CN115385969B - A polyanion group positive electrode material precursor and preparation method thereof, positive electrode material prepared from the precursor and battery - Google Patents
A polyanion group positive electrode material precursor and preparation method thereof, positive electrode material prepared from the precursor and battery Download PDFInfo
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Abstract
The invention relates to a polyanion group positive electrode material precursor, a preparation method thereof, a positive electrode material prepared from the precursor and a battery, wherein the chemical formula of the positive electrode material precursor is MnxNiyCozA(1‑x‑y‑z)[CO3]a[C2O4]b[OH]2(1‑a‑b),, the precursor or the precursor after heat treatment and a lithium source compound are uniformly mixed and then calcined, and after the calcination is finished, the precursor is cooled to room temperature, so that the target positive electrode material is obtained. The positive electrode material precursor has high sphericity and high tap density, the preparation process is simple, the current industrial process is matched, industrial production is easy to realize, and the positive electrode material prepared by the positive electrode material precursor has uniform element distribution, high tap density, stable structure and good multiplying power performance and circulation stability.
Description
Technical Field
The invention relates to the field of lithium ion battery materials and electrochemistry, in particular to a polyanion group positive electrode material precursor, a preparation method thereof, a positive electrode material prepared from the precursor and a battery.
Background
Lithium ion batteries are first used in 3C fields such as mobile phones and notebooks due to their high energy density, long service life, and good safety. With the advent of emerging electric vehicles and the rapid development of large-scale energy storage grids, traditional commercial lithium ion batteries have failed to meet the demand for higher specific energy. The layered ternary positive electrode material is being subjected to rapid commercial permeation due to its excellent cycle, low price and high specific discharge capacity, and the lithium-rich ternary positive electrode material has been widely studied in recent years due to its ultra-high specific capacity (more than 250mAh/g, even more than 300 mAh/g).
The structure determines the performance, which in turn significantly affects the synthesis method. For a mature commercial product, the conditions of the overall synthetic route will determine the nature of the final product. Among the numerous preparation methods of ternary cathode materials, the current method for industrial production application is mainly a coprecipitation method. The product obtained by the coprecipitation method is a precursor of the positive electrode material and can be classified into a hydroxide system, a carbonate system and an oxalate system according to the difference of precipitants.
If Mn element exists in the hydroxide system, the Mn element is easily oxidized in the drying and washing processes to lead to precursor phase separation, and after mixing and calcining with lithium salt, a locally enriched Li 2MnO3 component is easily generated, and the high-potential oxygen is easily separated to cause structural damage, so that potential safety hazards are brought while the electrochemical performance of the material is influenced.
The precipitate prepared by the carbonate system and/or the oxalate system is more stable in air and has strong oxidation resistance, but CO 2 is generated from the precursor body when the precipitate is mixed and sintered with lithium salt, so that the porosity of the material is higher, the density and the strength of the material are reduced, and the practical application of the material is restricted.
It can be seen that the above systems all have respective problems in preparing the positive electrode material, and in order to improve the battery performance, the prior art has an electrochemical performance of the material modified by doping, for example, patent application CN102790209a discloses a positive electrode material for a lithium ion battery, comprising a compound of formula Li 1+xMXδOε-δ, wherein M is one or more of Ni, co and Mn, X is one or more of F, cl, br, I and S, X is 0< x.ltoreq. 0.33,0< δ.ltoreq.0.2, 0< epsilon.ltoreq.10. The method for preparing the cathode material of the oxygen-site doped anions and the method for preparing the cathode material of the lithium ion battery are provided, in fact, F, cl, br, I anions mentioned in the scheme are all-1 valence, transition metal valence change is needed when O with the valence of-2 valence is replaced, the formed cathode material is in a metastable state, in addition, F, cl and lithium ions are combined more tightly, impurity LiX is easy to form in the calcining process instead of entering an O lattice site, and in addition, br, I and S are large in size and difficult to enter the O lattice site. There are also materials modified by surface coating, for example, the invention patent CN 112993259B provides a coated ternary cathode material, a method for preparing the same and a lithium ion battery. The coated ternary positive electrode material comprises an inner core of a ternary positive electrode active material co-doped with aluminum, zirconium and fluorine and a coating layer coated on the surface of the inner core, wherein the coating layer comprises zirconium hydrogen phosphate and a boron compound. It should be noted that the doping and coating are difficult to solve the problems of poor uniformity of the mixed materials, poor interface contact caused by multiphase coexistence after calcination, and the like, and are not beneficial to the performance of the materials.
