KR20170076222A - Positive active material for rechargeable lithium battery, method of preparing the same, and rechargeable lithium battery including the same - Google Patents

Abstract

A method of manufacturing a cathode active material for a lithium secondary battery according to an embodiment of the present invention is to wash the cathode active material containing nickel with a wash water containing strong acid. In addition, the lithium secondary battery according to another embodiment of the present invention includes the cathode active material obtained according to the above-described method in the anode.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery, and a lithium secondary battery including the same. BACKGROUND ART [0002]

The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery and a lithium secondary battery comprising the same.

The positive electrode active material, which is one of the elements constituting the lithium secondary battery, has a structure capable of releasing / inserting lithium ions in general. Among them, the cathode active material having a high manganese content shows high stability and low capacity. However, in order to realize the above-mentioned high-output large-sized battery type, it is necessary to develop a cathode active material having excellent capacity and stability.

On the other hand, the higher the nickel content of the positive electrode active material, the higher the capacity thereof. However, it is pointed out that the stability is low as compared with the cathode active material having a high manganese content, and the electrochemical capacity is lowered due to repeated charge and discharge, so that the life characteristic is poor.

Specifically, in the case of the positive electrode active material containing nickel, the oxidation number of the nickel ion changes to Ni ^{4 +} after the lithium ion is removed from the Ni ²⁺ , and Ni ^{4 +} is unstable, .

Since oxygen is generated during such a chemical change, the stability is evaluated to be low, and the nickel oxide is stable and can not exhibit its electrochemical capacity. In addition, since such a phenomenon is intensified at a higher temperature than a normal temperature, there is a problem that the stability at a high temperature and the life characteristics are further deteriorated.

In this regard, various researches have been made to improve the lifetime characteristics while ensuring a high capacity of the lithium secondary battery, but a fundamental solution to the above-mentioned problems has not yet been proposed.

It is another object of the present invention to provide a method for producing a positive electrode active material for a lithium secondary battery improved in structural stability and electrochemical characteristics, and to provide a lithium secondary battery comprising the positive electrode active material thus prepared in a positive electrode.

In one embodiment of the present invention, there is provided a method of manufacturing a lithium secondary battery including: preparing a lithium composite oxide including Ni, Co, and Mn; And washing the lithium composite oxide with water,

Wherein the step of washing the lithium composite oxide is carried out using a wash liquid containing strong acid and a solvent.

A method for producing a positive electrode active material for a lithium secondary battery is provided.

The molar concentration of the strong acid in the washing liquid containing the strong acid and the solvent may be 0.001 to 0.05 M. [ The strong acid may be hydrochloric acid (HCl), nitric acid (HNO ₃ ), phosphoric acid (H ₃ PO ₄ ), or a mixture thereof.

The molar content of Ni in the lithium composite oxide to be water-treated may be 80 mol% or more.

More specifically, the step of washing the lithium composite oxide comprises: firstly washing the lithium composite oxide with a wash water containing the strong acid and a solvent; And secondly washing the primary washed lithium composite oxide with water.

The first step of washing the lithium composite oxide with a strong acid and a solvent includes supplying the lithium composite oxide to a washing liquid containing the strong acid and a solvent, And stirring to prepare a first slurry; And filtering the first slurry to obtain a primary washed lithium composite oxide.

The step of adding the lithium composite oxide to a washing solution containing the strong acid and a solvent and stirring to prepare a first slurry is carried out at a temperature ranging from 10 to 15 ° C for 10 seconds to 10 minutes ≪ / RTI >

At this time, the volume ratio of the lithium composite oxide to the wash liquid containing the strong acid and the solvent may be 2: 1 to 1: 2.

The second step of washing the first lithium-containing composite oxide with water may include the steps of: adding the primary lithium-lithium compound oxide to the water and stirring to prepare a second slurry; And filtering the second slurry to obtain a secondary washed lithium composite oxide.

