KR100633287B1 - Double-layer cathode active materials for high capacity & high rate capability, method of preparing thereof and lithium secondary battery using thereby - Google Patents

Abstract

Provided are a positive electrode active material for a lithium secondary battery which is high in capacity and charge density, is improved in lifetime characteristics and is excellent in thermal stability, and its preparation method. The positive electrode active material has a dual layer structure which comprises an inner part represented by Li_delta [Ni_x Co_(1-2x) Mn_x]O2 (wherein 1.0<=delta<=1.2 and 0.01<=x<=0.5), and an outer part represented by Li_delta [Ni_x Co_y Mn_(1-(x+y))]O2 (wherein 1.0<=delta<=1.2, 0.5<=x<=1.0 and 0.01<=y<=0.2) or Li_delta CoO2 (wherein 1.0<=delta<=1.2). Preferably the thickness of the outer part is 5-50 % of the total thickness of the positive electrode active material; the inner part has an average diameter of 1-8 micrometers; and the entire particle of positive electrode active material has an average diameter of 9-20 micrometers.

Description

A cathode active material for a lithium secondary battery having a double layer structure having a high capacity and a high rate characteristic, a method of manufacturing the same, and a lithium secondary battery using the same {Double-layer cathode active materials for high capacity & high rate capability, method of preparing etc and lithium secondary battery using

Figure 1a is a composite oxide powder obtained by drying (Ni _1/2 Mn _1/2 ) (OH) ₂ in a 110 ℃ hot air dryer for 24 hours, Figure 1b is a shell in (Ni _1/2 Mn _1/2 ) (OH) ₂ part of the Co (OH) ₂ was 1.5 hours reaction in the form of powder, Figure 1c _{(Ni 1/2 Mn 1/2) (OH} ) 2 to Co (OH) ₂ to 3 hours that the powder, Fig. 1d is ( _{Ni 1/2 Mn 1/2) (OH)} Co (OH) 2 powder in which the camera picture of reaction 4 hours _2.

2 shows (Ni _1/2 Mn _1/2 ) (OH) ₂ and [(Ni _1/2 Mn _1/2 ) _x (Ni _0.8 Co _0.1 Mn _0.1 ) _1-x ] (OH) ₂ and [(Ni FE-SEM photograph of the positive electrode active material powder of _1/2 Mn _1/2 ) _x Co _1-x ] (OH) ₂ ,

3 shows Li [Ni _1/2 Mn _1/2 ] O ₂ , Li [(Ni _1/2 Mn _1/2 ) _x (Ni _0.8 Co _0.1 Mn _0.1 ) _1-x ] O ₂ , Li [(Ni _{1 / 2} Mn _1/2 ) _x Co _1-x ] O ₂ sintered powder particles X-ray diffraction pattern (XRD).

4 shows Li [Ni _1/2 Mn _1/2 ] O ₂ , Li [(Ni _1/2 Mn _1/2 ) _x (Ni _0.8 Co _0.1 Mn _0.1 ) _1-x ] O ₂ , Li [(Ni _{1 / 2} Mn _1/2 ) _x Co _1-x ] O ₂ 2.8-4.3V Charge-discharge Discharge capacity with cycles tested at 0.1C.

5 is Li [Ni _1/2 Mn _1/2 ] O ₂ , Li [(Ni _1/2 Mn _1/2 ) _x (Ni _0.8 Co _0.1 Mn _0.1 ) _1-x ] O ₂ , Li [(Ni _{1 / 2} Mn _1/2 ) _x Co _1-x ] O ₂ discharge capacity with 5 cycles tested at 2.8-4.3V 0.2C, 0.5C, 1C, 2C, 3C.

Figure 6 is a data on the differential weight thermal analysis after 4.3V charging of Li [Ni _1/2 Mn _1/2 ] O ₂ , Li [(Ni _1/2 Mn _1/2 ) _x Co _1-x ] O ₂ .

7 shows (Ni _1/3 Co _1/3 Mn _1/3 ) (OH) ₂ and [(Ni _1/3 Co _1/3 Mn _1/3 ) _x (Ni _0.7 Co _0.1 Mn _0.2 ) _1-x ] FE-SEM photo of precursor powder of (OH) ₂ ,

8 shows Li [(Ni _1/3 Co _1/3 Mn _1/3 )] O ₂ and Li [(Ni _1/3 Co _1/3 Mn _1/3 ) _x (Ni _0.7 Co _0.1 Mn _0.2 ) _1- FE-SEM photograph of the positive electrode active material powder of _x ] O ₂ ,

9 shows Li [(Ni _1/3 Co _1/3 Mn _1/3 )] O ₂ and Li [(Ni _1/3 Co _1/3 Mn _1/3 ) _x (Ni _0.7 Co _0.1 Mn _0.2 ) _{1- x} ] X-ray diffraction pattern (XRD) of the positive electrode active material powder particles of O ₂ ,

10 shows Li [(Ni _1/3 Co _1/3 Mn _1/3 )] O ₂ and Li [(Ni _1/3 Co _1/3 Mn _1/3 ) _x (Ni _0.7 Co _0.1 Mn _0.2 ) _{1- x} ] O ₂ charge and discharge curves of the second cycle tested under 3.0 ~ 4.3V charge-discharge 0.1C,

11 shows Li [Ni _0.33 Co _0.33 Mn _0.3 Mg _0.04 ] O ₂ and Li [(Ni _0.33 Co _0.33 Mn _0.3 Mg _0.04 ) _x (Ni _0.7 Co _0.1 Mn _0.16 Mg _0.04 ) _1-x ] O ₂ 3.0 to 4.3V Charge-discharge Curve of the second cycle tested at 0.1C.

