KR101815998B1 - Preparation method of functional cathode active material - Google Patents

Abstract

The present invention relates to a method for manufacturing a functional positive electrode active material, comprising effectively removing unreacted lithium compounds remaining on the surface of a nickel-based positive electrode active material for a lithium secondary battery without damage of the surface and the inside of particles, thereby stabilizing an electrode manufacturing process, and providing a positive electrode active material having high energy density and excellent thermal stability.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for producing a functional cathode active material,

An object of the present invention is to provide a method for effectively removing unreacted lithium compound remaining on the surface of a nickel-based positive electrode active material for a lithium secondary battery without damaging the surface and inside of the particle, thereby stabilizing the process for producing an electrode, And a method for producing a functional cathode active material capable of providing a cathode active material.

Lithium secondary batteries are increasingly in demand due to the rapid development of electronic industries such as computers and communication devices, and long-life batteries with long service life are required. In order to meet this requirement, a material having a high energy density is required.

The main materials of the lithium secondary battery are an anode, a cathode, a separator, and an electrolytic solution. The double anode sends the lithium ion held at the time of charging to the cathode, and upon receiving the lithium again, the content of lithium in the anode determines the capacity of the battery.

In general, the nickel-based lithium metal composite oxide, which is a high capacity anode, has a high energy density due to its high capacity, energy density and power, but the stability of the slurry during electrode production is deteriorated due to the unreacted lithium compound remaining on the surface. As a result, a gas is generated due to the reaction, which causes an increase in internal resistance and causes serious problems in terms of performance, lifetime and thermal stability. That is, when lithium impurities are present on the surface of the positive electrode active material, the reaction between the unreacted lithium compound and the electrolyte causes a swelling phenomenon in the lithium secondary battery to lower the stability and lifetime of the battery, Adverse effects.

In order to solve this problem, many companies and researchers have conducted studies to reduce the lithium on the surface, but the surface and inside of the cathode active material particles in the process of removing unreacted lithium compounds are damaged to deteriorate the performance, The unreacted lithium compound is not removed and thus has a problem in the electrode manufacturing process.

For example, Korean Patent Laid-Open Publication No. 10-2015-0047052 discloses a method of treating a lithium metal composite oxide cathode material with an alcohol containing an organic acid, but the removal efficiency of the unreacted lithium compound is low, , The acid component remains in the active material, or the lithium organic salt formed by the reaction with the unreacted lithium compound remains, resulting in generation of gas due to reaction with the electrolyte and decomposition, deterioration of performance and stability.

Therefore, the unreacted lithium compound present in the cathode active material for lithium secondary batteries is removed, and the surface damage of the cathode active material generated by the removal process and the cause of degradation of the performance and stability of gas generation by decomposition of the electrolyte are controlled, More development of cathode active material is needed.

Korean Patent Publication No. 10-2015-0047052 (Aug.

An object of the present invention is to dissolve and remove an unreacted lithium compound present as an impurity in a cathode active material for a lithium secondary battery. Specifically, the present invention provides a cathode active material having high energy density and excellent thermal stability by effectively removing unreacted lithium compounds remaining on the surface of the cathode active material for a lithium secondary battery without damaging the surface and the interior of the particles.

Another object of the present invention is to provide a method for removing unreacted lithium compounds with high efficiency without damaging the surface and the interior of the cathode active material without using an organic acid and an additive in the process of removing the unreacted lithium compound.

The present invention also provides a cathode active material in which the unreacted lithium compound on the surface of the cathode active material is reduced or completely eliminated with high efficiency according to the process of the present invention.

The present invention also provides a positive electrode and a lithium secondary battery having the same, wherein the positive electrode is manufactured by using the removed positive electrode active material in which the unreacted lithium compound on the surface of the positive electrode active material is substantially reduced.

The present inventors have conducted extensive research to achieve the above object and as a result have found that a solvent which effectively removes unreacted lithium compounds and a solvent which does not damage the cathode active material particles are selected, It was possible to produce a cathode active material having a high energy density and excellent electrochemical performance and thermal stability while having low reactivity lithium compound.