The step of charging the primary washed lithium composite oxide into the water and stirring to prepare the second slurry can be performed at a temperature ranging from 10 to 15 캜 for 10 seconds to 30 minutes.

At this time, the volume ratio of the primary washed lithium composite oxide to the water may be 2: 1 to 1: 2.

The step of filtering the second slurry to obtain a secondary water-washed lithium composite oxide may be performed for 1 second to 10 minutes, whereby the moisture content in the secondary washed lithium composite oxide is 5 wt% ≪ / RTI >

Washing the lithium composite oxide with water; Thereafter, drying the washed lithium complex oxide may further include drying the washed lithium complex oxide.

The step of drying the washed lithium composite oxide may be performed at a temperature range of 80 to 160 캜 for 30 minutes to 4 hours.

Meanwhile, preparing the lithium composite oxide containing Ni, Co, and Mn may include preparing an active material precursor including Ni, Co, and Mn; And firing a mixture of the active material precursor and the lithium source material to obtain a lithium composite oxide.

The mixture of the active material precursor and the lithium source material may further include a doping source material, and the doping source material may be a compound containing at least one element selected from the group consisting of Zr, Ti, and Al, or a mixture of the above compounds.

According to another embodiment of the present invention, cathode; And an electrolyte disposed between the positive electrode and the negative electrode, wherein the positive electrode includes the positive electrode active material prepared by the above-described method.

It is another object of the present invention to provide a method for producing a positive electrode active material for a lithium secondary battery improved in structural stability and electrochemical characteristics, and to provide a lithium secondary battery comprising the positive electrode active material thus prepared in a positive electrode.

Figs. 1 to 4 are SEM photographs of the surfaces of the positive electrode active materials of Examples 2 to 3 and Comparative Examples 1 and 2, respectively.
FIGS. 5 and 6 are graphs showing the results of measurement of the battery voltage at 25 ° C at room temperature, 2.5 to 4.25 V cut-off, and CC / CV mode (CV current: 1 / 200C) for the batteries of Examples 1 to 3 and Comparative Examples 1 and 2 (FIG. 5) and 0.5 C lifetime characteristics (FIG. 6, 20 cycles) were recorded.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. 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. Like reference numerals refer to like elements throughout the specification.

Thus, in some embodiments, well-known techniques are not specifically described to avoid an undesirable interpretation of the present invention. Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. Whenever a component is referred to as "including" an element throughout the specification, it is to be understood that the element may include other elements, not the exclusion of any other element, unless the context clearly dictates otherwise. Also, singular forms include plural forms unless the context clearly dictates otherwise.

In one embodiment of the present invention, there is provided a method of manufacturing a lithium secondary battery including: preparing a lithium composite oxide including Ni, Co, and Mn; And washing the lithium composite oxide with water,

Wherein the step of washing the lithium composite oxide is carried out using a wash liquid containing strong acid and a solvent.

A method for producing a positive electrode active material for a lithium secondary battery is provided.

According to one embodiment of the present invention, the lithium remaining on the surface can be minimized by washing the positive electrode active material containing nickel with a washing solution containing strong acid.

In addition, the positive electrode active material subjected to water washing according to one embodiment of the present invention is applied to a positive electrode of a lithium secondary battery to suppress the generation of gas by residual lithium during charging and discharging of the battery to improve battery safety, And life characteristics can be improved.

Specifically, the lithium composite oxide containing Ni, Co, and Mn is prepared by mixing a precursor including Ni, Co, and Mn with a lithium raw material and then calcining, and lithium carbonate (Li ₂ CO ₃ ) and lithium hydroxide (LiOH) are inevitably present.

Such residual lithium inevitably exists on the surface of the lithium composite oxide unless the lithium composite oxide produced through the calcination process can be stored without being exposed to moisture in the atmosphere.

