CN114566624A - 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
- CN114566624A CN114566624A CN202210202055.5A CN202210202055A CN114566624A CN 114566624 A CN114566624 A CN 114566624A CN 202210202055 A CN202210202055 A CN 202210202055A CN 114566624 A CN114566624 A CN 114566624A
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- China
- Prior art keywords
- lithium
- potassium
- transition metal
- composite oxide
- metal composite
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- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 100
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 99
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 55
- 229910052723 transition metal Inorganic materials 0.000 claims abstract description 121
- 239000002905 metal composite material Substances 0.000 claims abstract description 112
- 239000002245 particle Substances 0.000 claims abstract description 111
- 239000011164 primary particle Substances 0.000 claims abstract description 72
- OBTSLRFPKIKXSZ-UHFFFAOYSA-N lithium potassium Chemical compound [Li].[K] OBTSLRFPKIKXSZ-UHFFFAOYSA-N 0.000 claims abstract description 44
- 150000003112 potassium compounds Chemical class 0.000 claims description 60
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 39
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 claims description 38
- 239000011591 potassium Substances 0.000 claims description 38
- 229910052700 potassium Inorganic materials 0.000 claims description 38
- 229910001868 water Inorganic materials 0.000 claims description 37
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 33
- 238000000034 method Methods 0.000 claims description 32
- 239000000843 powder Substances 0.000 claims description 31
- 239000007864 aqueous solution Substances 0.000 claims description 26
- 238000005406 washing Methods 0.000 claims description 20
- 238000002156 mixing Methods 0.000 claims description 18
- 239000002904 solvent Substances 0.000 claims description 17
- 238000004519 manufacturing process Methods 0.000 claims description 16
- 238000002149 energy-dispersive X-ray emission spectroscopy Methods 0.000 claims description 14
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 13
- 239000000243 solution Substances 0.000 claims description 13
- 229910052717 sulfur Inorganic materials 0.000 claims description 13
- 239000011593 sulfur Substances 0.000 claims description 13
- 229910000343 potassium bisulfate Inorganic materials 0.000 claims description 12
- CHKVPAROMQMJNQ-UHFFFAOYSA-M potassium bisulfate Chemical group [K+].OS([O-])(=O)=O CHKVPAROMQMJNQ-UHFFFAOYSA-M 0.000 claims description 9
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims description 7
- 229910052808 lithium carbonate Inorganic materials 0.000 claims description 7
- YQCIWBXEVYWRCW-UHFFFAOYSA-N methane;sulfane Chemical compound C.S YQCIWBXEVYWRCW-UHFFFAOYSA-N 0.000 claims description 7
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 6
- 238000010438 heat treatment Methods 0.000 claims description 6
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- 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
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 21
- 230000000052 comparative effect Effects 0.000 description 19
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- 239000010936 titanium Substances 0.000 description 3
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- 229920002134 Carboxymethyl cellulose Polymers 0.000 description 2
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 2
- IAZDPXIOMUYVGZ-UHFFFAOYSA-N Dimethylsulphoxide Chemical compound CS(C)=O IAZDPXIOMUYVGZ-UHFFFAOYSA-N 0.000 description 2
- 229910000733 Li alloy Inorganic materials 0.000 description 2
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 2
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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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- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
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- VAYTZRYEBVHVLE-UHFFFAOYSA-N 1,3-dioxol-2-one Chemical compound O=C1OC=CO1 VAYTZRYEBVHVLE-UHFFFAOYSA-N 0.000 description 1
- SJHAYVFVKRXMKG-UHFFFAOYSA-N 4-methyl-1,3,2-dioxathiolane 2-oxide Chemical compound CC1COS(=O)O1 SJHAYVFVKRXMKG-UHFFFAOYSA-N 0.000 description 1
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- 229910052708 sodium Inorganic materials 0.000 description 1
- 229910000029 sodium carbonate Inorganic materials 0.000 description 1
- 229910052596 spinel Inorganic materials 0.000 description 1
- 239000011029 spinel Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 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
- 229910052715 tantalum Inorganic materials 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
- 239000013585 weight reducing agent Substances 0.000 description 1
- 229910052727 yttrium Inorganic materials 0.000 description 1
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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
- H01M4/362—Composites
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- H—ELECTRICITY
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- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- H—ELECTRICITY
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- 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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- 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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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
A positive 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 moieties formed between the primary particles. The life characteristics and capacity characteristics can be improved by preventing the deformation of the layered structure of the primary particles and removing the 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 of manufacturing the same.
