KR101630421B1 - Positive active material for lithium secondary battery, method of preparing same and a lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a cathode active material for a lithium secondary battery and a method of manufacturing the same, and a cathode active material comprising an inner core, an inner layer surrounding the inner core, and an outer layer surrounding the inner layer, A first inner layer surrounding the core, a second inner layer surrounding the first inner layer, and a third inner layer surrounding the second inner layer, the active material comprising a transition metal, The metal is present in a concentration gradient increasing continuously from the inner core to the first inner layer and the second inner layer, and in the second inner layer, the third inner layer has a concentration gradient continuously decreasing from the outer layer to the inner layer The present invention provides a positive electrode active material for a lithium secondary battery and a method for producing the same.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery using the same. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a cathode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery using the same.

Due to the rapid development of science and technology, mobile electronic products and various communication devices have recently been released, and the demand for lithium secondary batteries, which are power sources for these devices, is rapidly increasing. In addition, due to the increased interest in the environment, there has been an increasing tendency to reduce the dependence of fossil fuels, which has led to problems in application to electric vehicles and mass storage devices.

However, lithium secondary batteries are still in the development stage, and they can not completely solve the problem of high price, high capacity and thermal stability, so that the businesses of electric vehicles and high capacity batteries are not rapidly growing.

Currently available lithium secondary batteries in electronic products are made of LiCoO ₂ cathode active material because of its excellent charge / discharge characteristics and thermal stability of LiCoO ₂ . However, since cobalt raw materials are high in price and harmful to the human body, development of other cathode active materials is required in recent years.

In addition, LiNiO ₂ has a large discharge capacity and low cost, but it is difficult to commercialize LiNiO _{2 because} its structure collapses easily during charging and discharging and its thermal stability due to oxidation water problem is low. In order to solve this problem, studies have been made to replace Co with another transition metal in the Ni sites, but the thermal stability problem has not been solved yet.

Therefore, a ternary alloy having superior thermal stability, that is, a cathode active material using Ni-Mn-Co, has been developed more than a cathode active material using a binary alloy.

On the other hand, the ternary alloy _{[Li (Ni 1/3 Mn} 1/3 Co 1/3) O 2] on the positive active material is to be the content of Ni increases in order to realize a high capacity but is tried a lot, and Ni content using The capacity is increased but the thermal stability is lowered. Therefore, the thermal stability of the cathode active material using the ternary alloy is still a problem. In order to solve this problem, coating or doping method was used, but the improvement effect was insignificant.

Accordingly, efforts to develop a cathode active material for a lithium secondary battery that has a high capacity and an improved thermal stability as well as excellent lifetime characteristics have been continued.

In order to solve the above problems, one embodiment of the present invention provides a cathode active material for a lithium secondary battery.

Another embodiment of the present invention provides a method for producing a cathode active material for a lithium secondary battery.

According to another embodiment of the present invention, there is provided a lithium secondary battery including the anode material for the lithium secondary battery.

One embodiment includes a cathode active material comprising an inner core, an intermediate layer surrounding the inner core, and an outer layer surrounding the intermediate layer, the intermediate layer comprising a first intermediate layer surrounding the inner core, A second intermediate layer, and a third intermediate layer surrounding the second intermediate layer, wherein the active material includes a transition metal, and the transition metal has a concentration that continuously increases from the internal core to the first intermediate layer and the second intermediate layer And is present in a concentration gradient continuously decreasing from the second intermediate layer toward the third intermediate layer and the outer layer. The present invention also provides a cathode active material for a lithium secondary battery.

The transition metal may be Ni.

Wherein the active material comprises another transition metal and the transition metal is present in a concentration gradient continuously decreasing from the inner core toward the first intermediate layer and the second intermediate layer, and in the second intermediate layer, Can be present in a continuously increasing concentration gradient toward the outer layer.

The other transition metal may be Co, Mn, Mg, Zn, Ca, Sr, Cu, Zr, P, Fe, Al, Ga, In, Cr, Ge, or combinations thereof.

The Ni content of the inner core may be 50 mol% to 80 mol%, for example, 50 mol% to 70 mol% with respect to the total amount of transition metals in the cathode active material, and the Ni content of the second intermediate layer may be Can be from 70 mol% to 99 mol%, for example, from 80 mol% to 99 mol%.

