KR20090126964A - Electrochemical cell - Google Patents

Abstract

PURPOSE: An electrochemical cell is provided to ensure excellent reversible capacity, cycle lifetime characteristic, especially, cycle lifetime characteristic at a high-index. CONSTITUTION: A positive active material for an electrochemical cell comprises a compound represented by chemical formula 1: Li_x[Li_(1-y-z)M^1_yM^2_z]O_(2-α)D_α with a nanowire shape. In chemical formula 1, 0.8 <= x <= 1.1, 0 <= y <= 0.5, 0 <=z <= 0.5, 0 <= α <= 0.05, M^1 and M^2 are at least one kind of different transition elements; and D is selected from the group consisting of O, F, S, P, and their combination.

Description

Electrochemical cell {ELECTROCHEMICAL CELL}

The present invention relates to an electrochemical cell, and more particularly, to an electrochemical cell having a high reversible capacity and excellent cycle life characteristics.

There is an increasing need for high performance and high capacity of batteries used as power sources for portable electronic devices and electric vehicles.

A battery generates power by using a material capable of electrochemical reactions at a positive electrode and a negative electrode. A typical example of such a battery is a lithium secondary battery that generates electric energy by a change in chemical potential when lithium ions are intercalated / deintercalated at a positive electrode and a negative electrode.

The lithium secondary battery is manufactured by using a material capable of reversible intercalation / deintercalation of lithium ions as a positive electrode and a negative electrode active material, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.

Recently, research on nanomaterials has been actively used as active materials used in such batteries. This can increase the area of contact between the active material layer of the electrode and the electrolyte because the nanomaterial has a very large specific surface area, resulting in a large site participating in the battery reaction and shortening the diffusion path of lithium ions. This is because the intercalation reaction of lithium ions can be facilitated.

As the nanomaterial cathode active material, a method of preparing nanowires such as lithium-Ni-defective Li _x Mn _0.67 Ni _0.3 O ₂ by chemically oxidizing an initial bulk LiMn _0.5 Ni _0.5 O ₂ powder has been studied. As the cathode active material is prepared by performing an acid treatment, a lithium is very insufficient, that is, a compound having an x value of less than 1 is prepared. The reversible capacity of this nanowire was about 160 mAh / g at 4.8-2 V and 20 mA / g current density.

Recently, Mn _- rich lithium metal oxides such as Li [Li _{1 / 3-2x / 3} Mn _{2 / 3-x / 3} M _x ] O ₂ anodes have recently been used among lithium composite metal oxides used as positive electrode active materials. In the case of charging at 4.5V or more, a high capacity of 200 mAh / g or more can be obtained, and thus it has been importantly studied as a positive electrode active material for lithium secondary batteries. However, the positive electrode active material has a problem in that, despite the high capacity advantage, the capacity decreases rapidly at a high rate. For example, when the Li [Ni _0.2 Li _0.2 Mn _0.6 ] O ₂ active material is charged and discharged by increasing the current from 20 to 200 mA / g, a capacity reduction of more than 50% appears. In recent years, there has been a study of improving the rate characteristic by preparing a Li [Ni _0.41 Li _0.08 Mn _0.51 ] O ₂ nanoplate active material by a coprecipitation method. However, there is still a lot of research into improving high rate characteristics.

SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to provide a cathode active material for an electrochemical cell which is excellent in reversible capacity and excellent in cycle life characteristics, particularly at high rates.

Another object of the present invention is to provide a method for producing the cathode active material.

Still another object of the present invention is to provide an electrochemical cell including the cathode active material.

Technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

A first embodiment of the present invention for achieving the above object is to provide a cathode active material represented by the following formula (1) having a nanowire (nanowire) shape.

[Formula 1]

Li _x [Li _1-yz M ¹ _y M ² _z ] O _2-α D _α

Wherein 0.8 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.5, 0 ≦ α ≦ 0.05,

M ¹ and M ² are one or more different transition metal elements,

D is selected from the group consisting of O, F, S, P, and combinations thereof)

In addition, a second embodiment of the present invention is a method for producing the positive electrode active material, the method for producing an oxide nanowire containing M ¹ and M ² ; Mixing the oxide nanowires with a lithium compound; Leaving the mixture; Drying the left product.