Background
Secondary batteries are batteries that can be repeatedly charged and discharged, and with the development of the information communication and display industries, secondary batteries have been widely used as power sources for various portable electronic communication devices, such as video cameras, mobile phones, notebook computers, and the like. In addition, in recent years, battery packs including secondary batteries have also been developed and applied to power sources of environmentally friendly automobiles such as hybrid automobiles.
Examples of the secondary battery may include a lithium secondary battery, a nickel-cadmium battery, a nickel-hydrogen battery, etc., wherein the lithium secondary battery has a high operating voltage and an energy density per unit weight, which are advantageous in terms of a charging speed and weight reduction, and thus research and development are actively being conducted.
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, for example, in the form of a pouch, that houses 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 oxides.
As the application range of lithium secondary batteries is expanded, there is a need for lithium secondary batteries having longer life, high capacity, and operational stability. In the lithium-transition metal composite oxide used as the positive electrode active material, when the 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 degraded.
For example, korean laid-open patent publication No. 10-0821523 discloses a method for removing lithium salt impurities by washing a lithium-transition metal composite oxide with water, but there is a limit in sufficiently removing impurities and damage may be caused to the particle surface in the water washing process.
[ Prior art documents ]
Korean granted 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 operation stability and electrochemical characteristics, and a method of manufacturing the same.
An object of the present invention is to provide a lithium secondary battery having improved operation stability and electrochemical characteristics.
Technical scheme
The positive 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 moieties can include lithium-potassium-sulfur containing moieties that contain lithium, potassium, and sulfur.
In some embodiments, the primary particles may have a hexagonal close-packed (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 particle measured by a carbon-sulfur (CS) analyzer may be 1100ppm to 4500ppm with respect to the total weight of the lithium-transition metal composite oxide particle.
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 potassium signal of the lithium-potassium containing moieties measured by the EDS may be 1.2 to 4 times the average potassium signal in the primary particles measured by the EDS.
In some embodiments, lithium carbonate (Li) remaining on the surface of the lithium-transition metal composite oxide particles2CO3) 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.
A method for manufacturing a positive 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 solution of a potassium compound; and heat-treating the mixed primary lithium-transition metal composite oxide particles and the potassium compound aqueous solution to form lithium-transition metal composite oxide particles including a plurality of primary particles and lithium-potassium-containing moieties formed between the primary particles.
In some embodiments, the aqueous potassium compound solution is formed by mixing a solvent with a potassium compound powder, and the potassium compound powder may be added in an amount of 0.2 to 1.9 wt% with respect 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% by weight 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) And (3) 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 being subjected to 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 embodiment; and a negative electrode disposed opposite to the positive electrode.
Advantageous effects
The positive 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 moieties formed between the primary particles. In this case, residual lithium on the surface of the lithium-transition metal composite oxide reacts with the potassium-containing compound to be converted into the lithium-potassium-containing moiety, so that initial capacity and battery efficiency characteristics can be improved.
In some embodiments, by forming lithium-potassium containing moieties having a hexagonal close-packed structure between primary particles in a lithium-transition metal composite oxide, the surfaces of the primary particles are protected by the lithium-potassium containing moieties, so that the lifetime characteristics and driving stability can be improved.
In the method of manufacturing a positive electrode active material according to an embodiment of the 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 and 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 solution of the potassium compound may be mixed with the primary lithium-transition metal composite oxide particles.
In this case, primary particles of the lithium-transition metal composite oxide particles can be prevented from being deformed from a hexagonal close-packed structure to a face-centered cubic structure during the water washing treatment. Thereby, the initial capacity and the life characteristics of the secondary battery can be prevented from being lowered. In addition, residual lithium between the surface portion of the lithium-transition metal composite oxide particle and the primary particle is removed, so that the life characteristic may be prevented from being lowered due to gas generation, and the battery resistance may be lowered, so that the initial capacity may 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 a schematic plan view and a sectional view of a lithium secondary battery according to an exemplary embodiment, respectively.
Fig. 4 is an HR-TEM image of the lithium-transition metal composite oxide particles according to example 1.
Fig. 5 is an HR-TEM image of the 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 region and the region between the primary particles (for example, lithium-potassium-containing portion) of examples 1 to 5.
