KR101506680B1 - Cathode active material for lithium secondary battery and manufacturing method of the same - Google Patents

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery and a method for producing the same, which comprises preparing a coprecipitation compound by mixing an aqueous metal solution containing nickel and manganese and a basic aqueous solution, drying the coprecipitation compound to prepare an active material precursor, A method for producing a cathode active material for a lithium secondary battery, which comprises laminating an active material precursor and a lithium salt to produce a lithium composite metal oxide of Formula 1, wherein the lithium composite metal oxide has a layered structure.
[Chemical Formula 1]
Li [Ni _1-y Mn _y ] O ₂
In Formula 1, 0.05? Y? 0.55.

Description

Technical Field [0001] The present invention relates to a cathode active material for a lithium secondary battery, and a cathode active material for a lithium secondary battery,

The present invention relates to a cathode active material for a lithium secondary battery and a method of manufacturing the same. More particularly, the present invention relates to a cathode active material for a lithium secondary battery comprising a nickel-manganese system not containing cobalt and a method for producing the same.

Recently, since the lithium-ion secondary battery appeared in 1991, it has been widely used as a power source 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.

LiCoO2 is mainly used as a positive electrode active material in a small-sized lithium ion secondary battery currently available on the market. LiCoO2 is a superior material with stable charge and discharge characteristics, excellent electron conductivity, high stability and flat discharge voltage characteristics, but Co is required to develop other cathode material because it has low storage capacity, high cost and toxicity to human body.

The material with the layered crystal structure most favored as a substitute for LiCoO2 is Li [Ni0.5Mn0.5] O2 and Li [Ni0.5Mn0.5] O2 mixed with nickel-manganese and nickel-cobalt-manganese 1: 1 or 1: And a lithium composite metal oxide such as [Ni1 / 3Co1 / 3Mn1 / 3] O2. 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.

An oxide of a layered structure is used as a high capacity anode material for a lithium ion battery is a lithium cobalt oxide (LCO; LiCoO ₂₎ and a ternary composite oxide _{(NMC; Li [Ni x Mn} y Co z] O 2) , etc. have been developed in use have. These oxides are commonly characterized as containing cobalt.

Cobalt (Co) used for a layered structure cathode material for a lithium ion battery has a small amount and a high cost, and has a problem of toxicity to the human body and environmental pollution. The present invention solves the above problems by developing a high-capacity cathode material composed only of nickel (Ni) and manganese (Mn) without adding cobalt.

In order to solve the above problems, the present invention provides a method for producing a cathode active material for a lithium secondary battery containing no cobalt.

In one or more embodiments of the present invention, there is provided a process for preparing a coprecipitation compound by mixing a metal aqueous solution containing nickel and manganese, and a basic aqueous solution; Drying the coprecipitated compound to prepare an active material precursor; And mixing the lithium salt with the active material precursor to form a lithium composite metal oxide of Formula 1, wherein the lithium composite metal oxide has a layered structure.

[Chemical Formula 1]

Li [Ni _1-y Mn _y ] O ₂

In Formula 1, 0.05? Y? 0.55.

The calcination temperature may be 700-1000 ° C, and the co-precipitation compound may be dried at 100-200 ° C.

The basic aqueous solution is characterized by being at least one aqueous solution selected from NaOH and KOH.

Wherein y is in the range of 0.05 to less than 0.15, the calcination temperature is 700 to 800 ° C, the cation mixing degree of Ni ²⁺ in the Li layer in the cathode active material structure is 2.8 to 3.1%, y is 0.15 Or more and less than 0.25, the calcination temperature is 730 to 830 ° C, and the degree of cation mixing of Ni ²⁺ in the Li layer in the active material structure may be 5.0 to 5.3%.

When y is in the range of 0.25 or more and less than 0.35, the baking temperature is 800 to 900 ° C, and the cation mixing degree of Ni ²⁺ in the Li layer in the active material structure may be 5.5 to 5.9% When the ratio is 0.35 or more and less than 0.45, the firing temperature is 800 to 900 ° C, and the degree of cation mixing of Ni ²⁺ in the Li layer in the active material structure may be 6.4 to 6.8%.

When y is in the range of 0.45 or more and less than 0.55, the calcination temperature is 900 to 1000 ° C, and the degree of cation mixing of Ni ²⁺ in the Li layer in the active material structure may be 7.2 to 7.5%.

