CN117466268A - Method for synthesizing composite polyanion positive electrode material in alkaline environment - Google Patents

Method for synthesizing composite polyanion positive electrode material in alkaline environment Download PDF

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CN117466268A
CN117466268A CN202311391493.1A CN202311391493A CN117466268A CN 117466268 A CN117466268 A CN 117466268A CN 202311391493 A CN202311391493 A CN 202311391493A CN 117466268 A CN117466268 A CN 117466268A
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sodium
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containing compound
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赵阿龙
曹余良
刘长禹
陈晓洋
朱勇
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Shenzhen Jana Energy Technology Co ltd
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Abstract

The invention discloses a method for synthesizing a composite polyanion positive electrode material in an alkaline environment, which comprises the following steps: s1, preparing a raw material solution: adding an anion source into a solvent to dissolve the anion source, adding an alkaline additive, and adjusting the pH range to 10-12 to obtain a raw material solution; s2, preparing a precursor solution: adding a transition metal ion source, a sodium source and a carbon source into a raw material solution to form a precipitate, and simultaneously performing liquid-phase sanding to obtain a precursor solution which is uniformly dispersed; s3, preparing uniform precursor powder: heating and drying the precursor solution to obtain uniform precursor powder composed of sodium element, transition metal ion element, anion source and carbon source; s4, sintering at a high temperature: and calcining the precursor powder at high temperature in a protective atmosphere to obtain the composite polyanion anode material. The invention has the characteristics of good system stability, high compaction density, strong process controllability and excellent electrochemical performance.

Description

Method for synthesizing composite polyanion positive electrode material in alkaline environment
Technical Field
The invention relates to the technical field of sodium ion batteries, in particular to a method for synthesizing a composite polyanion positive electrode material in an alkaline environment.
Background
With the continuous development of modern science and technology, the living standard of people is greatly improved, but the problems of environmental pollution and the exhaustion of non-renewable energy sources such as petroleum are also more and more serious. Therefore, clean secondary energy such as wind energy, tidal energy, solar energy, etc. is coming into the field of view of people, and has been developed to a great extent. However, the discontinuities, uncertainties, and instabilities of wind, solar, etc. all subject the use of these clean energy sources to significant resistance. The more effective solution is to store the obtained electric energy, and the stability, the use cost and the environmental protection of the secondary battery have great advantages in view of the important role of the secondary battery in large-scale energy storage, so the secondary battery becomes the first choice. Among all secondary batteries, lithium/sodium ion batteries are certainly licensed, and particularly lithium ion batteries have been well studied. However, the lithium resource is unevenly distributed, and the lithium resource cannot meet the requirement of large-scale energy storage due to factors such as insufficient reserves. Correspondingly, the sodium ion battery has a working principle similar to that of a lithium ion battery, has abundant sodium resource reserves, low cost and no pollution to the environment, and is the technology most hopefully applied to large-scale energy storage at present.
The current main current positive electrode materials of sodium ion batteries comprise transition metal oxides, polyanions, prussian blue compounds and organic compounds, and each material has respective advantages and disadvantages. The transition metal oxide is easy to absorb water and react with air, and is often accompanied by various phase changes in the process of sodium ion deintercalation, so that the cycle stability is poor. The transition metal ion of the Prussian blue compound is dissolved, and the crystal water is difficult to remove, so that gas is easily generated at a high potential. The electron conductivity of the organic cathode material is generally poor and is easily dissolved in an organic electrolyte. The polyanion type material often has an open three-dimensional framework structure, so that the polyanion type material has good cycle stability and excellent multiplying power performance, and is the optimal choice of commercial sodium ion batteries.