Description of the reference numerals
100: positive electrode 105: positive current collector
107: positive electrode lead 110: positive electrode active material layer
120: negative electrode active material layer 125: negative 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 same.
Hereinafter, embodiments of the present invention are explained 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 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 moieties formed between the primary particles.
In some embodiments, the primary particles may have a crystallographically 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 of 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 surface of the lithium-transition metal composite oxide particle may be increased. Therefore, in order to remove the residual lithium, a water washing process or a non-water washing process (e.g., incipient wetness method) may be performed. Thus, for example, when x is 0.8 or greater, the above process for removing residual lithium may have a substantial meaning.
Ni may be provided as a transition metal associated with power and capacity of a lithium secondary battery. Therefore, as described above, by adopting 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 an 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 comprise a lithium-potassium-sulfur (Li-K-S) containing moiety comprising lithium, potassium, and sulfur (S). For example, the lithium-potassium containing moiety can include a LiKSO4. In this case, due to the LiKSO4The excellent conductivity of the secondary battery can improve the power characteristics of the secondary battery.
In some embodiments, the primary particles of the lithium-transition metal composite oxide particles may have a hexagonal close-packed (hexagonal close-packed) structure. Therefore, a large amount of lithium and transition metal elements having a stable structure in a layered form 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 portion measured by Energy Dispersive Spectroscopy (EDS) may be greater than the potassium concentration in the primary particles 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 potassium signal of the lithium-potassium containing moieties measured by the EDS may be 1.2 to 4 times the average potassium signal in the primary particles.
When the ratio of the average value of the potassium signal satisfies the above range, lithium-potassium containing moieties having a hexagonal close-packed structure may be sufficiently formed between the primary particles included in the lithium-transition metal composite oxide particles. In this case, the surface of the primary particle may be protected by the lithium-potassium containing moiety, thereby reducing the area of the primary particle 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 has been sufficiently removed, the electrochemical characteristics of the secondary battery can be improved.
In some embodiments, the content of the lithium precursor remaining on the surface of the lithium-transition metal composite oxide particle may be adjusted.
For example, lithium carbonate (Li) remaining on the surface of the lithium-transition metal composite oxide particles2CO3) 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.
When the contents of lithium carbonate and lithium hydroxide satisfy the above ranges, resistance is reduced upon lithium ion migration, so that initial capacity characteristics and power characteristics of the lithium secondary battery may be improved, and life characteristics upon repeated charge and discharge may be improved.
In some embodiments, the sulfur content included in the lithium-transition metal composite oxide particle may be 1100ppm to 4500ppm with respect to the total weight of the lithium-transition metal composite oxide particle. For example, the lithium-sulfur compound present on the surface of the lithium-transition metal composite oxide particle can not only protect the surface of the particle from the electrolyte, but also favorably act on the electrolyte and lithium ion migration on the surface. In this case, while the remaining lithium and the below-described potassium compound are sufficiently removed, the capacity characteristics and the lifetime characteristics can be prevented from being degraded due to the excessive addition of potassium. Therefore, it is possible to maintain power characteristics while improving the capacity retention rate of the secondary battery.
The sulfur content can be measured, for example, by a carbon-sulfur (CS) analyzer (carbon-sulfur 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 the 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 metal salts. The metal salt may include nickel salt, manganese salt, and cobalt salt.
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 precipitating agent may include an alkaline compound, 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·H2O), ammonium carbonate (e.g. NH)3HCO3) And the like.
The temperature of the coprecipitation reaction may 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 alone or in combination of two or more.
In an exemplary embodiment, an aqueous solution of a potassium compound 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 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% with respect 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, the capacity characteristics and lifetime characteristics can be prevented from being lowered due to the excessive addition of the potassium compound. 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% by weight 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, the deformation of the layered structure of the primary particles due to the addition of an excessive amount of the solvent can be prevented. Therefore, the life 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 so that the content thereof is 50% by weight or less with respect to the weight of the solvent to prepare an aqueous solution of the potassium compound. When the potassium compound powder and the solvent are added in the above range, the potassium compound powder is sufficiently dissolved in the solvent and the residual lithium and potassium compound are sufficiently reacted, so that the workability can be improved.
In some embodiments, the potassium compound powder may be potassium hydrogen sulfate (KHSO)4) The powder, and in this case, the aqueous potassium compound solution may be KHSO4An aqueous solution.
For example, the solvent may be pure water (de-ionized water, DIW)).
