KR101657265B1 - Porous manganese-based cathode active material, a method of making the same and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a porous manganese-based cathode active material that is made porous by wet milling, spray drying and firing processes under optimized conditions, and a lithium secondary battery having improved rate characteristics including the cathode active material, , The porous manganese-based cathode active material has a desired level of BET specific surface area, tap density, and powder characteristics, and the cathode active material particles have an appropriate particle size, so that the electrode process can be satisfactorily performed. Also, since the lithium secondary battery including the porous manganese-based cathode active material according to the present invention exhibits a high rate characteristic, high capacity lithium can be preferably used for applications requiring secondary batteries.

Description

[0001] The present invention relates to a porous manganese-based cathode active material, a method for producing the same, and a lithium secondary battery comprising the cathode active material,

The present invention relates to a porous manganese-based cathode active material, a method for producing the same, and a lithium secondary battery including the cathode active material. More specifically, the present invention relates to a lithium secondary battery comprising a manganese- And a lithium secondary battery having an improved rate characteristic including the positive electrode active material.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs and even electric vehicles are expanding, efforts for research and development of electrochemical devices are becoming more and more specified.

The electrochemical device is one of the most attracting fields in this respect. Of particular interest is the development of secondary batteries capable of charging and discharging. In recent years, in order to improve the capacity density and specific energy, Research and development on the design of electrodes and batteries are underway. In particular, with the progress of portable and wireless devices, there is a growing demand for a lithium secondary battery that is small, lightweight, and has a high energy density. With this non-aqueous electrolyte secondary battery, the positive electrode active material such as _{LiCoO 2, LiNi 1/3 Co} 1/3 Mn 1/3 O 2, LiNiO 2, LiNi 0 .8 Co 0 .2 O 2, LiMn 2 O 4, LiMnO 2 Complex oxides such as lithium and transition metals are known.

Among them, a lithium secondary battery using a lithium cobalt composite oxide (LiCoO ₂ ) as a cathode active material is widely used as a battery having a high energy density because a high voltage is possible. However, research on cobalt source, which is a raw material of lithium cobalt composite oxide, is rare and high in price and can be substituted therefor. Lithium nickel composite oxides have a disadvantage that they are high in capacity and excellent in high-temperature characteristics, are difficult to synthesize, are inferior in safety when used as a battery, and require care in storage. Lithium manganese composite oxides have a disadvantage of low capacity and inferior high temperature characteristics (cycle, storage), but they are inexpensive, relatively easy to synthesize, and excellent in safety when used as a battery. In order to compensate for the drawbacks of the cathode active materials, a multicomponent composite active material having a combination of cathode active materials has been proposed.

On the other hand, in the conventional production method of a manganese-based cathode active material, a method of producing a precursor using a hydroxide coprecipitation method followed by calcination together with a lithium source has been used. In this coprecipitation method, the size and surface state of the cathode active material tend to be determined in the step of synthesizing the precursor, and the manganese-based cathode active material produced by coprecipitation has a problem in that it exhibits a low rate characteristic. In order to solve such a low rate characteristic, a method of increasing the BET value by reducing the particle size of the cathode active material has been considered. However, in such a method, there is a problem that the tap density of the cathode active material, Another problem arises.

The present invention has been made to solve the above problems, and provides a manganese-based cathode active material having a tap density, a powder property, and an electrode processability of a desired level of a cathode active material, I want to.

According to an aspect of the present invention, there is provided a porous manganese-based cathode active material having a specific surface area ranging from 1.5 m ² / g to 2.5 m ² / g and having a particle diameter ranging from 5 μm to 20 μm. Is provided:

[Chemical Formula 1]

Li _x Ni _y Mn _z Co _{1 - y - z} O ₂

In the above formula, z> y, z> 1-y-z, and x≥1.

The porous manganese-based cathode active material may have pores having a diameter of several nanometers to several hundreds of nanometers.

The porous manganese based cathode active material may have a tap density ranging from 1.3 g / cc to 2.0 g / cc.

According to another aspect of the present invention, there is provided a lithium secondary battery comprising the above-described porous manganese-based cathode active material.

The lithium secondary battery may have a 2.0 C / 0.1 C rate ranging from 90% to 97%.

According to another aspect of the present invention, there is provided a method for producing the aforementioned porous manganese based cathode active material, comprising the steps of:

S1) wetting a manganese (Mn) source, a nickel (Ni) source, a cobalt (Co) source in a solvent to obtain a slurry;

S2) adding and mixing sucrose, a lithium source or both to the slurry;

S3) wet pulverizing the mixed slurry to obtain primary particles;

S4) spray drying the primary particles to obtain secondary particles; And

S5) firing the secondary particles.