Composite polyanion-type materials are generally framework structures composed of alkali metal ions, transition metal ions, and two anionic groups connected to each other in a co-point/line/plane fashion. With sodium iron pyrophosphate (Na) 4 Fe 3 (PO 4 ) 2 P 2 O 7 ) For example, the material comprises [ PO 4 ]And [ P ] 2 O 7 ]Two anionic groups. In the prior art, the synthesis of the material mainly adopts a liquid phase spray drying-calcining method, but the material is synthesized in an acidic environment, and P 2 O 7 4- Acidic hydrolysis reaction occurs to form PO 4 3- Thereby leading to PO during synthesis 4 3- Excess, PO 4 3- And P 2 O 7 4- Is unbalanced in proportion to produced Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 The product has poor crystallinity and contains a large amount of NaFePO 4 Impurities limit the exertion of electrochemical properties.
Disclosure of Invention
The invention aims to provide a method for synthesizing a composite polyanion positive electrode material in an alkaline environment, which has the characteristics of good system stability, high compaction density, strong process controllability and excellent electrochemical performance.
The invention can be realized by the following technical scheme:
the invention discloses a method for synthesizing a composite polyanion positive electrode material in an alkaline environment, which comprises the following steps:
s1, preparing a raw material solution: adding an anion source into a solvent to dissolve the anion source, adding an alkaline additive, and adjusting the pH range to 10-12 to obtain a raw material solution;
s2, preparing a precursor solution: adding a transition metal ion source, a sodium source and a carbon source into a raw material solution to form a precipitate, and simultaneously performing liquid-phase sanding to obtain a precursor solution which is uniformly dispersed;
s3, preparing uniform precursor powder: heating and drying the precursor solution to obtain uniform precursor powder composed of sodium element, transition metal ion element, anion source and carbon source;
s4, sintering at a high temperature: and calcining the precursor powder at high temperature in a protective atmosphere to obtain the composite polyanion anode material.
The invention discloses a method for synthesizing a composite polyanion positive electrode material in an alkaline environment. In a liquid alkaline environment (10<pH<12 The transition metal ions react with pyrophosphate and phosphate to rapidly generate ferric pyrophosphate and ferric phosphate precipitate, thereby ensuring the integrity of the pyrophosphate and PO 4 3- And P 2 O 7 4- The ratio of (2) remains unchanged. Meanwhile, the precipitate can ensure close contact of iron, sodium and anion groups, and the liquid-phase sanding can completely and uniformly mix ferric pyrophosphate, ferric phosphate, sodium source and carbon source, so that the reaction in the calcination process is fully carried out. The method has simple operation, low cost of raw materials, and the synthesized Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 Good crystallinity of NaFePO 4 The amount of impurities is small, and excellent electrochemical performance can be exhibited.
Further, the anion source is F - 、P 2 O 7 4- 、CO 3 2- 、BO 3 3- 、SiO 4 4- 、SO 3 2- One or both of these.
Further, the solvent is one or more of water, ethanol, chloroform, acetone, benzene, diethyl ether, ethyl acetate, carbon tetrachloride and other inorganic or organic solvents.
Further, the alkaline additive is one or more than two of sodium hydroxide solution, ammonium bicarbonate solution, ammonium acetate solution, esterquat, ammonium citrate, tetraethylammonium sulfate, ammonium oxalate monohydrate, cetyltrimethylammonium fluoride and dimethyl alkyl chloride-C12-18-ethanol ammonium salt.
Further, the transition metal source is an iron-containing compound, a manganese-containing compound, a vanadium-containing compound, a cobalt-containing compound, a nickel-containing compound, and/or a titanium-containing compound; the iron-containing compound is one or more than two of ferric nitrate, ferrous nitrate, ferric sulfate, ferrous sulfate and/or ferrous acetate; the manganese-containing compound is one or more than two of manganese nitrate, manganese acetate and/or manganese sulfate; the vanadium-containing compound is one or more than two of vanadium nitrate, vanadium sulfate and/or vanadium acetate; the cobalt-containing compound is cobalt nitrate and/or cobalt sulfate and cobalt acetate; the nickel-containing compound is one or more than two of nickel nitrate, nickel sulfate and/or nickel acetate; the titanium-containing compound is one or more than two of titanium nitrate, titanium sulfate and/or titanium acetate.
Further, the sodium source is one or more of sodium bicarbonate, sodium formate, sodium acetate, sodium nitrate, sodium sulfate, sodium citrate, sodium propionate, sodium acrylate, sodium benzoate and/or sodium bisulfate.