In an exemplary embodiment, the primary lithium-transition metal composite oxide particles and the aqueous solution of the potassium compound may be mixed. In this case, potassium and/or sulfur contained in the aqueous solution of a potassium compound may be converted into lithium-potassium-containing moieties (for example, lithium-potassium-sulfur-containing moieties) by reacting with residual lithium present on the surfaces of the primary lithium-transition metal composite oxide particles. Thus, lithium-transition metal composite oxide particles including primary particles and lithium-potassium containing moieties can be obtained.
For example, impurities present on the surface of the primary lithium-transition metal composite oxide particles may be removed by the mixing process. For example, in order to improve the yield of the lithium metal oxide particles or the stability of the synthesis process, a lithium precursor (lithium salt) may be used in excess. In this case, lithium hydroxide (LiOH) and lithium carbonate (Li) are included2CO3) May remain on the surface of the primary lithium-transition metal composite oxide particles.
Further, 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 in the manufacture of the positive electrode. In this case, the residual lithium content on the surface of the lithium-transition metal composite oxide particles may increase.
When the residual lithium is removed by water washing (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 are caused, possibly resulting in damage or collapse of the layered structure of the primary particles. In addition, since the layered structure is transformed into a face-centered cubic structure, a spinel structure and/or a halite structure rather than 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., the incipient wetness method) is performed using the potassium compound aqueous solution without performing the water washing treatment, passivation caused by the potassium-containing compound may be achieved on the surface of the lithium-transition metal composite oxide particles when the mixing process is performed. For example, lithium-potassium containing moieties in which lithium and potassium are combined may be formed between primary particles having a hexagonal close-packed structure.
The term "incipient wetness method" used in the present invention means, for example, a method of adding water or an aqueous solution of a potassium compound 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, a spraying method or the like, without performing a water washing treatment of adding water in an amount substantially the same as or similar to the total weight of the lithium-transition metal composite oxide particles and stirring.
In addition, 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 the surface of the particles from being oxidized by water and the layered structure from being damaged.
For example, when the potassium compound powder is directly mixed with the lithium-transition metal composite oxide particles instead of the potassium compound aqueous 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 in which 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 electrolytic solution, the surfaces of the primary particles cannot be sufficiently protected, and residual lithium remains on the surfaces between the primary particles, possibly resulting in an increase in battery resistance. Therefore, the capacity and power characteristics of the battery may be degraded.
According to exemplary embodiments of the present invention, the incipient wetness method may be performed using an aqueous solution of a potassium compound as described above. In this case, the potassium compound aqueous solution penetrates between the primary particles by capillary force and reacts with residual lithium between the primary particles, so that lithium-potassium containing moieties may be formed between the primary particles.
In some embodiments, the content of the potassium compound in the aqueous potassium compound solution may be 0.1 to 2% by weight with respect 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 the surface portion of the primary lithium-transition metal composite oxide particle and at the position where residual lithium originally exists between the primary particles, and the layered structure of the primary particles can be prevented from being damaged or collapsed substantially as in the case of the water washing treatment.
After the mixing process, the cathode active material including the primary particles and the lithium-potassium containing moiety may be obtained through a heat treatment (calcination) process (e.g., step S30).
For example, the primary lithium-transition metal composite oxide particles and lithium-potassium containing moieties that have undergone a mixing process may be heat-treated using a calciner. Thereby, lithium-transition metal composite oxide particles in which lithium-potassium containing moieties 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, residual lithium on the surface of the primary lithium-transition metal composite oxide particles and the potassium compound of the aqueous solution of the potassium compound may be sufficiently combined to form lithium-potassium-containing moieties.
Fig. 2 and 3 are a schematic plan view and a sectional view of a lithium secondary battery according to an exemplary embodiment, respectively.
Hereinafter, a lithium secondary battery including a positive electrode containing the above-described positive electrode active material for a lithium secondary battery will be provided with reference to fig. 2 and 3.
Referring to fig. 2 and 3, the lithium secondary battery may include a cathode 100, an anode 130, and a separation film 140, the cathode 100 including a cathode active material including the above lithium-potassium containing moiety.
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 a positive electrode current collector 105.
For example, a 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 and the like in a solvent. The slurry is applied to a positive electrode current collector 105, and then pressed and dried to prepare a positive electrode.