The present invention relates to a positive electrode active material for a lithium secondary battery having a double layer structure and a method of manufacturing the same, and more specifically, a nickel, manganese, cobalt-based positive electrode active material having a high stability and low-cost properties inside and a high capacity nickel-based, high outside The present invention relates to a positive electrode active material having a double layer structure having a high capacity, high packing density, improved lifespan characteristics, and excellent thermal safety.

Li-ion secondary batteries have been widely used as power sources for portable devices since they emerged in 1991 as small, light and large capacity batteries. Recently, with the rapid development of electronics, telecommunications, and computer industry, camcorders, mobile phones, notebook PCs, etc. have emerged and are developing remarkably, and the demand for lithium ion secondary battery as a power source to drive these portable electronic information communication devices is increasing day by day. It is increasing.

In particular, research on power sources for electric vehicles that hybridize an internal combustion engine and a lithium secondary battery has been actively conducted in the United States, Japan, and Europe. However, although the use of lithium ion batteries is considered as a large battery for electric vehicles in terms of energy density, nickel hydride batteries are still in the development stage and in particular in terms of safety, and the biggest challenge is high price and safety.

In particular, the positive electrode active materials such as LiCoO ₂ and LiNiO ₂ which are currently commercially used have a disadvantage in that the crystal structure is unstable due to de-lithography at the time of charging and thus the thermal characteristics are very poor.

That is, when a battery in an overcharged state is heated to 200 to 270 ° C., a sudden structural change occurs, and a reaction of releasing oxygen in the lattice proceeds due to such a structural change (JRDahn et al., Solid State Ionics, 69,265). (1994).

Commercially available small lithium ion _secondary batteries use LiCoO ₂ for the positive electrode and carbon for the negative electrode. LiCoO ₂ is an excellent material having stable charging and discharging characteristics, excellent electronic conductivity, high stability, and flat discharge voltage characteristics. However, cobalt is low in reserve, expensive, and toxic to human body.

LiNiO ₂ having a layered structure such as LiCoO ₂ has a large discharge capacity but is difficult to synthesize a material having a pure layered structure, and Li _x Ni having a rocksalt type structure because of Ni ⁴⁺ ions which are highly reactive after charging. Excess oxygen is released as it transitions to _1-x O, which has not yet been commercialized due to lifetime and thermal instability.

To improve this, attempts have been made to replace a portion of nickel with a transition metal element to shift the exothermic start temperature to a slightly higher temperature side or to broaden the exothermic peak to prevent rapid exotherm (T.Ohzuku et al., J.). Electrochem. Soc., 142, 4033 (1995), Japanese Patent Application Laid-Open No. 237-361), yet no satisfactory results have been obtained.

In addition, LiNi _1-x Co _x O ₂ (x = 0.1 to 0.3) material in which a part of nickel was substituted with cobalt showed excellent charge and discharge characteristics and life characteristics, but thermal safety problems were not solved.

In addition, the composition and manufacturing techniques of Li-Ni-Mn-based composite oxides partially substituted with Mn having excellent thermal stability at Ni sites or Li-Ni-Mn-Co-based composite oxides substituted with Mn and Co are well known. have.

For example, in Japanese Patent No. 8-171910, an alkaline solution is mixed with a mixed aqueous solution of Mn and Ni to coprecipitate Mn and Ni, and lithium hydroxide is mixed with the coprecipitation compound and then calcined to form LiNi _x Mn _1-x O ₂ ( 0.7≤x≤0.95) has been disclosed.

Recently, Japanese Patent No. 2000-227858 discloses a positive electrode active material having a new concept of making a solid solution by uniformly dispersing Mn and Ni compounds at the atomic level, instead of partially substituting a transition metal to LiNiO ₂ or LiMnO ₂ .

However, according to European Patent 0918041 or US Patent 6040090, LiNi _1-x Co _x Mn _y O ₂ (0 <y≤0.3) has improved thermal stability compared to the conventional Ni and Co-only materials, but the reactivity of Ni ⁴⁺ There is a problem to commercialize.

In addition, in European Patent 0872450 A1 and B1, Li _a Co _b Mn _c MdNi _{1- (b + c + d)} O ₂ (M = B, Al, Si.Fe ₎ in which Ni and other metals are substituted in place of Ni and Co. , Cr, Cu, Zn, W, Ti, Ga) type, but the thermal stability of the Ni-based still has not been solved.

Accordingly, the present invention has been made to solve the above problems of the prior art, the inside of the nickel, manganese, cobalt-based transition metal mixed anode having a high stability, low-cost properties using the hydroxide co-precipitation method, the outside is in contact with the electrolyte Composed of high capacity nickel-based anode or cobalt-based anode (hereinafter transition metal anode) with high ion conductivity, it provides cathode active material with double layer structure with high capacity, high packing density, improved lifespan, and excellent thermal stability. Is in.