The manganese source, the nickel source, and the cobalt source may be used to provide 0.1 to 0.4 moles of nickel and 0.1 to 0.4 moles of cobalt relative to 1 mole of manganese.

The manganese source may comprise Mn ₂ O ₃ , MnO ₂ , Mn ₃ O ₄ , MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylate, manganese citrate, manganese fatty acid, Or a mixture of two or more thereof.

The nickel source is _{Ni (OH) 2, NiO,} NiOOH, NiCO 3 and 2Ni (OH) ₂ and 4H ₂ O, NiC ₂ O ₄ and _{2H 2 O, Ni (NO 3} ) 2 and 6H ₂ O, NiSO _4, NiSO ₄ .6H ₂ O, nickel and nickel halides, and mixtures of two or more thereof.

The cobalt source is _{Co (OH) 2, CoO,} Co 2 O 3, Co 3 O 4, CoCOOH, Co (OCOCH 3) 2 and _{4H 2 O, CoCl 2, Co} (NO 3) 2 and 6H ₂ O and Co (SO ₄ ) ₂ .7H ₂ O, and mixtures of two or more thereof.

The sucrose, the lithium source, or both may be used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the total of the manganese source, the nickel source, and the cobalt source constituting the cathode active material.

The calcination may be carried out at a temperature ranging from 500 ° C to 1000 ° C.

The porous manganese-based cathode active material according to the present invention has a desired BET specific surface area, tap density and powder characteristics, and the cathode active material particles have an appropriate particle size, thereby satisfactorily achieving an electrode process.

Further, the lithium secondary battery including the porous manganese based cathode active material according to the present invention exhibits a high rate characteristic.

Hereinafter, the present invention will be described in detail. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The terms " to " used in connection with the numerical ranges in this specification are understood to include the upper and lower limits of the numerical range.

In one aspect of the present invention, there is provided a porous manganese-based cathode active material represented by the following general formula (1)

[Chemical Formula 1]

Li _x Ni _y Mn _z Co _{1 - y - z} O ₂

In the above formula, z> y, z> 1-y-z, and x≥1.

The porous manganese-based cathode active material is preferably applied to a lithium secondary battery to have a BET specific surface area ranging from 1.5 m ² / g to 2.5 m ² / g when measuring BET specific surface area by a nitrogen adsorption method in order to exhibit a desired rate Do. When the BET specific surface area is smaller than the lower limit value, it is difficult to obtain a desired rate. When the BET specific surface area is larger than the upper limit value, the BET specific surface area becomes undesirable in terms of the size and mechanical strength of the cathode active material.

In addition, the porous manganese-based cathode active material may have a size of secondary particles ranging from 5 μm to 20 μm, that is, a long diameter. When the porous manganese-based cathode active material has a long diameter smaller than the lower limit value, the tap density is lowered to lower the powder properties and the electrode processability, while when the porous manganese cathode active material has a larger diameter than the upper limit value, it is difficult to obtain the desired rate characteristic.

The porous manganese-based cathode active material of the present invention is also characterized by being super-porous.

The manganese-based cathode active material has a tap density ranging from 1.3 g / cc to 2.0 g / cc.

In another aspect of the present invention, the manganese-based cathode active material represented by the following formula (1) of the present invention can be produced by a method comprising the steps of:

[Chemical Formula 1]

Li _x Ni _y Mn _z Co _{1 - y - z} O ₂

In the above formula, z> y, z> 1-y-z, and x≥1.

S1) wetting a solvent with a constant concentration of a manganese (Mn) source, a nickel (Ni) source, and a cobalt (Co) source to obtain a slurry;

S2) adding and mixing sucrose, a lithium source or both to the slurry;

S3) wet pulverizing the mixed slurry to obtain primary particles having a diameter of 300 to 500 nm;

S4) spray drying the primary particles to obtain secondary particles; And

S5) firing the secondary particles.

S1) is a step of wetting a manganese (Mn), nickel (Ni), and cobalt (Co) source in a solvent to obtain a slurry.

In this case, each of the manganese (Mn), nickel (Ni), and cobalt (Co) sources may be a compound containing manganese, nickel and cobalt.

