Doping coating method, method for modifying ternary cathode material by adopting method and application
阅读说明：本技术 掺杂包覆方法、采用该方法对三元正极材料改性的方法和应用 (Doping coating method, method for modifying ternary cathode material by adopting method and application ) 是由 万江涛 张宁 张勇杰 刘满库 刘海松 江卫军 于 2021-07-30 设计创作，主要内容包括：本发明公开了一种掺杂包覆方法、采用该方法对三元正极材料改性的方法和应用,所述掺杂包覆方法包括以下步骤：1)将掺杂包覆添加剂与助溶剂混合,预烧后进行洗涤,干燥后得到低熔点添加剂；2)采用所述的低熔点添加剂,利用烧结的方法,对待改性材料进行掺杂处理和/或包覆处理。本发明的方法可以适当降低掺杂和包覆的烧结温度和时间,可以适当提高掺杂的均一度和包覆结合牢固程度,还可以降低工艺要求,具有广阔的应用前景。(The invention discloses a doping and coating method, a method for modifying a ternary cathode material by adopting the method and application, wherein the doping and coating method comprises the following steps: 1) mixing the doped coating additive with a cosolvent, presintering, washing, and drying to obtain a low-melting-point additive; 2) the low-melting-point additive is adopted, and a sintering method is utilized to carry out doping treatment and/or coating treatment on the material to be modified. The method of the invention can properly reduce the sintering temperature and time of doping and cladding, can properly improve the uniformity of doping and the cladding bonding firmness, can also reduce the process requirement, and has wide application prospect.)
1. A doping cladding method is characterized by comprising the following steps:
(1) mixing the doped coating additive with a cosolvent, presintering, washing, and drying to obtain a low-melting-point additive;
(2) the low-melting-point additive is adopted, and a sintering method is utilized to carry out doping treatment and/or coating treatment on the material to be modified.
2. The doping modification method of claim 1, wherein the doping capping additive of step (1) independently comprises at least one of an oxide or hydroxide of titanium, aluminum, zinc, calcium, magnesium, zirconium, scandium, yttrium, cerium, or vanadium;
preferably, the co-solvent of step (1) comprises at least one of a halide, carbonate or hydroxide of lithium, sodium or potassium, the halide comprising at least one of fluoride, chloride or bromide;
preferably, the co-solvents in step (1) include a first co-solvent, a second co-solvent and a third co-solvent, the first co-solvent and the second co-solvent are selected from two of halide or carbonate, and the third co-solvent is hydroxide;
preferably, the molar ratio of the first cosolvent to the second cosolvent to the third cosolvent is (0-5): 0-5, preferably (0.1-2): 1-2;
preferably, the mass ratio of the doped coating additive to the cosolvent in the step (1) is 1 (0.8-20), and preferably 1 (2-10).
3. The doping coating method according to claim 1 or 2, wherein the mixing of step (1) is performed in a high-speed mixer, and the mixing time is 5min to 10 min;
preferably, the temperature rise speed of the pre-sintering in the step (1) is 3-15 ℃/min;
preferably, the temperature of the pre-sintering in the step (1) is 500-1200 ℃;
preferably, the pre-sintering time in the step (1) is 2-8 h.
4. The dopant cladding method of any one of claims 1 to 3, wherein the method is subjected to a pulverization step after the pre-sintering of step (1) and before washing;
preferably, the detergent used in the washing in the step (1) is water;
preferably, in the washing process, the solid-liquid ratio is 1 (1-3);
preferably, the washing process is accompanied by stirring, and the rotating speed of the stirring is 400 rpm-600 rpm;
preferably, the washing temperature is 40-60 ℃;
preferably, the washing time is 20min to 30 min;
preferably, the washing is repeated 2 to 3 times;
preferably, step (1) is ground until the particle size of the low melting point additive is less than 0.8 μm.
5. The dopant cladding method of any one of claims 1 to 4, wherein the material to be modified in step (2) comprises at least one of an electrode material or a fast ion conductor.
