CN114566624B - Positive electrode active material for lithium secondary battery and lithium secondary battery comprising same - Google Patents
Positive electrode active material for lithium secondary battery and lithium secondary battery comprising same Download PDFInfo
- Publication number
- CN114566624B CN114566624B CN202210202055.5A CN202210202055A CN114566624B CN 114566624 B CN114566624 B CN 114566624B CN 202210202055 A CN202210202055 A CN 202210202055A CN 114566624 B CN114566624 B CN 114566624B
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- Prior art keywords
- lithium
- transition metal
- composite oxide
- metal composite
- potassium
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- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 95
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 94
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 53
- 229910052723 transition metal Inorganic materials 0.000 claims abstract description 119
- 239000002905 metal composite material Substances 0.000 claims abstract description 110
- 239000002245 particle Substances 0.000 claims abstract description 108
- 239000011164 primary particle Substances 0.000 claims abstract description 69
- OBTSLRFPKIKXSZ-UHFFFAOYSA-N lithium potassium Chemical compound [Li].[K] OBTSLRFPKIKXSZ-UHFFFAOYSA-N 0.000 claims abstract description 41
- 150000003112 potassium compounds Chemical class 0.000 claims description 61
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 38
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical group [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 claims description 35
- 229910052700 potassium Inorganic materials 0.000 claims description 35
- 239000011591 potassium Substances 0.000 claims description 35
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 31
- 239000000843 powder Substances 0.000 claims description 30
- 238000000034 method Methods 0.000 claims description 22
- 238000005406 washing Methods 0.000 claims description 20
- 238000004519 manufacturing process Methods 0.000 claims description 19
- 239000002904 solvent Substances 0.000 claims description 17
- 238000002156 mixing Methods 0.000 claims description 16
- 239000002243 precursor Substances 0.000 claims description 14
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 13
- 229910052717 sulfur Inorganic materials 0.000 claims description 13
- 239000011593 sulfur Substances 0.000 claims description 13
- CHKVPAROMQMJNQ-UHFFFAOYSA-M potassium bisulfate Chemical group [K+].OS([O-])(=O)=O CHKVPAROMQMJNQ-UHFFFAOYSA-M 0.000 claims description 11
- 229910000343 potassium bisulfate Inorganic materials 0.000 claims description 11
- 238000002149 energy-dispersive X-ray emission spectroscopy Methods 0.000 claims description 10
- 150000003624 transition metals Chemical class 0.000 claims description 8
- 238000010438 heat treatment Methods 0.000 claims description 7
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims description 7
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 6
- YQCIWBXEVYWRCW-UHFFFAOYSA-N methane;sulfane Chemical compound C.S YQCIWBXEVYWRCW-UHFFFAOYSA-N 0.000 claims description 6
- 229910052760 oxygen Inorganic materials 0.000 claims description 6
- 239000001301 oxygen Substances 0.000 claims description 6
- MBORNUMAQYILPP-UHFFFAOYSA-N [K].[Li][S] Chemical compound [K].[Li][S] MBORNUMAQYILPP-UHFFFAOYSA-N 0.000 claims description 4
- 239000012298 atmosphere Substances 0.000 claims description 3
- 239000000243 solution Substances 0.000 description 26
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 21
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- 238000000926 separation method Methods 0.000 description 9
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 3
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 3
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- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- 239000011149 active material Substances 0.000 description 2
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- 150000001868 cobalt Chemical class 0.000 description 2
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- HXJUTPCZVOIRIF-UHFFFAOYSA-N sulfolane Chemical compound O=S1(=O)CCCC1 HXJUTPCZVOIRIF-UHFFFAOYSA-N 0.000 description 1
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical compound S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 description 1
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 1
- 229910001887 tin oxide Inorganic materials 0.000 description 1
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- 239000003981 vehicle Substances 0.000 description 1
- 229910052727 yttrium Inorganic materials 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
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
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
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- 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
-
- 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
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- 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
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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- 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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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- 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
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- Chemical & Material Sciences (AREA)
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- General Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Composite Materials (AREA)
- Manufacturing & Machinery (AREA)
- Crystallography & Structural Chemistry (AREA)
- Battery Electrode And Active Subsutance (AREA)
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Abstract
The positive electrode active material for a lithium secondary battery according to an embodiment of the present invention includes lithium-transition metal composite oxide particles including a plurality of primary particles, the lithium-transition metal composite oxide particles including lithium-potassium-containing portions formed between the primary particles. The life characteristics and capacity characteristics can be improved by preventing deformation of the layered structure of the primary particles and removing residual lithium.
Description
Technical Field
The present invention relates to a positive electrode active material for a lithium secondary battery and a method for manufacturing the same. And more particularly, to a positive electrode active material for a lithium metal oxide-based lithium secondary battery and a method for manufacturing the same.
Background
The secondary battery is a battery that can be repeatedly charged and discharged, and with the development of information communication and display industries, the secondary battery has been widely used as a power source for various portable electronic communication devices, such as video cameras, mobile phones, notebook computers, and the like. In addition, in recent years, a battery pack including a secondary battery has also been developed and applied to a power source of an environment-friendly vehicle such as a hybrid vehicle.
Examples of the secondary battery may include a lithium secondary battery, a nickel-cadmium battery, a nickel-hydrogen battery, and the like, in which the operating voltage and the energy density per unit weight of the lithium secondary battery are high, which is advantageous in terms of charging speed and light weight, and thus research and development are actively underway.
The lithium secondary battery may include: an electrode assembly including a positive electrode, a negative electrode, and a separation membrane (separator); and an electrolyte impregnating the electrode assembly. In addition, the lithium secondary battery may further include a case in the form of, for example, a soft pack, which accommodates the electrode assembly and the electrolyte.
As the positive electrode active material of the lithium secondary battery, a lithium-transition metal composite oxide can be used. Examples of the lithium-transition metal composite oxide may include nickel-based lithium metal oxide.
As the application range of lithium secondary batteries expands, lithium secondary batteries having longer life, high capacity and operation stability are demanded. In the lithium-transition metal composite oxide used as the positive electrode active material, when chemical structure is not uniform due to lithium precipitation or the like, it may be difficult to realize a lithium secondary battery having a desired capacity and life. In addition, when the lithium-transition metal composite oxide structure is deformed or damaged upon repeated charge and discharge, life stability and capacity retention characteristics may be lowered.
