is mixed such that the molar ratio of Li: F contained in the cathode active material is 1: 0.01-0.05. If the molar ratio of fluorine is less than 0.01, the coating amount of fluorine in the cathode active material may be reduced, and the effect due to the fluorine coating may not be sufficiently exhibited. On the other hand, if the molar ratio is more than 0.05, . The fluorine source as LiF, NaF, KF, CsF, RbF, TiF, AgF, AgF₂, BaF 2, CaF 2, CuF 2, CdF 2, FeF 2, HgF 2, Hg 2 F 2, MnF 2, MgF 2, NiF ₂ , PbF ₂ , SnF ₂ , SrF ₂ , XeF ₂ , ZnF ₂ , AlF ₃ , BF ₃ , BiF ₃ , CeF ₃ , CrF ₃ , DyF ₃ , EuF ₃ , GaF ₃ , GdF ₃ , FeF ₃ , HoF ₃ , _{InF 3, LaF 3, LuF 3} , MnF 3, NdF 3, VOF 3, PrF 3, SbF 3, ScF 3, SmF 3, TbF 3, TiF 3, TmF 3, YF 3, YbF 3, TIF 3, CeF 4 _{, GeF 4, HfF 4, SiF} 4, SnF 4, TiF 4, VF 4, ZrF 4, NbF 5, SbF 5, TaF 5, BiF 5, MoF 6, ReF 6, SF 6 , and selected from the group consisting of WF ₆ One or more of them may be used, and LiF is preferably used.

Heat-treating a mixture of _{Li α (NH 4) β PO} 4 (α + β = 3) is the lithium metal lithium source and the source of phosphate to the composite oxide particles engraved coating layer is formed is represented by the general formula (2) in the heat treatment step the secondary The NH ₄ is removed from the supply source, and Li and PO ₄ are diffused from the surface of the lithium metal composite oxide particle in an ionic form into the interior of the lithium metal complex oxide particle, Thereby forming a coating layer.

In this case, the mixing amount of Li _alpha (NH ₄ ) _β PO ₄ (α + β = 3) is preferably 1 to 10 mol% based on the total lithium amount contained in the cathode active material, , The ratio of intaglio coating of the lithium metal phosphorus oxide may be reduced and it may be insufficient to suppress the desorption of oxygen from the surface of the cathode active material under a high voltage. On the other hand, if it exceeds 10 mol%, the content of the lithium metal composite oxide is relatively decreased There is a possibility that the capacity of the included secondary battery is lowered.

Meanwhile, the lithium metal complex oxide represented by Formula 1 may be prepared by: synthesizing a transition metal compound precursor; And mixing the precursor of the transition metal compound and a source of Li, followed by heat treatment at 600 to 1000 ° C.

Specifically, a method for producing the lithium metal composite oxide will be described below.

First, a transition metal hydroxide precursor in the hydroxide form is synthesized.

For the synthesis of a precursor in the form of a transition metal hydroxide, it is preferred to use one selected from the group consisting of nickel sulfate, nickel nitrate and nickel carbonate in the form of a salt dissolved in water; Cobalt sulfate, cobalt nitrate and cobalt carbonate; The aqueous solution is prepared by dissolving one selected from the group consisting of manganese sulfate, manganese nitrate, and manganese carbonate at a constant molar concentration, and then, by using at least one base selected from the group consisting of NaOH, NH ₄ OH, and KOH, 12 &lt; / RTI &gt; in the form of hydroxides.

At this time, when the pH is lower than 10, the particle aggregation rate is larger than the nucleation rate of the particles, and the particle size may grow to 3 μm or more. When the pH is higher than 12, The particles are not agglomerated and there may arise a problem that it is difficult to obtain a transition metal hydroxide in which each component of the transition metal such as Ni, Co, Mn is homogeneously mixed.

The SO ₄ ^2- , NH ₄ ⁺ , NO ₃ ^- , Na ⁺ , K ⁺ adsorbed on the surface of the precipitated powder is washed several times with distilled water to synthesize a high purity transition metal hydroxide precursor. The thus-synthesized transition metal hydroxide precursor is dried in an oven at 150 ° C for at least 24 hours so that the water content is 0.1 wt% or less.

