Sodium-ion battery positive electrode material and preparation method thereof

Abstract

The invention relates to the technical field of sodium-ion batteries, in particular to a sodium-ion battery positive electrode material and a preparation method thereof.The sodium-ion battery positive electrode material comprises a sodium ferric sulfate precursor and a carbon coating layer coating the surface of the sodium ferric sulfate precursor; the sodium ferric sulfate precursor comprises a sodium source, an iron source, an antioxidant and halogenated carboxylic acid; and the carbon coating layer is formed by coating and sintering phosphate. Aiming at the problem that a carbon-coated positive electrode material in the prior art is easy to form defect points, the carbonization temperature in the sintering process is reduced by adding halogenated carboxylic acid into a precursor, so that the carbonization effect is improved, the probability of forming the defect points is reduced, and halogen ions are introduced into a carbon-coated layer in the sintering process to improve the conductivity; meanwhile, surface coating is carried out through phosphate, so that reaction of the positive electrode and electrolyte under a high-voltage condition can be effectively inhibited, gradual deterioration of the material structure due to moisture absorption in the circulation process is avoided, and the circulation stability of the material is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to a sodium ion battery positive electrode material and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries are considered to be a sustainable energy source with good development prospects. Due to its high safety, high energy density, long service life and other advantages, it has been widely used in various portable mobile devices, electric vehicles and energy storage and other fields. However, due to the uneven distribution of global lithium resources and the rapid and large consumption today, the production and use cost will be affected. Therefore, sodium ion batteries similar to the working principle of lithium ion batteries have been widely studied and concerned in the global energy storage field due to their wide distribution of sodium resources. Among them, the positive electrode material is a key link in the whole battery system, and its cycle stability, output voltage, thermal stability, output capacity and power density are decisive factors in the whole battery system. At present, the positive electrode materials of sodium ion batteries mainly include layered oxides, polyanions and prussian blue. Among them, the polyanion compound has an open framework structure, a low energy ion migration path and an adjustable voltage range, which has a significant advantage in the sodium ion battery positive electrode material. Especially the polyanion type sodium iron sulfate positive electrode material is widely concerned because of its low production cost and high working voltage. However, the conductivity of the polyanion type sodium iron sulfate positive electrode material is generally poor, and good energy storage properties are difficult to play, and the material is easy to absorb water and is easy to be oxidized by oxygen in the air, which leads to the failure of the material.

[0003] In view of this problem, some solutions have been proposed in the prior art.

[0004] For example, Chinese patent CN202411330183.3 provides a sodium ion positive electrode material, a preparation method thereof and a sodium ion battery. The sodium ion positive electrode material comprises, from the inside to the outside, an inner core layer, a first coating layer and a second coating layer; the inner core layer comprises sodium iron pyrophosphate phosphate; the first coating layer comprises carbon; and the second coating layer comprises sodium iron sulfate. The sodium ion positive electrode material retains the active sodium ions of the main material, has a high specific capacity, a low energy barrier, and the active sodium ions can easily enter the electrolyte through the coating layer, thereby improving the ion conductivity of the positive electrode material and the stability, and effectively protecting the sodium ion positive electrode material from corrosion by the electrolyte.

[0005] For another example, a Chinese patent CN202411167744.2 discloses a sodium iron sulfate positive electrode material and a preparation method and application thereof. The preparation method of the sodium iron sulfate positive electrode material comprises the following steps: S1: mixing a sodium source, an iron source, a sulfur source, an antioxidant, an organic carbon source, an inorganic carbon source, a dispersing agent, a defoaming agent, and deionized water to obtain a suspension; S2: performing spray drying treatment on the suspension obtained in S1 to obtain a sodium iron sulfate positive electrode material precursor; and S3: sintering the sodium iron sulfate positive electrode material precursor obtained in S2 to obtain the sodium iron sulfate positive electrode material. The sodium iron sulfate positive electrode material has a uniform carbon coating layer on the surface, which can effectively isolate moisture and carbon dioxide in the air as a protective barrier layer, does not have defect sites, and can improve the air stability of the sodium iron sulfate positive electrode material, thereby providing the sodium iron sulfate positive electrode material with the ability to be stored in a long-term natural environment and excellent electrochemical performance.