The positive electrode 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 (polymethylmethacrylate), 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, a PVDF-based binder may be used as a binder for forming the positive electrode. In this case, the amount of the binder used to form the cathode active material layer 110 may be reduced, and the amount of the cathode 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 transfer 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, such as LaSrCoO3、LaSrMnO3Perovskite (perovskite) substances of (i) 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.
Any substance known in the art that can intercalate and deintercalate lithium ions may be used as the anode active material 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, mesocarbon microbeads (MCMB) calcined at 1500 ℃ or less, mesopitch-based carbon fibers (MPCF), and the like. Examples of the crystalline carbon may include graphite-based carbons 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.
The negative electrode collector 125 may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably may include copper or a copper alloy.
In some embodiments, a slurry may be prepared by mixing and stirring the negative 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 those described above can be used. In some embodiments, as a binder for forming the negative electrode, 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 cathode 100 and the anode 130. The separation membrane 140 may include a porous polymer membrane made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, ethylene/methacrylate copolymer, and the like. The separation membrane 140 may include a non-woven fabric formed of glass fibers having a high melting point, polyethylene terephthalate fibers, or the like.
According to an exemplary embodiment, an electrode unit is defined by the cathode 100, the anode 130, and the separation membrane 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 (folding), and the like of the separation membrane 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 composed of, for example, Li+X-And an anion (X) of said 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-And so on.
As the organic solvent, for example, Propylene Carbonate (PC), Ethylene Carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), propyl methyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ -butyrolactone, propylene sulfite, tetrahydrofuran, and the like can be used. These compounds may be used alone or in combination of two or more.
As shown in fig. 3, tabs (a positive tab and a negative tab) may protrude from the positive current collector 105 and the negative current collector 125 belonging to each electrode unit, respectively, and may extend to one side of the case 160. The tabs may be fused together with the one side of the case 160 to form electrode leads (the positive lead 107 and the negative 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 pouch type (pouch), a coin type (coin), or the like.
According to exemplary embodiments, the chemical stability of the positive active material may be improved by doping or coating of a potassium-containing compound to suppress the decrease in capacity and average voltage, achieving a lithium secondary battery having improved life and long-term stability.
Hereinafter, preferred embodiments are set forth to aid in understanding the present invention, but these embodiments are merely intended to illustrate the present invention and not 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 changes and modifications fall within the scope of the claims.
Example 1
Preparation of Primary lithium-transition Metal Complex oxide particles (S10)
Using by N2Bubbling for 24 hours to remove the internal dissolved oxygen, mixing NiSO at the ratio of 0.88:0.09:0.03 respectively4、CoSO4And MnSO4. The solution was placed in a 50 ℃ reactor using NaOH and NH3·H2Performing coprecipitation reaction for 48 hours by using O as a precipitating agent and a chelating agent to obtain Ni as a transition metal precursor0.88Co0.09Mn0.03(OH)2. The precursor obtained was dried at 80 ℃ for 12 hours and then again at 110 ℃ for 12 hours.
Lithium hydroxide and the transition metal precursor were added to a dry high-speed mixer at a ratio of 1.01:1, and mixed uniformly for 5 minutes. The mixture was placed in a calciner, ramped up to 710 ℃ to 750 ℃ at a ramp rate of 2 ℃/minute and held at 710 ℃ to 750 ℃ for 10 hours. During the temperature rise and holding period, oxygen was continuously introduced at a flow rate of 10 mL/min. After the calcination is finished, the mixture is naturally cooled to room temperature, and is crushed and classified to obtain a positive electrode active material LiNi0.88Co0.09Mn0.03O2Primary lithium-transition metal composite oxide particles in the form of primary particles.
Preparation of aqueous Potassium Compound solution and mixing (S20) and Heat treatment (S30)
Will be relative to that obtainedThe total weight of the obtained primary lithium-transition metal composite oxide particles was 0.8% by weight of potassium hydrogen sulfate (KHSO)4) The 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, followed by stirring, so that potassium bisulfate powder was sufficiently dissolved in the pure water to prepare an aqueous potassium compound solution.
The prepared aqueous solution of the potassium compound is added to the primary lithium-transition metal composite oxide particles and mixed.
The mixture was put into a calciner, and while supplying oxygen at a flow rate of 10 mL/min, was heated to a temperature between 200 ℃ and 400 ℃ at a heating rate of 2 ℃/min, and was held at the heated temperature for 10 hours. After the calcination, the resultant was classified by 325 mesh (mesh) to obtain a positive electrode active material.
