KR20190081609A - Positive electrode active material for rechargable lithium battery, method of preparing the same, and rechargable lithium battery including the same - Google Patents

Abstract

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 comprising the positive electrode active material. The positive electrode active material for a lithium secondary battery can be provided, which is a secondary particle in which lithium metal oxide primary particles are aggregated. The lithium metal oxide particles have a layered structure. The powder resistance of the secondary particles is 80-300 ohm-cm, and the grain size is 50 nm or less. A positive electrode active material with enhanced initial discharge capacity, output characteristics, and cycle characteristics can be provided.

Description

TECHNICAL FIELD The present invention relates to a positive electrode 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 The present invention relates to a positive active material for a lithium secondary battery,

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

2. Description of the Related Art In recent years, portable electronic devices such as AV devices and personal computers have been rapidly made portable and wireless, and as a driving power source therefor, there is a growing demand for secondary batteries having small and lightweight high energy densities. In recent years, development and commercialization of electric vehicles and hybrid vehicles have been made for the global environment, and thus there is a growing demand for lithium ion secondary batteries having excellent storage characteristics. Under such circumstances, a lithium ion secondary battery having a large charge / discharge capacity and an excellent life characteristic has been attracting attention.

Conventionally, LiMn ₂ O ₄ of a spinel type structure, LiMnO ₂ of a zigzag layer type structure, LiCoO ₂ and LiNiO ₂ of a layered rock salt type structure are generally used as a cathode active material useful for a high energy type lithium ion secondary battery having a voltage of 4 V class Among them, a lithium ion secondary battery using LiNiO ₂ is attracting attention as a battery having a high charge / discharge capacity.

However, this material is inferior in durability in charging and discharging cycles, and further improvement in characteristics is required.

Recently, in the NiCo binary system excluding Mn, the capacity increase effect is expected by maximizing the content of Ni. However, it is necessary to use additional dopant due to the formation of NiO and the mixing of cations.

In this case, the use of B (boron) is known in consideration of the shape and internal density of the particles, but the sensitivity of the B is higher than that of other elements, so that a significant decrease in the capacity is necessary when the internal densification effect is added .

Therefore, finding a combination of dopants that increase the internal density of the particles while minimizing the capacity reduction by replacing B remains a challenge for the NiCo 2 source system.

And to provide a positive electrode active material for a lithium secondary battery securing a high output characteristic.

In one embodiment of the present invention, the lithium metal oxide particles are a secondary particle in which lithium metal oxide primary particles are aggregated, the lithium metal oxide particles have a layered structure, the powder resistance of the secondary particles is 80 to 300 ohm-cm, wherein the cathode active material has a grain size of 50 nm or less.

The secondary particles may be in a hollow form.

The Ni ^{2 +} content of the compound may be 2.5% or less when the Rietveld is measured.

The secondary particles may be represented by the following formula (1).

[Chemical Formula 1]

Li _? [(Ni _x Co _y Mn _z ) _{1 -?} A _? ] O ₂

Wherein A is at least one selected from the group consisting of Zr, Ti, Al and Mg, 0.98 ≦ α ≦ 1.02, 0.001 ≦ β ≦ 0.015, 0.80 ≦ x ≦ 0.85, and 0.09 ≦ y ≦ 0.12, and 0.06 ≦ z ≦ 0.08. It is either.

The c / a axis ratio of the cathode active material may be 4.9415-4.9420.

In another embodiment of the present invention, there is provided a method of preparing a precursor comprising: preparing a precursor comprising Ni, Co, and Mn; And at least one doping raw material selected from Zr, Ti, Al, and Mg to the precursor; And a step of dry-mixing and calcining the lithium source material, wherein at least one doping raw material selected from Zr, Ti, Al, and Mg is added to the precursor; Wherein the firing temperature includes a temperature rising period, a holding period, and a cooling period, and the temperature condition of the holding period is 710-750 ° C. in the initial holding period And a final sustain period temperature range of 770-790 DEG C. The present invention also provides a method for producing a cathode active material for a lithium secondary battery.

At least one doping raw material selected from Zr, Ti, Al, and Mg is added to the precursor; And a step of firing the lithium raw material after dry mixing, the total firing time may be 10-50 hours.

The maintenance interval may be performed for 15-20 hours.

The final temperature of the heating section may be 730-740 ° C, and the final temperature of the heating section may be 770-780 ° C.

According to another embodiment of the present invention, there is provided a positive electrode comprising a positive electrode active material according to an embodiment of the present invention; A negative electrode comprising a negative electrode active material; And an electrolyte positioned between the positive electrode and the negative electrode.

It is possible to provide a positive electrode active material having improved initial discharge capacity, output characteristics and cycle characteristics.