Specific examples of the manganese (Mn) source include manganese oxides such as Mn ₂ O ₃ , MnO ₂ and Mn ₃ O ₄ , MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylate, Manganese halides such as manganese, manganese halides such as oxyhydroxide and manganese chloride, and the like, but are not limited thereto. Of these manganese compounds, MnO ₂ , Mn ₂ O ₃ , and Mn ₃ O ₄ are preferable from the viewpoint of not generating gases such as NO _x , SO _x , and CO ₂ in the subsequent firing process, Do. These manganese compounds may be used alone or in combination of two or more.

Specific examples of the nickel (Ni) source is _{Ni (OH) 2, NiO,} NiOOH, NiCO 3 and 2Ni (OH) ₂ and 4H ₂ O, NiC ₂ O ₄ and _{2H 2 O, Ni (NO 3} ) 2 and 6H ₂ O, NiSO ₄ , NiSO ₄ .6H ₂ O, fatty acid nickel, and nickel halide, but are not limited thereto. Among these nickel compounds, Ni (OH) ₂ , NiO, NiOOH, NiCO ₃ .2Ni (OH) ₂ .4H ₂ O, which do not generate harmful substances such as NO _x and SO _x , , And nickel compounds such as NiC ₂ O ₄ .2H ₂ O are preferable. In addition, Ni (OH) ₂ , NiO, and NiOOH are available as inexpensive industrial raw materials and have high reactivity. These nickel compounds may be used singly or in combination of two or more.

Cobalt (Co) Specific examples of the source of the _{Co (OH) 2, CoO,} Co 2 O 3, Co 3 O 4, CoCOOH, Co (OCOCH 3) 2 and _{4H 2 O, CoCl 2, Co} (NO 3) 2 and 6H ₂ O, and Co (SO ₄ ) ₂ .7H ₂ O, but the present invention is not limited thereto. Of these, Co (OH) ₂ , CoO, Co ₂ O ₃ , and Co ₃ O ₄ are preferable in that no harmful substances such as NO _x and SO _x are generated during the firing process. Further, Co (OH) ₂ is more preferable because it is commercially available at low cost and has high reactivity. These cobalt compounds may be used singly or in combination of two or more.

The Mn, Ni, and Co sources are used in a specific composition to form the porous manganese-based cathode active material represented by the general formula (1). That is, Mn, Ni, and Co sources are added to the solvent so that 0.1 to 0.4 moles of nickel and 0.1 to 0.4 moles of cobalt are added to 1 mole of manganese.

The solvent may be selected from the group consisting of water, acetone, methanol, ethanol, isopropyl alcohol, and combinations thereof, but is not limited thereto.

Step S2) is a step of adding sucrose, a lithium source or both to the slurry.

S2), pores are formed in the cathode active material due to the source of lithium. Therefore, the use amount of sucrose and lithium source is one factor for determining the pore size and porosity of the manganese-based cathode active material. In the present invention, sucrose, the lithium source, or both may be used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of total of the manganese source, the nickel source, and the cobalt source constituting the cathode active material. If the amount is used in an amount less than the lower limit value, pores are not formed sufficiently. If the amount is used in an amount larger than the upper limit value, the porosity becomes excessively large, and the mechanical strength of the cathode active material can not be secured at a certain level.

A lithium source is _{Li 2 CO 3, LiNO 3,} LiNO 2, LiOH, LiOH · H 2 O, LiH, LiF, LiCl, LiBr, LiI, CH 3 OOLi, Li 2 O, Li 2 SO 4, dicarboxylic acid Li, citric acid Li, fatty acid Li, alkyl lithium and the like. These lithium sources generate pores in the spray-dried secondary particles by generating decomposed gas or generating decomposed gas during firing, and Li ₂ CO ₃ , LiOH, and LiOH · H ₂ O form SO _x and NO _x It is preferable from the viewpoint that it is easy to handle without causing harmful substances and is relatively inexpensive. The lithium compounds may be used singly or in combination of two or more.

Unlike the lithium source, sucrose fills carbon into the atmosphere during the sintering process and forms pores at the site of the carbon. In particular, sucrose is advantageous in terms of price and solubility, and it is particularly advantageous to use sucrose in a spray drying process. In addition, the use of sucrose is advantageous in terms of the electrical conductivity of the material because it is highly likely to form a carbon coating.

Step S3) is a step of wet pulverizing the mixed slurry to obtain primary particles of the manganese-based cathode active material.