The transition metal compound precursor thus prepared is represented by the formula Ni _a Co _b Mn _c (OH) ₂ (0.1 ≤ a <0.5, 0 ≤ b <0.7, 0.2 ≤ c <0.9, a + b + c = 1) It is preferred that the transition metal hydroxide is in the form of a transition metal hydroxide.

After the dried transition metal hydroxide precursor and the Li source are homogeneously mixed, the lithium metal complex oxide is obtained by performing the first heat treatment for 5 to 30 hours at a temperature of 600 to 1000 ° C.

If the heat treatment temperature is less than 600 ° C, the reaction between the Li source and the transition metal hydroxide precursor may not be performed well. On the other hand, when the temperature exceeds 1000 ° C, the particle size of the active material is excessively increased, . As the lithium source, at least one selected from the group consisting of Li ₂ CO ₃ , LiOH, LiNO ₃ and LiCH ₃ COO can be used, and Li ₂ CO ₃ and LiOH can be preferably used.

<Cathode Active Material>

The cathode active material of the present invention is a lithium metal composite oxide particle having a layered structure represented by the following Chemical Formula 1; A first intaglio coating layer formed on the surface of the lithium metal composite oxide particle and expressed by the following formula (2); And a second intaglio coating layer represented by the following formula (3) formed inside the surface of the lithium metal composite oxide particle having the first intaglio coating layer formed thereon.

Formula 1

Li _{1 + x} Ni _a Co _b Mn _c O _{2 + d}

(Where 0 <x <0.33, 0 <a <0.4, 0 <b <0.4, 0.4 <c <0.9, -0.5 <d <0.5, x + a + b + c = 1)

(2)

Li _{1 + x} Ni _a Co _b Mn _c O _{2 + d} F _z

0.4, 0 <b <0.4, 0.4 <c <0.9, -0.5 <d <0.5, x + a + b + c = 0.1, One)

(3)

Li _{1 + y} Ni _a Co _b Mn _c PO _{4 + ez} F _z

0.1 <y <0.33, 0.01 <z <0.05, 0 <a <0.4, 0 <b <0.4, 0.4 <c <0.9, -0.5 <e <0.5).

FIG. 1 is a conceptual view of a cathode active material according to the present invention in which fluorine and lithium metal phosphates are doubly intaglio coated, wherein the lithium metal complex oxide (A) represented by the formula (1) (C) formed on the surface of the lithium metal composite oxide particle on which the first intagliating coating layer (B) is formed, and a second intagliating coating layer (C) The structure of the active material is conceptually explained.

The lithium metal complex oxide represented by Formula 1 has a layered crystal structure in which an excess amount of lithium is mixed in the cationic layer of the transition metal corresponding to the range of x, and manganese in the metal other than lithium is substituted with another metal . However, when the excess lithium content is 0.33 mol or more, the resistance of the positive electrode active material increases and the output of the positive electrode active material decreases, which is not preferable.

Specifically, the lithium metal composite oxide is composed of two phases represented by a layered lithium-transition metal oxide LiMO ₂ (where M is Ni, Co and Mn) and a layered Li ₂ MnO ₃ due to excess lithium .

The layered LiMO ₂ Li ₂ MnO ₃ having a layered structure is an inactive region having Mn ⁴⁺ at about 4.4 V or less. When a voltage of about 4.4 V or more is applied, however, As shown in the reaction formula (2), oxygen is released from Li ₂ MnO ₃ and lithium is extracted to become electrochemically active, and a high capacity of 240 to 250 mAh / g or more can be expressed.

LiMO ₂ → MO ₂ + Li ⁺ + e ^- ... ... (One)

Li ₂ MnO ₃ ? MnO ₂ + 2Li ⁺ + 1 / 2O ₂ + 2e ^- ... ... (2)

However, in order to exhibit such a high capacity, the activation step through initial charging is necessarily required under a high voltage of 4.6 V or more. Therefore, the life of the secondary battery is degraded due to decomposition of the electrolyte at high voltage and generation of self-generated oxygen.

