Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G53/00—Compounds of nickel
  • C01G53/40—Nickelates
  • C01G53/42—Nickelates containing alkali metals, e.g. LiNiO2
  • C01G53/44—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese
  • C01G53/50—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese of the type [MnO2]n-, e.g. Li(NixMn1-x)O2, Li(MyNixMn1-x-y)O2
• • H—ELECTRICITY
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
• • H—ELECTRICITY
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
  • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
  • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/50—Solid solutions
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  • C01P2002/54—Solid solutions containing elements as dopants one element only
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  • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
  • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
• • C—CHEMISTRY; METALLURGY
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  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
  • C01P2002/77—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by unit-cell parameters, atom positions or structure diagrams
• • C—CHEMISTRY; METALLURGY
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  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/11—Powder tap density
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  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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  • C01P2006/40—Electric properties
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  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/80—Compositional purity
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/10—Process efficiency
  • Y02P20/129—Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines

Definitions

• the present invention relates to a Ni-based lithium mixed transition metal oxide and a cathode active material for a secondary battery comprising the same. More specifically, the Ni-based lithium mixed transition metal oxide according to the present invention has a given composition and exhibits intercalation/deintercalation of lithium ions into/from mixed transition metal oxide layers ("MO layers") and interconnection of MO layers via the insertion of some MO layer-derived Ni ions into intercalation/deintercalation layers (reversible lithium layers) of lithium ions, thereby improving the stability of the crystal structure upon charge/discharge to provide an excellent sintering stability.
• a battery comprising such a cathode active material can exert a high capacity and a high cycle stability.
• lithium mixed transition metal oxide exhibits excellent storage stability and chemical resistance, and decreased gas evolution, thereby resulting in an excellent high-temperature stability and the feasibility of mass production at low costs.
• lithium secondary batteries having a high-energy density and voltage, a long cycle lifespan and a low self-discharge rate are commercially available and widely used.
• lithium-containing cobalt oxide As cathode active materials for the lithium secondary batteries, lithium- containing cobalt oxide (LiCoO 2 ) is largely used. In addition, consideration has been made of using lithium-containing manganese oxides such as LiMnO 2 having a layered crystal structure and LiMn 2 O 4 having a spinel crystal structure, and lithium-containing nickel oxides (LiNiO 2 ).
• LiCoO 2 is currently widely used due to superior general properties including excellent cycle characteristics, but suffers from low safety, expensiveness due to finite resources of cobalt as a raw material, and limitations in practical and mass application thereof as a power source for electric vehicles (EVs) and the like.
• Lithium manganese oxides such as LiMnO 2 and LiMn 2 O 4
• LiMnO 2 and LiMn 2 O 4 are abundant resources as raw materials and advantageously employ environmentally-friendly manganese, and therefore have attracted a great deal of attention as a cathode active material capable of substituting LiCoO 2 .
• these lithium manganese oxides suffer from shortcomings such as a low capacity and poor cycle characteristics.
• lithiutn/nickel-based oxides including LiNiO 2 are inexpensive as compared to the aforementioned cobalt-based oxides and exhibit a high discharge capacity upon charging Io 4.3 V.
• the reversible capacity of doped LiNiO 2 approximates about 200 mAh/g which exceeds the capacity of LiCoO 2 (about 165 mAh/g). Therefore, despite a slightly lower average discharge voltage and a slightly lower volumetric density, commercial batteries comprising LiNiO 2 as the cathode active material exhibit an improved energy density.
• the LiNiO 2 - based cathode active materials suffer from some limitations in practical application thereof, due to the following problems.
• LiNi ⁇ 2 -based oxides undergo sharp phase transition of the crystal structure with volumetric changes accompanied by repeated charge/discharge cycling, and thereby may suffer from cracking of particles or formation of voids in grain boundaries. Consequently, intercalation/deintercalation of lithium ions may be hindered to increase the polarization resistance, thereby resulting in deterioration of the charge/discharge performance.
• conventional prior arts attempted to prepare a LiNiO 2 -based oxide by adding an excess of a Li source and reacting reaction components under an oxygen atmosphere.
• the thus-prepared cathode active material under the charged state, undergoes structural swelling and destabilization due to the repulsive force between oxygen atoms, and suffers from problems of severe deterioration in cycle characteristics due to repeated charge/discharge cycles.
• LiNiO 2 has a problem associated with evolution of an excess of gas during storage or cycling. That is, in order to smoothly form the crystal structure, an excess of a Li source is added during manufacturing of the LiNiO 2 -based oxide, followed by heat treatment. As a result, water-soluble bases including Li 2 CO 3 and LiOH as reaction residues remain between primary particles and thereby they decompose or react with electrolytes to thereby produce CO 2 gas, upon charging.
• LiNiO 2 particles have an agglomerate secondary particle structure in which primary particles are agglomerated to form secondary particles and consequently a contact area with the electrolyte further increases to result in severe evolution of CO 2 gas, which in turn unfortunately leads to the occurrence of battery swelling and deterioration of the high- temperature safety.
• LiNiO 2 suffers from a sharp decrease in the chemical resistance of a surface thereof upon exposure to air and moisture, and gelation of slurries by polymerization of a NMP-PVDF slurry due to a high pH value. These properties of LiNiO 2 cause severe processing problems during battery production.