For example, korean patent publication No. 10-0821523 discloses a method for removing lithium salt impurities by washing lithium-transition metal composite oxide with water, but there are limitations in sufficiently removing impurities and damage to particle surfaces may be caused in the water washing process.
[ Prior Art literature ]
Korean patent publication No. 10-0821523
Disclosure of Invention
Technical problem to be solved
An object of the present invention is to provide a positive electrode active material for a lithium secondary battery having improved working stability and electrochemical characteristics, and a method for manufacturing the same.
An object of the present invention is to provide a lithium secondary battery having improved operational stability and electrochemical characteristics.
Technical proposal
The positive electrode active material for a lithium secondary battery according to an embodiment of the present invention includes: a lithium-transition metal composite oxide particle comprising a plurality of primary particles, wherein the lithium-transition metal composite oxide particle comprises lithium-potassium containing moieties formed between the primary particles.
In some embodiments, the lithium-potassium-containing moiety may include a lithium-potassium-sulfur-containing moiety that contains lithium, potassium, and sulfur.
In some embodiments, the primary particles may have a close-packed hexagonal (hexagonal close-packed) structure.
In some embodiments, the lithium-transition metal composite oxide particles may not include primary particles having a face-centered cubic (FACE CENTERED cubic) structure.
In some embodiments, the sulfur content of the lithium-transition metal composite oxide particles, as measured by a carbon-sulfur (CS) analyzer, may be 1100ppm to 4500ppm relative to the total weight of the lithium-transition metal composite oxide particles.
In some embodiments, the potassium concentration of the lithium-potassium containing moiety measured by Energy Dispersive Spectroscopy (EDS) may be greater than the potassium concentration in the primary particles measured by the EDS.
In some embodiments, the average value of the potassium signal of the lithium-potassium containing fraction measured by the EDS may be 1.2 to 4 times the average value of the potassium signal in the primary particles measured by the EDS.
In some embodiments, the content of lithium carbonate (Li 2CO3) remaining on the surface of the lithium-transition metal composite oxide particles may be 2500ppm or less, and the content of lithium hydroxide (LiOH) remaining on the surface of the lithium-transition metal composite oxide particles may be 2500ppm or less.
The method for manufacturing a positive electrode active material for a lithium secondary battery according to an embodiment of the present invention includes the steps of: preparing primary lithium-transition metal composite oxide particles; mixing the primary lithium-transition metal composite oxide particles with an aqueous potassium compound solution; and heat-treating the mixed primary lithium-transition metal composite oxide particles and the aqueous potassium compound solution to form lithium-transition metal composite oxide particles including a plurality of primary particles and lithium-potassium-containing portions formed between the primary particles.
In some embodiments, the aqueous potassium compound solution is formed by mixing a solvent with a potassium compound powder, which may be added in an amount of 0.2 to 1.9 wt% relative to the total weight of the primary lithium-transition metal composite oxide particles.
In some embodiments, the solvent may be added in an amount of 2 to 15 wt% relative to the total weight of the primary lithium-transition metal composite oxide particles.
In some embodiments, the potassium compound powder may be potassium hydrogen sulfate (KHSO 4) powder.
In some embodiments, the heat treatment may be performed at 200 ℃ to 400 ℃ under an oxygen atmosphere.
In some embodiments, the primary lithium-transition metal composite oxide particles may be mixed with the aqueous potassium compound solution without a water washing treatment.
The lithium secondary battery according to an embodiment of the present invention includes: a positive electrode including a positive electrode active material layer including the positive electrode active material for a lithium secondary battery according to the above-described embodiment; and a negative electrode disposed opposite to the positive electrode.
Advantageous effects
The positive electrode active material according to an embodiment of the present invention may include lithium-transition metal composite oxide particles including a plurality of primary particles, and the lithium-transition metal composite oxide particles may include lithium-potassium-containing portions formed between the primary particles. In this case, residual lithium located on the surface of the lithium-transition metal composite oxide is converted into the lithium-potassium containing moiety by reaction with a potassium containing compound, so that initial capacity and battery efficiency characteristics can be improved.
In some embodiments, by forming lithium-potassium containing moieties having a close-packed hexagonal structure between primary particles in the lithium-transition metal composite oxide, the surfaces of the primary particles are protected by the lithium-potassium containing moieties, so that life characteristics and driving stability can be improved.
In the method of manufacturing a positive electrode active material according to an embodiment of the present invention, the potassium compound aqueous solution may be prepared by mixing 2 to 15 wt% of a solvent with respect to the total weight of the primary lithium-transition metal composite oxide particles with 0.2 to 1.9 wt% of a potassium compound powder with respect to the total weight of the primary lithium-transition metal composite oxide particles, without including a water washing treatment process. The aqueous potassium compound solution may be mixed with primary lithium-transition metal composite oxide particles.
In this case, it is possible to prevent the primary particles of the lithium-transition metal composite oxide particles from deforming from the close-packed hexagonal structure to the face-centered cubic structure during the water washing treatment. Thus, the initial capacity and life characteristics of the secondary battery can be prevented from being reduced. Further, residual lithium located between the surface portion of the lithium-transition metal composite oxide particles and the primary particles is removed, so that deterioration of life characteristics due to gas generation can be prevented, and battery resistance is reduced, so that initial capacity can be improved.
Drawings
Fig. 1 is a process flow diagram illustrating a method of manufacturing a positive electrode active material according to an exemplary embodiment.
Fig. 2 and 3 are schematic plan and sectional views of a lithium secondary battery according to an exemplary embodiment, respectively.
FIG. 4 is an HR-TEM image of lithium-transition metal composite oxide particles according to example 1.
FIG. 5 is an HR-TEM image of lithium-transition metal composite oxide particles according to comparative example 1.
Fig. 6 is an FFT image in the region a of fig. 4 (B) and the region B of fig. 5 (B).
Fig. 7 is a graph showing potassium signal values of the primary particle regions and the regions between the primary particles (e.g., lithium-potassium-containing portions) of examples 1 to 5.