A third embodiment of the present invention is to provide an electrochemical cell including the cathode active material.

The positive electrode active material of the present invention has a high reversible capacity and excellent cycle life characteristics, particularly at high rates.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

The cathode active material according to the first embodiment of the present invention includes a compound represented by Chemical Formula 1 having a nanowire shape.

[Formula 1]

Li _x [Li _1-yz M ¹ _y M ² _z ] O _2-α D _α

Wherein 0.8 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.5, 0 ≦ α ≦ 0.05,

M ¹ and M ² are one or more different transition metal elements, M ¹ is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe and combinations thereof, wherein M ² is Al, Ni, Co , Mn, Cr, Fe, and combinations thereof.

D is also selected from the group consisting of O, F, S, P, and combinations thereof.

In Chemical Formula 1, "[]" means that lithium is substituted with a part of the metal sites of M ¹ and M ² . As such, when lithium is replaced with a part of the metal sites of M ¹ and M ² , flatness is large at about 4.5 V, and the capacity is increased.

In the cathode active material of the present invention, the nanowires preferably have a length of 0.5 μm to 50 μm. When the length of the nanowire is shorter than 0.5 μm, the lithium reaction site becomes smaller and the high rate characteristic is lowered, which is not preferable. The longer the length of the nanowire is, the better, but since it is almost impossible to manufacture more than 50 μm, the maximum 50 μm is It is suitable.

In addition, the nanowires preferably have a diameter of 50 to 100nm. When the diameter of the nanowires is smaller than 50 nm, there is a problem in that irreversible capacity increases due to large side reactions with the electrolyte.

The cathode active material of the present invention has a nanowire shape and has a layered structure. The nanowire structure has many sites where lithium ions can be removed / inserted, and the lithium diffusion distance is shortened, thereby improving high rate characteristics.

The cathode active material of the present invention may be manufactured to have a nanowire shape according to a manufacturing method according to a hydrothermal reaction as follows according to the second embodiment of the present invention.

First, oxide nanowires containing M ¹ and M ² are prepared. Hereinafter, the oxide nanowire manufacturing process will be described in more detail.

Gels are prepared by adding a gel former to the M ¹ compound solution. In this case, as the M ¹ compound, a compound containing a metal element consisting of Al, Ni, Co, Mn, Cr, Fe, and combinations thereof may be used, and examples thereof include halides, nitrates, and the like. For example KMnO ₄ can be used. Water, ethanol or nucleic acid may be used as a solvent in the M ¹ compound solution. Fumaric acid may be used as the gel forming agent.

Subsequently, the gel obtained is subjected to primary heat treatment. At this time, the first heat treatment process is preferably carried out for 1 to 20 hours at 400 to 700 ℃. The primary heat treatment process is 700 ℃ If carried out at a higher temperature, the structure of the material to be produced is decomposed, which is undesirable, and if it is carried out at temperatures lower than 400 ° C., it is not preferred as KMnO ₄ is prepared, which is not fully crystallized and may cause decay.

The heat treated gel is then mixed with the M ² compound. In this case, as the M ² compound, a compound containing a metal element consisting of Al, Ni, Co, Mn, Cr, Fe, and combinations thereof may be used. For example, nitride, halide, or a hydrate thereof may be used. . Specific examples of the M ² compound include Co (NO ₃ ) ₆ .6H ₂ O, CoCl ₂ , Ni (NO ₃ ) ₆ .6H ₂ O, NiCl _2, or a combination thereof. The ratio of the heat-treated gel and the M ² mixture is suitably 1: 10 to 1: 50 by weight.

The resulting mixture is also subjected to a second heat treatment. According to this process, oxide nanowires containing M ¹ and M ² are produced. The secondary heat treatment process is preferably performed for 2 to 48 hours at 150 to 250 ℃. If the secondary heat treatment process is performed at a temperature outside the temperature range, it is not preferable because the desired product cannot be prepared. At this time, the diameter of the prepared oxide nanowire is 20 to 60nm, the length is 0.5㎛ 50㎛.