Fig. 1 shows the result of measurement of the powder resistance.
Fig. 2 shows the result of analyzing the content of Ni ^{2 +} in the 3b site.
Figure 3 shows the c / a axis value analysis result.
Fig. 4 shows results of electrochemical property evaluation.
5 and 6 are profiles of the firing temperature holding period.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

Cathode active material

In one embodiment of the present invention, the lithium metal oxide particles are a secondary particle in which lithium metal oxide primary particles are aggregated, the lithium metal oxide particles have a layered structure, the powder resistance of the secondary particles is 80 to 300 ohm-cm, A cathode active material for a lithium secondary battery having a grain size of 50 nm or less.

The powder resistance may be 80 to 300 ohm-cm.

Powder resistance can be measured by using a powder resistance meter (MCP-PD51) measuring 3.5 g of active material and measuring 4, 8, 12, 16 and 20 KN pressure with 4-pin probe under the condition of start range -3ohm and 10V.

When such a powder resistance range is satisfied, there is an effect that the initial capacity and efficiency increase and the output characteristics are improved.

The secondary particles may be in a hollow form. The hollow form means that a hollow portion is contained in the secondary particle. These hollow portions can communicate with the outside of the secondary particle. In the case of such a hollow secondary particle, the efficiency is increased and the high output characteristic is improved.

The Ni ^{2 +} content of the compound may be 2.5% or less when the Rietveld is measured. More specifically, it may be 1.5% or more and 2% or less. When this range is satisfied, there is an effect that the cation mixing phenomenon is reduced, the irreversible capacity is decreased, and the rate characteristic is improved.

The c / a axis ratio of the cathode active material may be 4.9415 - 4.9420. When this range is satisfied, it can be confirmed that the two-dimensional planar structure in the layered structure is developed, and the diffusion of lithium can be improved due to the increase of the interlayer of 6c-site.

The secondary particles may be represented by the following formula (1).

[Chemical Formula 1]

Li _? [(Ni _x Co _y Mn _z ) _{1 -?} A _? ] O ₂

In Formula 1,

0.98??? 1.02, 0.001??? 0.015, 0.80? X? 0.85, and 0.09? Y? 0.12 and 0.06? Z? 0.08, and A is at least one selected from Zr, Ti, Al and Mg.

When such a molar ratio is satisfied, the cycle characteristics at ordinary temperature and high temperature can be simultaneously improved. Additionally, the initial capacity reduction can be minimized.

In addition, the initial capacity decrease can be minimized through the above combination, and the capacity retention rate and life characteristics can be improved when the battery is cycled for a long period of time at room temperature and high temperature.

Method for producing cathode active material

In another embodiment of the present invention, at least one doping raw material selected from Zr, Ti, Al, and Mg is added to the precursor; Wherein the firing temperature includes a temperature rising period, a holding period, and a cooling period, and the temperature condition of the holding period is 710-750 ° C. in the initial holding period And a final sustain period temperature range of 770-790 DEG C. The present invention also provides a method for producing a cathode active material for a lithium secondary battery.

More specifically, the total firing time can be 10-50 hours. The maintenance interval may be performed for 15-20 hours.

The final temperature of the heating section may be 730-740 ° C, and the final temperature of the heating section may be 770-780 ° C.

At this time, it is important to set the final firing temperature range to the above-mentioned range. When the temperature range is satisfied, the powder resistance increases and the cation mixing phenomenon decreases, thereby reducing the irreversible capacity, thereby increasing the initial capacity and efficiency and improving the output characteristics.

In the case where lithium does not enter into the structure during the sintering of the active material, the Cubic phase grows more rapidly in the crystal structure when the temperature rises rapidly to the final firing temperature.

Therefore, it is necessary to increase the time for the lithium to enter the structure sufficiently and to increase the rate of formation of the layered structure by relatively long firing at a low temperature.

The temperature can then be increased slightly above the firing temperature to compensate for the amount of fired heat that was lacking during the initial heating process and to grow the crystal.

Conditions for this will be described in more detail in the following embodiments.

The composition of the precursor used and the description of the doping element are the same as those of the above-mentioned cathode active material, so that the description thereof will be omitted.

Lithium secondary battery

Another embodiment of the present invention provides a lithium secondary battery comprising a cathode, a cathode, and an electrolyte solution containing the cathode active material.

The positive electrode includes a positive electrode collector and a positive electrode active material layer formed on the positive electrode collector. The cathode active material layer includes the above-described cathode active material, and optionally, a binder, a conductive material, or a combination thereof.

Hereinafter, a redundant description of the above-mentioned positive electrode active material will be omitted, and the remaining constitution of the lithium secondary battery will be described.

As the collector, aluminum may be used, but the present invention is not limited thereto.

The binder may be selected from, for example, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers comprising ethylene oxide, Styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like can be used.

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 metal powders such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, 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 the current collector.