Description of the reference numerals
100: Positive electrode 105: positive electrode current collector
107: Positive electrode lead 110: positive electrode active material layer
120: Negative electrode active material layer 125: negative electrode current collector
127: Negative electrode lead 130: negative electrode
140: Separation membrane 150: electrode assembly
160: Outer casing
Detailed Description
Embodiments of the present invention provide a positive electrode active material including lithium-transition metal composite oxide particles and a lithium secondary battery including the positive electrode active material.
Hereinafter, embodiments of the present invention are described in detail. However, these embodiments are merely examples, and the present invention is not limited to the specific embodiments described as examples.
In an exemplary embodiment, the positive electrode active material may include lithium-transition metal composite oxide particles including a plurality of primary particles, and the lithium-transition metal composite oxide particles may include lithium-potassium (Li-K) -containing portions formed between the primary particles.
In some embodiments, the primary particles may have a crystallographic single-crystal or polycrystalline structure.
For example, the primary particles may include nickel (Ni), and may further include at least one of cobalt (Co) or manganese (Mn).
For example, the primary particles may be represented by the following chemical formula 1.
[ Chemical formula 1]
LiaNixM1-xO2+y
In chemical formula 1, a may be 0.9.ltoreq.a.ltoreq.1.2, x may be 0.5.ltoreq.x.ltoreq.0.99, and y may be-0.1.ltoreq.z.ltoreq.0.1. M may represent at least 1 element selected from Na, mg, ca, Y, ti, zr, hf, V, nb, ta, cr, mo, W, mn, co, fe, cu, ag, zn, B, al, ga, C, si, sn, ba or Zr.
In some preferred embodiments, the molar ratio or concentration x of Ni in chemical formula 1 may be 0.8 or more.
For example, when the composition having a High nickel (High-Ni) content in which x is 0.8 or more is employed, calcination of the lithium-transition metal composite oxide particles may be performed at a relatively low temperature. In this case, the amount of residual lithium generated on the surfaces of the lithium-transition metal composite oxide particles can be increased. Accordingly, in order to remove the residual lithium, a water washing process or a non-water washing process (e.g., an initial wetting process) may be performed. Thus, for example, when x is 0.8 or more, the above-described process for removing residual lithium may have a substantial meaning.
Ni may be provided as a transition metal related to power and capacity of a lithium secondary battery. Therefore, as described above, by employing a high nickel composition in the lithium-transition metal composite oxide particles, a high power positive electrode and a high power lithium secondary battery can be provided.
However, as the Ni content increases, the long-term storage stability and life stability of the positive electrode or the secondary battery may relatively deteriorate. However, according to the exemplary embodiment, conductivity may be maintained by including Co, and life stability and capacity retention characteristics may be improved by Mn.
In some embodiments, the lithium-potassium-containing moiety may include a lithium-potassium-sulfur (Li-K-S) containing lithium, potassium, and sulfur (S). For example, the lithium-potassium containing moiety may include LiKSO 4. In this case, the power characteristics of the secondary battery can be improved due to the excellent conductivity of LiKSO 4.
In some embodiments, the primary particles of the lithium-transition metal composite oxide particles may have a close-packed hexagonal (hexagonal close-packed) structure. Therefore, a large amount of lithium and transition metal elements having a layered form stable structure can be included even in a small space, so that the capacity characteristics and the life characteristics of the secondary battery can be improved.
In some embodiments, the potassium concentration of the lithium-potassium containing moiety as measured by Energy Dispersive Spectroscopy (EDS) may be greater than the potassium concentration in the primary particles as measured by the EDS. In this case, the lithium-transition metal composite oxide particles may form a concentration gradient between the primary particles and the lithium-potassium containing portion.
For example, the average value of the potassium signal of the lithium-potassium containing fraction measured by the EDS may be 1.2 to 4 times the average value of the potassium signal in the primary particles.
When the ratio of the average value of the potassium signals satisfies the above range, lithium-potassium-containing portions having a close-packed hexagonal structure can be sufficiently formed between the primary particles included in the lithium-transition metal composite oxide particles. In this case, the surface of the primary particles may be protected by the lithium-potassium containing moiety, thereby reducing the area of the primary particles exposed to the electrolyte. Therefore, the life characteristics of the secondary battery can be improved. In addition, since the residual lithium on the surface of the lithium-transition metal composite oxide particles is in a state where it has been sufficiently removed, the electrochemical characteristics of the secondary battery can be improved.
In some embodiments, the content of lithium precursor remaining on the surfaces of the lithium-transition metal composite oxide particles may be adjusted.
For example, the content of lithium carbonate (Li 2CO3) remaining on the surfaces of the lithium-transition metal composite oxide particles may be 2500ppm or less, and the content of lithium hydroxide (LiOH) remaining on the surfaces of the lithium-transition metal composite oxide particles may be 2500ppm or less.
When the contents of lithium carbonate and lithium hydroxide satisfy the above ranges, resistance is reduced at the time of lithium ion migration, so that initial capacity characteristics and power characteristics of the lithium secondary battery can be improved, and life characteristics at the time of repeated charge and discharge can be improved.
In some embodiments, the sulfur content included in the lithium-transition metal composite oxide particles may be 1100ppm to 4500ppm relative to the total weight of the lithium-transition metal composite oxide particles. For example, the lithium-sulfur compound present on the surface of the lithium-transition metal composite oxide particles can not only protect the surface of the particles from the electrolyte, but can also advantageously act on the electrolyte and the migration of lithium ions on the surface. In this case, while the residual lithium and the potassium compound described below are sufficiently removed, deterioration of capacity characteristics and lifetime characteristics due to excessive addition of potassium can be prevented. Therefore, the power characteristics can be maintained while improving the capacity retention rate of the secondary battery.
For example, the sulfur content may be measured by a carbon-sulfur (CS) analyzer.
Fig. 1 is a process flow diagram illustrating a method of manufacturing a positive electrode active material according to an exemplary embodiment.
Hereinafter, a method of manufacturing the above-described exemplary embodiment of a positive electrode active material for a lithium secondary battery will be provided with reference to fig. 1.
Referring to fig. 1, primary lithium-transition metal composite oxide particles may be prepared (e.g., step S10).