The oxide nanowires and a lithium compound are mixed. Lithium nitrate, lithium acetate, lithium hydroxide and the like may be used as the lithium compound, but is not limited thereto. The mixing ratio of the oxide nanowires and the lithium compound is preferably 1: 2 to 1: 4 weight ratio. In this step, a metal compound may be further added. Further addition of the metal compound results in a form in which some of the manganese is replaced by metal in the final product. Al, Ni, Co, Cr or Fe may be used as the metal, and examples of the metal compound may be an oxide, nitrate salt, acetate salt or hydroxide of the metal. This mixing step may be carried out dry or may be carried out wet using an organic solvent as the mixing medium. Alcohol, such as ethanol, or acetone can be used as an organic solvent.

The mixture is then left to stand, and this leaving process is suitably carried out at 200 to 250 ° C. for 12 to 48 hours. If the leaving process is performed under conditions outside of the temperature and time, it is not preferable because a positive electrode active material having a desired wire shape cannot be obtained.

The left product is then dried, and this drying process is suitably carried out at 100 to 200 ° C. for 12 to 48 hours.

In the process of mixing the oxide nanowires and the lithium compound, the diameter of the oxide nanowires is slightly increased, and the diameters of the nanowires constituting the compound represented by the following Formula 1, which is the final cathode active material, are 50 nm to 100 nm, and the length is 0.5 μm to 50. [Mu] m.

[Formula 1]

Li _x [Li _1-yz M ¹ _y M ² _z ] O _2-α D _α

Wherein 0.8 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.5, 0 ≦ α ≦ 0.05,

M ¹ and M ² are one or more different transition metal elements, M ¹ is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe and combinations thereof, wherein M ² is Al, Ni, Co , Mn, Cr, Fe, and combinations thereof.

D is also selected from the group consisting of O, F, S, P, and combinations thereof.

The positive electrode active material of the present invention can be usefully used for the positive electrode of an electrochemical cell such as a lithium secondary battery. The lithium secondary battery includes a negative electrode and an electrolyte including a negative electrode active material together with a positive electrode.

The positive electrode is prepared by mixing a positive electrode active material according to the present invention, a conductive material, a binder and a solvent to prepare a positive electrode active material composition, and then coating and drying the aluminum active material directly. Alternatively, the cathode active material composition may be cast on a separate support, and then the film obtained by peeling from the support may be manufactured by laminating on an aluminum current collector.

The conductive material is carbon black, graphite, metal powder, the binder is vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene And mixtures thereof. In addition, N-methylpyrrolidone, acetone, tetrahydrofuran, decane, etc. are used as a solvent. In this case, the content of the positive electrode active material, the conductive material, the binder, and the solvent is used at a level commonly used in a lithium secondary battery.

Like the positive electrode, the negative electrode is mixed with a negative electrode active material, a binder, and a solvent to prepare an anode active material composition.The negative electrode active material film coated directly on the copper current collector or cast on a separate support body and peeled from the support is a copper current collector. It is prepared by lamination. 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, and for example, lithium metal, lithium alloy, coke, artificial graphite, natural graphite, organic polymer compound combustor, carbon fiber, or the like is used. . In addition, a conductive material, a binder, and a solvent are used similarly to the case of the positive electrode mentioned above.

The separator may be used as long as it is commonly used in lithium secondary batteries. For example, polyethylene, polypropylene, polyvinylidene fluoride or two or more multilayer films thereof may be used, and a polyethylene / polypropylene two-layer separator, It goes without saying that a mixed multilayer film such as polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene / polypropylene three-layer separator and the like can be used.

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

Although the solvent of the said non-aqueous electrolyte is not specifically limited, Chain carbonate methyl acetate, ethyl acetate, such as cyclic carbonate dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, Esters such as propyl acetate, methyl propionate, ethyl propionate and γ-butyrolactone 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 2-methyltetra Amides, such as nitriles, dimethylformamide, such as ethers, acetonitrile, such as hydrofuran, etc. can be used. These can be used individually or in combination of two or more. In particular, a mixed solvent of a cyclic carbonate and a linear carbonate can be preferably used.

As the electrolyte, a gel 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.

