CN115745030B - Potassium ion battery anode material, precursor thereof and preparation method - Google Patents
Potassium ion battery anode material, precursor thereof and preparation method Download PDFInfo
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Abstract
The invention belongs to the technical field of battery materials, and discloses a precursor of a positive electrode material of a potassium ion battery, a preparation method of the precursor and the positive electrode material. The invention provides a NiCo-PBA modified potassium ion battery anode material precursor, which has a two-layer structure, wherein the inner layer is NiCo-PBA, and the outer layer is nickel-cobalt-manganese ternary material. In the preparation process, niCo-PBA is prepared as seed crystal, and then a coprecipitation method is adopted to grow a nickel-cobalt-manganese ternary material on the surface of the crystal nucleus. Magnesium may be further doped into the ternary nickel-cobalt-manganese material. The NiCo-PBA modified potassium ion battery anode material precursor provided by the invention can not only effectively promote the transportation of potassium ions, but also bear K after being sintered to obtain the anode material + The high stress caused by continuous insertion/extraction can further improve the diffusion rate of electrolyte, and has high-efficiency ion transmission and structural stability. Magnesium is further doped in the precursor material, so that the electrochemical performance and the application prospect of the material can be further improved.
Description
Technical Field
The invention belongs to the technical field of battery materials, and particularly relates to a precursor of a positive electrode material of a potassium ion battery and a preparation method of the precursor.
Background
Sodium and potassium are the same family of elements, are similar in chemical properties to lithium, are abundant in resources, and are considered as the most promising alternatives to LIBs. In addition, K + Diffusion process in organic electrolyte is faster, approaching Li + The redox potential of/Li (-2.93 vs. -3.04V), PIBs, is one of the most promising candidates for the next generation of large scale energy storage systems. However, PIBs have low capacity and short cycle life due to structural collapse of many cathode materials in severe potassium adding/removing processes caused by larger ionic radius, low energy density and larger structural stress in dynamic decoupling processes. Therefore, the development of suitable cathode materials, anode materials, and high performance electrolytes has become critical to improving the electrochemical performance of PIBs. Current research is focused mainly on layered transition metal oxides, organic compounds, polyanionic compounds and prussian blue analogues. Among them, layered transition metal oxides have proved to be very promising cathode materials for lithium ion batteries and semiconductor batteries due to their high theoretical capacity, low cost, and stable structure. But it is at K + P occurs when the plug is removed 3 -O 3 The phase change causes high stress at the phase boundary, which leads to cracking of the active material and severely affects electrochemical performance.
Disclosure of Invention
Aiming at the problems existing in the prior art, the first object of the invention is to provide a NiCo-PBA modified and magnesium doped potassium ion battery anode material precursor; a second object of the present invention is to provide a method for preparing the aforementioned precursor; a third object of the present invention is to provide a positive electrode material.
Prussian Blue (PB) and Prussian Blue Analogues (PBAs) have a porous three-dimensional structure, the interstitial space is surrounded by water molecules and alkali metal ions (Na + 、K + Etc.), high electrochemical surface area, enhanced charge transport, tailored electronic properties, and exposed surfaces make them ideal materials for electrochemical energy conversion. The layered oxide of the positive electrode material of the potassium ion battery and the Prussian blue polymer are combined, so that the transportation of potassium ions can be effectively promoted, and K can be born + High stress caused by continuous insertion/extraction.
Specifically, the present invention provides the following technical solutions.
Firstly, the invention provides a NiCo-PBA modified potassium ion battery anode material precursor, wherein the precursor has a two-layer structure, the inner layer is NiCo-PBA, and the outer layer is nickel-cobalt-manganese ternary material.
Further, the NiCo-PBA of the inner layer is cubic.
Further, it is preferred that the side length of the NiCo-PBA of the inner layer is 1/9~1/5 of the precursor diameter.
Further, magnesium is doped in the nickel-cobalt-manganese ternary material of the outer layer. Further preferably, the magnesium doping amount is 1500 to 5000ppm.
Secondly, the invention provides a preparation method of the precursor, which comprises the following steps:
step S1, dissolving nickel salt and a structure directing agent in water to obtain a mixed solution A; dissolving potassium hexacyanocobaltate in water to obtain a mixed solution B;
step S2, stirring and mixing the mixed solution A and the mixed solution B to obtain mixed slurry C;
s3, carrying out solid-liquid separation on the mixed slurry C, washing, drying and separating the obtained solid phase to obtain NiCo-PBA with a cube structure;
s4, preparing a precipitant solution, a complexing agent solution, reaction kettle bottom solution and a mixed salt solution of nickel, cobalt and manganese;
s5, adding NiCo-PBA with a cube structure into the reaction kettle base solution as seed crystals, and then adding a precipitator solution, a complexing agent solution and a mixed salt solution of nickel, cobalt and manganese in parallel flow into the reaction kettle base solution for coprecipitation reaction;
and S6, stopping the reaction when the granularity D50 of the reaction slurry in the step S5 reaches 5-10 mu m, aging, filtering the reaction slurry, and washing, drying, sieving and removing iron from a filtered solid phase to obtain a NiCo-PBA modified precursor.