6. A method for modifying a ternary positive electrode material by using the doping coating method according to any one of claims 1 to 5, wherein the method comprises the following steps:
(a) preparing the low melting point additive by the method of any one of claims 1-5;
(b) mixing the ternary positive active substance with a doping agent, and sintering for the first time to obtain a primary sintered product;
(c) crushing the primary sintered product, mixing with a coating agent, and sintering for the second time to obtain a modified ternary cathode material;
wherein the dopant of step (b) and the capping agent of step (c) are both selected from the low melting point additives of step (a).
7. The method according to claim 6, wherein the dopant in the step (b) is used in an amount of 0-1% and not 0% by mass of the ternary positive electrode active material;
preferably, the temperature of the primary sintering in the step (b) is 820-910 ℃;
preferably, the time of the primary sintering in the step (b) is 5 to 20 hours.
Preferably, the dosage of the doping agent in the step (c) is 0.01-1% of the mass of the primary sintered product;
preferably, the temperature of the secondary sintering in the step (c) is 300-800 ℃;
preferably, the time of the secondary sintering in the step (c) is 1-8 h.
8. Method according to claim 6 or 7, characterized in that it comprises the following steps:
(a) mixing the doping additive and a cosolvent, presintering, washing, drying to obtain a low-melting-point doping additive, and then carrying out wet grinding for 0.5-2 h by using ethanol as a dispersing agent to ensure that the particle size of the low-melting-point doping additive is less than 0.8 mu m;
mixing the coating additive with a cosolvent, presintering, washing, drying to obtain a low-melting-point coating additive, and then carrying out wet grinding for 0.5-2 h by using ethanol as a dispersing agent to ensure that the particle size of the low-melting-point coating additive is less than 0.8 mu m;
(b) mixing a ternary positive electrode active substance with a low-melting-point doping additive, wherein the dosage of the low-melting-point doping additive is 0-1% of the mass of the ternary positive electrode active substance and does not contain 0%, and sintering at 820-910 ℃ for 5-20 h to obtain a primary sintered product;
(c) and crushing the primary sintered product, and then mixing the crushed primary sintered product with a low-melting-point coating additive, wherein the using amount of the low-melting-point coating additive is 0.01-1% of the mass of the primary sintered product, and sintering the primary sintered product at the temperature of 300-800 ℃ for 1-8 h to obtain the modified ternary cathode material.
9. The modified ternary cathode material prepared by the method of any one of claims 6 to 8, characterized in that the modified ternary cathode material comprises a ternary cathode material core with a doping element and a coating layer coated on the surface of the ternary cathode material core, wherein the coating layer comprises a coating element.
10. A lithium ion battery comprising the modified ternary cathode material of claim 9.
Technical Field
The invention relates to the technical field of material preparation and modification, in particular to a doping coating method, a method for modifying a ternary cathode material by adopting the method and application.
Background
The nickel-cobalt-manganese ternary cathode material has an important position in new energy lithium battery materials, and with the continuous research and development of the materials, the safety, the cycle, the multiplying power and other properties of the materials can be improved to a certain extent through proper doping and coating, so that the overall electrochemical properties of the materials are exerted more fully.
The existing doping and coating methods are few, and have a good modification effect, but have certain defects, and how to dope and coat by a simple and easy method, and the doping and coating effects are better as much as possible, so that the doping and coating methods need to be developed and optimized more deeply.
Most of the existing doping and coating processes adopt a hydroxide precursor physical mixing mode to add Li source and doping additive for sintering so as to achieve the doping effect, and then secondary sintering is carried out to mix materials and add nano-scale coating oxide mixed materials for sintering; or directly carrying out coprecipitation doping at a precursor stage and then mixing the nanometer-scale coated oxide; doping and coating are carried out by adopting wet coprecipitation outer coating, sol-gel coating, atom coating and the like; there are also processes of performing doping and cladding operations at a time by using a spraying method, and the like.