The lithium salt is 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 , One selected from the group consisting of LiCl and LiI is possible.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred examples of the present invention and the present invention is not limited to the following examples.

(Example 1)

A solution containing 7.2 g of KMnO ₄ and 200 ml of distilled water was slowly stirred at 40 ° C. for 30 minutes, and in order to cause a rapid endothermic reaction, 2.1 g of fumariic acid was added to the obtained mixture to prepare a brown gel. The gel was annealed at 400 ° C. for 6 hours and annealed again at 700 ° C. for 12 hours, and the resulting dark black powder was washed thoroughly with water six times and then vacuum dried at 200 ° C. overnight.

The prepared product was confirmed that the K _{0 .3} MnO ₂ is prepared ICP-MS (inductively coupled plasma mass spectrometry, ICPS-1000IV, Shimadzu) to K- Burnet site (birnessite) analysis.

The prepared K _0.3 MnO ₂ was mixed in 100 ml distilled water with Co (NO ₃ ) ₆ .6H ₂ O in a weight ratio of 1: 8, and the mixture was left in an autoclave at 200 ° C. for 5 days, and then washed six times with water for reaction. Impurities and dissolved K ions that could be generated during the process were removed. The product was measured by ICP-MS and found to be Co _0.4 Mn _0.6 O ₂ nanowire. This nanowire had a diameter of 50 nm and a length of 1 mu m.

LiNO ₃ · H ₂ O and the prepared Co _0.4 Mn _0.6 O ₂ nanowires were mixed in 100 ml distilled water in a 4: 1 weight ratio, and moved to an autoclave and left at 200 ° C. for 2 days. The prepared powder was washed with water and dried at 120 ° C. under vacuum to prepare Li _0.88 [Li _0.18 Co _0.33 Mn _0.49 ] O ₂ nanowire cathode active material. The diameter of this positive electrode active material nanowire was 80 nm and the length was 1 micrometer. This positive electrode active material was a material having a layered structure.

Approximately 20 mg of the positive electrode active material and the super P carbon black (MMM, Belgium and polyvinylidene fluoride binder (Kureha, Japan)) were stirred well in N: methyl-2-pyrrolidone in a 90: 5: 5 weight ratio to slurry Was prepared, and the slurry was coated on Al-foil and dried for 20 minutes at 130 ° C. to prepare a positive electrode, wherein a positive electrode active material loading amount was 20 mg / cm ² (electrode thickness except 20 μm of Al current collector).

A coin-type test cell (size 2016) was manufactured in a helium-filled glove box using the positive electrode, the lithium counter electrode, and the microporous polyethylene separator. At this time, ethylene carbonate / diethylene carbonate / ethyl methyl carbonate (30: 30: 40% by volume) in which 1M LiPF ₆ was dissolved was used (Cheil Industries, Korea). After the addition of the electrolyte, the test cell was chemicalized at room temperature for 24 hours before the electrochemical experiment.

(Comparative Example 1)

The secondary particles (aggregates) having an average particle diameter of 1-20 μm formed by aggregation of primary particles having an average particle diameter of 80-200 nm, using Li [Ni _0.20 Li _0.2 Mn _0.6 ] O ₂ nanoparticles as a negative electrode active material. Except that was carried out in the same manner as in Example 1 to prepare a battery.

(Comparative Example 2)

A battery was manufactured in the same manner as in Example 1, except that Li [Ni _0.41 Li _0.08 Mn _0.51 ] O ₂ nanoparticles having an average particle diameter of 20-200 nm were used as the negative electrode active material.