Further, in a part of the preferred embodiments of the present invention, the structure directing agent is at least one of polyvinylpyrrolidone (PVP), citric acid, sodium citrate; the concentration of the structure directing agent in the mixed solution A is 0.5-1.2 mol/L, and the concentration of nickel ions is 0.6-1.3 mol/L.
Further, in some preferred embodiments of the present invention, the concentration of potassium hexacyanocobaltate in the mixed solution B is 0.3-0.8 mol/L.
Further, in a partially preferred embodiment of the present invention, the precipitant is NaOH, KOH, na 2 CO 3 、NaHCO 3 At least one of the precipitant solutions has a concentration of 2-9 mol/L; the complexing agent is at least one of ammonia water, ammonium bicarbonate, citric acid and ethylenediamine tetraacetic acid, and the concentration of the complexing agent solution is 1-6 mol/L.
In a further preferred embodiment of the present invention, the total concentration of the metal ions of nickel, cobalt and manganese in the mixed salt solution of nickel, cobalt and manganese is 1 to 5mol/L.
Further, in some preferred embodiments of the present invention, the pH value of the bottom solution of the reaction kettle is controlled to be 11-12, and the ammonia concentration is controlled to be 5.5-8.0 g/L.
Further, in a part of the preferred embodiments of the present invention, the temperature of the coprecipitation reaction in step S5 is 55 to 75 ℃, the pH value in the coprecipitation reaction is 11 to 12, and the ammonia concentration is 5.5 to 8.0g/L.
Further, in some preferred embodiments of the present invention, the flow rate of the complexing agent solution is 5-20 mL/min, the flow rate of the precipitant solution is 2-15 mL/min, and the flow rate of the mixed salt solution of nickel, cobalt and manganese is 10-50 mL/min.
Further, in a part of the preferred embodiment of the present invention, a magnesium salt solution is added as a dopant during the coprecipitation reaction described in step S5. Preferably, the concentration of the magnesium salt solution is 0.1-0.6 mol/L, and the flow rate is 0.5-3.5 mL/min.
Based on the same inventive concept, the invention provides a positive electrode material, which is obtained by pre-sintering the precursor of the NiCo-PBA modified potassium ion battery positive electrode material, mixing with a potassium source and sintering.
Further, in a part of the preferred embodiments of the present invention, the pre-sintering process is: preheating for 4-8 hours in an air atmosphere at 200-500 ℃.
Further, in some preferred embodiments of the present invention, the pre-heated precursor material is ball-milled and mixed with a potassium source, and then calcined at 750-950 ℃ for 8-16 hours in an oxygen atmosphere.
Further, in a partially preferred embodiment of the present invention, the potassium source is preferably potassium carbonate.
The PB/PBA adopts a periodic network structure formed by connecting metal and cyano, has higher specific surface area and adjustable porosity, has controllable morphology, is easy to functionalize, has customized electronic performance and an exposed surface, can enhance charge transport, and is made into an ideal material for electrochemical conversion. The NiCo-PBA polymer has a cubic structure with smooth surface, a rough edge compared with the surface, and has the characteristics of a three-dimensional open structure, small primary nano particle size and large specific surface area, and can increase available active sites, and has better electrolyte diffusivity and good structural stability. The laminar ternary positive electrode material with NiCo-PBA as crystal nucleus can promote potassium ion transport and bear K + The high stress caused by continuous insertion/extraction can further improve the diffusion rate of electrolyte, and has high-efficiency ion transmission and structural stability.
The inventor finds that during the application process of the positive electrode material of the potassium ion battery, K in the lamellar compound + The vacancy arrangement has a strong repulsive force, and the phase transition causes high stress at the phase boundary, resulting in cracking of the active material, leading to lower reversible capacity and multi-stage phase inversion, affecting electrochemical performance. Further doping inactive magnesium in the coprecipitation process of the precursor, so that the precursor has a predation effect in a crystal structure, the stability of a layered structure is enhanced, and K is enlarged + Diffusion layer, optimized Mn 3+ Jahn-Teller distortion. The magnesium doped oxide with a stable lamellar structure is combined with the NiCo-PBA crystal nucleus with controllable structure and larger surface area, so that the cycling stability of the potassium ion battery can be effectively improved, the electrolyte diffusion rate can be improved, and the electrochemical performance and the application prospect of the composite material can be improved.