[0006] However, in actual implementation, the inventors found that although the carbon coating layer is used to wrap the precursor in the technical solutions, the wrapping is still not uniform due to the process precision problem in actual application, which leads to defect sites, so that the positive electrode material is easy to be oxidized by air and absorb water, and some materials also have poor electrical conductivity. SUMMARY

[0007] To solve the above problems in the prior art, a sodium ion battery positive electrode material is provided.

[0008] On the other hand, a preparation method of the sodium ion battery positive electrode material is also provided.

[0009] The specific technical solutions are as follows:

[0010] A sodium ion battery positive electrode material comprises a sodium iron sulfate precursor and a carbon coating layer wrapped on the surface of the sodium iron sulfate precursor.

[0011] The sodium iron sulfate precursor comprises a sodium source, an iron source, an antioxidant, and a halogenated carboxylic acid.

[0012] The carbon coating layer is formed by phosphate coating sintering.

[0013] On the other hand, the mass of carbon elements in the halogenated carboxylic acid is between 0.5-15% of the sum of the mass of the sodium source and the mass of the iron source.

[0014] The halogenated carboxylic acid comprises at least one of a fluorinated carboxylic acid, a chlorinated carboxylic acid, a brominated carboxylic acid, or an iodinated carboxylic acid.

[0015] On the other hand, the antioxidant comprises at least one of ascorbic acid, citric acid, phytic acid, uric acid, oxalic acid, formic acid, and acetic acid.

[0016] In another aspect, the mass of the phosphate is between 0.1-5% of the mass of the positive electrode material precursor;

[0017] The phosphate comprises at least one of sodium phosphate, sodium pyrophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate.

[0018] In another aspect, the sodium source comprises at least one of sodium sulfate, sodium bisulfate, sodium carbonate, sodium bicarbonate, sodium nitrate, sodium hydroxide;

[0019] The iron source comprises at least one of ferrous sulfate, ferrous carbonate, ferrous oxalate.

[0020] A preparation method of a sodium ion battery positive electrode material, for preparing the above-mentioned sodium ion battery positive electrode material;

[0021] The preparation method comprises:

[0022] Step S1: a sodium source, an iron source, an antioxidant, and a halogenated carboxylic acid are put into deionized water and mixed to form a material solution;

[0023] Step S2: the material solution is subjected to spray drying to obtain a sodium ferrous sulfate precursor;

[0024] Step S3: the sodium ferrous sulfate precursor is mixed with a phosphate, and then sintered to obtain the sodium ion battery positive electrode material.

[0025] In another aspect, in the step S1, the solid content of the material solution is between 15-40% of the mass of the solution.

[0026] In another aspect, the step S1 comprises stirring and mixing the material solution, the stirring speed is 100-500r / min, and the stirring time is between 0.5-4h.

[0027] In another aspect, in the step S2, the inlet air temperature of the spray drying is between 120-300℃, and the outlet air temperature is between 60-180℃.

[0028] In another aspect, in the step S3, the sintering process comprises a first-stage sintering and a second-stage sintering;

[0029] The temperature of the first-stage sintering is between 100-300℃, and the time is between 0.1-12h;

[0030] The temperature of the second-stage sintering is between 300-420℃, and the time is between 1-24h.

[0031] The above technical solution has the following advantages or beneficial effects:

[0032] In view of the problem that the carbon-coated positive electrode material in the prior art is prone to form defect sites, in the scheme, the carbonization temperature in the sintering process is reduced by adding halogenated carboxylic acid in the precursor, thereby improving the carbonization effect and reducing the probability of defect site formation, and the surface is coated with phosphate to effectively inhibit the reaction between the positive electrode and the electrolyte under high voltage conditions, thereby avoiding the gradual degradation of the material structure due to moisture absorption during the cycle process, and improving the cycle stability of the material.