For example, CN111682198A discloses a step-by-step graded doped ternary cathode material and a preparation method thereof, comprising the following steps: fully mixing a ternary material precursor, a first lithium source and a doping agent a, and sintering at 750-950 ℃ for 2-8 h to obtain a lithiation product; lithiation of the product, second lithiumFully mixing the source and the dopant b, and sintering at 750-950 ℃ for 2-8 h to obtain the stepped gradient doped ternary cathode material, wherein the dopant a is Rh2O3、MoO3Or PdO, and the dopant b is SrO or La2O3Mg or SrO2One or more of (a). For another example, CN104916837A discloses a preparation method of an aluminum-doped ternary cathode material, wherein a coprecipitation method is adopted to prepare an aluminum-doped ternary cathode material precursor, so that the physical and chemical properties of the ternary cathode material precursor are improved, the bulk density and the cycle performance of the nickel-cobalt-manganese ternary cathode material are improved, and a surface coating is adopted to modify the aluminum-doped ternary cathode material, so as to improve the performance of the aluminum-doped ternary cathode material.
The common property of doping and cladding by adopting the process is that metal or nonmetal oxides, hydroxides and other raw materials are adopted, most of the compounds doped with the cladding metal elements have higher melting points, so that the doping and cladding temperature is higher, the doping uniformity and the cladding adhesion firmness have certain defects, and the final doping and cladding effect is weakened.
Disclosure of Invention
In view of the above problems in the prior art, the present invention aims to provide a doping coating method, a method for modifying a ternary cathode material using the doping coating method, and applications of the doping coating method.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a dopant cladding method, comprising the steps of:
(1) mixing the doped coating additive with a cosolvent, presintering, washing, and drying to obtain a low-melting-point additive;
(2) the low-melting-point additive is adopted, and a sintering method is utilized to carry out doping treatment and/or coating treatment on the material to be modified.
The doping and cladding method is not limited to doping and cladding materials, and can be doping alone or cladding alone. The actual treatment process performed in step (2) is the standard.
The "dope coating additive" in the present invention may be a dope additive or a coating additive. The kind is not particularly limited, and those skilled in the art can select from dopants and capping agents commonly used in the art as needed.
The method only carries out cosolvent sintering treatment on a small amount of doped coating additive, has little residue after elution, and hardly introduces other impure phases because the low-melting-point additive is used in a subsequent sintering process in a small amount, generally less than 1%.
The invention adopts a molten salt presintering treatment method, firstly, the doped coating additive and the cosolvent are mixed and presintering is carried out to convert the doped coating additive and the cosolvent into a compound with a low melting point, then, the cosolvent is washed and removed, and then, the material is used for doping and/or coating. The method has the advantages that: firstly, the sintering temperature and time of doping and cladding can be properly reduced, the cladding sintering temperature is reduced by about 10-50 ℃ compared with that of a common oxide material, and the time is reduced by 0.5-3 h, so that better doping and cladding effects can be achieved; secondly, the uniformity of doping and the cladding bonding firmness can be properly improved, the capacity and the first obvious influence are not generated, and the cycle performance is improved by 0.5-2%; the process requirements can be reduced, for example, the particle size requirement of the raw material doped coating additive is not strict, the micron or submicron size can also meet the requirement, and the material processing performance of about 1 micron is better; for another example, the low melting point additive used in the doping and/or cladding process has a reduced size requirement and does not need to be crushed into particularly small nano-materials, typically having a particle size of less than 0.8 μm.
In the invention, the adding sequence of the cosolvent cannot be changed, if the doped coating additive, the cosolvent and the material to be treated are directly mixed and sintered, although the sintering temperature and time can be reduced, the doping uniformity and the coating bonding firmness cannot be effectively improved, and a part of the cosolvent is remained in a final product and cannot be removed, so that the product performance is deteriorated. The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution. Preferably, the doped cladding additive of step (1) independently comprises at least one of an oxide or hydroxide of titanium, aluminum, zinc, calcium, magnesium, zirconium, scandium, yttrium, cerium, or vanadium.