In addition, another object of the present invention to provide a method for producing a positive electrode active material having the double layer structure.

In addition, another object of the present invention to provide a lithium secondary battery using a positive electrode active material having the double layer structure.

The present invention to achieve the above object, according to a lithium secondary battery positive electrode active material having a double layer structure, the inside is expressed by a composition formula _{Li δ [Ni x Co 1-2x Mn} x] O 2 (1.0≤δ≤1.2, 0.01≤x≤0.5 ) And the outside is Li _δ [Ni _x Co _y Mn _{1- (x + y)} ] O ₂ (1.0 ≦ _δ ≦ 1.2, 0.5 ≦ _x ≦ 1.0, 0.01 ≦ _y ≦ 0.2) or Li _δ CoO ₂ ( It provides a positive electrode active material for a lithium secondary battery having a double layer structure of high capacity, high rate characteristics, characterized in that consisting of 1.0≤δ≤1.2).

In addition, the present invention is a positive electrode active material for a lithium secondary battery having a double-layer structure, the inside is Li _δ [Ni _x Co _1-2x Mn _xa M _a ] O ₂ (M is Mg, Zn, Ca, Sr, Cu, Zr At least one element selected from the group consisting of P, Fe, Al, Ga, In, Cr, Ge, Sn, Ti, Mo, W, Nd, 1.0≤δ≤1.2, 0.01≤x≤0.5, 0.01≤a ≤0.1) and the outer is Li _δ [Ni _x Co _y Mn _{1- (x + y + z)} N _z ] O ₂ (N is selected from the group consisting of Mg, Zn, Ca, Sr, Cu, Zr At least one element, 1.0 ≤ δ ≤ 1.2, 0.5 ≤ x ≤ 1.0, 0.01 ≤ y ≤ 0.2, 0.01 ≤ z ≤ 0.1), the positive electrode active material for a lithium secondary battery having a high capacity, high rate bilayer structure to provide.

The thickness of the outer layer is 5% to 50% of the total thickness of the positive electrode active material.

Said internal average particle diameter is 1-8 micrometers, and the average particle diameter of all the particles of the said positive electrode active material shall be 9-20 micrometers.

The present invention provides a lithium secondary battery using a cathode active material for a lithium secondary battery having a double layer structure.

 In another aspect, the present invention is a manufacturing method for providing the positive electrode active material in the first step of obtaining a spherical precipitate by simultaneously mixing nickel, manganese, cobalt-based transition metal aqueous solution, ammonia aqueous solution and basic aqueous solution in the reactor; A second step of obtaining a precipitate of a double layer composite metal hydroxide covered with a transition metal hydroxide by simultaneously mixing the transition metal mixed solution, the ammonia solution and the basic aqueous solution in the reactor with the precipitate; Drying or depositing the precipitate to obtain a double layer composite metal hydroxide or a double layer composite metal oxide; Method for producing a positive electrode active material for a lithium secondary battery having a double layer structure of a high capacity, high rate characteristics, characterized in that it comprises a fourth step of obtaining a double layer lithium composite metal oxide by mixing a lithium salt in the double layer composite metal hydroxide or double layer composite metal oxide. To provide.

In the first step, an aqueous solution including two or more metal salts is mixed and used as a precursor. The molar ratio of ammonia and metal salts is 0.2 to 0.4, and the pH of the reaction solution is adjusted to 10.5 to 12 for 10 to 20 hours. It features.

The second step is characterized by adjusting the thickness of the outer layer by adjusting the reaction time to 1 to 10 hours.

The third step may be dried at 110 ° C. for 15 hours or heated at 400 to 550 ° C. for 5 to 10 hours.

The third step is characterized in that the preliminary firing step by maintaining for 5 hours at 300 ~ 550 ° C, 10 hours at 700 ~ 1100 ° C, annealing at 600 ~ 750 ° C for 10 hours.

The reaction atmosphere of the aqueous transition metal solution is nitrogen flow, the pH is 10.5 to 12.5, the reaction temperature is 30 to 80 ℃, characterized in that the reaction stirrer rpm is 500 to 2000.

Hereinafter, a cathode active material for a lithium secondary battery having a double layer structure according to the present invention and a manufacturing method thereof will be described in detail.

Method for producing a positive electrode active material for a lithium secondary battery having a double layer structure according to the present invention comprises the first step of obtaining a spherical precipitate by simultaneously mixing nickel, manganese, cobalt-based transition metal aqueous solution, ammonia aqueous solution and basic aqueous solution in the reactor; Step 2 to obtain a precipitate of a double-layer composite metal hydroxide salt covered with a transition metal hydroxide by simultaneously mixing the transition metal mixed solution, ammonia solution and basic aqueous solution on the precipitate on the reactor; Drying or depositing the precipitate to obtain a double layer composite metal oxide; And a four step of obtaining a double-layer lithium composite metal oxide by mixing a lithium precursor with the double-layer composite metal hydroxide or composite metal oxide.

Inside _δ composition formula Li [Ni _x Co _1-2x Mn _x] O ₂ is made of a (1.0≤δ≤1.2, 0.01≤x≤0.5), _δ exterior Li [Ni _x Co _y Mn _{1- (x + y )} ] O ₂ (1.0 ≦ _δ ≦ 1.2, 0.5 ≦ x ≦ 1.0, 0.01 ≦ y ≦ 0.2) or Li _δ CoO ₂ (1.0 ≦ _δ ≦ 1.2).