[0033] Further, by adding halogenated carboxylic acid in the precursor, halogen ions are introduced into the carbon coating layer during the sintering process, thereby introducing additional holes as charge carriers in the carbon coating layer, further improving the electronic conductivity of the carbon coating layer. BRIEF DESCRIPTION OF DRAWINGS

[0034] Reference will be made to the accompanying drawings to more fully describe embodiments of the present application. However, the accompanying drawings are only used for illustration and explanation, and do not constitute a limitation on the scope of the present application.

[0035] Figure 1 The present application includes: DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0037] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0038] The present application will be further described below with reference to the drawings and specific embodiments, but is not limited by the present application.

[0039] The present application includes:

[0040] A sodium ion battery positive electrode material, the sodium ion battery positive electrode material comprising a sodium iron sulfate precursor and a carbon coating layer coated on the surface of the sodium iron sulfate precursor;

[0041] The sodium iron sulfate precursor is composed of a sodium source, an iron source, an antioxidant and a halogenated carboxylic acid;

[0042] The carbon coating layer is formed by phosphate coating and sintering.

[0043] Specifically, to solve the problem that defects are easily formed in the prior art carbon-coated positive electrode material, in the scheme, halogenated carboxylic acid is added as a carbon source in the precursor, halogenated carboxylic acid has a significantly lower carbonization temperature than other organic carbon sources, which reduces the temperature node of the initial carbonization in the sintering process, thereby improving the carbonization effect and reducing the probability of defect point formation.

[0044] Further, by adding phosphate in the sintering process in the sodium iron sulfate precursor, the positive electrode material can be further coated with phosphate in the sintering process, thereby effectively inhibiting the reaction between the positive electrode and the electrolyte under high voltage conditions, avoiding the gradual degradation of the material structure due to moisture absorption during the cycle process, and improving the cycle stability of the material.

[0045] Further, by adding halogenated carboxylic acid in the precursor and sintering, halogen ions will be left in the carbon coating layer of the finished product, and the halogen ions can introduce holes as charge carriers in the carbon coating layer, thereby improving the conductivity of the carbon coating layer on the surface, compensating for the problem of conductivity decline caused by defect points, and improving the electrical performance of the positive electrode material.

[0046] In one embodiment, the mass of carbon elements of the halogenated carboxylic acid is between 0.5-15% of the sum of the mass of the sodium source and the iron source.

[0047] The halogenated carboxylic acid includes at least one of fluorinated carboxylic acid, chlorinated carboxylic acid, brominated carboxylic acid, or iodinated carboxylic acid.

[0048] Specifically, to achieve better carbon coating effect, in the embodiment, the halogenated carboxylic acid is determined to be one of fluorinated carboxylic acid, chlorinated carboxylic acid, brominated carboxylic acid, or iodinated carboxylic acid, or a combination of multiple, to achieve a lower carbonization temperature of the carbon source, thereby reducing the probability of defect occurrence.

[0049] At the same time, to achieve complete coating of the material, the mass of carbon elements of the halogenated carboxylic acid is determined to be between 0.5-15% of the sum of the mass of the sodium source and the iron source, thereby achieving a relatively complete coating effect.

[0050] In one embodiment, the antioxidant includes at least one of ascorbic acid, citric acid, phytic acid, uric acid, oxalic acid, formic acid, and acetic acid.

[0051] Specifically, considering that the carbon coating layer in the prior art will have defect points during the coating process, and the defect part is easy to combine with the positive electrode material and oxidize, in the embodiment, an antioxidant is also added to the positive electrode material to delay the oxidation process. At the same time, the antioxidant is determined to be at least one of ascorbic acid, citric acid, phytic acid, uric acid, oxalic acid, formic acid, and acetic acid to achieve good antioxidant effect.