Specifically, one aspect of the present invention relates to a method for producing a functional cathode active material, which comprises mixing and stirring a cathode active material with a mixed solution of an organic solvent and water capable of phase-separating water, and extracting and removing unreacted lithium compound.

In one embodiment of the present invention, when extracting the unreacted lithium compound, the cathode active material may be firstly mixed with an organic solvent, and then water may be added and mixed.

In one embodiment of the present invention, the step of extracting and removing the lithium compound may include a step of phase-separating the mixed solution containing the cathode active material into an organic solvent layer and a water layer, and then removing the water layer .

In one embodiment of the present invention, after the step of removing the water layer, the organic solvent layer may be filtered and dried.

In one aspect of the present invention, after the filtration, it may further comprise a cleaning step.

In one embodiment of the present invention, the method may further include a step of performing heat treatment after any one step or two or more steps selected in the filtration step, the drying step and the washing step.

In one embodiment of the present invention, the heat treatment may be performed at 300 캜 to 900 캜.

In one embodiment of the present invention, the specific gravity of the organic solvent may be more than 1.0.

In one embodiment of the present invention, the organic solvent may be any one or two or more mixed solvents selected from halogenated hydrocarbon compounds.

In one embodiment of the present invention, the mixed solution may have a volume ratio of organic solvent to water of 1: 0.5 to 10.

In one embodiment of the present invention, the lithium compound may be selected from LiOH, Li ₂ CO _3, and mixtures thereof.

In one embodiment of the present invention, the stirring may be performed at 4 to 45 DEG C for 1 minute to 1 hour.

The cathode active material produced according to the production method of the present invention can provide a cathode active material having a low energy content of unreacted lithium compound and excellent electrochemical performance and thermal stability and a high energy density.

In the case of applying the positive electrode active material according to the present invention to a lithium secondary battery, it is possible to prevent gelation through a stable slurry and to stabilize the electrode manufacturing process, thereby obtaining battery characteristics excellent in life, capacity and safety .

1 is an initial charge / discharge graph of Example 3 and Comparative Example 1. Fig.
Fig. 2 is a graph of life span of Example 3 and Comparative Example 1. Fig.
3 is an FE-SEM (scanning microscope) photograph of Example 3. Fig.
4 is an FE-SEM (scanning microscope) photograph of Comparative Example 1. Fig.

Hereinafter, the present invention will be described in more detail by way of concrete examples or examples. It should be understood, however, that the invention is not limited thereto and that various changes and modifications may be made without departing from the spirit and scope of the invention.

Unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention is merely intended to effectively describe a specific embodiment and is not intended to limit the invention.

Also, the singular forms as used in the specification and the appended claims are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The present invention provides a method for preparing a functional cathode active material, which comprises mixing and stirring a cathode active material with a mixed solution of an organic solvent and water capable of phase separation, and extracting and removing unreacted lithium compound.

More specifically, the method for producing a functional cathode active material of the present invention comprises:

a) an extraction step of placing the cathode active material in a mixed solution of an organic solvent and water capable of phase separation and stirring to dissolve the remaining lithium compound,

b) phase-separating the mixed solution into an organic solvent layer and a water layer, removing the water layer, and

c) filtering the organic solvent layer

. ≪ / RTI >

The present invention also provides a method for producing the functional cathode active material of the present invention

a) an extraction step of placing the cathode active material in a mixed solution of an organic solvent and water capable of phase separation and stirring to dissolve the remaining lithium compound,

b) phase-separating the mixed solution into an organic solvent layer and a water layer, removing the water layer,

c) filtering the organic solvent layer, and

d) drying,

. ≪ / RTI >

Further, in one embodiment of the present invention, if necessary, after the filtration of step c), a washing step may be further included.

In one embodiment of the present invention, the method may further include a step of performing heat treatment after the step of filtering, the step of drying and the step of washing, or after two or more steps, if necessary.

In one embodiment of the present invention, the lithium compound is selected from LiOH, Li ₂ CO ₃ and mixtures thereof.

Hereinafter, each step of the production method of the present invention will be described in more detail.

