KR20080096093A - LB (NVCOM) O2 based positive electrode active material for lithium secondary battery and method of manufacturing same - Google Patents

Abstract

The present invention provides a method for producing a Li [NiCoMn] O ₂ based positive electrode active material for a lithium secondary battery, wherein Li ₂ CO ₃ , MnCO ₃ , NiO, and Co ₃ O ₄ are weighed as a starting material of the positive electrode active material for a lithium secondary battery. And mixing NaCl grinding aid with the weighed starting material to pulverize the powder, heat treating the pulverized powder and removing the NaCl grinding aid from the heat-treated powder. According to the manufacturing method of the present invention, it is possible to shorten the heat treatment process and time, thereby reducing the manufacturing cost. In addition, a cathode active material having a uniform composition ratio in the final powder can be obtained.

Lithium secondary battery, positive electrode active material, solid state synthesis method, NaCl, grinding aid

Description

Active cathode material Li (NiCoMn) O2 for lithium ion secondary battery and method for preparing the same}

1 is a view showing a synthesis process of the positive electrode active material according to the first embodiment of the present invention.

FIG. 2 is a diagram showing an XRD (X-Ray Diffraction) analysis result of the cathode active material powder prepared according to the first embodiment of the present invention.

Figure 3a is a view showing the particle size shape results of the positive electrode active material powder prepared according to the first embodiment of the present invention.

Figure 3b is a view showing the particle size distribution results of the positive electrode active material powder prepared according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a component mapping result of the cathode active material powder prepared according to the first embodiment of the present invention. FIG. 4A is a component mapping result of the powder using acetone, and FIG. 4B is a mapping result of the powder using NaCl. The figure shown.

5 is a view showing a synthesis process of a positive electrode active material according to a second embodiment of the present invention.

6 is a view showing the results of XRD analysis of the positive electrode active material powder prepared according to the second embodiment of the present invention.

7 is a view showing the particle size shape and particle size distribution results of the positive electrode active material powder prepared according to the second embodiment of the present invention.

8 is a view showing the SEM-EDX analysis results of the positive electrode active material powder prepared according to the second embodiment of the present invention.

The present invention relates to a method for producing a cathode active material for a lithium secondary battery and a cathode active material produced thereby, and more particularly to a method for producing a cathode active material for a lithium secondary battery using a solid phase synthesis method and a cathode active material produced thereby.

A battery generates electric power by using a material capable of chemical reaction of a cell at a positive electrode and a negative electrode. Factors that determine the battery's performance, safety and reliability, such as battery capacity, lifespan, and power, are the electrochemical properties and thermal stability of active materials that participate in the electrochemical reactions of the positive and negative electrodes.

Among the battery active materials currently used, lithium has a large electric capacity per unit mass and a high electronegativity, thereby providing a battery having a high voltage. However, since lithium metal itself has a problem of securing stability, batteries that use intercalation and deintercalation of lithium metal or lithium ions as active materials for batteries have been actively studied. A typical example of such a battery is a lithium secondary battery that generates electrical energy by oxidation and reduction when lithium ions are intercalated / deintercalated at a cathode and an anode. Lithium secondary batteries are manufactured by using a material capable of reversible intercalation / deintercalation of lithium ions as an active material of a positive electrode and a negative electrode, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.

LiCoO ₂ was used as a cathode active material of a lithium secondary battery. However, LiCoO ₂ required development of a substitute material due to a high price and environmental hazards due to a limited amount of Co. As an alternate material of LiCoO ₂ LiNiO ₂ and the like is _{LiMn 2 O 4, LiNi 0 .5} Co 0 .5 O 2, Li [NiCoMn] O 2. LiCoO ₂ and LiNiO ₂ have an explosion risk due to the generation of oxygen when overcharged, and a vent cap is required for the battery, and LiMn ₂ O ₄ has no oxygen generation when overcharged and is relatively relatively to Co. Although the price of Mn, which is abundant element, is inexpensive, there is a disadvantage in that the charge capacity is low and the discharge capacity decreases rapidly as the charge / discharge cycle is repeated.