For example, primary lithium-transition metal composite oxide particles may be prepared by reacting a transition metal precursor with a lithium precursor. The transition metal precursor (e.g., ni-Co-Mn precursor) may be prepared by a coprecipitation reaction.
For example, the transition metal precursor may be prepared by a coprecipitation reaction of a metal salt. The metal salts may include nickel salts, manganese salts, and cobalt salts.
Examples of the nickel salt may include nickel sulfate, nickel hydroxide, nickel nitrate, nickel acetate, hydrates thereof, and the like. Examples of the manganese salt may include manganese sulfate, manganese acetate, hydrates thereof, and the like. Examples of the cobalt salt may include cobalt sulfate, cobalt nitrate, cobalt carbonate, hydrates thereof, and the like.
The metal salt may be mixed with a precipitant and/or a chelating agent in a ratio satisfying the content or concentration ratio of each metal described with reference to chemical formula 1 to prepare an aqueous solution. The aqueous solution may be co-precipitated in a reactor to produce a transition metal precursor.
The precipitants may include basic compounds such as sodium hydroxide (NaOH), sodium carbonate (Na 2CO3), and the like. The chelating agent may include, for example, aqueous ammonia (e.g., NH 3·H2 O), ammonium carbonate (e.g., NH 3HCO3), and the like.
The temperature of the coprecipitation reaction can be adjusted, for example, in the range of about 40 to 60 ℃. The reaction time may be adjusted in the range of about 24 hours to 72 hours.
The lithium precursor compound may include, for example, lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, lithium hydroxide, and the like. These compounds may be used singly or in combination of two or more.
In an exemplary embodiment, an aqueous potassium compound solution may be added to the primary lithium-transition metal composite oxide particles and mixed (e.g., step S20).
In some embodiments, the aqueous potassium compound solution may include a solvent and a potassium compound powder added to the solvent.
For example, the potassium compound powder may be added in an amount of 0.2 to 1.9 wt% relative to the total weight of the primary lithium-transition metal composite oxide particles. In this case, while the residual lithium and potassium compound are sufficiently reacted, deterioration of capacity characteristics and lifetime characteristics due to excessive addition of the potassium compound can be prevented. Therefore, with an appropriate sulfur content, a positive electrode active material having excellent life characteristics and capacity characteristics can be realized.
For example, the solvent may be used in an amount of 2 to 15 wt% relative to the total weight of the primary lithium-transition metal composite oxide particles. In this case, while the potassium compound powder is sufficiently dissolved, deformation of the layered structure of the primary particles due to addition of an excessive amount of solvent can be prevented. Therefore, the lifetime characteristics can be improved while maintaining the capacity characteristics and the power characteristics.
In some embodiments, the potassium compound powder may be added to the solvent such that its content is 50 wt% or less with respect to the weight of the solvent to prepare the aqueous potassium compound solution. When the potassium compound powder and the solvent are added in the above-mentioned ranges, the potassium compound powder is sufficiently dissolved in the solvent and the residual lithium and the potassium compound are sufficiently reacted, whereby the manufacturability can be improved.
In some embodiments, the potassium compound powder may be potassium hydrogen sulfate (KHSO 4) powder, and in this case, the aqueous potassium compound solution may be an aqueous KHSO 4 solution.
For example, the solvent may be pure water (de-ionized water, DIW).
In an exemplary embodiment, primary lithium-transition metal composite oxide particles and the aqueous potassium compound solution may be mixed. In this case, potassium and/or sulfur contained in the aqueous potassium compound solution may react with residual lithium present on the surfaces of the primary lithium-transition metal composite oxide particles to be converted into a lithium-potassium-containing portion (e.g., a lithium-potassium-sulfur-containing portion). Thus, lithium-transition metal composite oxide particles including primary particles and lithium-potassium-containing portions can be obtained.
For example, impurities present on the surfaces of the primary lithium-transition metal composite oxide particles may be removed by the mixing process. For example, in order to increase the yield of lithium metal oxide particles or the stability of the synthesis process, a lithium precursor (lithium salt) may be excessively used. In this case, lithium precursors including lithium hydroxide (LiOH) and lithium carbonate (Li 2CO3) may remain on the surfaces of the primary lithium-transition metal composite oxide particles.
In addition, for example, the higher the Ni content included in the lithium-transition metal composite oxide particles, the more the calcination can be performed at a lower temperature at the time of manufacturing the positive electrode. In this case, the residual lithium content on the surfaces of the lithium-transition metal composite oxide particles may increase.
When the residual lithium is removed by washing with water (water washing treatment) in substantially the same amount as the positive electrode active material, the residual lithium may be removed, but oxidation of the surface of the primary lithium-transition metal composite oxide particles and side reaction with water may be caused, possibly resulting in damage or collapse of the layered structure of the primary particles. In addition, since the layered structure is deformed into a face-centered cubic structure, a spinel structure, and/or a rock salt structure instead of a close-packed hexagonal structure due to water, the lithium-nickel-based oxide may be hydrolyzed to form nickel impurities, such as NiO or Ni (OH) 2.
However, according to the exemplary embodiment of the present invention, since the mixing process (e.g., initial wetting process) is performed using the aqueous solution of the potassium compound without performing the water washing process, passivation caused by the potassium-containing compound may be achieved on the surfaces of the lithium-transition metal composite oxide particles when the mixing process is performed. For example, lithium-potassium-containing moieties that combine lithium and potassium can be formed between primary particles having a close-packed hexagonal structure.
The term "incipient wetness method" used in the present invention means, for example, a method in which water or an aqueous solution of a potassium compound is added in an amount of 15% by weight or less relative to the total weight of the lithium-transition metal composite oxide particles by, for example, spraying or the like, without performing a water washing treatment in which water is added in an amount substantially the same as or similar to the total weight of the lithium-transition metal composite oxide particles and stirred.
Further, since the water washing treatment is not performed, for example, the lithium-transition metal composite oxide particles may not include primary particles having a face-centered cubic structure. Therefore, residual lithium can be effectively removed while preventing oxidation of the particle surface due to water and deterioration of the layered structure.