The Ni content of the outer layer may be from 50 mol% to 80 mol%, for example, from 50 mol% to 70 mol%, based on the total amount of transition metals in the cathode active material.

The average particle size of the cathode active material may be 5 탆 to 15 탆, for example, 7 탆 to 13 탆, for example, 8 탆 to 12 탆.

The thickness of the outer layer may be between 5% and 50%, for example between 10% and 50%, relative to the total cathode active material radius.

The inner core and the outer layer may comprise a lithium-containing compound represented by the following general formula (1).

[Chemical Formula 1]

Li [Ni _{1 - (x + y + z)} Co _x Mn _y M _z ] O ₂

Zn, Ca, Sr, Cu, Zr, P, and Z are selected from the group consisting of 0 <x≤0.2, 0.2 <y≤0.4, 0≤z≤0.1, 0.3≤x + At least one element selected from the group consisting of Fe, Al, Ga, In, Cr, Ge, Sn,

The first intermediate layer and the third intermediate layer may include a lithium-containing compound represented by the following formula (2), and the second intermediate layer may include a lithium-containing compound represented by the following formula (3).

(2)

Li [Ni _{1 - (x 1 + y 1 + z 1 )} Co _{x 1} Mn _{y 1} M _{z 1} ] O ₂

Mg, Zn, Ca, Sr, Cu, Zr, P, and Z are selected from 0, 1, At least one element selected from the group consisting of Fe, Al, Ga, In, Cr, Ge, Sn,

(3)

Li [Ni _{1 - (x 2 + y 2 + z 2 )} Co _{x 2} Mn _{y 2} M _{z 2} ] O ₂

Mg, Zn, Ca, Sr, Cu, Zr, P, and Z are selected from the group consisting of 0 <x2≤0.1, 0 <y2≤0.3, 0≤z2≤0.1, 0.01≤x2 + At least one element selected from the group consisting of Fe, Al, Ga, In, Cr, Ge, Sn,

Another embodiment is a process for producing a first metal salt aqueous solution containing not more than 50 mol% (excluding 0 mol%), such as not more than 10 mol% (exclusive of 0 mol%) of Ni and other transition metals relative to the total amount of the first metal salt aqueous solution ; Preparing a second aqueous metal salt solution containing at least 50 mol% (excluding 100 mol%) of Ni and other transition metals based on the total amount of the second metal salt aqueous solution; Coprecipitating in a reactor while adding a second solution onto the first solution; Stopping the addition of the first solution and injecting only the second solution into the reactor to keep the Ni concentration in the reactor constant; Adding a third solution to the solution in which the Ni concentration is kept constant and coprecipitating in a reactor; Drying the precursor that is the coprecipitated precipitate; And mixing the dried precursor and the lithium salt, followed by a heat treatment, to obtain a cathode active material for a lithium secondary battery.

The step of adding and co-precipitating the second solution on the first solution may be a step of adding and coprecipitating the solution so that the addition rate of the second solution gradually increases.

Adding the second solution to the first solution and coprecipitating it, and adding the third solution to the solution in which the Ni concentration is kept constant, the co-precipitation is performed for 3 hours to 12 hours, for example, 3 hours to 10 hours can do.

The step of stopping the addition of the second solution and keeping the Ni concentration in the solution constant can be carried out for 6 to 20 hours, for example 8 to 16 hours.

Other transition metals in the first metal salt aqueous solution and the second metal salt aqueous solution may be selected from the group consisting of Co, Mn, Mg, Zn, Ca, Sr, Cu, Zr, P, Fe, Al, Ga, In, Cr, Ge, Lt; / RTI &gt;

The lithium salt is _{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, LiN (SO 2 CF 3) 2, _{LiN (SO 3 C 2 F 5} ) 2, LiC 4 F 9 SO 3, LiClO 4, LiAlO 2, LiAlCl 4, LiN (C m F 2m +1 SO 2) (C n F 2n +1 SO 2) (m And n is a natural number such as m and n is an integer of 1 to 100), Li ₂ CO _{3 ,} LiH, LiBr, LiF, LiNO ₃ , LiNO ₂ , Li ₂ O, Li ₂ SO ₄ and LiOH Lt; / RTI &gt;

The first solution, the second solution and the third solution may each independently include a dispersant.

The dispersing agent may be citric acid, tartaric acid, glycolic acid, maleic acid, or a combination thereof.

Further boric acid may be added as an additive in the preparation of the first solution, the second solution and the third solution.