[0052] In one embodiment, the mass of the phosphate is between 0.1-5% of the mass of the positive electrode material precursor;

[0053] The phosphate includes at least one of sodium phosphate, sodium pyrophosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate.

[0054] Specifically, to achieve a better coating effect of the positive electrode material, in the embodiment, after the positive electrode material precursor is obtained by mixing, a phosphate is added for sintering coating, thereby forming a carbon-phosphate coating layer, which can effectively inhibit the reaction between the positive electrode and the electrolyte under high voltage conditions, avoid the gradual deterioration of the material structure due to moisture absorption during the cycle process, and improve the cycle stability of the material.

[0055] Meanwhile, to effectively inhibit the reaction between the positive electrode material and the electrolyte, the phosphate is determined as one or a combination of sodium phosphate, sodium pyrophosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate.

[0056] In addition, to achieve complete coating effect, the mass of the phosphate in the embodiment is determined to be between 0.1-5% of the mass of the positive electrode material precursor.

[0057] In one embodiment, the sodium source includes at least one of sodium sulfate, sodium bisulfate, sodium carbonate, sodium bicarbonate, sodium nitrate, and sodium hydroxide.

[0058] The iron source includes at least one of ferrous sulfate, ferrous carbonate, and ferrous oxalate.

[0059] A preparation method of a sodium ion battery positive electrode material is used to prepare the sodium ion battery positive electrode material described above.

[0060] As shown in Figure 1 , the preparation method includes:

[0061] Step S1: Put the sodium source, the iron source, the antioxidant, and the halogenated carboxylic acid into deionized water and mix to form a material solution;

[0062] Step S2: Spray dry the material solution to obtain a sodium ferrous sulfate precursor;

[0063] Step S3: Mix the sodium ferrous sulfate precursor with the phosphate, and then sinter to obtain the sodium ion battery positive electrode material.

[0064] Specifically, to achieve a more uniform material mixing and preparation effect of the coating layer, in the embodiment, first, the sodium source, the iron source, the antioxidant, and the halogenated carboxylic acid are put into deionized water and mixed to form a material solution, so that the above raw materials are uniformly dispersed in the deionized water.

[0065] Subsequently, spray drying is performed to uniformly mix the above materials and evaporate the deionized water, to obtain the sodium ferric sulfate precursor.

[0066] Finally, the sodium ferric sulfate precursor is mixed with the phosphate to incorporate the phosphate into the sodium ferric sulfate precursor, and then sintering is performed to carbonize the halogenated carboxylic acid in the sodium ferric sulfate precursor and form a carbon-phosphate coating layer together with the phosphate, to finally obtain the sodium-ion battery positive electrode material.

[0067] In one embodiment, in step S1, the solid content of the material solution is between 15-40% of the solution mass.

[0068] Specifically, to achieve effective mixing of the materials, in this embodiment, the solid content of the material solution is between 15-40% of the solution mass, so that the above materials can be uniformly dispersed in the material solution.

[0069] In one embodiment, step S1 includes stirring and mixing the material solution, the stirring speed is 100-500 r / min, and the stirring time is between 0.5-4 h.

[0070] Specifically, to achieve better mixing effect of the materials, in this embodiment, the materials are uniformly dispersed in the solution by stirring and mixing.

[0071] Specifically, the stirring process can use a paddle stirrer or a magnetic suspension stirrer to stir the solution.

[0072] First, deionized water is placed in the stirring tank, and then the materials are sequentially added, including the sodium source, the iron source, the antioxidant, and the halogenated carboxylic acid, and then the stirrer is started at a set speed for a predetermined time, so that the materials are uniformly dispersed in the solution.

[0073] In one embodiment, in step S2, the inlet air temperature of the spray drying is between 120-300℃, and the outlet air temperature is between 60-180℃.

