CN117107350A - High-nickel monocrystal material and preparation method and application thereof - Google Patents
High-nickel monocrystal material and preparation method and application thereof Download PDFInfo
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- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 title claims abstract description 384
- 239000000463 material Substances 0.000 title claims abstract description 318
- 229910052759 nickel Inorganic materials 0.000 title claims abstract description 230
- 238000002360 preparation method Methods 0.000 title claims abstract description 38
- 238000005245 sintering Methods 0.000 claims abstract description 254
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 119
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 119
- RSNHXDVSISOZOB-UHFFFAOYSA-N lithium nickel Chemical compound [Li].[Ni] RSNHXDVSISOZOB-UHFFFAOYSA-N 0.000 claims abstract description 108
- 238000002156 mixing Methods 0.000 claims abstract description 42
- 238000001816 cooling Methods 0.000 claims abstract description 41
- 238000004321 preservation Methods 0.000 claims abstract description 38
- 238000010438 heat treatment Methods 0.000 claims abstract description 35
- 239000000203 mixture Substances 0.000 claims abstract description 32
- 230000007547 defect Effects 0.000 claims abstract description 31
- 239000002243 precursor Substances 0.000 claims abstract description 25
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 20
- 238000009792 diffusion process Methods 0.000 claims abstract description 17
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 10
- 239000001301 oxygen Substances 0.000 claims abstract description 10
- 238000004364 calculation method Methods 0.000 claims abstract description 7
- 239000013078 crystal Substances 0.000 claims description 205
- 238000000034 method Methods 0.000 claims description 67
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 41
- 238000009766 low-temperature sintering Methods 0.000 claims description 38
- 239000002245 particle Substances 0.000 claims description 38
- 230000008569 process Effects 0.000 claims description 31
- 229910013716 LiNi Inorganic materials 0.000 claims description 27
- 150000002500 ions Chemical class 0.000 claims description 21
- 238000003837 high-temperature calcination Methods 0.000 claims description 20
- 229910052751 metal Inorganic materials 0.000 claims description 13
- 239000002184 metal Substances 0.000 claims description 13
- 238000006243 chemical reaction Methods 0.000 claims description 12
- 230000004913 activation Effects 0.000 claims description 8
- 238000007599 discharging Methods 0.000 claims description 8
- 238000004519 manufacturing process Methods 0.000 claims description 8
- 150000002739 metals Chemical class 0.000 claims description 7
- 230000007704 transition Effects 0.000 claims description 7
- IIPYXGDZVMZOAP-UHFFFAOYSA-N lithium nitrate Chemical compound [Li+].[O-][N+]([O-])=O IIPYXGDZVMZOAP-UHFFFAOYSA-N 0.000 claims description 6
- 239000000126 substance Substances 0.000 claims description 6
- 229910052723 transition metal Inorganic materials 0.000 claims description 6
- 150000003624 transition metals Chemical class 0.000 claims description 6
- 229910052721 tungsten Inorganic materials 0.000 claims description 5
- 229910052720 vanadium Inorganic materials 0.000 claims description 5
- 229910052727 yttrium Inorganic materials 0.000 claims description 5
- 239000007789 gas Substances 0.000 claims description 4
- 229910003002 lithium salt Inorganic materials 0.000 claims description 4
- 159000000002 lithium salts Chemical class 0.000 claims description 4
- INHCSSUBVCNVSK-UHFFFAOYSA-L lithium sulfate Inorganic materials [Li+].[Li+].[O-]S([O-])(=O)=O INHCSSUBVCNVSK-UHFFFAOYSA-L 0.000 claims description 3
- 230000035484 reaction time Effects 0.000 claims description 3
- RBTVSNLYYIMMKS-UHFFFAOYSA-N tert-butyl 3-aminoazetidine-1-carboxylate;hydrochloride Chemical compound Cl.CC(C)(C)OC(=O)N1CC(N)C1 RBTVSNLYYIMMKS-UHFFFAOYSA-N 0.000 claims description 3
- 229910015118 LiMO Inorganic materials 0.000 claims description 2
- 150000001768 cations Chemical class 0.000 claims description 2
- 238000002844 melting Methods 0.000 claims description 2
- 230000008018 melting Effects 0.000 claims description 2
- 230000000052 comparative effect Effects 0.000 description 74
- 238000002441 X-ray diffraction Methods 0.000 description 30
- 239000010410 layer Substances 0.000 description 28
- 238000012360 testing method Methods 0.000 description 27
- 229910013290 LiNiO 2 Inorganic materials 0.000 description 18
- 229910013292 LiNiO Inorganic materials 0.000 description 14
- 230000015572 biosynthetic process Effects 0.000 description 14
- 238000001354 calcination Methods 0.000 description 14
- 239000011248 coating agent Substances 0.000 description 14
- 238000000576 coating method Methods 0.000 description 14
- 238000001878 scanning electron micrograph Methods 0.000 description 14
- 238000012512 characterization method Methods 0.000 description 12
- 238000009616 inductively coupled plasma Methods 0.000 description 12
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 10
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 10
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- 239000003792 electrolyte Substances 0.000 description 7
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 7
- 239000007774 positive electrode material Substances 0.000 description 7
- 230000009467 reduction Effects 0.000 description 7
- 229910052782 aluminium Inorganic materials 0.000 description 6
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 6
- 239000006184 cosolvent Substances 0.000 description 6
- 238000010586 diagram Methods 0.000 description 6
- 239000011888 foil Substances 0.000 description 6
- 239000000047 product Substances 0.000 description 6
- 235000002639 sodium chloride Nutrition 0.000 description 6
- 239000011780 sodium chloride Substances 0.000 description 6
- 238000003776 cleavage reaction Methods 0.000 description 5
- 230000005012 migration Effects 0.000 description 5
- 238000013508 migration Methods 0.000 description 5
- 239000011164 primary particle Substances 0.000 description 5
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- 238000001228 spectrum Methods 0.000 description 5
- 238000003786 synthesis reaction Methods 0.000 description 5
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 4
- 229910013553 LiNO Inorganic materials 0.000 description 4
- 230000009286 beneficial effect Effects 0.000 description 4
- 230000008901 benefit Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 238000002474 experimental method Methods 0.000 description 4
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 2
- TWRXJAOTZQYOKJ-UHFFFAOYSA-L Magnesium chloride Chemical compound [Mg+2].[Cl-].[Cl-] TWRXJAOTZQYOKJ-UHFFFAOYSA-L 0.000 description 2
- AFCARXCZXQIEQB-UHFFFAOYSA-N N-[3-oxo-3-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)propyl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(CCNC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 AFCARXCZXQIEQB-UHFFFAOYSA-N 0.000 description 2
- VEQPNABPJHWNSG-UHFFFAOYSA-N Nickel(2+) Chemical compound [Ni+2] VEQPNABPJHWNSG-UHFFFAOYSA-N 0.000 description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 239000003153 chemical reaction reagent Substances 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 238000002447 crystallographic data Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 239000008367 deionised water Substances 0.000 description 2
- 229910021641 deionized water Inorganic materials 0.000 description 2
- 238000000840 electrochemical analysis Methods 0.000 description 2
- 238000000921 elemental analysis Methods 0.000 description 2
- 238000000227 grinding Methods 0.000 description 2
- 238000011534 incubation Methods 0.000 description 2
- 239000011229 interlayer Substances 0.000 description 2
- URIIGZKXFBNRAU-UHFFFAOYSA-N lithium;oxonickel Chemical compound [Li].[Ni]=O URIIGZKXFBNRAU-UHFFFAOYSA-N 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 150000002815 nickel Chemical group 0.000 description 2
- 229910001453 nickel ion Inorganic materials 0.000 description 2
- 229910017604 nitric acid Inorganic materials 0.000 description 2
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 2
- 238000004626 scanning electron microscopy Methods 0.000 description 2
- 229910052708 sodium Inorganic materials 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- YLZOPXRUQYQQID-UHFFFAOYSA-N 3-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)-1-[4-[2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidin-5-yl]piperazin-1-yl]propan-1-one Chemical compound N1N=NC=2CN(CCC=21)CCC(=O)N1CCN(CC1)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F YLZOPXRUQYQQID-UHFFFAOYSA-N 0.000 description 1
- 102100034013 Gamma-glutamyl phosphate reductase Human genes 0.000 description 1
- 101001133924 Homo sapiens Gamma-glutamyl phosphate reductase Proteins 0.000 description 1
- 229910012820 LiCoO Inorganic materials 0.000 description 1
- 239000010405 anode material Substances 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000010406 cathode material Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 230000001351 cycling effect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 239000012153 distilled water Substances 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000005315 distribution function Methods 0.000 description 1
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- 239000000428 dust Substances 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
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- 230000007613 environmental effect Effects 0.000 description 1
- 230000005284 excitation Effects 0.000 description 1
- 230000004927 fusion Effects 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 229910001629 magnesium chloride Inorganic materials 0.000 description 1
- 235000011147 magnesium chloride Nutrition 0.000 description 1
- 238000002161 passivation Methods 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 235000011164 potassium chloride Nutrition 0.000 description 1
- 239000001103 potassium chloride Substances 0.000 description 1
- 238000005036 potential barrier Methods 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000011533 pre-incubation Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
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- 235000015598 salt intake Nutrition 0.000 description 1
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/02—Elements
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B1/00—Single-crystal growth directly from the solid state
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Crystallography & Structural Chemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The embodiment of the invention relates to a high-nickel monocrystal material and a preparation method and application thereof, wherein the preparation method comprises the following steps: mixing part or all of the lithium source with the nickel precursor to obtain a mixture; preheating and preserving heat of the mixture for 2-5 hours at 150-500 ℃ under the oxygen-enriched atmosphere, and then heating to 600-750 ℃ in a low temperature section for sintering for 2-15 hours to obtain a high-nickel polycrystalline material; according to the unique image dynamics relation G.alpha.exp (-Q/RT) t 1/n And the relationship between defect concentration and defect generation energy and temperatureDetermining sintering temperature and heat preservation time, continuously heating the high-nickel polycrystalline material to the sintering temperature at the speed of 10 ℃/min-30 ℃/min, maintaining the heat preservation time at the sintering temperature to obtain a high-temperature sintered material, and then cooling; calculation formula d= (1/2D) a according to thermodynamic stability and ion diffusion coefficient D 2 ν 0 exp(‑E A /k B T) determining the temperature and time of mixed-discharge control sintering, and carrying out mixed-discharge control sintering on the high-temperature sintering material at the temperature of mixed-discharge control sintering to obtain the high-nickel monocrystal material; in the high nickel monocrystal material, the lithium nickel mixed discharge rate is below 4%.
Description
Technical Field
The invention relates to the technical field of new energy, in particular to a high-nickel monocrystalline material and a preparation method and application thereof.
Background
In recent years, new energy industries such as electric automobiles, consumer electronics, power station energy storage and the like are increasingly developed, and the requirements on lithium ion batteries are increasingly increased. The positive electrode material is a key material for lithium ion batteries, and thus a positive electrode material with high specific energy density, long life and low cost is urgently needed.
High nickel positive electrode materials have attracted considerable attention due to their advantages in terms of high energy density, better low temperature performance, cost effectiveness and environmental friendliness. Compared with cobalt, nickel has lower price, so the high nickel anode material can be used as LiCoO with high price 2 Alternatives to the positive electrode material. In order to greatly reduce the cost of battery materials, high nickel positive electrode materials with higher nickel content are needed. In addition, by single crystallization of the high-nickel positive electrode material, namely, the primary particle size is increased, the surface area of the positive electrode particles, which is subjected to side reaction with electrolyte, can be reduced, so that the cycle life of the material is remarkably prolonged, and the thermal safety of the material is improved.
The current preparation method of the high-nickel monocrystal material is mainly divided into four types: (1) A one-step sintering method, i.e. directly sintering a lithium source and a precursor at a high temperature in one step after mixing, for example, in patent CN202110870461, directly sintering by a one-step method at 700-800 ℃; (2) A two-stage sintering method, namely, sintering at a high temperature and then sintering at a low temperature, such as the two-stage method adopted in patent CN 202110986973; (3) Auxiliary sintering with cosolvent, namely, using cosolvent as sintering promoter, such as patent CN202211298607, and using cosolvent such as sodium chloride, magnesium chloride, potassium chloride, etc., to promote sintering of monocrystal; (4) The ion exchange wet chemical method is to synthesize sodium-electric high-nickel monocrystal with sodium source and precursor and then synthesize lithium-electric high-nickel monocrystal with ion exchange method. In the above preparation methods, the cosolvent is used for assisting the sintering process, and the step of removing the cosolvent is needed after the sintering is completed, so that the process is complex and has high cost, and the cosolvent can only promote the integrity of the crystal form, but can not effectively promote the growth of the single crystal, so that the single crystal size is small. The ion exchange method is also relatively complicated in process, passivation is easy to occur on the surface of the formed high-nickel monocrystal, the electrochemical discharge capacity of the material is poor, the lithium salt consumption is high in the preparation process, and the sodium electric monocrystal is needed to be synthesized first and then subjected to ion exchange in the synthesis process to obtain the lithium electric monocrystal, so that the cost is high. Therefore, sintering processes are mainly used in the prior art to prepare high nickel single crystal materials.