In one embodiment of the present invention, the step (a) is a step of dissolving the unreacted lithium compound to extract the cathode active material by mixing the mixture into a mixed solution of an organic solvent and water capable of phase separation with water and stirring. The stirring conditions may be, but not limited to, 4 to 45 ° C, more preferably 10 to 30 ° C, and may be performed at room temperature. However, as long as the object of the present invention can be achieved, It does not. In this case, stirring may be performed using a stirrer, and the stirring time may be, for example, 1 minute to 1 hour to allow the unreacted lithium compound to be extracted, but the present invention is not limited thereto.

In one aspect of the present invention, the positive electrode active material is not particularly limited as long as it is a positive electrode active material containing lithium used for a lithium secondary battery.

Examples of the general cathode active material used for lithium secondary batteries include, but are not limited to, lithium-nickel-based oxides, lithium-manganese-based oxides, lithium-manganese-cobalt-based oxides, lithium- Lithium-nickel-cobalt oxide, lithium-nickel-manganese-cobalt oxide and lithium-nickel-cobalt-aluminum oxide.

More specifically, it may be represented by, for example, the following formula (1), but it is not limited thereto.

[Chemical Formula 1]

Li _{(1 + x)} Ni _a Co _b M _c O ₂

X? 0.35, 0.3? A? 0.98, 0? B? 0.35, 0.01? C? 0.7, and M is at least one element selected from the group consisting of a transition metal, a 2A group element and a 3B group element.

More specifically, in one embodiment of the present invention, the transition metal includes all the transition metals except Ni and Co, the group 2A element includes Be, Mg, Ca, Sr, Ba and Ra, and the group 3B element includes B , Al, Ga, In, and Tl.

In one embodiment of the present invention, the organic solvent is not limited as long as it is phase-separated with water. From the viewpoint of phase separation, it is possible to select various organic compounds which are phase-separated, such as, for example, ether compounds such as ethyl ether, tetrahydrofuran and propyl ether, halogenated hydrocarbon compounds such as methylene dichloride and aldehyde compounds such as benzaldehyde .

It is more preferable to use one having a specific gravity larger than 1.0 at normal temperature (25 DEG C) while being phase-separated with water. This is because an unreacted lithium compound, specifically, for example, lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), or the like is dissolved in the water layer due to phase separation and the lithium compound In the organic solvent layer.

When the specific gravity exceeds 1, the unreacted lithium compound dissolved in the water is extracted into water and extracted into the water layer in the upper part, and the cathode active material is precipitated in the lower organic solvent layer. The lithium ion contained in the positive electrode active material can be prevented from being dissolved in water to be extracted.

However, even when the specific gravity is lower than that of water, it falls within the scope of the present invention as long as the object of the present invention is achieved. For example, if an organic solvent having a specific gravity lower than that of water, that is, a specific gravity smaller than 1 is used, the cathode active material containing lithium ions together with the unreacted lithium compound remains in the lower water layer, An organic solvent having a specific gravity larger than 1.0 is more preferred, but it is not excluded from the present invention. In the present invention, when an organic solvent having a specific gravity lower than 1.0 is used, the unreacted lithium compound is extracted and dissolved in the aqueous phase by stirring, and then lithium or lithium ions continuously extracted in the aqueous phase from the cathode active material precipitated in the aqueous phase It is advisable to perform filtration as soon as possible after stirring is completed.

However, in the present invention, when unreacted lithium compounds are extracted using only water from which unreacted lithium compounds are extracted and dissolved, it is not effective to prevent damage to the cathode active material by the organic solution, I exclude things.

In the present invention, the control of the ratio of the water to the organic solvent is not limited so long as the object of the present invention can be achieved. That is, in the present invention, the composition ratio of the organic solvent and water is not limited as long as phase separation of the organic solvent layer and the water layer occurs. In order to further increase the effect of the present invention, the volume ratio of organic solvent to water is preferably 1: 0.5 to 10, more preferably 1: 1 to 4: But it is obvious that it is not limited thereto.

If the organic solvent and water that are phase-separable outside the above range are mixed, it is not excluded from the present invention, but the removal of lithium ions can be minimized during the extraction and removal of the lithium impurity by stirring in the composition ratio. Since these effects can be confirmed, description of separate data is omitted in the present invention.