(A) prefiring by holding at 250 to 650 ° C for 5 to 20 hours, (b) preheating at 700 to 1000 ° C for 10 to 30 hours And (c) annealing at 500 ° C to 750 ° C for 10 hours to 20 hours.

Another embodiment of the present invention provides a lithium secondary battery comprising the cathode active material for the lithium secondary battery.

The cathode active material for a lithium secondary battery according to an embodiment of the present invention has an intermediate layer containing a high concentration of Ni between the inner core and the outer layer to improve the capacity characteristics of the lithium secondary battery. In addition, the Ni content in the intermediate layer gradually increases as the Ni content of the inner core gradually increases, and gradually decreases as the Ni content approaches the outer layer. Therefore, the process conditions for preparing the cathode active material for a lithium secondary battery are facilitated by coprecipitation, Since the Ni concentration is low, the thermal stability during charging and discharging of the lithium secondary battery can be maximized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing the constitution of a cathode active material precursor according to Preparation Example 1; FIG.
FIG. 2 is a batch type reactor process chart used in Production Example 1. FIG.
3 is a flow chart showing a method for producing an active material according to Production Example 1. Fig.
4 is a graph showing mole% of Ni, Mn and Co according to the reaction time according to Production Example 1. FIG.
5 is an SEM photograph of the cathode active material precursor according to Production Example 1. FIG.

Hereinafter, exemplary embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Hereinafter, a cathode active material for a lithium secondary battery according to an embodiment will be described with reference to FIG.

A cathode active material for a lithium secondary battery according to an embodiment includes a cathode active material (1, 10), an intermediate layer (20) surrounding the internal core, and an outer layer (5, 30) surrounding the intermediate layer, Wherein the intermediate layer comprises a first intermediate layer (2) surrounding the inner core, a second intermediate layer (3) surrounding the first intermediate layer, and a third intermediate layer (4) surrounding the second intermediate layer, Wherein the transition metal is present in a concentration gradient continuously increasing from the inner core (1, 10) toward the first intermediate layer (2) and the second intermediate layer (3), and the transition metal exists in the second intermediate layer 3, the third intermediate layer 4, and the outer layers 5 and 30, as shown in FIG.

For example, the transition metal may be Ni.

In addition, the cathode active material for lithium secondary batteries may include another transition metal other than Ni, and the transition metal may exist in a concentration gradient continuously decreasing from the inner core toward the first intermediate layer and the second intermediate layer And may be present in a concentration gradient continuously increasing from the second intermediate layer to the third intermediate layer and the outer layer.

For example, the another transition metal may be Co, Mn, Mg, Zn, Ca, Sr, Cu, Zr, P, Fe, Al, Ga, In, Cr, Ge, or combinations thereof.

That is, the cathode active material for a lithium secondary battery has five layers including an inner core, a first intermediate layer, a second intermediate layer, a third intermediate layer, and an outer layer, the Ni content of the inner core and the outer layer may be lowest, The Ni content of the second intermediate layer may be the highest and the Ni content of the first intermediate layer and the third intermediate layer may be higher than the Ni content of the inner core and the outer layer and lower than the Ni content of the second intermediate layer.

When the Ni content decreases from the inner core to the outer layer of the cathode active material for a lithium secondary battery, the thermal stability can be increased. However, at the interface between the inner core and the outer layer during charging and discharging of the battery, And the lifetime characteristics of the battery are deteriorated.

However, in the cathode active material for a lithium secondary battery according to one embodiment, the Ni content increases from the inner core to the intermediate layer, and the concentration of Ni decreases again from the intermediate layer to the outer layer. As a result, It is possible to prevent the structural collapse caused by the secondary battery, thereby improving the lifetime characteristics of the battery.

That is, since the positive electrode active material for a lithium secondary battery has a concentration gradient increasing and decreasing with increasing Ni content from the inner core to the outer layer, Co, Mn and the like other than Ni have a decreasing and increasing concentration gradient, The crystal structure is stabilized because there is no abrupt phase boundary region at the interface of each layer.

Further, as the Ni content decreases from the intermediate layer to the outer layer, the thermal stability can also be increased.

For example, the Ni content of the inner core may be 50 mol% to 80 mol%, for example, 50 mol% to 70 mol% with respect to the total amount of transition metals in the cathode active material, and the Ni content of the second intermediate layer, The Ni content of the outer layer may be from 50 mol% to 80 mol%, such as 50 mol%, based on the total amount of transition metals in the cathode active material, To 70 mol%.