However, in a battery in which a lithium composite oxide in which residual lithium is present on the surface thereof is applied to a positive electrode as a positive electrode active material, generation of gas by residual lithium during charging and discharging causes generation of problems such as initial capacity decrease and initial charge- Lt; / RTI >

As a well-known method to solve this problem, there is a method of removing residual lithium by using water as a washing solution. However, lithium carbonate (Li ₂ CO ₃ ) has low solubility in water (1.54 g / 100 mL at 0 캜, 1.43 g / 100 mL at 10 캜, 1.29 g / 100 mL at 25 캜, 1.08 g / 100 mL, etc.) and the use of water as a washing solution.

Further, as the time for which the lithium composite oxide is washed with water (i.e., the time for which the lithium composite oxide is in contact with water) becomes longer, not only the lithium remaining on the surface but also the lithium present therein dissolves, . Lithium dissolving at this time is mainly lithium hydroxide (LiOH), which can be converted into lithium carbonate (Li ₂ CO ₃ ) form.

As a result, a battery in which a positive electrode active material washed with water is applied to a positive electrode may still cause problems such as an increase in resistance and a decrease in capacity.

The inventors of the present invention decided to remove lithium (particularly lithium carbonate (Li ₂ CO ₃ )) remaining on the surface of the lithium composite oxide for a short period of time by using a strong acid in recognition of the above problems.

 In fact, by using a washing liquid containing a solvent such as water and a strong acid, only the lithium remaining on the surface is effectively removed from the surface of the lithium composite oxide while minimizing the contact time of the lithium composite oxide with water, It was confirmed that the initial capacity, initial charging / discharging efficiency, lifetime characteristics and the like of the battery were improved. This is experimentally supported through examples, comparative examples, and evaluation examples to be described later.

Hereinafter, the washing liquid used in one embodiment of the present invention, the lithium composite oxide to be subjected to the water treatment using the same, and the characteristics of each step will be described in detail.

Specifically, when the lithium composite oxide is firstly washed with strong acid diluted with the solvent and then washed with water secondly, residual lithium can be removed more effectively. In the first washing step, lithium carbonate (Li ₂ CO ₃ ) is mainly removed by the strong acid diluted in the solvent, and lithium hydroxide (LiOH) is mainly removed by the water in the second washing step.

More specifically, in the first washing step, lithium carbonate (Li ₂ CO ₃ ) has a low solubility in water, but it can be converted into a substance having high solubility by reacting with strong acid, will be.

[Chemical reaction formula 1] Li ₂ CO ₃ + 2HCl → 2LiCl + CO ₂ + H ₂ O

[Chemical reaction formula 2] Li ₂ CO ₃ + HNO ₃ → LiNO ₃ + CO ₂ + H ₂ O

[Chemical reaction formula 2] 3Li ₂ CO ₃ + 2H ₃ PO ₄ → 2LiPO ₄ + 3CO ₂ + 3H ₂ O

In the chemical reaction formula 1 to 3, but illustrating a strong acid, hydrochloric acid (HCl), respectively, with nitric acid (HNO _3), and phosphoric acid (H ₃ PO _4), this kind of strong acid is not limited, as is generally known in p K _a <-1.74, or a mixture of two or more thereof. The p K _a <-1.74 is a representative example of the acid, hydrochloric acid (HCl), nitric acid (HNO _3), phosphoric acid (H ₃ PO ₄₎ or the like.

Such a strong acid may be diluted in a solvent to prepare a solution having a molar concentration of the strong acid in the range of 0.001 to 0.05 M, and this solution may be used as a wash liquid. When the molar concentration range is satisfied, the residual lithium on the surface of the lithium composite oxide can be effectively removed.

At this time, the type of the solvent is not limited, and water such as DI water, distilled water and the like can be used.

However, if the molar concentration of the diluted strong acid in the solvent exceeds 0.05 M, there is a problem that the lithium in the lithium composite oxide is removed or the surface thereof is damaged. If the molar concentration is less than 0.001 M, the effectiveness of using strong acid may be insignificant.

To the strong acid diluted in the solvent, the volume ratio of the lithium composite oxide is 2: 1 to 1: 2, and the mixture is stirred to induce lithium carbonate (Li ₂ CO ₃ ) removal reaction on the surface of the lithium composite oxide .