Li [NiCoMn] O ₂ is currently the most popular material due to its high capacity and high thermal stability, but due to the difficulty of the synthesis process such as composition ratio control, much research is still required for industrialization.

On the other hand, the synthesis method of the positive electrode active material for lithium secondary batteries includes a coprecipitation method, a sol-gel method, a solid phase synthesis method, a thermal spray method, a combustion method and the like.

The coprecipitation method is to precipitate the composite metal component solution in the reactor at the same time. According to the characteristics of the raw metal to be used, the pH is controlled by using a coprecipitation agent such as NH ₄ OH, and the precipitate is formed. It is a method of producing a secondary spherical powder of the aggregated form by causing collisions between particles. However, when control of the amount of coprecipitation and the control of the reaction environment is uncertain, a non-uniform coprecipitation may result in a powder of a mixture rather than a compound form, which causes an unsuitable problem as a positive electrode material, making it difficult to mass-produce.

The sol-gel method is a synthesis method using hydrolysis and liquefaction using metal-alkoxides. The powder synthesized by this method has a finer particle, a larger surface area, a uniform particle size distribution, and a uniform composition of the ions of the raw material compared to the powder synthesized by the solid phase reaction to be described below. There is no need for repeated sintering and pulverization and it can be synthesized at low temperature. In general, however, metal nitrate is used as a starting material, and LiNO ₃ and Mn (NO ₃ ) ₂ · 6H ₂ O react well by absorbing moisture in the air, which requires drying before weighing. It is important to control the presence of metal ions. In addition, since the decomposition reaction of the organic matter remaining in the powder occurs rapidly during the drying process of more than 100 ℃ because the powder is scattered in the reactor, the yield is low, there is a problem that industrial applications, such as contamination of the reactor.

Compared to the above synthesis methods, which are difficult to commercialize due to complicated processes, the solid phase synthesis method is a general method of synthesizing LiCoO ₂ material. There is an advantage to mass production. However, since the raw material powder in the solid state is mechanically mixed, there is a limitation in uniform mixing, and there is a problem in that the uniformity of the composition and particle size of the final powder is low.

The present invention aims at controlling the composition ratio of the positive electrode active material powder, making the particle size uniform, and miniaturizing the particle size, in order to solve the problems of the solid phase synthesis method as described above.

The present invention provides a method for producing a Li [NiCoMn] O ₂ based positive electrode active material for a lithium secondary battery, wherein Li ₂ CO ₃ , MnCO ₃ , NiO, and Co ₃ O ₄ are weighed as a starting material of the positive electrode active material for a lithium secondary battery. And mixing NaCl grinding aid with the weighed starting material to pulverize the powder, heat treating the pulverized powder and removing the NaCl grinding aid from the heat-treated powder.

In addition, the stoichiometric ratio is preferably Li ₂ CO ₃ : MnCO ₃ : NiO: Co ₃ O ₄ = 1: 1/3: 1/3: 1/3.

In addition, the mixing ratio of the weighed starting material and the NaCl grinding aid is preferably in the range of 1: 2 to 1: 4 by mass ratio.

In addition, the heat treatment may be performed by heat treating the pulverized powder sequentially for 1 hour at 650 ° C. for 10 hours at 950 ° C.

In addition, the step of removing the NaCl grinding aid is preferably performed by washing with ultrapure water.

Moreover, it is preferable to dry at 100 degreeC for 12 hours after wash | cleaning with the said ultrapure water.

In addition, before the heat treatment step, it is preferable to further include the step of pre-heat treatment and the step of grinding the pre-heat-treated powder.

In addition, it is preferable to provide a Li [NiCoMn] O ₂ based positive electrode active material for a lithium secondary battery manufactured according to the above method.