Therefore, the positive electrode active material of the present invention is formed by intaglio coating the lithium metal phosphorus represented by the above formula (3) having a strong bonding force with oxygen at the outermost part of the lithium metal composite oxide, thereby forming Li ₂ MnO ₃ It is possible to improve the lifetime characteristics of the secondary battery.

On the other hand, the content of the fluorine-containing lithium metal complex oxide represented by Formula 2 is preferably 1 to 5 mol% based on the total amount of lithium contained in the cathode active material, and when the content is less than 1 mol% The effect due to the addition may not be sufficiently exhibited. On the other hand, if it exceeds 5 mol%, the resistance of the electrode may increase and the output may be lowered.

The content of the lithium metal phosphate represented by Formula 3 is preferably 1 to 10 mol% based on the total amount of lithium contained in the positive electrode active material. When the content of the lithium metal phosphate is less than 1 mol%, the positive electrode active material It may be insufficient to prevent the desorption of oxygen from the Li ₂ MnO ₃ existing in the outermost portion, while when it exceeds 10 mol%, the content of the lithium metal composite oxide is relatively decreased, so that it is difficult to secure a desired level of battery capacity It is not preferable.

&Lt; Lithium Secondary Battery Containing Cathode Active Material >

The positive electrode active material according to the present invention can be utilized as a positive electrode material of a lithium secondary battery and has the same structure as a known secondary battery except for the cathode active material composition and crystal structure and is manufactured by the same known manufacturing method .

Preferably, the lithium secondary battery can be manufactured by putting a porous separator between an anode and a cathode and introducing an electrolyte into the lithium secondary battery, which is a common method widely known in the art. The electrolyte was prepared using a mixed solution of 1.3 M LiPF ₆ EC (ethylene carbonate): DMC (dimethyl carbonate): EC in a weight ratio of 5: 3: 2 as a cathode, lithium metal as a separation membrane, do.

Hereinafter, a lithium secondary battery including a method for producing a cathode active material according to the present invention and a cathode active material produced thereby will be described in detail with reference to preferred embodiments and comparative examples. However, these embodiments are only a preferred embodiment of the present invention, and the present invention should not be interpreted as being limited by these embodiments.

Example 1

① Synthesis of transition metal hydroxide precursors

Nickel sulfate (NiSO ₄ ), cobalt sulfate (CoSO ₄ ) and manganese sulfate (MnSO ₄ ) were mixed at a molar ratio of 2: 2: 6 to prepare a 2M aqueous metal salt solution. The prepared metal salt aqueous solution was introduced into a 10 L continuous reactor at a rate of 0.5 L / h.

Ammonia water (NH ₄ OH) at a concentration of 2 M was fed through the ammonia supply unit of the reactor at a rate of 0.5 L / hr, and an aqueous solution of sodium hydroxide (NaOH) at a concentration of 2 M was automatically supplied through the sodium hydroxide aqueous solution supply unit , pH 10.8 was maintained through pH meter and control unit. The temperature of the reactor was adjusted to 50 캜, the residence time (RT) was adjusted to 10 hours, and the stirring was carried out at a speed of 500 rpm.

The reaction solution thus obtained was filtered through a filter, purified by distilled water, and then dried in an oven at 120 ° C. for 24 hours to synthesize a transition metal hydroxide precursor Ni _0.2 Co _0.2 Mn _0.6 (OH) ₂ .

② Cathode active material synthesis

A 1 molar equivalent of a transition metal hydroxide precursor synthesized in the above (1) and 0.58 molar equivalent of lithium carbonate (Li ₂ CO ₃ ) were mixed and then subjected to a primary heat treatment at 700 ° C. for 10 hours to synthesize a lithium metal composite oxide.

The synthesized lithium metal composite oxide was mixed with 0.03 molar equivalent of LiF and then subjected to a secondary heat treatment at 600 ° C. for 3 hours to form a lithium metal composite having a first intaglio coating layer formed of a lithium metal oxide containing fluorine on the surface of the lithium metal composite oxide Oxide was obtained.