The average particle size of the cathode active material may be 5 탆 to 15 탆, for example, 7 탆 to 13 탆, for example, 8 탆 to 12 탆. When the average particle diameter of the positive electrode active material is within the above range, the production of the positive electrode active material having a concentration gradient is facilitated, the moving distance of lithium ions is appropriate, and the rate characteristic is excellent.

The thickness of the outer layer may be between 5% and 50%, for example between 10% and 50%, relative to the total cathode active material radius. When the thickness of the outer layer is within the above range, the thermal stability can be improved. However, when the temperature is outside the above range, the discharge capacity is reduced.

For example, the inner core and the outer layer may include a lithium-containing compound represented by the following formula (1), and the first intermediate layer and the third intermediate layer may include a lithium-containing compound represented by the following formula And the second intermediate layer may include a lithium-containing compound represented by the following formula (3).

[Chemical Formula 1]

Li [Ni _{1 - (x + y + z)} Co _x Mn _y M _z ] O ₂

(2)

Li [Ni _{1 - (x 1 + y 1 + z 1 )} Co _{x 1} Mn _{y 1} M _{z 1} ] O ₂

(3)

Li [Ni _{1 - (x 2 + y 2 + z 2 )} Co _{x 2} Mn _{y 2} M _{z 2} ] O ₂

In the above Formulas 1 to 3,

0 <x? 0.2, 0.2 <y? 0.4, 0? Z? 0.1, 0.3? X + y + z? 0.5, 0 <x1? 0.1, 0 <y1? 0.3, 0? Z1? 0.1, Mg, Zn, Ca, Sr, Cu, Zr, P, and Z are selected from the group consisting of y1 + z1? 0.4, 0 <x2? 0.1, 0 <y2? 0.3, 0? z2? 0.1, 0.01? x2 + y2 + z2? At least one element selected from the group consisting of Fe, Al, Ga, In, Cr, Ge, Sn, and combinations thereof.

When the composition of the inner core, the first intermediate layer, the second intermediate layer, the third intermediate layer, and the outer layer is as described above, it is possible to manufacture a cathode active material for lithium secondary batteries having excellent life stability characteristics and high capacity characteristics and excellent thermal stability. Do.

Hereinafter, a method of manufacturing a cathode active material for a lithium secondary battery according to another embodiment will be described with reference to FIG.

Another method for producing a cathode active material for a lithium secondary battery is a method for producing a cathode active material for a lithium secondary battery, which comprises 50 mol% or less (excluding 0 mol%), for example, 10 mol% or less (excluding 0 mol% (S1) preparing a first aqueous metal salt solution; (S2) a second metal salt aqueous solution containing at least 50 mol% (exclusive of 100 mol%) of Ni and other transition metals relative to the total amount of the second metal salt aqueous solution; Adding a second solution to the first solution and coprecipitating it in a reactor (S3); Stopping the addition of the first solution so that only the second solution is added to keep the Ni concentration of the solution in the reactor constant (S4); (S5) adding a third solution to the solution in which the Ni concentration is kept constant and coprecipitating it in the reactor; Drying (S6) the precursor as the coprecipitated precipitate; And a step (S7) of mixing the precursor and the lithium salt followed by heat treatment.

The step of adding the second solution to the first solution and coprecipitating it in the reactor may be a step of coprecipitating in the reactor by adding the solution so that the addition rate of the second solution gradually increases.

According to the above manufacturing method, the second solution is added to the first solution, and the coprecipitation proceeds, thereby gradually increasing the Ni content from the inside. When a certain period of time has elapsed, the supply of the first solution is stopped and only the second solution is supplied so that the concentration of the solution is kept constant to some extent. Through this, an intermediate layer is formed.

And the second solution may be continuously supplied, the third solution may be added, and the third intermediate layer and the outer layer may be formed by coprecipitation in the reactor. This leads to a decrease in Ni content.

Further, according to the above production method, the Ni concentration is not too high at the start of coprecipitation, so that it is not necessary to form a high pH and the initial growth can be stabilized, and the Ni concentration in the vicinity of the outer layer is low, The other transition metal concentration is high and the thermal stability and lifetime characteristics are improved.