• a lithium source such as LiOH-H 2 O
• a mixed transition metal hydroxide under an oxygen or syngas atmosphere (i.e. CO 2 -deficient atmosphere)
• an additional step such as intermediary washing or coating, is included to remove impurities in the production of LiNiO 2 , this leads to a further increase in production costs.
• the present invention provides a lithium mixed transition metal oxide having a novel structure with a specific composition formula and interconnection of reversible lithium intercalation/deintercalation layers via the insertion of some of mixed transition metal oxide layer-derived Ni ions into the reversible lithium layers.
• the aforesaid prior art oxide has a structure different than that of the lithium mixed transition metal oxide of the present invention, that is, suffers from significant problems associated with severe gas evolution at high temperatures and structural stability, resulting from the inclusion of large amounts of impurities such as lithium carbonates, instead of having the reversible lithium layer with partial insertion of Ni ions.
• a lithium mixed transition metal oxide as will be illustrated hereinafter, has a given composition and a specific atomic-level structure, it is possible to realize superior thermal stability, and high cycle stability in conjunction with a high capacity, due to improvements in the stability of the crystal structure upon charge/discharge. Further, such a lithium mixed transition metal oxide can be prepared in a substantially water-soluble base-free form and therefore exhibits excellent storage stability, reduced gas evolution and thereby excellent high-temperature safety in conjunction with the feasibility of industrial-scale production at low production costs. The present invention has been completed based on these findings.
• FIG. 1 is a schematic view showing a crystal structure of a conventional Ni- based lithium transition metal oxide
• FIG. 2 is a schematic view showing a crystal structure of a Ni-based lithium mixed transition metal oxide according to an embodiment of the present invention
• FIGS. 3 and 4 are graphs showing a preferred composition range of a Ni-based lithium mixed transition metal oxide according to the present invention.
• FIG. 5 is an FESEM (Field Emission Scanning Electron Microscope) image (x
• 6A FESEM image of a sample as received
• 6B FESEM image of a sample after heating to 850 ° C in air;
• FIG. 7 is an FESEM image showing the standard pH titration curve of commercial high-Ni LiNiO 2 according to Comparative Example 2.
• A Sample as received
• B After heating of a sample to 800 °C under an oxygen atmosphere
• C Copy of A;
• FIG. 8 is a graph showing a pH titration curve of a sample according to Comparative Example 3 during storage of the sample in a wet chamber.
• A Sample as received
• B After storage of a sample for 17 hrs
• C After storage of a sample for 3 days;
• FIG. 9 is a graph showing a pH titration curve of a sample according to Example 2 during storage of the sample in a wet chamber.
• A Sample as received
• B After storage of a sample for 17 hrs
• C After storage of a sample for 3 days;
• FIG. 10 is an SEiM image of a sample according to Example 3.
• FIG. 11 shows the Rietveld refinement on X-ray diffraction patterns of a sample according to Example 3.
• FIG. 12 is a graph showing electrochemical properties Of LiNiMO 2 according to Example 3 in Experimental Example 1.
• 12A Graph showing voltage profiles and rate characteristics at room temperature (1 to 7 cycles);
• 7B Graph showing cycle stability at 25 ° C and 60 ° C and a rate of C/5 (3.0 to 4.3V);
• 7C Graph showing discharge profiles (at C/10 rate) for Cycle 2 and Cycle 31, obtained during cycling at 25 0 C and 60 °C;
• FIG. 13 is a graph showing DCS values for samples of Comparative Examples 3 and 4 in Experimental Example 2.
• FIG. 14 is a graph showing DCS values for LiNiMO 2 according to Example 3 in Experimental Example 2;
• FIG. 15 is a graph showing electrophysical properties of a polymer cell according to one embodiment of the present invention in Experimental Example 3;
• FIG. 16 is a graph showing swelling of a polymer cell during high-temperature storage in Experimental Example 3.
• FIG. 17 is a graph showing lengths of a-axis and c-axis of crystallographic unit cells of samples having different ratios of Li:M in Experimental Example 4.
• a lithium mixed transition metal oxide having a composition represented by Formula I below, wherein lithium ions undergo intercalation/deintercalation into/from mixed transition metal oxide layers ("MO layers”) and some of MO layer-derived Ni ions are inserted into intercalation/deintercalation layers of lithium ions ("reversible lithium layers”) thereby resulting in the interconnection between the MO layers.
• MO layers mixed transition metal oxide layers
• reversible lithium layers intercalation/deintercalation layers
• A is a dopant
• a conventional lithium transition metal oxide has a layered crystal structure as shown in FIG. 1, and performs charge/discharge processes through lithium insertion and desertion into/from the MO layers.
• the oxide having such a structure is used as a cathode active material, desertion of lithium ions from the reversible lithium layers in the charged state brings about swelling and destabilization of the crystal structure due to the repulsive force between oxygen atoms in the MO layers, and thus suffers from problems associated with sharp decreases in the capacity and cycle characteristics, resulting from changes in the crystal structure due to repeated charge/discharge cycles.
• the lithium mixed transition metal oxide in accordance with the present invention does not undergo disintegration of the crystal structure with maintenance of the oxidation number of Ni ions inserted into the reversible lithium layers, thereby being capable of maintaining a well-layered structure, even when lithium ions are released during a charge process.
• a battery comprising the lithium mixed transition metal oxide having such a structure as a cathode active material can exert a high capacity and a high-cycle stability.