In addition, the order of introduction of the water and the organic solvent is also important in the present invention, but the scope of the present invention falls within the scope of achieving the object of the present invention even if the order is changed. In order to achieve the object of the present invention, it is more preferred in the present invention that the cathode active material is first stirred with an organic solvent and then water is introduced. That is, in the present invention, the positive electrode active material is added to an organic solvent capable of being phase-separated with water, and the mixture is stirred to sufficiently pour the organic solvent on the surface and inside pores of the positive electrode active material. Do. As described above, by stirring the organic solvent first, it is possible to prevent excessive extraction of lithium ions contained in the surface and inside of the cathode active material, and to extract the unreacted lithium compound stably without damaging the particles of the cathode active material have. Next, the unreacted lithium compound remaining on the surface of the cathode active material is dissolved and extracted in water during the addition of water and stirred, and then unnecessary unreacted lithium compound is dissolved and dissolved in the water layer, The unreacted lithium compound can be efficiently removed.

In this case, the stirring time is not limited in the course of the stirring and the addition to the organic solvent. For example, stirring may be performed for 1 minute to 1 hour without limitation, and then, But is not limited to, stirring for 1 minute to 1 hour.

In one embodiment of the present invention, the organic solvent having a specific gravity of more than 1 is not limited so far as it is phase-separated by water. For example, the organic solvent may be a compound represented by RXm as a halogenated hydrocarbon compound. Wherein R is C_One~ C₃₀Alkyl, C_One~ C₃₀Alkoxy, C₂~ C₃₀Alkenyl, C₂~ C₃₀of Alkynyl, C₆~ C₃₀Aryl, C₆~ C₃₀Aralkyl or C₆~ C₃₀And the alkyl, alkoxy, alkenyl, alkynyl, aryl, aralkyl or alkylaryl group may be unsubstituted or substituted with a heteroatom selected from N, O and S, and X is selected from the group consisting of F, Cl, Br, I, and m is equal to or less than the range of the number of CH in R.

Examples of such halogenated hydrocarbon compounds include methyl chloride, dichloromethane, trichloromethane, tetrachloromethane, 1,1,2-tribromoethane (1, 1 2-tribromoethane, chlorobenzene, chlorobenzaldehyde, benzyl chloride, benzyl bromide, 1,1-dichloroethane, 1,2- 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, It is also possible to use 2-dichloropropane, chlorocyclopentane, chlorocyclohexane, dichlorocyclohexane, dichlorobenzene, trichlorobenzene, hexachlorobenzene, hexachlorobenzene) and bromobenzene. It can be used, and are not limited thereto.

Although not preferred in the present invention, various organic solvents such as ether-based, ester-based, and ketone-based ones having a specific gravity of less than 1 may be used and are not limited as long as they can be phase-separated with water.

In one embodiment of the present invention, the temperature of the mixed solution in the extraction step is not particularly limited. For example, it is preferable to set the temperature to 4 to 45 ° C because it is advantageous in terms of handleability or extraction efficiency.

In one embodiment of the present invention, the mixing ratio of the cathode active material and the mixed solution in the extraction step may be 1: 1 to 1: 5 by weight, but is not limited thereto.

In one embodiment of the present invention, the step b) is a step of phase separation into an organic solvent layer and a water layer, and removing a water layer to remove an unreacted lithium compound, wherein the phase separation is stopped by stirring Phase separation. When the organic solvent layer and the water layer are completely separated, the unreacted lithium compound can be removed by removing the water layer.

In one embodiment of the present invention, the step c) may further include separating the cathode active material by filtering the organic solvent layer, and may further include the post-filtration cleaning step as needed. In this case, the solvent used in the washing step may be one which is the same as or different from the organic solvent used in the phase separation process, and one or two or more organic solvents referred to as organic solvents that can be used in the phase separation process may be used . Further, if necessary, water may be used to further carry out an additional cleaning step in the form of a shower or the like.