In one or more embodiments of the present invention, a cathode active material for a lithium secondary battery manufactured by any one of the above methods may be provided.

According to the embodiments of the present invention, a low-cost, environmentally friendly, high-capacity cathode material for a lithium secondary battery can be manufactured.

1 to 5 are graphs showing lifetime characteristics of a cathode active material manufactured according to an embodiment of the present invention.
6 to 8 are graphs showing a discharge capacity, a capacity retention rate, and a cation mixing ratio of a cathode active material manufactured according to an embodiment of the present invention.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described in detail below. 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.

The structural instability of the Ni-based cathode active material can be overcome to some extent by adding a dissimilar metal (Co, Mn). In the examples according to the present invention, the lithium-metal composite oxide having a Li [Ni1-yMny] O2 composition without addition of Co element, which has a small amount and is expensive, toxic and has a problem of environmental pollution, In order to improve the stability, the range of y was limited to 0.05 to 0.55. More specifically, the ratio of Ni to Mn was 9: 1, 8: 2, 7: 3, 6: 4, and 5: 5. In addition, discharge capacity and lifetime characteristics were improved by the degree of cation mixing in Li + and Ni2 + cathode active material structures. The cation means Li ⁺ and Ni ²⁺ in the examples according to the present invention.

Hereinafter, a method of manufacturing a cathode active material for a lithium secondary battery according to an embodiment of the present invention will be described in detail.

First, in the embodiment of the present invention, a coprecipitation compound is prepared by mixing an aqueous metal solution including nickel and manganese and a basic aqueous solution for a coprecipitation reaction. The coprecipitation reaction means, for example, a reaction in which a nickel salt or a manganese salt is dissolved in distilled water, and then an aqueous ammonia solution as a chelating agent, a NaOH aqueous solution or a KOH aqueous solution as a basic aqueous solution is added to the reactor to cause precipitation. That is, the coprecipitation reaction is a reaction in which two or more elements are simultaneously precipitated in an aqueous solution using a neutralization reaction to obtain a complex hydroxide.

The coprecipitated compound is dried to prepare an active material precursor, and the active material precursor and the lithium salt are mixed and calcined to prepare a lithium composite metal oxide represented by the following formula (1).

 [Chemical Formula 1]

Li [Ni _1-y Mn _y ] O ₂

In Formula 1, 0.05? Y? 0.55.

When the value of y is less than 0.05, the battery capacity decreases. When the value of y exceeds 0.55, the safety of the battery is deteriorated. Therefore, the y value in the embodiment of the present invention is limited to the above range.

The lithium composite metal oxide has a layered structure. That is, in the embodiment of the present invention, the cathode active material is a layered lithium composite oxide. The lithium composite oxide includes a layered structure in which oxygen ions, metal ions including nickel and manganese, . During the preparation of the lithium composite oxide, Ni ions having a size similar to that of Li ions are mixed with the positions of Li ions. When such incorporation occurs, the structural stability and thermal stability of the lithium composite oxide deteriorate, so that the lifetime characteristics and the charge / discharge characteristics of the battery are greatly reduced when used as the cathode active material of the lithium secondary battery. Therefore, It is possible to reduce the mixing ratio and thereby improve the charging / discharging characteristics and the structural stability.

In the embodiment according to the present invention, the temperature in the baking step is limited to 700 to 1000 ° C, and the baking atmosphere is preferably an oxidizing atmosphere of air or oxygen, and drying of the coprecipitation compound is performed in the range of 100 to 200 ° C do.

The coprecipitated compound obtained in the above step is dried or heat treated to prepare a precursor of a cathode active material. If the precursor is dried only, the precursor of the active material maintains a complex hydroxide form, and when it is heat treated, it is converted into a complex oxide form. The heat treatment is performed at 400 to 550 ° C, and the precursor is formed into a transition metal complex oxide type precursor through the heat treatment.

In the embodiment of the present invention, when the y value is 0.05 or more and less than 0.15, the calcination temperature is in the range of 700 to 800 ° C. , The degree of cationic mixing of Ni ²⁺ in the Li layer in the active material structure is limited to 2.8 to 3.1%, and when the y value is 0.15 or more and less than 0.25, the calcination is performed in the range of 730 to 830 ° C, limiting the amount of Ni ²⁺ cations mixed on the Li layer by 5.0 ~ 5.3%, and the y value of Ni in the Li layer in the active material structure subjected to baking in a range of 800 ~ 900 ℃ when more than 0.25 less than 0.35 ^{second + Is} limited to 5.5 to 5.9%, and when the y value is 0.35 or more and less than 0.45, calcination is performed in the range of 900 to 1000 ° C, and the degree of mixing of the cation of Ni ²⁺ in the Li layer in the active material structure is 6.4 to 6.8%.

