KR20170076348A - Positive active material for rechargeable lithium battery, method of preparing the same, and rechargeable lithium battery including the same - Google Patents

Abstract

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 comprising the same, wherein the cathode active material is represented by the following chemical formula 1 and has a central particle diameter of 0.3 to 1.5 탆.
[Chemical Formula 1]
_{Li a Ni b Co c Mn d} M e O 2 (a = 1.0-1.1, b = 0.5-0.8, c / d = 1.0-1.5, e = 0.00-0.01, b + c + d + e = 1.0)

Description

TECHNICAL FIELD 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 same. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

A cathode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery comprising the same.

Recently, with regard to the tendency to miniaturize and lighten portable electronic devices, there is an increasing need for high performance and large capacity of batteries used as power sources for these devices.

Cells generate electricity by using materials that can electrochemically react to the positive and negative electrodes. A representative example of such a battery is a lithium secondary battery that generates electrical energy by a change in chemical potential when the lithium ions are intercalated / deintercalated in the positive electrode and the negative electrode.

The lithium secondary battery is manufactured by using a material capable of reversible intercalation / deintercalation of lithium ions as a positive electrode and a negative electrode active material, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.

As a cathode active material of a lithium secondary battery, a lithium composite metal compound is used. For example, composite metal oxides such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ and LiMnO ₂ have been studied.

Of the above cathode active materials, Mn-based cathode active materials such as LiMn ₂ O ₄ and LiMnO ₂ are easy to synthesize and are relatively inexpensive and have excellent thermal stability compared to other active materials in overcharging, However, it has a disadvantage of low capacity.

LiCoO ₂ is a typical cathode active material commercially available and commercially available since it has good electric conductivity, high battery voltage of about 3.7 V, excellent cycle life characteristics, stability and discharge capacity. However, since LiCoO ₂ is expensive, it accounts for more than 30% of the battery price, which causes the price competitiveness to deteriorate.

LiNiO ₂ also exhibits the highest discharge capacity of the battery among the above-mentioned cathode active materials, but it is difficult to synthesize LiNiO ₂ . Also, the high oxidation state of nickel causes degradation of battery life and electrode life, and there is a problem that self discharge is severe and reversibility is low. In addition, it is difficult to commercialize it because the stability is not completely secured.

As described above, there have been provided cathode active materials for lithium secondary batteries including various coating layers for improving battery characteristics in the prior art.

The present invention provides a positive electrode active material for a lithium secondary battery improved in structural stability and electrochemical characteristics, and a lithium secondary battery including the positive electrode active material.

According to an embodiment of the present invention, there is provided a cathode active material for a lithium secondary battery, which is represented by the following Chemical Formula 1 and is in a single crystal state with a center particle diameter of 0.3 to 1.5 탆.

[Chemical Formula 1]

_{Li a Ni b Co c Mn d} M e O 2 (a = 1.0-1.1, b = 0.5-0.8, c / d = 1.0-1.5, e = 0.00-0.01, b + c + d + e = 1.0)

The cathode active material is in a pulverized form, and the difference in specific surface area before and after pulverization may be 0.2-0.5 g / m ² .

In another embodiment of the present invention, a lithium source material; Metal raw materials including Ni, Co, and Mn; And an organic acid additive to prepare a slurry; Spray drying the slurry to produce a precursor material; Firing the precursor material to obtain a lithium composite oxide; And pulverizing and monocrystallizing the obtained lithium composite oxide. The present invention also provides a method for producing a lithium secondary battery.

In the step of obtaining the lithium composite oxide by firing the precursor material, voids in the lithium composite oxide may be formed due to generation of gas due to decomposition of the lithium source material and / or the organic acid additive during firing.

The step of pulverizing and monocrystallizing the obtained lithium composite oxide may be performed by a mechanical milling method.

The step of spray-drying the slurry to produce a precursor material may be carried out under a condition of a hot air temperature of 250 to 300 ° C and an exhaust hot air temperature of 100 to 150 ° C.