In an ideal case, lithium and a transition metal interlayer in the layered high-nickel material are distributed, so that a lithium layer and a transition metal layer are formed at intervals, and lithium ions have two-dimensional ion transmission channels. In practice, the high nickel material generally has a certain degree of lithium nickel mixed discharge: mainly embodied in that part of nickel ions are distributed in the lithium layer. Ni present in the lithium layer 2+ Diffusion of lithium ions is hindered and Ni in the lithium layer 2+ Is also difficult to oxidize, and if serious lithium nickel mixed discharge occurs, the lithium ion diffusion capacity is reduced, and the material capacity is poor. Compared with the high-nickel polycrystalline material, the sintering method commonly used at present is used for preparing the high-nickel monocrystalline material, the high-sintering temperature is generally required, and the high-temperature sintering can lead to serious lithium nickel mixed discharge in the high-nickel monocrystalline material, so that the dynamics performance of the material is poor and the specific discharge capacity is low. Jeff Dahn et al (Journal of The Electrochemical Society,166 (10) A1956-A1963 (2019)) also show that single crystal high nickel materials have a discharge specific capacity reduced by about 20mAh/g compared to polycrystalline high nickel materials.
In general, in the existing preparation method of the high-nickel monocrystal material, in order to ensure growth of the monocrystal, a higher sintering temperature is still required, and an excessively high sintering temperature and an excessively long high-temperature sintering time can promote growth of the monocrystal, but also cause serious lithium-nickel mixed discharge in the material, so that the coulomb efficiency of the material is lower, the discharge specific capacity is lower, the material dynamics is poorer, and particularly, the capacity exertion under high multiplying power is less. Therefore, the high-nickel monocrystal material obtained by the current preparation method has the problems of low coulomb efficiency, low specific discharge capacity, poor material dynamics, poor rate capability and the like. The above-mentioned disadvantages limit the application of the high nickel single crystal cathode material.
Disclosure of Invention
Aiming at the defects of the existing high-nickel monocrystal positive electrode material preparation process, the invention aims to overcome the defects of low discharge specific capacity, poor cycle performance, poor dynamic performance, low coulomb efficiency, poor rate capability and the like of the material caused by the increase of lithium-nickel mixed discharge of the high-nickel monocrystal material due to high-temperature sintering, and provides the high-nickel monocrystal material, the preparation method and the application thereof, and the high-nickel monocrystal material and the preparation method and the application thereof are provided, wherein the high-nickel monocrystal material lithium-nickel mixed discharge rate is lower than 4 percent by reasonably controlling the high-temperature sintering step and increasing the low-temperature mixed discharge control sintering process, so that the material has high discharge specific capacity and excellent cycle performance.
To this end, in a first aspect, an embodiment of the present invention provides a method for preparing a high nickel single crystal material, the method comprising:
mixing part or all of the lithium source with the nickel precursor to obtain a mixture; the chemical formula of the nickel precursor is as follows: ni (Ni) x M 1-x (OH) 2 Wherein x is more than or equal to 0.8 and less than or equal to 1, and M is one or more of Co, mn, ti, mg, al, ca, cr, fe, zn, Y, zr, la, V, mo, nb, W, sm; the molar ratio of the lithium content in the part or all of the lithium sources to the total metal content in the nickel precursor is greater than 1;
preheating and preserving heat of the mixture for 2-5 hours at 150-500 ℃ under the oxygen-enriched atmosphere, and then heating to 600-750 ℃ in a low temperature section for sintering for 2-15 hours to obtain a high-nickel polycrystalline material;
According to the unique image dynamics relation G.alpha.exp (-Q/RT) t 1/n And the relationship between defect concentration and defect generation energy and temperatureDetermining sintering temperature and heat preservation time, continuously heating the high-nickel polycrystalline material to the sintering temperature at the speed of 10 ℃/min-30 ℃/min, maintaining the heat preservation time at the sintering temperature to obtain a high-temperature sintered material, and then cooling; wherein G is the size of a single crystal, exp (-Q/RT) is an exponential function, Q represents the activation energy of the reaction, R is the ideal gas constant, T is the temperature, the unit is Kelvin, T is the reaction time, n is the number of reaction stages,% ofNionNi (3 a) sites is the ratio of Ni atoms in the Li site,% ofNionNi (3 b) sites is the ratio of Ni atoms in the Ni layer, ΔE is the defect reaction generation energy in the case where the concentration defect reaches the thermodynamic equilibrium state, k B Is the boltzmann constant;
according to the calculation formula d= (1/2D) a of the ion diffusion coefficient D 2 ν 0 exp(-E A /k B T) determining mixed control sintering temperature and mixed control sintering time of mixed control sintering, carrying out mixed control sintering on the high-temperature sintering material at the mixed control sintering temperature, and keeping the mixed control sintering time to obtain the high-nickel monocrystal material; wherein d is the diffusion dimension, a is the transition length, v 0 For collision frequency, E A Is the activation energy of ion transition, k B Is Boltzmann constant, T is temperature; in the high-nickel monocrystal material, the lithium nickel mixed discharge rate is below 4%.
Preferably, the sintering temperature of the high-temperature sintering material obtained by sintering is 800-1100 ℃, and the heat preservation time is 0-5h;
the sintering temperature is controlled to be 600-780 ℃ by mixing and discharging, and the sintering time is controlled to be 5-200 h by mixing and discharging; the sintering time of the mixed discharge control is preferably m times of the heat preservation time, and m is more than or equal to 10; preferably, the sintering time of the mixed discharge control is more than or equal to 15 hours;
the lithium nickel mixed discharge rate of the high nickel monocrystal material is below 2%.
Preferably, when the mixture is obtained by mixing part of lithium source and nickel precursor, the high-nickel polycrystalline material is supplemented with the rest of lithium source and/or the high-temperature sintered material is supplemented with the rest of lithium source after the temperature is reduced and/or the rest of lithium source is supplemented in the mixed-discharge controlled sintering process;
the rest lithium source is supplemented one or more times, so that the molar ratio of lithium to the total amount of other metals in the high-nickel single crystal material is 1.01:1-1.10:1, preferably satisfying 1.01:1-1.05:1.
Preferably, the lithium source is a low melting point lithium salt comprising: lithium nitrate, lithium hydroxide, lithium sulfate, CH 3 One or more of COOLi; the nickel precursor is Ni x Co y Mn 1-x-y (OH) 2 Wherein x is more than or equal to 0.8 and less than or equal to 1, and y is more than or equal to 0 and less than or equal to 0.2.
Preferably, the step of performing mixed-batch controlled sintering on the high-temperature sintered material at the mixed-batch controlled sintering temperature to obtain the high-nickel single crystal material specifically comprises the following steps:
cooling the high-temperature sintering material obtained after high-temperature calcination at 800-1100 ℃ to 600-780 ℃ for low-temperature sintering; or,
cooling the high-temperature sintering material obtained after high-temperature calcination at 800-1100 ℃ to room temperature, and then, raising the temperature to 600-780 ℃ again for low-temperature sintering;
further preferably, the low-temperature sintering is a segmented low-temperature sintering; more preferably, the sintering is performed at 700 ℃ to 780 ℃ for 1 to 10 hours, then at 680 ℃ to 700 ℃ for 10 to 50 hours, then at 650 ℃ to 680 ℃ for 10 to 50 hours, and finally at 600 ℃ to 650 ℃ for 10 to 50 hours.
In a second aspect, an embodiment of the present invention provides a high-nickel monocrystalline material, which includes the high-nickel monocrystalline material prepared by the preparation method described in the first aspect;
the lithium nickel mixed discharge rate of the high nickel monocrystal material is below 4%.
Preferably, the chemical formula of the high nickel single crystal material is as follows: liNi x M 1-x O 2 The method comprises the steps of carrying out a first treatment on the surface of the X is more than or equal to 0.8 and less than or equal to 1, M is one or more than or equal to Co, mn, ti, mg, al, ca, cr, fe, zn, Y, zr, la, V, mo, nb, W, sm, and the molar ratio of lithium to the total amount of other metals is 1.01:1-1.10:1, preferably 1.01:1-1.05:1, a step of; preferably, the high nickel single crystal material is LiNi x Co y Mn 1-x-y O 2 Wherein x is more than or equal to 0.8 and less than or equal to 1, and y is more than or equal to 0 and less than or equal to 0.2.
Preferably, the high nickel monocrystal material is a laminar alpha-NaFeO with R-3m space group 2 Hexagonal LiMO of structure 2 Phase-rich lithium layered oxide, liMO 2 Part of the LiNi exists in the lamellar part formed by transition metal and oxygen element in the structure 6 Cation arrangement; the lithium nickel mixed discharge rate of the high-nickel monocrystal material is less than 2%, and the grain size of monocrystal particles of the monocrystal material is 1.5-5 mu m.
In a third aspect, an embodiment of the present invention provides a secondary battery, including the high-nickel single crystal material prepared by the preparation method described in the first aspect, or the high-nickel single crystal material described in the second aspect.
According to the preparation method of the high-nickel monocrystalline material, provided by the embodiment of the invention, the calcination temperature and time of a low-temperature section are controlled, so that a large number of polycrystalline particles with smaller particle size are ensured to be generated, then the polycrystalline material is heated to a high-temperature section, and meanwhile, the heating rate is controlled, so that the polycrystalline particles can be ensured to grow into monocrystalline particles rapidly due to the growth kinetic effect before the mixed discharge is obviously increased, and the crystal grains of the synthesized monocrystalline particles are loose, have larger particle size and are not easy to agglomerate. By controlling the high-temperature calcination temperature and time, the heat preservation time at the temperature is reduced, for example, the shortest heat preservation time is 0, and the occurrence of lithium nickel mixed discharge phenomenon caused by thermodynamic effect in the single crystal growth process can be avoided to the greatest extent; finally, the high-nickel monocrystal material is cooled after high-temperature calcination, and mixed-discharge control sintering is carried out for a long time at 600-780 ℃, so that the reduction of lithium-nickel mixed-discharge phenomenon is further promoted.
The invention adopts a multi-stage sintering method of preheating heat preservation, low temperature sintering, high temperature calcining and low temperature sintering, and fully utilizes thermodynamic principles to improve the synthesis process of the high nickel monocrystal material, namely, according to the relationship between the unique dynamics and the relationship between defect concentration and defect generation energy and temperature, the high temperature sintering temperature and heat preservation time are determined through the change rule of crystal size, mixed discharge and the like obtained through experimental observation, the material with larger particle size can be obtained at the sintering temperature, then the temperature is quickly reduced, the mixed discharge controlled low temperature sintering temperature and sintering time are determined according to the thermodynamic stability and ion diffusion coefficient D, and the mixed discharge phenomenon in the monocrystal material is reduced through controlling the sintering process. The invention not only realizes the reduction of the mixed discharge phenomenon by avoiding the long-time calcination in the high temperature section as much as possible, but also ensures that enough and effective monocrystalline materials can be synthesized and the monocrystalline materials are distributed in a regular lamellar structure.
Drawings
FIG. 1 is a schematic diagram showing the initial growth behavior of a single crystal;
FIG. 2 is a schematic diagram showing average size of particles of lithium nickelate single crystal after sintering at corresponding temperature for 5 hours;
FIG. 3 is a graph showing the relationship between the size G of a sample of lithium nickel oxide single crystal sintered at 850 ℃ for 1h,4h, and 7h and the sintering time t;
FIG. 4 is a schematic diagram showing the relationship between sintering lnG and lnt at 850 ℃;
FIG. 5 shows LiNiO after 10h sintering at 650 DEG C 2 The relation diagram of lithium nickel mixed discharge and sintering time when the sample is sintered at 850 ℃;
FIG. 6 is a schematic diagram showing the relationship between sintering temperature and defect formation energy;
FIG. 7 is a schematic diagram showing the relationship between lithium nickel mixed discharge and sintering temperature;
FIG. 8a shows the LiNiO prepared in example 1 of the present invention 2 Scanning Electron Microscope (SEM) images of single crystal material;
FIG. 8b shows the LiNiO obtained in example 1 of the present invention 2 X-ray diffraction (XRD) patterns of single crystal materials;
fig. 9 is a first-week charge-discharge graph of example 1 and comparative example 1 of the present invention;
FIG. 10a is a Scanning Electron Microscope (SEM) image of a comparative sample prepared according to example 2 of the present invention;
FIG. 10b is an X-ray diffraction (XRD) pattern of a comparative sample prepared in example 2 of the present invention;
FIG. 10c shows the LiNi obtained in example 2 of the present invention 0.92 Co 0.03 Mn 0.05 O 2 Scanning Electron Microscope (SEM) images of single crystal material;
FIG. 10d shows the LiNi obtained in example 2 of the present invention 0.92 Co 0.03 Mn 0.05 O 2 X-ray diffraction (XRD) patterns of single crystal materials;
FIG. 11 is a first week charge-discharge graph of inventive example 2 and comparative example 2;
FIG. 12a is an SEM image of a sample 3a of the material obtained according to example 3 of the present invention;
FIG. 12b is an SEM image of a sample 3b of the material obtained according to example 3 of the present invention;
Fig. 13a is a first week charge-discharge graph of examples 3, 4 of the present invention;
FIG. 13b is a first week charge-discharge graph of comparative example 3 of the present invention;
FIG. 14a is an SEM image of a sample 4a of the material obtained according to example 4 of the present invention;
FIG. 14b is an SEM image of a sample 4b of the material prepared according to example 4 of the invention;
FIG. 15 is an SEM image of a high-nickel single crystal material obtained in example 5 of the present invention;
FIG. 16 is a first cycle charge-discharge graph of example 5 of the present invention;
FIG. 17 is an SEM image of a high-nickel single crystal material obtained in example 6 of the invention;
FIG. 18 is a first cycle charge-discharge graph of example 6 of the present invention;
FIG. 19a is an SEM image of a high-nickel single crystal material prepared according to example 7 of the invention;
FIG. 19b is an XRD pattern of the high nickel single crystal material obtained in example 7 of the present invention;
FIG. 20 is a graph showing cycle performance of example 7 and comparative example 4 of the present invention;
FIG. 21 is a graph showing the cycling performance of electrochemical tests of examples 8-9 of the present invention;
FIG. 22a is an SEM image of a high-nickel single crystal material prepared according to comparative example 1 of the present invention;
FIG. 22b is an XRD pattern of the high nickel single crystal material obtained by the preparation of comparative example 1 of the present invention;
FIG. 23a is an SEM image of a high-nickel single crystal material prepared according to comparative example 2 of the present invention;
FIG. 23b is an XRD pattern of the high nickel single crystal material obtained by the preparation of comparative example 2 of the present invention;
FIG. 24 is an SEM image of a high-nickel single crystal material prepared according to comparative example 3 of the present invention;
FIG. 25a is an SEM image of a high-nickel single crystal material prepared according to comparative example 4 of the present invention;
FIG. 25b is an XRD pattern of the high nickel single crystal material obtained by the preparation of comparative example 4 of the present invention;
FIG. 26a is an SEM image of a high-nickel single crystal material prepared according to comparative example 5 of the present invention;
FIG. 26b is an XRD pattern of the high nickel single crystal material obtained by the preparation of comparative example 5 of the present invention;
FIG. 27 is a graph showing the cycle performance of comparative example 5 of the present invention.