In addition, the inside of the cathode active material for a lithium secondary battery having a double layer structure of the present invention is a composition formula Li _δ [Ni _x Co _1-2x Mn _xa M _a ] O ₂ (M is Mg, Zn, Ca, Sr, Cu, Zr, P At least one element selected from the group consisting of, Fe, Al, Ga, In, Cr, Ge, Sn, Ti, Mo, W, Nd, 1.0≤δ≤1.2, 0.01≤x≤0.5, 0.01≤a≤0.1 ) And the outside is Li _δ [Ni _x Co _y Mn _{1- (x + y + z)} N _z ] O ₂ (N is at least one selected from the group consisting of Mg, Zn, Ca, Sr, Cu, Zr) Element, 1.0 ≦ δ ≦ 1.2, 0.5 ≦ x ≦ 1.0, 0.01 ≦ y ≦ 0.2, and 0.01 ≦ z ≦ 0.1).

The reactor has a rotary blade designed in reverse wing type, 1 to 4 baffles are separated from the inner wall by 2 to 3 cm, and these baffles are used to uniformly mix the upper and lower parts of the reactor. Installed. The reverse wing design is also designed for uniform mixing up and down, and the separation of the baffles installed on the inner surface of the reactor from the inner wall controls the intensity and direction of the waves and increases the turbulent effect to solve the local nonuniformity of the reaction solution. It is to.

In the method of manufacturing the cathode active material of the present invention, unlike the ammonia complex method in which ammonia water is first mixed with a conventional metal solution and then precipitated, two or more types of metal salt solutions, aqueous ammonia solution, and NaOH solution are respectively added to the reactor. By introducing, it is possible to prevent the initial oxidation of manganese ions to obtain a precipitate in which the uniformity of particles and metal elements are uniformly distributed.

Hereinafter, the metal hydroxide method, which is a method of manufacturing a cathode active material for a lithium secondary battery having a layered rock salt structure and a double layer structure, will be described in detail.

Ni: Co: Mn: M is a: b: 1- (a + b + c): c (M is Mg, Zn, Ca, Sr, Cu, Zr, P, Fe, Al, Ga, In, Cr , Ge, Sn), dissolved in distilled water at a desired ratio. At this time, it is preferable that the substituted metal salt is selected from two or more kinds. The nickel-based metal precursor, an aqueous ammonia solution and a basic solution are put into a reactor and mixed.

At this time, the aqueous metal solution is used in the concentration of 1M to 3M, the aqueous ammonia solution is preferably 20% to 40% of the concentration of the metal solution, the NaOH aqueous solution is preferably used 4M to 5M concentration.

The concentration of the aqueous ammonia solution is 20% to 40% of the concentration of the aqueous metal solution because ammonia reacts one-to-one with the metal precursor, but the intermediate product can be recovered and used again as ammonia, further increasing the crystallinity of the positive electrode active material. This is because it is an optimal condition for stabilization.

In addition, the NaOH aqueous solution is injected so that the pH of the mixed solution is maintained at 10.5 to 12, and the reaction time in the reactor is preferably adjusted to 10 to 20 hours.

To describe the first step in more detail, first, nickel, manganese, cobalt and substituted metal salts are dissolved in distilled water, and then introduced into the reactor with ammonia water solution and NaOH aqueous solution to cause precipitation. The coprecipitation method is a method of obtaining a composite hydroxide by simultaneously precipitating two or more elements by using a neutralization reaction in an aqueous solution.

Here, the average time for the mixed solution to stay in the reactor is adjusted to 6 hours, the pH is maintained at 10.5 to 11.5 and the temperature of the reactor at 50 to 60 ℃. The reason for raising the temperature of the reactor is that it is difficult to obtain a high-density complex hydroxide because the cobalt hydroxide produced is precipitated in complex salt form at a low temperature.

Next, after obtaining the precursor hydroxide forming the inner layer, the metal salt forming the outer layer is reacted for 1 to 10 hours under the same reaction conditions to obtain a double layered composite hydroxide. The thickness of the outer layer is controlled by the synthesis time of the outer layer precursor in the reactor.

The average particle diameter of the primary particles formed by the nickel and manganese cathode active materials prepared by the coprecipitation method is 1 to 8 µm, and the average particle diameter of the secondary particles formed by the transition metal mixed cathode active material covering the surface of the primary particles is 9 It is preferable that it is 20 micrometers.

This is because lithium having a double layer structure is obtained by increasing the reactivity of charging and discharging and improving the high rate characteristics of the battery by setting the average particle diameter of the primary particles to 1 to 8 µm, and by setting the average particle diameter of the secondary particles to 9 to 20 µm. This is because the electrode can be increased in capacity by increasing the chargeability of the cathode active material for secondary batteries and improving the coating power.

In addition, Li _δ [Ni _x Co _y Mn _{1- (x + y + z)} M _z ] coated on the outside to utilize the characteristics of the internal Li _δ [Ni _x Co _1-2x Mn _xa M _a ] O _{2 in} the double layer structure. The thickness of O ₂ is preferably 5% to 50% of the total thickness of the double layer positive electrode active material. In order to further utilize the properties, it is preferable to set it to 30% or less, more preferably 5% or less. However, when the thickness of Li _δ [Ni _x Co _y Mn _{1- (x + y + z)} M _z ] O _{2 applied to} the outside is 5% or less, the characteristics of the external composition are inferior.