The present invention is a method of manufacturing a positive electrode active material of a lithium secondary battery using a solid-state synthesis method, and among them, to control the composition ratio, particle size and the like, Li [NiCoMn] O ₂ based positive electrode active material by adding NaCl as a grinding aid during the grinding process To prepare.

As starting materials for the positive electrode active material, Li ₂ CO ₃ , MnCO ₃ , NiO, and Co ₃ O ₄ are weighed in stoichiometric ratios. Preferably, the stoichiometric ratio of Li ₂ CO ₃ , MnCO ₃ , NiO, and Co ₃ O ₄ is 1: 1/3: 1/3: 1/3 in order. Mix the NaCl grinding aid into the weighed starting material. Preferably, the weighed starting material and NaCl are mixed in the mass ratio in the range of 1: 2 to 1: 4. When the ratio of the weighed starting material and NaCl is less than 1: 2, the amount of NaCl is insufficient, and thus it is difficult to function as a grinding aid.In 1: 4 and above, a large amount of ultrapure water is required to clean the grinding aid later. As a result, the cleaning time is also long, which is inefficient in terms of productivity.

The mixed starting material and NaCl grinding aid are then ground to a powder. The ground powder is heat treated. Preferably, the heat treatment is performed at 650 ° C. for 1 hour and at 950 ° C. for 10 hours. In the heat-treated powder, Li [NiCoMn] O ₂ based positive electrode active material is prepared by drying at 100 ° C. for 12 hours using 3000 ml of ultrapure water to remove NaCl grinding aid.

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

(Example 1)

1 is a view showing a synthesis process of the positive electrode active material prepared by the solid phase synthesis method according to a first embodiment of the present invention. As shown in FIG. 1, Li ₂ CO ₃ , MnCO ₃ , NiO, and Co ₃ O ₄ were used as starting materials to synthesize a Li [NiCoMn] O ₂ material, which is a lithium secondary battery positive electrode active material. The starting material was weighed in a stoichiometric composition ratio (Li ₂ CO ₃ : 1 mol, MnCO ₃ : 1/3 mol, NiO: 1/3 mol, Co ₃ O _4: 1/3 mol), and no grinding aid was added. The process was carried out by dividing the process into a process using a predetermined amount of grinding aid.

The grinding aid used was NaCl, heptane (heptane), ultrapure water (DI-water), acetone, ethanol was used. Heptane, ultrapure water, acetone and ethanol among the grinding aids are representative grinding aids conventionally used as a control for comparison with the case of using NaCl of the present invention. The amount of grinding aid used was four times the total weighed starting material in the case of NaCl, 80 ml for other wet grinding aids, heptane, di-water, acetone, ethanol. The amount of was used. The weighed material was mixed and ground for a period of time using agate bowls. Then, in the case of powder using a wet grinding aid such as heptane, ultrapure water, acetone and ethanol, the powder was dried at 100 ° C. for 12 hours to remove the grinding aid. Then, dried powder (powder using wet grinding aid), powder using NaCl grinding aid, and powder without grinding aid were placed in an alumina crucible and sequentially heat treated at 650 ° C. for 1 hour and at 950 ° C. for 10 hours. , Final powder was obtained.

When NaCl grinding aid was used, NaCl was removed using a sufficient amount of ultrapure water (DI-Water) 3000ml after heat treatment, and the final powder was obtained after drying at 100 ° C for 24 hours.

In each case, XRD analysis was performed to confirm the crystal structure of the final powder obtained. The XRD analysis results of the final powder (anode active material powder) are compared and shown in FIG. 2. As a result, when the wet grinding aids heptane, ultrapure water, acetone and ethanol were used, the peak of NiMnO ₂ , which is an impurity phase, was observed as a whole.