The current collector may be a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foil, a copper foil, a polymer substrate coated with a conductive metal, or a combination thereof.

The negative electrode active material layer includes a negative electrode active material, a binder composition, and / or a conductive material.

The negative electrode active material 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.

Descriptions of the negative electrode active material, the binder composition and the conductive material will be omitted.

The electrolyte includes a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent and the lithium salt can be used as long as they are compatible with each other, so that detailed explanation is omitted.

Examples of the present invention, comparative examples thereof, and evaluation examples thereof will be described below. The following examples are only illustrative of the present invention and are not intended to limit the scope of the present invention.

Example  One

(1) Preparation of cathode active material

The desired Li _{1 . 0138} Ni _{0. 8171} Co _{0 . 1044} Mn _{0 . 0685} Zr _{0 . 0014} Ti _{0. 0027} Mg _{0. To} be a stoichiometric molar ratio of ₀₀₆ O ₂ , the nickel-based metal hydroxide precursor Ni _{0 . 82} Co _{0 . 11,} the Mn _{0 .07} (OH) _2, the lithium source material LiOH, ZrO _2, of Zr raw material Ti raw material is TiO ₂ and Mg raw material of Mg (OH) _2, were mixed in a dry process.

A mixture of 650 g of the dry mixture was filled in a mullite saggar and sintered in an oxygen (O ₂ ) atmosphere at a sintering temperature range of 735 to 780, And baked for a total of 30 hours.

The material thus obtained was pulverized and classified to obtain an average particle diameter of 5.7 占 퐉 and obtained as the cathode active material of Example 1.

Specific firing conditions are shown in Figs. 5, 6, and Table 2 below.

(2) Production of lithium secondary battery (Half-cell)

(NMP) solvent such that the mass ratio of the positive electrode active material to the conductive material (Super-P) and the binder (PVDF) of Example 1 was 90: 5: 5 (active material: conductive material: And uniformly mixed.

The mixture was spread evenly on an aluminum foil and then NMP was evaporated by hot air drying. The mixture was squeezed by a roll press and vacuum-dried for 12 hours in a 100-120 vacuum oven to prepare a positive electrode. Li-metal was used as a counter electrode, and 1.2 mol of LiBF ₄ solution was used as a liquid electrolyte in a mixed solvent of ethylene carbonate (EC): dimethyl carbonate (DMC) = 1: 1 as an electrolytic solution. A coin-type half-coin cell was prepared.

Example  2

The desired Li _{1 . 0138} Ni _{0. 8167} Co _{0 . 1043} Mn _{0 . 0684} Zr _{0 . 0014} Ti _{0. 0027} Mg _{0. 006} A1 _{0 . To} be a stoichiometric molar ratio of ₀₀₆ O ₂ , the nickel-based metal hydroxide precursor Ni _{0 . 82} Co _{0 . 11 Mn 0 .07 (OH) 2} , in which the Mg (OH) of the lithium raw material LiOH, Zr raw material ZrO _2, TiO ₂ Ti raw material, and Mg raw material _2, Al source material Al (OH) ₃ materials were dry mixed.

The subsequent steps were the same as in Example 1, and were obtained as the cathode active material of Example 2 with an average particle diameter of 5.8 mu m thereafter.

Comparative Example  One

Li _{1 . 0138} Ni _{0. 8171} Co _{0 . 1044} Mn _{0 . 0685} Zr _{0 . 0014} Ti _{0. 0027} Mg _{0. 006} O object ₂ by dry mixing the raw materials, and a firing holding temperature is 755 interval condition, and the remainder was prepared for half-cell for producing an active material by the same process as in Example 1, containing the same.

Comparative Example  2

Li _{1 . 0138} Ni _{0. 8171} Co _{0 . 1044} Mn _{0 . 0685} Zr _{0 . 0014} Ti _{0. 0027} Mg _{0. 006} O object ₂ by dry mixing the raw materials and the sintering temperature maintenance section 700 and> 790, condition, and the remainder was prepared for half-cell for producing an active material by the same process as in Example 1, containing the same.

[Table 1]

[Table 2]

A specific graph of the firing temperature profile shown in Table 2 can be referred to FIG. 5 and FIG. 6.

Evaluation example  One ( Powder  Resistance, crystal structure measurement)

Powder resistance can be 80 or more and 300 ohm-cm or less. Powder resistance can be measured by using a powder resistance meter (MCP-PD51) measuring 3.5 g of active material and measuring 4, 8, 12, 16 and 20 KN pressure with 4-pin probe under the condition of start range -3ohm and 10V. When such a powder resistance range is satisfied, there is an effect that the initial capacity and efficiency increase and the output characteristics are improved.