For example, when the potassium compound powder is directly mixed with the lithium-transition metal composite oxide particles instead of the aqueous potassium compound solution, since the potassium compound powder does not have capillary force (CAPILLARY FORCE), it cannot penetrate between the primary particles, and most of the potassium compound powder may react with residual lithium present on the surfaces of the secondary particles where the primary particles are aggregated. For example, it may be formed in a form in which lithium-potassium-containing portions are coated on the surfaces of the secondary particles. In this case, when immersed in the electrolyte, the surfaces of the primary particles cannot be sufficiently protected, and residual lithium remains on the surfaces between the primary particles, which may cause an increase in battery resistance. Therefore, the capacity and power characteristics of the battery may be degraded.
According to an exemplary embodiment of the present invention, the initial wetting method may be performed using an aqueous solution of a potassium compound as described above. In this case, the aqueous potassium compound solution permeates between the primary particles by capillary force and reacts with residual lithium between the primary particles, so that lithium-potassium-containing portions can be formed between the primary particles.
In some embodiments, the potassium compound content in the aqueous potassium compound solution may be 0.1 to 2wt% relative to the total weight of the primary lithium-transition metal composite oxide particles. In this case, the lithium-potassium-containing portion is formed to have an appropriate lithium/potassium content at a position where residual lithium originally exists between the surface portion of the primary lithium-transition metal composite oxide particles and the primary particles, substantially as in the case of the water washing treatment, and the layered structure of the primary particles can be prevented from being damaged or collapsed.
After the mixing process, a positive electrode active material including primary particles and a lithium-potassium-containing portion may be obtained through a heat treatment (calcination) process (e.g., step S30).
For example, the primary lithium-transition metal composite oxide particles and the lithium-potassium-containing portion subjected to the mixing process may be heat-treated using a calciner. Thereby, lithium-transition metal composite oxide particles in which lithium-potassium-containing portions are fixed between the primary particles can be obtained.
For example, the heat treatment may be performed at 200 ℃ to 400 ℃ under an oxygen atmosphere. In this case, the potassium compound of the aqueous solution of the residual lithium and potassium compound on the surfaces of the primary lithium-transition metal composite oxide particles can be sufficiently combined to form the lithium-potassium-containing portion.
Fig. 2 and 3 are schematic plan and sectional views of a lithium secondary battery according to an exemplary embodiment, respectively.
Hereinafter, a lithium secondary battery including a positive electrode including the positive electrode active material for a lithium secondary battery described above will be provided with reference to fig. 2 and 3.
Referring to fig. 2 and 3, the lithium secondary battery may include a positive electrode 100, a negative electrode 130, and a separation membrane 140, the positive electrode 100 including a positive electrode active material including the above-described lithium-potassium containing portion.
The positive electrode 100 may include a positive electrode active material layer 110, and the positive electrode active material layer 110 is formed by applying a positive electrode active material including the above-described lithium-transition metal composite oxide particles to the positive electrode current collector 105.
For example, the slurry may be prepared by mixing and stirring primary lithium-transition metal composite oxide particles mixed with an aqueous solution of a potassium compound with a binder, a conductive material, and/or a dispersant, etc. in a solvent. The slurry is applied to the positive electrode current collector 105, and then pressed and dried to prepare a positive electrode.
The positive electrode current collector 105 may include, for example, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably may include aluminum or an aluminum alloy.
The binder may include, for example, an organic binder such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile (polyacrylonitrile), polymethyl methacrylate (polymethyl methacrylate), or the like, or a water-based binder such as styrene-butadiene rubber (SBR), or the like, and may be used together with a thickener such as carboxymethyl cellulose (CMC).
For example, PVDF-based binders may be used as binders for forming the positive electrode. In this case, the amount of the binder for forming the positive electrode active material layer 110 may be reduced, and the amount of the positive electrode active material may be relatively increased, so that the power and capacity of the secondary battery may be improved.
The conductive material may be included to promote electron migration between active material particles. For example, the conductive material may include: carbon-based conductive materials such as graphite, carbon black, graphene, carbon nanotubes, and the like; and/or metal-based conductive materials including, for example, tin oxide, titanium oxide, perovskite (perovskie) species such as LaSrCoO 3、LaSrMnO3, and the like.
The anode 130 may include an anode current collector 125 and an anode active material layer 120 formed by coating an anode active material on the anode current collector 125.
The negative electrode active material may use any material known in the art that can intercalate and deintercalate lithium ions without particular limitation. For example, it is possible to use: carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, and the like; a lithium alloy; silicon or tin, etc. Examples of the amorphous carbon may include hard carbon, coke, mesophase carbon microspheres (mesocarbon microbead, MCMB) calcined at 1500 ℃ or less, mesophase pitch-based carbon fibers (mesophase pitch-based carbon fiber, MPCF), and the like. Examples of the crystalline carbon may include graphite-based carbon such as natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and the like. The elements included in the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, or the like.
Negative electrode current collector 125 may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, and preferably may include copper or copper alloys.
In some embodiments, the slurry may be prepared by mixing and stirring the anode active material with a binder, a conductive material, and/or a dispersant, etc. in a solvent. The slurry is applied to the negative electrode current collector, and then the negative electrode 130 may be prepared by pressing and drying.
As the binder and the conductive material, substantially the same or similar substances as described above can be used. In some embodiments, as a binder for forming the anode, for example, for compatibility with a carbon-based active material, a water-based binder such as styrene-butadiene rubber (SBR) or the like may be included, and may be used together with a thickener such as carboxymethyl cellulose (CMC).
The separation membrane 140 may be interposed between the positive electrode 100 and the negative electrode 130. The separation membrane 140 may include a porous polymer membrane made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, an ethylene/methacrylate copolymer, or the like. The separation membrane 140 may include a non-woven fabric formed of glass fiber having a high melting point, polyethylene terephthalate fiber, or the like.
According to an exemplary embodiment, an electrode unit is defined by the positive electrode 100, the negative electrode 130, and the separation film 140, and a plurality of the electrode units may be stacked to form an electrode assembly 150, for example, in the form of a jelly roll (jelly roll). For example, the electrode assembly 150 may be formed by winding (winding), laminating (lamination), folding (folding), or the like of the separation film 140.
The electrode assembly may be accommodated in the case 160 together with an electrolyte, so that a lithium secondary battery may be defined. According to an exemplary embodiment, the electrolyte may use a non-aqueous electrolyte.