Detailed Description
The technical scheme of the invention is further described in detail through the drawings and the embodiments.
The embodiment of the invention provides a high-nickel monocrystal material and a preparation method thereof, wherein a multi-stage sintering method of preheating, heat preservation, low-temperature sintering, high-temperature calcination and low-temperature sintering is adopted, a thermodynamic principle is utilized to improve the synthesis process of the high-nickel monocrystal material, and the mixed discharge phenomenon in the monocrystal material is reduced by controlling the sintering process.
In the high-nickel single crystal material prepared by the preparation method of the high-nickel single crystal material, the high nickel refers to a material with the nickel element content of more than 80% in transition metal in a layered oxide anode.
The preparation method of the high-nickel monocrystal material comprises the following steps:
Step 1, mixing part or all of lithium sources with a nickel precursor to obtain a mixture;
specifically, the chemical formula of the nickel precursor is: ni (Ni) x M 1-x (OH) 2 Wherein x is more than or equal to 0.8 and less than or equal to 1, and M is one or more of Co, mn, ti, mg, al, ca, cr, fe, zn, Y, zr, la, V, mo, nb, W, sm;
the molar ratio of lithium content in some or all of the lithium source to the total amount of metal in the nickel precursor is greater than 1. The molar ratio of lithium in the lithium source to the total amount of metal in the nickel precursor is higher than 1:1, up to 10:1, but when the molar ratio is too high, the reaction product needs to be soaked in deionized water or alcohol liquid at a lower temperature for a period of time, so that the residual of the excess lithium source is dissolved in the liquid, and then the liquid is poured off. Repeating the above operation for a plurality of times to ensure that the lithium content in the sintering process is only slightly higher than the content of other metals; preferably, the total amount of all lithium sources is 1.05-1.2:1 in terms of molar ratio of Li to total amount of metal in the nickel precursor. The content of the lithium source is controlled so as to obtain a high nickel single crystal material in a slightly lithium-rich state, and the ratio of the two may be any value within the above range, for example, 1.05:1, 1.1:1, 1.15:1, 1.2:1, and is not limited to the above values.
Under the condition that the mixture is obtained by mixing part of lithium sources with nickel precursors, the method further comprises the steps of supplementing the rest of lithium sources for the high-nickel polycrystalline material obtained in the step 2, or supplementing the rest of lithium sources for the high-temperature sintering material after the temperature is reduced in the step 3, or supplementing the rest of lithium sources in the mixed discharge control sintering process in the step 4; the remainder of the lithium source is replenished one or more times, so long as the molar ratio of lithium to the total amount of other metals in the final high nickel single crystal material is made to satisfy 1.01: 1-1.10:1.
The lithium source specifically adopts low-melting-point lithium salt, and can comprise: lithium nitrate, lithium hydroxide, lithium sulfate, CH 3 One or more of COOLi; the nickel precursor is Ni x Co y Mn 1-x-y (OH) 2 Wherein x is more than or equal to 0.8 and less than or equal to 1, and y is more than or equal to 0 and less than or equal to 0.2.
Step 2, preheating and preserving heat of the mixture for 2-5 hours at 150-500 ℃ under the oxygen-enriched atmosphere, and then heating to 600-750 ℃ in a low temperature section for sintering for 2-15 hours to obtain a high-nickel polycrystalline material;
the oxygen-enriched atmosphere may be a pure oxygen atmosphere, an oxygen-enriched air atmosphere, an atmosphere having a high oxygen content in a mixed gas of oxygen and an inert gas, or the like, and is not limited to the exemplified case.
Preheating and maintaining at 150-500 deg.c for 2-5 hr to promote complete and homogeneous lithiation of the precursor, with the temperature being any value in the range, such as 150 deg.c, 180 deg.c, 200 deg.c, 300 deg.c, 400 deg.c, 500 deg.c, not limited to the values; the sintering time may be any value within the above range, such as 2h, 3h, 4h, 5h, and is not limited to the above values.
Sintering at 600-750deg.C for 2-15 hr to obtain a large amount of high nickel polycrystalline particles with small particle diameter, wherein the temperature can be any value within the above range, such as 600 deg.C, 610 deg.C, 620 deg.C, 630 deg.C, 640 deg.C, 650 deg.C, 660 deg.C, 670 deg.C, 680 deg.C, 690 deg.C, 700 deg.C, 710 deg.C, 720 deg.C, 730 deg.C, 740 deg.C, 750 deg.C, not limited to the above values; the sintering time may be any value within the above range, such as 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, and is not limited to the above value; the sintering time at the low temperature section is relatively long, and the high-nickel polycrystalline material can be generated easily.
Step 3, according to the unique image dynamics relation G.alpha.exp (-Q/RT) t 1/n And the relationship between defect concentration and defect generation energy and temperatureDetermining sintering temperature and heat preservation time, continuously heating the high-nickel polycrystalline material to the sintering temperature at 10 ℃/min-30 ℃/min, maintaining the heat preservation time at the sintering temperature to obtain a high-temperature sintering material, and then cooling;
Wherein G is the size of a single crystal, exp (-Q/RT) is an exponential function, Q represents the activation energy of the reaction, R is an ideal gas constant, T is temperature, the unit is Kelvin, T is the reaction time, and n is the reaction progression; % Ni on Li (3 a) sites is the ratio of Ni atoms in the Li site, and% of Ni on Ni (3 b) sites is the ratio of Ni atoms in the Ni layer; ΔE is the defect reaction energy of formation when the concentration of defects reaches the thermodynamic equilibrium state, and in the theoretical assumption, the energy of formation is considered to be independent of temperature, k B Is the boltzmann constant.
Single crystal growth at high temperature means that fusion of small particles produces a large single crystal, and the initial growth behavior of the single crystal can be explained by a neck growth mechanism, as shown in fig. 1. However, the neck length mechanism may correspond to different material migration mechanisms at different temperatures, and the size G of the single crystal may show different relationships with the sintering time t under different material migration mechanisms. The unique image dynamics relation is G.alpha.exp (-Q/RT) t 1/n N is 2,3,5,6,7, etc. (different values of n correspond to different mechanisms), it is known that the growth rate of the crystal is slowed down with the extension of sintering time and G is exponentially increased with the increase of sintering temperature regardless of the sintering mechanism.
Consider the matching of the theoretical predictive relationship with the actual situation. The average size of the particles after sintering the lithium nickelate single crystal at the corresponding temperature for 5 hours is shown in fig. 2. It is known that in practical cases, the average size and sintering temperature approximately show an exponential relationship, which coincides with the theoretical prediction value.
FIG. 3 shows the relation between the size G of the high nickel single crystal sample obtained by sintering at 850 ℃ for 1h,4h and 7h and the sintering time t, and FIG. 4 shows the relation between the sintering lnG and lnt at 850 ℃ with a better linear relation, wherein n is about 6.67 and between 6 and 7 according to the slope of 0.15, which is consistent with the theoretical prediction. In the process of sintering from 4 hours to 7 hours, the growth of the single crystal size is greatly slowed down, and the grain size growth of more than 5 hours of sintering is considered to be less, so that the high-temperature sintering time of 5 hours is enough from the viewpoint of single crystal growth, and the method is more suitable for sintering single crystals.
The samples reach mixed discharge under thermodynamic equilibrium state, and a certain time is required. The experiment shows that the growth of the mixed row and the time approximately show a direct proportion relation, the result is shown in figure 5, and figure 5 is LiNiO after being sintered for 10 hours at 650 DEG C 2 The samples were sintered at 850 ℃ in relation to lithium nickel misce bene and sintering time. It is known that the degree of mixing increases approximately linearly with the sintering time after 1h of sintering. Therefore, the extension of the sintering time at high temperature increases the lithium nickel mixed discharge degree. Considering that the mixed grain growth and time approximately show a direct proportion, and the grain growth and the secondary to the seventh of the time show a direct proportion, when sintering is carried out for a long time, the relative growth rate of the mixed grain is higher than the growth rate of the grain, so that a shorter sintering time should be selected in a high-temperature sintering interval to reduce the mixed grain. Since the purpose of high-temperature sintering is to facilitate growth of the high-nickel single crystal material to obtain the high-nickel single crystal material, according to the above, the single crystal growth is slow after sintering for 5 hours, so that the high-temperature sintering time exceeding 5 hours has no obvious influence on the positive excitation effect of the increase of the single crystal size, and the phenomenon of lithium nickel mixed discharge is greatly increased, thereby comprehensively considering the effects of single crystal growth and lithium nickel mixed discharge reduction. Therefore, the time of high temperature sintering should be not more than 5 hours, both from the theoretical and practical standpoint of the growth of miscibility.
The unique image dynamics relation G.alpha.exp (-Q/RT) t 1/n Is more consistent with the actual situation. According to this relationship, the sintering temperature at the high temperature section and the sufficient crystal growth time are selected in the present invention to promote the growth of single crystals. Materials having a particle size of 1.5 μm or less are not suitable for smear, and it is considered in the battery world that dust having a small particle size needs to be removed to satisfy battery performance requirements, and therefore, the particle size of the resultant single crystal needs to be controlled to 1.5 μm or more. Considering that the growth of the single crystal size in sintering for 5 hours has been greatly slowed down, fig. 2 is the average size of the particles obtained by sintering lithium nickelate single crystals at different temperatures for 5 hours, respectively. As is clear from FIG. 2, the single crystal size obtained by sintering at 800℃for 5 hours is about 1.5. Mu.m, and the single crystal grain size obtained by sintering at a temperature lower than 800℃for 5 hours is small, so that the minimum sintering temperature in the high temperature stage single crystal generation step is selected to be 800℃based on the single crystal growth mechanism and crystal size.
On the other hand, although high temperature sintering promotes single crystal growth, it also causes lithium nickel mixed discharge, and serious lithium nickel mixed discharge greatly reduces the electrochemical capacity of the material, so that the material needs to be avoided. Considering the mechanism of defect formation, for high temperature sintering, the thermodynamic equilibrium equation can be used to describe the relationship between defect concentration and defect generation energy and temperature
The "lithium nickel mixed discharge" mainly means that Ni atoms enter into the lithium layer, so that not only is the structure of the layered material distorted, but also the nickel atoms existing in the lithium layer can seriously obstruct lithium ion transmission.
In the practical situation, the production energy has a certain relation with the temperature, and the sample is sintered for 15 hours at 670 ℃, 700 ℃, 800 ℃, 1000 ℃ and 1100 ℃ by a one-step method through sintering, so that the sample after 15 hours of sintering is considered to be in a thermodynamic equilibrium state. And (3) performing XRD refining to obtain lithium nickel mixed discharge, and calculating defect generation energy corresponding to the position of the nickel atom occupying 3a according to the mixed discharge result, wherein the defect generation energy is shown in the following table 1.
TABLE 1
Based on its sintering temperature and defect formation energy fig. 6, the inventors found that defect formation can be temperature dependent. The lower the temperature, the higher the defect formation energy, the lower the defect formation energy, which can be inversely proportional to the temperature. Considering the above equation, the temperature increases, T increases while ΔE decreases, and the right side of the equation increases, indicating that mixed-row generation is easier. Therefore, the relationship can be applied to a temperature range of the high nickel material polycrystal synthesis temperature or higher.