When y is in the range of 0.45 or more and less than 0.55, the calcination temperature is 900 to 1000 ° C, and the degree of cation mixing of Ni ²⁺ in the Li layer in the active material structure is limited to 7.2 to 7.5%.

In the firing process for producing the cathode active material having the composition of the formula LiNi _1-y Mn _y O ₂ , the firing temperature increases as the value of y increases to form a well-developed layered structure. A battery using a cathode active material having a poorly developed structure is required to be fired at an appropriate temperature since its discharge capacity and life characteristics are deteriorated. However, as the firing temperature increases, the amount of cation mixing, which causes the Ni ²⁺ ions to enter the Li layer, increases, which results in degradation of the electrochemical properties. Therefore, in order to produce a cathode active material having excellent electrochemical characteristics such as discharge capacity and lifetime characteristics, it is necessary to develop a layered structure through a proper firing temperature in an embodiment according to the present invention, It needs to be limited.

In addition, a sintering additive may be added when the active material precursor and the lithium salt are mixed. When the sintering additive is added, the sintering temperature can be lowered.

Hereinafter, embodiments of the present invention will be described in more detail.

 [Example 1]

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 >

An aqueous metal solution in which the molar ratio of nickel sulfate and manganese sulfate was mixed at a ratio of 9: 1 and an ammonia solution were continuously introduced into the reactor. The pH was adjusted by feeding sodium hydroxide solution for pH adjustment.

The impeller speed was controlled to 1000 rpm and the average residence time of the solution in the reactor was adjusted to about 6 hours by adjusting the flow rate so that the reaction could be continuously obtained after the reaction reached a steady state. The metal complex hydroxide was filtered, washed with water, and dried in a 110 占 폚 hot air dryer for 15 hours.

After mixing with the metal complex hydroxide and the lithium salt, the mixture was calcined at a temperature of 730 캜 for 15 hours to obtain a cathode active material (Li [Ni _1-y Mn _y ] O ₂ ) powder.

[Example 1-1]

A cathode active material powder was prepared in the same manner as in Example 1, except that the calcination temperature was changed to 750 ° C in Example 1.

[Example 1-2]

A cathode active material powder was prepared in the same manner as in Example 1, except that the calcination temperature was changed to 780 캜 in Example 1.

[Example 2]

(Li [Ni _1-y Mn _y ] O ₂ ) was prepared in the same manner as in Example 1, except that the molar ratio of nickel sulfate and manganese sulfate was 8: 2.

[Example 2-1]

A cathode active material powder was prepared in the same manner as in Example 2, except that the calcination temperature was changed to 780 캜 in Example 2.

[Example 2-2]

A cathode active material powder was prepared in the same manner as in Example 2, except that the calcination temperature was changed to 810 캜 in Example 2.

[Example 3]

(Li [Ni _1-y Mn _y ] O ₂ ) was prepared in the same manner as in Example 1, except that the molar ratio of nickel sulfate and manganese sulfate was 7: 3.

[Example 3-1]

A cathode active material powder was prepared in the same manner as in Example 3, except that the calcination temperature was changed to 850 캜 in Example 3.

[Example 3-2]

The cathode active material powder was prepared in the same manner as in Example 3, except that the calcination temperature was changed to 870 캜 in Example 3.

[Example 4]

(Li [Ni _1-y Mn _y ] O ₂ ) was prepared in the same manner as in Example 1, except that the molar ratio of nickel sulfate and manganese sulfate was 6: 4.

[Example 4-1]

The cathode active material powder was prepared in the same manner as in Example 4, except that the calcination temperature was changed to 870 캜 in Example 4.

[Example 4-2]

A cathode active material powder was prepared in the same manner as in Example 4, except that the calcination temperature was changed to 900 ° C in Example 4.

[Example 5]

(Li [Ni _1-y Mn _y ] O ₂ ) was prepared in the same manner as in Example 1, except that the molar ratio of nickel sulfate and manganese sulfate was 5: 5.

[Example 5-1]

A cathode active material powder was prepared in the same manner as in Example 5, except that the calcination temperature was changed to 950 캜 in Example 3.