The nonaqueous electrolytic solution includes a lithium salt as an electrolyte and an organic solvent. The lithium salt is represented by Li +X-, for example, and the anion (X -) of the lithium salt may include F-、Cl-、Br-、I-、NO3 -、N(CN)2 -、BF4 -、ClO4 -、PF6 -、(CF3)2PF4 -、(CF3)3PF3 -、(CF3)4PF2 -、(CF3)5PF-、(CF3)6P-、CF3SO3 -、CF3CF2SO3 -、(CF3SO2)2N-、(FSO2)2N-、CF3CF2(CF3)2CO-、(CF3SO2)2CH-、(SF5)3C-、(CF3SO2)3C-、CF3(CF2)7SO3 -、CF3CO2 -、CH3CO2 -、SCN-、(CF3CF2SO2)2N- or the like.
The organic solvent may be, for example, propylene carbonate (propylene carbonate, PC), ethylene carbonate (ethylene carbonate, EC), diethyl carbonate (diethyl carbonate, DEC), dimethyl carbonate (dimethyl carbonate, DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ -butyrolactone, propylene sulfite, tetrahydrofuran, and the like. These compounds may be used singly or in combination of two or more.
As shown in fig. 3, tabs (positive and negative tabs) may protrude from the positive and negative current collectors 105 and 125, respectively, belonging to each electrode unit, and may extend to one side of the case 160. The tab may be fused with the one side of the case 160 to form electrode leads (the positive electrode lead 107 and the negative electrode lead 127) extending or exposed to the outside of the case 160.
The lithium secondary battery may be manufactured, for example, in a cylindrical shape using a can, an angular shape, a soft pack (pouch), a coin shape (can), or the like.
According to an exemplary embodiment, the chemical stability of the positive electrode active material may be improved by doping or coating of a potassium-containing compound to suppress a decrease in capacity and average voltage, realizing a lithium secondary battery having improved life and long-term stability.
In the following, preferred embodiments are set forth to aid in understanding the present invention, but these embodiments are merely for illustrating the present invention and are not intended to limit the claims, and various changes and modifications may be made to the embodiments within the scope and technical spirit of the present invention, which will be apparent to those skilled in the art, and these modifications are within the scope of the claims.
Example 1
Preparation of Primary lithium-transition metal composite oxide particles (S10)
NiSO 4、CoSO4 and MnSO 4 were mixed in a ratio of 0.88:0.09:0.03, respectively, using distilled water from which internal dissolved oxygen was removed by bubbling with N 2 for 24 hours. The solution was put into a reactor at 50 ℃ and co-precipitation reaction was performed for 48 hours using NaOH and NH 3·H2 O as precipitants and chelating agents to obtain Ni 0.88Co0.09Mn0.03(OH)2 as a transition metal precursor. The precursor obtained was dried at 80 ℃ for 12 hours and then dried again at 110 ℃ for 12 hours.
Lithium hydroxide and the transition metal precursor are added into a dry high-speed mixer in a ratio of 1.01:1, and uniformly mixed for 5 minutes. The mixture was placed in a calciner, heated to 710 ℃ to 750 ℃ at a heating rate of 2 ℃/min, and maintained at 710 ℃ to 750 ℃ for 10 hours. Oxygen was continuously fed at a flow rate of 10 mL/min during the temperature increase and hold. After the calcination is completed, naturally cooled to room temperature, and pulverized and classified, primary lithium-transition metal composite oxide particles in the form of primary particles of the positive electrode active material LiNi 0.88Co0.09Mn0.03O2 are obtained.
Preparation of aqueous Potassium Compound solution, mixing (S20) and Heat treatment (S30)
Potassium hydrogen sulfate (KHSO 4) powder was added to pure water (deionized water, DIW) in an amount of 5 wt% relative to the total weight of the obtained primary lithium-transition metal composite oxide particles, and stirred after that, the potassium hydrogen sulfate powder was sufficiently dissolved in the pure water to prepare an aqueous potassium compound solution.
The prepared aqueous potassium compound solution was added to the primary lithium-transition metal composite oxide particles and mixed.
The mixture was put into a calciner, heated to a temperature between 200 ℃ and 400 ℃ at a heating rate of 2 ℃/min while oxygen was supplied at a flow rate of 10 mL/min, and maintained at the heated temperature for 10 hours. After calcination, the positive electrode active material was obtained by classification through 325 mesh (mesh).
Manufacturing of lithium secondary battery
A secondary battery was manufactured using the positive electrode active material. Specifically, the positive electrode active material, acetylene Black (Denka Black) as a conductive material, and PVDF as a binder were mixed at a mass ratio of 93:5:2, respectively, to prepare a positive electrode slurry, and then, the slurry was coated on an aluminum current collector and then dried and pressed to prepare a positive electrode. After the pressing, the target (target) electrode density of the positive electrode was adjusted to 3.0 g/milliliter (g/cc).
Lithium metal is used as the anode active material.
The positive electrode and the negative electrode prepared as above were cut (notching) into circles of diameters Φ14 and Φ16, respectively, and laminated, and an electrode unit was prepared by disposing a separation film (polyethylene, thickness: 13 μm) cut to Φ19 between the positive electrode and the negative electrode. The electrode unit is put into a coin-type battery shell with the diameter of 20mm and the height of 1.6mm, electrolyte is injected into the battery shell and assembled, and the battery shell is aged for more than 12 hours, so that the electrolyte impregnates the inside of the electrode.
The electrolyte was prepared by dissolving 1M LiPF 6 in an EC/EMC (30/70; volume ratio) mixed solvent.
The secondary battery prepared as described above was subjected to formation charge and discharge (charge condition CC-CV 0.1c 4.3v 0.005c CUT-OFF (CUT-OFF), discharge condition CC 0.1c 3v CUT-OFF).
Example 2
A positive electrode active material and a lithium secondary battery were obtained in the same manner as in example 1, except that potassium hydrogen sulfate (KHSO 4) powder was added in an amount of 0.4% by weight relative to the total weight of the primary lithium-transition metal composite oxide particles.