Disclosure of Invention
The invention relates to a method which is widely applied to ternary positive electrode material preparation at present, namely a coprecipitation method, and provides a preparation method of a precursor of a polyanion group positive electrode material, wherein soluble salts of Mn, ni, co and A are mixed with salts or alkali containing carbonate radicals, oxalate radicals and hydroxyl radicals, and react under the action of a complexing agent to form the precursor, so that the precursor has high sphericity and high tap density. Under the heating condition, the existing hydroxide containing Mn is moderately oxidized in the air, so that single precursor particles can be compacted together, and after lithium addition and calcination, the precursor containing oxalate or carbonate can generate CO2, so that proper porosity is ensured.
Further, by optimizing the lithium/metal ratio and the calcination conditions, the cathode material with high sphericity, high tap density and excellent electrochemical performance can be synthesized, and particularly has good multiplying power performance and cycle stability.
The specific scheme is as follows:
the preparation method of the polyanion group positive electrode material precursor comprises the following steps:
(1) Preparing a mixed salt solution, namely preparing soluble salts of Mn, ni, co and doping element A into 0.1-4.0mol/L aqueous solution, alcohol solution or a mixed solution of the two to obtain solution X;
(2) Preparing a mixed alkali solution, namely preparing a salt or alkali containing anionic groups CO 3 2-,C2O4 2-,OH- into a water solution, an alcohol solution or a mixed solution of the water solution and the alcohol solution with the concentration of 0.1-4.0mol/L, and simultaneously adding ammonium ions as complexing agents to obtain a solution Y;
(3) Adding water or alcohol or a mixed solution of the water and the alcohol into a reaction kettle as a solvent, simultaneously introducing the solution X obtained in the step (1) and the solution Y obtained in the step (2) into the reaction kettle at a flow rate ratio of 1-2:0.5-4 for reaction, and washing, filtering and drying after the reaction is finished to obtain a precursor of the positive electrode material;
The positive electrode material precursor has a chemical formula ：MnxNiyCozA(1-x-y-z)[CO3]a[C2O4]b[OH]2(1-a-b),, wherein x, y and z are each independently positive numbers greater than 0 and less than 1, the doping element A is metal, 0.ltoreq.1-x-y-z.ltoreq.0.1, a and b are each independently positive numbers greater than 0 and less than 1, and the ratio of the total mole number of Mn, ni, co and the doping element A to O is between 2 and 4.
Further, in the step (1), the soluble salt of Mn, ni, co or A is selected from at least one of sulfate, acetate or nitrate thereof, and the doping element A is at least one of Al, mg, ca, ti, V, cr, fe, cu and Zn;
Optionally, in the step (2), the carbonate ion is at least one of sodium carbonate, potassium carbonate, sodium bicarbonate or potassium bicarbonate, the oxalate ion is at least one of oxalic acid, sodium hydrogen oxalate, sodium oxalate, potassium oxalate or potassium hydrogen oxalate, the hydroxide ion is at least one of sodium hydroxide and potassium hydroxide, the ammonium ion is at least one of ammonia water, ammonium carbonate or ammonium bicarbonate, and preferably, the concentration of the ammonium ion is 0.01-1.0mol/L.
In the step (3), the reaction conditions in the reaction kettle are that the solvent in the initial reaction kettle is water, alcohol or a mixed solution of the water and the alcohol, the volume of the solvent accounts for 20-80% of that of the final mixed suspension liquid, the final mixed suspension liquid is formed by precipitation generated by the reaction of the solution X and the solution Y, soluble salt and the solvent, the temperature in the reaction kettle is 50-75 ℃, the reaction time is 5-10 hours, the reaction pH is 7.0-11, the stirring speed is 200r/min-1000r/min, and after the reaction is finished, the reaction is aged for 3-10 hours, and then the reaction product is washed, filtered and dried;
Preferably, the solution adopted by the washing and filtering is water, alcohol or a mixture of the water and the alcohol, and the washing and filtering is dried at 80-120 ℃ for 5-15 hours after the filtering.
The invention also protects the positive electrode material precursor prepared by the preparation method of the polyanion group positive electrode material precursor, wherein the positive electrode material precursor is spherical, has the particle size of 3-10 mu m, is uniformly dispersed, and has the tap density of 1.8-1.9g/cm 3.
The invention also provides a positive electrode material, which is obtained by mixing the positive electrode material precursor or the positive electrode material precursor after heat treatment with a lithium source compound and calcining at 400-900 ℃.
Further, the heat treatment condition of the positive electrode material precursor after the heat treatment is that the temperature is 400-600 ℃ and the time is 2-10 hours;
Optionally, the calcination comprises 2 stages, first at 400-600 ℃ for 2-8 hours, followed by 750-900 ℃ for 5-20 hours.