* XRD measurement

The X-ray diffraction pattern of the Co _0.4 Mn _0.6 O ₂ nanowire and Li _0.88 [Li _0.12 Co _0.33 Mn _0.49 ] O ₂ nanowire cathode active material prepared in Example 1 was measured using a Cu target tube, and the results were obtained. Is shown in FIG. As shown in FIG. 1, Co _0.4 Mn _0.6 O ₂ nanowires have two major peaks at about 12 ° (110) and about 25 ° (200) scattering angles, which are obtained from K-Bernesite The results were similar to Ni _0.45 Mn _0.55 O ₂ . Therefore, it can be seen that the manufactured Co _0.4 Mn _0.6 O ₂ nanowires have a structure similar to that of vernesite. In addition, it can be seen that the Li _0.88 [Li _0.12 Co _0.33 Mn _0.49 ] O ₂ nanowire positive electrode active material prepared in Example 1 had a hexagonal layered structure having a R3m space group. In addition, Li _0.88 [Li _0.12 Co _0.33 Mn _0.49 ] O ₂ nanowire positive electrode active material prepared in Example 1 showed a small peak near 20 °, and thus, lithium was substituted as part of the metal site.

The lattice constants of a and c of the prepared cathode active materials were 2.834 and 14.208Å, and very weak regular lattice diffraction at about 20 ° and 24 ° corresponds to the order of Li, Co, and Mn ions at the transition metal site of the layered lattice. Known. In addition, as shown in FIG. 1, a very high peak is shown in the (003) plane compared to other peaks. This means that the orientation of the nanowires is on one side, and a peak at the (003) plane means that the strength of the positive electrode active material is high.

ICP-MS results of the positive electrode active material prepared according to Example 1 indicate that Li _1.3 Co _0.4 Mn _0.6 O _4.9 is formed, which is standardized to LiMnO ₂ , and the compound is represented by the chemical formula of Li _0.88 [Li _0.12 Co _0.33 Mn _0.49 ] O ₂ . It may also be indicated by.

* SEM and TEM photographs and energy-dispersive X-ray spectrometry (EDS) measurements

2 shows TEM and SEM photographs and EDS measurement results of the Co _0.4 Mn _0.6 O ₂ nanowire prepared in Example 1 and the prepared Li _0.88 [Li _0.12 Co _0.33 Mn _0.49 ] O ₂ nanowire cathode active material. TEM images were measured using a JEOL 2100F electron microscope operating at 200kV.

In Figure 2 (a) is a TEM picture of Co _0.4 Mn _0.6 O ₂ nanowires prepared in Example 1, (b) is a SEM picture of Li _0.88 [Li _0.12 Co _0.33 Mn _0.49 ] O ₂ nanowires positive electrode active material . Also, in FIG. 2, (d) is a TEM image of Li _0.88 [Li _0.12 Co _0.33 Mn _0.49 ] O ₂ nanowire positive electrode active material, and (e) is HREM (high-high) for one of the wires shown in (d). resolution electron microscopy). The sample for measuring this HREM was prepared by dispersing the positive electrode active material prepared in Example 1 in acetone, and then volatilizing it in a carbon-coated copper grid.

As shown in FIG. 2A, it can be seen that the Co _0.4 Mn _0.6 O ₂ nanowires prepared in Example 1 have a diameter of 40 nm and a length greater than 1 μm. In addition, as shown in (b) of FIG. 2, the positive electrode active material prepared by reacting Co _0.4 Mn _0.6 O ₂ nanowires with lithium nitrate has an increase in the size of the nanowires to have a diameter of 100 nm and a length greater than 3 μm. Able to know. In addition, looking at the enlarged picture of the edge portion of the nanowire inserted in (b) of Figure 2, it can be seen that the positive electrode active material particles are composed of agglomerated individual nanowires. In addition, looking at the TEM picture in Figure 2 (d) the diameter of the prepared positive electrode active material nanowire was about 50nm. The HREM photograph of FIG. 2 e shows that the nanowire has a layered structure having a lattice fringe image of the (003) plane corresponding to 0.46 nm. In addition, abnormally grown nanowires with a diameter of 50 nm and a length of 10 μm were observed.

Figure 2 (c) is a graph showing the EDS measurement results of the positive electrode active material prepared in Example 1, it can be seen that both the Co and Mn present in the prepared positive electrode active material. In addition, the results of measuring ICP-MS of the cathode active material prepared in Example 1 showed a stoichiometry of Li _0.88 [Li _0.12 Co _0.33 Mn _0.49 ] O ₂ .