• the lithium mixed transition metal oxide in accordance with the present invention is very excellent in the thermal stability as the crystal structure is stably maintained even upon sintering at a relatively high temperature during a production process.
• LiMO 2 when conventional high-nickel LiMO 2 is subjected to high- temperature sintering in air containing a trace amount of CO 2 , LiMO 2 decomposes with a decrease of Ni 3+ as shown in the following reaction below, during which amounts of impurities Li 2 CO 3 increase.
• the lithium mixed transition metal oxide in accordance with the present invention due to the stability of the atomic-level structure, does not involve formation of Li 2 CO 3 impurities resulting from oxygen deficiency due to decrease and decomposition of Ni 3+ as shown in the above reaction, in conjunction with no degradation of the crystal structure, even when it is subjected to high-temperature sintering under an air atmosphere. Further, there are substantially no water-soluble bases, as the lithium mixed transition metal oxide of the present invention can be prepared without addition of an excess of a lithium source. Accordingly, the lithium mixed transition metal oxide of the present invention exhibits excellent storage stability, decreased gas evolution and thereby excellent high- temperature stability simultaneously with the feasibility of industrial-scale production at low production costs.
• lithium mixed transition metal oxide in accordance with the present invention is used interchangeably with the term “LiNiMO 2 ", and the term “Ni inserted and bound into the reversible lithium layers” is used interchangeably with the term “inserted Ni”. Therefore, NiM in LiNiMO 2 is a suggestive expression representing a complex composition of Ni, Mn and Co in Formula I.
• the lithium mixed transition metal oxide may have a structure wherein Ni 2+ and Ni 3+ coexist in the MO layers and some of Ni 2+ are inserted into the reversible lithium layers. That is, in such a structure of the metal oxide, all of Ni ions inserted into the reversible lithium layers are Ni 2+ and the oxidation number of Ni ions is not changed in the charge process.
• Ni 2+ and Ni 3+ coexist in a Ni-excess lithium transition metal oxide, an oxygen atom-deficient state is present under given conditions (reaction atmosphere, Li content, etc.) and therefore insertion of some Ni 2+ ions into the reversible lithium layers may occur with changes in the oxidation number of Ni.
• composition of the lithium mixed transition metal oxide should satisfy the following specific requirements as defined in Formula I:
• Nii. (a+b) means a content of Ni 3+ . Therefore, if a mole fraction of Ni 3+ exceeds 0.35 (a+b ⁇ 0.65), it is impossible to implement an industrial-scale production in air, using Li 2 C ⁇ 3 as a raw material, so the lithium transition metal oxide should be produced using LiOH as a raw material under an oxygen atmosphere, thereby presenting a problems associated with decreased production efficiency and consequently increased production costs. On the other hand, if a mole fraction of Ni 3+ is lower than 0.15 (a+b > 0.85), the capacity per volume of LiNiMO 2 is not competitive as compared to LiCoO 2 .
• the total mole fraction of Ni including Ni 2+ and Ni 3+ in LiNiMO 2 of the present invention is preferably a relatively nickel-excess as compared to manganese and cobalt and may be in a range of 0.4 to 0.7. If a content of nickel is excessively low, it is difficult to achieve a high capacity. Conversely, if a content of nickel is excessively high, the safety may be significantly lowered. In conclusion, the lithium transition metal oxide (LiNiMO 2 ) exhibits a large volume capacity and low raw material costs, as compared to lithium cobalt-based oxides.
• the mole fraction of Ni 2+ should be appropriately adjusted taking into consideration such problems that may occur.
• the mole fraction of Ni 2+ may be in a range of 0.05 to 04, based on the total content of Ni.
• Ni 2+ is inserted into and serves to support the MO layers
• Ni 2+ is preferably contained in an amount enough to stably support between MO layers such that the charge stability and cycle stability can be improved to a desired level, and at the same time it is inserted in an amount not so as to hinder intercalation/deintercalation of lithium ions into/from the reversible lithium layers such that rate characteristics are not deteriorated.
• the mole fraction of Ni 2+ inserted and bound into the reversible layers may be preferably in a range of 0.03 to 0.07, based on the total content ofNi.
• the content of Ni 2+ or the content of inserted Ni 2+ may be determined by controlling, for example, a sintering atmosphere, the content of lithium, and the like. Therefore, when a concentration of oxygen in the sintering atmosphere is high, the content OfNi 2+ will be relatively low.
• a content of cobalt (b) is in a range of 0.1 to 0.4. If the content of cobalt is excessively high (b > 0.4), the overall cost of a raw material increases due to a high content of cobalt, and the reversible capacity somewhat decreases. On the other hand, if the content of cobalt is excessively low (b ⁇ 0.1), it is difficult to achieve sufficient rate characteristics and a high powder density of the battery at the same time.
• LiNiMO 2 may further comprise trace amounts of dopants.
• the dopants may include aluminum, titanium, magnesium and the like, which are incorporated into the crystal structure.
• other dopants such as B, Ca, Zr, F, P, Bi, Al, Mg, Zn, Sr, Ga, In, Ge, and Sn, may be included via the grain boundary accumulation or surface coating of the dopants without being incorporated into the crystal structure.
• These dopants are included in amounts enough to increase the safety, capacity and overcharge stability of the battery while not causing a significant decrease in the reversible capacity. Therefore, a content of the dopant is in a range of less than 5% (k ⁇ 0.05), as defined in Formula I.