Further, the proportion of the positive electrode material precursor and the lithium source compound is according to the mole total of Li elements in the lithium source compound, wherein the mole total of Mn, ni, co and doping element A in the positive electrode material precursor=0.9-1.6;
Optionally, the tap density of the positive electrode material is 2.1-2.8g/cm 3, the initial 0.1C discharge specific capacity is 200-300mAh/g under a voltage window of 2.0-4.6V, the initial coulomb efficiency is 85% -95%, and the capacity retention rate is 90-99% after 100 times of 1C charge and discharge.
The invention also provides a preparation method of the positive electrode material, wherein the positive electrode material precursor or the positive electrode material precursor after heat treatment is mixed with a lithium source compound and then calcined at 400-900 ℃;
Preferably, the lithium source compound is at least one of lithium carbonate, lithium hydroxide (hydration), lithium oxalate, lithium chloride, lithium acetate (hydration) or lithium nitrate, and the proportion of the positive electrode material precursor and the lithium source compound is according to the mole total of Li ions in the lithium source compound, wherein the mole total of Mn, ni and Co and doping element A in the positive electrode material precursor=0.9-1.6;
Preferably, the calcination comprises 2 stages, calcination at 400-600 ℃ for 2-8 hours followed by calcination at 750-900 ℃ for 5-20 hours.
The invention also provides an electrode, a battery comprising the positive electrode material and the electrode.
The beneficial effects are that:
In the invention, the preparation method of the precursor of the multi-anionic group positive electrode material adopts salt or alkali containing anionic groups CO 3 2-,C2O4 2-,OH- to prepare 0.1-4.0mol/L aqueous solution, alcohol solution or mixed solution of the two, and after the anionic groups are mixed, the sphericity of the precursor can be improved, so that the tap density is improved, and meanwhile, the agglomeration problem of the precursor caused by calcination is solved.
In the precursor material, the Mn-containing hydroxide precursor is moderately oxidized in the air, so that single precursor particles can be compacted together, agglomeration among the particles is reduced, and after lithium addition and calcination, the precursor containing oxalate or carbonate can generate CO 2, so that proper porosity is ensured, and better tap density is obtained.
Further, the invention synthesizes the positive electrode material with high sphericity, high tap density and excellent electrochemical performance through optimizing the ratio of lithium to metal and the calcination condition.
In a word, the preparation method of the polyanion group positive electrode material precursor provided by the invention has the advantages of simple synthesis process, matching with the current industrial flow, uniform distribution of the elements of the obtained positive electrode material, stable structure and good multiplying power performance and circulation stability.
Drawings
In order to more clearly illustrate the technical solutions of the present invention, the following brief description will be made on the accompanying drawings, which are given by way of illustration only and not limitation of the present invention.
FIG. 1 is a scanning electron microscope image of a positive electrode material precursor synthesized in example 1 of the present invention;
FIG. 2 is an XRD pattern of a precursor of the cathode material synthesized in example 1 of the present invention;
FIG. 3 is a scanning electron microscope image of the positive electrode material obtained after calcination in example 1 of the present invention;
FIG. 4 is a scanning electron microscope image of a precursor of the positive electrode material of comparative example 1 of the present invention;
FIG. 5 is an XRD pattern of a precursor of a positive electrode material of comparative example 1 of the present invention;
FIG. 6 is a scanning electron microscope image of a precursor of the positive electrode material of comparative example 2 of the present invention;
Fig. 7 is a scanning electron microscope image of a precursor of the positive electrode material of comparative example 3 of the present invention.
Detailed Description
Preferred embodiments of the present invention will be described in more detail below. While the preferred embodiments of the present invention are described below, it should be understood that the present invention may be embodied in various forms and should not be limited to the embodiments set forth herein. The specific techniques or conditions are not identified in the examples and are performed according to techniques or conditions described in the literature in this field or according to the product specifications. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention. In the examples below, "%" refers to weight percent, unless explicitly stated otherwise.
Example 1
The embodiment provides a high sphericity high tap density positive electrode material precursor and a corresponding high tap density lithium-rich positive electrode material, which are prepared according to the following steps:
(1) Preparing a mixed salt solution, namely preparing a sulfate with the molar ratio of metal elements of 4:1:1=Mn to Ni to Co into a 2mol/L aqueous solution.
(2) Preparing a mixed alkali solution, namely preparing aqueous solution of sodium carbonate, sodium oxalate and sodium hydroxide with the molar ratio of anionic groups of 8:1:2 (= CO 3:C2O4: OH) into 0.5mol/L, and adding ammonia water as a complexing agent, wherein the concentration of ammonium ions is 0.05mol/L.