Example 3
A positive electrode active material and a lithium secondary battery were obtained in the same manner as in example 1, except that potassium hydrogen sulfate (KHSO 4) powder was added in an amount of 1.6% by weight relative to the total weight of the primary lithium-transition metal composite oxide particles.
Example 4
A positive electrode active material and a lithium secondary battery were obtained in the same manner as in example 1, except that potassium hydrogen sulfate (KHSO 4) powder was added in an amount of 0.1% by weight relative to the total weight of the primary lithium-transition metal composite oxide particles.
Example 5
A positive electrode active material and a lithium secondary battery were obtained in the same manner as in example 1, except that potassium hydrogen sulfate (KHSO 4) powder was added in an amount of 2.0% by weight relative to the total weight of the primary lithium-transition metal composite oxide particles.
Comparative example 1
A positive electrode active material and a lithium secondary battery were obtained in the same manner as in example 1, except that the step of mixing the primary lithium-transition metal composite oxide particles with an aqueous potassium compound solution was not performed, but the primary lithium-transition metal composite oxide particles were added to pure water in an amount of 100% by weight relative to the total weight of the primary lithium-transition metal composite oxide particles, stirred for 10 minutes, subjected to a water washing treatment and filtered, and then dried under vacuum at 130 to 170 ℃ for 12 hours.
Comparative example 2
A positive electrode active material and a lithium secondary battery were obtained in the same manner as in example 1, except that pure water was used instead of the aqueous potassium compound solution, and 5 wt% of pure water was added and mixed with respect to the total weight of the primary lithium-transition metal composite oxide particles.
The above examples and comparative example 2 were carried out by the initial wetting method by adding a small amount of solution or water, not by the water-washing treatment by adding substantially the same amount of water as the positive electrode active material; the water washing treatment was performed in comparative example 1.
Experimental example 1
(1) High resolution transmission electron microscope (High Resolution Transmission ElectronMicroscope, HR-TEM) and fast Fourier transform (Fast Fourier Transform, FFT) analysis
By performing HR-TEM analysis and FFT image analysis on cross sections of the lithium-transition metal composite oxide particles obtained according to the above examples and comparative examples, the structure of the compound present in the primary particle region and the lithium-potassium-containing portion (region between the primary particles) was analyzed.
(2) Calculation of mean value of Potassium Signal
The lithium-transition metal composite oxide particles obtained according to the above examples and comparative examples were subjected to Line scan (Line scan) by STEM-EDS, and the potassium signal value of the primary particle region and the region (e.g., lithium-potassium-containing portion) between the primary particles was continuously measured. Thereafter, the potassium signal average of the primary particles and the lithium-potassium-containing fraction was calculated by averaging the potassium signal values of each region.
(3) Measurement of Sulfur content
For measuring the sulfur (S) content, a C/S analyzer (carbon/sulfur analyzer; model name: CS844, manufacturer: LECO) was used, and the amount of the sample was selected based on the measurement value range of the standard sample measured at the time of drawing the calibration curve.
Specifically, 0.02g to 0.04g of the lithium-transition metal composite oxide particles obtained according to the above examples and comparative examples were added to a ceramic crucible, at which time the combustion improver (LECOCEL II) and the IRON filings (IRON chips) were added together in a ratio of 1:1.
Thereafter, O 2 as a combustion gas was supplied at a rate of 3L/min in a high-frequency induction furnace and burned at about 2600 ℃ to 2700 ℃. The sulfur oxide-based inorganic compound gas (e.g., sulfuric acid gas) generated by the combustion is passed through an infrared detection cell, and the change in the amount of infrared absorption compared to the blank (blank) is measured to quantitatively detect the sulfur content in the lithium-transition metal composite oxide particles.
The potassium hydrogen sulfate powder addition amount, the solvent addition amount, and the measurement and evaluation results of the above are shown in table 1 below.
TABLE 1
FIG. 4 is an HR-TEM image of lithium-transition metal composite oxide particles according to example 1. Specifically, fig. 4 (a) is an HR-TEM image of the lithium-transition metal composite oxide particles of example 1, and fig. 4 (b) is an HR-TEM image of the surface area (area 1) of the primary particles in fig. 4 (a) enlarged.
FIG. 5 is an HR-TEM image of lithium-transition metal composite oxide particles according to comparative example 1. Specifically, fig. 5 (a) is an HR-TEM image of the lithium-transition metal composite oxide particles of comparative example 1, and fig. 5 (b) is an HR-TEM image of the inner region (region 2) of the primary particles in fig. 5 (a) enlarged.
Fig. 6 is an FFT image in the region a of fig. 4 (B) and the region B of fig. 5 (B). Specifically, (a) of fig. 6 is an FFT image of the region a enlarged in (B) of fig. 4, and (B) of fig. 6 is an FFT image of the region B enlarged in (B) of fig. 5.
Referring to fig. 4 to 6, in the case of comparative example 1, since the water washing process was performed instead of the initial wetting process, the layered structure of the primary particle inner region (for example, region 2 of (a) of fig. 5 and region B of (B) of fig. 5) was also changed from the close-packed hexagonal structure to the face-centered cubic structure as shown in (B) of fig. 6, with a relatively low probability of the layered structure damage.
On the other hand, in the case of example 1 in which the mixing process (e.g., initial wetting) is performed by adding the aqueous solution of the potassium compound, the layered structure of the primary particles (e.g., region 1 of (a) of fig. 4 and region a of (b) of fig. 4) having a relatively high probability of deterioration of the layered structure is maintained in a close-packed hexagonal structure as shown in (a) of fig. 6.
Fig. 7 is a graph showing potassium signal values of the primary particle regions and the regions between the primary particles (e.g., lithium-potassium-containing portions) of examples 1 to 5.
As shown in fig. 7, in examples 1 to 3, the ratio of the average value of potassium signals in the region between primary particles to the average value of potassium signals in the primary particles (potassium signal ratio) satisfies the range of 1.2 to 4.
However, in the case of example 4 in which the addition amount of the potassium compound powder is less than 0.2% by weight relative to the primary lithium-transition metal composite oxide particles, the potassium signal ratio is less than 1.2 times, and therefore it is difficult to judge the lithium-potassium containing portion within the lithium-transition metal composite oxide particles.