• the dopants may be preferably added in an amount of ⁇ 1%, within a range that can improve the stability without causing deterioration of the reversible capacity.
• a ratio (Li/M) of Li to the transition metal (M) decreases, the amount of Ni inserted into the MO layers gradually increases. Therefore, if excessive amounts of Ni ions go down into the reversible lithium layers, a movement of Li + during charge/discharge processes is hampered to thereby lead to problems associated with a decrease in the reversible capacity or deterioration of the rate characteristics.
• the Li/M ratio is excessively high, the amount of Ni inserted into the MO layer is excessively low, which may undesirably lead to structural instability, thereby presenting decreased safety of the battery and poor lifespan characteristics. Further, at an excessively high Li/M value, amounts of unreacted Li 2 CO 3 increase to thereby result in a high pH-titration value, i.e. production of large amounts of impurities, and consequently the chemical resistance and high-temperature stability may be deteriorated. Therefore, in one preferred embodiment, the ratio of Li:M in LiNiMO 2 may be in a range of 0.95 to 1.04: 1.
• the lithium mixed transition metal oxide in accordance with the present invention is substantially free of water-soluble base impurities, particularly Li 2 CO 3 .
• Ni-based lithium transition metal oxides contain large amounts of water-soluble bases such as lithium oxides, lithium sulfates, lithium carbonates, and the like.
• These water-soluble bases may be bases, such as Li 2 CO 3 and LiOH, present in LiNiMO 2 , or otherwise may be bases produced by ion exchange (H + (water) ⁇ r -> Li + (surface, an outer surface of the bulk)), performed at the surface Of LiNiMO 2 .
• the bases of the latter case are usually present as a negligible level.
• the former water-soluble bases are formed primarily due to unreacted lithium raw materials upon sintering. This is because as a conventional Ni-based lithium transition metal oxide employs relatively large amounts of lithium and low-temperature sintering so as to prevent the collapse of a layered crystal structure, the resulting metal oxide has relatively large amounts of grain boundaries as compared to the cobalt-based oxides and lithium ions do not sufficiently react upon sintering.
• LiNiMO 2 in accordance with the present invention since LiNiMO 2 in accordance with the present invention, as discussed hereinbefore, stably maintains the layered crystal structure, it is possible to carry out a sintering process at a relatively high-temperature under an air atmosphere and thereby LiNiMO 2 has relatively small amounts of grain boundaries.
• the particle surfaces are substantially free of lithium salts such as lithium carbonates, lithium sulfates, and the like.
• there is no need to add an excess of a lithium source upon production of LiNiMO 2 so it is possible to fundamentally prevent a problem associated with the formation of impurities due to the unreacted lithium source remaining in the powder.
• the phrase "is (are) substantially free of water-soluble bases” refers to an extent that upon titration of 200 mL of a solution containing the lithium mixed transition metal oxide with 0.1M HCl, a HCl solution used to reach a pH of less than 5 is preferably consumed in an amount of less than 20 mL, more preferably less than 10 mL.
• 200 mL of the aforementioned solution contains substantially all kinds of the water-soluble bases in the lithium mixed transition metal oxide, and is prepared by repeatedly soaking and decanting 1O g of the lithium mixed transition metal oxide.
• a cathode active material powder is added to 25 mL of water, followed by brief stirring.
• About 20 mL of a clear solution is separated and pooled from the powder by soaking and decanting. Again, about 20 mL of water is added to the powder and the resulting mixture is stirred, followed by decanting and pooling. The soaking and decanting are repeated at least 5 times. In this manner, total 100 mL of the clear solution containing water-soluble bases is pooled.
• a 0.1M HCl solution is added to the thus-pooled solution, followed by pH titration with stirring. The pH profile is recorded as a function of time.
• a flow rate may be selected within a range that titration takes about 20 to 30 min.
• the content of the water-soluble bases is given as an amount of acid that was used until the pH reaches a value of less than 5.
• a method of preparing the lithium mixed transition metal oxide in accordance with the present invention may be preferably carried out under an oxygen-deficient atmosphere.
• the oxygen -deficient atmosphere may be an atmosphere with an oxygen concentration of preferably 10% to 50%, more preferably 10% to 30%.
• the lithium mixed transition metal oxide can be prepared by a solid-state reaction of Li 2 CO 3 and mixed transition metal precursors in the air atmosphere. Therefore, it is also possible to solve various problems associated with increased production costs and the presence of large amounts of water-soluble bases, which are suffered by conventional arts of making the lithium transition metal oxide involving adding, mixing and sintering of LiOH and each transition metal precursor under an oxygen atmosphere.
• the present invention enables production of the lithium mixed transition metal oxide having a given composition and a high content of nickel via a simple solid-state reaction in air, using a raw material that is cheap and easy to handle. Therefore, it is possible to realize a significant reduction of production costs and high-efficiency mass production.
• the lithium mixed transition metal oxide in accordance with the present invention employs Li 2 CO 3 and the mixed transition metal precursor as the reaction materials, and can be prepared by reacting reactants in an oxygen-deficient atmosphere, preferably in air.
• an oxygen-deficient atmosphere preferably in air.
• the lithium mixed transition metal oxide in accordance with the present invention is very excellent in the sintering stability at high temperatures, i.e. the thermodynamic stability, due to a stable crystal structure.