(3) Adding deionized water into a reaction kettle as a solvent, simultaneously introducing the mixed salt solution obtained in the step (1) and the mixed alkali solution obtained in the step (2) into the reaction kettle at a flow rate ratio of approximately 1:4 for reaction, controlling the pH value to be 8.5, controlling the reaction temperature to be 60 ℃, stirring at a speed of 500r/min, reacting for 10 hours, and washing, filtering and drying to obtain a positive electrode material precursor after the reaction is finished.
(4) And (3) taking lithium carbonate and a precursor according to the molar ratio of total metal ions of manganese, cobalt and nickel ions to lithium ions in the step (1-3) of 1:1.5, uniformly mixing, sintering for 4 hours at 450 ℃, and then sintering for 12 hours at 850 ℃ to obtain the target lithium-rich cathode material Li 1.2Mn0.534Co0.133Ni0.133O2.
(5) The positive electrode material is mixed with carbon black and PVDF according to the mass ratio of 8:1:1, and is uniformly ground by taking N-methyl pyrrolidone as a solvent, then coated on an aluminum foil and placed in a blast drying oven for drying at 100 ℃ for 12 hours. After removal, the electrode wafer was cut after several rolls on a roller press. The lithium ion battery high-voltage electrolyte is prepared from lithium ion battery high-voltage electrolyte produced by Beijing chemical reagent research, and a button battery is arranged in a glove box and tested on a new Wei battery test system, wherein the temperature is 25 ℃.
Example 2
The embodiment provides a layered lithium-rich cathode material with high sphericity and high tap density, which is prepared according to the following steps, and is different from the preparation method provided in the embodiment 1 in that in the step (4), the precursor is sintered for 5 hours at 500 ℃, and then the obtained oxide and lithium carbonate are uniformly mixed according to the molar ratio of total metal ions of manganese, cobalt and nickel ions to lithium ions of 1:1.5, sintered for 4 hours at 450 ℃ and sintered for 12 hours at 850 ℃ to obtain the target lithium-rich cathode material.
Example 3
The embodiment provides a layered lithium-rich cathode material with high sphericity and high tap density, which is prepared according to the following steps, and is different from the preparation method provided in embodiment 1 in that in the step (1), metal acetate is used for replacing metal sulfate, and the rest steps are completely consistent.
Example 4
The present embodiment provides a layered lithium-rich cathode material with high sphericity and high tap density, which is prepared according to the following steps, and is different from the preparation method provided in embodiment 1 in that in step (1), when preparing a mixed salt solution, a sulfate with a metal element molar ratio of 4:1:0.025:0.025:0.025=mn: ni: co: fe: al: mg is configured into an aqueous solution with a molar ratio of 2 mol/L. The remaining conditions were identical.
Example 5
The present example provides a layered lithium-rich cathode material with high sphericity and high tap density, which is prepared according to the following steps, unlike the preparation method provided in example 1, in the step (2), when a mixed alkali solution is prepared, potassium carbonate, potassium oxalate and potassium hydroxide with the molar ratio of anionic groups of 8:1:2 (=co 3:C2O4: OH) are prepared as 2mol/L aqueous solutions, and ammonia water is added as a complexing agent, and the concentration of ammonium ions is 0.2mol/L. In the step (3), the mixed salt solution obtained in the step (1) and the mixed alkali solution obtained in the step (2) are simultaneously introduced into a reaction kettle for reaction at a speed ratio of approximately 1:1, the pH value is controlled at 8.7, and the stirring speed is 500r/min. The remaining conditions were identical.
Example 6
The embodiment provides a layered cathode material with high sphericity and high tap density, which is prepared according to the following steps, and is different from the preparation method provided in embodiment 1 in that in step (4), lithium carbonate and a precursor are uniformly mixed according to the molar ratio of total metal ions of manganese, cobalt and nickel ions to lithium ions of 1:1, and the rest conditions are identical.
Example 7
The embodiment provides a layered cathode material with high sphericity and high tap density, which is prepared according to the following steps, and is different from the preparation method provided in embodiment 1 in that in step (4), lithium carbonate and a precursor are uniformly mixed according to the molar ratio of total metal ions of manganese, cobalt and nickel ions to lithium ions of 1:1.4, and the rest conditions are identical.
Example 8
The embodiment provides a layered cathode material with high sphericity and high tap density, which is prepared according to the following steps, and is different from the preparation method provided in embodiment 1 in that in step (4), lithium carbonate and a precursor are uniformly mixed according to the molar ratio of total metal ions of manganese, cobalt and nickel ions to lithium ions of 1:1.6, and the rest conditions are identical.