The specific method of the wet grinding process is not limited, but may be performed, for example, by ball milling, and may be carried out at a temperature of 30 ° C to 70 ° C for 12 to 24 hours. Below 30 ° C, there is a problem that the raw materials are not mixed well or the raw material is not dissolved well, and undesired by-products may be produced at a temperature higher than 70 ° C. In addition, particles formed in the course of less than 12 hours may become non-uniform, and if it exceeds 24 hours, new particles having different sizes and shapes other than the spherical shape to be manufactured may be formed.

Grinding media commonly used in ball milling may include yttrium, stabilized zirconia beads having a hardness close to diamond hardness, or even more softer grinding media based on polystyrene or other similar polymers.

The content of the raw material compound contained in the slurry, that is, the total content of nickel, manganese, cobalt, sucrose, and lithium source is not particularly limited in the present invention, but may be 50 wt% to 60 wt% . If the total weight ratio is less than the lower limit value, the spherical particles produced by spray drying are liable to become smaller or more likely to be broken due to the low concentration of the slurry, and if the upper limit is exceeded, it may be difficult to maintain the uniformity of the slurry.

The wet-milled primary particles may have a particle size in the range of 300 to 500 nm.

S4) to obtain secondary particles.

The spray drying may be carried out by a method and conditions customary in the art, for example, at a temperature of 50 to 300 ° C. Examples of the gas supplied during spray drying include air and nitrogen. The spraying means is not particularly critical, and a spray drying device known in the art can be used.

Subsequently, the obtained secondary particles are fired in S5).

By this step, the carbon or gas present in the secondary particles is removed, and pores are formed, so that the porous cathode active material can be formed.

The firing can be performed at a temperature of 500 ° C to 1000 ° C, preferably 900 ° C to 940 ° C, and is generally performed for 30 minutes to 20 hours, preferably 5 hours to 10 hours or less. If the firing time is too short, it is difficult to obtain a manganese-based cathode active material with good crystallinity, and if it is too long, pulverization may be difficult.

The atmosphere at the time of firing may be air or an inert gas atmosphere such as nitrogen or argon depending on the composition or structure of the target compound.

The porous manganese-based cathode active material obtained as described above is mixed with a conductive material and a binder according to a conventional method known in the art to form a slurry, and a positive electrode collector such as a foil manufactured by aluminum, nickel, The anode is manufactured by applying it to the whole.

In addition, a negative electrode can be manufactured according to a conventional method known in the art. As a non-limiting example of the negative electrode active material, a conventional negative electrode active material that can be used for a negative electrode of an electrochemical device can be used. In particular, lithium metal or a lithium alloy, carbon, petroleum coke, activated carbon, Lithium-adsorbing materials such as graphite or other carbon-based materials and the like are preferable. Non-limiting examples of cathode current collectors include foils made by copper, gold, nickel or copper alloys or combinations thereof.

As the separator that can be interposed between the anode and the cathode, a porous polyethylene, a polyolefin film of a porous polypropylene, an organic / inorganic composite separator in which a porous coating layer is formed on a porous substrate, a nonwoven film, engineering plastic But are not limited thereto. As a process for applying a separator to an electrode, a lamination, stacking and folding process of a separator and an electrode can be performed in addition to a general winding process.

Is A ⁺ B in the electrolyte ^- the salts of the structure, such as, A ⁺ is Li ^+, Na ^+, include alkali metal cation or an ion composed of a combination thereof, such as K ^+, and B ^- is PF _{6 ^-,} BF ₄ ^{- , Cl -, Br -, I} -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO 2) 3 - and (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethylsulfoxide, dimethyl sulfoxide and the like. Is dissolved in an organic solvent consisting of acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma-butyrolactone, Or dissociated, but is not limited thereto. The electrolyte injection may be performed at an appropriate stage of the battery manufacturing process, depending on the manufacturing process and required properties of the final product. That is, it can be applied before assembling the cell or at the final stage of assembling the cell.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the above-described embodiments. Embodiments of the invention are provided to more fully describe the present invention to those skilled in the art.

Example  1-1: Preparation of cathode active material

_{Ni (OH) 2 0.15 ~ 0.2} M (mol / 1000㎖), MnO 2 0.4 ~ 0.7M , and so that the Co ₃ O ₄ 0.15 ~ 0.2M was poured into water 5000 ㎖. Then, sucrose was added so as to be 0.01 to 0.1M.

The starting materials were stirred for 10 minutes at 400 rpm in a stirrer so that the starting materials were homogeneously mixed, pulverized for 30 minutes using zirconia beads having a diameter of 1 mm in a home made equipment, and dispersed to obtain a slurry. The particle size (D ₅₀ ) of the obtained primary particles was 300 to 500 nm.