Compared with the prior art, the invention has the following obvious beneficial technical effects:
(1) The NiCo-PBA modified potassium ion battery anode material precursor provided by the invention can not only effectively promote the transportation of potassium ions, but also bear K after being sintered to obtain the anode material + The high stress caused by continuous insertion/extraction can further improve the diffusion rate of electrolyte, and has high-efficiency ion transmission and structural stability.
(2) Magnesium is further doped in the precursor material, so that the electrochemical performance and the application prospect of the material are improved.
(3) The precursor material and the positive electrode material provided by the invention are used for a potassium ion battery, and the potassium ion battery has the characteristics of low cost, abundant resources and environmental friendliness, and has a wide application prospect.
(4) The preparation method of the precursor provided by the invention can directly utilize the existing precursor production line, does not increase the site and equipment investment, and is beneficial to popularization and application.
Drawings
FIG. 1 is an SEM image of NiCo-PBA obtained in example 1;
FIG. 2 is an SEM and EDS image of a NiCo-PBA modified magnesium doped precursor obtained in example 1; (a) is an SEM image of a NiCo-PBA modified/magnesium doped precursor at a magnification of 1000, (b) is an SEM image of a NiCo-PBA modified magnesium doped precursor at a magnification of 20000, and (c) - (f) are elemental surface profiles of Ni, co, mn, mg, respectively;
FIG. 3 shows XRD patterns of the NiCo-PBA modified/magnesium doped precursor and the NiCo-PBA modified precursor obtained in examples 1 and 5, wherein (a) is an XRD overall pattern, and (b) is an XRD pattern with 2 theta in the range of 37-66;
fig. 4 is a graph showing the rate performance of the battery assembled from the positive electrode materials obtained in example 1 and example 5 and the normal NCM811 positive electrode material.
Detailed Description
The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments are shown, for the purpose of illustrating the invention, but the scope of the invention is not limited to the specific embodiments shown.
Unless defined otherwise, all technical and scientific terms used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the scope of the present invention.
Unless otherwise specifically indicated, the various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or may be prepared by existing methods.
The invention firstly provides a NiCo-PBA modified potassium ion battery anode material precursor, wherein the precursor has a two-layer structure, the inner layer is NiCo-PBA, and the outer layer is nickel-cobalt-manganese ternary material.
The NiCo-PBA polymer has a cubic structure with smooth surface, a rough edge compared with the surface, and has the characteristics of a three-dimensional open structure, small primary nano particle size and large specific surface area, and can increase available active sites, and has better electrolyte diffusivity and good structural stability. The laminar ternary positive electrode material with NiCo-PBA as crystal nucleus can promote potassium ion transport and bear K + The high stress caused by continuous insertion/extraction can further improve the diffusion rate of electrolyte, and has high-efficiency ion transmission and structural stability.
In a specific embodiment, the NiCo-PBA of the inner layer is cubic. Further, it is preferred that the side length of the NiCo-PBA of the inner layer is 1/9~1/5 of the precursor diameter.
The Prussian blue coordination polymer crystal can generate reversible crystal structure change under the influence of guest molecules, and has elastic structure characteristics. The coordination polymer has the advantages that a shape memory effect can be generated when the crystal size of the coordination polymer is smaller, the energy barrier required by the transformation of the structure with smaller crystal particle size is higher, the specific surface area is smaller, the diffusion barrier during adsorption is large, and the molecules are relatively difficult to enter the gaps; the Prussian blue coordination polymer is controlled to have the particle size smaller than or equal to 500nm, the specific surface area is larger, molecules easily enter gaps, the diffusion resistance is small, and the adsorption capacity is larger. Therefore, controlling the size of Prussian blue crystals in the composite precursor material plays a very important role in the application of the Prussian blue crystals in the KIBs, and the crystal material with proper size shows the shortest potassium ion diffusion distance in the KIBs and can show excellent rate performance.
In a specific embodiment, magnesium is doped in the nickel-cobalt-manganese ternary material of the outer layer. Further preferably, the magnesium doping amount is 1500 to 5000ppm.
Inactive magnesium is doped in the coprecipitation process of the precursor, so that the precursor has a predation effect in a crystal structure, the stability of a layered structure is enhanced, and K is enlarged + Diffusion layer, optimized Mn 3+ Jahn-Teller distortion. The magnesium doped oxide with a stable lamellar structure is combined with the NiCo-PBA crystal nucleus with controllable structure and larger surface area, so that the cycling stability of the potassium ion battery can be effectively improved, and the diffusion rate of electrolyte can be improved. As the doping amount of magnesium increases, the two diffraction peaks (108) and (110) are obviously separated, and the peak type of the peak is gradually sharpened and then widened, the diffraction peak is shifted to a large angle direction, and the interplanar distance is gradually reduced. The peak intensity of the diffraction peak I003/I104 is higher than that of the mixed discharge condition of the reactive cations, and the ratio is increased and the mixed batch of the cations is weakened. The peak intensity ratio of I003/I104 shows a trend of increasing before decreasing along with the increase of the magnesium doping amount, so that the magnesium doping amount is controlled to 1500-5000 ppm, the diffusion of ions is facilitated, and the electrochemical performance is improved.