In addition, in the internal cathode active material Li _δ [Ni _x Co _1-2x Mn _xa M _a ] O ₂ , the oxidation _numbers of Ni, Co, and Mn are +2, +3, +4, where M is +2, +3, +4, +6 possible) In the cathode active material Li _δ [Ni _x Co _y Mn _{1- (x + y + z)} M _z ] O ₂ , the oxidation number of Ni is +2 and the oxidation number of Mn is + It is preferable that the oxidation number of tetravalent and Co is + 3-valent, and M which is a substituted metal is + 2-valent.

In particular, the +4 valence of Mn can prevent the structural transition (yan-teller effect) caused by the oxidation / reduction reaction of +3 or +4 of Mn in the existing tetragonal or layered LiMnO ₂ . Structural stabilization during discharging can improve lifespan.

Next, the obtained double layer composite metal hydroxide is washed with distilled water and then filtered and dried at 110 ° C. for 24 hours or heat treated at 450 ° C. for 5 hours to be used as a precursor.

Next, a dry method of sufficiently mixing the double layer composite metal hydroxide or composite metal oxide and lithium salt, or a chelating agent such as citric acid, tartaric acid, glycolic acid, maleic acid, etc. mixed with the double layer composite metal hydroxide or composite metal oxide and lithium salt. Distilled water is removed using a wet method of mixing in an aqueous solution.

Finally, by firing for 10 to 20 hours in an oxidizing atmosphere of air or oxygen at 750 to 1000 ℃ to prepare a cathode active material for a lithium secondary battery having a double layer structure.

It is preferable that the specific target of the positive electrode active material for lithium secondary batteries which has a double layer structure manufactured by the said method is 3 m <2> / g or less. This is because when the specific target is 3 m 2 / g or more, the reactivity with the electrolyte is increased and gas generation is increased.

The reactor has a rotor blade designed in reverse wing type, and has 1 to 4 baffles spaced 2 to 3 cm apart from the inner wall, and these baffles are used to uniformly mix the upper and lower parts of the reactor. Installed. The reverse wing design is also designed for uniform mixing up and down, and the separation of the baffles installed on the inner surface of the reactor from the inner wall controls the intensity and direction of the waves and increases the turbulent effect to solve the local nonuniformity of the reaction solution. It is to. Therefore, when using the reactor, the tap density of the obtained hydroxide is improved by about 10% or more than when using the conventional reactor. The tap density of the hydroxide is 1.95 g / cm 3, preferably 2.1 g / cm 3 or more, and more preferably 2.4 g / cm 3.

Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 10, but the present invention is not limited to these embodiments.

Example 1

4 liters of distilled water was put into the coprecipitation reactor (capacity 4L, the output of the rotary motor more than 80W), and nitrogen gas was bubbled into the reactor at a rate of 0.5 liters / minute to remove dissolved oxygen. Stirring at 1000 rpm while maintaining the temperature of the reactor at 50 ℃.

Nickel sulfate and manganese sulfate molar ratios of 1.2: 1.2 were mixed in a 2.4 M aqueous metal solution at 0.3 liters per hour and a 4.8 M ammonia solution at 0.03 liters per hour in the reactor. In addition, a pH of 4.8 M sodium hydroxide solution was supplied to adjust the pH to maintain a pH of 11.

Impeller speed was adjusted to 1000 rpm. By adjusting the flow rate, the average residence time of the solution in the reactor was about 6 hours, and after the reaction reached a steady state, a steady state duration was given to the reactant to obtain a more dense composite metal hydroxide.

Nickel sulfate and manganese sulfate metal aqueous solution supplied to the composite metal hydroxide in a molar ratio of 1.2: 1.2 to a steady state was replaced with a molar ratio of 1.92: 0.24: 0.24 of nickel sulfate, manganese sulfate and cobalt sulfate for 1 to 6 hours. The reaction was carried out under the same conditions.

Next, a spherical nickel manganese cobalt composite hydroxide was continuously obtained through an overflow pipe. The composite metal hydroxide was filtered, washed with water, and dried in a 110 ° C. hot air dryer for 12 hours to obtain a precursor in the form of a metal composite oxide.

After mixing the precursor and lithium nitrate (LiNO ₃ ) in a 1: 1.05 molar ratio, the mixture was heated at a temperature increase rate of 2 ° C./min, and then preliminarily baked at 200 ° C. to 400 ° C. for 12 hours, followed by 12 hours at 720 ° C. Firing was carried out to obtain a positive electrode active material powder having a double layer composed of Li [Ni _1/2 Mn _1/2 ] O _{2 inside} and Li [Ni _0.8 Co _0.1 Mn _0.1 ] O ₂ .

A slurry was prepared by mixing a positive electrode active material for a lithium secondary battery having a double layer structure prepared by the above method, acetylene black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 80:10:10. The slurry was uniformly applied to an aluminum foil having a thickness of 20 μm, and vacuum dried at 120 ° C. to prepare a cathode for a lithium secondary battery.