Preferably, the co-solvent of step (1) comprises at least one of a halide, carbonate or hydroxide of lithium, sodium or potassium, the halide comprising at least one of fluoride, chloride or bromide;
preferably, the co-solvents in step (1) include a first co-solvent, a second co-solvent and a third co-solvent, the first co-solvent and the second co-solvent are selected from two of halide or carbonate, and the third co-solvent is hydroxide;
preferably, the molar ratio of the first cosolvent to the second cosolvent to the third cosolvent is (0-5): 0-5, and in the preferred technical scheme, the melting temperature can be optimized, the content of impurity elements can be reduced, and the cost of the molten salt can be optimized by selecting the mixed molten salt, wherein the molar ratio of the first cosolvent to the second cosolvent to the third cosolvent can be (0.1-5): 0.1-2), (0.1-2): 0.5-3), (1-4): 0.5-4) or (0.5-1.5): 0.5-1.5, and the like, and preferably (0.1-2): 1-2.
In one embodiment, the first co-solvent and/or the second co-solvent in the mixed solution comprises lithium salt, which is beneficial to reduce the generation of heterogeneous phase and provide active elements to improve the electrochemical performance.
Preferably, the mass ratio of the doped coating additive to the cosolvent in the step (1) is 1 (0.8-20), such as 1:0.8, 1:1, 1:1.5, 1:2, 1:3, 1:4, 1:5, 1:7, 1:8, 1:10, 1:12, 1:13, 1:14, 1:15, 1:17, or 1:20, and preferably 1 (2-10).
Preferably, the mixing in step (1) is performed in a high-speed mixer, and the mixing time is 5min to 10min, such as 5min, 6min, 8min or 10 min.
Preferably, the temperature rising rate of the pre-sintering in the step (1) is 3 ℃/min to 15 ℃/min, such as 3 ℃/min, 5 ℃/min, 6 ℃/min, 8 ℃/min, 10 ℃/min, 12 ℃/min or 15 ℃/min, and the like.
Preferably, the temperature of the pre-sintering in step (1) is 500 ℃ to 1200 ℃, such as 500 ℃, 600 ℃, 700 ℃, 750 ℃, 800 ℃, 900 ℃, 1000 ℃, 1100 ℃, 1200 ℃ or the like.
Preferably, the pre-sintering time in step (1) is 2h to 8h, such as 2h, 3h, 3.5h, 4h, 5h, 6h, 7h or 8 h.
Preferably, the method is carried out in a crushing step before the pre-sintering and washing step (1).
Preferably, the detergent used in the washing in step (1) is water.
Preferably, the solid-liquid ratio in the washing process is 1 (1-3), such as 1:1, 1:1.5, 1:1.7, 1:1.8, 1:2, 1:2.5 or 1: 3.
Preferably, the washing is accompanied by stirring at a speed of 400rpm to 600rpm, for example 400rpm, 425rpm, 450rpm, 500rpm, 550rpm, 600rpm, or the like.
Preferably, the temperature of the washing is 40 ℃ to 60 ℃, such as 40 ℃, 45 ℃, 50 ℃, 55 ℃, or 60 ℃ and the like.
Preferably, the washing time is 20min to 30min, such as 20min, 22min, 25min or 30 min.
In the invention, the washing can be repeatedly carried out, and the filter residue directly enters the next round of washing operation after each suction filtration. The number of washing repetitions is not limited, and may be, for example, 2 to 3 repetitions.
In one embodiment, the wash water is evaporated for crystallization and the co-solvent is reused.
Preferably, step (1) is ground to a particle size of the low melting point additive of less than 0.8 μm, such as 0.8 μm, 0.7 μm, 0.6 μm, 0.55 μm, 0.52 μm, and the like.