The step of firing the precursor material to obtain a lithium composite oxide may be performed at 800 to 900 ° C for 8 to 12 hours.

The step of calcining the precursor material to obtain a lithium composite oxide may be performed at a temperature raising rate of 2-4 ° C / min.

In the step of obtaining the lithium composite oxide by firing the precursor material, the primary particle size of the lithium composite oxide obtained may be 0.5 to 1 탆.

In the step of obtaining the lithium composite oxide by firing the precursor material, the tap density of the lithium complex oxide obtained may be 1.3 to 1.6 g / cm < ² >.

The single crystal cathode active material obtained by pulverizing and monocrystallizing the obtained lithium composite oxide may be in a single crystal state of 0.3 to 1.5 占 퐉 based on the center particle diameter.

The organic acid additive may be selected from the group consisting of fumaric acid, adipic acid, succinic acid, tartaric acid, glutaric acid, citric acid, Maleic acid, oxalic acid, malonic acid, or a combination thereof.

The lithium source material may be lithium carbonate.

The lithium composite oxide composition may be represented by the following formula (1).

[Chemical Formula 1]

_{Li a Ni b Co c Mn d} M e O 2 (a = 1.0-1.1, b = 0.5-0.8, c / d = 1.0-1.5, e = 0.00-0.01, b + c + d + e = 1.0)

E in the above formula may include doping elements of B, Al, Ti, Zr, Ba, or combinations thereof.

The cathode active material may further include a coating layer of B, Al, Ti, Zr, Ba or a combination thereof.

In another embodiment of the present invention, cathode; And an electrolyte positioned between the positive electrode and the negative electrode, wherein the positive electrode includes the positive electrode active material according to an embodiment of the present invention.

It is possible to provide a positive electrode active material for a lithium secondary battery having improved characteristics.

1 is a SEM photograph of a cathode active material of Example 1 and Comparative Examples 1 and 2.
Fig. 2 shows SEM photographs of the cathode active materials of Examples 1 and 3.
3 is a graph showing the rate capability of Examples 1 to 3 and Comparative Examples 1 and 2 for 0.1C to 4.0C at a cut-off of 3.0 to 4.3V.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims. Like reference numerals refer to like elements throughout the specification.

Thus, in some embodiments, well-known techniques are not specifically described to avoid an undesirable interpretation of the present invention. Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. Whenever a component is referred to as "including" an element throughout the specification, it is to be understood that the element may include other elements, not the exclusion of any other element, unless the context clearly dictates otherwise. Also, singular forms include plural forms unless the context clearly dictates otherwise.

In one embodiment of the present invention, a lithium source material; Metal raw materials including Ni, Co, and Mn; And an organic acid additive to prepare a slurry; Spray drying the slurry to produce a precursor material; Firing the precursor material to obtain a lithium composite oxide; And pulverizing and monocrystallizing the obtained lithium composite oxide. The present invention also provides a method for producing a lithium secondary battery.

In one embodiment of the present invention, the target cathode material is a single crystal having a grain size of 0.3 to 1.5 占 퐉 and may include a state in which the crystal grain is doped with a different kind of metal or a state in which the crystal grain is coated on the surface.

The cathode material in a single crystal state can be improved in high-rate characteristics with a high surface area. At the same time, it is possible to maintain the performance without particle collapse under high rolling conditions for high energy density.

In addition, the volume expansion of charge and discharge is minimized by doping and / or coating with dissimilar metals, thereby minimizing problems such as crystal collapse and peeling.

The step of firing a precursor containing the raw material of Li, Ni, Co, and / or Mn and the organic acid additive uniformly to obtain a lithium composite oxide is characterized in that a gas resulting from the decomposition of lithium, Thereby forming a uniform void in the lithium composite oxide.

The positive electrode active material according to one embodiment of the present invention can be usefully used as a positive electrode of a lithium secondary battery. The lithium secondary battery includes a cathode and an electrolyte including an anode active material together with a cathode.