Example 9
The present example provides a layered cathode material with high sphericity and high tap density, which is prepared according to the following steps, which is different from the preparation method provided in example 1 in that in step (4), the sintering condition is changed to sintering at 450 ℃ for 4 hours, followed by sintering at 800 ℃ for 15 hours, and the remaining conditions are identical.
Example 10
This example provides a high sphericity, high tap density layered cathode material prepared according to the following procedure, which differs from the preparation method provided in example 1 in that in step (4), the sintering conditions are changed to sintering at 450 ℃ for 4 hours, followed by sintering at 880 ℃ for 10 hours, the remaining conditions being identical.
Example 11
The present example provides a high sphericity, high tap density, cobalt-free layered lithium-rich cathode material prepared according to the following steps, which is different from the preparation method provided in example 1 in that in step (1), when a mixed salt solution is prepared, a sulfate with a metal element molar ratio of 4:2=mn: ni is configured as a 2mol/L aqueous solution. Other conditions were completely identical.
Example 12
The embodiment provides a layered lithium-rich cathode material with high sphericity and high tap density, which is prepared according to the following steps, and is different from the preparation method provided in the embodiment 1 in that in the step (2), sodium carbonate, sodium oxalate and sodium hydroxide with the molar ratio of anionic groups of 9:0.5:1 (=co 3:C2O4: OH) are prepared into an aqueous solution with the molar ratio of 1.0mol/L when a mixed alkali solution is prepared, and ammonia water is added as a complexing agent, wherein the concentration of ammonium ions is 0.1mol/L. In the step (3), the mixed salt solution obtained in the step (1) and the mixed alkali solution obtained in the step (2) are simultaneously introduced into a reaction kettle for reaction at a speed ratio of approximately 1:2, the pH value is controlled at 8.2, and the stirring speed is 300r/min. The remaining conditions were identical.
Example 13
The present example provides a layered lithium-rich cathode material with high sphericity and high tap density, which is prepared according to the following steps, unlike the preparation method provided in example 1, in the step (2), when preparing a mixed alkali solution, potassium carbonate, potassium oxalate and potassium hydroxide with an anionic group molar ratio of 9.5:0.25:0.5 (=co 3:C2O4: OH) are prepared into an aqueous solution of 2.0mol/L, and ammonia water is added as a complexing agent, and the ammonium ion concentration is 0.2mol/L. In the step (3), the mixed salt solution obtained in the step (1) and the mixed alkali solution obtained in the step (2) are simultaneously introduced into a reaction kettle for reaction at a flow rate ratio of approximately 1:1, the reaction temperature is 55 ℃, the pH value is controlled at 9.0, and the stirring speed is 400r/min. The remaining conditions were identical.
Example 14
The present example provides a layered lithium-rich cathode material with high sphericity and high tap density, which is prepared according to the following steps, unlike the preparation method provided in example 1, in the step (2), when preparing a mixed alkali solution, potassium carbonate, potassium oxalate and potassium hydroxide with an anionic group molar ratio of 9.0:0.25:1.5 (=co 3:C2O4: OH) are prepared into an aqueous solution of 2.0mol/L, and ammonia water is added as a complexing agent, and the ammonium ion concentration is 0.2mol/L. In the step (3), the mixed salt solution obtained in the step (1) and the mixed alkali solution obtained in the step (2) are simultaneously introduced into a reaction kettle for reaction at a flow rate ratio of approximately 1:1, the reaction temperature is 55 ℃, the pH value is controlled at 9.0, and the stirring speed is 400r/min. The remaining conditions were identical.
Example 15
The present example provides a layered lithium-rich cathode material with high sphericity and high tap density, which is prepared according to the following steps, unlike the preparation method provided in example 1, in the step (2), when preparing a mixed alkali solution, potassium carbonate, potassium oxalate and potassium hydroxide with an anionic group molar ratio of 9.0:0.75:0.5 (=co 3:C2O4: OH) are prepared as an aqueous solution of 2.0mol/L, and ammonia water is added as a complexing agent, and the ammonium ion concentration is 0.2mol/L. In the step (3), the mixed salt solution obtained in the step (1) and the mixed alkali solution obtained in the step (2) are simultaneously introduced into a reaction kettle for reaction at a flow rate ratio of approximately 1:1, the reaction temperature is 55 ℃, the pH value is controlled at 9.0, and the stirring speed is 400r/min. The remaining conditions were identical.
Example 16
The embodiment provides a layered lithium-rich cathode material with high sphericity and high tap density, which is prepared according to the following steps, and is different from the preparation method provided in embodiment 1 in that in step (2), ammonium carbonate is added as a complexing agent when preparing a mixed alkali solution, and the concentration of ammonium ions is 0.05mol/L. The remaining conditions were identical.