The kind of the material to be modified in the present invention is not particularly limited, and may be, for example, at least one of an electrode material or a fast ion conductor. The electrode material may be a positive electrode material or a negative electrode material, examples of the positive electrode material may include a ternary positive electrode material, a cobalt-free binary positive electrode material, lithium iron phosphate, lithium cobaltate, and the like, and examples of the fast ion conductor may include titanium aluminum lithium phosphate, germanium aluminum lithium phosphate, and the like, but are not limited to the above-mentioned materials, and other materials commonly used in the art and suitable for doping or coating by a sintering method are applicable to the present invention.
In a second aspect, the present invention provides a method for modifying a ternary positive electrode material using the method of the first aspect, the method comprising the steps of:
(a) preparing the low melting point additive using the method of the first aspect;
(b) mixing the ternary positive active substance with a doping agent, and sintering for the first time to obtain a primary sintered product;
(c) crushing the primary sintered product, mixing with a coating agent, and sintering for the second time to obtain a modified ternary cathode material;
wherein, the dopant in the step (b) and the coating agent in the step (c) are both selected from the low-melting-point additive in the step (a), and the dopant and the coating agent can be the same or different in kind.
The specific types of the dopant in step (b) and the capping agent in step (c) are not limited in the present invention, and can be selected by those skilled in the art according to the needs, for example, the dopant can be aluminum oxide, and the capping agent can be zirconium oxide.
In one embodiment, the morphology of the modified ternary cathode material is spherical. Preferably, the amount of the dopant used in step (b) is 0% to 1% by mass of the ternary positive electrode active material and does not contain 0%, for example, 0.01%, 0.02%, 0.05%, 0.1%, 0.5%, 0.6%, 0.8%, 1%, or the like.
Preferably, the temperature of the primary sintering in step (b) is 820-910 ℃, such as 820 ℃, 850 ℃, 880 ℃, 900 ℃ or 910 ℃, etc.
Preferably, the time for the primary sintering in step (b) is 5h to 20h, such as 5h, 6h, 8h, 10h, 12h, 13h, 15h, 16h, 18h or 20 h.
Preferably, the amount of the dopant used in step (c) is 0.01 to 1% of the mass of the primary sintered product, such as 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, or 1%.
Preferably, the temperature of the secondary sintering in step (c) is 300 ℃ to 800 ℃, such as 300 ℃, 400 ℃, 500 ℃, 550 ℃, 600 ℃, 650 ℃, 700 ℃, or 800 ℃, and the like.
Preferably, the time for the secondary sintering in step (c) is 1h to 8h, such as 1h, 2h, 3h, 5h, 6h, 7h or 8 h.
As a further preferable technical solution of the method for modifying a ternary cathode material according to the present invention, the method comprises the steps of:
(a) mixing the doping additive and a cosolvent, presintering, washing, drying to obtain a low-melting-point doping additive, and then carrying out wet grinding for 0.5-2 h by using ethanol as a dispersing agent to ensure that the particle size of the low-melting-point doping additive is less than 0.8 mu m;
mixing the coating additive with a cosolvent, presintering, washing, drying to obtain a low-melting-point coating additive, and then carrying out wet grinding for 0.5-2 h by using ethanol as a dispersing agent to ensure that the particle size of the low-melting-point coating additive is less than 0.8 mu m;
(b) mixing a ternary positive electrode active substance with a low-melting-point doping additive, wherein the dosage of the low-melting-point doping additive is 0-1% of the mass of the ternary positive electrode active substance and does not contain 0%, and sintering at 820-910 ℃ for 5-20 h to obtain a primary sintered product;
(c) and crushing the primary sintered product, and then mixing the crushed primary sintered product with a low-melting-point coating additive, wherein the using amount of the low-melting-point coating additive is 0.01-1% of the mass of the primary sintered product, and sintering the primary sintered product at the temperature of 300-800 ℃ for 1-8 h to obtain the modified ternary cathode material.