The positive electrode is prepared by preparing a positive electrode active material composition by mixing a positive electrode active material according to an embodiment of the present invention, a conductive material, a binder and a solvent, and then directly coating and drying on the aluminum current collector. Or by casting the positive electrode active material composition on a separate support, then peeling the support from the support, and laminating the resulting film on an aluminum current collector.

The conductive material may be carbon black, graphite, metal powder, and the binder may include vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene And mixtures thereof. Further, N-methylpyrrolidone, acetone, tetrahydrofuran, decane and the like are used as the solvent. At this time, the content of the cathode active material, the conductive material, the binder and the solvent is used at a level normally used in a lithium secondary battery.

The negative electrode is prepared by mixing the negative electrode active material, the binder and the solvent in the same manner as the positive electrode. The anode active material composition is coated directly on the copper current collector or cast on a separate support, and the negative active material film, Laminated. At this time, the negative electrode active material composition may further contain a conductive material if necessary.

As the negative electrode active material, a material capable of intercalating / deintercalating lithium is used. For example, lithium metal, lithium alloy, coke, artificial graphite, natural graphite, organic polymeric compound combustion material, . The conductive material, the binder and the solvent are used in the same manner as in the case of the above-mentioned anode.

The separator may be polyethylene, polypropylene, polyvinylidene fluoride or a multilayer film of two or more thereof. The separator may be a polyethylene / polypropylene double-layer separator, It is needless to say that a mixed multilayer film such as a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator and the like can be used.

As the electrolyte to be charged into the lithium secondary battery, a non-aqueous electrolyte or a known solid electrolyte may be used, and a lithium salt dissolved therein may be used.

The solvent of the non-aqueous electrolyte is not particularly limited, but cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; Chain carbonates such as dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate; Esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and? -Butyrolactone; Ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane and 2-methyltetrahydrofuran; Nitriles such as acetonitrile; Amides such as dimethylformamide and the like can be used. These may be used singly or in combination. Particularly, a mixed solvent of cyclic carbonate and chain carbonate can be preferably used.

As the electrolyte, a gelated polymer electrolyte in which an electrolyte solution is impregnated with a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li ₃ N can be used.

Wherein the lithium salt is selected from the group consisting of LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiCl, and LiI.

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

Example  One

Based on the total composition _{Li a Ni b Co c Mn d} M e O 2 (a = 1.0-1.1, b = 0.5-0.8, c / d = 1.0-1.5, e = 0.00-0.01, b + c + d + e = 1.0), a Li source is used for the production of a cathode active material, one of oxide, hydroxide,

The source material of Ni and Co, Mn is oxide, hydroxide, nitrate, superoxide, precursor of hydroxide state designed to one or target composition, and

The organic acid may be selected from the group consisting of fumaric acid, adipic acid, succinic acid, tartaric acid, glutaric acid, citric acid, maleic acid, oxalic acid, Oxalic acid and malonic acid were wet-milled and spray-dried to obtain precursors in which each raw material was uniformly contained in the precursor particles.

More specifically, Li ₁ CO _{3 ,} Ni (OH) ₂ , Mn ₃ O ₄ , and Co (OH) ₂ were used as starting materials for the present experiment to prepare Li _{1 .0} Ni _{0 .6} Co _{0 .2} Mn _{0 .2} O _2. The organic acid (citric acid) was added in an amount of 3 to 5 wt% of the weighed weight, and pure water was added thereto so that the solid / liquid ratio became 5: 5.

The raw materials were stirred at 400 rpm for 10 minutes in a stirrer so as to be uniformly mixed, and then pulverized and dispersed at a high speed in a wet grinding apparatus (Mincer, Netzsch) to form a slurry. Zirconia beads having a diameter of 0.65 mm were used for wet grinding and dispersing, and the grinding time was fixed to 30 minutes. The slurry was pulverized and dispersed until the particle size (D50) of the particles in the pulverized slurry became 0.3 탆 or less, at which time the viscosity of the slurry was adjusted to 500 cp or less.

The slurry was dried and molded using a spray dryer (manufactured by Ain Systems Co.), the hot air temperature was 250 to 300 ° C, and the hot air temperature was 100 to 150 ° C.