In an embodiment of the present invention, the step (d) is not limited to the step of drying the filtered cathode active material, provided that the solvent adsorbs between the pores of the cathode active material or on the surface thereof or the solvent present in the pores is sufficiently removed . For example, it can be dried in an air atmosphere, an oxygen atmosphere, an inert atmosphere such as nitrogen or argon, or an atmosphere in a vacuum atmosphere at 40 to 350 ° C, more preferably 70 to 250 ° C.

In an embodiment of the present invention, the cathode active material is heated to 300 to 900 ° C, preferably to 300 to 700 ° C, after filtration in step c), after filtration and washing in step c), or after drying in step d) And a heat treatment step. When the heat treatment process is performed, unstable structures and interface non-uniformities that can be formed due to lack of lithium on the surface of the cathode active material or a part of the grain boundary of the primary particles can be eliminated. If the surface of the positive electrode active material or a part of the interface of the primary particles lacks lithium and has an unstable structure, the resistance of the active material increases, which may lead to deterioration of performance, lifetime and safety of the battery. Therefore, heat treatment is performed to solve this problem, thereby eliminating nonuniformity and preventing increase in resistance.

In the cathode active material produced by the production method of the present invention, the residual lithium compound content may be 0.4 wt% or less in the total amount of the cathode active material. And preferably 0.1 to 0.3% by weight. According to the production method of the present invention, it is possible to have an improved removal efficiency of 30%, preferably 70% or more, compared with the background process.

The present invention also provides a positive electrode comprising the functional cathode active material produced by the above process.

The present invention also provides a lithium secondary battery produced using the positive electrode.

In the present invention, the anode is prepared by mixing the functional cathode active material of the present invention and a binder with a solvent to prepare a slurry and applying the slurry to a current collector. It may also contain additional conductive agents as needed.

Since the binder, the solvent, the conductive agent, and the like can be used as they are in the method of manufacturing the positive electrode of the present invention, the functional positive electrode active material according to the present invention can be used as it is.

The present invention also provides a lithium secondary battery comprising a positive electrode, a negative electrode, and a porous separator for preventing a short circuit between the positive electrode and the negative electrode, which are made of a functional positive electrode active material. The negative electrode or separator in the secondary battery can be used as long as it is used in the technical field. Therefore, detailed description will be omitted in the present invention.

The lithium secondary battery using the functional cathode active material produced by the production method of the present invention can attain excellent physical properties such as capacity, lifetime characteristics and stability.

Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. In the present invention, the composition ratio means a weight ratio, unless otherwise specified.

<Evaluation method>

1. Scanning electron microscope photo analysis

 The surface of the cathode active material was observed using a Hitachi S-4800 FE-SEM (field emission scanning microscope).

2. Measurement of the amount of unreacted lithium compound

The amount of unreacted lithium compound in the cathode active material was measured by a pH titration method using the wader method, and the method is as follows.

5 g of each of the prepared cathode active materials was stirred for 20 minutes in 100 g of distilled water, and 50 g of the filtrate obtained by filtration was collected. When 5 drops of 0.1 M phenolphthalein solution is added to this solution, it turns red. The red solution was added dropwise with 0.1 N HCl standard solution until the color of the solution turned colorless while stirring. This was the first optimal point.

To the colorless solution was added 5 drops of 0.1 M methyl orange solution and titrated with 0.1 N HCl solution until the solution turned from yellow to red. This was the second optimal point.

The amounts of lithium carbonate (Li ₂ CO ₃ ) and lithium hydroxide (LiOH), which are unreacted lithium compounds contained in the cathode active material, were calculated through 0.1 N HCl addition of the first optimum point and the second optimum point.

3. Electrochemical evaluation experiment

The electrochemical conditions for evaluating the initial charge / discharge capacity and efficiency of the lithium secondary battery were as follows.

 - Initial charge: CC / CV 0.1C, 4.3V, 1 / 20C cut-off

 - Initial discharge: CC 0.1C, 3.0V cut-off

The prepared coin-type lithium secondary battery was charged at a constant current and a total voltage until the end-of-charge voltage of 4.3 V with a charging current of 0.1 C at a temperature of 25 ° C., and discharged at a constant current of 3.0 V with a discharge current of 0.1 C, .