 [Example 5-2]

A cathode active material powder was prepared in the same manner as in Example 5, except that the calcination temperature was changed to 980 캜 in Example 3.

[Experimental Example 1]

Super-P as a cathode active material and conductive material prepared in Examples 1 to 5-2, and polyvinylidene fluoride (PVdF) as a binder were mixed at a weight ratio of 85: 7.5: 7.5, respectively, to prepare a slurry. The slurry was uniformly applied to an aluminum foil having a thickness of 20 占 퐉, and vacuum dried at 120 占 폚 to prepare a positive electrode.

Using the prepared positive electrode and lithium foil as counter electrodes, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) was used as a separator, and a solvent mixture of ethylmethyl carbonate in a volume ratio of 3: 3 A coin cell was manufactured according to a conventional manufacturing process using a liquid electrolyte in which LiPF6 was dissolved at a concentration of 1.2M. The electrochemical characteristics of the semi-coin battery thus prepared were measured.

1 to 5 are graphs showing lifetime characteristics of a cathode active material manufactured according to an embodiment of the present invention. Referring to FIG. 1, lifetime characteristics are somewhat improved in Examples 1-1 and 1-2, In Example 1, the best life characteristic was shown. This is also true in Figs. That is, when the ratio of nickel to manganese, that is, the y value is 0.1, the firing temperature is the best at 730 ° C., and when the y value is 0.2, the firing temperature is 750 ° C. and the y value is 0.3 When the firing temperature is 820 占 폚 and the y value is 0.4, the firing temperature is 850 占 폚, and when the y-value is 0.5, the firing temperature is the most excellent at 920 占 폚.

6 to 8 are graphs showing a discharge capacity, a capacity retention rate, and a cation mixing ratio of a cathode active material manufactured according to an embodiment of the present invention. Referring to FIG. 6, the primary discharge capacity in the embodiment of the present invention is The capacity retention ratio in the 100th cycle was mostly around 90%, and the capacity retention ratios in Examples 1, 2, 3, 4, and 5 were different from those in other examples (for example, , Examples 1-1, 1-2, 2-1, 2-2, etc.).

In addition, referring to FIG. 8, as the content of manganese increases, that is, the y value increases, the incorporation ratio of nickel ions in the lithium layer increases gradually. As described above, it is desirable to keep the mixing ratio of the positive and negative ions low, because it deteriorates battery life and charge / discharge characteristics. In FIG. 8, it can be seen that the cases of Examples 1, 2, 3, 4, and 5 showed a slightly lower cation mixing ratio than those of the other Examples.

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 .

Claims (10)

Preparing a coprecipitation compound by mixing an aqueous metal solution containing nickel and manganese and a basic aqueous solution;
Drying the coprecipitated compound to prepare an active material precursor;
And mixing the lithium salt with the active material precursor to form a lithium composite metal oxide of Formula 1,
Wherein the lithium composite metal oxide has a layered structure.
[Chemical Formula 1]
Li [Ni _1-y Mn _y ] O ₂
In the formula (1), 0.05? Y <0.45,
If y is in the range of 0.05 to less than 0.15, the firing temperature is 700 to 800 ° C, and the cation mixing degree of Ni ²⁺ in the Li layer in the cathode active material structure is 2.8 to 3.1%
When y is in the range of 0.15 or more and less than 0.25, the calcination temperature is 730 to 830 ° C, the cation mixing degree of Ni ²⁺ in the Li layer in the active material structure is 5.0 to 5.3%
When y is in the range of 0.25 or more and less than 0.35, the firing temperature is 800 to 900 DEG C, the cation mixing degree of Ni ²⁺ in the Li layer in the active material structure is 5.5 to 5.9%
Wherein the calcining temperature is 800 to 900 DEG C and the degree of cation mixing of Ni2 ⁺ in the Li layer in the active material structure is 6.4 to 6.8% when y is in the range of 0.35 to less than 0.45. A method for manufacturing a cathode active material for a battery. delete The method according to claim 1,
Wherein the step of drying the coprecipitation compound is performed at a temperature of 100 to 200 ° C. The method according to claim 1,
Wherein the basic aqueous solution is at least one aqueous solution selected from NaOH and KOH. delete delete delete delete delete A cathode active material for a lithium secondary battery, which is produced by the method of any one of claims 1, 3, and 4.

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