These peaks of NiMnO ₂ are caused by the uneven distribution of Li raw materials in other particles. Since the solid phase reactions tend to occur on the surface of the powder, other mediums when the particles of the powder are large or unevenly mixed It is easy to produce a compound (NiMnO ₂₎ . To solve this problem, the particles of the powder must be finely ground.

However, in the case of the powder using the NaCl grinding aid, although it is the grinding by agate bowl as shown in FIG. 2, (102) / (006) peaks and (110) / (108) peaks, which are typically free of impurities, have a structure. Is clearly visible.

3A and 3B show SEM observations of particle size shapes and distribution results of the positive electrode active material powder prepared according to Example 1. FIG. The SEM results show the finest particle size and uniform particle size distribution in the powder using NaCl grinding aid.

According to Figure 3b, the average particle size of the powder without the grinding aid is about 8.4㎛, and as a wet grinding aid, about 6.2㎛ using heptane, about 5㎛ using ultrapure water, using acetone In the case of about 5.2 μm, and ethanol is about 5.8 μm, coarse particles having a particle size of 15 μm or more and nonuniform particle size distribution can be confirmed.

On the other hand, in the case of using the NaCl grinding aid according to the present invention shows a fine average particle of about 1㎛, the largest particle size can be confirmed a uniform particle size distribution within 5㎛.

Component mapping results of the positive electrode active material powder in which the composition ratio in the powder particles were confirmed through SEM-EDX are shown in FIGS. 4A and 3B and Tables 1 to 3 below. Figure 4a is a result of the component mapping of the powder using acetone as a grinding aid, it can be seen that the components are unevenly distributed. Particularly, the particles in the circle in FIG. 4A are assumed to be manganese oxide without nickel and cobalt components. On the other hand, Figure 4b as a result of the component mapping of the powder using NaCl as a grinding aid, it was confirmed that the proportion of the components are uniformly distributed as a whole. For reference, in this experiment, Li in the Li [NiCoMn] O ₂ based positive electrode active material had a small atomic weight, and thus was not detected on the EDX.

EDX result of powder without grinding aid ingredient weight% atom% O 31.43 62.16 Mn 24.77 14.27 Co 23.29 12.51 Ni 20.52 11.06 Total amount 100.00

EDX result of powder using acetone as grinding aid ingredient weight% atom% C 1.30 4.42 O 14.16 36.18 Mn 13.38 9.95 Co 39.35 27.30 Ni 31.81 22.15 Total amount 100.00

EDX result of powder using NaCl as grinding aid ingredient weight% atom% C 2.93 7.25 O 31.62 58.80 Na 0.00 0.00 Cl 0.15 0.13 Mn 22.10 11.97 Co 21.64 10.92 Ni 21.57 10.93 Total amount 100.00

Tables 1 to 3 show the EDX results of the powders according to the grinding aid. When comparing the atomic percentages of Ni, Co and Mn among the component elements, the initial (initial) weighing was performed between [NiCoMn] in the final powder of Li [NiCoMn] O ₂ based active material in the case of NaCl grinding aid according to the present invention. The stoichiometric composition ratio (Ni: Co: Mn = 1/3: 1/3: 1/3) is best maintained.

That is, the final powder (Li [NiCoMn] O ₂ based positive electrode active material) obtained by using a NaCl grinding aid has a uniform component ratio (first stoichiometric composition ratio, Ni: Co: Mn = 1/3: 1/3: 1/3) and no other impurity phase is formed. In addition, it can be seen that NaCl grinding aid was almost completely removed using ultrapure water. However, in the case of the powder not using the grinding aid and the powder using the acetone grinding aid, an impurity phase was formed to maintain the component ratio.

(Example 2)

In Example 1, it was determined that the reaction occurred on the surface of the powder during the solid phase reaction, so that the particles of the powder were mixed largely or unevenly. In order to solve this problem, in Example 2, the particles of the powder were ball milled (ball milling) was further finely ground, and the experiment was performed by increasing the heat treatment time during the heat treatment process.