In addition, the fabricated cathode active material nanowires can be identified (003) plane as the spacing distance is about 4.1 하면 when the interlayer distances are repeated at the same interval in the TEM photograph shown in FIG. 2D. It can be seen from the layered hexagonal structure. In addition, the BET (Brunauer-Emmett-Teller) specific surface area of the manufactured cathode active material was measured, and found to be 50 m ² / g.

* Charging / discharging characteristics

In the battery using the positive electrode active material of Example 1, the discharge rate of 0.2C, 1C, 3C, 5C, 10C and 15C (1C = 240mAh / g) corresponding to 245, 242, 238, 230, 225 and 220mAh / g (charge rate is After charging and discharging was performed at a rate of 4.8 to 2V at a fixed rate of 1C, the initial discharge capacity and voltage are shown in FIG. 3. 3, it can be seen that after the one-time charging process, the continuous charging / discharging was performed while increasing the charging / discharging speed, and the flat portion disappeared. When using a Li ₂ MnO ₃ -based oxide, it is reported that an unusual flat flat surface appears at about 4.5V, whereas, as shown in FIG. 3, Li _0.88 [Li _0.18 Co _0.33 Mn _0.49 ] O ₂ is about 4.6. It can be seen that V has an inclined flat portion. As such, the presence of a flat portion inclined at about 4.6 V instead of the flat flat portion in Li _0.88 [Li _0.18 Co _0.33 Mn _0.49 ] O ₂ nanowire is a phenomenon that occurs when the Co or Cr content is increased. This is thought to be the result obtained because the transition metal may be further included in the redox reaction, and oxygen is not required for the sample having the transition metal content so that all Li is removed from the Li layer.

In addition, as shown in FIG. 3, during one cycle at 0.2C, the charge and discharge capacities were 283 and 245 mAh / g, and the coulombic efficiency was 87%.

In addition, the cycle life characteristics of the battery using the positive electrode active material of Example 1 was charged and discharged three times at 0.2C, four times at 1C, five times at 3C, seven times at 5C, 11 times at 10C, and 20 times at 15C. The results are shown in (a) of FIG. 4, and the cycle life characteristics of 50 charge / discharge cycles at 1 C are shown in FIG. 4 (b).

As shown in (a) of FIG. 4, the capacity retention rate at 15C to 0.2C was 90%, and 98% even after repeated cycles at 15C. In addition, as shown in Fig. 4B, the capacity retention rate was 92% after 50 cycles at 1C.

In addition, in order to determine the rate characteristics according to the particle distribution and particle size, for example, in the Li [Ni _0.20 Li _0.2 Mn _0.6 ] O ₂ nanoparticles of Comparative Example 1, primary particles having an average particle diameter of 80-200 nm are aggregated. It is distributed as secondary particles (aggregates) having an average particle diameter of 1-20 µm. The nanoparticles of Comparative Example 1 exhibited a single discharge capacity of about 280 mAh / g at 20 mA / g, but the discharge capacity was significantly reduced from 210 mA / g to 400 mAh / g.

In contrast, the nanowire positive electrode active material of Example 1 had a uniform diameter of about 50 nm, and a discharge capacity of 245 mAh / g at 48 mA / g, and 200 mAh / g at 3000 mA / g was obtained. It can be seen that it is very superior to Example 1.

In addition, an average particle diameter of Li [Li Ni _{0 .41 0 .08 0 .51} Mn] O ₂ nanoparticles (BET specific surface area was 24m ² / g) of Comparative Example 2 20-200nm capacity retention ratio is at 1200mA / g current speed , 89%, while nanowires were 94%, very high. This capacity retention is very large, especially at high current rates.

From these results, it can be predicted that the capacity retention rate of nanowires will be much higher than nanoparticles at current rates of 1200 mA / g or more. These results show that nanowires with high specific surface area increase the area of contact between the active material layer of the electrode and the electrolyte, thereby reducing the diffusion path of the active material particles into the lattice, and also reducing the strain of lithium intercalation. Therefore, it is thought to exhibit improved cycle characteristics than nanoparticles.

All simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

1 is a graph showing X-ray diffraction measurements of Co _0.4 Mn _0.6 O ₂ nanowires and Li _0.88 [Li _0.12 Co _0.33 Mn _0.49 ] O ₂ nanowires prepared in Example 1 of the present invention.