0.02 molar equivalent of Li (NH ₄ ) ₂ PO ₄ was mixed with the lithium metal composite oxide having the first intaglio coating layer formed thereon and then subjected to a third heat treatment at 600 ° C. for 3 hours to form a lithium metal composite oxide A cathode active material powder having a second intaglio coating layer containing phosphorous oxide was obtained on the surface of the particles.

Comparative Example 1

1 molar equivalent of a transition metal hydroxide precursor synthesized in Example 1 (1) and 0.58 molar equivalent of lithium carbonate (Li ₂ CO ₃ ) were mixed and heat-treated at 700 ° C. for 10 hours to synthesize a lithium metal composite oxide To obtain a positive electrode active material powder.

Comparative Example 2

The lithium metal complex oxide prepared in Comparative Example 1 was mixed with 0.03 molar equivalent of LiF and then heat-treated at 600 ° C for 3 hours to synthesize a lithium metal complex oxide having a fluorine-rich coating on the surface of the lithium metal composite oxide To obtain a positive electrode active material powder.

&Lt; Evaluation of battery capacity and service life characteristics &

Denka Black, a conductive material, and polyvinylidene fluoride (PVDF), which is a binder, were mixed in a weight ratio of 92: 4: 4 to prepare a slurry, in which the cathode active material synthesized in Example 1 and Comparative Examples 1 and 2 was mixed. The slurry was uniformly coated on an aluminum (Al) foil to prepare a positive electrode electrode plate.

A mixture of lithium metal as a cathode, a porous PE separator as a separator, and a mixture of 1,3M LiPF ₆ EC (dimethyl carbonate): EC in a weight ratio of 5: 3: 2 was used as an electrolyte Thereby preparing a coin cell type lithium secondary battery.

Battery capacity

The prepared coin cell was allowed to stand at a constant temperature of 25 ° C for 24 hours, and then a lithium secondary battery charge / discharge test apparatus (Toyo System) was used. The voltage range of the test cell was set to 3.0 to 4.6 V, / CV (Constant Voltage) mode, charging / discharging was carried out at a current of 0.2 C and the discharge capacity was obtained.

Life characteristics

After the first cycle, the voltage range of the test cell was set to 2.5 to 4.6 V, the current of 1 C was charged / discharged in the CC / CV mode, and the cycle was repeated for 50 cycles. The capacity retention rate was calculated by the following formula.

Capacity retention rate (%) = (discharge capacity after 50 charge / discharge / initial discharge capacity) * 100

The discharge capacity and capacity retention rate of the lithium secondary battery including the cathode active material prepared in Example 1, Comparative Example 1 and Comparative Example 2 according to the above evaluation method are shown in Table 1 below.

Discharge capacity (mAh / g) Capacity retention rate (%) Example 1 241 94 Comparative Example 1 230 87 Comparative Example 2 235 89

As can be seen from Table 1, in the case of the secondary battery including the cathode active material of Example 1 in which fluorine and lithium metal phosphorous were doubly coated on the lithium metal composite oxide according to the present invention, It can be seen that the battery capacity and lifetime characteristics are significantly improved as compared with Example 1 and Comparative Example 2 in which only fluorine coating is performed.

Claims (11)