Example 17
The present example provides a layered lithium-rich cathode material with high sphericity and high tap density, which is prepared according to the following steps, unlike the preparation method provided in example 1, in that lithium carbonate is replaced with lithium carbon hydroxide (anhydrous) in step (4). The remaining conditions were identical.
Example 18
The present example provides a layered lithium-rich cathode material with high sphericity and high tap density, which is prepared according to the following steps, which is different from the preparation method provided in example 1 in that lithium carbonate is replaced by lithium oxide in step (4). The remaining conditions were identical.
Example 19
The embodiment provides a layered lithium-rich cathode material with high sphericity and high tap density, which is prepared according to the following steps, and is different from the preparation method provided in embodiment 1 in that the solvent adopted in the preparation of the precursor is an ethanol aqueous solution with the volume fraction of 20%, namely, the ethanol aqueous solution is used for replacing deionized water in step (3) and is added into a reaction kettle to serve as the solvent. The remaining conditions were identical.
Comparative example 1
The comparative example provides a positive electrode material precursor and a corresponding positive electrode material, and the preparation method is different from that of example 1 in that in step (2), an aqueous sodium carbonate solution with an alkali solution of 2.0mol/L is prepared, and ammonia water is added as a complexing agent, wherein the concentration of ammonium ions is 0.2mol/L. In the step (3), the mixed salt solution obtained in the step (1) and the mixed alkali solution obtained in the step (2) are simultaneously introduced into a reaction kettle for reaction at a speed ratio of approximately 1:1, and the pH value is controlled at 7.8. The remaining conditions were identical.
Comparative example 2
The comparative example provides a positive electrode material precursor and a corresponding positive electrode material, and the preparation method is different from that of example 1 in that in step (2), sodium carbonate and sodium hydroxide with an anionic group molar ratio of 9:2 (=co 3: OH) are prepared into an aqueous solution of 2.0mol/L, and ammonia water is added as a complexing agent, and the ammonium ion concentration is 0.2mol/L. In the step (3), the mixed salt solution obtained in the step (1) and the mixed alkali solution obtained in the step (2) are simultaneously introduced into a reaction kettle for reaction at a flow rate ratio of approximately 1:1. The remaining conditions were identical.
Comparative example 3
The comparative example provides a positive electrode material precursor and a corresponding positive electrode material, and the preparation method is different from that of example 1 in that in step (2), sodium carbonate and sodium oxalate with an anionic group molar ratio of 9:1 (=co 3:C2O4) are prepared into an aqueous solution of 0.5mol/L, and ammonia water is added as a complexing agent, and the ammonium ion concentration is 0.05mol/L. The remaining conditions were identical.
The materials and batteries prepared in the examples and comparative examples were tested, the results are shown in fig. 1-7, and the test data are summarized in table 1.
The precursor of the positive electrode material of the polyanion group has high sphericity, uniform size and good dispersion as shown in fig. 1, 4,6 and 7, the precursor of the positive electrode material of the comparative example 1 has nearly spherical shape and uniform size in fig. 4, the precursor of the positive electrode material of the comparative example 2 has chips and poor sphericity of particles due to the existence of OH groups in fig. 6, and the precursor of the positive electrode material of the comparative example 3 has different sizes in the form of agglomeration.
As can be seen from fig. 3, the positive electrode material obtained by sintering the mixed lithium in example 1 still maintains a spherical shape, has a uniform size, and is well dispersed.
Fig. 2 and 5 are XRD full spectra of materials, wherein fig. 2 is an XRD full spectrum of the positive electrode material precursor of example 1, the X-ray diffraction pattern of which exhibits three sets of diffraction peaks corresponding to X-ray diffraction patterns of carbonate, oxalate, and hydroxide, and in particular, characteristic diffraction peaks of hydroxide and oxalate occur between 15-20 ° in 2θ angle when the anode target is a copper target.
Fig. 5 is an XRD full spectrum of the precursor of the positive electrode material of comparative example 1, which uses a carbonate phase as a main phase, but does not show diffraction peaks corresponding to oxalate and hydroxide precursors at 2θ=18° to 20 °.
Table 1 table of properties of the positive electrode material precursor and the positive electrode material property data corresponding to examples and comparative examples
Table 1 shows the positive electrode material precursors and positive electrode material property performance data tables corresponding to the examples and comparative examples, and has the following characteristics:
(1) As can be seen from comparative examples 1-19 and comparative examples 1-3, the polyanionic group positive electrode material precursor exhibits higher tap density overall, and the corresponding positive electrode material (example 6, which is not lithium-rich except for) exhibits higher tap density, first coulombic efficiency, first discharge specific capacity, 1C 100-turn capacity retention.