Further, in the case of example 5 in which the addition amount of the potassium compound powder is greater than 1.9% by weight relative to the primary lithium-transition metal composite oxide particles, the potassium signal ratio exceeds 4 times.
On the other hand, in the case of example 1, the signal ratio of potassium from the region between the primary particles (for example, lithium-potassium-containing portion) to the 50nm interval was uniformly shown to be 2.63 times.
Experimental example 2
(1) Measurement of residual lithium (Li 2CO3, liOH) content
In a 250mL flask, 1.5g of the positive electrode active material of the examples and comparative examples was weighed, 100g of deionized water was added, and then a magnetic bar was placed, and stirred at 60rpm for 10 minutes. After that, filtration was performed using a vacuum flask, and 100g of the filtrate was taken. The obtained solution was placed in an automatic measuring instrument (automatic titrator (Auto titrator)) container and was automatically titrated with 0.1N HCl with reference to the Wader method to measure Li 2CO3 and LiOH contents in the solution.
(2) Measurement of initial charge-discharge capacity and evaluation of initial capacity efficiency
After the lithium secondary batteries prepared according to the above examples and comparative examples were charged in a chamber at 25 deg.c (CC-CV 0.1c 4.3v 0.005c cut-off), the battery capacity (initial charge capacity) was measured, and then discharged (CC 0.1c 3.0v cut-off), and then the battery capacity (initial discharge capacity) was measured.
The initial capacity efficiency was evaluated by converting the value of the measured initial discharge capacity divided by the measured initial charge capacity into a percentage (%).
(3) Measurement of capacity retention (Life characteristics) upon repeated charging and discharging
The lithium secondary batteries according to examples and comparative examples were repeatedly charged (CC/CV 0.5c 4.3v 0.05c cut-off) and discharged (CC 1.0c 3.0v cut-off) 300 times, and then the capacity retention rate was evaluated by dividing the 300 th discharge capacity by the percentage of the value of the first discharge capacity.
The evaluation results are shown in table 2 below.
TABLE 2
Referring to table 2, the example of performing the initial wetting by mixing the aqueous potassium compound solution generally reduced the lithium content remaining on the surface of the lithium-transition metal composite oxide particles, and the initial capacity efficiency was good, ensuring excellent life characteristics, as compared with the comparative example.
In the case of example 1, in which the ratio of the primary particles to the average value of the potassium signal of the lithium-potassium containing portion satisfies the prescribed range (for example, 1.2 to 4), not only the initial capacity is maintained, but also the passivation effect of the lithium-containing potassium compound formed by the reaction with the residual lithium on the surface of the lithium-transition metal composite oxide particles is ensured, as compared with comparative example 2 in which the initial wetting method is performed using only pure water of the same weight% instead of the aqueous potassium compound solution.
However, in the case of example 4 in which the addition amount of the potassium compound powder was less than 0.2% by weight, the potassium compound reacted with the residual lithium was insufficient, and therefore the residual lithium was slightly increased and the capacity retention rate was slightly lowered as compared with examples 1 to 3.
In addition, in the case of example 5 in which the addition amount of the potassium compound powder exceeds 1.9 wt%, potassium reacting with residual lithium increases, thereby securing excellent residual lithium reducing effect, but discharge capacity, efficiency, and life characteristics slightly decrease as compared with examples 1 to 3 due to the addition of the excessive amount of the potassium compound. Further, compared with example 3, the content of residual lithium carbonate (Li 2CO3) was rather increased due to unreacted potassium hydrogen sulfate and lithium potassium-based compound on the surface of the active material. In example 5, a trade-off (trade-off) phenomenon occurs in which the capacity retention rate is relatively improved due to a decrease in the discharge capacity.
In the case of comparative example 1 using the conventional water washing method, the residual lithium reduction effect was excellent, but the initial capacity, efficiency, life and electrochemical properties were greatly reduced compared with those of example and comparative example 2 due to deformation of the layered structure of the primary particles during the water washing treatment.
Claims (9)
1. A method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the steps of:
preparing primary lithium-transition metal composite oxide particles by reacting a transition metal precursor with a lithium precursor;
mixing the primary lithium-transition metal composite oxide particles with an aqueous potassium compound solution; and
Heat-treating the mixed primary lithium-transition metal composite oxide particles and the aqueous potassium compound solution to form lithium-transition metal composite oxide particles including a plurality of primary particles and lithium-potassium-containing portions formed between the primary particles,
Wherein the content of lithium carbonate (Li 2CO3) remaining on the surfaces of the lithium-transition metal composite oxide particles is 2500ppm or less, the content of lithium hydroxide (LiOH) remaining on the surfaces of the lithium-transition metal composite oxide particles is 2500ppm or less,
Wherein the average value of the potassium signal of the lithium-potassium containing fraction measured by energy dispersive spectroscopy EDS is 1.2 to 4 times the average value of the potassium signal in the primary particles measured by EDS,
Wherein the aqueous potassium compound solution is formed by mixing a solvent with the potassium compound powder, and the solvent is added in an amount of 2 to 15% by weight relative to the total weight of the primary lithium-transition metal composite oxide particles.
2. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein,
The lithium-potassium-containing portion includes a lithium-potassium-sulfur-containing portion that contains lithium, potassium, and sulfur.
3. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein,
The primary particles have a close-packed hexagonal structure.
4. The method for producing a positive electrode active material for a lithium secondary battery according to claim 3, wherein,
The lithium-transition metal composite oxide particles do not include primary particles having a face-centered cubic structure.
5. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein,
The sulfur content of the lithium-transition metal composite oxide particles measured by a carbon-sulfur (CS) analyzer is 1100ppm to 4500ppm with respect to the total weight of the lithium-transition metal composite oxide particles.
6. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein,
The potassium compound powder is added in an amount of 0.2 to 1.9 wt% relative to the total weight of the primary lithium-transition metal composite oxide particles.
7. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein,
The potassium compound powder is potassium hydrogen sulfate (KHSO 4) powder.
8. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein,
The heat treatment is performed at 200 ℃ to 400 ℃ under an oxygen atmosphere.
9. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein,
The primary lithium-transition metal composite oxide particles are mixed with the aqueous potassium compound solution without being subjected to a water washing treatment.
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