Forming a first intaglio coating layer represented by the following formula (2) inward from the surface of the lithium metal composite oxide particle by mixing a fluorine source with a lithium metal composite oxide particle represented by the following formula (1) and subjecting it to a first heat treatment; And
The lithium metal complex oxide particle having the first intagliated coating layer formed thereon is mixed with Li _alpha (NH ₄ ) _β PO ₄ (α + β = 3) And forming a second intaglio coating layer represented by the following formula (3) inward from the surface of the cathode active material:
Formula 1
Li _{1 + x} Ni _a Co _b Mn _c O _{2 + d}
(Where 0 <x <0.33, 0 <a <0.4, 0 <b <0.4, 0.4 <c <0.9, -0.5 <d <0.5, x + a + b + c = 1)
(2)
Li _{1 + x} Ni _a Co _b Mn _c O _{2 + d} F _z
0.4, 0 <b <0.4, 0.4 <c <0.9, -0.5 <d <0.5, x + a + b + c = 0.1, One)
(3)
Li _{1 + y} Ni _a Co _b Mn _c PO _{4 + ez} F _z
0.1 <y <0.33, 0.01 <z <0.05, 0 <a <0.4, 0 <b <0.4, 0.4 <c <0.9, -0.5 <e <0.5). The method according to claim 1,
Wherein the first and second heat treatment temperatures are 500 to 700 占 폚. The method according to claim 1,
Wherein the fluorine source is mixed such that the molar ratio of Li: F contained in the cathode active material is 1: 0.01 to 0.05. The method according to claim 1,
The fluorine source may be LiF, NaF, KF, CsF, RbF, TiF, AgF, AgF₂, BaF 2, CaF 2, CuF 2, CdF 2, FeF 2, HgF 2, Hg 2 F 2, MnF 2, MgF 2, NiF ₂ , PbF ₂ , SnF ₂ , SrF ₂ , XeF ₂ , ZnF ₂ , AlF ₃ , BF ₃ , BiF ₃ , CeF ₃ , CrF ₃ , DyF ₃ , EuF ₃ , GaF ₃ , GdF ₃ , FeF ₃ , HoF ₃ , _{InF 3, LaF 3, LuF 3} , MnF 3, NdF 3, VOF 3, PrF 3, SbF 3, ScF 3, SmF 3, TbF 3, TiF 3, TmF 3, YF 3, YbF 3, TIF 3, CeF 4 _{, GeF 4, HfF 4, SiF} 4, SnF 4, TiF 4, VF 4, ZrF 4, NbF 5, SbF 5, TaF 5, BiF 5, MoF 6, ReF 6, SF 6 , and selected from the group consisting of WF ₆ Wherein the positive electrode active material is at least one selected from the group consisting of lithium, The method according to claim 1,
The _{Li α (NH 4) β PO} 4 (α + β = 3) Amount of the method of producing a cathode active material characterized in that 1 to 10 mol%, based on the total amount of lithium contained in the positive electrode active material. The method according to claim 1,
The lithium metal composite oxide may be,
Synthesizing a transition metal compound precursor; And
Wherein the transition metal compound precursor is mixed with a Li source and then heat-treated at 600 to 1000 占 폚. The method according to claim 6,
Wherein the lithium source is at least one selected from the group consisting of Li ₂ CO ₃ , LiOH, LiNO ₃ and LiCH ₃ COO. A layered lithium metal composite oxide particle expressed by the following formula (1);
A first intaglio coating layer formed on the surface of the lithium metal composite oxide particle and expressed by the following formula (2); And
And a second intaglio coating layer formed inside the surface of the lithium metal composite oxide particle on which the first intaglio coating layer is formed and expressed by the following Formula 3:
Formula 1
Li _{1 + x} Ni _a Co _b Mn _c O _{2 + d}
(Where 0 <x <0.33, 0 <a <0.4, 0 <b <0.4, 0.4 <c <0.9, -0.5 <d <0.5, x + a + b + c = 1)
(2)
Li _{1 + x} Ni _a Co _b Mn _c O _{2 + d} F _z
0.4, 0 <b <0.4, 0.4 <c <0.9, -0.5 <d <0.5, x + a + b + c = 0.1, One)
(3)
Li _{1 + y} Ni _a Co _b Mn _c PO _{4 + ez} F _z
0.1 <y <0.33, 0.01 <z <0.05, 0 <a <0.4, 0 <b <0.4, 0.4 <c <0.9, -0.5 <e <0.5). 9. The method of claim 8,
Wherein the content of the fluorine-containing lithium metal complex oxide expressed by the general formula (2) is 1 to 5 mol% based on the total amount of lithium contained in the cathode active material. 9. The method of claim 8,
Wherein the content of lithium metal phosphate represented by Formula 3 is 1 to 10 mol% based on the total amount of lithium contained in the positive electrode active material. A cathode comprising the cathode active material of any one of claims 8 to 10;
A negative electrode comprising a negative electrode active material; And
And an electrolyte existing between the positive electrode and the negative electrode.

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