(2) As can be seen from comparative examples 1 and 2, the precursor calcination was performed first, which helps to increase the tap density of the positive electrode material after sintering, but the performance was slightly reduced.
(3) As can be seen from comparative examples 1, 6, 7, 8, the ratio of metal to Li content significantly affects the tap density and electrochemical properties of the material, and the appropriate ratio can be considered according to specific requirements. For example, when the total number of moles of Li ions in the lithium source compound is equal to Mn, ni and Co in the precursor of the positive electrode material=0.9-1.6, the obtained positive electrode material has higher tap density and better rate capability and cycle stability in the charge and discharge process.
(4) As can be seen from comparative examples 1, 9 and 10, the calcination conditions can also significantly affect the tap density and electrochemical properties of the positive electrode material, and the optimum properties of the positive electrode material can be exhibited at a suitable temperature and calcination time. For metals Mn, ni, co and Li in a molar ratio of 1:1.5, the calcination conditions are preferably 450 calcination for 4 hours and 850 sintering for 12 hours.
(5) As can be seen from comparative examples 1, 17, 18, different lithium sources can also affect the tap density and electrochemical performance of the cathode material. The lithium salt and the mixed lithium salt may be appropriately selected according to specific requirements. For example, when the lithium source compound in the step (4) is lithium oxide, the tap density of the positive electrode material can be increased, but the electrochemical performance is slightly reduced, and when the lithium source compound is lithium carbonate, the rate performance and the cycle stability of the battery can be improved.
(6) In comparative examples 1 and 19, it is understood that the choice of solvent can also affect the properties of the precursor and the corresponding positive electrode material, and optimizing the solvent can further enhance the electrochemical properties of the material. In view of cost, synthesis safety and material performance, deionized water is preferably used as a solvent in the step (3), so that the low-rate performance and the high-rate cycle stability performance of the battery can be improved.
The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the specific details of the above embodiments, and various simple modifications can be made to the technical solution of the present invention within the scope of the technical concept of the present invention, and all the simple modifications belong to the protection scope of the present invention.
In addition, the specific features described in the above embodiments may be combined in any suitable manner without contradiction. The various possible combinations of the invention are not described in detail in order to avoid unnecessary repetition.
Moreover, any combination of the various embodiments of the invention can be made without departing from the spirit of the invention, which should also be considered as disclosed herein.
Claims (19)
1. The preparation method of the polyanion group positive electrode material precursor is characterized by comprising the following steps of:
(1) Preparing a mixed salt solution, namely preparing soluble salts of Mn, ni, co and doping element A into 0.1-4.0mol/L aqueous solution, alcohol solution or a mixed solution of the two to obtain solution X;
(2) Preparing a mixed alkali solution, namely preparing a salt or alkali containing anionic groups CO 3 2-,C2O4 2-,OH- into a water solution, an alcohol solution or a mixed solution of the water solution and the alcohol solution with the concentration of 0.1-4.0mol/L, and simultaneously adding ammonium ions as complexing agents to obtain a solution Y;
(3) Adding water or alcohol or a mixed solution of the water and the alcohol into a reaction kettle as a solvent, simultaneously introducing the solution X obtained in the step (1) and the solution Y obtained in the step (2) into the reaction kettle at a flow rate ratio of 1-2:0.5-4 for reaction, and washing, filtering and drying after the reaction is finished to obtain a precursor of the positive electrode material;
The positive electrode material precursor has a chemical formula ：MnxNiyCozA(1-x-y-z)[CO3]a[C2O4]b[OH]2(1-a-b),, wherein x, y and z are each independently positive numbers greater than 0 and less than 1, the doping element A is metal, 0.ltoreq.1-x-y-z.ltoreq.0.1, a and b are each independently positive numbers greater than 0 and less than 1, and the ratio of the total mole number of Mn, ni, co and the doping element A to O is between 2 and 4.
2. The method of preparing a polyanionic group positive electrode material precursor according to claim 1, wherein in the step (1), the soluble salt of Mn, ni, co or A is selected from at least one of sulfate, acetate or nitrate thereof, and the doping element A is at least one of Al, mg, ca, ti, V, cr, fe, cu and Zn.