Fig. 7 shows the relationship between lithium nickel misce and sintering temperature. It was found that the mix-up increased approximately exponentially with increasing sintering temperature, and the mix-up increased more significantly at high temperatures, and about 55% of Ni occupied the lithium layer in the sample with high sintering temperature of 1100 c, at which point it was considered to be almost completely converted into the electrochemically inactive rock salt phase. While the temperature increases, the percentage of Ni occupying the lithium layer increases further, and experiments show that in the case that 55% or more of Ni occupies the lithium layer, the mixing discharge can not be reduced to a level within 4% by sintering. And finally, the temperature upper limit of 1100 ℃ is selected as the sintering temperature of the high-temperature section by combining the relation between crystal growth and mixed growth and temperature.
Therefore, the sintering temperature is 800-1100 ℃ and the heat preservation time is 0-5h. Wherein 0 hour means that the material is heated to 800-1100 ℃ and immediately begins to be cooled, and the purpose of high-temperature calcination is realized in the process of heating.
Heating to 800-1100 deg.c for 0-5 hr to convert high nickel polycrystal material into high nickel monocrystal material, and the temperature may be any value in the range, such as 800 deg.c, 820 deg.c, 840 deg.c, 860 deg.c, 880 deg.c, 900 deg.c, 920 deg.c, 940 deg.c, 960 deg.c, 980 deg.c, 1000 deg.c, 1020 deg.c, 1040 deg.c, 1060 deg.c, 1080 deg.c, 1100 deg.c, not limited to the values; the incubation time may be any value within the above range, such as 0h, 0.1h, 0.2h, 0.3h, 0.5h, 0.7h, 0.9h, 1h, 2h, 3h, 4h, 5h, and is not limited to the above values; on the premise of ensuring the growth of single crystals, the heat preservation time of the high-temperature section is as short as possible, because the disordered rock salt phase is a thermodynamically stable phase at the temperature, the calcination temperature and the heat preservation time of the high-temperature section are fully controlled in order to avoid the increase of lithium nickel mixed discharge as much as possible and ensure that high-nickel polycrystalline particles grow into single crystal particles.
Step 4, according to the calculation formula D= (1/2D) a of thermodynamic stability and ion diffusion coefficient D 2 ν 0 exp(-E A /k B T) determining mixed control sintering temperature and mixed control sintering time of mixed control sintering, carrying out mixed control sintering on the high-temperature sintering material at the mixed control sintering temperature, and keeping the mixed control sintering time to obtain the high-nickel monocrystal material; wherein d is the diffusion dimension, a is the transition length, v 0 For collision frequency, E A Is the activation energy of ion transition, k B Is the boltzmann constant, and T is the temperature.
And determining a sintering temperature interval of the mixed discharge control step according to an experimental rule. NCM811 with lower mixed emission below 780 ℃ is a thermodynamically stable phase, and LiNiO with lower mixed emission below 670 DEG C 2 The thermodynamically stable phase of other high nickel materials with lower miscibility is between these two temperatures. Therefore, in order to reduce mixing, calcination should be performed at a lower temperature for a certain time. In addition, the sintering temperature is properly reduced within a certain range, which is beneficial to obtaining the high-nickel material with little lithium enrichment. Because of the proper temperature reduction sintering, part of lithium ions can enter NiO 6 The positions of Ni are substituted in the layer, thereby forming a lithium-rich high nickel material. Such as LiNiO 2 When sintered below 670 ℃, part of lithium ions replace part of Ni positions. To achieve a slightly lithium rich state, the ratio of lithium to transition metal in the product should not exceed 1.05, while the sintering temperature should not be below 600 ℃, otherwise excessive lithium occupying the nickel layer would also cause a decrease in material properties.
According to thermodynamic equilibrium relation between defects and temperature, the mixed discharge can be recovered after sintering at a high temperature section at a low temperature Duan Shaojie. However, recovery of miscibility in the low temperature zone will be closely related to ion migration rate.
Consider ion diffusionThe calculation formula of the coefficient is D= (1/2D) a 2 ν 0 exp(-E A /k B T), the ion diffusion coefficient at different temperatures is mainly determined by exp (-E) A /k B T) determination. Assuming that the activation energy of the ion transition is unchanged at different temperatures, the value is 1eV, and exp (-E) at each temperature is calculated A /k B T), and the multiplying power relative to the ion diffusion coefficient at 670 ℃, as shown in table 2.
TABLE 2
It is generally believed that the actual activation energy is on the order of 1eV, and it can be seen from the table that the ion mobility at high temperature, i.e., 800-1100 c, is several times or even tens of times that at 670 c, where the higher the temperature, the greater the ion diffusion coefficient. Therefore, after ion migration occurs during sintering at a high temperature, it is necessary to restore Ni occupation in a formed more lithium layer at least for several times or even tens times sintering at a low temperature, and before it is possible to restore the mixed emission caused by high temperature sintering to the maximum extent, for example, the ion diffusion coefficient at 1100 ℃ is about 47 times of 670 ℃, so that when the high temperature sintering temperature is 1100 ℃ and the mixed emission control sintering temperature is 670 ℃ at a low temperature, the sintering time is at least 47 times or more times of the high temperature sintering time, whereby the mixed emission restoration (reduction) process can be promoted. When the high-temperature sintering temperature is 800 ℃, the sintering time is about 5 times of the high-temperature sintering time when the mixed discharge control sintering temperature is 670 ℃. Considering that the time of high-temperature sintering is controlled within 5 hours, the low-temperature sintering time can be controlled between 5 hours and 200 hours according to the ion diffusion coefficient analysis. Preferably, the advantage of faster ion diffusion at relatively high temperatures can be exploited for staged sintering, reducing the total sintering time.
The invention comprehensively considers the balance of the lithium nickel mixed discharge rate and the micro lithium-rich state, and limits the temperature and time of mixed discharge control sintering: the sintering temperature is controlled to be 600-780 ℃ by mixing and the sintering time is controlled to be 5-200 h by mixing. Furthermore, the mixed control sintering time for reducing mixed emission by low-temperature sintering is preferably m times of the high-temperature sintering heat preservation time, and m is more than or equal to 10; preferably, the mixed discharge control sintering time is more than or equal to 15h, because the heat preservation time is long enough to be more beneficial to the conversion of the disordered rock salt structure into the layered structure based on the potential barrier of the layered structure and the disordered rock salt structure, thereby obtaining the high-nickel single crystal material with lower lithium nickel mixed discharge rate.
In the low-temperature sintering process for reducing mixed discharge, the material is sintered at a low temperature of 600-780 ℃ and the heat preservation time is 5-200 h, so as to promote the transformation of rock salt phase to lamellar phase, thereby obtaining the high-nickel monocrystal material with extremely low lithium-nickel mixed discharge degree. Since sintering of the high temperature section is necessary for synthesizing the high nickel single crystal material, occurrence of lithium nickel mixed discharge is unavoidable. According to the invention, after high-temperature sintering, long-time heat preservation sintering at a low-temperature section is further arranged, so that the disordered rock salt phase structure can be converted into a lamellar phase structure. The temperature may be any value within the above range, such as 600 ℃, 610 ℃, 620 ℃, 630 ℃, 640 ℃, 650 ℃, 660 ℃, 670 ℃, 680 ℃, 690 ℃, 700 ℃, 710 ℃, 720 ℃, 730 ℃, 740 ℃, 750 ℃, 760 ℃, 770 ℃, 780 ℃, and not limited to the above values; the incubation time may be any value within the above range, such as 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 18h, 20h, 30h, 40h, 50h, 60h, 70h, 80h, 90h, 100h, 110h, 120h, 130h, 140h, 150h, 160h, 170h, 180h, 190h, 200h, and is not limited to the above values.
The low-temperature sintering is carried out at 600-780 ℃, and can be one-time sintering, for example, the following concrete steps are: cooling the high-temperature sintering material obtained after high-temperature calcination at 800-1100 ℃ to 600-780 ℃ for low-temperature sintering; or cooling the high-temperature sintering material obtained after high-temperature calcination at 800-1100 ℃ to room temperature, and then re-heating to 600-780 ℃ for low-temperature sintering. The low-temperature sintering may be a low-temperature sintering in a segment in the above temperature range, specifically, the low-temperature sintering may be a sintering at a plurality of different temperatures in the above temperature range, may be a sintering in segments from low to high temperature values, may be a sintering in segments from low to high temperature to low temperature, or may be a sintering in segments from high to low temperature values. For example, sintering is performed at 700℃to 780℃for 1 to 10 hours, followed by 680℃to 700℃for 10 to 50 hours, followed by 650℃to 680℃for 10 to 50 hours, and finally 600℃to 650℃for 10 to 50 hours. In a specific example, the material may be sintered at 610 ℃ for 10 hours, then heated to 670 ℃ for 10 hours, then cooled to 680 ℃ for 10 hours, finally heat-preserved at 700 ℃ for 10 hours, or may be sintered at low temperature-high temperature-low temperature for 10 hours, for example, sintered at 610 ℃ for 10 hours, then heated to 670 ℃ for 10 hours, then heated to 700 ℃ for 10 hours, finally heat-preserved at 680 ℃ for 10 hours, or may be sintered at different temperatures from high to low for example, sintered at 700 ℃ for 10 hours, then cooled to 680 ℃ for 10 hours, then cooled to 670 ℃ for 10 hours, and finally heat-preserved at 610 ℃ for 10 hours. The specific embodiment of the present invention is not limited to the above-described embodiments, and may be any method as long as the method is sintering in the above-described temperature range.
The single crystal material of the present invention is a positive electrode particle having a larger primary particle and a diameter of 1.5 μm or more.
The molar ratio of lithium to the total amount of other metals in the high-nickel single crystal material is 1.01:1-1.10:1, and the preferable range is 1.01:1-1.05:1. Any value within the above ranges, for example, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1, 1.10:1, is not limited to the above values. The high nickel monocrystal material synthesized by the preparation process is in a slightly lithium-rich state, so that Ni is formed 2+ After being fully oxidized and migrate to the nickel layer, thus not only greatly reducing Ni 2+ At the same time, a small excess of Li is present in the site of the lithium layer + Can also enter the nickel layer for storage, thereby obtaining the high nickel material with Li in the lithium layer and the nickel layer interlayer distribution and the nickel layer. The control of the content of lithium source, the reaction atmosphere and/or the sintering method can be beneficial to the monocrystal material to be in a slightly lithium-rich state, so that Ni in the lithium layer is effectively reduced 2+ The barrier to the transmission of lithium ions is reduced, and as a trace amount of lithium ions are also contained in the nickel layer, an additional lithium source is formed and provided in the charge and discharge process, and the discharge specific capacity of the high-nickel monocrystal material can be improved. Meanwhile, the invention is in a slightly lithium-rich state, and the distortion of a nickel layer in the layered structure is avoided.
In the high-nickel monocrystal material prepared by the method, the lithium nickel mixed discharge rate is below 4%. Preferably, the lithium nickel mixed discharge rate of the high nickel single crystal material is below 2%. Wherein, the lithium nickel mixed row value is the nickel atom ratio in the lithium layer, c is the height of the unit cell, and a is the length and width (equal to the length and width) of the unit cell. The parameters of the unit cells such as lithium nickel misce-line, a, c and the like are obtained directly by carrying out Rietveld refinement on XRD data of the samples.
The Rietveld structure refinement refers to a method for obtaining sample crystal structure information by utilizing full spectrum information of polycrystalline diffraction data, calculating polycrystalline diffraction spectrum by combining a peak shape function on the basis of a crystal structure model and structural parameters, and adjusting the structural parameters and the peak shape parameters by using a least square method to enable the calculated diffraction spectrum to be consistent with an experimental spectrum, so that an initial crystal structure gradually approaches to a real crystal structure. Rietveld refinement is mainly aimed at obtaining phase quantitative results, crystallinity and relatively accurate crystal structure parameters, such as unit cell parameters, grain size, microscopic strain, atomic coordinates, occupancy and temperature factors, from high-quality powder diffraction data, so as to obtain information of expansion coefficient, doping concentration, bond length, bond angle, etc.
According to the diffraction spectrum calculation formula:the following functions were constructed:
wherein: i φ，h ＝{LAPCF 2 } φ，h ；S Φ Is the structural factor of phase phi, L h Comprises Lorentzian factor, polarization factor, multiple factor, A h To absorb factors, P h C as a preferred orientation function h F is a special correction factor h As structural factor, b i For backing intensity, h represents the XRD diffraction peak, Ω is a peak shape function (including sample and instrument parts), Ω is T i -T Φ,h T is a function of (1) i Is the diffraction angle, T Φ,h Is the standard diffraction angle position corresponding to the h peak of phase phi. X is X 2 To refine error, y i For observation under 2 theta angleIntensity of diffraction, y c,i To the theoretical diffraction intensity at the same angle, w i As weights, α is a refined parameter. And optimizing and solving the minimum by using Newton Laplains algorithm, thereby obtaining the unit cell parameters such as lithium nickel mixed discharge and the like corresponding to the minimum.