Further, the carbon source is one or a mixture of more than two of glucose, sucrose, starch, maltose, lactose, polyvinyl alcohol, cyclodextrin, polyacrylic acid, polyacrylonitrile, cellulose and/or polyethylene.
Further, in step S2, the liquid-phase sanding rotational speed is 1000-1500r/min, and the sanding time is 4-8 hours.
Further, in step S3, the heating and drying method includes spray drying, oil bath/water bath drying, flash drying, and the heating temperature is 105-115 ℃, so that the solvent can be guaranteed to volatilize rapidly within the range, and the raw materials are not deteriorated due to high temperature.
Further, in step S4, the protective atmosphere is nitrogen, hydrogen, carbon monoxide, argon, a nitrogen-hydrogen mixture or an argon-hydrogen mixture.
Further, in the step S4, the sintering temperature is 500-800 ℃, and the heat preservation time is 3-15H.
The method for synthesizing the composite polyanion positive electrode material in the alkaline environment has the following beneficial effects:
firstly, the system stability is good, and in the process of the invention, the anionic groups can be kept intact in a precipitate manner by providing an alkaline environment, so that the proportion among the anionic groups is ensured to be kept stable;
secondly, the compaction density is high, and the pH value of the solution has a larger influence on the characteristics of materials in the process of the invention. The particle size of the generated precipitate can be regulated by controlling the PH value, small particles are beneficial to preparing high-rate nanoscale materials, and large particles are beneficial to preparing compact high-compaction materials;
thirdly, the process controllability is strong, in the process of the invention, the uniform mixing among sodium ions, transition metal ions and anionic groups is realized by adopting a liquid-phase sand grinding mixing mode, the process synthesis controllability is improved, and the uniform material contact is beneficial to the growth of crystals at high temperature
Fourth, electrochemical performance is excellent, in the technological process of the invention, the carbon source is cracked into carbon in situ at high temperature, can guarantee the carbon source to disperse and fill uniformly on the surface of particle and in its gap, thus construct the stereoscopic conductive network, greatly increase its electronic conductivity. .
Detailed Description
In order to better understand the technical solution of the present invention, the following describes the product of the present invention in further detail with reference to examples.
The invention discloses a method for synthesizing a composite polyanion positive electrode material in an alkaline environment, which comprises the following steps:
s1, preparing a raw material solution: adding an anion source into a solvent to dissolve the anion source, adding an alkaline additive, and adjusting the pH range to 10-12 to obtain a raw material solution;
s2, preparing a precursor solution: adding a transition metal ion source, a sodium source and a carbon source into a raw material solution to form a precipitate, and simultaneously performing liquid-phase sanding to obtain a precursor solution which is uniformly dispersed;
s3, preparing uniform precursor powder: heating and drying the precursor solution to obtain uniform precursor powder composed of sodium element, transition metal ion element, anion source and carbon source;
s4, sintering at a high temperature: and calcining the precursor powder at high temperature in a protective atmosphere to obtain the composite polyanion anode material.
Further, the anion source is F - 、P 2 O 7 4- 、CO 3 2- 、BO 3 3- 、SiO 4 4- 、SO 3 2- One or both of these.
Further, the solvent is one or more of water, ethanol, chloroform, acetone, benzene, diethyl ether, ethyl acetate, carbon tetrachloride and other inorganic or organic solvents.
Further, the alkaline additive is one or more than two of sodium hydroxide solution, ammonium bicarbonate solution, ammonium acetate solution, esterquat, ammonium citrate, tetraethylammonium sulfate, ammonium oxalate monohydrate, cetyltrimethylammonium fluoride and dimethyl alkyl chloride-C12-18-ethanol ammonium salt.