The initial efficiency was determined according to the following formula (1).

[Formula 1]

Initial efficiency (%) = (discharge capacity in the first cycle / charge capacity in the first cycle) × 100

4. Lifetime characteristics

The electrochemical evaluation conditions for the lifetime characteristics were as follows and repeated 100 times.

 - Charging: CC / CV 0.5C, 4.3V, 1 / 20C cut-off

 - Discharge: CC 0.5C, 3.0V cut-off.

The prepared coin-type lithium secondary battery was charged at a constant current and a full-voltage condition at a charging current of 0.5 C at a temperature of 25 캜 up to a charging end voltage of 4.3 V and discharged at a constant current of 3.0 V with a discharging current of 0.5 C, .

After the first cycle, the battery was charged and discharged at a current of 0.5 C to repeat 100 cycles. Life characteristics were obtained according to the following formula (2).

[Formula 2]

Life characteristics (%) = (discharge capacity in the 100th cycle / discharge capacity in the first cycle) × 100

Example 1

10 g of LiNi0.8Co0.15Al0.05O2 cathode active material was added to 10 mL of 1,2-dichloroethane at room temperature at 25 DEG C, and the mixture was stirred for 20 minutes. Then, 10 mL of pure water was further added thereto and further stirred for 20 minutes . After stopping the stirring, the upper water layer was removed after waiting for the two solvents to completely separate. The organic solvent layer was filtered and dried in a vacuum state at 100 DEG C for 12 hours to obtain a lithium metal composite oxide.

The positive electrode active material for a lithium secondary battery prepared in Example 1, Super-P as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were dispersed in a weight ratio of 94: 3: 3 to N-methyl- N-methyl-2-pyrrolidone), and a uniformly dispersed slurry was prepared using a Thinky Mixer. The slurry was uniformly applied to an aluminum foil having a thickness of 15 탆, dried at 130 캜, and rolled using a roll paste to prepare a positive electrode for a lithium secondary battery.

A porous polypropylene membrane (W-scope Korea) having a thickness of 21 탆 was used as a separator, and a mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3: 7 was used as a counter electrode (negative electrode) using the electrolyte prepared by dissolving LiPF ₆ in a concentration of 1.0M in the solvent was prepared in usual manner if a CR2016 coin-type lithium secondary battery.

The properties of the produced lithium secondary battery were measured and are shown in Table 2 below.

Examples 2 to 9

As shown in Table 1, the same procedure as in Example 1 was carried out except that the kind of organic solvent, the ratio of water and the stirring time were different in Example 1. In the case of Examples 7 to 9, heat treatment after drying was added The procedure of Example 1 was repeated except that the heat treatment temperature was changed. The results are shown in Table 2. &lt; tb &gt; &lt; TABLE &gt;

Comparative Example 1

It did not remove the unreacted lithium compound LiNi _{0. 8} Co _{0 . 15} Al _{0 . 05} &lt; / _RTI &gt; O &lt; ₂ &gt; to prepare a lithium secondary battery. The properties of the produced lithium secondary battery were measured and are shown in Table 2 below.

Comparative Example 2

Example 1 was carried out in the same manner as in Example 1, except that water was not used, only 1,2-dichloroethane was used, and the weight ratio of 1,2-dichloroethane and the cathode active material was 1: 1. Are shown in Table 2.

Comparative Example 3

Example 1 was repeated except that 1,2-dichloroethane was not used, only water was used, and the weight ratio of water to the cathode active material was 1: 1. The results are shown in Table 2 .