According to the invention, a 6-order spherical harmonic function is used for fitting the preferred orientation so as to reduce the fitting error (the spherical harmonic function is a group of space complete orthogonal bases, and the linear combination of the spherical harmonic function is used for fitting the space probability distribution function of the crystal face diffraction peak so as to better determine the preferred orientation, and the specific principle can refer to GSAS II official course (subversion. Xray. Aps. Anl. Gov/pyGSAS/Tutorials/2DTexture/Texture analysis of 2D data in GSAS-II. Htm). Finally, the more accurate lithium nickel mixed discharge rate and the numerical values of a and c can be obtained, and then the index of the optimal mixed discharge degree of the reaction lamellar material of the lithium nickel mixed discharge value and the c/a value measured by the method can be calculated.
The preparation method of the high-nickel monocrystalline material provided by the invention adopts a method of preheating, heat preservation, low-temperature sintering, high-temperature calcining and low-temperature sintering, and can obtain the high-nickel monocrystalline material with excellent electrochemical performance. Specifically, the method comprises the steps of firstly, preserving the mixture at 150-500 ℃ for a period of time to promote complete and uniform lithiation of the precursor, so that the discharge capacity of the product is higher and the consistency of the product is better; then sintering for 5-15h at a low temperature of 600-750 ℃ to synthesize a high-nickel polycrystalline material, so that the problem of serious lithium nickel mixed discharge caused by directly forming a single crystal material at a high temperature in one step can be effectively avoided by obtaining the polycrystalline material which is uniform in lithiation, lower in mixed discharge, better in performance and higher in capacity; then heating the high-nickel polycrystalline material to a high temperature Duan Shaojie and preserving heat, wherein the sintering temperature and time are determined by the relationship between the unique image dynamics and the relationship between the defect concentration and the defect generation energy and the temperature, so that the high-temperature sintering is utilized to promote the growth of primary particles of the polycrystalline to become single crystals and reduce the lithium nickel mixed discharge degree as much as possible; and finally, determining the temperature and time of the low-temperature section through thermodynamic stability and ion diffusion coefficient so as to further promote the reduction of the lithium nickel mixed discharge phenomenon.
The invention adopts a multi-stage sintering method of preheating, heat preservation, low-temperature sintering, high-temperature calcination and low-temperature sintering, and fully utilizes the thermodynamic principle to improve the synthesis process of the high-nickel monocrystal material, namely, the mixed discharge phenomenon in the monocrystal material is reduced by controlling the sintering process. The invention not only realizes the reduction of the mixed discharge phenomenon by avoiding the long-time calcination in the high temperature section as much as possible, but also ensures that enough and effective monocrystalline materials can be synthesized and the monocrystalline materials are distributed in a regular lamellar structure.
The present invention will be further described with reference to the following examples, which are provided for the purpose of more clearly illustrating the objects and advantages of the present invention, and further, the examples described in the present invention are only some examples, based on the examples described in the present invention, which are obtained by those skilled in the art without making any inventive effort.
The experimental examples do not specify specific experimental procedures or conditions, and can be performed according to the operations or conditions of conventional experimental procedures described in the literature in the field. The reagents or apparatus used were conventional reagent products commercially available without the manufacturer's knowledge. The blue electricity tester model is CT3002A.
Example 1
This example prepares a LiNiO 2 The preparation method of the monocrystalline material comprises the following steps:
(1) LiOH.H 2 O and Ni (OH) 2 Uniformly mixing according to a molar ratio of 1.08:1;
(2) Sintering the mixture obtained in the step (1) for 3 hours at 485 ℃ in pure oxygen atmosphere, then heating to 650 ℃ for 2 hours, heating to 850 ℃ at 10 ℃/min for 5 hours, then cooling to 650 ℃ and preserving heat for 48 hours to obtain LiNiO 2 The SEM and XRD of the single crystal material is shown in figure 8.
As shown in FIG. 8a, the single crystal grain size prepared in example 1 is about 2-3 microns, and the particle size is uniform and the morphology is similar, which indicates that the single crystal grain prepared in the invention has uniform morphology.
As shown in fig. 8b, XRD test shows that the material prepared in example 1 has typical cleavage of (006) peak and (102) characteristic peak, and the (003) peak and (104) peak are stronger than each other, and are in a layered structure. And the lithium nickel mixing rate is 3.30% through Rietveld refinement.
Characterization of electrochemical properties:
(1) coating of a single-crystal high-nickel pole piece: single crystal high nickel according to mass ratio (same as below): conductive carbon black (SP): polyvinylidene fluoride (PVDF) =80:10:10 was homogenized, coated on 20um thick aluminum foil, and pole piece areal density was about 5mg/cm 2 ；
(2) And (3) battery assembly: button battery shell R2032 with metallic lithium as a negative electrode is used for buckling and assembling, a diaphragm made of Polyethylene (PE) with double surfaces coated with aluminum oxide is adopted, and 80 mu L of electrolyte is dripped;
(3) Testing the charge and discharge performance at 25 ℃): the assembled battery of the sample in example 1 was tested using a blue tester, and the prepared coin cell was put in a constant temperature oven at 25 ℃ for charge and discharge testing, with a voltage range of 2.75V-4.3V,0.1C (1c=200 mA/g) charge and discharge. The electrochemical properties are shown in fig. 9 and table 3.
Example 2
This example prepares a LiNi 0.92 Co 0.03 Mn 0.05 O 2 The preparation method of the monocrystalline material comprises the following steps:
(1)LiOH·H 2 o and LiNO 3 Uniformly mixing according to a molar ratio of 0.62:0.38 to obtain a lithium source mixture;
(2) Mixing the lithium source mixture with Ni 0.92 Co 0.03 Mn 0.05 (OH) 2 Mixing according to the ratio of 1.08:1;
(3) Sintering the mixture obtained in the step (2) at 485 ℃ for 3 hours, then sintering at 700 ℃ for 5 hours, heating to 900 ℃ at 15 ℃/min for 5 hours, then cooling to 700 ℃ and preserving heat for 25 hours to obtain the LiNi 0.92 Co 0.03 Mn 0.05 O 2 A monocrystalline material.
SEM and XRD of the resulting single crystal material are shown in fig. 10c-d, and in addition, after sintering the mixture of step (3) at 485 ℃ for 3 hours, followed by sintering at 700 ℃ for 5 hours, a part of the sample was taken out as a comparative sample, and SEM and XRD tests were performed as shown in fig. 10 a-b.
As shown in FIG. 10aSEM, the primary particles of the product obtained after sintering at 700℃for 5 hours were small, 0.2-0.5 μm, and were polycrystalline particles. As can be seen from fig. 10b, the cleavage of the (006) peak and the (102) characteristic peak is obvious, and the peak-to-peak intensity ratio of the (003) peak to the (104) peak is greater than 1, which indicates that a layered material is obtained, the lithium nickel mixed discharge of which is 2.7%, and indicates that a high nickel polycrystalline material with lower lithium nickel mixed discharge is obtained in the low temperature sintering process before high temperature calcination.
As shown in FIG. 10c, the high nickel single crystal obtained in example 2 had a particle size of about 1.5. Mu.m. As can be seen from the XRD analysis chart shown in fig. 10d, the material prepared in example 2 has typical cleavage of characteristic peaks such as (006) and (102) and has a layered structure. A typical layered structure material was obtained in example 2, and it was found that lithium nickel was mixed to 3.8% by calculation.
Characterization of electrochemical properties:
(1) coating of a single-crystal high-nickel pole piece: according to the single crystal high nickel: SP: PVDF=90:5:5 was homogenized, coated on 20um thick aluminum foil, and pole piece areal density was about 4mg/cm 2 ；
(2) And (3) battery assembly: button battery shell R2032 with metallic lithium as a negative electrode is used for buckling and assembling, a PE diaphragm with double surfaces coated with aluminum oxide is adopted, and 80 mu L of electrolyte is dripped;
(3) testing the charge and discharge performance at 25 ℃): the assembled battery of the sample of example 2 was tested using a blue electric tester, and the prepared coin cell was placed in a constant temperature oven at 25 ℃ for charge and discharge testing at a current of 0.1C (1c=200 mA/g) and a voltage in the range of 2.7-4.3V. The electrochemical properties are shown in fig. 11 and table 3.
Example 3
LiOH·H 2 O and Ni 0.92 Co 0.03 Mn 0.05 (OH) 2 According to the mole ratio of 1.06:1, respectively sintering according to the following two sintering methods:
1) Presintering at 485 ℃ for 5h, sintering at 720 ℃ for 6h, rapidly heating to 960 ℃ at a heating rate of 10 ℃/min, and then cooling to 720 ℃ at a cooling rate of 10 ℃/min, and preserving heat for 6h to obtain the high-nickel monocrystal material LiNi 0.92 Co 0.03 Mn 0.05 O 2 The sample name is sample 3a, and the lithium nickel mixed discharge rate of the material is 3.3%;
2)485℃presintering for 5h, sintering at 720 ℃ for 6h, rapidly heating to 1000 ℃ at a heating rate of 10 ℃/min, and then cooling to 720 ℃ at a cooling rate of 10 ℃/min, and preserving heat for 6h to obtain the high-nickel monocrystal material LiNi 0.92 Co 0.03 Mn 0.05 O 2 The sample name is sample 3b, and the lithium nickel mixed discharge rate of the material is 3.4%.
In FIG. 12, SEM images of samples 3a and 3b are shown, and it can be seen that the high nickel single crystal particles were not completely dispersed, and that the average size of the single crystal particles was about 1.5. Mu.m.
Characterization of electrochemical properties:
(1) coating of a single-crystal high-nickel pole piece: according to the single crystal high nickel: SP: PVDF=90:5:5 was homogenized, coated on 15um thick aluminum foil, and pole piece areal density was about 10mg/cm 2 ；
(2) And (3) battery assembly: button battery shells of R2032, which are used as a negative electrode, are subjected to buckling assembly, a diaphragm made of common PE (polyethylene) material is adopted, and 40 mu L of electrolyte is dripped;
(3) testing the charge and discharge performance at 25 ℃): the assembled battery of the sample in example 3 was tested using a blue electric tester, and the prepared coin cell was put in a constant temperature oven at 25 ℃ for charge and discharge testing at a test current of 0.1C (1c=200 mA/g) and a voltage range of 2.7-4.3V. The electrochemical properties are shown in fig. 13a and table 3.
Example 4
LiOH·H 2 O and Ni 0.92 Co 0.03 Mn 0.05 (OH) 2 According to the mole ratio of 1.08:1, respectively sintering according to the following two sintering methods:
1) Presintering at 485 ℃ for 5h, sintering at 720 ℃ for 10h, rapidly heating to 960 ℃ at a heating rate of 10 ℃/min, and then cooling to 720 ℃ at a cooling rate of 10 ℃/min, and preserving heat for 16h to obtain the high-nickel monocrystal material LiNi 0.92 Co 0.03 Mn 0.05 O 2 The sample name is sample 4a, and the lithium nickel mixed discharge rate of the material is 1.9%;
2) Presintering at 485 ℃ for 5h, sintering at 720 ℃ for 10h, rapidly heating to 1000 ℃ at a heating rate of 10 ℃/min, and then cooling to 720 ℃ at a cooling rate of 10 ℃/min, and preserving heat for 16h to obtain the high-nickel monocrystal material LiNi 0.92 Co 0.03 Mn 0.05 O 2 The sample name is sample 4b, and the lithium nickel mixed discharge rate of the material is 1.9%.
FIGS. 14a-b are SEM images of samples 4a and 4b, respectively, and it can be seen from the drawings that the high nickel single crystal particles were not completely dispersed, and that the single crystal particles had an average size of about 1.5. Mu.m.
Characterization of electrochemical properties:
the pole piece coating, battery assembly and charge and discharge performance test were the same as in example 3. The electrochemical properties are shown in fig. 13a and table 3.
Example 5
(1) Will CH 3 COOLi、LiNO 3 、Li 2 SO 4 The molar ratio is 0.2:0.4:0.2 mixing to obtain a lithium source mixture;
(2) Mixing the lithium source mixture with Ni (OH) 2 Uniformly mixing according to the molar ratio of lithium to nickel of 1.08:1, sintering the mixture at 485 ℃ for 3 hours, then sintering at 650 ℃ for 15 hours, cooling to room temperature, washing with absolute ethanol at 2 ℃ for three times, and washing with distilled water for 1 time to obtain polycrystalline LiNiO 2 A material. Subsequently, the polycrystalline LiNiO 2 Mixing the material and LiOH uniformly according to the molar ratio of 100:2, continuously heating to 900 ℃ at 20 ℃/min after mixing, preserving heat and sintering for 0.5h, and then cooling to 670 ℃ at 10 ℃/min and sintering for 66h to obtain the high-nickel monocrystal LiNiO 2 A material. The SEM of the single crystal material obtained is shown in fig. 15.
As shown in FIG. 15, the single crystal material synthesized in example 5 had a particle diameter of about 2. Mu.m, and a lithium nickel mixed discharge rate of 2.7%.
Electrochemical performance test:
(1) coating of a single-crystal high-nickel pole piece: according to the single crystal high nickel: SP: PVDF=90:5:5 was homogenized, coated on 15um thick aluminum foil, and pole piece areal density was about 10mg/cm 2 ；
(2) And (3) battery assembly: button battery shells of R2032, which are used as a negative electrode, are subjected to buckling assembly, a diaphragm made of common PE (polyethylene) material is adopted, and 40 mu L of electrolyte is dripped;
(3) testing the charge and discharge performance at 25 ℃): the assembled battery of the sample of example 4 was tested using a blue electric tester, and the prepared coin cell was put in a constant temperature oven at 25 ℃ for charge and discharge testing with a test current in the range of 2.7-4.3V at 0.1C (1c=200 mA/g), and electrochemical properties as shown in fig. 16 and table 3.