The invention mixes the additive used for doping and the additive used for coating with the latent solvent respectively, presintering, washing, drying, grinding, mixing and sintering for the first time, mixing and sintering for the second time, and then prepares the ternary material, the latent solvent is selected as the raw material to carry out melting sintering on the high-melting-point compound to convert the high-melting-point compound into the low-melting-point compound, and then the newly prepared low-melting-point compound is utilized to carry out doping and coating, thereby having good effect, properly reducing the temperature of doping and coating and improving the effect of doping and coating. Wherein, the doping additive and the coating additive are converted into low-melting-point substances which are easier to dope and coat through the step (a), so that better doping and coating effects can be obtained; the residual cosolvent can be effectively removed through washing, the product purity is improved, and the generation of impure phases is reduced.
The method can also be used for preparing fast ion conductors, such as titanium aluminum lithium phosphate, germanium aluminum lithium phosphate and the like for doping and coating.
In a third aspect, the invention provides a modified ternary cathode material prepared by the method in the second aspect, and the modified ternary cathode material comprises a ternary cathode material core with a doping element and a coating layer coated on the surface of the ternary cathode material core, wherein the coating layer comprises a coating element.
The modified ternary cathode material prepared by the method has the advantages that the doping elements are uniformly distributed, the coating layer is uniform and compact, and the improvement of the comprehensive performance of the material is facilitated.
In a fourth aspect, the invention provides a lithium ion battery, which comprises the modified ternary cathode material of the second aspect.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a novel doping and coating method, which adopts a molten salt presintering treatment method, and comprises the steps of mixing an element compound to be doped and coated (namely a doping and coating additive) and a cosolvent for presintering, converting the element compound to a compound with a low melting point (namely a low melting point additive), washing to remove the cosolvent, and doping and/or coating by using the material.
The method has the advantages that: the sintering temperature and time of doping and cladding can be properly reduced, the uniformity of doping and the cladding bonding firmness can be properly improved, the requirement on the granularity of an element compound (such as an oxide raw material) to be doped and clad is not strict, the micron-sized or submicron-sized dimension can also meet the requirement, and the final presintering treatment product does not need to be crushed into a particularly small nano material and only needs to be less than 0.8 mu m. Fast ion conductors such as: lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, and the like.
Drawings
Fig. 1 is an SEM image of the modified ternary cathode material of example 1.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
Example 1
The embodiment provides a modified ternary cathode material, which comprises an Al-doped nickel-cobalt-manganese core and a coating layer coated on the surface of the core, wherein the coating layer contains a coating element Al.
The embodiment also provides a preparation method of the modified ternary cathode material, which comprises the following steps:
premixing: premixing the additive and the cosolvent according to the weight ratio of 1:2, and premixing for 10min in a high-speed mixer.
In this embodiment, the additive is aluminum oxide, and the cosolvent is a mixture of sodium hydroxide, lithium carbonate, and potassium chloride at a molar ratio of 1:1: 1. The mixed molten salt can optimize the melting temperature, reduce the content of impurity elements and optimize the cost composition of the molten salt.
Secondly, pre-sintering: and putting the mixed materials into a sagger, setting the temperature rise speed to be 5 ℃/min, the sintering temperature to be 600 ℃, and the sintering time to be 2 h.
Washing: preliminarily crushing the pre-sintered product, and then putting the pre-sintered product into pure water for eluting the cosolvent, wherein the solid-liquid ratio is 1: 1; stirring at 500rpm, washing at 50 deg.C for 30min, repeating washing twice, and directly washing the filter residue after each suction filtration. Washing water is evaporated for crystallization, and the cosolvent is repeatedly used.
Drying and crushing: and drying the washed solid particles, and then grinding for 0.5h by using ethanol as a wet material of a dispersing agent to ensure that the particle size of the wet material is less than 0.8 mu m, thereby obtaining the low-melting-point additive.