Production of lithium secondary battery
A secondary battery was produced 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 electrode density of the positive electrode was adjusted to 3.0 g/milliliter (g/cc).
Lithium metal is used as a negative electrode active material.
The positive electrode and the negative electrode prepared as above were cut (notching) into circles having diameters Φ 14 and Φ 16, respectively, and laminated, and an electrode unit was prepared by disposing a separation film (polyethylene, thickness: 13 μm) cut into Φ 19 between the positive electrode and the negative electrode. The electrode unit was placed in a coin-type battery case having a diameter of 20mm and a height of 1.6mm, and an electrolyte was injected and assembled, and aged for 12 hours or more to impregnate the inside of the electrode with the electrolyte.
The electrolyte solution is prepared by mixing 1M LiPF6Dissolved in an EC/EMC (30/70; volume ratio) mixed solvent.
The secondary battery prepared as described above was subjected to chemical 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
Except that 0.4% by weight of potassium hydrogen sulfate (KHSO) was added relative to the total weight of the primary lithium-transition metal composite oxide particles4) Except for the powder, a positive electrode active material and a lithium secondary battery were obtained in the same manner as in example 1.
Example 3
Except that 1.6% by weight of potassium hydrogen sulfate (KHSO) was added relative to the total weight of the primary lithium-transition metal composite oxide particles4) Except for the powder, a positive electrode active material and a lithium secondary battery were obtained in the same manner as in example 1.
Example 4
Except that 0.1% by weight of potassium hydrogen sulfate (KHSO) was added relative to the total weight of the primary lithium-transition metal composite oxide particles4) Except for the powder, a positive electrode active material and a lithium secondary battery were obtained in the same manner as in example 1.
Example 5
Except that 2.0% by weight of potassium hydrogen sulfate (KHSO) was added relative to the total weight of the primary lithium-transition metal composite oxide particles4) Except for the powder, a positive electrode active material and a lithium secondary battery were obtained in the same manner as in example 1.
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 the aqueous solution of a potassium compound was not performed, but the primary lithium-transition metal composite oxide particles were added to pure water in an amount of 100% by weight based on the total weight of the primary lithium-transition metal composite oxide particles, stirred for 10 minutes to perform a water washing treatment, filtered, and then dried at 130 ℃ to 170 ℃ for 12 hours under vacuum.
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 potassium compound aqueous solution, and that 5 wt% of pure water with respect to the total weight of the primary lithium-transition metal composite oxide particles was added and mixed.
The above examples and comparative examples 2 were performed by an incipient wetness method in which a small amount of solution or water was added, not by a water washing treatment in which substantially the same amount of water as that of the positive electrode active material was added; the water washing treatment was performed in comparative example 1.
Experimental example 1
(1) High Resolution Transmission Electron microscope (High Resolution Transmission Electron)
Microscope, HR-TEM) and Fast Fourier Transform (FFT) analysis
The structures of compounds present in the primary particle region and lithium-potassium containing portion (region between primary particles) were analyzed by HR-TEM analysis and FFT image analysis of the cross sections of the lithium-transition metal composite oxide particles obtained according to the above examples and comparative examples.
(2) Calculation of the mean value of the Potassium signals
The lithium-transition metal composite oxide particles obtained according to the above examples and comparative examples were Line-scanned (Line scan) by STEM-EDS, and potassium signal values of the primary particle region and the region between the primary particles (for example, lithium-potassium containing portion) were continuously measured. Thereafter, by averaging the potassium signal values of each region, the average values of the potassium signals of the primary particles and the lithium-potassium containing portions were calculated.
(3) Measurement of the Sulfur content
In order to measure the content of sulfur (S), a C/S analyzer (carbon/sulfur analysis equipment; model name: CS844, manufacturer: LECO) was used, and the amount of the sample was selected according to the measurement value range of the standard sample measured when the calibration curve was drawn.
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 pieces (IRON chip) were added together at a ratio of 1: 1.
Thereafter, O as a combustion gas was supplied at a rate of 3L/min in a high-frequency induction furnace2And burned at about 2600 c to 2700 c. The sulfur-oxide-based inorganic compound gas (e.g., sulfuric acid gas) generated by the combustion is passed through an infrared ray detection cell, and a change in an infrared ray absorption amount compared to a blank (blank) is measured to quantitatively detect the sulfur content in the lithium-transition metal composite oxide particles.