• the lithium source material and the mixed transition metal material may be preferably added in a ratio of 0.95 to 1.04:1 when producing the lithium mixed transition metal oxide in accordance with the present invention, there is no need to add an excess of a lithium source and it is possible to significantly reduce the possibility of retention of the water-soluble bases which may derive from the residual lithium source.
• a heat exchanger may be employed to further enhance the efficiency of energy utilization by pre-warming the in-flowing air before it enters the reactor, while cooling the out-flowing air.
• a cathode active material for a secondary battery comprising the aforementioned lithium nickel-based oxide.
• the cathode active material in accordance with the present invention may be comprised only of the lithium mixed transition metal oxide having the above-specified composition and the specific atomic-level structure, or where appropriate, it may be comprised of the lithium mixed transition metal oxide in conjunction with other lithium- containing transition metal oxides.
• lithium-containing transition metal oxides may include, but are not limited to, layered compounds such as lithium cobalt oxide (LiCoO 2 ) and lithium nickel oxide (LiNiO 2 ), or compounds substituted with one or more transition metals; lithium manganese oxides such as compounds of Formula Li 1+y Mn 2- y0 4 (0 ⁇ y ⁇ 0.33), LiMnC ⁇ 3 , LiMn 2 O 3 , and LiMnO 2 ; lithium copper oxide (Li 2 CuO 2 ); vanadium oxides such as LiV 3 Os, V 2 O 5, and Cu 2 V 2 O 7 ; Ni-site type lithium nickel oxides of Formula LiNii.
• layered compounds such as lithium cobalt oxide (LiCoO 2 ) and lithium nickel oxide (LiNiO 2 ), or compounds substituted with one or more transition metals
• lithium manganese oxides such as compounds of Formula Li 1+y Mn 2- y0 4 (0 ⁇ y ⁇ 0.33), LiMnC ⁇ 3 , LiMn 2 O 3
• y M y O 2 Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and 0.01 ⁇ y ⁇ 0.3); lithium manganese composite oxides of Formula LiMn 2 .
• a lithium secondary battery comprising the aforementioned cathode active material.
• the lithium secondary battery is generally comprised of a cathode, an anode, a separator and a lithium salt-containing non-aqueous electrolyte. Methods for preparing the lithium secondary battery are well-known in the art and therefore detailed description thereof will be omitted herein.
• the cathode is, for example, fabricated by applying a mixture of the above- mentioned cathode active material, a conductive material and a binder to a cathode current collector, followed by drying. If necessary, a filler may be further added to the above mixture.
• the cathode current collector is generally fabricated to have a thickness of 3 to 500 ⁇ m.
• materials for the cathode current collector there is no particular limit to materials for the cathode current collector, so long as they have high conductivity without causing chemical changes in the fabricated battery.
• the materials for the cathode current collector mention may be made of stainless steel, aluminum, nickel, titanium, sintered carbon, and aluminum or stainless steel which was surface-treated with carbon, nickel, titanium or silver.
• the current collector may be fabricated to have fine irregularities on the surface thereof so as to enhance adhesion to the cathode active material.
• the current collector may take various forms including films, sheets, foils, nets, porous structures, foams and non- woven fabrics.
• the conductive material is typically added in an amount of 1 to 50% by weight, based on the total weight of the mixture including the cathode active material.
• the conductive material there is no particular limit to the conductive material, so long as it has suitable conductivity without causing chemical changes in the fabricated battery.
• conductive materials including graphite such as natural or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fibers and metallic fibers; metallic powders such as carbon fluoride powder, aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives.
• the binder is a component assisting in binding between the electrode active material and the conductive material, and in binding of the electrode active material to the current collector.
• the binder is typically added in an amount of 1 to 50% by weight, based on the total weight of the mixture including the cathode active material.
• binder examples include polyvinylidene fluoride, polyvinyl alcohols, carboxymethyleellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinyl pyrollidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluoro rubber and various copolymers.
• the filler is an optional ingredient used to inhibit cathode expansion. There is no particular limit to the filler, so long as it does not cause chemical changes in the fabricated battery and is a fibrous material.
• the filler there may be used olefin polymers such as polyethylene and polypropylene; and fibrous materials such as glass fiber and carbon fiber.
• the anode is fabricated by applying an anode active material to an anode current collector, followed by drying. If necessary, other components as described above may be further included.
• the anode current collector is generally fabricated to have a thickness of 3 to 500 ⁇ m.
• materials for the anode current collector there is no particular limit to materials for the anode current collector, so long as they have suitable conductivity without causing chemical changes in the fabricated battery.
• materials for the anode current collector mention may be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel having a surface treated with carbon, nickel, titanium or silver, and aluminum-cadmium alloys.
• the anode current collector may also be processed to form fine irregularities on the surfaces thereof so as to enhance adhesion to the anode active material.
• the anode current collector may be used in various forms including films, sheets, foils, nets, porous structures, foams and non-woven fabrics.