In this case, the time for removing the residual lithium from the surface of the lithium composite oxide by the strong acid diluted in the solvent is 10 seconds to 10 minutes. Compared with the case where the distilled water is washed with water as the wash liquid, Only the lithium remaining on the surface can be effectively removed while minimizing the contact time.

In order to expose to such short time moisture, the amount of washing liquid and washing time can be controlled according to the dilution concentration of strong acid. Also, when the lithium composite oxide is mixed so as to exceed 2: 1, it is in a paste form so that it is not completely immersed in the wash liquid, and uniform water washing may be difficult.

At this time, the temperature of the strong acid diluted in the solvent is kept as low as 10 to 15 ° C to remove lithium carbonate (Li ₂ CO ₃ ) from the surface of the lithium composite oxide at the surface of the lithium composite oxide, The reaction can be controlled slowly.

If the temperature is higher than 15 deg. C, the lithium composite oxide can be strongly affected by the solvent as well as the strong acid, and lithium in the lithium composite oxide can also be removed by the solvent. However, at an excessively low temperature of less than 10 deg. C, the reaction of removing residual lithium from the surface of the lithium composite oxide is excessively slowed and the time period affected by the solvent is increased. In this case, Lithium can also be removed.

As described above, lithium carbonate (Li ₂ CO ₃ ) removal reaction is performed on the surface of the lithium composite oxide by using a strong acid diluted in a solvent, and then filtered to obtain a lithium composite oxide washed first.

The lithium composite oxide washed firstly may be used as a cathode active material, but it can be used as a cathode active material by removing secondary lithium by further water washing with water.

Specifically, when the primary washed lithium composite oxide is charged into water and stirred, lithium hydroxide (LiOH) remaining on the surface of the primary washed lithium composite oxide can be removed. Of course, lithium carbonate (Li ₂ CO ₃ ) can also be removed at this time. However, as mentioned above, since lithium carbonate (Li ₂ CO ₃ ) has low solubility in water, it mainly has a greater effect of removing lithium hydroxide (LiOH) in the second washing step.

Specifically, in the second water washing step, the lithium composite oxide washed firstly is poured into the water and stirred to prepare a second slurry, which is then filtered to obtain a secondary washed lithium composite oxide .

The time for removing lithium hydroxide (LiOH) from the surface of the primary washed lithium composite oxide by controlling the temperature of the water at 10 to 15 ° C when the primary washed lithium composite oxide is put into the water, For 10 seconds to 30 minutes.

At this time, the volume ratio of the primary washed lithium composite oxide to the water may be 2: 1 to 1: 2.

In the step of filtering the second slurry, a vacuum flask or a filter press may be used. At this time, the pressure-reducing flask simply pulls moisture by suction from the lower part, but the filter press has an advantage of easily removing moisture in a short time by the principle of pushing water with a positive pressure from the upper part.

Specifically, by using the filter press, it is possible to recover a solid within 5% water content within a short time of 10 minutes or less from the second slurry.

Specifically, depending on the particle size in the second slurry, moisture is removed within 1 second to 5 minutes in the case of a large particle size in the range of 8 to 13 mu m and 1 second to 10 minutes in the case of small particle size ranging from 3 to 6 mu m, Can be lowered to less than 5%.

The lithium composite oxide is washed with water only after the first washing step or after the first washing step and after the second washing step so that the lithium composite oxide is washed with water, And drying the composite oxide.

The step of drying the washed lithium composite oxide may be performed by vacuum drying for 30 minutes to 4 hours at a temperature range of 80 to 160 ° C in order to reduce the air exposure time and to remove moisture.

However, since the water-repellent lithium composite oxide has a high moisture content, proton exchange may occur when the lithium composite oxide is dried in the temperature range immediately above, which may cause a capacity drop as a cathode active material. have.

Thus, there is an advantage of a step of filtering the second slurry before drying the washed lithium complex oxide in the temperature range,

On the other hand, the lithium composite oxide to be washed with water is not particularly limited, but the lithium complex oxide represented by the following general formula (1) can be used.