In addition, since coprecipitation takes place at various stages, the active material can be grown without abrupt change at the interface, so that the peeling phenomenon does not occur.

The reactor is designed such that the rotary blades are designed with a forward or reverse blade type, and one to four baffles are spaced apart from the inner wall by 2 cm to 3 cm, and these baffles are used to mix the upper and lower parts inside the reactor A cylinder-shaped cylinder is installed between the baffle and the rotary vane for uniformity. The reverse bladed design is for uniform vertical mixing. Separating the baffle installed on the inner surface of the reactor from the inner wall adjusts the intensity and direction of the wave, and enhances the turbulent effect to solve the local nonuniformity of the reaction liquid. will be. Therefore, when the reactor is used, the tap density of the obtained precursor is improved by about 10% or more as compared with the case where the conventional reactor is used. For example, the tap density of the precursor is 1.95 g / cm3, such as 2.1 g / cm3 or more, such as 2.4 g / cm3.

For example, the step of coprecipitation by adding a second solution onto the first solution and the step of co-precipitation by adding a third solution to a solution in which the Ni concentration is kept constant may be performed for 3 to 12 hours, for example, 3 to 10 hours , Such as 5 hours to 7 hours.

For example, the step of stopping the addition of the second solution and keeping the Ni concentration in the solution constant may be performed for 6 to 20 hours, for example 8 to 16 hours.

Other transition metals in the first metal salt aqueous solution and the second metal salt aqueous solution may be selected from the group consisting of Co, Mn, Mg, Zn, Ca, Sr, Cu, Zr, P, Fe, Al, Ga, In, Cr, Ge, Lt; / RTI &gt; The content of other transition metals in the first metal salt aqueous solution is higher than the Ni content, and the content of other transition metals in the second metal salt aqueous solution may be lower than the Ni content.

The first solution, the second solution and the third solution may each independently include a dispersant.

The dispersing agent may be citric acid, tartaric acid, glycolic acid, maleic acid, or a combination thereof. When the dispersant is mixed with the metal salt aqueous solution and the basic aqueous solution simultaneously, the molar ratio of the dispersant to the metal salt aqueous solution may be 0.2 to 0.5: 1, for example, 0.2 to 0.4: 1. When the molar ratio of the dispersant and the aqueous metal salt solution is within the above range, the crystallinity of the cathode active material can be enhanced and stabilized.

Examples of the basic aqueous solution include NaOH and KOH. However, it is not limited thereto, and any aqueous solution having a basicity that is commonly used can be used.

The basic aqueous solution may have a concentration of 1M to 5M.

Further boric acid may be added as an additive in the preparation of the first solution, the second solution and the third solution. When boric acid is added, the sintering temperature will be lowered by about 10 ° C because the sintering will be liquid phase sintering. When the firing temperature is lowered, the energy saving effect is obtained.

The lithium salt is mixed with the active material precursor, which is the intermediate layer (first intermediate layer, second intermediate layer, and third intermediate layer) having the continuous concentration gradient of the internal core and the transition metal thus obtained, and then heat-treated to obtain an active material .

(A) prefiring by holding at 250 to 650 ° C for 5 to 20 hours, (b) preliminarily calcining the lithium salt at 700 to 1000 ° C for 10 to 30 hours (C) annealing at 600 ° C to 750 ° C for 10 to 20 hours.

The lithium salt is _{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, LiN (SO 2 CF 3) 2, _{LiN (SO 3 C 2 F 5} ) 2, LiC 4 F 9 SO 3, LiClO 4, LiAlO 2, LiAlCl 4, LiN (C m F 2m +1 SO 2) (C n F 2n +1 SO 2) (m And n is a natural number such as m and n is an integer of 1 to 100), Li ₂ CO _{3 ,} LiH, LiBr, LiF, LiNO ₃ , LiNO ₂ , Li ₂ O, Li ₂ SO ₄ and LiOH Lt; / RTI &gt;

Another embodiment of the present invention provides a lithium secondary battery comprising the cathode active material for the lithium secondary battery. The lithium battery includes a cathode including the cathode active material having the above-described structure, a cathode including the anode active material, and an electrolyte. The separator may further include a separator positioned between the anode and the cathode.

The positive electrode includes a current collector and a positive electrode active material layer formed on one or both surfaces of the current collector. The current collector may be an aluminum current collector, but is not limited thereto.

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

The positive electrode active material is as described above.