• carbon such as non-graphitizing carbon and graphite-based carbon
• metal composite oxides such as LI y Fe 2 O 3 (0 ⁇ y ⁇ l), LI y WO 2 (O ⁇ y ⁇ l) and Sn x Me 1 - X MeVO 2 (Me: Mn, Fe, Pb or Ge; Me 1 : Al, B, P, Si, Group I, Group II and Group III elements of the Periodic Table of the Elements, or halogens; 0 ⁇ x ⁇ l; l ⁇ y ⁇ 3; and l ⁇ z ⁇ 8); lithium metals; lithium alloys; silicon-based alloys; tin-based alloys; metal oxides such as SnO, SnO 2 , PbO, PbO 2 , Pb 2 O 3 , Pb 3 O 4 , Sb 2 O 3 , Sb 2 O 4 , Sb 2 O 5 , GeO, GeO 2 , Bi 2 O 3 , Bi
• the separator is interposed between the cathode and anode.
• an insulating thin film having high ion permeability and mechanical strength is used.
• the separator typically has a pore diameter of 0.01 to 10 im and a thickness of 5 to 300 ⁇ m.
• sheets or non-woven fabrics made of an olefin polymer such as polypropylene and/or glass fibers or polyethylene, which have chemical resistance and hydrophobicity are used.
• a solid electrolyte such as a polymer
• the solid electrolyte may also serve as both the separator and electrolyte.
• the lithium salt-containing non-aqueous electrolyte is composed of an electrolyte and a lithium salt.
• a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte may be utilized.
• organic solid electrolyte utilized in the present invention, mention may be made of polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohols, polyvinylidene fluoride, and polymers containing ionic dissociation groups.
• inorganic solid electrolyte utilized in the present invention, mention may be made of nitrides, halides and sulfates of lithium such as Li 3 N, LiI, Li 5 NI 2 , Li 3 N-LiI-LiOH, LiSiO 4 , LiSiO 4 -LiI-LiOH, Li 2 SiS 3 , Li 4 SiO 4 , Li 4 SiO 4 -LiI-LiOH, and Li 3 PO 4 -Li 2 S-SiS 2 .
• nitrides, halides and sulfates of lithium such as Li 3 N, LiI, Li 5 NI 2 , Li 3 N-LiI-LiOH, LiSiO 4 , LiSiO 4 -LiI-LiOH, Li 2 SiS 3 , Li 4 SiO 4 , Li 4 SiO 4 -LiI-LiOH, and Li 3 PO 4 -Li 2 S-SiS 2 .
• the lithium salt is a material that is readily soluble in the above-mentioned non-aqueous electrolyte and may include, for example, LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiB 10 Cl 10 , LiPF 6 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiAlCl 4 , CH 3 SO 3 Li, CFsSO 3 Li, (CF 3 SO 2 ) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate, and imide.
• pyridine triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxy ethanol, aluminum trichloride, or the like may be added to the non-aqueous electrolyte.
• the non-aqueous electrolyte may further include halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride. Further, in order to improve high-temperature storage characteristics, the non-aqueous electrolyte may additionally include carbon dioxide gas.
• a lithium mixed transition metal oxide comprising a mixed transition metal of Ni, Mn and Co, wherein lithium ions undergo intercalation/deintercalation into/from mixed-transition metal oxide layers ("MO layers”) and some of MO layer-derived Ni ions are inserted into intercalation/deintercalation layers of lithium ions (“reversible lithium layers”) thereby resulting in interconnection of the MO layers.
• the use of nickel-based lithium mixed transition metal oxide as the cathode active material may bring about the collapse of the crystal structure upon intercalation/deintercalation of lithium ions.
• the lithium mixed transition metal oxide in accordance with the present invention exhibits stabilization of the crystal structure due to nickel ions inserted into the reversible lithium layers and therefore does not undergo additional structural collapse that may result from oxygen desorption, thereby simultaneously improving the lifespan characteristics and safety.
• the present invention provides a lithium mixed transition metal oxide having a composition represented by Formula II below, wherein a cation mixing ratio with location of some Ni in lithium sites is in a range of 0.02 to 0.07 based on the total content of Ni, to thereby stably support the layered crystal structure.
• M" is a mixed transition metal of Ni, Mn and Co
• A' is at least one element selected from the group consisting of B, Ca, Zr, S, F, P, Bi, Al, Mg, Zn, Sr, Cu, Fe, Ga, In, Cr, Ge and Sn.
• the cation mixing ratio is particularly preferably in a range of 0.02 to 0.07, upon considering both of the charge and cycle stability and the rate characteristics. When the cation mixing ratio is within the above-specified range, the crystal structure can be further stably maintained and intercalation/deintercalation of lithium ions can be maximized.
• the present invention provides a lithium mixed transition metal oxide having a composition of Formula II, wherein a ratio of lithium to a mixed transition metal (M) is in a range of 0.95 to 1.04, and some Ni are inserted into lithium sites to thereby stably support a layered crystal structure.
• the lithium mixed transition metal oxide exhibits excellent stability, lifespan characteristics and rate characteristics. Further, this metal oxide has a high capacity, as well as high chemical resistance and high-temperature stability due to substantially no water-soluble bases.
• the lithium mixed transition metal oxide having a composition of Formula II and the ratio of lithium to the mixed transition metal (M) of 0.95 to 1.04 may be a lithium mixed transition metal oxide wherein a cation mixing ratio with location of some Ni in lithium sites is in a range of 0.02 to 0.07 based on the total content of Ni to thereby stably support the layered crystal structure.
• a range of the cation mixing ratio is as defined above.