In addition, the invention provides a preparation method of the precursor, which comprises the following steps:
step S1, dissolving nickel salt and a structure directing agent in water to obtain a mixed solution A; dissolving potassium hexacyanocobaltate in water to obtain a mixed solution B;
step S2, stirring and mixing the mixed solution A and the mixed solution B to obtain mixed slurry C;
s3, carrying out solid-liquid separation on the mixed slurry C, washing, drying and separating the obtained solid phase to obtain NiCo-PBA with a cube structure;
s4, preparing a precipitant solution, a complexing agent solution, reaction kettle bottom solution and a mixed salt solution of nickel, cobalt and manganese;
s5, adding NiCo-PBA with a cube structure into the reaction kettle base solution as seed crystals, and then adding a precipitator solution, a complexing agent solution and a mixed salt solution of nickel, cobalt and manganese in parallel flow into the reaction kettle base solution for coprecipitation reaction;
and S6, stopping the reaction when the granularity D50 of the reaction slurry in the step S5 reaches 5-10 mu m, aging, filtering the reaction slurry, and washing, drying, sieving and removing iron from a filtered solid phase to obtain a NiCo-PBA modified precursor.
In a specific embodiment, the structure directing agent is at least one of polyvinylpyrrolidone (PVP), citric acid, sodium citrate; the concentration of the structure directing agent in the mixed solution A is 0.5-1.2 mol/L, and the concentration of nickel ions is 0.6-1.3 mol/L.
In a specific embodiment, the concentration of the potassium hexacyanocobaltate in the mixed solution B is 0.3-0.8 mol/L.
In a particularly preferred embodiment, the precipitant is NaOH, KOH, na 2 CO 3 、NaHCO 3 At least one of the precipitant solutions has a concentration of 2-9 mol/L; the complexing agent is at least one of ammonia water, ammonium bicarbonate, citric acid and ethylenediamine tetraacetic acid, and the concentration of the complexing agent solution is 1-6 mol/L.
In a specific embodiment, the total concentration of metal ions of nickel, cobalt and manganese in the nickel-cobalt-manganese mixed salt solution is 1-5 mol/L.
In a specific embodiment, the pH value of the bottom solution of the reaction kettle is controlled to be 11-12, and the ammonia concentration is controlled to be 5.5-8.0 g/L.
In a specific embodiment, the temperature of the coprecipitation reaction in the step S5 is 55-75 ℃, the pH value in the coprecipitation reaction process is 11-12, and the ammonia concentration is 5.5-8.0 g/L.
In the specific implementation, the flow rate of the complexing agent solution is 5-20 mL/min, the flow rate of the precipitant solution is 2-15 mL/min, and the flow rate of the nickel-cobalt-manganese mixed salt solution is 10-50 mL/min.
In a specific embodiment, magnesium salt solution is added as a dopant during the co-precipitation reaction described in step S5. Preferably, the concentration of the magnesium salt solution is 0.1-0.6 mol/L, and the flow rate is 0.5-3.5 mL/min.
The invention further provides a positive electrode material, which is obtained by pre-sintering the precursor of the NiCo-PBA modified potassium ion battery positive electrode material, mixing the precursor with a potassium source and sintering.
In a specific embodiment, the pre-sintering process is: preheating for 4-8 hours in an air atmosphere at 200-500 ℃.
In the specific embodiment, the material preheated by the precursor is ball-milled and mixed with a potassium source, and then calcined for 8-16 hours at 750-950 ℃ in an oxygen atmosphere.