A Rigaku-Ultima IV X-ray diffractometer (Cu Kα) was used to obtain the XRD pattern of the crystal structure and was measured at 1 deg / min and 10 ° -90 ° (2theta / deg). The XRD pattern obtained was analyzed by Rietveld refinement using Win plot with ICP analysis in Full Prof program.

The results are shown in Table 1 above.

Fig. 1 shows the result of measurement of the powder resistance. In Fig. 1, black is Comparative Example 1, red is Comparative Example 2, and blue is the result of Example 1.

The positive electrode active material according to the Example had the highest powder resistance measurement value, and it was confirmed that the capacity retention rate and the life characteristics were improved when the battery was continuously cycled in the room temperature and high temperature environment.

Fig. 2 shows the result of analyzing the content of Ni ^{2 +} in the 3b site. In Fig. 2, black is Comparative Example 1, red is Comparative Example 2, and blue is the result of Example 1.

Comparative Examples 1 and 2 had higher Ni ^{2 +} contents than those of Example 1, so that cation mixing phenomenon appeared to increase irreversible capacity and deteriorate output characteristics. Example 1 has the lowest content of Ni ^{2 +} , so that the cation mixing phenomenon is reduced, and it is confirmed that the capacity retention rate and the life characteristics are improved when the battery is cycled for a long time at room temperature and high temperature environment.

Evaluation example  3 ( Coin cell  Evaluation results)

A CR2032 coin type half cell (coin cell) was assembled in a controlled humidity drier and aged at room temperature for 12 hours to assure electrolytic solution impregnation and electrochemical equilibrium after cell assembly.

The coin cell was evaluated using a TOSCAT-3100 battery tester. First, charging and discharging were repeated for 2 cycles by applying a current density of 0.1 C at a room temperature (25 ° C) voltage range of 3.0 V - 4.2 V, and then 1.0 C current density was applied in the same voltage range, Respectively, at 25 DEG C for 500 cycles and at 45 DEG C for 350 cycles. The initial capacity and coulombic efficiency at the Mars stage and the capacity retention rate during the cycle evaluation are shown in the table.

The results are shown in Table 1 above.

Fig. 4 shows the results of the electrochemical property evaluation. In FIG. 4, black is Comparative Example 1, red is Comparative Example 2, and blue is the result of Example 1. Example 1 was evaluated to have a higher capacity retention rate during cycle evaluation than Comparative Example 1 and Comparative Example 2. In Comparative Example 2, the capacity retention ratio was evaluated to be higher than that in Comparative Example 1. [ Layered structure is further stabilized by the change of plastic profile and cycle life is improved.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. As will be understood by those skilled in the art. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (10)

Secondary particles in which lithium metal oxide primary particles are aggregated,
The lithium metal oxide particles have a layered structure,
The powder resistance of the secondary particles is 80 to 300 ohm-cm,
A cathode active material for a lithium secondary battery having a grain size of 50 nm or less.
The method according to claim 1,
Wherein the secondary particles are in a hollow form.
The method according to claim 1,
Wherein the compound has a Ni ^{2 +} content of 2.5% or less as measured by Rietveld.
The method according to claim 1,
Wherein the secondary particles are represented by the following Formula 1:
[Chemical Formula 1]
Li _? [(Ni _x Co _y Mn _z ) _{1 -?} A _? ] O ₂
In Formula 1,
0.98??? 1.02, 0.001??? 0.015, 0.80? X? 0.85, and 0.09? Y? 0.12, 0.06? Z? 0.08,
A is at least one selected from Zr, Ti, Al, and Mg.
The method according to claim 1,
Wherein the c / a axis ratio of the positive electrode active material is 4.9415 to 4.9420.
Preparing a precursor comprising Ni, Co, and Mn; And
At least one doping raw material selected from Zr, Ti, Al, and Mg is added to the precursor; And a step of dry-mixing and firing the lithium raw material,
At least one doping raw material selected from Zr, Ti, Al, and Mg is added to the precursor; And calcining the lithium raw material after dry mixing,
The firing temperature includes a temperature rising section, a holding section, and a cooling section,
Wherein a temperature range of the first sustain period is 710-750 占 폚 and a final sustain period temperature range is 770-790 占 폚. The method of manufacturing a cathode active material for a lithium secondary battery according to claim 1,
The method according to claim 6,
At least one doping raw material selected from Zr, Ti, Al, and Mg is added to the precursor; And calcining the lithium raw material after dry mixing,
Wherein the total firing time is 10 to 50 hours.
The method according to claim 6,
Wherein the maintaining period is performed for 15-20 hours.
The method according to claim 6,
Wherein the final temperature of the heating section is 730-740 ° C and the final temperature of the holding section is 770-780 ° C.
A cathode comprising the cathode active material according to any one of claims 1 to 5;
A negative electrode comprising a negative electrode active material; And
An electrolyte positioned between the anode and the cathode;
≪ / RTI >

Images