3. The method for preparing a polyanionic group positive electrode material precursor according to claim 2, wherein in the step (2), carbonate ions are at least one of sodium carbonate, potassium carbonate, sodium bicarbonate or potassium bicarbonate, oxalate ions are at least one of oxalic acid, sodium hydrogen oxalate, sodium oxalate, potassium oxalate or potassium hydrogen oxalate, hydroxide ions are at least one of sodium hydroxide and potassium hydroxide, and ammonium ions are at least one of ammonia water, ammonium carbonate or ammonium bicarbonate.
4. The method for preparing a polyanionic group positive electrode material precursor according to claim 3, wherein the concentration of the ammonium ion is 0.01-1.0mol/L.
5. The method for preparing the polyanion group positive electrode material precursor according to any one of claims 1 to 4, wherein in the step (3), the reaction condition in the reaction kettle is that the solvent in the initial reaction kettle is water, alcohol or a mixed solution of the water and the alcohol, the solvent volume accounts for 20 to 80 percent of the final mixed suspension liquid, the final mixed suspension liquid is formed by precipitation generated by the reaction of the solution X and the solution Y, soluble salt and the solvent, the temperature in the reaction kettle is 50 to 75 ℃, the reaction time is 5 to 10 hours, the reaction pH is 7.0 to 11, the stirring speed is 200r/min to 1000r/min, and aging is carried out for 3 to 10 hours after the reaction is finished, and washing, filtering and drying are carried out.
6. The method for preparing a polyanionic group positive electrode material precursor according to claim 5, wherein the solution used for washing and filtering is water, alcohol or a mixture of the water and the alcohol, and the solution is dried after filtering and is dried at 80-120 ℃ for 5-15 hours.
7. The positive electrode material precursor prepared by the preparation method of the polyanion group positive electrode material precursor according to any one of claims 1-6 is characterized in that an X-ray diffraction pattern of the positive electrode material precursor presents three sets of diffraction peaks corresponding to X-ray diffraction patterns of carbonate, oxalate and hydroxide, and the positive electrode material precursor is spherical, has a particle size of 3-10 mu m, is uniformly dispersed, and has a tap density of 1.8-1.9g/cm 3.
8. The positive electrode material precursor according to claim 7, wherein when the anode target is a copper target, characteristic diffraction peaks of hydroxide and oxalate occur at an angle of 2. Theta. Of 15 to 20 ℃.
9. A positive electrode material characterized by being obtained by mixing the positive electrode material precursor according to claim 7 or 8 or the positive electrode material precursor after heat treatment with a lithium source compound and calcining at 400-900 ℃.
10. The positive electrode material according to claim 9, wherein the heat treatment condition of the positive electrode material precursor after the heat treatment is 400-600 ℃ for 2-10 hours.
11. The positive electrode material according to claim 10, wherein the calcination comprises 2 stages, wherein the calcination is performed at 400 to 600 ℃ for 2 to 8 hours and then at 750 to 900 ℃ for 5 to 20 hours.
12. The positive electrode material according to any one of claims 9 to 11, wherein the ratio of the positive electrode material precursor to the lithium source compound is such that the molar sum of Li elements in the lithium source compound is Mn, ni, co and the doping element A molar sum of the positive electrode material precursor=0.9 to 1.6.
13. The positive electrode material according to claim 12, wherein the lithium source compound is at least one of lithium carbonate, lithium hydroxide hydrate, lithium oxalate, lithium chloride, lithium acetate hydrate or lithium nitrate.
14. The positive electrode material according to claim 12, wherein the tap density of the positive electrode material is 2.1-2.8g/cm 3, the initial 0.1C discharge specific capacity is 200-300mAh/g under a voltage window of 2.0-4.6V, the initial coulomb efficiency is 85% -95%, and the capacity retention rate is 90-99% after 100 times of 1C charging and discharging.
15. A method for producing a positive electrode material, characterized in that the positive electrode material precursor according to claim 7 or 8, or the positive electrode material precursor after heat treatment, is mixed with a lithium source compound and then calcined at 400 to 900 ℃.
16. The method for preparing a positive electrode material according to claim 15, wherein the lithium source compound is at least one of lithium carbonate, lithium hydroxide hydrate, lithium oxalate, lithium chloride, lithium acetate hydrate or lithium nitrate, and the ratio of the positive electrode material precursor to the lithium source compound is such that the total number of moles of Li ions in the lithium source compound is Mn, ni, co and the total number of moles of doping element A in the positive electrode material precursor=0.9 to 1.6.
17. The method of producing a positive electrode material according to claim 15, wherein the calcination comprises 2 stages, wherein the calcination is performed at 400 to 600℃for 2 to 8 hours and then at 750 to 900℃for 5 to 20 hours.
18. An electrode comprising the positive electrode material of any one of claims 9-14.
19. A battery comprising the electrode of claim 18.
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