Further, the transition metal source is an iron-containing compound, a manganese-containing compound, a vanadium-containing compound, a cobalt-containing compound, a nickel-containing compound, and/or a titanium-containing compound; the iron-containing compound is one or more than two of ferric nitrate, ferrous nitrate, ferric sulfate, ferrous sulfate and/or ferrous acetate; the manganese-containing compound is one or more than two of manganese nitrate, manganese acetate and/or manganese sulfate; the vanadium-containing compound is one or more than two of vanadium nitrate, vanadium sulfate and/or vanadium acetate; the cobalt-containing compound is cobalt nitrate and/or cobalt sulfate and cobalt acetate; the nickel-containing compound is one or more than two of nickel nitrate, nickel sulfate and/or nickel acetate; the titanium-containing compound is one or more than two of titanium nitrate, titanium sulfate and/or titanium acetate.
Further, the sodium source is one or more of sodium bicarbonate, sodium formate, sodium acetate, sodium nitrate, sodium sulfate, sodium citrate, sodium propionate, sodium acrylate, sodium benzoate and/or sodium bisulfate.
Further, the carbon source is one or a mixture of more than two of glucose, sucrose, starch, maltose, lactose, polyvinyl alcohol, cyclodextrin, polyacrylic acid, polyacrylonitrile, cellulose and/or polyethylene.
Further, in step S2, the liquid-phase sanding rotational speed is 1000-1500r/min, and the sanding time is 4-8 hours.
Further, in step S3, the heating and drying method includes spray drying, oil bath/water bath drying, flash drying, and heating at 105-115 ℃.
Further, in step S4, the protective atmosphere is nitrogen, hydrogen, carbon monoxide, argon, a nitrogen-hydrogen mixture or an argon-hydrogen mixture.
Further, in the step S4, the sintering temperature is 500-800 ℃, and the heat preservation time is 3-15H.
Application example 1 Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 Synthesis of/C and electrochemical Properties thereof
Example Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 The synthesis of/C comprises the following steps:
s1, preparing a raw material solution: adding water into ammonium dihydrogen phosphate and sodium pyrophosphate according to a molar ratio of 2:1 to completely dissolve the ammonium dihydrogen phosphate and sodium pyrophosphate, and simultaneously adding a proper amount of ammonia water solution to adjust the pH value to 10 to obtain a clear raw material solution (solution A);
s2, preparing a precursor solution: adding ferric nitrate into the solution A according to the amount of 3:1 with sodium pyrophosphate, adding glucose at the same time, fully stirring to form soft small particle sediment, simultaneously carrying out liquid-phase sanding, wherein the rotating speed of a sanding machine is 1200r/min, the sanding time is 6 hours, at the moment, obtaining uniformly-dispersed suspension, and fully sanding in the step to obtain a suspension, namely a precursor solution, of which the materials are completely and uniformly mixed;
s3, preparing precursor powder: spray drying the precursor solution at 105 ℃, collecting and recycling volatilized ammonia gas to obtain precursor powder which is prepared by uniformly mixing iron, sodium and anion groups;
s4, sintering at a high temperature: the precursor powder is kept at 600 ℃ for 10 hours in nitrogen atmosphere, and then naturally cooled to obtain Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 and/C material.
Na is mixed with 4 Fe 3 (PO 4 ) 2 P 2 O 7 and/C, AB, PVDF, mixing and homogenizing for 15 minutes according to the mass ratio of 8:1:1 to obtain uniform slurry. The slurry was coated on aluminum foil using a 150 μm four-sided fabricator, and then the film was dried in a vacuum oven at 100 ℃ for 12 hours. Punching the electrode film to a wafer with the diameter of 12mm by using a sheet punching machine, and taking metal sodium as a counter electrode, wherein the concentration of NaClO is 1mol/L 4 EC+DEC (1:1vol%) +5% FEC was electrolyte, and the separator was a PP/PE/PP three-layer separator, and a CR2016 type coin cell was assembled in a glove box.
Table 1 shows that Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 The compacted density of the material/C is 2.02g/cm 3 Its compacted density is higher than that of comparative example 1 (1.72 g/cm 3 ) The main reason is that in the step 1, ammonia water is added to adjust the PH to 10, so that soft small particle sediment is generated, iron, sodium and anion groups in the raw materials are in close contact, and in the subsequent sintering process, the material is easy to nucleate and crystallize, larger single crystal particles are generated, and further the material with larger compaction density is formed.