Li _x Ni _a Co _b Mn _c M _{d d} O ₂

In the above formula (1), M1 is Zr, Mg, Al, Ni, Mn, Zn, Fe, Cr, Mo or W, Me is represented by the following formula 2, 0.90? X? 1.07, 0.7? , 0 <b? 0.3, 0 <c? 0.3, 0 <d <0.01, and a + b + c + d = 1.

In this regard, preparing the lithium composite oxide containing Ni, Co, and Mn includes: preparing an active material precursor including Ni, Co, and Mn; And firing a mixture of the active material precursor and the lithium source material to obtain a lithium composite oxide.

The mixture of the active material precursor and the lithium source material may further include a doping source material, and the doping source material may be a compound containing at least one element selected from the group consisting of Zr, Ti, and Al, or a mixture of the above compounds.

The cathode active material prepared according to one embodiment of the present invention can be usefully used for the anode of a lithium secondary battery. The lithium secondary battery includes a cathode and an electrolyte including an anode active material together with a cathode.

The positive electrode is prepared by preparing a positive electrode active material composition by mixing a positive electrode active material according to an embodiment of the present invention, a conductive material, a binder and a solvent, and then directly coating and drying on the aluminum current collector. Or by casting the positive electrode active material composition on a separate support, then peeling the support from the support, and laminating the resulting film on an aluminum current collector.

The conductive material may be carbon black, graphite, metal powder, and the binder may include vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene And mixtures thereof. Further, N-methylpyrrolidone, acetone, tetrahydrofuran, decane and the like are used as the solvent. At this time, the content of the cathode active material, the conductive material, the binder and the solvent is used at a level normally used in a lithium secondary battery.

The negative electrode is prepared by mixing the negative electrode active material, the binder and the solvent in the same manner as the positive electrode. The anode active material composition is coated directly on the copper current collector or cast on a separate support, and the negative active material film, Laminated. At this time, the negative electrode active material composition may further contain a conductive material if necessary.

As the negative electrode active material, a material capable of intercalating / deintercalating lithium is used. For example, lithium metal, lithium alloy, coke, artificial graphite, natural graphite, organic polymeric compound combustion material, . The conductive material, the binder and the solvent are used in the same manner as in the case of the above-mentioned anode.

The separator may be polyethylene, polypropylene, polyvinylidene fluoride or a multilayer film of two or more thereof. The separator may be a polyethylene / polypropylene double-layer separator, It is needless to say that a mixed multilayer film such as a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator and the like can be used.

As the electrolyte to be charged into the lithium secondary battery, a non-aqueous electrolyte or a known solid electrolyte may be used, and a lithium salt dissolved therein may be used.

The solvent of the non-aqueous electrolyte is not particularly limited, but cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; Chain carbonates such as dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate; Esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and? -Butyrolactone; Ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane and 2-methyltetrahydrofuran; Nitriles such as acetonitrile; Amides such as dimethylformamide and the like can be used. These may be used singly or in combination. Particularly, a mixed solvent of cyclic carbonate and chain carbonate can be preferably used.

As the electrolyte, a gelated polymer electrolyte in which an electrolyte solution is impregnated with a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li ₃ N can be used.

Wherein the lithium salt is selected from the group consisting of LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiCl, and LiI.

Hereinafter, the embodiment will be described in detail. The following examples are illustrative of the present invention only and are not intended to limit the scope of the present invention.

Examples 1 to 2

(1) Preparation of cathode active material

The object to be washed used in Example 1 is Li (Ni _0.8 CO _0.1 Mn _0.1 ) O ₂ having a layered form.