[0074] Specifically, to achieve better spray drying effect, in this embodiment, the inlet air temperature of the spray drying is controlled to be between 120-300℃, and the outlet air temperature is controlled to be between 60-180℃, to control the drying time.

[0075] In one embodiment, in step S3, the sintering process includes first-stage sintering and second-stage sintering.

[0076] The first-stage sintering temperature is between 100-300℃, and the time is between 0.1-12 h.

[0077] The second-stage sintering temperature is between 300-420℃, and the time is between 1-24 h.

[0078] Specifically, to achieve better sintering effect, in the embodiment, the sintering process is designed as a segmented sintering process. Specifically, the sodium iron sulfate precursor needs to form a stable carbon-phosphate coating layer through the sintering process.

[0079] Among them, the carbon element in the sodium iron sulfate precursor is provided by the halogenated carboxylic acid, and the halogen substituent group reduces the carbonization temperature of the carboxylic acid. The carbonization site is formed by controlling the water and partial carbonization of the sodium iron sulfate precursor in the first sintering process at 100-300℃.

[0080] Subsequently, the second sintering process is entered, and the sodium iron sulfate positive electrode material is obtained by sintering the sodium iron sulfate precursor by increasing the temperature to 300-420℃ and sintering for 1-24h, and the halogenated carboxylic acid is further completely carbonized to form a dense carbon-phosphate coating layer.

[0081] The above technical solution can adopt the following embodiments:

[0082] Embodiment one:

[0083] First, a certain mass of Na2SO4 and FeSO4·7H2O is taken according to the Na / Fe molar ratio of 8:5.

[0084] Subsequently, deionized water is added to the stirrer reaction kettle, the reaction kettle is charged with Na2SO4 and FeSO4·7H2O, and ascorbic acid is added according to 2% of its mass, and chloroacetic acid is added according to 6% of its mass (calculated by the mass of carbon element in chloroacetic acid).

[0085] All the above reagents are added to the stirrer reaction kettle, the stirrer speed is set to 400r / min, and stirring is carried out for 3h to make all the reagents fully dissolved, and finally a material solution with a solid content of 40% is obtained.

[0086] Then, the material solution is subjected to spray drying treatment, the inlet air temperature of the spray drying is 200℃, and the outlet air temperature is 100℃, and the sodium iron sulfate precursor is obtained.

[0087] The sodium iron sulfate precursor and 1% of sodium hydrogen phosphate of the mass of the sodium iron sulfate precursor are put into the ball mill and ball-mixed.

[0088] Then the product obtained by ball-mixing is transferred to a box furnace, and first sintered at 200℃ for 10h under a nitrogen protective atmosphere, and then sintered at 375℃ for 12h to obtain a sodium iron sulfate positive electrode material.

[0089] Embodiment two:

[0090] First, take a certain mass of Na2SO4 and FeSO4·7H2O according to the Na / Fe molar ratio of 8:5.

[0091] Subsequently, add deionized water to the stirrer reaction kettle, put Na2SO4 and FeSO4·7H2O into the reaction kettle, and put ascorbic acid according to 2% of the mass and chloroacetic acid (calculated by the mass of carbon in chloroacetic acid) according to 0.5% of the mass.

[0092] Put all the above reagents into the stirrer reaction kettle, set the stirrer speed to 400 r / min, stir for 3 h, and fully dissolve all the reagents to finally obtain a material solution with a solid content of 40%.

[0093] Then, the material solution is subjected to spray drying treatment, the inlet air temperature of spray drying is 200℃, and the outlet air temperature is 100℃, to obtain a sodium ferric sulfate precursor.

[0094] Put the sodium ferric sulfate precursor and 1% of disodium hydrogen phosphate of the mass of the sodium ferric sulfate precursor into the ball mill and ball mill mix them.