At the same time, the results in Table 1 show that the specific surface area of the material is only 10.2. 10.2 m 2 Per g, as compared with comparative example 1 (13.2 m) 2 /g) is about 22.7% lower, indicating a lower porosity between the materials, which corresponds to a greater compacted density.
In addition, the reversible capacity of the material at 0.1C rate is 110mAh/g, which is far higher than 98mAh/g in comparative example 1, and the capacity retention at 5C rate is 98.2%, which is far higher than 89.2% in comparative example 1. It shows that inhibiting the hydrolysis of anionic groups, maintaining the proportion of anionic groups, and improving the nucleation crystallinity of the material has great improvement on the performance of the material.
Application example 2 Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 Synthesis of/C and electrochemical Properties thereof
Example Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 The synthesis of/C comprises the following steps:
s1, preparing a raw material solution: adding water into ammonium dihydrogen phosphate and sodium pyrophosphate according to a molar ratio of 2:1 to completely dissolve the ammonium dihydrogen phosphate and sodium pyrophosphate, and simultaneously adding a proper amount of ammonia water solution to adjust the pH value to 11 to obtain a clear raw material solution (solution A);
s2, preparing a precursor solution: adding ferric nitrate into the solution A according to the amount of 3:1 with sodium pyrophosphate, adding glucose, fully stirring to form compact precipitate, simultaneously carrying out liquid-phase sanding, wherein the rotating speed of a sand mill is 1200r/min, the sanding time is 6 hours, at this time, obtaining uniformly-dispersed suspension, and fully sanding in the step to obtain a uniformly-mixed suspension of materials, namely a precursor solution;
s3, preparing precursor powder: spray drying the precursor solution at 105 ℃, collecting and recycling volatilized ammonia gas to obtain precursor powder which is prepared by uniformly mixing iron, sodium and anion groups;
s4, sintering at a high temperature: the precursor powder is kept at 600 ℃ for 10 hours in nitrogen atmosphere, and then naturally cooled to obtain Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 and/C material.
Na is mixed with 4 Fe 3 (PO 4 ) 2 P 2 O 7 and/C, AB, PVDF, mixing and homogenizing for 15 minutes according to the mass ratio of 8:1:1 to obtain uniform slurry. The slurry was coated on aluminum foil using a 150 μm four-sided fabricator, and then the film was dried in a vacuum oven at 100 ℃ for 12 hours. Punching the electrode film to a wafer with the diameter of 12mm by using a sheet punching machine, and taking metal sodium as a counter electrode, wherein the concentration of NaClO is 1mol/L 4 EC+DEC (1:1vol%) +5% FEC was electrolyte, and the separator was a PP/PE/PP three-layer separator, and a CR2016 type coin cell was assembled in a glove box.
Table 1 shows that Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 The compacted density of the material/C is 2.13g/cm 3 Its compacted density is higher than that of comparative example 1 (1.72 g/cm 3 ) About 23.8%, and is mainly caused by that in the step 1, ammonia water is added to adjust the pH value to 11, so that compact precipitate is formed, iron, sodium and anion groups in the raw materials are tightly contacted, and in the subsequent sintering process, the material is easy to nucleate and crystallize, large single crystal particles are formed, and compact density is formedA material with a high degree.
At the same time, the results in Table 1 show that the specific surface area of the material is only 9.0. 9.0 m 2 Per g, as compared with comparative example 1 (13.2 m) 2 /g) is about 31.8% lower, indicating a lower porosity between the materials, which corresponds to a greater compacted density.
In addition, the reversible capacity of the material at 0.1C rate is 117 mAh/g, which is far higher than 98mAh/g in comparative example 1, and the capacity retention at 5C rate is 96.3%, which is far higher than 89.2% in comparative example 1. It shows that inhibiting the hydrolysis of anionic groups, maintaining the proportion of anionic groups, and improving the nucleation crystallinity of the material has great improvement on the performance of the material.