Example 6
(1) LiOH.H 2 O and LiNO 3 Uniformly mixing according to the molar ratio of 0.62:0.38 to obtain a lithium source mixture;
(2) Mixing the lithium source mixture with Ni (OH) 2 The lithium and nickel are mixed according to the molar ratio of 5:1, and a higher lithium ratio is used, so that the single crystal with more uniform size can be burned. Sintering the mixture at 485 ℃ for 3 hours, then sintering at 650 ℃ for 15 hours, heating to 910 ℃ at 10 ℃/min for 5 minutes, cooling to 700 ℃ at 10 ℃/min for 10 hours, cooling to 685 ℃ for 20 hours, cooling to 670 ℃ for 30 hours, finally preserving heat at 610 ℃ for 20 hours, washing the product with deionized water at 2 ℃ for three times, centrifuging, and drying to obtain single crystal LiNiO 2 The SEM of the material is shown in fig. 17.
As shown in FIG. 17, the single crystal particles were uniform in size and particle diameter of 1-2. Mu.m.
The step of electrochemical performance testing comprises:
(1) coating of a single-crystal high-nickel pole piece: according to the single crystal high nickel: SP: PVDF=90:5:5, coated on 15um thick aluminum foil, pole piece areal density of about 8mg/cm2;
(2) and (3) battery assembly: button battery shell R2032 with metallic lithium as a negative electrode is used for buckling and assembling, a PE diaphragm with one side coated with alumina is adopted, and 60 mu L of electrolyte is dripped;
(3) testing the charge and discharge performance at 25 ℃): the assembled battery of example 5 was tested using a blue electric tester, and the prepared coin cell was subjected to a charge-discharge test in a constant temperature oven at 25 ℃ at a test current of 0.1C (1c=200 mA/g) and a voltage in the range of 2.7-4.3V, the initial cycle charge-discharge curve of which is shown in fig. 18, and the single crystal lithium nickel oxide exhibited a capacity exceeding 218mAh/g, exceeding that of the single crystal high nickel material reported previously.
Example 7
LiOH·H 2 O and Ni (OH) 2 Uniformly mixing according to a molar ratio of 1.10:1, sintering at 485 ℃ for 3 hours, then sintering at 650 ℃ for 10 hours in pure oxygen atmosphere, then heating to 1100 ℃ at a rate of 20 ℃/min, rapidly cooling to 700 ℃ at a rate of 20 ℃/min after the temperature reaches 1100 ℃ for 5 hours, then cooling to 685 ℃ at a rate of 10 ℃/min for 10 hours, then cooling to 670 ℃ for 50 hours at a rate of 10 ℃/min, finally cooling to 610 ℃ for 20 hours at a rate of 10 ℃/min, naturally cooling, and obtaining single crystal LiNiO 2 The SEM and XRD patterns of the material are shown in figure 19.
As shown in fig. 19a, it can be seen from SEM of single crystal material that the material has a typical single crystal morphology, and single crystal particles are large in size, with an average particle size of 2 μm. As shown in fig. 19b, the XRD pattern showed a 1.8% miscibility gap.
Characterization of electrochemical properties:
(1) coating of a single-crystal high-nickel pole piece: according to the single crystal high nickel: SP: PVDF=90:5:5 was homogenized, coated on 15um thick aluminum foil, and pole piece areal density was about 8mg/cm 2 ；
(2) And (3) battery assembly: button battery shell R2032 with metallic lithium as a negative electrode is used for buckling and assembling, a PE diaphragm with one side coated with alumina is adopted, and 60 mu L of electrolyte is dripped;
(3) long cycle performance test at 30 ℃): the assembled battery of example 6 was tested using a blue tester, and the prepared coin cell battery was put in a constant temperature oven at 30 ℃ for charge and discharge testing at a test current of 0.1C (1c=200 mA/g) at the first week, followed by 100 cycles at a rate of 1C over a voltage interval of 2.7-4.3V. The cycle performance curve is shown in fig. 20.
Elemental analysis:
the element proportion of the single crystal material is tested by adopting Inductively Coupled Plasma (ICP), and the specific testing steps are as follows: the sample was dissolved in nitric acid and tested for its characteristic line intensity to obtain elemental content. The results are shown in Table 4.
Example 8
LiOH·H 2 O and Ni 0.96 Co 0.02 Mn 0.02 (OH) 2 Mixing according to the mol ratio of 1.09:1, mixingSintering the material at 485 ℃ for 3 hours, then sintering at 650 ℃ for 5 hours, heating to 950 ℃ at the speed of 20 ℃/min, rapidly cooling to 680 ℃ at the speed of 20 ℃/min, sintering for 10 hours, then cooling to 670 ℃ for sintering for 10 hours, cooling, and grinding to obtain the single crystal compound. Then according to the single crystal compound and LiOH H 2 O is uniformly mixed according to the mol ratio of 100:1, and finally, the temperature is kept at 650 ℃ for 10 hours, and the temperature is naturally reduced, thus obtaining single crystal LiNi 0.96 Co 0.02 Mn 0.02 O 2 A material.
Inductively coupled plasma spectroscopy (ICP) test results showed a Li/Ni ratio of 1.02:1.00, which indicates a slightly lithium rich state of the single crystal material level. The lithium nickel mixed discharge rate of the single crystal material is 2.42 percent through XRD refinement.
Characterization of electrochemical properties:
the pole piece coating, battery assembly and charge and discharge performance test were the same as in example 3.
Example 9
LiOH·H 2 O and Ni 0.96 Co 0.02 Mn 0.02 (OH) 2 Mixing according to the mol ratio of 1.07:1, sintering the mixture at 485 ℃ for 3 hours, then heating to 650 ℃ for 5 hours, then heating to 950 ℃ at 30 ℃/min, rapidly cooling to 680 ℃ at 20 ℃/min for 10 hours, then cooling to 670 ℃ for 10 hours, cooling and grinding. Finally preserving heat for 10 hours at 650 ℃, naturally cooling to obtain single crystal LiNi 0.96 Co 0.02 Mn 0.02 O 2 . The inductively coupled plasma spectroscopy (ICP) test showed a Li/Ni ratio of 0.99:1.00. the lithium nickel mixed discharge rate of the XRD refined single crystal material is 2.83%.
Characterization of electrochemical properties:
the pole piece coating, battery assembly and charge and discharge performance test were the same as in example 3.
The results of the electrochemical tests of examples 8-9 are shown in FIG. 21.
Comparative example 1
LiOH·H 2 O and Ni (OH) 2 Mixing according to the ratio of 1.08:1, sintering the mixture at 485 ℃ for 3 hours, and then heating to 850 ℃ at 10 ℃/min for 15 hours to obtain LiNiO 2 A monocrystalline material. SEM and XRD of the resulting material are shown in FIG. 22Shown.
As shown in FIG. 22a, the single crystal size was 1-2 μm by SEM analysis,
as shown in FIG. 22b, the XRD analysis shows that the 003/104 peak intensity is relatively low, and XRD refinement shows that the lithium nickel mixed discharge is 10.14% and the mixed discharge is serious.
Characterization of electrochemical properties:
the pole piece coating, battery assembly and charge and discharge performance test were the same as in example 1. The electrochemical properties are shown in fig. 9 and table 3.
Comparative example 2
(1)LiOH·H 2 O and LiNO 3 Mixing according to a molar ratio of 0.62:0.38 to obtain a lithium source mixture;
(2) Mixing the lithium source mixture with Ni 0.92 Co 0.03 Mn 0.05 (OH) 2 Mixing according to the ratio of 1.08:1;
(3) Sintering the mixture obtained in the step (2) at 485 ℃ for 3 hours, then sintering at 900 ℃ for 5 hours, and preserving heat at 700 ℃ for 25 hours to obtain the LiNi 0.92 Co 0.03 Mn 0.05 O 2 A monocrystalline material. SEM and XRD of the resulting material are shown in figure 23.
As shown in fig. 23 a. As can be seen from SEM analysis, the grain size of the single crystal material was about 1.5. Mu.m, which is similar to that of example 2.
As shown in fig. 23b, lithium nickel misce was calculated to be 14.2% by XRD test results.
Characterization of electrochemical properties:
the pole piece coating, battery assembly and charge and discharge performance test were the same as in example 2. The electrochemical properties are shown in fig. 11 and table 3.
Comparative example 3
LiOH.H 2 O and Ni 0.92 Co 0.03 Mn 0.05 (OH) 2 Mixing according to the mol ratio of 1.06:1, sintering the mixture at 870 ℃ for 15 hours to obtain the LiNi 0.92 Co 0.03 Mn 0.05 O 2 A monocrystalline material. As shown in FIG. 24, the SEM of the single crystal was found to be about 0.5 to 1.0. Mu.m.
Characterization of electrochemical properties:
the pole piece coating, battery assembly and charge and discharge performance test were the same as in example 3. The electrochemical properties are shown in FIG. 13b and Table 3.
Comparative example 4
LiOH.H 2 O and Ni (OH) 2 Mixing according to the ratio of 1.08:1, sintering for 3 hours at 485 ℃, then sintering for 15 hours at 650 ℃, and naturally cooling to obtain the polycrystalline LiNiO 2 A material. SEM and XRD thereof are shown in fig. 25.
As shown in FIG. 25a, the secondary particles of the polycrystalline material of the comparative example had a particle size of 3-4 μm and the primary particles had a size of 0.2-0.5 μm, and the XRD results shown in FIG. 25b indicate that the prepared material had cleavage of typical (006) peaks and (102) characteristic peaks, and the structural laminarity thereof remained good.
Characterization of electrochemical properties:
pole piece coating, battery assembly and charge and discharge performance testing were the same as in example 7. The electrochemical properties are shown in fig. 20 and table 3.
Comparative example 5
(1) LiOH.H 2 O and Ni (OH) 2 Uniformly mixing according to a molar ratio of 1.08:1;
(2) Sintering the mixture obtained in the step (1) for 3 hours at 485 ℃ in pure oxygen atmosphere, then heating to 650 ℃ for 2 hours, heating to 850 ℃ at 10 ℃/min for 5 hours, and then cooling to room temperature to obtain LiNiO 2 The SEM and XRD of the single crystal material is shown in FIG. 26. SEM showed that single crystal size was 2-4 μm, XRD results showed (006) and (102) peak cleavage to be very insignificant, and finishing results showed that XRD finishing gave 6.94% of its lithium nickel misce bene.
Characterization of electrochemical properties:
the pole piece coating, battery assembly and charge and discharge performance test were the same as in example 1. The electrochemical properties are shown in fig. 27 and table 3.
TABLE 3 Table 3
Inductively coupled plasma spectroscopy (ICP) test results:
the element proportion of the monocrystalline material is tested by ICP, and the specific testing steps are as follows: the sample was dissolved in nitric acid and tested for its characteristic line intensity to obtain elemental content. ICP elemental analysis was performed for examples 7 to 9 and comparative example 4, and the ICP results are shown in Table 4. The molar ratio of lithium and nickel elements in the partially synthesized single crystal lithium nickelate is greater than 1, and the partially synthesized single crystal lithium nickelate shows a slightly lithium-rich component.
| Sample of | Li/ppm | Ni/ppm | Li: ni (molar ratio) |
| Example 7 | 68973.02 | 575331.85 | 1.02 |
| Example 8 | 65391.67 | 543285.24 | 1.02 |
| Example 9 | 72161.12 | 618927.39 | 0.99 |
| Comparative example 4 | 70494.81 | 582434.12 | 1.03 |
TABLE 4 Table 4
Performance analysis:
1) Example 1 LiNiO was prepared by a multistage sintering method of preheating, heat preservation, low temperature sintering, high temperature calcination and low temperature sintering, namely 485℃3h to 650℃2h to 850℃5h to 650℃48h 2 A monocrystalline material; comparative example 1 was prepared by a high temperature one-step sintering method, namely 485℃3h to 850℃15h 2 A monocrystalline material. In example 1, the low temperature sintering step was performed before and after the high temperature sintering at 850 ℃, whereas in comparative example 1, the low temperature sintering step was not performed before and after the high temperature sintering at 850 ℃.
As can be seen from FIGS. 8a and 22a, the single crystal size of example 1 was 2 to 3. Mu.m, and the single crystal size of comparative example 1 was 1 to 2. Mu.m. It can be seen that the single crystal material obtained in example 1 was larger in size and smaller in specific surface area, whereas the high-nickel single crystal material obtained in comparative example 1 was smaller in grain size by sintering only by the high-temperature one-step method. This shows that the growth of single crystal grains is facilitated by the preparation method of the present invention.