• the present invention provides a lithium mixed transition metal oxide comprising mixed transition metal oxide layers ("MO layers") of Ni, Mn and Co, and lithium-ion intercalation/deintercalation layers (reversible lithium layers), wherein the MO layers and the reversible lithium layers are alternately and repeatedly disposed to form a layered crystal structure, the MO layers contain Ni 3+ and Ni 2+ , and some Ni 2+ ions derived from the MO layers are inserted into the reversible lithium layers.
• MO layers mixed transition metal oxide layers
• reversible lithium layers lithium-ion intercalation/deintercalation layers
• the present invention provides a lithium mixed transition metal oxide having a composition of Formula I and showing intercalation/deintercalation of lithium ions into/from mixed transition metal oxide layers ("MO layers"), wherein the MO layers contain Ni 3+ and Ni 2+ , and some Ni 2+ ions derived from the MO layers are inserted into the reversible lithium layers, due to preparation of the lithium mixed transition metal oxide by a reaction of raw materials under an 0 2 -deficient atmosphere.
• MO layers mixed transition metal oxide layers
• a conventional lithium transition metal oxide has a crystal structure with no insertion of Ni 2+ ions into the MO layer by the reaction of raw materials under an oxygen atmosphere
• the lithium mixed transition metal oxide in accordance with the present invention has a structure wherein relatively large amounts of Ni 2+ ions are produced by carrying out the reaction under an oxygen-deficient atmosphere and some of the thus-produced Ni 2+ ions are inserted into the reversible lithium layers. Therefore, as illustrated hereinbefore, the crystal structure is stably maintained to thereby exert superior sintering stability, and a secondary battery comprising the same exhibits excellent cycle stability.
• secondary particles were maintained intact without being collapsed, and the crystal size increased with an increase in the sintering temperature.
• a unit cell volume did not exhibit a significant change with an increase in the sintering temperature, thus representing that there was no significant oxygen-deficiency and no significant increase of cation mixing, in conjunction with essentially no occurrence of lithium evaporation.
• the crystallographic data for the thus-prepared lithium mixed transition metal oxide are given in Table 1 below, and FESEM images thereof are shown in FIG. 5. From these results, it was confirmed that the lithium mixed transition metal oxide is LiNiMO 2 having a well-layered crystal structure with the insertion of nickel at a level of 3.9 to 4.5% into a reversible lithium layer. Further, it was also confirmed that even though Li 2 CO 3 was used as a raw material and sintering was carried out in air, proper amounts of Ni 2+ ions were inserted into the lithium layer, thereby achieving the structural stability.
• Sample B sintered at 900 ° C, exhibited a high c:a ratio and therefore excellent crystallinity, a low unit cell volume and a reasonable cation mixing ratio.
• Sample B showed the most excellent electrochemical properties, and a BET surface area of about 0.4 to 0.8 m 2 /g.
• FIG. 6 shows a FESEM image of a commercial sample as received and a FESEM image of the same sample heated to 850 "C in air; and it can be seen that the sample heated to a temperature of T ⁇ 850 ° C exhibited structural collapse. This is believed to be due to that Li 2 CO 3 , formed during heating in air, melts to thereby segregate particles.
• the pH titration was carried out at a flow rate of > 2 L/min for 400 g of a commercial sample having a composition of LiNio.sCoo. 2 O 2 .
• the results thus obtained are given in FIG. 7.
• Curve A represents pH titration for the sample as received
• Curve B represents pH titration for the sample heated to 800 ° C in a flow of pure oxygen for 24 hours. From the analysis results of pH profiles, it can be seen that the contents of Li 2 CO 3 before and after heat treatment were the same therebetween, and there was no reaction of Li 2 CO 3 impurities.
• the pH titration was carried out for a sample of the lithium mixed transition metal oxide in accordance with Example 2 prior to exposure to moisture, and samples stored in a wet chamber (90% RH) at 60 ° C in air for 17 hours and 3 days, respectively.
• the results thus obtained are given in FIG. 9.
• the sample of Comparative Example 3 stored for 17 hours
• the sample of Comparative Example 3 exhibited consumption of about 20 mL of HCl
• the sample of Example 2 stored for 17 hours
• exhibited consumption of 10 mL of HCl thus showing an about two-fold decrease in production of the water-soluble bases.
• the sample of Comparative Example 3 exhibited consumption of about 110 mL of HCl, whereas the sample of Example 2 exhibited consumption of 26 mL of HCl, which corresponds to an about five-fold decrease in production of the water-soluble bases. Therefore, it can be seen that the sample of Example 2 decomposed at a rate about five-fold slower than that of the sample of Comparative Example 3. Then, it can be confirmed that the lithium mixed transition metal oxide of Example 2 exhibits superior chemical resistance even when it is exposed to air and moisture.
• pH titration 12 mL of 0.1 M HCl was consumed per 1O g cathode, an initial content of Li 2 COs was low, and the content of Li 2 CO 3 after storage was slightly lower (80 to 90%) as compared to the sample of Comparative Example 3, but a higher content of Li 2 CO 3 was formed than in the sample of Example 2. Consequently, it was confirmed that the aforementioned high-Ni LiNiO 2 shows no improvements in the stability against exposure to the air even when it was surface- coated, and also exhibits insignificant improvements in the electrochemical properties such as the cycle stability and rate characteristics.
• FIG. 10 shows an SEM image of the thus-prepared cathode active material
• FIG. 11 shows results of Rietveld refinement. Referring to these drawings, it was confirmed that the sample exhibits high crystallinity and well-layered structure, a mole fraction of Ni 2+ inserted into a reversible lithium layer is 3.97%, and the calculated value and the measured value of the mole fraction of Ni 2+ are approximately the same.