Complex water of [ M' (CN) 6] vacancies in the Prussian blue crystal lattice of the inner core is difficult to thoroughly remove by a common heat treatment method, and the water molecules occupy redox active sites, block ion deintercalation channels and reduce the initial specific capacity and rate capability of the material. Meanwhile, the precursor hydroxide is decomposed to generate a large amount of moisture in the calcining process, and evaporation of the moisture takes away a large amount of heat energy and corrodes the internal structure of the equipment. Therefore, the precursor is preheated at low temperature before being mixed with the potassium salt, on one hand, raw material impurities are removed, the purity of the battery material is ensured, and the safety performance is improved; on the other hand, the precursor loses part of crystal water, the internal gap is increased, and part of internal structural stress is reduced, so that the contact area is increased when the precursor and potassium salt are mixed and calcined, the grain growth and development are more complete, and the multiplying power and the cycle stability of the composite material are improved. The proper calcination temperature can increase the material diffusion coefficient, promote the diffusion of ions and vacancies and the material transfer process of particle rearrangement, so that the tap density of the material is increased, and the surface moisture content is low; the oxygen-deficient compound is easy to generate when the calcining temperature is too high, and secondary crystallization is promoted, so that the granularity of the material is increased, the specific surface area is reduced, and the ion extraction and intercalation are not facilitated; if the calcination temperature is too low, the reaction is incomplete, an amorphous material is easily formed, the crystallization property of the positive electrode material is poor, impurities are easily generated, and the cycle stability and durability are reduced.
In a specific embodiment, the potassium source is preferably potassium carbonate.
Example 1
(1) Preparing a mixed solution A with the concentration of nickel sulfate of 0.8mol/L and the concentration of sodium citrate of 0.9 mol/L; preparing a mixed solution B with the concentration of potassium hexacyanocobaltate of 0.6 mol/L;
(2) Adding the mixed solution A into the mixed solution B at a flow rate of 0.8mL/min under stirring, and standing for 24h at room temperature;
(3) Centrifuging the obtained mixed solution, controlling the centrifuging speed to 7000rpm, washing with ethanol solution for 3 times, and drying overnight in a 100 ℃ oven to obtain cube NiCo-PBA with side length of 500 nm;
(4) Mixing industrial 28wt% ammonia water with deionized water to prepare an ammonia water solution with the concentration of 3mol/L as a complexing agent solution; mixing NaOH and deionized water, and adjusting the concentration of the NaOH solution to 6mol/L to serve as a precipitant solution;
(5) NiSO was carried out according to the molar ratio Ni: co: mn=8:1:1 4 、CoSO 4 、MnSO 4 Dissolving in hot water at 70 ℃, stirring until the metal ions are completely dissolved, and preparing a metal salt solution with the total concentration of 2 mol/L; the doped magnesium salt MgSO 4 Mixing with deionized water to prepare magnesium sulfate solution with the concentration of 0.3 mol/L;
(6) 1.2L of hot water is introduced into a 3L reaction kettle, the stirring rotation speed of the reaction kettle is regulated and controlled to 360rpm, the temperature is controlled to be 60 ℃, then ammonia water solution and NaOH solution are introduced into the reaction kettle at the flow rates of 6mL/min and 8mL/L respectively, the reaction kettle is fully stirred for 30min, the pH value is controlled to be 11.45-11.55, and the ammonia concentration is controlled to be 6.5-7g/L;
(7) Uniformly dispersing 30g of polymer NiCo-PBA serving as seed crystal in bottom solution of a reaction kettle, and then adding a metal salt solution and a magnesium sulfate solution into the reaction kettle in a stirring state at flow rates of 25mL/min and 1.5mL/min respectively; ammonia water and NaOH are regulated to flow according to the reaction process, the pH value is controlled to be 11.45-11.55, the ammonia concentration is controlled to be 6.5-7g/L, and the granularity is controlled to be 5 mu m;
(8) Aging the mixed slurry in a stirring state, and then washing, drying, sieving and deironing to obtain a NiCo-PBA modified magnesium doped precursor with coarse primary particles and close packing;
and pre-sintering the precursor in air at 450 ℃ for 5 hours, mixing the precursor with potassium carbonate according to a molar ratio of 1:0.8, ball-milling the mixture in a ball mill for 2 hours, and calcining the mixture in an oxygen atmosphere at 850 ℃ for 12 hours after uniform mixing to obtain the anode material.
FIG. 1 is an SEM image of the NiCo-PBA obtained in step (3), from which it can be seen that the NiCo-PBA exhibits a smooth-surfaced nanocube structure.
FIG. 2 is an SEM image of a NiCo-PBA modified, magnesium doped precursor from step (8), as can be seen from FIGS. 2 (a), (b) for a composite material of densely packed secondary microspheres composed of sub-micron sized primary particles; the elemental plane distribution patterns of (c) - (f) in fig. 2 can be seen for the presence of Ni, co, mn, mg element, particularly Mg distributed throughout the structure, further confirming that Mg is uniformly doped internally.