As shown in Table 3, single crystal LiNiO prepared in example 1 2 The lithium nickel mixed rate of (3.3%) was found to be 3.3%, while the single crystal LiNiO prepared in comparative example 1 was obtained 2 The lithium nickel miscibility of (2) was 10.14%, the lithium nickel miscibility of example 1 was significantly lower than that of comparative example 1, and the c/a in example 1 was 4.931 as shown by the parameters of the single crystal material, whereas the improvement in c/a was only 4.925 as shown by comparative example 1, which also indicates that the kinetic properties of the single crystal material of example 1 were better. In combination with the charge and discharge properties of both shown in fig. 9, the first-week specific discharge capacity of example 1 was 192.2mAh/g, the first-week coulomb efficiency was 80.5%, and the first-week specific discharge capacity of comparative example 1 was only 146.89mAh/g, and the first-week coulomb efficiency was only 66.1%. Thus, example 1 was significantly higher than comparative example 1 in terms of specific capacity at the first week, and also in terms of coulombic efficiency at the first week, the specific capacity of discharge was nearly 50mAh/g higher than comparative example 1, and the coulombic efficiency at the first week was nearly 15%. Thus, it can be seen that although example 1 and comparative example 1 are both single crystal LiNiO 2 The invention adopts the technology of converting high nickel polycrystal into high nickel monocrystal and combining post-treatment low-temperature calcination, so that the microstructure of the material is obviously changed, and the lithium nickel mixed discharge rate is 3.3 percent. It can be seen that the electrochemical properties of the high nickel monocrystal material, such as specific discharge capacity, initial cycle coulomb efficiency and the like, are obviously improved through the improvement of the microstructure.
In addition, comparative example 5 compared with example 1, the preparation process was 485℃3h to 650℃2h to 850℃5h, and there was no long-time low-temperature heat-preserving step at 650℃48h after high-temperature calcination, and single crystal LiNiO was prepared 2 The lithium nickel mixed discharge rate of (2) was 6.94%, which was about twice the lithium nickel mixed discharge rate of example 1. In combination with the charge and discharge performance, the first-week discharge specific capacity of comparative example 5 was only 159.4mAh/g, and the first-week coulomb efficiency was only 72.1%. Thus, example 1 was significantly higher than comparative example 5, both in terms of first week specific discharge capacity and first week coulombic efficiency. It is found that the high nickel single crystal material which is not subjected to subsequent low-temperature long-time heat preservation has higher lithium nickel mixed discharge, and the electrochemical performance is obviously inferior to that of the example 1. The lithium nickel mixed discharge of comparative example 5 was reduced by 3.2% as compared with comparative example 1, and the specific discharge capacity and the first-week coulombic efficiency were both increased. The side surface shows that the high-nickel polycrystalline material is synthesized firstly and then grown up by heating to form the high-nickel single crystal material, so that the lithium-nickel mixed discharge rate of the single crystal material can be effectively reduced.
2) Example 2 preparation of LiNi at 485℃for 3h-700℃for 5h-900℃for 5h-700℃for 25h 0.92 Co 0.03 Mn 0.05 O 2 A monocrystalline material; comparative example 2 is a preparation of LiNi by sintering at both ends, namely 485℃3h-900℃5h-700℃25h 0.92 Co 0.03 Mn 0.05 O 2 A monocrystalline material. In comparative example 2, the low-temperature sintering step before the high-temperature sintering at 870 ℃ was not performed.
As shown in fig. 10a-b, example 2 of the present invention was calcined at 900 ℃ for 5 hours at 700 ℃ to obtain a high nickel polycrystalline material, which had a lithium nickel mixed discharge rate of only 2.7% due to the characteristics of the material itself, and further as can be seen from fig. 10 (c) - (d) and table 1, by sintering at 900 ℃ in combination with subsequent low temperature insulation, the high nickel polycrystalline material was converted into a high nickel single crystal material, the single crystal grain size was about 1.5 μm, and the lithium nickel mixed discharge rate was slightly increased, only 3.8%. Comparative example 2 does not have a step of forming a high nickel polycrystalline material, which is obtained by directly heating the raw material to 870 ℃ after pre-heat preservation and sintering it, and it can be seen from fig. 23a that the grain size of the single crystal material is about 1.5 μm, and example 2 is similar to comparative example 2 in terms of the size of single crystal grains, but the lithium nickel mixed discharge rate of the high nickel single crystal material is as high as 14.2% and is higher than that of example 2 by about 10.4% even if heat preservation treatment for up to 25 hours is used in post-treatment in comparative example 2. Therefore, due to the lack of a low-temperature calcination process before high-temperature calcination, namely, the high-nickel single crystal material converted from the high-nickel polycrystalline material, even if the high-stage calcination is finished and the low-temperature treatment is carried out for a long time, the serious problem of lithium nickel mixed discharge still exists.
As shown in Table 3, the LiNi obtained in example 2 0.92 Co 0.03 Mn 0.05 O 2 Lithium nickel mixed discharge rate of single crystal material is 3.8%, and single crystal LiNiO prepared in comparative example 2 2 The lithium nickel mixed discharge rate of example 2 is significantly lower than that of comparative example 2, the first-week discharge specific capacity of example 2 is 183.3mAh/g, the first-week coulomb efficiency is 76.0% and the first-week discharge specific capacity of comparative example 2 is only 132.2mAh/g, and the first-week coulomb efficiency is only 71.2% as seen in combination with the charge and discharge performance of both shown in fig. 11. Thus, example 2 was significantly higher than comparative example 2 in terms of specific discharge capacity at the first week, and also in terms of coulombic efficiency at the first week, which was 4.8% higher than comparative example 2 by about 51 mAh/g. Thus, it can be seen that although example 2 and comparative example 2 are both single crystal LiNi 0.92 Co 0.03 Mn 0.05 O 2 The material, however, since example 2 adds a low temperature sintering step at 700 ℃ for 5 hours before promoting single crystal growth by high temperature sintering at 900 ℃, a large amount of high nickel polycrystalline particles are generated, thereby avoiding the serious lithium nickel mixed discharge problem caused by the single crystal material generated by the two-stage sintering method of the comparative example 2, which comprises high temperature and low temperature. Formation of nickel polycrystalline material due to lack of low temperature Duan Gao In the step, even if the comparative example 2 is subjected to a low temperature heat preservation process of 700 ℃ for 25 hours after the end of calcination at a high temperature section of 900 ℃, the problem of lithium nickel mixed discharge is still difficult to avoid. In the embodiment 2, the electrochemical performance of the material such as specific discharge capacity can be remarkably improved by multi-stage temperature sintering such as low-temperature Duan Gao nickel polycrystalline material generation, high-temperature stage single crystal grain growth and the like. The invention adopts the process of converting high nickel polycrystal into high nickel monocrystal and combining post-treatment low-temperature calcination, so that the microstructure of the material is obviously changed, and the lithium nickel mixing rate is greatly reduced. It can be seen that the electrochemical properties of the high nickel monocrystal material, such as specific discharge capacity, initial cycle coulomb efficiency and the like, are obviously improved through the improvement of the microstructure.
3) Sample 3a of example 3 was prepared to LiNi at 485℃3h-720℃6h-960℃0h-720℃6h 0.92 Co 0.03 Mn 0.05 O 2 A monocrystalline material. Sample 3b is prepared by preparing LiNi at 485 ℃ for 3h-720 ℃ for 6h-1000 ℃ for 0h-720 ℃ for 6h 0.92 Co 0.03 Mn 0.05 O 2 A monocrystalline material; sample 4a of example 4 was prepared to LiNi at 485℃5h-720℃10h-960℃0h-720℃16h 0.92 Co 0.03 Mn 0.05 O 2 A monocrystalline material. Sample 4b is prepared by preparing LiNi at 485 deg.C for 5h-720 deg.C for 10h-1000 deg.C for 0h-720 deg.C for 16h 0.92 Co 0.03 Mn 0.05 O 2 A monocrystalline material; comparative example 3 is a LiNi prepared by one-step high temperature sintering, namely, 870 ℃ for 15 hours 0.92 Co 0.03 Mn 0.05 O 2 A monocrystalline material.
As can be seen from FIGS. 12 and 24, the single crystal size of example 3 was about 1.5. Mu.m, and the single crystal size of comparative example 3 was 0.5 to 1.0. Mu.m. It can be seen that the single crystal material obtained in example 3 has a larger size than that of comparative example 3 and a smaller specific surface area, which indicates that the growth of single crystal grains is facilitated by the preparation method of the present invention.
As shown in Table 3, the lithium-nickel mixed ratios of samples 3a and 3b of example 3 were 3.3% and 3.4%, respectively, the lithium-nickel mixed ratios of samples 4a and 4b of example 4 were 1.9% and 2.3%, respectively, and the lithium-nickel mixed ratios of comparative example 3 were 10.3%, respectively. It can be seen that sample 3b of example 3 has a lithium nickel miscibility higher than that of sample 3a by 0.1% due to the higher sintering temperature; sample 4b of example 4 showed a relatively higher lithium-nickel mixed emission rate than sample 4a due to the higher high temperature sintering temperature, indicating that sintering at the high temperature stage resulted in an increase in lithium-nickel mixed emission, but no significant increase in lithium-nickel mixed emission occurred due to the preparation process of preheating insulation-low temperature sintering-high temperature calcination-low temperature sintering of the present invention. Moreover, it can be seen that, since the sintering time of example 4 is longer than that of example 3 in the final low temperature zone, the lithium nickel mixed discharging rate is also obviously reduced, which also shows that under the same conditions, if the sintering time is reasonably prolonged by controlling the lithium nickel mixed discharging, the lithium nickel mixed discharging phenomenon can be obviously improved. And compared with the single crystal material obtained by the preparation method of the comparative example 3 in the examples 3-4, the single crystal material obtained by the preparation method of the comparative example 3 has serious lithium nickel mixed discharge problem, and the lithium nickel mixed discharge ratio of the single crystal material is high and is as high as 10.3 percent by adopting 870 ℃ one-step high-temperature sintering.
As can be seen from fig. 13a and 13b, the initial specific discharge capacity of comparative example 3 was only 129.2mAh/g, and the initial coulombic efficiency was 69.6% and the specific discharge capacity was low. The first discharge specific capacities of samples 3a and 3b of example 3 were 190.0Ah/g and 188.9mmAh/g, respectively, the first coulombic efficiencies were 77.4% and 76.0%, respectively, and the first discharge specific capacities of samples 4a and 4b of example 4 were 199.82mAh/g and 198.32mAh/g, respectively, and the first coulombic efficiencies were 80.0% and 82.8%, respectively. The first discharge specific capacity and first coulombic efficiency of examples 3-4 were significantly higher than comparative example 3. Therefore, the multi-stage sintering method can obviously improve the lithium nickel mixed discharge phenomenon, promote the ordering of the materials, further improve the structural reversibility of the materials in the charge-discharge process, and has high specific discharge capacity and first-week coulomb efficiency.
4) In example 5, the molar ratio of the lithium source mixture to the nickel precursor was 1.08:1, and after pre-heat preservation, the high nickel polycrystalline material was obtained by sintering at 650 ℃ for 15 hours, and after the high nickel polycrystalline material was obtained, a part of the lithium source was supplemented, and then single crystal LiNiO was obtained by high temperature sintering 2 The material was then incubated at low temperature for up to 66 hours. The lithium nickel miscibility of the material obtained in example 5 was 2.7%.
Example 6 lithium Source mixtureThe molar ratio of the lithium source to the nickel precursor is 5:1, and an excessive lithium source is adopted, so that a single crystal material with more uniform size can be burned out by using a higher lithium ratio. After high-temperature sintering, preparing single crystal LiNiO by adopting a segmented low-temperature sintering process 2 The material is 700 ℃ for 10h-685 ℃ for 20h-670 ℃ for 30h-610 ℃ for 20h. The lithium nickel miscibility of the material obtained in example 6 was 1.9%.
Compared with the single crystal LiNiO in example 1 2 The materials, examples 5 and 6, reduced the lithium nickel miscibility by 0.6% and 1.4%. The first-week specific discharge capacities of examples 5 and 6 were 207.9mAh/g and 218.2mAh/g, respectively, the first-week coulomb efficiencies were 85.0% and 85.9%, whereas the first-week specific discharge capacity of example 1 was only 192.6mAh/g, and the first-week coulomb efficiency was 80.5%. It can be seen that although likewise single crystal LiNiO 2 The materials, however, the lithium nickel miscibility, the first week coulombic efficiency and the first week specific discharge capacity of examples 5 and 6 were all superior to those of example 1. The preparation process of example 5 was changed to be longer in two low temperatures Duan Duanshao mainly before and after calcination at high temperature, and the ratio of the molar ratio of the lithium source to the precursor metal was higher by the lithium supplementing process, as compared with example 1, so that single crystal LiNiO 2 The microstructure of the materials is obviously different, the lithium nickel mixed discharge rate is obviously reduced, and the electrochemical performance such as the first-week discharge specific capacity and the first-week coulomb efficiency are obviously better. In example 6, on the basis of example 5, not only the proportion of lithium source is increased, but also the method of staged cooling and long-time heat preservation is adopted after high-temperature calcination, namely, the low-temperature section is the staged low-temperature sintering. The lithium nickel mixed discharge rate of example 6 was further reduced, and the first-week discharge specific capacity and the first-week coulombic efficiency were further improved, as compared with example 5.