The binder serves to adhere the positive electrode active material particles to each other and to adhere the positive electrode active material to the current collector well. Examples of the binder include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinylchloride, Such as polyvinyl chloride, polyvinyl fluoride, polymers comprising ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, Styrene-butadiene rubber, epoxy resin, nylon, and the like may be used, but the present invention is not limited thereto.

The conductive material is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, , Metal fibers such as carbon fiber, copper, nickel, aluminum, and silver, metal fibers, and the like, and conductive materials such as polyphenylene derivatives may be used alone or in combination.

The negative electrode includes a current collector and a negative electrode active material layer formed on one or both surfaces of the current collector.

The negative electrode active material layer includes a material capable of reversibly intercalating / deintercalating lithium ions, a lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

As a material capable of reversibly intercalating / deintercalating lithium ions, any carbonaceous anode active material commonly used in lithium ion secondary batteries can be used as the carbonaceous material. Typical examples thereof include crystalline carbon , Amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in the form of amorphous, plate-like, flake, spherical or fibrous type. Examples of the amorphous carbon include soft carbon (soft carbon) Or hard carbon, mesophase pitch carbide, fired coke, and the like.

As the lithium metal alloy, a lithium-metal alloy may be selected from the group consisting of lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, An alloy of a selected metal may be used.

A material capable of doping and dedoping the lithium are _{Si, SiO a (0 <a} <2), Si-B alloy (wherein B is an alkali metal, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, Rare earth elements and combinations thereof, but not Si), Sn, SnO ₂ , Sn-B (wherein B is at least one element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Element and an element selected from the group consisting of combinations thereof, and not Sn), and at least one of them may be mixed with SiO ₂ . As the element B, at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Se, Te, Po, and combinations thereof.

The electrolyte includes a lithium salt and an organic solvent.

The lithium salt serves as a source of lithium ions in the battery to enable operation of a basic lithium secondary battery and to promote the movement of lithium ions between the positive electrode and the negative electrode. Specific examples of the lithium salt are as described above.

The concentration of the lithium salt can be used within the range of about 0.1M to about 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has an appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance and the lithium ion can effectively move.

The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the organic solvent, for example, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based or aprotic solvent may be used. Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC) EC), propylene carbonate (PC), and butylene carbonate (BC) may be used. As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate , gamma -butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, and the like can be used. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. As the ketone solvent, cyclohexanone may be used have. Examples of the non-protonic solvent include R-CN (wherein R is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, and examples thereof include methyl, ethyl, propyl, isopropyl, A double bond aromatic ring or an ether bond); amines such as dimethylformamide; dioxolanes such as 1,3-dioxolane; sulfolanes; and the like.

The organic solvents may be used singly or in combination of one or more. If one or more of them are mixed, the mixing ratio may be appropriately adjusted according to the performance of the desired cell.

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

Hereinafter, embodiments of the present invention will be described in detail with reference to examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

( Example : Preparation of cathode active material and lithium secondary battery)

(Reactor preparation)

4 L of distilled water was placed in a reactor (capacity 20 L, rotation speed of 80 W or more, 200 rpm or more), and nitrogen gas was bubbled into the reactor at a rate of 5 L / min to remove dissolved oxygen in the reactor. The stirrer was rotated at 300 rpm to 700 rpm while maintaining the temperature of the reactor at 50 캜. The agitating blades were rotated at low rpm or high rpm as required in each reaction step.

(Preparation of first solution and third solution)

Preparation of aqueous solutions of first and third metal salts of 2M concentration in which the nickel sulfate, manganese sulfate and cobalt sulfate were mixed at a molar ratio of 0.1: 0.6: 0.3 was added to the reactor.

(Preparation of second solution)

Preparation of a second metal salt aqueous solution having a concentration of 2M in which nickel sulfate, manganese sulfate, and cobalt sulfate were mixed at a molar ratio of 0.90: 0.05: 0.05

(Preparation of cathode active material precursor)

The second solution is added to the first solution at a constant rate of 0.5 L / h for 3 hours while coprecipitating in the reactor. Thereafter, the addition rate of the second solution is set to 0.3 L / h. Thereafter, the addition of the first solution is stopped, and only the second solution is injected into the reactor at a rate of 0.2 L / h. The mixture is kept for 12 hours so that the concentration of the mixture in the second solution becomes constant.