Item Organic solvent water Water: organic solvent
(Volume ratio) Agitation time before water injection
(min) Agitation time after water injection
(min) Drying temperature
(° C) Heat treatment
Temperature
(° C) Example 1 1.2-dichloroethane use 1: 1 20 20 100 - Example 2 1.2-dichloroethane use 1: 1 0 20 100 - Example 3 1.2-dichloroethane use 1: 1 20 40 100 - Example 4 1.2-dichloroethane use 1: 1 20 60 100 - Example 5 1.2-dichloroethane use 2: 1 20 20 100 - Example 6 1.1-dichloroethane use 4: 1 20 20 100 - Example 7 1.2-dichloroethane use 1: 1 20 40 100 500 Example 8 1.2-dichloroethane use 1: 1 20 40 100 700 Example 9 1.2-dichloroethane use 1: 1 20 40 100 900 Comparative Example 1 - - - - - - - Comparative Example 2 1.2-dichloroethane - - 20 - 100 - Comparative Example 3 - use - - 20 100 -

Item Electrochemical evaluation Unreacted lithium compound (residual lithium) Initial charge
(mAh / g) Initial discharge amount
(mAh / g) Initial efficiency
(%) Life characteristics
(%, 100 times) LiOH
(wt%) Li ₂ CO ₃
(wt%) Sum
(wt%) Example 1 221 197 89 84 0.05 0.25 0.30 Example 2 217 193 89 85 0.10 0.21 0.31 Example 3 217 193 89 89 0.14 0.11 0.25 Example 4 217 194 89 83 0.10 0.11 0.21 Example 5 213 194 91 81 0.02 0.15 0.17 Example 6 210 188 90 85 0.02 0.15 0.17 Example 7 216 192 89 68 0.02 0.45 0.47 Example 8 220 198 90 71 0.02 0.43 0.45 Example 9 220 193 88 66 0.02 0.78 0.80 Comparative Example 1 216 193 89 65 0.45 0.63 1.08 Comparative Example 2 215 195 91 64 0.40 0.97 1.37 Comparative Example 3 209 186 89 60 0.01 0.18 0.19

As shown in Table 2, when the cathode active material prepared according to the present invention was used, the content of the unreacted lithium compound was smaller than that of Comparative Example 1, .

In addition, in Comparative Example 2 using only an organic solvent, it was found that the content of the lithium compound was rather increased as compared with Comparative Example 1.

Also, in Comparative Example 3 using only water, the content of the unreacted lithium compound was significantly lowered as compared with Comparative Example 1, but the cathode active material was damaged and the life characteristic was lowered.

Fig. 1 shows the initial charging / discharging graph of Example 3 and Comparative Example 1, and Fig. 2 shows the lifetime graph of Example 3 and Comparative Example 1. Fig. As shown in Fig. 1 and Fig. 2, it can be seen that the life characteristics in Example 3 are improved compared with Comparative Example 1 in which no treatment is performed.

Fig. 3 is a scanning electron microphotograph of Example 3, and Fig. 4 is a scanning electron microphotograph of Comparative Example 1. Fig. As shown in FIG. 3, after the unreacted lithium compound was removed by the production method of the present invention, it was found that there was no surface damage of the cathode active material.

Claims (12)

Mixing the positive electrode active material with an organic solvent that can be phase-separated with water by a specific gravity difference, adding water, mixing, and stirring to extract and remove the unreacted lithium compound.
delete The method according to claim 1,
The step of extracting and removing the lithium compound includes separating the mixed solution containing the cathode active material into an organic solvent layer and a water layer, and then removing the water layer.
The method of claim 3,
Removing the water layer, filtering the organic solvent layer, and drying the organic solvent layer.
5. The method of claim 4,
Further comprising, after the filtration, a cleaning step.
6. The method of claim 5,
Further comprising the step of performing heat treatment after any one step or two or more steps selected from the filtration step, the drying step and the washing step.
The method according to claim 6,
Wherein the heat treatment is performed at a temperature of 300 to 900 占 폚.
The method according to claim 1,
Wherein the organic solvent has a specific gravity of more than 1.0.
9. The method of claim 8,
Wherein the organic solvent is any one or a mixture of two or more selected from halogenated hydrocarbon compounds.
The method according to claim 1,
Wherein the mixed solution has an organic solvent: water in a volume ratio of 1: 0.5 to 10.
The method according to claim 1,
Wherein the lithium compound is selected from LiOH, Li ₂ CO _3, and mixtures thereof.
The method according to claim 1,
Wherein said stirring is carried out at 4 to 45 DEG C for 1 minute to 1 hour.

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