Specifically, NiSO ₄ , CoSO ₄ , and MnSO ₄ are used as a metal raw material to prepare a metal solution having a concentration of 1 to 3 mol / L, and mixed at a molar ratio of NH ₄ OH / NH ₃ = And the mixture was gradually added to the metal solution and stirred to prepare a precursor. The solution containing the prepared precursor was filtered and solid / liquid separated, and the obtained solid material (i.e., precursor) was dried in an oven at 110 ° C for over 12 hours. The dried precursor was mixed with 0.95-1.1 mol LiOH and then calcined at 650 ° C to 950 ° C to obtain a cathode active material having a composition of Li (Ni _0.8 CO _0.1 Mn _0.1 ) O ₂ .

For the water washing process, hydrochloric acid (HCl), nitric acid (HNO ₃ ) and phosphoric acid (H ₃ PO ₄ ) were diluted with DI water, respectively, so that the molar concentration of acid in each solution became 0.01 M Respectively. In Example 1, nitric acid diluted with ultrapure water was used as a washing solution, and in Example 2, phosphoric acid diluted with ultrapure water was used as a washing solution.

The NCM cathode active material was added to each washing solution and stirred for 1 minute in an agitator maintained at a temperature of 10 to 15 캜 to prepare a primary slurry. At this time, the primary slurry of each example was prepared in a volume ratio of NCM cathode active material: wash liquid = 1: 1.

Thereafter, the primary slurry was filtered using a vacuum flask, and then washed with water twice.

Specifically, the cathode active material subjected to the first washing treatment was put into water and stirred for 1 minute in an agitator maintained at a temperature of around 10 캜 to prepare a secondary slurry. At this time, the secondary slurry of the example was prepared in a volume ratio of NCM cathode active material: water = 1: 1.

Thereafter, the secondary slurry was filtered using a filter press for about 10 minutes or more, and then the separated solid powder

Placed in a vacuum oven at 150 캜, and dried under vacuum conditions for 2 hours or more to obtain a cathode active material which was finally washed.

(2) Production of lithium secondary battery

For the evaluation of the battery chemistry, N (N, N'-diphenyl-N, N'-dicyclohexylcarbodiimide) was used in a weight ratio of 92.5: 3.5: 4 (cathode active material: binder: conductive material) -Methyl-2-pyrrolidone solvent to prepare a slurry.

This slurry was evenly applied to an aluminum foil, followed by compression in a roll press and vacuum drying in a 100 vacuum oven for 12 hours to prepare a positive electrode.

A 2032 half coin cell was prepared according to a conventional method using Li-metal as a counter electrode and 1 mol of LiPF ₆ solution as a liquid electrolyte in a mixed solvent of EC: EMC = 1: 2 as an electrolyte .

Comparative Example 1

NCM positive electrode active material was used as a positive electrode active material without being subjected to any washing treatment, and a coin battery was produced in the same manner as in Examples 1 to 3.

Comparative Example 2

The NCM cathode active material was rinsed with water only and used as a cathode active material, and a coin battery was produced in the same manner as in Examples 1 to 3. The water washing treatment using water was the same as that of the secondary washing treatment methods of Examples 1 to 3.

Evaluation example 1

Lithium remaining on the surfaces of the respective cathode active materials of Examples 1 to 2 and Comparative Examples 1 to 2 was measured.

Comparative Example 1 Comparative Example 2 Example 1 Example 2 LiOH residual amount 11,072 ppm 1,480 ppm 1,391 ppm 1,431 ppm Li ₂ CO ₃ residual amount 5,660 ppm 8,132 ppm 3,335 ppm 3,700 ppm Total residual lithium amount 16,732 ppm 9,612 ppm 4,726 ppm 5,131 ppm

As shown in Table 1, the total amount of residual lithium in the case of rinsing with water only (Comparative Example 2) was reduced compared with the case where no water was washed at all (Comparative Example 1), and the residual lithium in the form of lithium hydroxide (LiOH) , The residual lithium in the form of lithium carbonate (LiCO ₃ ) is rather increased. This is because, as described above, the residual lithium in the form of lithium hydroxide (LiOH) is converted into lithium carbonate (LiCO ₃ ) form by water.