Thereafter, the third solution was added continuously at a rate of 0.5 L / hr for 6 hours while the second solution was continuously supplied, and coprecipitated in the reactor. The coprecipitate was washed and dried to obtain an inner core, a first intermediate layer, A second intermediate layer, a third intermediate layer, and an outer layer is obtained.

(Cathode active material production)

The precursor and lithium hydroxide (LiOH) were mixed at a molar ratio of 1: 1.03, heated at a heating rate of 2 DEG C / min, prebaked at 300 DEG C to 500 DEG C for 5 hours, Followed by calcination at 700 ° C to 900 ° C for 10 hours to 20 hours. Accordingly, the inner core and the outer layer is _{Li [Ni 0 .6 Co 0 .1} Mn 0 .3] comprises a lithium-containing compound of the O _2, the first intermediate layer and third intermediate layer is Li [Ni _{0 .8} Co _{0. 05} Mn _{0 .15} ] O ₂ , and the second intermediate layer comprises a lithium-containing compound of Li [Ni _{0 .9} Co _{0 .05} Mn _{0 .05} ] O ₂ . To obtain an active material powder.

(Production of lithium secondary battery)

The cathode active material, the conductive material (denka black, denka), and the binder (PVDF-HFP, kurea) according to the above manufacturing method were mixed at a ratio of 92: 4: 4 (wt% / wt% / wt%). Subsequently, the mixture was uniformly applied to an aluminum foil (16 mu m) and uniformly pressed at a pressure of 1 ton in a roll press. And then vacuum-dried in a vacuum oven at 100 DEG C to prepare a positive electrode. At this time, the loading amount of the cathode active material was 0.006 g / cm ² , and the rolling rate was 15.3%. A coin type half cell of the CR2032 standard was manufactured using the PE separator (16 탆, SKI) and metal lithium as the negative electrode plate. At this time, a liquid electrolyte containing 1.0 M of LiPF ₆ was used as a mixed solvent having EC: DMC = 1: 1 (v / v) as an electrolyte.

Scanning Electron Microscope ( SEM ) Measurement result

FIG. 5 shows a photograph of the surface of the cathode active material according to the above-mentioned production method taken by scanning electron microscope (SEM). In Fig. 5, it is confirmed that the fine particles are uniformly present on the surface of the positive electrode active material.

While the present invention has been described in connection with certain exemplary embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

1, 10: internal core
2: first intermediate layer
3: Second intermediate layer
4: third middle layer
5, 30: outer layer
20: middle layer

Claims (21)