The anode and the lithium foil were used as counter electrodes, and a porous polyethylene membrane (Celgard ELC, Celgard 2300, thickness: 25 μm) was used as a separator, and ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1. A coin battery was manufactured according to a known manufacturing process using a liquid electrolyte in which LiPF ₆ was dissolved at a concentration of 1 M in a solvent. The manufactured coin battery was evaluated for the positive electrode active material in the 3.0 ~ 4.3 volt region using an electrochemical analyzer (Toyo System, Toscat 3100U).

Comparative Example 1

The powder was prepared in the same manner as in Example 1, except that Li [Ni _1/2 Mn _1/2 ] O ₂ was prepared, which did not have a Li [Ni _0.8 Co _0.1 Mn _0.1 ] O ₂ layer externally. It synthesize | combined and produced the coin type half cell.

Example 2

Except that Li [(Ni _1/2 Mn _1/2 ) _x (Co) _1-x ] O ₂ having a LiCoO ₂ composition instead of a Li [Ni _0.8 Co _0.1 Mn _0.1 ] O ₂ layer was prepared when the cathode active material was manufactured. Then, the powder was synthesized in the same manner as in Example 1, and a coin-type half cell was prepared.

1a is a composite oxide powder obtained by drying (Ni _1/2 Mn _1/2 ) (OH) ₂ in a 110 ° C. warm air dryer for 12 hours, and FIG. 1b shows Co in (Ni _1/2 Mn _1/2 ) (OH) ₂ . (OH) ₂ for 1.5 hours the reaction was powdered, Figure 1c (Ni _1/2 Mn _1/2) (OH) ₂ to Co (OH) ₂ to 3 hours that the powder, Fig. 1d is a (Ni _{1 / 2} Mn _1/2) (OH) is a camera picture of Co (powder having OH) ₂ to 4 hours in the _second.

Figure 2 is _{(Ni .1 / 2 Mn 1/2)} (OH) 2 and _{[(Ni 1/2 Mn 1/2) x} (Ni 0.8 Co 0.1 Mn 0.1) 1-x] (OH) 2 and [( It is a FE-SEM photograph of the positive electrode active material powder of Ni _1/2 Mn _1/2 ) _x Co _1-x ] (OH) ₂ . Of double layer structure [(Ni _1/2 Mn _1/2 ) _x (Ni _0.8 Co _0.1 Mn _0.1 ) _1-x ] (OH) ₂ and [(Ni _1/2 Mn _1/2 ) _x Co _1-x ] (OH) ₂ of The positive electrode active material powder _{(Ni .1 / 2 Mn 1/2)} (OH) gajina the same particle shape as the _second powder, it can be seen that the thread-like material going indicating the characteristics of the precursor powder to the surface surrounding the surface.

3 shows Li [Ni _1/2 Mn _1/2 ] O ₂ , Li [(Ni _1/2 Mn _1/2 ) _x (Ni _0.8 Co _0.1 Mn synthesized in Example 1, Example 2, and Comparative Example 1 _0.1 ) X-ray diffraction pattern (XRD) of _1-x ] O ₂ , Li [(Ni _1/2 Mn _1/2 ) _x Co _1-x ] O ₂ sintered powder particles was shown. In the diffraction peaks of all the powders, the (006) and (102) peak separations, the (018) and (110) peak separations are well represented, and the lithium composite oxide has a space ratio of 1 or more. It can be seen that it has a hexagonal-NaFeO ₂ structure having a group R-3m and is a layered compound having excellent crystallinity even after being formed in a double layer structure.

4 shows discharge capacities according to cycles in which each material synthesized by the method of Example 1, Example 2 and Comparative Example 1 was tested with an applied current of 0.4 mA in the range of 2.8-4.3 V. FIG.

Li [Ni _1/2 Mn _1/2 ] O ₂ , Li [(Ni _1/2 Mn _1/2 ) _x (Ni _0.8 Co _0.1 Mn _0.1 ) ₁ experimented at 2.8-4.3V, 0.4mA _-x ] O ₂ , Li [(Ni _1/2 Mn _1/2 ) _x Co _1-x ] O ₂ cycles discharge capacity according to Li [(Ni _1/2 Mn _1/2 ) _x (Ni _0.8 Co _0.1 Mn _0.1 ) _1-x ] O ₂ , Li [(Ni _1/2 Mn _1/2 ) _x Co _1-x ] O ₂ cathode active materials showed an initial capacity increase and excellent cycle characteristics. Li [Ni _1/2 Mn _1/2 ] O ₂ continues to cycle with an initial capacity of 147 mAh / g, while Li [(Ni _1/2 Mn _1/2 ) _x Co _1-x ] O ₂ electrodes Shows a capacity of 157mAh / g with an increase of 10mAh / g, and the capacity of Li [(Ni _1/2 Mn _1/2 ) _x (Ni _0.8 Co _0.1 Mn _0.1 ) _1-x ] O ₂ increases with the amount of Ni. As planned according to the high capacity of 164mAh / g.