Mixing materials and burning: according to NCM 811: the low melting point additive obtained in the step (iv) was added to the low melting point additive (weight ratio) 100:0.3, and primary sintering was performed at 850 ℃ for 15 hours using NCM811, to obtain a primary sintered product.
Sixthly, mixing materials and roasting: crushing the primary sintered product, mixing with the low-melting-point additive which is 0.8% of the mass of the crushed product and sintering for 3 hours at 550 ℃ to obtain the modified ternary cathode material.
Example 2
The embodiment provides a modified ternary cathode material, which comprises a Ti-doped nickel-cobalt-manganese core and a coating layer coated on the surface of the core, wherein the coating layer contains a coating element Ti.
The embodiment also provides a preparation method of the modified ternary cathode material, which comprises the following steps:
premixing: premixing the additive and the cosolvent according to the weight ratio of 1:5, and premixing for 10min in a high-speed mixer.
In this embodiment, the additive is titanium dioxide, and the cosolvent is a mixture of sodium chloride, lithium hydroxide, and potassium fluoride in a molar ratio of 2:1: 0.2. The mixed molten salt can optimize the melting temperature, reduce the content of impurity elements and optimize the cost composition of the molten salt.
Secondly, pre-sintering: and putting the mixed materials into a sagger, setting the temperature rise speed to be 8 ℃/min, the sintering temperature to be 700 ℃, and the sintering time to be 2 h.
Washing: preliminarily crushing the pre-sintered product, and then putting the pre-sintered product into pure water for eluting the cosolvent, wherein the solid-liquid ratio is 1: 1; stirring at 500rpm, washing at 50 deg.C for 30min, repeating washing twice, and directly washing the filter residue after each suction filtration. Washing water is evaporated for crystallization, and the cosolvent is repeatedly used.
Drying and crushing: and drying the washed solid particles, and then grinding for 1h by using ethanol as a wet material of a dispersing agent to enable the particle size to be less than 0.8 mu m, thereby obtaining the low-melting-point additive.
Mixing materials and burning: polymorphic according to NCM 811: the low-melting additive obtained in the step (iv) was added to the low-melting additive at a weight ratio of 100:0.5, and the primary sintering of NCM811 polycrystal was carried out at 810 ℃ for 12 hours to obtain a primary sintered product.
Sixthly, mixing materials and roasting: crushing the primary sintered product, mixing with the additive which is 0.3% of the mass of the crushed product and obtained in the step (iv), and sintering for 3 hours at 680 ℃ to obtain the modified ternary cathode material.
Example 3
The embodiment provides a modified ternary cathode material, which comprises an NCM811 core and a coating layer coated on the surface of the NCM811 core, wherein the coating layer comprises coating elements Ti, Al and P.
The embodiment also provides a preparation method of the modified ternary cathode material, which comprises the following steps:
premixing: premixing the additive and the cosolvent according to the weight ratio of 1:10, and premixing for 10min in a high-speed mixer.
In this embodiment, the additive is titanium dioxide, aluminum oxide, ammonium dihydrogen phosphate (molar ratio 1.7:0.15:3.0), and the cosolvent is a mixture of sodium chloride, lithium hydroxide, and potassium bromide in a molar ratio of 1:2: 0.1. The mixed molten salt can optimize the melting temperature, reduce the content of impurity elements and optimize the cost composition of the molten salt.
Secondly, pre-sintering: and putting the mixed materials into a sagger, setting the temperature rise speed to be 10 ℃/min, the sintering temperature to be 1100 ℃, and the sintering time to be 5 h.
Washing: preliminarily crushing the pre-sintered product, and then putting the pre-sintered product into pure water for eluting the cosolvent, wherein the solid-liquid ratio is 1: 2; stirring at 500rpm, washing at 50 deg.C for 30min, repeating washing twice, and directly washing the filter residue after each suction filtration. Washing water is evaporated for crystallization, and the cosolvent is repeatedly used.