Therefore, the extension of the calcination time at the low temperature section before high-temperature calcination can promote the generation of more high-nickel polycrystalline small particles, be more beneficial to the growth of subsequent single crystal particles, and avoid the serious lithium nickel mixed discharge problem caused by one-time high-temperature calcination as much as possible; the low-temperature heat preservation time after high-temperature calcination is prolonged, so that the transformation of a rock salt phase layered structure is facilitated, the lithium nickel mixed discharge phenomenon is obviously relieved, and meanwhile, the monocrystalline material can be promoted more quickly by adopting a segmented low-temperature heat preservation modeThe disordered rock salt structure is converted into a layered structure, and the lithium nickel mixed discharge can be reduced more quickly due to higher ion migration rate at high temperature, but the lithium nickel mixed discharge is more serious than the lithium nickel mixed discharge sintered at low temperature in a thermodynamic equilibrium state, so that the mixed discharge can be reduced more quickly through multi-stage low-temperature heat preservation sintering, the sintering time is shortened, and the cost is saved. In addition, the proportion of the lithium source in example 5 was higher than that in example 1, and the proportion of the lithium source in example 6 was significantly higher than that in example 1, and Ni was caused by controlling the content of the lithium source 2+ Is fully oxidized and migrates to the nickel layer, thereby avoiding Ni 2+ This is also why the single crystal materials of examples 5 to 6 are more excellent in performance in the occupation of the lithium layer. Therefore, mixed discharge can be further reduced by prolonging the low-temperature sintering time before and after high-temperature calcination, the microstructure of the single crystal material can be improved by controlling the content of the lithium source, and the material order can be remarkably improved, so that the high-nickel single crystal material has higher specific discharge capacity. The present examples 5 and 6 can exhibit an ultra-high specific discharge capacity by modification of the manufacturing process. Wherein the specific discharge capacity of example 6 far exceeds that of the existing single crystal LiNiO 2 A material.
5) Example 7 and comparative example 4
In example 7, the molar ratio of the lithium source mixture to the nickel precursor is 1.10:1, the high nickel polycrystalline material is obtained by sintering at 650 ℃ for 10 hours after pre-heat preservation, and then the single crystal LiNiO is obtained by carrying out sectional cooling at 700 ℃ for 5 hours to 685 ℃ for 10 hours to 670 ℃ for 50 hours to 610 ℃ for 20 hours after heat preservation at 1100 ℃ for 0 hour 2 A material. Comparative example 4, however, was directly sintered at 650℃for 15 hours after pre-incubation to give polycrystalline LiNiO 2 A material.
Example 7 Single Crystal LiNiO 2 The lithium nickel mixed discharge rate of the material is 1.8%, and compared with the example 6, the low-temperature sintering time is longer, so that the mixed discharge is approximately equivalent or even lower. Comparative example 4 since it is polycrystalline material LiNiO 2 The lithium nickel mixed discharge rate is low and is 1.2 percent. It can be seen that the lithium nickel miscibility of example 7, although higher than that of the polycrystalline material, was almost the same as or similar to that of the polycrystalline lithium nickel miscibility. This also shows that the structure of the monocrystalline material of example 7 is more perfect. The first-week discharge specific capacity of example 7 was 219.5mAh/gThe first week coulombic efficiency was 86.9%, whereas the first week discharge specific capacity of comparative example 4 was 226.7mAh/g, the first week coulombic efficiency was 87.1%. The first-week charge and discharge performance of the common polycrystalline material is far superior to that of the monocrystalline material, but the monocrystalline material of the embodiment 7 of the invention has little difference in the first-week discharge specific capacity and coulombic efficiency, which indicates that the monocrystalline material has excellent electrochemical performance.
Further, fig. 20 shows charge-discharge cycle performance of example 7 and comparative example 4. As can be seen in combination with table 1, the cycle performance of example 7 is significantly better than that of comparative example 4. The initial specific discharge capacity of comparative example 4 was higher than that of example 7, the specific discharge capacity of example 7 began to exceed that of comparative example 4 after 10 weeks of charge-discharge cycles, and as the number of cycles increased, it can be seen that the specific discharge capacity of example 7 was significantly higher than that of comparative example 4, the specific discharge capacity of example 7 was 154.2mAh/g after 100 weeks of cycles, the capacity retention was 80.9%, and the polycrystalline material of comparative example 4 was severely attenuated after long cycles, the specific discharge capacity was 148.4mAh/g, and the capacity retention was only 65.5%. From this, it is understood that, although comparative example 4 is a polycrystalline material, the mixed discharge is lower and the capacity is higher, but the single crystal material of example 7 exhibits a longer cycle performance superior to that of the polycrystalline material and a better capacity retention, which is also an advantage peculiar to the single crystal material. As seen from the ICP test results in table 2, the molar ratio of Li element to nickel element in the single crystal material of example 7 was 1.02, and the molar ratio of Li element to nickel element in comparative example 4 was 1.03, both of which were in a slightly lithium-rich state, which was one of the reasons for low lithium-nickel mixing rate. The slightly lithium-rich state has larger influence on the single crystal material, and the single crystal material has better electrochemical performance.
Therefore, the monocrystalline material has better structural reversibility in the charge-discharge cycle process, can maintain structural stability, and has excellent electrochemical performance.
6) Examples 8 and 9 are both synthetic high nickel single crystal LiNi 0.96 Co 0.02 Mn 0.02 O 2 The material, except for the high proportion of lithium source in example 8, was supplemented with 1% LiOH H in the intermediate process 2 And O, other preparation process parameters are the same.ICP test results show that the molar ratio of Li/Ni in example 8 is 1.02 in the resulting single crystal material: 1.00, li/Ni ratio of 0.99 in example 9:1.00. example 8 the resulting single crystal material was slightly lithium rich due to the additional lithium source step.
From the results shown in tables 3 to 4 and FIG. 21, it is understood that the lithium-nickel mixed discharge rate of example 8 was 2.42%, the first-week specific discharge capacity was 211.2mAh/g, the first-week coulomb efficiency was 85.9%, and the lithium-nickel mixed discharge rate of example 9 was 2.83%, the first-week specific discharge capacity was 208.5mAh/g, and the first-week coulomb efficiency was 85.8%. From this, it can be seen that the single crystal material LiNi in a slightly lithium-rich state 0.96 Co 0.02 Mn 0.02 O 2 The lithium nickel mixed discharge is lower, which also shows that the occupation of nickel ions in a lithium layer can be effectively reduced by excessive lithium, and the monocrystal material in a slightly lithium-rich state has more excellent electrochemical properties such as first-week discharge specific capacity and the like. Electrochemical results show that the Ni96 monocrystal with slightly rich lithium has higher first week capacity and higher energy density. Therefore, when the high-nickel monocrystal material is in a slightly lithium-rich state, the high-nickel monocrystal material has higher specific discharge capacity and lower lithium-nickel mixed discharge rate.
The foregoing description of the embodiments has been provided for the purpose of illustrating the general principles of the invention, and is not meant to limit the scope of the invention, but to limit the invention to the particular embodiments, and any modifications, equivalents, improvements, etc. that fall within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (10)
1. A method for preparing a high nickel single crystal material, which is characterized by comprising the following steps:
mixing part or all of the lithium source with the nickel precursor to obtain a mixture; the chemical formula of the nickel precursor is as follows: ni (Ni) x M 1-x (OH) 2 Wherein x is more than or equal to 0.8 and less than or equal to 1, and M is one or more of Co, mn, ti, mg, al, ca, cr, fe, zn, Y, zr, la, V, mo, nb, W, sm; the lithium content of the partial or total lithium source and the nickel precursorThe molar ratio of the total amount of metal in the body is greater than 1;
preheating and preserving heat of the mixture for 2-5 hours at 150-500 ℃ under the oxygen-enriched atmosphere, and then heating to 600-750 ℃ in a low temperature section for sintering for 2-15 hours to obtain a high-nickel polycrystalline material;
according to the unique image dynamics relation G.alpha.exp (-Q/RT) t 1/n And the relationship between defect concentration and defect generation energy and temperature Determining sintering temperature and heat preservation time, continuously heating the high-nickel polycrystalline material to the sintering temperature at the speed of 10 ℃/min-30 ℃/min, maintaining the heat preservation time at the sintering temperature to obtain a high-temperature sintered material, and then cooling; wherein G is the size of a single crystal, exp (-Q/RT) is an exponential function, Q represents the activation energy of the reaction, R is the ideal gas constant, T is the temperature, T is the reaction time, n is the number of reaction stages,% of Ni on Ni (3 a) sites is the ratio of Ni atoms in the Li site,% of Ni on Ni (3 b) sites is the ratio of Ni atoms in the Ni layer, ΔE is the defect reaction generation energy in the case where the concentration defect reaches the thermodynamic equilibrium state, k B Is the boltzmann constant;
calculation formula d= (1/2D) a according to thermodynamic stability and ion diffusion coefficient D 2 ν 0 exp(-E A /k B T) determining mixed control sintering temperature and mixed control sintering time of mixed control sintering, carrying out mixed control sintering on the high-temperature sintering material at the mixed control sintering temperature, and keeping the mixed control sintering time to obtain the high-nickel monocrystal material; wherein d is the diffusion dimension, a is the transition length, v 0 For collision frequency, E A Is the activation energy of ion transition, k B Is Boltzmann constant, T is temperature; in the high-nickel monocrystal material, the lithium nickel mixed discharge rate is below 4%.
2. The method for producing a high nickel single crystal material according to claim 1, wherein,
sintering to obtain the high-temperature sintering material, wherein the sintering temperature is 800-1100 ℃, and the heat preservation time is 0-5h;
the sintering temperature is controlled to be 600-780 ℃ by mixing and discharging, and the sintering time is controlled to be 5-200 h by mixing and discharging; the sintering time of the mixed discharge control is preferably m times of the heat preservation time, and m is more than or equal to 10; preferably, the sintering time of the mixed discharge control is more than or equal to 15 hours;
the lithium nickel mixed discharge rate of the high nickel monocrystal material is below 2%.
3. The method for producing a high-nickel single-crystal material according to claim 1, wherein, in the case where a mixture is obtained by mixing a part of lithium source with nickel precursor, the high-nickel polycrystalline material is supplemented with a remaining part of lithium source and/or the high-temperature sintered material is supplemented with a remaining part of lithium source after the temperature is lowered and/or the sintering process is controlled by mixing and discharging;
the rest lithium source is supplemented one or more times, so that the molar ratio of lithium to the total amount of other metals in the high-nickel single crystal material is 1.01:1-1.10:1, preferably satisfying 1.01:1-1.05:1.
4. The method for producing a high nickel single crystal material according to claim 1, wherein the lithium source is a low melting point lithium salt, comprising: lithium nitrate, lithium hydroxide, lithium sulfate, CH 3 One or more of COOLi; the nickel precursor is Ni x Co y Mn 1-x-y (OH) 2 Wherein x is more than or equal to 0.8 and less than or equal to 1, and y is more than or equal to 0 and less than or equal to 0.2.
5. The method for producing a high-nickel single crystal material according to claim 1, wherein the step of performing the mixed-batch controlled sintering of the high-temperature sintered material at the mixed-batch controlled sintering temperature to obtain the high-nickel single crystal material comprises the steps of:
cooling the high-temperature sintering material obtained after high-temperature calcination at 800-1100 ℃ to 600-780 ℃ for low-temperature sintering; or,
and cooling the high-temperature sintering material obtained after high-temperature calcination at 800-1100 ℃ to room temperature, and then, raising the temperature to 600-780 ℃ again for low-temperature sintering.
6. The method for producing a high-nickel single crystal material according to claim 5, wherein the low-temperature sintering is a staged low-temperature sintering;
preferably, the sintering is performed at 700-780 ℃ for 1-10 hours, then at 680-700 ℃ for 10-50 hours, then at 650-680 ℃ for 10-50 hours, and finally at 600-650 ℃ for 10-50 hours.
7. A high nickel single crystal material, characterized in that the high nickel single crystal material comprises the high nickel single crystal material prepared by the preparation method of any one of the above claims 1-6;
the lithium nickel mixed discharge rate of the high nickel monocrystal material is below 4%.
8. The high-nickel single crystal material according to claim 7, wherein the high-nickel single crystal material has a chemical formula: liNi x M 1-x O 2 The method comprises the steps of carrying out a first treatment on the surface of the X is more than or equal to 0.8 and less than or equal to 1, M is one or more than or equal to Co, mn, ti, mg, al, ca, cr, fe, zn, Y, zr, la, V, mo, nb, W, sm, and the molar ratio of lithium to the total amount of other metals is 1.01:1-1.10:1, preferably 1.01:1-1.05:1, a step of; preferably, the high nickel single crystal material is LiNi x Co y Mn 1-x-y O 2 Wherein x is more than or equal to 0.8 and less than or equal to 1, and y is more than or equal to 0 and less than or equal to 0.2.
9. The high-nickel single crystal material according to claim 7 or 8, wherein the high-nickel single crystal material is a layered α -NaFeO having an R-3m space group 2 Hexagonal LiMO of structure 2 Phase-rich lithium layered oxide, liMO 2 Part of the LiNi exists in the lamellar part formed by transition metal and oxygen element in the structure 6 Cation arrangement; the lithium nickel mixed discharge rate of the high-nickel monocrystal material is less than 2%, and the grain size of monocrystal particles of the monocrystal material is 1.5-5 mu m.
10. A secondary battery comprising the high-nickel single-crystal material produced by the production method according to any one of claims 1 to 6, or the high-nickel single-crystal material according to any one of claims 7 to 9.
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