About 100 g of the prepared precursor powder was placed in an alumina crucible and fired at 860 ° C for 10 hours under an air flow of 5 l / min (at a heating rate of 3 ° C / min), whereby the decomposition gas of lithium raw material and organic acid A positive electrode active material having a high specific surface area in which pores in the particles were uniformly developed after firing was obtained.

The size of the unit particles (primary particles) of the cathode active material is 0.3 to 1 mu m, the tap density is 1.3 to 1.6 g / cm < ² > Respectively.

The produced cathode active material is characterized in that pores are developed due to the decomposition gas generated during firing between the crystal grains constituting the particles and is easily cracked by external physical force. Therefore, the crushing device (Rotor mill, manufactured by Retsch Co.) To obtain a single-crystal cathode active material having a center particle diameter of 0.3 to 1 占 퐉.

Al, Ti, Zr, Ba, or the like in an aqueous solution phase is wet-coated on the prepared single crystal cathode active material, and a single crystal cathode active material including a uniform coating layer can be obtained through a spray pyrolysis process.

Example  2-3

A cathode active material showing the compositions of Examples 2 to 3 was prepared in the same manner as in Example 1 except that ZrO _{2 and} TiO ₂ were used as additive materials in the stoichiometric ratio shown in Table 1 below.

division Cathode active material composition Example 1 Li [Ni Co _{0 .60 0 .20 0 .20} Mn] O ₂ Example 2 Li [Ni _{0 .60} Co _{0 .20} Mn _{0 .195} Zr _{0 .005} ] O ₂ Example 3 Li [Ni _{0 .60} Co _{0 .20} Mn _{0 .195} Ti _{0 .005} ] O ₂

Comparative Example  One

Is manufactured through a general co-precipitation reaction _{Li 1 .0 Ni 0 .6 Co 0} .2 Mn 0 .2 O was used as the positive electrode active material of the _second composition.

Comparative Example  2

The cathode active material of Li _{1 .0} Ni _{0 .6} Co _{0 .2} Mn _{0 .2} O ₂ composition using precursors prepared by wet pulverization and spray drying was used.

< Experimental Example  1> SEM  Measurement and Tap density  Measure

A representative SEM photograph of the positive electrode active material of Example 1 and Comparative Examples 1 and 2 is shown in FIG.

SEM photographs of the cathode active materials of Examples 1 to 3 before and after the crushing process are shown in Fig.

The specific surface area of the cathode active material particles was measured by a specific surface area meter (trade name: Micromeritics, Tristar-3000) and is shown in Table 2 below. As shown in Table 2, the active materials prepared by the wet spray drying and pulverizing processes in Examples 1 to 3 exhibited generally high specific surface area as compared with Comparative Examples, and the difference in specific surface area before and after pulverization was 0.2-0.5 .

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Before crushing 1.8 1.5 2.0 0.3 0.5 After grinding 2.0 1.8 2.2 - -

* Unit: m ² / g

The half-cell batteries manufactured in Examples 1 to 3 and Comparative Examples 1 and 2 were subjected to electrochemical analysis at 25 ° C in a voltage range of 3 to 4.3 V, 0.1, 0.5, 1.0, 2.0, and 4.0 using an electrochemical analyzer (Toyo, Toscat 3100) C discharge rate, and the results are shown in Table 3 and FIGS. 3 and 4 below.

Table 3 and FIG. 3 show the efficiency according to the charging / discharging performance and the discharging rate performed under conditions of 0.1, 0.5, 1.0, 2.0 and 4.0C at cut-off of 3.0 to 4.3V. As shown in Table 3 and FIG. 3, in the case of the active material prepared through the wet spray drying and pulverizing processes in Examples 1 to 3, the initial discharge capacity, the initial reversible efficiency and the rate characteristics were comparative examples 1, 2, respectively.

division 1 ^st discharge capacity
[@ 0.1 C, mAh / g] 1 ^st reversible efficiency
[@ char / disch,%] Rate characteristic
[@ 4.0 / 0.1C,%] Example 1 (before grinding) 182.3 93.4 86.5 Example 1 186.0 93.4 88.2 Example 2 185.3 93.2 87.8 Example 3 183.8 93.7 87.9 Comparative Example 1 173.4 87.0 84.2 Comparative Example 2 176.6 87.2 86.3

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, You will understand.