Example 2
(1) Preparing a mixed solution A with the concentration of nickel sulfate of 0.6mol/L and the concentration of polyvinylpyrrolidone (PVP) of 0.8mol/L; preparing a mixed solution B with the concentration of potassium hexacyanocobaltate of 0.5 mol/L;
(2) Adding the mixed solution A into the mixed solution B at a flow rate of 0.6mL/min under stirring, and standing for 24h at room temperature;
(3) Centrifuging the obtained mixed solution, controlling the centrifuging speed at 6000rpm, and washing 3 times with aqueous solution; drying overnight in an oven at 100 ℃ to obtain a cube NiCo-PBA with the side length of 700 nm;
(4) Mixing industrial 28% ammonia water with deionized water to prepare an ammonia water solution with the concentration of 4 mol/L; mixing NaOH and deionized water to prepare a NaOH solution with the concentration of 7 mol/L;
(5) NiSO was prepared according to a molar ratio Ni: co: mn=8.8:0.3:0.9 4 、CoSO 4 、MnSO 4 Dissolving in hot water at 70 ℃, stirring until the metal ions are completely dissolved, and preparing a metal salt solution with the total concentration of 2 mol/L; mgSO 4 Mixing with deionized water to prepare magnesium sulfate solution with the concentration of 0.13 mol/L;
(6) 1.8L of hot water is introduced into a 3L reaction kettle, the stirring rotation speed of the reaction kettle is regulated and controlled to 420rpm, the temperature is controlled to 60 ℃, then ammonia water solution and NaOH solution are introduced into the reaction kettle at the flow rates of 6mL/min and 4mL/L respectively, the reaction kettle is fully stirred for 60min, the pH value of reaction base solution is controlled to be 11.75-11.85, and the ammonia concentration is controlled to be 5.5-6.5g/L;
(7) Uniformly dispersing 15g of polymer NiCo-PBA serving as seed crystal in the reaction kettle base solution, respectively adding a metal salt solution and a magnesium sulfate solution into the reaction kettle base solution in a stirring state at flow rates of 25mL/min and 1.2mL/min, regulating and controlling the flow rates of an ammonia water solution and a NaOH solution according to the reaction process, controlling the pH value to be 11.75-11.85, controlling the ammonia concentration to be 5.5-6.5g/L, and controlling the granularity to be 5 mu m;
(8) Aging the mixed slurry in a stirring state, and then washing, drying, sieving and deironing to obtain a NiCo-PBA modified magnesium doped precursor with coarse primary particles and close packing;
and pre-sintering the precursor in the air at 450 ℃ for 5 hours, mixing the precursor with potassium carbonate according to the stoichiometric ratio of 1:0.8, ball-milling the mixture in a ball mill for 2 hours, and calcining the mixture in an oxygen atmosphere at 750 ℃ for 18 hours after uniform mixing to obtain the anode material.
Example 3
(1) Preparing a mixed solution A with nickel nitrate concentration of 0.8mol/L and polyvinylpyrrolidone (PVP) concentration of 1.1 mol/L; preparing a mixed solution B with the concentration of potassium hexacyanocobaltate of 0.5 mol/L;
(2) Adding the mixed solution A into the mixed solution B at a flow rate of 0.8mL/min under stirring, and standing for 24h at 40 ℃;
(3) Centrifuging the obtained mixed solution, controlling the centrifuging speed at 7000rpm, and washing with ethanol solution for 3 times; drying in an oven at 120 ℃ for 8 hours to obtain a cube NiCo-PBA with the side length of 2 mu m;
(4) NH4HCO3 is mixed with deionized water to prepare a solution with the concentration of 3mol/L; mixing Na2CO3 with deionized water to prepare a solution with the concentration of 7 mol/L;
(5) Dissolving Ni (NO 3) 2, co (NO 3) 2 and Mn (NO 3) 2 in hot water at 70 ℃ according to the molar ratio of Ni to Co to Mn=7:1:2, stirring until the Ni, co and Mn (NO 3) 2 are completely dissolved, and preparing a metal salt solution with the total concentration of metal ions of 2 mol/L; mixing Mg (NO 3) 2 with deionized water to prepare a magnesium nitrate solution with the concentration of 0.2 mol/L;
(6) 3.4L of hot water is introduced into a 5L reaction kettle, the stirring rotation speed of the reaction kettle is regulated and controlled to be 530rpm, the temperature is controlled to be 60 ℃, then NH4HCO3 solution and Na2CO3 solution are introduced into the reaction kettle at the flow rates of 6mL/min and 8mL/L respectively, the mixture is fully stirred for 60min, the pH value of the bottom solution of the reaction kettle is controlled to be 11.4-11.5, and the ammonia concentration is controlled to be 7.5-8g/L;
(7) Uniformly dispersing 25g of polymer NiCo-PBA serving as seed crystal in the reaction kettle base solution, respectively adding a metal salt solution and a magnesium nitrate solution into the reaction kettle base solution in a stirring state at the flow rates of 20mL/min and 1.8mL/min, and adding NH 4 HCO 3 Solution and Na 2 CO 3 The flow of the solution is regulated according to the reaction process, the pH value is controlled to be 11.4-11.5, the ammonia concentration is controlled to be 7.5-8g/L, and the granularity is controlled to be 10 mu m;
(8) Aging the mixed slurry in a stirring state, and then washing, drying, sieving and deironing to obtain a NiCo-PBA modified magnesium doped precursor with coarse primary particles and close packing;
and pre-sintering the precursor in air at 300 ℃ for 5 hours to form an oxide compound, mixing the oxide compound with potassium carbonate according to a stoichiometric ratio of 1:1, ball-milling the mixture in a ball mill for 2 hours, and calcining the mixture in an oxygen atmosphere at 800 ℃ for 14 hours to obtain the anode material.