In contrast, in the case of first washing with diluted strong acid followed by secondary washing with water (Examples 1 and 2), no washing at all (Comparative Example 1) but also with only water (Comparative Example 2) The total residual lithium amount is remarkably reduced. It is remarkable that both the lithium hydroxide (LiOH) form and the residual lithium amount in the lithium carbonate (LiCO ₃ ) form are remarkably reduced.

As a result, it can be seen that it is very effective to remove residual lithium in the form of lithium carbonate (LiCO ₃ ) by first washing with diluted strong acid, and then to secondly wash with water to remove residual lithium in the form of lithium hydroxide (LiOH) .

In addition, since the residual lithium levels in Examples 1 and 2 are similar, it can be seen that there is no difference according to the type of strong acid used in the first water washing.

On the other hand, the surface of each of the cathode active materials of Examples 2 to 3 and Comparative Examples 1 and 2 was observed with an SEM photograph (Figs. 1 to 4), but no apparent difference was found.

Evaluation example 2

The initial capacity (Fig. 5) of each cell of Examples 1 to 2 and Comparative Examples 1 to 2 was measured under conditions of room temperature at 25 캜, cut-off of 2.5 to 4.25 V and CV / CV mode (CV current: And 0.5 C lifetime characteristics (Fig. 6, 20 cycles).

In FIGS. 5 and 6, the initial discharge capacity of Comparative Example 1 was 198.4 mAh / g, the initial barrier efficiency was 86.0%, and the 0.5C capacity retention rate was 87.1%.

In addition, the initial discharge capacity of Comparative Example 2 was 202.8 mAh / g, the initial barrier efficiency was 87.7%, and the 0.5C capacity maintenance rate was 87.2%.

On the other hand, the initial discharge capacity of Example 1 (using nitric acid as a strong acid in the first wash) was 207.9 mAh / g, the initial bar source efficiency was 88.3%, and the 0.5C capacity retention rate was 99.5%.

In addition, the initial discharge capacity of Example 3 (phosphoric acid used as a strong acid in the first washing) was 206.1 mAh / g, the initial bath efficiency was 88.3%, and the 0.5C capacity maintenance rate was 99.5%.

This is because, by effectively removing residual lithium from Examples 1 and 2 in Comparative Example 2, it is possible to suppress the generation of gas by residual lithium during charging and discharging of the battery to improve battery safety and improve initial capacity and life characteristics This can be assessed by the effect of

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 (21)

