KR20150059820A - Manufacturing method of cathod active material for lithium rechargible battery by coprecipitation, and cathod active material for lithium rechargeable battery made by the same - Google Patents

Abstract

The present invention relates to a manufacturing method of positive electrode active materials for lithium secondary batteries using co-precipitation, which is allowed to control speed of supplying metallic salt according to the size of particles when co-precipitation reaction is made and accordingly has high tapped density in the whole particle, thereby improving properties of lithium secondary batteries, and positive electrode active materials for lithium secondary batteries manufactured by the same.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery by coprecipitation and a positive electrode active material precursor for a lithium secondary battery,

The present invention relates to a method for producing a cathode active material for a lithium secondary battery by coprecipitation and a cathode active material for a lithium secondary battery produced thereby.

Since its appearance in 1991, lithium ion secondary batteries have been widely used as power sources for portable devices. 2. Description of the Related Art In recent years, with the rapid development of the electronics, communication, and computer industries, camcorders, mobile phones, notebook PCs, and the like have been remarkably developed and demand for lithium ion secondary batteries as power sources for driving these portable electronic information communication devices . In recent years, research on a power source for an electric vehicle by hybridizing an internal combustion engine with a lithium secondary battery has been actively carried out in the United States, Japan, and Europe.

As a large-sized battery for an electric vehicle, although a nickel-metal hydride battery is used from the viewpoint of safety, a lithium-ion battery is considered from the viewpoint of energy density, but the biggest problem is high price and safety.

The cathode active materials such as LiCoO ₂ and LiNiO _{2 which} are currently in commercial use are disadvantageous in that their crystalline structure is unstable due to the depolymerization at the time of charging and the thermal characteristics are very poor. That is, when the battery in an overcharged state is heated to 200 to 270 ° C, an abrupt structural change occurs, and an oxygen release reaction in the lattice caused by such a structural change proceeds (JR Dahn et al., Solid State Ionics, 69, 265 )).

LiCoO ₂ is mainly used as a cathode active material in a small-sized lithium ion secondary battery currently available on the market. LiCoO ₂ is an excellent material with stable charge / discharge characteristics, excellent electron conductivity, high stability and flat discharge voltage characteristics, but Co is required to develop other cathode material because it has a low storage capacity, high cost and toxicity to human body.

LiNiO ₂ has a layered structure such as LiCoO ₂ , has a large discharge capacity, has the shortest cycle life and thermal instability, and has a problem in safety at high temperature and has not been commercialized yet.

In order to solve this problem, attempts have been made to broaden the exothermic peak in order to move the heat generation starting temperature to a slightly higher temperature side or prevent rapid heat generation by substituting a part of nickel with a transition metal element T. Ohzuku et al., J. Electrochem. Soc., 142, 4033 (1995), Japanese Unexamined Patent Publication No. 9-237631). However, still satisfactory results are not obtained.

As a material having a layered crystal structure most favored as an alternative material for LiCoO ₂ , there is a Li [Ni _{0 .5} Mn _{0 .5)} mixture of nickel-manganese and nickel-cobalt-manganese in a ratio of 1: 1 or 1: ] O ₂ and Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ . The lithium composite metal oxides are obtained by precipitating two or three elements simultaneously in an aqueous solution using a neutralization reaction to obtain precursors in the form of hydroxides or oxides, mixing the precursors with lithium hydroxide, and sintering the precursors. Unlike a typical coprecipitation reaction, coprecipitated particles containing manganese usually exhibit irregular platelets, and the tap density is only about half of that of nickel or cobalt.

Japanese Patent Application Laid-Open No. 2002-201028 discloses a lithium composite metal oxide using an inert precipitation method. At this time, the lithium composite metal oxide particles produced by the precipitation have not only a wide particle size distribution, but also have different disadvantages in the shape of primary particles.