Example 4
(1) Preparing a mixed solution A with the concentration of nickel nitrate of 0.7mol/L and the concentration of citric acid of 1.0 mol/L; preparing a mixed solution B with the concentration of potassium hexacyanocobaltate of 0.6 mol/L;
(2) Adding the mixed solution A into the mixed solution B at a flow rate of 0.5mL/min under stirring, and standing for 12h at room temperature;
(3) Centrifuging the obtained blue mixed solution, controlling the centrifuging speed at 8000rpm, and washing with ethanol solution for 3 times; drying overnight in an oven at 80 ℃; obtaining a cubic NiCo-PBA with a side length of 1 μm;
(4) NH4HCO3 is mixed with deionized water to prepare complexing agent solution with the concentration of 5mol/L; mixing NaOH and deionized water to prepare a precipitant solution with the concentration of 4 mol/L;
(5) Dissolving Ni (NO 3) 2, co (NO 3) 2 and Mn (NO 3) 2 in hot water at 70 ℃ according to the ratio of Ni to Co to Mn=6:1:3, stirring until the Ni, co and Mn=6:1:3 are completely dissolved, and preparing a metal salt solution with the total concentration of metal ions of 2 mol/L; mixing Mg (NO 3) 2 with deionized water to prepare a magnesium nitrate solution with the concentration of 0.25 mol/L;
(6) 3.4L of hot water is introduced into a 5L reaction kettle, the stirring rotation speed of the reaction kettle is regulated and controlled to 480rpm, the temperature is controlled to be 60 ℃, then a complexing agent solution and a precipitant solution are introduced into the reaction kettle at the flow rates of 3mL/min and 7mL/min respectively, the mixture is fully stirred for 60min, the pH value of the bottom solution of the reaction kettle is controlled to be 11.6-11.65, and the ammonia concentration is controlled to be 7.5-8g/L;
(7) Uniformly dispersing 33g of polymer NiCo-PBA serving as seed crystal in the reaction kettle base solution, adding a metal salt solution and a magnesium nitrate solution into the reaction kettle base solution in a stirring state at the flow rates of 20mL/min and 1.2mL/min respectively, adjusting the flow rates of NH4HCO3 and NaOH according to the reaction process, controlling the pH value to be 11.6-11.65, and controlling the ammonia concentration to be 7.5-8g/L until the slurry granularity D is 50-5 mu m;
(8) Aging the slurry in a stirring state, and then washing, drying, sieving and deironing to obtain a precursor which is coarse in primary particles, closely piled with NiCo-PBA modified and doped with magnesium;
and pre-sintering the precursor in air at 350 ℃ for 8 hours, mixing the precursor with potassium carbonate according to the stoichiometric ratio of 1:0.8, ball milling for 2 hours in a ball mill, and calcining for 10 hours in an oxygen atmosphere at 850 ℃ after uniform mixing to obtain the anode material.
Example 5
Example 5 differs from example 1 only in that: in the step (5), no magnesium sulfate solution is prepared, and in the step (7), no magnesium sulfate solution is added in the coprecipitation reaction process.
FIG. 3 is an XRD pattern of the NiCo-PBA modified/magnesium doped precursor obtained in step (8) of example 1 and the NiCo-PBA modified precursor obtained in step (8) of example 5, respectively. As can be seen from FIG. 3 (a), the pure phase material and the Mg-doped composite material have typical alpha-NaFeO 2 The lamellar hexagonal structure, the space group is a symmetrical lamellar structure of R3m, and obvious splitting of (006)/(102) and (108)/(110) peaks can be clearly seen from (b) of fig. 3, which shows that the lamellar structure has good structure, and no obvious peak position displacement is observed, so that the doping of the inner core Prussian blue and the outer shell Mg has no adverse effect on the crystal structure.