In addition, compared with the application example 1, the application example 2 is changed at the process end, and the amount of the ammonia water added in the former is more, so that a liquid environment with stronger alkalinity is obtained, the generated precipitate is more compact, larger single crystal particles are formed in the later sintering process, and a material with better crystallinity is obtained, so that the specific capacity is higher. However, in application example 1, the smaller single crystal particles can shorten the sodium ion diffusion distance to some extent, so that the rate capability (98.2%) is more excellent than application example 2 (96.3%). Therefore, the process can regulate the PH of the solution by changing the amount of the added ammonia water solution in the early stage, thereby realizing the switching of energy type and multiplying power type materials.
Application example 3 Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 Synthesis of/C and electrochemical Properties thereof
Example Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 The synthesis of/C comprises the following steps:
s1, preparing a raw material solution: adding water into ammonium dihydrogen phosphate and sodium pyrophosphate according to a molar ratio of 2:1 to completely dissolve the ammonium dihydrogen phosphate and sodium pyrophosphate, adding a proper amount of ammonia water solution, and regulating the pH value to be 12 to obtain a clear raw material solution (solution A);
s2, preparing a precursor solution: adding ferric nitrate into the solution A according to the amount of 3:1 with sodium pyrophosphate, adding glucose at the same time, fully stirring to form massive large-particle sediment, simultaneously carrying out liquid-phase sanding, wherein the rotating speed of a sanding machine is 1200r/min, the sanding time is 6 hours, obtaining uniformly-dispersed suspension at the moment, and obtaining a precursor solution which is the suspension with completely and uniformly mixed materials after fully sanding in the step;
s3, preparing precursor powder: spray drying the precursor solution at 105 ℃, collecting and recycling volatilized ammonia gas to obtain precursor powder which is prepared by uniformly mixing iron, sodium and anion groups;
s4, sintering at a high temperature: the precursor powder is kept at 600 ℃ for 10 hours in nitrogen atmosphere, and then naturally cooled to obtain Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 and/C material.
Na is mixed with 4 Fe 3 (PO 4 ) 2 P 2 O 7 and/C, AB, PVDF, mixing and homogenizing for 15 minutes according to the mass ratio of 8:1:1 to obtain uniform slurry. The slurry was coated on aluminum foil using a 150 μm four-sided fabricator, and then the film was dried in a vacuum oven at 100 ℃ for 12 hours. Punching the electrode film to a wafer with the diameter of 12mm by using a sheet punching machine, and taking metal sodium as a counter electrode, wherein the concentration of NaClO is 1mol/L 4 EC+DEC (1:1vol%) +5% FEC was electrolyte, and the separator was a PP/PE/PP three-layer separator, and a CR2016 type coin cell was assembled in a glove box.
Table 1 shows that Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 The compacted density of the material/C is 2.24g/cm 3 Its compacted density is higher than that of comparative example 1 (1.72 g/cm 3 ) About 30.2% higher, and the main reason is that in the step 1, ammonia water is added to adjust the PH to 12, so that massive large-particle precipitates are generated, iron, sodium and anion groups in the raw materials are tightly contacted, and in the subsequent sintering process, the material is easy to nucleate and crystallize, large single crystal particles are generated, and the material with large compaction density is further formed.
At the same time, the results in Table 1 show that the specific surface area of the material is only 8.3 m 2 Per g, as compared with comparative example 1 (13.2 m) 2 /g) is about 37.2% lower, indicating a low porosity between the materials, which corresponds to a large compacted density.
In addition, the reversible capacity of the material at 0.1C rate is 119 mAh/g, which is far higher than 98mAh/g in comparative example 1, and the capacity retention rate at 5C rate is 93.4%, which is far higher than 89.2% in comparative example 1. It shows that inhibiting the hydrolysis of anionic groups, maintaining the proportion of anionic groups, and improving the nucleation crystallinity of the material has great improvement on the performance of the material.