A cathode active material comprising an inner core, an intermediate layer surrounding the inner core, and an outer layer surrounding the intermediate layer, the cathode active material comprising Ni as a transition metal,
The intermediate layer comprising a first intermediate layer surrounding the inner core, a second intermediate layer surrounding the first intermediate layer, and a third intermediate layer surrounding the second intermediate layer,
The content of Ni is,
Is from 50 mol% to 80 mol% based on the total amount of transition metals in the inner core, 70 mol% to 99 mol% based on the total amount of transition metals in the second intermediate layer, 80% by mole,
A concentration gradient which continuously increases from the inner core to the first intermediate layer to the second intermediate layer and which is constant in the second intermediate layer and continuously decreases from the second intermediate layer to the third intermediate layer and the outer layer, &Lt; / RTI &gt;
Cathode active material for lithium secondary battery. delete The method according to claim 1,
Wherein the active material comprises another transition metal,
Wherein the transition metal is present in a concentration gradient continuously decreasing from the inner core toward the first intermediate layer and the second intermediate layer and has a concentration gradient continuously increasing from the second intermediate layer toward the third intermediate layer and the outer layer Existing,
Cathode active material for lithium secondary battery. The method of claim 3,
Wherein the another transition metal is a Co, Mn, Mg, Zn, Ca, Sr, Cu, Zr, P, Fe, Al, Ga, In, Cr, Ge, Sn or a combination thereof. delete delete The method according to claim 1,
Wherein the average particle diameter of the positive electrode active material is 5 to 15 占 퐉. The method according to claim 1,
Wherein the thickness of the outer layer is 5% to 50% with respect to the total cathode active material radius. The method according to claim 1,
Wherein the inner core and the outer layer comprise a lithium-containing compound represented by the following formula (1).
[Chemical Formula 1]
Li [Ni _{1- (x + y + z)} Co _x Mn _y M _z ] O ₂
Zn, Ca, Sr, Cu, Zr, P, and Z are selected from the group consisting of 0 <x≤0.2, 0.2 <y≤0.4, 0≤z≤0.1, 0.3≤x + At least one element selected from the group consisting of Fe, Al, Ga, In, Cr, Ge, Sn, 10. The method of claim 9,
Wherein the first intermediate layer and the third intermediate layer comprise a lithium-containing compound represented by the following formula (2)
Wherein the second intermediate layer comprises a lithium-containing compound represented by the following formula (3).
(2)
Li [Ni _{1 - (x 1 + y 1 + z 1 )} Co _{x 1} Mn _{y 1} M _{z 1} ] O ₂
Mg, Zn, Ca, Sr, Cu, Zr, P, and Z are selected from 0, 1, At least one element selected from the group consisting of Fe, Al, Ga, In, Cr, Ge, Sn,
(3)
Li [Ni _{1 - (x 2 + y 2 + z 2 )} Co _{x 2} Mn _{y 2} M _{z 2} ] O ₂
Mg, Zn, Ca, Sr, Cu, Zr, P, and Z are selected from the group consisting of 0 <x2≤0.1, 0 <y2≤0.3, 0≤z2≤0.1, 0.01≤x2 + At least one element selected from the group consisting of Fe, Al, Ga, In, Cr, Ge, Sn, Preparing a first solution and a third solution containing not more than 50 mol% of Ni and other transition metals with respect to the total amount of the first metal salt aqueous solution;
Preparing a second metal salt aqueous solution containing at least 50 mol% of Ni and other transition metals based on the total amount of the second metal salt aqueous solution;
Coprecipitating in a reactor while adding a second solution onto the first solution;
Stopping the addition of the first solution and keeping the Ni concentration in the solution constant while injecting only the second solution;
Coprecipitating in a reactor while adding the third solution to the solution in which the Ni concentration is kept constant;
Drying the precursor that is the coprecipitated precipitate; And
And mixing the precursor and the lithium salt, followed by heat treatment,
Wherein the step of coprecipitating the second solution by adding the second solution to the first solution is such that the addition rate of the second solution is gradually increased,
(Method for manufacturing cathode active material for lithium secondary battery). delete 12. The method of claim 11,
Adding a second solution to the first solution to coprecipitate the first solution, and adding the third solution to the solution to coprecipitate the solution for 3 to 12 hours. 12. The method of claim 11,
The step of stopping the addition of the second solution and keeping the Ni concentration in the solution constant is performed for 6 to 20 hours. 12. The method of claim 11,
Other transition metals in the first metal salt aqueous solution and the second metal salt aqueous solution may be selected from the group consisting of Co, Mn, Mg, Zn, Ca, Sr, Cu, Zr, P, Fe, Al, Ga, In, Cr, Ge, Wherein the cathode active material is a lithium secondary battery. 12. The method of claim 11,
The lithium salt is _{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, LiN (SO 2 CF 3) 2, _{LiN (SO 3 C 2 F 5} ) 2, LiC 4 F 9 SO 3, LiClO 4, LiAlO 2, LiAlCl 4, LiN (C m F 2m +1 SO 2) (C n F 2n +1 SO 2) (m And n is a natural number), at least one selected from the group consisting of Li ₂ CO _3, LiH, LiBr, LiF, LiNO ₃ , LiNO ₂ , Li ₂ O, Li ₂ SO ₄ and LiOH. 12. The method of claim 11,
Wherein the first solution, the second solution, and the third solution each further comprise a dispersing agent independently. 18. The method of claim 17,
Wherein the dispersing agent is citric acid, tartaric acid, glycolic acid, maleic acid, or a combination thereof. 12. The method of claim 11,
Wherein the first solution, the second solution, and the third solution are further added with boric acid as an additive in the preparation of the cathode active material for a lithium secondary battery. 12. The method of claim 11,
After the mixing of the precursor and the lithium salt,
(a) prefiring by holding at 250 DEG C to 650 DEG C for 5 to 20 hours,
(b) firing at 700 ° C to 1000 ° C for 10 hours to 30 hours,
(c) annealing at 600 ° C to 750 ° C for 10 hours to 20 hours. A lithium secondary battery comprising the cathode active material for a lithium secondary battery according to any one of claims 1, 3, 4, and 7 to 10.

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