The added amounts of potassium bisulfate powder, the added amounts of solvent, and the above-described measurement and evaluation results are shown in table 1 below for examples and comparative examples.
[ Table 1]
Fig. 4 is an HR-TEM image of the lithium-transition metal composite oxide particles according to example 1. Specifically, (a) of fig. 4 is an HR-TEM image of the lithium-transition metal composite oxide particle of example 1, and (b) of fig. 4 is an HR-TEM image enlarging the surface region (region 1) of the primary particle in (a) of fig. 4.
Fig. 5 is an HR-TEM image of lithium-transition metal composite oxide particles according to comparative example 1. Specifically, (a) of fig. 5 is an HR-TEM image of the lithium-transition metal composite oxide particle of comparative example 1, and (b) of fig. 5 is an HR-TEM image enlarged by the internal region (region 2) of the primary particle in (a) of fig. 5.
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 a region a enlarged by (B) of fig. 4, and (B) of fig. 6 is an FFT image of a region B enlarged by (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 incipient wetness method, the layered structure of the region inside the primary particles (for example, region 2 of fig. 5 (a) and region B of fig. 5 (B)) having a relatively low probability of layered structure breakdown also changed from the hexagonal close-packed structure to the face-centered cubic structure as shown in fig. 6 (B).
On the other hand, in the case of example 1 in which a mixing process (e.g., incipient wetness) is performed by adding an aqueous potassium compound solution, the layered structure of primary particles having a relatively high probability of layered structure damage (e.g., region 1 of fig. 4 (a) and region a of fig. 4 (b)) maintains a hexagonal close-packed structure as shown in fig. 6 (a).
Fig. 7 is a graph showing potassium signal values of the primary particle region and the region between the primary particles (for example, lithium-potassium-containing portion) of examples 1 to 5.
As shown in fig. 7, in examples 1 to 3, the ratio of the average value of potassium signal of the region between the primary particles to the average value of potassium signal within the primary particles (potassium signal ratio) satisfied 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 with respect to the primary lithium-transition metal composite oxide particles, the potassium signal ratio is less than 1.2 times, and thus it is difficult to judge the lithium-potassium-containing portion in the lithium-transition metal composite oxide particles.
Further, in the case of example 5 in which the addition amount of the potassium compound powder was more than 1.9% by weight with respect to the primary lithium-transition metal composite oxide particles, the potassium signal ratio exceeded 4 times.
On the other hand, in the case of example 1, the signal ratio of potassium ranging from the region between the primary particles (for example, lithium-potassium containing portion) to 50nm was uniformly shown to be 2.63 times.
Experimental example 2
2 3(1) Measurement of residual lithium (LiCO, LiOH) content
In a 250mL flask, 1.5g of the positive electrode active materials of examples and comparative examples were quantitatively charged, 100g of deionized water was added, and then placed in a magnetic rod, and stirred at 60rpm for 10 minutes. Then, the mixture was filtered through a vacuum flask, and 100g of the filtrate was collected. The taken solution was put into an automatic measuring instrument (Auto titrator) container and Auto titrated with 0.1N HCl with reference to the Wader method to measure Li in the solution2CO3And LiOH content.
(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 ℃ (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 percentage (%).
(3) Measurement of Capacity Retention ratio (Life characteristic) at repeated Charge and discharge
The lithium secondary batteries according to examples and comparative examples were repeatedly charged (CC/CV 0.5C 4.3V 0.05C cutoff) and discharged (CC 1.0C 3.0V cutoff) 300 times, and then the capacity retention rate was evaluated as a percentage of the value of the 300 th discharge capacity divided by the first discharge capacity.
The evaluation results are shown in table 2 below.
[ Table 2]
Referring to table 2, the examples of the incipient wetness method by mixing an aqueous solution of a potassium compound generally reduced the content of lithium remaining on the surface of lithium-transition metal composite oxide particles, had good initial capacity efficiency, and ensured excellent life characteristics, as compared to the comparative examples.
In the example 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 (e.g., 1.2 to 4), in the case of example 1, not only the initial capacity is maintained, but also the improved life characteristics are secured due to the passivation effect of the lithium-potassium containing compound formed by the reaction with the residual lithium on the surface of the lithium-transition metal composite oxide particles, as compared to comparative example 2 in which the incipient wetness method is performed using only pure water of the same weight% instead of the potassium compound aqueous solution.