In addition, application example 3 was changed at the process end compared with application example 1 and application example 2, the former added ammonia water in the maximum amount, thereby obtaining the most basic liquid environment, generating massive large particle precipitate, being beneficial to forming large single crystal particles in the later sintering process, thereby obtaining the material with better crystallinity, and therefore, the specific capacity is the highest. However, in application example 3, the excessively large single crystal particles prolonged the sodium ion diffusion distance to some extent, so that the rate performance (93.4%) was inferior to application example 1 and application example 2. It can be seen obviously that the continuous increase in PH is less in specific capacity but will lose greater rate capability. Therefore, the process can regulate the pH of the solution by changing the amount of the added ammonia water solution in the early stage, thereby realizing the switching of the energy type and rate type materials, and the recommended pH optimal value is 11.
Comparative example 1 Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 Synthesis of/C and electrochemical Properties thereof
Example Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 The synthesis of/C comprises the following steps:
step 1: adding water into ammonium dihydrogen phosphate and sodium pyrophosphate according to a molar ratio of 2:1 to completely dissolve the ammonium dihydrogen phosphate and sodium pyrophosphate, adding a proper amount of oxalic acid solution, and regulating the pH value to be 5 to obtain a clear solution (solution A);
step 2: adding ferric nitrate into the solution A according to the amount of 3:1 of sodium pyrophosphate, and simultaneously adding glucose, so as to obtain a pale yellow clear solution;
step 3: then, spray drying the precursor solution at 105 ℃ to obtain precursor powder which is uniformly mixed by iron, sodium and anion groups;
step 4: front is put forwardThe precursor powder is kept at 600 ℃ for 10 hours in nitrogen atmosphere, and then naturally cooled to obtain Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 and/C material.
Na is mixed with 4 Fe 3 (PO 4 ) 2 P 2 O 7 and/C, AB, PVDF, mixing and homogenizing for 15 minutes according to the mass ratio of 8:1:1 to obtain uniform slurry. The slurry was coated on aluminum foil using a 150 μm four-sided fabricator, and then the film was dried in a vacuum oven at 100 ℃ for 12 hours. Punching the electrode film to a wafer with the diameter of 12mm by using a sheet punching machine, and taking metal sodium as a counter electrode, wherein the concentration of NaClO is 1mol/L 4 EC+DEC (1:1vol%) +5% FEC was electrolyte, and the separator was a PP/PE/PP three-layer separator, and a CR2016 type coin cell was assembled in a glove box.
Table 1 shows that Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 The compacted density of the material/C is 1.72g/cm 3 Its compacted density was higher than that of application example 1 (2.02 g/cm 3 ) Low, having a specific surface area of 13.2. 13.2 m 2 /g, as compared with application example 1 (10.2 m) 2 High/g), corresponding to its lower compacted density, indicates that there are more voids between the materials. The main reason is that in an acidic environment, iron, sodium and anion groups are dissolved in water, precursor powder obtained by spraying is loose, and a core for crystallization nucleation is absent in the subsequent sintering process, so that the crystallinity is poor, and the compaction density is low.
In addition, the reversible capacity of the material at 0.1C rate is 98mAh/g, which is far lower than 110mAh/g in application example 1, and the capacity retention rate at 5C rate is 89.2%, which is far lower than 98.2% in application example 1. This is because, on the one hand, the poor crystallinity makes the transport of sodium ions more difficult, and on the other hand, the hydrolysis of the anionic groups in an acidic environment results in an imbalance in the proportion of anionic groups during the reaction, thus producing more heterogeneous species, greatly affecting the release of their electrochemical properties.
TABLE 1 Performance test results
The foregoing examples are merely exemplary embodiments of the present invention, which are described in more detail and are not to be construed as limiting the scope of the invention. It should be noted that modifications and improvements can be made by those skilled in the art without departing from the spirit of the invention, and that these obvious alternatives fall within the scope of the invention.