5 is Li [Ni _1/2 Mn _1/2 ] O ₂ , Li [(Ni _1/2 Mn _1/2 ) _x Co _1-x ] O _2, Li [(Ni _1/2 Mn _1/2 ) _The discharge capacity of each of the five cycles tested at 0.2C, 0.5C, 1C, 2C, and 3C of _x (Ni _0.8 Co _0.1 Mn _0.1 ) _1-x ] O ₂ was shown. Compared to _{Li [Ni 1/2 Mn 1/2] O} 2 Li [(Ni 1/2 Mn 1/2) x (Ni 0.8 Co 0.1 Mn 0.1) 1-x] indicates a superior performance in high-rate characteristics of the O ₂ have.

6 shows Li [Ni _1/2 Mn _1/2 ] O ₂ with 4.3V charge. Data on differential weighted thermal analysis of Li [(Ni _1/2 Mn _1/2 ) _x Co _1-x ] O ₂ . Li [Ni _1/2 Mn _1/2 ] O ₂ starts to generate heat at 250 ° C and shows the main exothermic peak at 300 ° C, while Li [(Ni _1/2 Mn _1/2 ) _x Co _1-x ] O ₂ The thermal stability was improved by the main heating peak at 310 ° C and the heat generation reduced by 2/3.

Example 3

Spherical nickel manganese cobalt magnesium composite metal hydroxides were synthesized under the same conditions as in Example 1 with a 2.4 M aqueous metal solution mixed with nickel sulfate, manganese sulfate and cobalt sulfate in a ratio of 0.8: 0.8: 0.8, and then nickel sulfate , And cobalt sulfate and manganese sulfate molar ratio of 1.68: 0.24: 0.48 was replaced with a 2.4 M aqueous metal solution and reacted under the same conditions for 1 to 10 hours. A double layer structure lithium composite metal oxide powder was synthesized in the same manner as in Example 1, and the half cell was prepared.

Comparative Example 3

 Nickel sulfate, manganese sulfate and cobalt sulfate molar ratio of Example 3 were mixed in a 2.4 M aqueous metal solution in a ratio of 0.8: 0.8: 0.8 in the same manner as in Example 1 to prepare a half cell.

In Figure 7 (Ni _1/3 Co _1/3 Mn _1/3 ) (OH) ₂ , [(Ni _1/3 Co _1/3 Mn _1/3 ) _x (Ni _0.7 Co _0.1 Mn _0.2 ) _1-x ] FE-SEM photograph of (OH) ₂ . As shown in the figure, [(Ni _1/3 Co _1/3 Mn _1/3 ) _x (Ni _0.7 Co _0.1 Mn _0.2 ) _1-x ] (OH) ₂ was more densely synthesized precursor, FE-SEM of Figure 8 In the photo, Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ , Li [(Ni _1/3 Co _1/3 Mn _1/3 ) _x (Ni _0.7 Co _0.1 Mn _0.2 ) _1-x ] O ₂ of It is easy to see the difference in particle shape. 9, Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ , Li [(Ni _1/3 Co _1/3 Mn _1/3 ) _x (Ni _0.7 Co _0.1 Mn _0.2 ) _1-x ] The X-ray diffraction pattern of O ₂ (XRD) shows well the (006) and (102) peak separations, the (018) and (110) peak separations in the diffraction peaks of all powders, and the peak ratios of (003) and (104) are 1 It can be seen from the above that the lithium composite oxide has a hexagonal-NaFeO ₂ structure having a space group R-3m and is a layered compound having excellent crystallinity even after being formed in a double layer structure. 10 is a charge / discharge curve of 3.0-4.3V, the inside of which is a third of the composition of the stability as the nickel-based layered positive electrode active material Li [(Ni _1/3 Co _1/3 Mn _1/3 ) _x (Ni _0.7 Co _0.1 Mn _0.2 ) _1-x ] O ₂ initial capacity was 171mAh / g and Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ was increased to about 164mAh / g to about 7mAh / g There is a number.

Example 4

A spherical nickel manganese cobalt magnesium composite metal hydroxide was synthesized under the same conditions as in Example 1 using a 2.4 M aqueous solution containing nickel sulfate, manganese sulfate, cobalt sulfate, and magnesium sulfate in a ratio of 0.8: 0.8: 0.704: 0.096. Then, nickel sulfate, cobalt sulfate, manganese sulfate, and magnesium sulfate were replaced with a 2.4 M aqueous solution having a molar ratio of 1.68: 0.24: 0.384: 0.096 and reacted under the same conditions as above for 1 to 10 hours. A double layer structure lithium composite metal oxide powder was synthesized in the same manner as in Example 1, and the half cell was prepared.

[Comparative Example 4]

Nickel sulfate, manganese sulfate, cobalt sulfate, and magnesium sulfate mole ratios of Example 4 were mixed in a ratio of 0.8: 0.8: 0.704: 0.096 to a metal solution of 2.4 M concentration in the same manner as in Example 1 to synthesize Li [(Ni _A half cell consisting of _0.33 Co _0.33 Mn _0.3 Mg _0.04 ) _x (Ni _0.7 Co _0.1 Mn _0.16 Mg _0.04 ) _1-x ] O ₂ was prepared.

11 is a charge / discharge curve of 3.0-4.3V, the inside of which is one-third of the composition of magnesium added to the positive electrode active material, the stability of the nickel-based layered positive electrode active material Li [(Ni _0.33 Co _0.33 Mn _0.3 Mg _0.04 ) _x (Ni _0.7 Co _0.1 Mn _0.16 Mg _0.04 ) The initial capacity of _1-x ] O ₂ was 169mAh / g and Li [Ni _0.33 Co _0.33 Mn _0.3 Mg _0.04 ] O ₂ was increased by about 8mAh / g to 161mAh / g. I can see.