Drying and crushing: and drying the washed solid particles, and then grinding for 1h by using ethanol as a wet material of a dispersing agent to enable the particle size to be less than 0.8 mu m, thereby obtaining the low-melting-point additive.
Mixing materials and burning: the primary sintering of NCM811 polycrystal was carried out at 800 ℃ for 12 hours without adding an additive to obtain a primary sintered product.
Sixthly, mixing materials and roasting: crushing the primary sintered product, mixing with the low-melting-point additive which is 0.6% of the mass of the crushed product and sintering for 5 hours at 450 ℃ to obtain the modified ternary cathode material.
Example 4
The difference between this example and example 1 is that in step (r), the cosolvent is sodium hydroxide and the content is the same as example 1.
Example 5
The difference between the embodiment and the embodiment 1 is that in the step (r), the weight ratio of the additive to the cosolvent is 1: 0.5.
Example 6
This example differs from example 1 in that in step (r), the additive to cosolvent weight ratio is 1: 15.
Comparative example 1
The comparative example is different from example 1 in that alumina was directly crushed to the same particle size as that after crushing in the step (iv) of example 1 without performing the step (iv) to the step (iv), and used for the first firing of the mixture in the subsequent step (v) and the second firing of the mixture in the step (iv).
Comparative example 2
The difference between the comparative example and the comparative example 1 is that the primary sintering temperature in the fifth step is 880 ℃, and the time is 15.5 hours; the secondary sintering temperature of the step (sixthly) is 575 ℃, and the time is 4 hours.
Comparative example 3
The comparative example provides a preparation method of a modified ternary cathode material, which comprises the following steps:
firstly, mixing materials and firstly burning: according to NCM 811: additive: mixing the cosolvent (weight ratio) 100:0.3:0.15, wherein the additive is aluminum oxide (granularity is less than 0.8 mu m), and the cosolvent is a mixture of sodium hydroxide, lithium carbonate and potassium chloride according to a molar ratio of 1:1:1, and performing primary sintering at 850 ℃ for 15 hours to obtain a primary sintered product.
Secondly, mixing materials and roasting: and crushing the primary sintered product, mixing with an additive accounting for 0.8% of the mass of the crushed product, and sintering for 3 hours at 550 ℃ for the second time to obtain the modified ternary cathode material.
And (3) performance detection:
the positive electrode materials prepared in each example and each comparative example are made into positive electrodes, the positive electrodes are assembled into a power-on state, the electrochemical performance is detected, and the capacity and the first effect of the product of 0.1C gram and the capacity retention rate of 50 weeks in 1C/1C circulation are obtained, and the results are shown in Table 1.
TABLE 1
And (3) analysis:
as can be seen from Table 1, the doping and/or cladding effect can be effectively improved by the method of the present invention, and the electrochemical performance of the material can be further improved.
It can be seen from the comparison between example 1 and example 4 that, by replacing the mixed molten salt of example 1 with a single co-solvent, NaOH, the electrochemical performance, especially the cycle performance, of the final product is reduced, although the material cost is slightly reduced, which may be due to the poor effect of the co-solvent and the possibility of generating more heterogeneous phases.
As can be seen from the comparison between example 1 and examples 5-6, the cosolvent content is too low, the cosolvent effect is reduced, and the cycle performance is reduced; if the solubility is too high, the solubilizing effect cannot be further improved.
It can be seen from the comparison between example 1 and comparative examples 1-2 that the capacity, first effect and cycle of the final product without the co-solvent processing step are all reduced, the doping coating effect cannot be effectively improved even if the sintering temperature and time are increased, and the capacity and first effect are also greatly reduced.
As can be seen from the comparison between example 1 and comparative example 3, the electrochemical performance of the calcined product directly added with the cosolvent can not be improved almost, and the solubilizing effect can not be reflected.
It should be noted that the method of the present invention is not limited to doping and/or cladding of the ternary cathode material, and has good applicability to the preparation of other electrode materials or other fast ion conductors.
The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.