[0095] Then, the ball-mixed product is transferred to a box furnace, first sintered at 200℃ for 10 h under a nitrogen protective atmosphere, and then sintered at 375℃ for 12 h to obtain a sodium ferric sulfate positive electrode material.

[0096] Example Three:

[0097] First, take a certain mass of Na2SO4 and FeSO4·7H2O according to the Na / Fe molar ratio of 8:5.

[0098] Subsequently, add deionized water to the stirrer reaction kettle, put Na2SO4 and FeSO4·7H2O into the reaction kettle, and put ascorbic acid according to 2% of the mass and chloroacetic acid (calculated by the mass of carbon in chloroacetic acid) according to 15% of the mass.

[0099] Put all the above reagents into the stirrer reaction kettle, set the stirrer speed to 400 r / min, stir for 3 h, and fully dissolve all the reagents to finally obtain a material solution with a solid content of 40%.

[0100] Then, the material solution is subjected to spray drying treatment, the inlet air temperature of spray drying is 200℃, and the outlet air temperature is 100℃, to obtain a sodium ferric sulfate precursor.

[0101] Put the sodium ferric sulfate precursor and 1% of disodium hydrogen phosphate of the mass of the sodium ferric sulfate precursor into the ball mill and ball mill mix them.

[0102] Then the product obtained by ball milling is transferred to a box furnace, first sintered at 200℃ for 10h under nitrogen atmosphere, then sintered at 375℃ for 12h, to obtain the sodium ferric sulfate positive electrode material.

[0103] Example Four:

[0104] First, a certain mass of Na2SO4 and FeSO4·7H2O is taken according to the Na / Fe molar ratio of 8:5.

[0105] Subsequently, deionized water is added to the stirrer reaction kettle, Na2SO4 and FeSO4·7H2O are put into the reaction kettle, ascorbic acid is put in according to 2% of its mass, and chloroacetic acid is put in according to 6% of its mass (calculated by the mass of carbon in chloroacetic acid).

[0106] All the above reagents are added to the stirrer reaction kettle, the stirrer speed is set to 400r / min, and stirring is carried out for 3h to make all the reagents fully dissolved, finally obtaining a material solution with a solid content of 40%.

[0107] Then, the material solution is subjected to spray drying treatment, the inlet air temperature of spray drying is 200℃, and the outlet air temperature is 100℃, to obtain the sodium ferric sulfate precursor.

[0108] The sodium ferric sulfate precursor and 0.1% of disodium hydrogen phosphate of the mass of the sodium ferric sulfate precursor are put into the ball mill and ball-mixed.

[0109] Then the product obtained by ball milling is transferred to a box furnace, first sintered at 200℃ for 10h under nitrogen atmosphere, then sintered at 375℃ for 12h, to obtain the sodium ferric sulfate positive electrode material.

[0110] Example Five:

[0111] First, a certain mass of Na2SO4 and FeSO4·7H2O is taken according to the Na / Fe molar ratio of 8:5.

[0112] Subsequently, deionized water is added to the stirrer reaction kettle, Na2SO4 and FeSO4·7H2O are put into the reaction kettle, ascorbic acid is put in according to 2% of its mass, and chloroacetic acid is put in according to 6% of its mass (calculated by the mass of carbon in chloroacetic acid).

[0113] All the above reagents are added to the stirrer reaction kettle, the stirrer speed is set to 400r / min, and stirring is carried out for 3h to make all the reagents fully dissolved, finally obtaining a material solution with a solid content of 40%.

[0114] Then, the material solution is subjected to spray drying treatment, the inlet air temperature of the spray drying is 200℃, and the outlet air temperature is 100℃, to obtain the sodium iron sulfate precursor.

[0115] The sodium iron sulfate precursor and 5% of the sodium phosphate dibasic by mass of the sodium iron sulfate precursor are put into a ball mill, and the two are ball-mixed.