• Example 6 respectively, as a cathode, and a lithium metal as an anode.
• the cells of Comparative Examples 5 and 6 exhibited a crystallographic density of 4.7 and 4.76 g/cm 3 , respectively, which were almost the same, and showed a discharge capacity of 157 to 159 niAh/g at a C/10 rate (3 to 4.3 V).
• a volume capacity of the cell of Comparative Example 5 is equal to a 93% level of LiCoO 2
• the cell of Comparative Example 6 exhibits a crystallographic density corresponding to a 94% level of LiCoO 2 . Therefore, it can be seen that a low content of Ni results in a poor volume capacity.
• a crystallographic density OfLiNiMO 2 in accordance with Example 3 was 4.74 g/cm 3 (cf. LiCoO 2 : 5.05 g/cm 3 ).
• a discharge capacity was more than 170 mAh/g (cf. LiCoO 2 : 157 mAh/g) at C/20, thus representing that the volume capacity of LiNiMO 2 was much improved as compared to LiCoO 2 .
• Table 4 summarizes electrochemical results of coin cells using LiNiMO 2 in accordance with Example 3 as a cathode, and FIG. 12 depicts voltage profiles, discharge curves and cycle stability.
• Comparative Example 3 Al/Ba-modified LiNiO 2
• Comparative Example 4 AlPO 4 -coated LiNiO 2
• the total accumulation of heat generation was large, i.e. well above 2000 kJ/g, thus indicating a low thermal stability (see FIG. 13).
• LiNiMO 2 of Example 3 in accordance with the present invention exhibited a low total heat evolution, and the initiation of an exothermic reaction at a relatively high temperature (about 260 "C) as compared to Comparative Examples 3 and 4 (about 200 °C) (see FIG. 14). Therefore, it can be seen that the thermal stability of LiNiMO 2 in accordance with the present invention is very excellent.
• Example 3 Using the lithium mixed transition metal oxide of Example 3 as a cathode active material, a pilot plant polymer cell of 383562 type was fabricated.
• the cathode was mixed with 17% LiCoO 2 , and the cathode slurry was NMP/PVDF-based slurry. No additives for the purpose of preventing gelation were added.
• the anode was MCMB.
• the electrolyte was a standard commercial electrolyte free of additives known to reduce excessive swelling. Experiments were carried out at 60 ° C and charge and discharge rates of C/5. A charge voltage was in a range of 3.0 to 4.3 V.
• FIG. 15 shows the cycle stability of the battery of the present invention (0.8 C charge, 1C discharge, 3 to 4 V, 2 V) at 25 0 C .
• An exceptional cycle stability (91% at C/l rate after 300 cycles) was achieved at room temperature. The impedance build up was low. Also, the gas evolution during storage was measured. The result thus obtained are given in FIG. 16.
• a 4 h-90 ° C fully charged (4.2 V) storage a very small amount of gas was evolved and only a small increase of thickness was observed. The increase of thickness was within or less than the value expected for good LiCoO 2 cathodes tested in similar cells under similar conditions. Therefore, it can be seen that LiNiMO 2 in accordance with the present invention exhibits very high stability and chemical resistance.
• Table 5 below provides the obtained crystallographic data.
• the unit cell volume changes smoothly according to the Li:M ratio.
• FIG. 17 shows its crystallographic map. AU samples are located on a straight line. According to the results of pH titration, the content of soluble base increases slightly with an increase of the Li:M ratio. The soluble base probably originates from the surface basicity (ion exchange) but not from the dissolution of Li 2 C ⁇ 3 impurities as observed in Comparative Example 1.
• the ratio of Li:M is particularly preferably in a range of 0.95 to 1.04 (Samples B, C and D) to ensure that the value of Ni 2+ inserted into the lithium layer is in a range of 3 to 7%.
• a lithium transition metal oxide was prepared in the same manner as in Example 4, except that a ratio of Li:M was set to 1 : 1 and sintering was carried out under an O 2 atmosphere. Then, X-ray analysis was carried out and the cation mixing was observed. The results thus obtained are given in Table 6 below.
• the lithium transition metal oxide of Comparative Example 7 exhibited a significantly low cation mixing ratio due to the heat treatment under the oxygen atmosphere. This case suffers from deterioration of the structural stability. That is, it can be seen that the heat treatment under the oxygen atmosphere resulted in the development of a layered structure due to excessively low cation mixing, but migration of Ni 2+ ions was hindered to an extent that the cycle stability of the battery is arrested.
• the cation mixing was observed by X-ray analysis and Rietveld refinement. The results thus obtained are given in Table 7 below.
• the cation mixing was observed by X-ray analysis and Rietveld refinement. The results thus obtained are given in Table 8 below.
• a lithium mixed transition metal oxide in accordance with the present invention has a specified composition and interconnection of MO layers via the insertion of some MO layer-derived Ni ions into reversible lithium layers, whereby the crystal structure can be stably supported to thereby prevent the deterioration of cycle characteristics.
• such a lithium mixed transition metal oxide exhibits a high battery capacity and is substantially free of impurities such as water-soluble bases, thereby providing excellent storage stability, decreased gas evolution and consequently superior high-temperature stability.

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