5 is a view showing a synthesis process of the positive electrode active material prepared by the solid phase synthesis method according to a second embodiment of the present invention. As shown in FIG. 5, Li ₂ CO ₃ , MnCO ₃ , NiO, and Co ₃ O ₄ , which are the same as those of Example 1, were used to synthesize a Li [NiCoMn] O ₂ material, which is a lithium secondary battery cathode active material. 5 mm of zirconia after weighing the starting material with a constant stoichiometric composition ratio (Li ₂ CO ₃ : 1 mol, MnCO ₃ : 1/3 mol, NiO: 1/3 mol, Co ₃ O ₄ : 1/3 mol) Primary ball milling was performed for 10 hours using the ball. The experiment was performed by dividing the process using the NaCl grinding aid according to the present invention, as a control, a powder process without adding the grinding aid during ball milling, and a process using ethanol and ultrapure water on behalf of the wet grinding aid.

After the first ball milling, the first heat treatment was performed at 480 ° C. for 5 hours. The temperature increase rate was 4 degrees C / min. After the primary heat treatment, secondary ball milling was further performed for 10 hours with a 5 mm ball. Thereafter, secondary heat treatment was performed at 650 ° C. for 5 hours and at 950 ° C. for 10 hours. In the case of using the NaCl grinding aid after the second heat treatment, NaCl was removed using a certain amount of ultrapure water (same conditions as in Example 1) to obtain a final powder.

In order to observe the crystallinity of the obtained powder was measured using XRD, the measured results are shown in FIG. In the final powder of the process using the NaCl grinding aid, the (102) / (006) peak and the (110) / (108) peak were clearly seen as in Example 1. However, in the case of the process powder without using the grinding aid and the process powder using the wet grinding aid, impurity phases were observed around 44 ° and 64 °, which was judged to be NiMnO ₂ phase.

In order to confirm the particle shape and particle size distribution of the powder, the particle size of the powder without the grinding aid and the powder using the wet grinding aid showed no large distribution as in Example 1, but also in Example 2 It was confirmed in FIG. 7 that the powder without the grinding aid and the process powder with the wet grinding aid showed a wider particle size distribution and coarse particle size than the process powder with the NaCl grinding aid, and the plate-shaped particles were observed. Can be. Such coarse particles adversely affect the stability evaluation of the battery.

SEM-EDX measurement results of the prepared cathode active material powder are shown in FIG. 8. Referring to FIG. 8, in the case of the powder without using the grinding aid, the ratios of Ni, Mn, and Co did not maintain uniformity with each other, and it was confirmed that they had an irregular ratio. The balance was irregular. Although the ratio using ethanol as a grinding aid in the control group seems to be somewhat uniform on the graph, the EDX measurement (weight%) results of the powder shown in Table 5 below show that the proportions of Ni, Mn, and Co are not balanced. You can see that it is not.

On the other hand, as in the present invention, in the case of the powder using NaCl as a grinding aid, it can be seen that the ratio of Ni, Mn, Co is almost the same as in Example 1.

Hereinafter, the EDX measurement value of the total powder is shown in Tables 4-7.

EDX measured value of powder without grinding aid ingredient weight% C 2.2 O 15.8 Mn 22.9 Co 27.7 Ni 31.4 total 100.00

EDX measurement value of powder using ethanol grinding aid ingredient weight% C 1.22 O 35.98 Mn 21.91 Co 20.81 Ni 20.08 total 100.00

EDX measurement value of powder using ultrapure water grinding aid ingredient weight% C 0.01 O 34.78 Mn 27.29 Co 18.65 Ni 20.05 total 100.00

EDX measurement value of powder using NaCl grinding aid ingredient weight% C 3.92 O 34.28 Mn 20.40 Co 20.40 Ni 20.99 total 100.00

According to the above, when NaCl grinding aid was used (Table 7), the contents of Mn, Co, and Ni in the final powder were almost the same, and all of them satisfied the uniform composition ratio. However, the powder without the grinding aid (Table 4) and the powder using the wet grinding aid (Table 5, Table 6) are considered to have lost the mixed powder during the process, the powder loss when using the NaCl grinding aid It does not occur, and it is judged that even in the final powder, the composition ratio is uniform.