Japanese Patent Application Laid-Open Nos. 2003-238165, 2003-203633, 2003-242976, 2003-197256, 2003-86182, 2003-68299 and 2003-59490, 0557240 and No. 0548988 disclose a method of dissolving a nickel salt, a manganese salt, a nickel salt, a manganese salt and a cobalt salt in an aqueous solution and then simultaneously introducing an alkali solution into the reactor to purge the metal hydroxide or oxide with a reducing agent or an inert gas And a method for producing a high-capacity cathode active material having improved charge / discharge reversibility and thermal stability by mixing this precursor with lithium hydroxide followed by firing.

However, in the above-described manufacturing method, since the supply rate of the metal salt is made constant in the process of forming the particles, the supply rate of the metal salt as the diameter of the particles increases toward the outside of the particles is insufficient, There is a problem that the voids increase between the primary particles at the outside of the particles to decrease the tap density of the whole particles and deteriorate the battery characteristics.

In order to solve the above problems, it is an object of the present invention to provide a method for producing a cathode active material for a lithium secondary battery by a new coprecipitation method which can exhibit a constant tap density both inside and outside of the particles.

The present invention has been made to solve the above problems

A metal salt aqueous solution, a chelating agent, and a basic aqueous solution to a reactor to coprecipitate to prepare a coprecipitation compound; And

Drying or heat-treating the coprecipitated compound to prepare an active material precursor;

Mixing the lithium salt with the active material precursor to form a lithium composite metal oxide of Formula 1; A method of manufacturing a precursor of a cathode active material for a lithium secondary battery,

Wherein the rate of supplying the metal salt aqueous solution to the reactor is increased according to an increase in the particle size of the coprecipitation compound in the step of coprecipitating the metal salt aqueous solution, the chelating agent, and the basic aqueous solution, A method for manufacturing a positive electrode active material for a battery is provided.

In the method for producing a cathode active material for a lithium secondary battery according to the present invention, the aqueous metal salt solution is characterized by containing one kind of salt selected from the group consisting of sulfate, nitrate, acetate, halide, hydroxide and combinations thereof.

In the method for producing a cathode active material for a lithium secondary battery according to the present invention, the chelating agent is one selected from the group consisting of an aqueous ammonia solution, an aqueous ammonium sulfate solution, and a mixture thereof.

The present invention also provides a cathode active material for a lithium secondary battery produced by the production method of the present invention.

The method for preparing a cathode active material for a lithium secondary battery according to the present invention exhibits a high tap density in the whole particle by controlling the supply rate of the metal salt with an increase in particle diameter during the coprecipitation reaction, thereby improving battery characteristics.

FIG. 1 and FIG. 2 illustrate the metal salt aqueous solution feed rate and particle growth rate according to the reaction time in one embodiment and comparative example of the present invention.
3 is a SEM photograph of a cross-section of a cathode active material prepared in one embodiment of the present invention and a comparative example.
FIG. 4 and FIG. 5 show the results of measurement of the charging / discharging characteristics and the life characteristics of the battery including the cathode active material prepared in the example of the present invention and the comparative example.

Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited by the following examples.

< Example  1: Concentration The gradient  Manufacture of positive electrode active material

4 liters of distilled water was placed in a coprecipitation reactor (capacity 4 L, output of a rotary motor 80 W or more), nitrogen gas was supplied to the reactor at a rate of 0.5 liter / min to remove dissolved oxygen, lt; / RTI &gt;

Thereafter, a 2.4 M metal aqueous solution mixed at a molar ratio of 40: 30: 30 of nickel sulfate, cobalt sulfate and manganese sulfate was fed at 0.3 liter / hour, and a 4.8 M ammonia solution at 0.03 liter / . In addition, a pH of 4.8 M was supplied to maintain the pH at 11 by adjusting the pH.

Then, the coprecipitation reaction was performed by controlling the impeller speed of the reactor to 1000 rpm. Then, the average residence time of the solution in the reactor was set to about 6 hours while the feed rate of the metal aqueous solution was increased from 0.3 liters / hour to 0.5 liters / hour. After the reaction reached a steady state, To give a more dense coprecipitation compound (complex metal hydroxide).

The coprecipitated compound was filtered, washed with water, and dried in a hot air dryer at 110 ° C for 15 hours to obtain an active material precursor (metal complex hydroxide, Ni0.4Co0.3Mn0.3 (OH) 2).