However, in the case of example 4 in which the amount of the potassium compound powder added was less than 0.2 wt%, the potassium-containing compound reacted with the residual lithium was insufficient, and thus the residual lithium was slightly increased and the capacity retention rate was slightly decreased as compared with examples 1 to 3.
In addition, in the case of example 5 in which the amount of the added potassium compound powder exceeds 1.9 wt%, potassium reacted with residual lithium is increased to secure an excellent residual lithium reduction effect, but the discharge capacity, efficiency, and life characteristics are slightly lowered as compared with examples 1 to 3 due to the addition of an excessive amount of the potassium compound. In addition, in comparison with example 3, lithium carbonate (Li) remained due to unreacted potassium hydrogensulfate and lithium potassium based compound on the surface of the active material2CO3) The content of (c) is increased instead. In addition, in example 5, a trade-off phenomenon (trade-off) occurs in which the capacity retention ratio is relatively increased due to a decrease in the discharge capacity.
In the case of comparative example 1 using a conventional water washing method, the residual lithium reduction effect was excellent, but the initial capacity, efficiency, lifetime, and electrochemical characteristics were greatly reduced as compared to examples and comparative example 2 due to the deformation of the layered structure of the primary particles during the water washing treatment.
Claims (15)
1. A positive active material for a lithium secondary battery, comprising:
lithium-transition metal composite oxide particles comprising a plurality of primary particles,
wherein the lithium-transition metal composite oxide particles include lithium-potassium-containing moieties formed between the primary particles.
2. The positive electrode active material for a lithium secondary battery according to claim 1,
the lithium-potassium-containing moieties include lithium-potassium-sulfur-containing moieties that contain lithium, potassium, and sulfur.
3. The positive electrode active material for a lithium secondary battery according to claim 1,
the primary particles have a hexagonal close-packed structure.
4. The positive electrode active material for a lithium secondary battery according to claim 3,
the lithium-transition metal composite oxide particles do not include primary particles having a face-centered cubic structure.
5. The positive electrode active material for a lithium secondary battery according to claim 1,
the sulfur content of the lithium-transition metal composite oxide particle measured by a carbon-sulfur (CS) analyzer is 1100ppm to 4500ppm with respect to the total weight of the lithium-transition metal composite oxide particle.
6. The positive electrode active material for a lithium secondary battery according to claim 1,
the potassium concentration of the lithium-potassium containing moiety measured by Energy Dispersive Spectroscopy (EDS) is greater than the potassium concentration in the primary particles measured by the EDS.
7. The positive electrode active material for a lithium secondary battery according to claim 6, wherein,
the average potassium signal of the lithium-potassium containing moieties measured by the EDS is 1.2 to 4 times the average potassium signal in the primary particles measured by the EDS.
8. The positive electrode active material for a lithium secondary battery according to claim 1,
lithium carbonate (Li) remaining on the surface of the lithium-transition metal composite oxide particles2CO3) Is 2500ppm or less, and the content of lithium hydroxide (LiOH) remaining on the surface of the lithium-transition metal composite oxide particles is 2500ppm or less.
9. A method for manufacturing a positive active material for a lithium secondary battery, comprising the steps of:
preparing primary lithium-transition metal composite oxide particles;
mixing the primary lithium-transition metal composite oxide particles with an aqueous solution of a potassium compound; and
heat-treating the mixed primary lithium-transition metal composite oxide particles and the potassium compound aqueous solution to form lithium-transition metal composite oxide particles including a plurality of primary particles and lithium-potassium-containing moieties formed between the primary particles.
10. The method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 9, wherein,
the potassium compound aqueous solution is formed by mixing a solvent with potassium compound powder,
the potassium compound powder is added in an amount of 0.2 to 1.9 wt% with respect to the total weight of the primary lithium-transition metal composite oxide particles.
11. The method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 10, wherein,
the solvent is added in an amount of 2 to 15 wt% relative to the total weight of the primary lithium-transition metal composite oxide particles.
12. The method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 10, wherein,
the potassium compound powder is potassium hydrogen sulfate (KHSO)4) And (3) powder.
13. The method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 9, wherein,
the heat treatment is performed at 200 to 400 ℃ under an oxygen atmosphere.
14. The method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 9, 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.
15. A lithium secondary battery comprising:
a positive electrode including a positive electrode active material layer including the positive electrode active material for a lithium secondary battery according to claim 1; and
and a negative electrode disposed opposite to the positive electrode.
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