On the other hand, as can be seen from Examples 1 and 2, in the case of using NaCl as the grinding aid, it can be observed a fine particle size and uniform particle size distribution.

In the case of using a NaCl grinding aid, unlike Example 2, in Example 1, although the heat treatment process and the heat treatment time were shortened, the obtained Li [NiCoMn] O ₂ -based positive electrode active material was more than in the case of Example 2 Fine particle size and uniform particle size distribution could be observed.

Therefore, when using NaCl as a grinding aid, the heat treatment process (preliminary heat treatment step) and the heat treatment time can be shortened, thereby reducing the manufacturing cost. In addition, it was possible to obtain a positive electrode active material having a uniform composition ratio even in the final powder.

According to the present invention, when preparing a cathode active material for a lithium secondary battery using a solid phase synthesis method, using a NaCl grinding aid during the powder grinding step, it prevents the re-agglomeration of the pulverized powder, fine powder to smooth solid phase reaction This was done. In addition, the use of the NaCl grinding aid showed excellent properties not only in miniaturization and uniformity of particle size, but also in composition ratio control.

In addition, in the production of the positive electrode active material, by using the NaCl grinding aid that mixes the reactant and the grinding aid, the heat treatment process and time can be shortened, thereby reducing the manufacturing cost and commercializing it.

Claims (8)

In the method for producing a Li [NiCoMn] O ₂ based positive electrode active material for a lithium secondary battery, Weighing Li ₂ CO ₃ , MnCO ₃ , NiO and Co ₃ O ₄ as a starting material of the cathode active material for a lithium secondary battery in a stoichiometric ratio; Mixing NaCl grinding aid with the weighed starting material to grind to powder; Heat treating the pulverized powder; And Method of manufacturing a Li [NiCoMn] O ₂ based positive electrode active material for a lithium secondary battery comprising the step of removing the NaCl grinding aid in the heat-treated powder. The method of claim 1, wherein the stoichiometric ratio is Li ₂ CO ₃ : MnCO ₃ : NiO: Co ₃ O ₄ = 1: 1/3: 1/3: 1/3 Li [NiCoMn for lithium secondary battery, characterized in that ] O ₂ -based positive electrode active material manufacturing method. According to claim 1, wherein the mixing ratio of the weighed starting material and the NaCl grinding aid is a mass ratio of 1: 2 to 1: 4 of the lithium secondary battery Li [NiCoMn] O ₂ based positive electrode active material Manufacturing method. The Li [NiCoMn] O ₂ system for lithium secondary battery according to claim 1, wherein the heat treatment is performed by sequentially heat treating the pulverized powder at 650 ° C. for at least 1 hour and at 950 ° C. for 10 hours. Method for producing a positive electrode active material. The method of claim 1, further comprising removing said NaCl grinding aid is a lithium secondary battery, characterized in that is carried out by washing with ultra pure Li [NiCoMn] O process for producing a _2-based positive electrode active material. The method of manufacturing a Li [NiCoMn] O ₂ -based positive electrode active material for a lithium secondary battery according to claim 5, wherein the ultrapure water is washed and then dried at 100 ° C. for 12 hours. The method of manufacturing a lithium [NiCoMn] O ₂ based positive electrode active material for lithium secondary batteries according to claim 1, further comprising, before the heat treatment, preliminary heat treatment and pulverizing the preheated powder. . A Li [NiCoMn] O ₂ based positive electrode active material for a lithium secondary battery prepared according to any one of claims 1 to 7.

Images