As described above, the present invention has been described for only one preferred embodiment, but it is apparent to those skilled in the art that various changes and modifications can be made within the technical spirit of the present invention based on the above embodiments. It is natural that such variations and modifications fall within the scope of the appended claims.

As described above, the positive electrode active material having a layered rock salt structure and a double layer structure prepared using the hydroxide co-precipitation method according to the present invention has excellent stability in nickel, manganese, cobalt-based positive electrode, and a nickel-based transition having a large capacity outside in contact with the electrolyte. It is composed of cobalt anode which is metal mixed system or high rate characteristic, so it has high capacity, high packing density, improved life characteristics and excellent thermal safety.

Claims (11)

In the positive electrode active material for a lithium secondary battery having a double layer structure, Inside _δ composition formula Li [Ni _x Co _1-2x Mn _x] O ₂ is made of a (1.0≤δ≤1.2, 0.01≤x≤0.5), _δ exterior Li [Ni _x Co _y Mn _{1- (x + y )} ] O ₂ (1.0≤δ≤1.2, 0.5≤x≤1.0, 0.01≤y≤0.2) or Li _δ CoO ₂ (1.0≤δ≤1.2), which has a high-capacity, high-rate bilayer structure Cathode active material for lithium secondary battery. In the positive electrode active material for a lithium secondary battery having a double layer structure, Inside is the formula Li _δ [Ni _x Co _1-2x Mn _xa M _a ] O ₂ (M is Mg, Zn, Ca, Sr, Cu, Zr, P, Fe, Al, Ga, In, Cr, Ge, Sn, At least one element selected from the group consisting of Ti, Mo, W, Nd, etc., 1.0 ≦ _δ ≦ 1.2, 0.01 ≦ x ≦ 0.5, 0.01 ≦ a ≦ 0.1), and the outside thereof is Li _δ [Ni _x Co _y Mn _{1- (x + y + z)} N _z ] O ₂ (N is at least one element selected from the group consisting of Mg, Zn, Ca, Sr, Cu, Zr, 1.0≤δ≤1.2, 0.5≤x≤1.0, 0.01 ≤ y ≤ 0.2, 0.01 ≤ z ≤ 0.1), the positive electrode active material for a lithium secondary battery having a double layer structure of high capacity, high rate characteristics. The cathode active material for a lithium secondary battery according to claim 1, wherein the outer layer has a thickness of 5% to 50% of the total thickness of the cathode active material. The cathode active material for a lithium secondary battery according to claim 1, wherein the internal average particle diameter is 1 to 8 µm and the average particle diameter of all the particles of the cathode active material is 9 to 20 µm. The lithium secondary battery using the positive electrode active material for lithium secondary batteries which has a double layer structure as described in any one of Claims 1-3.  A first step of simultaneously mixing nickel, manganese, cobalt-based transition metal aqueous solution, ammonia aqueous solution and basic aqueous solution in a reactor to obtain a spherical precipitate;  A second step of obtaining a precipitate of a double layer composite metal hydroxide covered with a transition metal hydroxide by simultaneously mixing the transition metal mixed solution, the ammonia solution and the basic aqueous solution in the reactor with the precipitate;  Drying or depositing the precipitate to obtain a double layer composite metal hydroxide or a double layer composite metal oxide;  Method for producing a positive electrode active material for a lithium secondary battery having a double layer structure of a high capacity, high rate characteristics, characterized in that it comprises a fourth step of obtaining a double layer lithium composite metal oxide by mixing a lithium salt in the double layer composite metal hydroxide or double layer composite metal oxide. . The method of claim 6, wherein the first step is used by mixing an aqueous solution containing two or more metal salts as a precursor, the molar ratio of ammonia and metal salt is 0.2 to 0.4, the pH of the reaction solution is adjusted to 10.5 to 10 to 10 A method of manufacturing a cathode active material for a lithium secondary battery having a double layer structure of high capacity and high rate characteristics, characterized by reacting for 20 hours. The method of claim 6, wherein in the second step, the thickness of the outer layer is adjusted by adjusting the reaction time to 1 to 10 hours. The method of claim 6, wherein the third step is to dry 15 hours at 110 ℃, or 5 to 10 hours at 400 to 550 ℃ characterized in that the manufacturing of a positive electrode active material for a lithium secondary battery having a double layer structure of high capacity, high rate characteristics Way. The method of claim 6, wherein the third step is a preliminary firing by maintaining at 300 ~ 550 ℃ 5 hours, firing 10 hours at 700 ~ 1100 ℃, high capacity, characterized in that for 10 hours at 600 ~ 750 ℃ , A method for producing a cathode active material for a lithium secondary battery having a double layer structure of high rate characteristics. The method of claim 6, wherein the reaction atmosphere of the aqueous solution of the transition metal is nitrogen flow, pH is 10.5 to 12.5, the reaction temperature is 30 to 80 ℃, high capacity, high rate, characterized in that the reaction stirrer rpm is 500 to 2000 A method for producing a cathode active material for a lithium secondary battery having a double layer structure of characteristics.

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