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 .

Claims (17)

(1)
Wherein the cathode active material is in a single crystal state with a center particle diameter of 0.3 to 1.5 占 퐉.
[Chemical Formula 1]
_{Li a Ni b Co c Mn d} M e O 2 (a = 1.0-1.1, b = 0.5-0.8, c / d = 1.0-1.5, e = 0.00-0.01, b + c + d + e = 1.0) The method according to claim 1,
Wherein the cathode active material is in a pulverized form and the difference in specific surface area before and after pulverization is 0.2-0.5 g / m ² .
Lithium raw material; Metal raw materials including Ni, Co, and Mn; And an organic acid additive to prepare a slurry;
Spray drying the slurry to produce a precursor material;
Firing the precursor material to obtain a lithium composite oxide; And
Crushing and monocrystallizing the obtained lithium composite oxide;
Wherein the positive electrode active material is a positive electrode active material.
The method of claim 3,
And calcining the precursor material to obtain a lithium composite oxide,
Wherein the pores in the lithium composite oxide are formed by the generation of gas due to decomposition of the lithium source material and / or the organic acid additive agent during firing.
The method of claim 3,
Wherein the step of crushing and monocrystallizing the obtained lithium composite oxide is performed by a mechanical milling method.
The method of claim 3,
Spray drying the slurry to produce a precursor material,
A hot air temperature of 250 to 300 DEG C, and an exhaust hot air temperature of 100 to 150 DEG C. The method for producing a cathode active material for a lithium secondary battery according to claim 1,
The method of claim 3,
And calcining the precursor material to obtain a lithium composite oxide,
At 800 to 900 DEG C for 8 to 12 hours.
The method of claim 3,
And calcining the precursor material to obtain a lithium composite oxide,
At a temperature rising rate of 2-4 DEG C / min. The method for producing a cathode active material for a lithium secondary battery according to claim 1,
The method of claim 3,
And calcining the precursor material to obtain a lithium composite oxide,
Wherein the lithium composite oxide has a primary particle size of 0.3 to 1 占 퐉.
The method of claim 3,
And calcining the precursor material to obtain a lithium composite oxide,
The tap density of the obtained lithium composite oxide was 1.3 to 1.6 g / cm &lt; ² &gt; By weight based on the total weight of the lithium secondary battery.
The method of claim 3,
The single crystal positive electrode active material obtained by pulverizing and monocrystallizing the obtained lithium composite oxide,
Wherein the cathode active material is in a single crystal state with a center particle diameter of 0.3 to 1.5 占 퐉.
The method of claim 3,
The organic acid additive may contain,
The organic acid may be selected from the group consisting of fumaric acid, adipic acid, succinic acid, tartaric acid, glutaric acid, citric acid, maleic acid, oxalic acid, (Oxailic acid), Malonic acid, or a combination thereof. The method for producing a cathode active material for a lithium secondary battery according to claim 1,
The method of claim 3,
Wherein the lithium source material is lithium carbonate.
The method of claim 3,
Wherein the composition of the lithium composite oxide is represented by the following formula (1).
[Chemical Formula 1]
_{Li a Ni b Co c Mn d} M e O 2 (a = 1.0-1.1, b = 0.5-0.8, c / d = 1.0-1.5, e = 0.00-0.01, b + c + d + e = 1.0) The method of claim 3,
Wherein the positive electrode active material comprises a doping element of B, Al, Ti, Zr, Ba, or a combination thereof.
The method of claim 3,
Wherein the positive electrode active material further comprises a coating layer of B, Al, Ti, Zr, Ba or a combination thereof.
anode; cathode; And an electrolyte positioned between the anode and the cathode,
The lithium secondary battery according to claim 1, wherein the positive electrode comprises the positive electrode active material according to claim 1.

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