[0116] Then, the product obtained by the ball-mixing is transferred into a box furnace, and is sintered at 200℃ for 10h under a nitrogen protective atmosphere, and then is continuously sintered at 375℃ for 12h, to obtain the sodium iron sulfate positive electrode material.

[0117] Comparative Example 1

[0118] First, a certain mass of Na2SO4 and FeSO4·7H2O is taken according to a Na / Fe molar ratio of 8:5.

[0119] Subsequently, deionized water is added into a stirrer reaction kettle, the reaction kettle is charged with the Na2SO4 and FeSO4·7H2O, and ascorbic acid is added according to 2% of the mass of the Na2SO4 and FeSO4·7H2O, and no chloroacetic acid is added.

[0120] All the reagents are added into the stirrer reaction kettle, the stirring speed of the stirrer is set to 400r / min, and stirring is performed for 3h, so that all the reagents are fully dissolved, and finally a material solution with a solid content of 40% is obtained.

[0121] Then, the material solution is subjected to spray drying treatment, the inlet air temperature of the spray drying is 200℃, and the outlet air temperature is 100℃, to obtain the sodium iron sulfate precursor.

[0122] The sodium iron sulfate precursor is transferred into a box furnace, and is sintered at 200℃ for 10h under a nitrogen protective atmosphere, and then is continuously sintered at 375℃ for 12h, to obtain the sodium iron sulfate positive electrode material.

[0123] Comparative Example 2

[0124] First, a certain mass of Na2SO4 and FeSO4·7H2O is taken according to a Na / Fe molar ratio of 8:5.

[0125] Subsequently, deionized water is added into a stirrer reaction kettle, the reaction kettle is charged with the Na2SO4 and FeSO4·7H2O, and ascorbic acid is added according to 2% of the mass of the Na2SO4 and FeSO4·7H2O, and no chloroacetic acid is added.

[0126] All the reagents are added into the stirrer reaction kettle, the stirring speed of the stirrer is set to 400r / min, and stirring is performed for 3h, so that all the reagents are fully dissolved, and finally a material solution with a solid content of 40% is obtained.

[0127] Then, the material solution is subjected to spray drying treatment, the inlet air temperature of the spray drying is 200℃, and the outlet air temperature is 100℃, to obtain the sodium iron sulfate precursor.

[0128] The sodium iron sulfate precursor and 1% of the sodium iron sulfate precursor by mass of disodium hydrogen phosphate are put into a ball mill, and the two are ball-mixed.

[0129] Then, the product obtained by the ball-mixing is transferred into a box furnace, and is sintered at 200℃ for 10h and then at 375℃ for 12h under a nitrogen protective atmosphere, to obtain the sodium iron sulfate positive electrode material.

[0130] Comparative Example 3

[0131] First, a certain mass of Na2SO4 and FeSO4·7H2O is taken according to a Na / Fe molar ratio of 8:5.

[0132] Subsequently, deionized water is added into a stirrer reaction kettle, the reaction kettle is charged with Na2SO4 and FeSO4·7H2O, ascorbic acid is added according to 2% of the mass of Na2SO4 and FeSO4·7H2O, and chloroacetic acid is added according to 6% of the mass of Na2SO4 and FeSO4·7H2O (calculated based on the mass of carbon in the chloroacetic acid).

[0133] All the above reagents are added into the stirrer reaction kettle, the stirring speed is set to 400r / min, and stirring is performed for 3h to make all the reagents fully dissolved, to finally obtain a material solution with a solid content of 40%.

[0134] Then, the material solution is subjected to spray drying treatment, the inlet air temperature of the spray drying is 200℃, and the outlet air temperature is 100℃, to obtain the sodium iron sulfate precursor.

[0135] The sodium iron sulfate precursor is transferred into a box furnace, and is sintered at 200℃ for 10h and then at 375℃ for 12h under a nitrogen protective atmosphere, to obtain the sodium iron sulfate positive electrode material.