Figure 2 is a Co _{0 .4} Mn _{0 .6} O ₂ nanowires of a TEM image (a) and the produced _{Li 0 .88 [Li 0 .12 Co} 0 .33 Mn 0 .49 prepared in Example 1 of the present invention; ] SEM photograph (b), TEM photograph (d), HREM photograph (e), and EDS measurement result (c) of the O ₂ nanowire positive electrode active material.

3 illustrates 0.2C, 1C, 3C, 5C, 10C and 15C (1C = 240mAh / g) corresponding to 245, 242, 238, 230, 225 and 220mAh / g of a battery using the positive electrode active material of Example 1 of the present invention. ) Graph showing the initial discharge capacity and voltage after charging and discharging at a rate of discharge (charge rate is fixed at 1C) between 4.8 and 2V.

4 is a cycle life characteristic result of performing 20 charge / discharge cycles at 0.2C to 15C, increasing the charge / discharge rate of the battery using the positive electrode active material of Example 1 of the present invention, and charging / discharging 50 times at 1C. Graph showing cycle life characteristic results (b).

Claims (15)

Cathode active material for electrochemical cells comprising a compound represented by the following formula (1) having a nanowire shape [Formula 1] Li _x [Li _1-yz M ¹ _y M ² _z ] O _2-α D _α Wherein 0.8 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.5, 0 ≦ α ≦ 0.05, M ¹ and M ² are one or more different transition metal elements, D is selected from the group consisting of O, F, S, P, and combinations thereof) The method of claim 1, M ¹ is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, and combinations thereof, Wherein M ² is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe and combinations thereof. The method of claim 1, The nanowire is a positive electrode active material for an electrochemical cell having a length of 0.5㎛ 50㎛. The method of claim 1, The nanowires have a diameter of 50nm to 100nm positive electrode active material for an electrochemical cell. The method of claim 1, The cathode active material is a cathode active material for an electrochemical cell having a layered structure. Preparing oxide nanowires containing M ¹ and M ² ; Mixing the oxide nanowires with a lithium compound; Leaving the mixture; Drying the neglected product The manufacturing method of the positive electrode active material for electrochemical cells represented by following General formula (1) which has a nanowire shape containing a process. [Formula 1] Li _x [Li _1-yz M ¹ _y M ² _z ] O _2-α D _α Wherein 0.8 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.5, 0 ≦ α ≦ 0.05, M ¹ and M ² are one or more different transition metal elements, D is selected from the group consisting of O, F, S, P, and combinations thereof) The method of claim 6, The mixing ratio of the oxide nanowires and the lithium compound is 1: 2 to 1: 4 weight ratio of the manufacturing method of the positive electrode active material for electrochemical cells. The method of claim 6, In the step of mixing the oxide nanowires and the lithium compound, a method for producing a positive electrode active material for an electrochemical cell which is further added to a metal compound. The method of claim 6, The leaving process is carried out at 200 to 250 ° C. for 12 to 48 hours. The method of claim 6, The drying process is a method for producing a positive electrode active material for an electrochemical cell that is carried out at 100 to 200 ℃ for 12 to 48 hours. The method of claim 6, Oxide nanowires containing the M ¹ and M ² A gel was prepared by adding a gel former to the M ¹ compound solution; First heat treating the gel; Mixing the heat treated gel with a M ² compound; Method of producing a positive electrode active material for an electrochemical cell which is prepared by a process of secondary heat treatment of the mixture. The method of claim 11, The gel forming agent is fumaric acid manufacturing method of the positive electrode active material for an electrochemical cell. The method of claim 11, The primary heat treatment is a method of producing a positive electrode active material for an electrochemical cell that is carried out at 400 to 700 ℃ for 1 to 20 hours. The method of claim 11, The secondary heat treatment is a method for producing a positive electrode active material for an electrochemical cell that is carried out at 150 to 250 ℃ for 2 to 48 hours. A positive electrode including a positive electrode active material; A negative electrode including a negative electrode active material; And Contains an electrolyte, The electrochemical cell, wherein the positive electrode active material is the positive electrode active material according to any one of claims 1 to 5.

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