Claims (10)

1. The method for synthesizing the composite polyanion positive electrode material in the alkaline environment is characterized by comprising the following steps of:
s1, preparing a raw material solution: adding an anion source into a solvent to dissolve the anion source, adding an alkaline additive, and adjusting the pH range to 10-12 to obtain a raw material solution;
s2, preparing a precursor solution: adding a transition metal ion source, a sodium source and a carbon source into a raw material solution to form a precipitate, and simultaneously performing liquid-phase sanding to obtain a precursor solution which is uniformly dispersed;
s3, preparing uniform precursor powder: heating and drying the precursor solution to obtain uniform precursor powder composed of sodium element, transition metal ion element, anion source and carbon source;
s4, sintering at a high temperature: and calcining the precursor powder at high temperature in a protective atmosphere to obtain the composite polyanion anode material.
2. The method for synthesizing a composite polyanionic positive electrode material in an alkaline environment according to claim 1, wherein: the anion source is F - 、P 2 O 7 4- 、CO 3 2- 、BO 3 3- 、SiO 4 4- 、SO 3 2- One or both of these.
3. The method for synthesizing a composite polyanionic positive electrode material in an alkaline environment according to claim 1, wherein: the solvent is one or more of water, ethanol, chloroform, acetone, benzene, diethyl ether, ethyl acetate, carbon tetrachloride, etc.
4. The method for synthesizing a composite polyanionic positive electrode material in an alkaline environment according to claim 1, wherein: the alkaline additive is one or more of sodium hydroxide solution, ammonium bicarbonate solution, ammonium acetate solution, esterquat, ammonium citrate, tetraethylammonium sulfate, ammonium oxalate monohydrate, cetyltrimethylammonium fluoride and dimethyl alkyl chloride-C12-18-ethanol ammonium salt.
5. The method for synthesizing a composite polyanionic positive electrode material in an alkaline environment according to claim 1, wherein: the transition metal source is an iron-containing compound, a manganese-containing compound, a vanadium-containing compound, a cobalt-containing compound, a nickel-containing compound and/or a titanium-containing compound;
the iron-containing compound is one or more than two of ferric nitrate, ferrous nitrate, ferric sulfate, ferrous sulfate and/or ferrous acetate;
the manganese-containing compound is one or more than two of manganese nitrate, manganese acetate and/or manganese sulfate;
the vanadium-containing compound is one or more than two of vanadium nitrate, vanadium sulfate and/or vanadium acetate;
the cobalt-containing compound is cobalt nitrate and/or cobalt sulfate and cobalt acetate;
the nickel-containing compound is one or more than two of nickel nitrate, nickel sulfate and/or nickel acetate;
the titanium-containing compound is one or more than two of titanium nitrate, titanium sulfate and/or titanium acetate.
6. The method for synthesizing a composite polyanionic positive electrode material in an alkaline environment according to claim 1, wherein: the sodium source is one or more of sodium bicarbonate, sodium formate, sodium acetate, sodium nitrate, sodium sulfate, sodium citrate, sodium propionate, sodium acrylate, sodium benzoate and/or sodium bisulfate.
7. The method for synthesizing a composite polyanionic positive electrode material in an alkaline environment according to claim 1, wherein: the carbon source is one or more of glucose, sucrose, starch, maltose, lactose, polyvinyl alcohol, cyclodextrin, polyacrylic acid, polyacrylonitrile, cellulose and/or polyethylene.
8. The method for synthesizing a composite polyanionic positive electrode material in an alkaline environment according to claim 1, wherein: in the step S2, the liquid-phase sanding speed is 1000-1500r/min, and the sanding time is 4-8 hours.
9. The method for synthesizing a composite polyanionic positive electrode material in an alkaline environment according to claim 1, wherein: in step S3, the heating and drying mode comprises spray drying, oil bath/water bath drying and flash drying, and the heating temperature is 105-115 ℃.
10. The method for synthesizing a composite polyanionic positive electrode material in an alkaline environment according to claim 1, wherein: in the step S4, the protective atmosphere is nitrogen, hydrogen, carbon monoxide, argon, nitrogen-hydrogen mixture or argon-hydrogen mixture; in the step S4, the sintering temperature is 500-800 ℃, and the heat preservation time is 3-15H.
CN202311391493.1A 2023-10-25 2023-10-25 Method for synthesizing composite polyanion positive electrode material in alkaline environment Pending CN117466268A (en)

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