Preparing a lithium composite oxide comprising Ni, Co, and Mn; And
And washing the lithium composite oxide with water,
Wherein the step of washing the lithium composite oxide is carried out using a wash liquid containing strong acid and a solvent.
(Method for producing positive electrode active material for lithium secondary battery).
The method according to claim 1,
The molar concentration of the strong acid in the washing liquid containing the strong acid and the solvent,
0.001 to 0.05 M,
(Method for producing positive electrode active material for lithium secondary battery).
The method according to claim 1,
The strong acid,
Hydrochloric acid (HCl), nitric acid (HNO _3), phosphoric acid (H ₃ PO _4), or in that a mixture thereof,
(Method for producing positive electrode active material for lithium secondary battery).
The method according to claim 1,
Washing the lithium composite oxide with water,
Firstly washing the lithium composite oxide with a wash water containing the strong acid and a solvent; And
And washing the primary washed lithium composite oxide with water for a second time.
(Method for producing positive electrode active material for lithium secondary battery).
5. The method of claim 4,
The first step of washing the lithium composite oxide with a washing solution containing the strong acid and the solvent,
Adding the lithium composite oxide to a washing solution containing the strong acid and a solvent, and stirring to prepare a first slurry; And
And filtering the first slurry to obtain a primary washed lithium composite oxide.
(Method for producing positive electrode active material for lithium secondary battery).
6. The method of claim 5,
Adding the lithium composite oxide to a washing solution containing the strong acid and a solvent and stirring the slurry to prepare a first slurry,
Lt; RTI ID = 0.0 &gt; 15 C &lt; / RTI &gt;
(Method for producing positive electrode active material for lithium secondary battery).
6. The method of claim 5,
Adding the lithium composite oxide to a washing solution containing the strong acid and a solvent and stirring the slurry to prepare a first slurry,
Lt; RTI ID = 0.0 &gt; 10 &lt; / RTI &gt;
(Method for producing positive electrode active material for lithium secondary battery).
6. The method of claim 5,
Adding the lithium composite oxide to a washing solution containing the strong acid and a solvent and stirring to prepare a first slurry,
Wherein the volume ratio of the lithium composite oxide to the wash liquid containing the strong acid and the solvent is 2: 1 to 1: 2.
(Method for producing positive electrode active material for lithium secondary battery).
5. The method of claim 4,
Secondly washing the primary washed lithium composite oxide with water,
Adding the first washed lithium composite oxide to the water and stirring to prepare a second slurry; And
And filtering the second slurry to obtain a secondary washed lithium composite oxide.
(Method for producing positive electrode active material for lithium secondary battery).
10. The method of claim 9,
Adding the first washed lithium composite oxide to the water and stirring to prepare a second slurry,
Lt; RTI ID = 0.0 &gt; 15 C &lt; / RTI &gt;
(Method for producing positive electrode active material for lithium secondary battery).
10. The method of claim 9,
Adding the first washed lithium composite oxide to the water and stirring to prepare a second slurry,
Lt; RTI ID = 0.0 &gt; 10 &lt; / RTI &gt;
(Method for producing positive electrode active material for lithium secondary battery).
10. The method of claim 9,
Adding the water-washed lithium composite oxide to the water and stirring to prepare a second slurry,
Wherein the volume ratio of the primary washed lithium composite oxide to the water is from 2: 1 to 1: 2.
(Method for producing positive electrode active material for lithium secondary battery).
10. The method of claim 9,
Filtering the second slurry to obtain a secondary washed lithium composite oxide,
Lt; RTI ID = 0.0 &gt; 1 &lt; / RTI &gt;
(Method for producing positive electrode active material for lithium secondary battery).
10. The method of claim 9,
And filtering the second slurry to obtain a secondary washed lithium composite oxide,
Wherein the second water-washed lithium composite oxide has a water content of less than 5 wt%
(Method for producing positive electrode active material for lithium secondary battery).
The method according to claim 1,
Washing the lithium composite oxide with water; Since the,
And drying the washed lithium composite oxide.
(Method for producing positive electrode active material for lithium secondary battery).
16. The method of claim 15,
Drying the washed lithium composite oxide,
Lt; RTI ID = 0.0 &gt; 80-160 C. &lt; / RTI &gt;
(Method for producing positive electrode active material for lithium secondary battery).
16. The method of claim 15,
Drying the washed lithium composite oxide; Quot;
RTI ID = 0.0 &gt; 30 minutes &lt; / RTI &gt; to 4 hours.
(Method for producing positive electrode active material for lithium secondary battery).
The method according to claim 1,
Wherein the molar content of Ni in the lithium composite oxide containing Ni, Co, and Mn is 80 mol% or more.
(Method for producing positive electrode active material for lithium secondary battery).
The method according to claim 1,
Preparing a lithium composite oxide comprising Ni, Co, and Mn,
Preparing an active material precursor comprising Ni, Co, and Mn; And
And firing a mixture of the active material precursor and the lithium source material to obtain a lithium composite oxide.
(Method for producing positive electrode active material for lithium secondary battery).
20. The method of claim 19,
Wherein the mixture of the active material precursor and the lithium source material further comprises a doping raw material,
Wherein the doping source material is a compound containing at least one element selected from the group consisting of Zr, Ti, and Al, or a mixture of the above compounds.
(Method for producing positive electrode active material for lithium secondary battery).
anode; cathode; And an electrolyte positioned between the anode and the cathode,
Wherein the anode comprises the cathode active material produced by the process according to claim &lt; RTI ID = 0.0 &gt; 1. &lt; / RTI &
Lithium secondary battery.

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