The performance of the positive electrode materials prepared in example 1 and example 5 and NCM811 positive electrode materials produced and sold by the applicant were compared. The method comprises the following steps: and assembling the positive electrode shell, the positive electrode plate, the electrolyte, the diaphragm, the negative electrode plate, the gasket and the negative electrode shell into the button cell. The specification of the positive and negative electrode shells is CR2032; the thickness of the gasket is 1mm, and the diaphragm is made of glass fiber; electrolyte KPF 6 And a mixed electrolyte of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1. And (3) weighing the anode material, the binder and acetylene black according to the ratio of 7:2:1, adding the anode material, the binder and the acetylene black into a weighing bottle, dropwise adding N-methylpyrrolidone as a solvent, stirring for 6-7 hours until all substances are uniformly mixed, uniformly coating the mixed slurry on an aluminum foil current collector, vacuum drying at 80 ℃ for 12 hours, finally cutting by a sheet punching machine to obtain an anode sheet with the diameter of 1.4cm, sequentially assembling an anode shell, the anode sheet, electrolyte, a diaphragm, the electrolyte, a cathode sheet, a gasket and a cathode shell in a glove box under the argon atmosphere, and pressing by using a sealing machine to obtain the button cell.
The rate performance of the battery was tested and the results are shown in fig. 4. From the graph, the rate performance of the battery containing the positive electrode material prepared by the embodiment is obviously improved, and the discharge capacity has a slow decay trend along with the increase of the current density and has higher electrochemical reversibility.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (7)
1. The NiCo-PBA modified potassium ion battery anode material precursor is characterized in that the precursor has a two-layer structure, the inner layer is NiCo-PBA, and the outer layer is nickel-cobalt-manganese ternary material; the NiCo-PBA of the inner layer is a cube, and the Ni-Co-Mn ternary material of the outer layer is doped with magnesium.
2. The NiCo-PBA modified positive electrode material precursor of a potassium ion battery of claim 1, wherein the inner layer of NiCo-PBA has a side length of 1/9~1/5 of the precursor material diameter.
3. The method for preparing a NiCo-PBA modified positive electrode material precursor for a potassium ion battery according to claim 1 or 2, comprising the steps of:
step S1, dissolving nickel salt and a structure directing agent in water to obtain a mixed solution A; dissolving potassium hexacyanocobaltate in water to obtain a mixed solution B;
step S2, stirring and mixing the mixed solution A and the mixed solution B to obtain mixed slurry C;
s3, carrying out solid-liquid separation on the mixed slurry C, washing, drying and separating the obtained solid phase to obtain NiCo-PBA with a cube structure;
s4, preparing a precipitant solution, a complexing agent solution, reaction kettle bottom solution and a mixed salt solution of nickel, cobalt and manganese;
s5, adding NiCo-PBA with a cube structure into the reaction kettle base solution as seed crystals, and then adding a precipitator solution, a complexing agent solution and a mixed salt solution of nickel, cobalt and manganese in parallel flow into the reaction kettle base solution for coprecipitation reaction; adding magnesium salt solution as doping agent in the coprecipitation reaction process;
and S6, stopping the reaction when the granularity D50 of the reaction slurry in the step S5 reaches 5-10 mu m, aging, filtering the reaction slurry, and washing, drying, sieving and removing iron from a filtered solid phase to obtain a NiCo-PBA modified precursor.
4. The method of claim 3, wherein the structure directing agent is at least one of polyvinylpyrrolidone, citric acid, and sodium citrate; the concentration of the structure directing agent in the mixed solution A is 0.5-1.2 mol/L, and the concentration of nickel ions is 0.6-1.3 mol/L; the concentration of the potassium hexacyanocobaltate in the mixed solution B is 0.3-0.8 mol/L; the precipitant is NaOH, KOH, na 2 CO 3 、NaHCO 3 At least one of the precipitant solutions has a concentration of 2-9 mol/L; the saidThe complexing agent is at least one of ammonia water, ammonium bicarbonate, citric acid and ethylenediamine tetraacetic acid, and the concentration of the complexing agent solution is 1-6 mol/L; the total concentration of metal ions of nickel, cobalt and manganese in the nickel-cobalt-manganese mixed salt solution is 1-5 mol/L; the pH value of the bottom solution of the reaction kettle is controlled to be 10-12, and the ammonia concentration is controlled to be 5.0-8.5 g/L.
5. The method according to claim 3, wherein the temperature of the coprecipitation reaction in step S5 is 55-75 ℃, the pH value during the coprecipitation reaction is 10-12, and the ammonia concentration is 5.0-8.5 g/L.
6. The cathode material is characterized in that after the precursor of the cathode material of the NiCo-PBA modified potassium ion battery is presintered, the presintered precursor is ball-milled and mixed with a potassium source, and then the mixture is calcined at 750-850 ℃ for 8-16 hours in an oxygen atmosphere, so that the cathode material is obtained.
7. The positive electrode material of claim 6, wherein the pre-sintering process is: preheating for 4-8 hours in an air atmosphere at 200-500 ℃.
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