Subsequently, the slurry was spray-dried by using a spray dryer at a hot air temperature of 250 to 300 占 폚 and an exhaust hot air temperature of 100 to 150 占 폚 to obtain secondary particles having a particle diameter in the range of 5 占 퐉 to 20 占 퐉.

Subsequently, a lithium source was added and the mixture was calcined at a temperature of 850 to 950 DEG C for 5 to 10 hours to obtain a porous manganese-based cathode active material.

Example  1-2: The lithium secondary battery  Produce

The mixture was uniformly mixed so that the ratio of the cathode active material, the conductive material (Super P) and the binder (PVDF) obtained in Example 1-1 was 94: 3: 3. The mixture was spread evenly on an aluminum foil, pressed uniformly with a roll press, and vacuum dried in a vacuum oven at 100 캜 for 12 hours to prepare a positive electrode.

As negative electrode, commercially available graphite and Si-based material of a high capacity material were mixed in an amount of 9: 1 by weight, acetylene black and CMC / SBR were mixed at a weight ratio of 8: 1: 1, Methylpyrrolidone and high shear mixing was performed at a level of 18,000 rpm or less at the shear pressure applied to the slurry as a criterion for passing the capillary diameter of 100 μm at the MFD mixer. The anode mixture slurry was coated on a copper foil having a thickness of 10 탆 by a doctor blade method, semi-dried, and cut to a predetermined size. At this time, the cell was dried at 120 DEG C for about one day in a vacuum state before assembly.

As a separator, a separator was interposed between the anode and the cathode using a monolayer polyethylene separator, and 1 mol of LiPF ₆ solution was added to an EC / EMC = 1/3 mixed solvent as an electrolytic solution. A battery was prepared according to the manufacturing method.

Claims (11)

A carbon coating is further formed on the porous manganese-based cathode active material having a specific surface area in the range of 1.5 m ² / g to 2.5 m ² / g and a particle diameter in the range of 5 μm to 20 μm, Wherein the porous manganese-based cathode active material comprises:
[Chemical Formula 1]
Li _x Ni _y Mn _z Co _{1- y z} O ₂
In the above formula, z> y, z> 1-yz, and x≥1.
The method according to claim 1,
Wherein the porous manganese-based cathode active material has a tap density in the range of 1.3 g / cc to 2.0 g / cc.
A lithium secondary battery comprising the porous manganese based cathode active material according to claim 1 or 2.
delete A method for producing the porous manganese-based cathode active material according to claim 1, comprising the steps of:
S1) wetting a manganese (Mn) source, a nickel (Ni) source, a cobalt (Co) source in a solvent to obtain a slurry;
S2) adding and mixing a lithium source to the slurry;
S3) wet pulverizing the mixed slurry to obtain primary particles;
S4) spray drying the primary particles while adding sucrose to obtain secondary particles; And
S5) firing the secondary particles.
6. The method of claim 5,
Wherein the manganese source, the nickel source, and the cobalt source are used such that 0.1 to 0.4 moles of nickel and 0.1 to 0.4 moles of cobalt are added per mole of manganese.
6. The method of claim 5,
The manganese source may comprise Mn ₂ O ₃ , MnO ₂ , Mn ₃ O ₄ , MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylate, manganese citrate, manganese fatty acid, Or a mixture of two or more thereof.
6. The method of claim 5,
The nickel source is _{Ni (OH) 2, NiO,} NiOOH, NiCO 3 and 2Ni (OH) ₂ and 4H ₂ O, NiC ₂ O ₄ and _{2H 2 O, Ni (NO 3} ) 2 and 6H ₂ O, NiSO _4, NiSO ₄ .6H ₂ O, nickel and nickel halides, and mixtures thereof.
6. The method of claim 5,
The cobalt source is _{Co (OH) 2, CoO,} Co 2 O 3, Co 3 O 4, CoCOOH, Co (OCOCH 3) 2 and _{4H 2 O, CoCl 2, Co} (NO 3) 2 and 6H ₂ O and Co (SO ₄ ) ₂ 쨌 7H ₂ O. 2. The production method according to claim 1,
6. The method of claim 5,
Wherein the sucrose, the lithium source, or both are used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the total of the manganese source, the nickel source, and the cobalt source constituting the cathode active material.
6. The method of claim 5,
Wherein the calcination is carried out at a temperature range of 500 to 1000 占 폚.