The obtained active material precursor was mixed with lithium hydroxide (LiOH), heated at a heating rate of 1 ° C / min, and then prebaked at 500 ° C for 10 hours, followed by calcination at 950 ° C for 20 hours to obtain a cathode active material powder (Li [Ni0.4Co0.3Mn0.3] O2).

< Comparative Example >

The cathode active material powder (Li [Ni0.4Co0.3Mn0.3] O2) was obtained in the same manner as in Example 1, except that the feed rate of the metal aqueous solution was kept constant at 0.3 liter / hour.

< Experimental Example > Particle size measurement with reaction time

In the examples and comparative examples, the metal aqueous solution feed rate and particle size were measured according to the coprecipitation reaction time, and the results are shown in FIGS. 1 and 2. FIG.

In the case of the embodiment of the present invention, as shown in FIG. 1, the particle size is uniformly grown in one dimension by increasing the feed rate of the metal aqueous solution as the particles grow, 2, it can be seen that the growth rate of the particle size decreases with the reaction time.

< Experimental Example > SEM  Measure

SEM photographs were taken of the cross-sections of the active material particles prepared in the Examples and Comparative Examples, and the results are shown in FIG. As shown in FIG. 3, the internal and external densities of the comparative example are different from each other. On the other hand, the active material particles produced in the embodiment of the present invention exhibit a uniform density from the inside to the outside of the particle.

< Experimental Example > Tap density  And Specific surface area  Measure

The tap density and specific surface area of the active material particles prepared in the above Examples and Comparative Examples were measured and the results are shown in Table 1 below. As shown in the following Table 1, the primary particles are densely grown in the embodiment of the present invention, so that the tap density is increased by 5% or more and the specific surface area is reduced by 40% or more as compared with the comparative example.

< Manufacturing example > Battery Manufacturing

Acetylene black was mixed with polyvinylidene fluoride (PVdF) as a binder and the cathode active material prepared in Example 1 and Comparative Example 1 at a weight ratio of 80:10:10 to prepare a slurry. The slurry was uniformly applied to an aluminum foil having a thickness of 20 탆 and vacuum-dried at 120 캜 to prepare a positive electrode for a lithium secondary battery.

A mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 1 was used as a separator, using the above anode and lithium foil as counter electrodes, and using a porous polyethylene membrane (Celgard 2300, thickness: A coin cell was prepared according to a conventionally known production process using a liquid electrolyte in which LiPF6 was dissolved in a solvent at a concentration of 1M.

< Experimental Example > Charging and discharging  Measurement of characteristics and life characteristics

Charge-discharge characteristics and life characteristics were measured for the batteries prepared in the above production examples, and the results are shown in FIGS. 4 and 5. FIG. 4 and 5, it can be seen that the battery manufactured from the cathode active material of the embodiment of the present invention improves the charge-discharge characteristics and the life characteristics.

Claims (4)

A metal salt aqueous solution, a chelating agent, and a basic aqueous solution to a reactor to coprecipitate to prepare a coprecipitation compound; And
Drying or heat-treating the coprecipitated compound to prepare an active material precursor;
Mixing the lithium salt with the active material precursor to form a lithium composite metal oxide of Formula 1; A method of manufacturing a precursor of a cathode active material for a lithium secondary battery,
Wherein the rate of supplying the metal salt aqueous solution to the reactor is increased according to an increase in the particle size of the coprecipitation compound in the step of coprecipitating the metal salt aqueous solution, the chelating agent, and the basic aqueous solution, Method for producing cathode active material for battery
The method according to claim 1,
Wherein the metal salt aqueous solution contains one kind of salt selected from the group consisting of sulfate, nitrate, acetate, halide, hydroxide, and combinations thereof.
The method according to claim 1,
Wherein the chelating agent is one selected from the group consisting of an aqueous ammonia solution, an aqueous ammonium sulfate solution, and a mixture thereof.
A positive electrode active material for a lithium secondary battery produced by the production method of any one of claims 1 to 3

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