[0136] Comparative Example 4

[0137] First, a certain mass of Na2SO4 and FeSO4·7H2O is taken according to a Na / Fe molar ratio of 8:5.

[0138] Subsequently, deionized water is added into a stirrer reaction kettle, the reaction kettle is charged with Na2SO4 and FeSO4·7H2O, ascorbic acid is added according to 2% of the mass of Na2SO4 and FeSO4·7H2O, and chloroacetic acid is added according to 6% of the mass of Na2SO4 and FeSO4·7H2O (calculated based on the mass of carbon in the chloroacetic acid).

[0139] All the above reagents were added into the agitator reactor, the rotation speed of the agitator was set to 400 r / min, and the reagents were stirred for 3 h to make them fully dissolved, and finally a material solution with a solid content of 40% was obtained.

[0140] Then, the material solution was subjected to spray drying treatment, the inlet air temperature of the spray drying was 200 ℃, and the outlet air temperature was 100 ℃, and thus a sodium ferric sulfate precursor was obtained.

[0141] The sodium ferric sulfate precursor and 1% of the sodium ferric sulfate precursor by mass of Na2HPO4 were put into a ball mill for ball milling mixing.

[0142] Then, the product obtained by the ball milling mixing was transferred into a box furnace, and first sintered at 200 ℃ for 10 h under a nitrogen protective atmosphere, and then sintered at 375 ℃ for 12 h, and thus a sodium ferric sulfate positive electrode material was obtained.

[0143] Comparative Example Five:

[0144] First, a certain mass of Na2SO4 and FeSO4·7H2O were taken according to a Na / Fe molar ratio of 8:5.

[0145] Subsequently, deionized water was added into the agitator reactor, the reactor was charged with the Na2SO4 and FeSO4·7H2O, and according to 2% of the mass of the Na2SO4 and FeSO4·7H2O, ascorbic acid was added, and according to 6% of the mass of the Na2SO4 and FeSO4·7H2O, glucose (calculated according to the mass of carbon in the glucose) was added.

[0146] All the above reagents were added into the agitator reactor, the rotation speed of the agitator was set to 400 r / min, and the reagents were stirred for 3 h to make them fully dissolved, and finally a material solution with a solid content of 40% was obtained.

[0147] Then, the material solution was subjected to spray drying treatment, the inlet air temperature of the spray drying was 200 ℃, and the outlet air temperature was 100 ℃, and thus a sodium ferric sulfate precursor was obtained.

[0148] The sodium ferric sulfate precursor and 1% of the sodium ferric sulfate precursor by mass of Na2HPO4 were put into a ball mill for ball milling mixing.

[0149] Then, the product obtained by the ball milling mixing was transferred into a box furnace, and first sintered at 200 ℃ for 10 h under a nitrogen protective atmosphere, and then sintered at 375 ℃ for 12 h, and thus a sodium ferric sulfate positive electrode material was obtained.

[0150] After the above materials were respectively prepared, the above materials were respectively tested, including:

[0151] Test One:

[0152] The above sodium ferric sulfate positive electrode material is mixed with conductive agent acetylene black and binder PVDF in a mass ratio of 80:10:10, and a proper amount of 1-methyl-2-pyrrolidone is added for ball milling for 1 h to prepare a slurry, which is uniformly coated on an aluminum sheet, dried, and pressed to prepare a positive electrode sheet with a compacted density of 2.0 g / cm3. A PC (propylene carbonate) solution of 1 mol / L NaClO4 is used as an electrolyte, and a metal sodium sheet is used as a negative electrode to assemble a 2032 button cell.

[0153] For the button cell, the Siken test system is used for electrical performance testing. In the range of 2.0-4.5 V of the charge and discharge cutoff voltage, the discharge specific capacity under 0.1 C is tested.

[0154] Then, the rate performance test is performed: the charge and discharge cutoff voltage is 2.0-4.5 V, the discharge capacity under 1 C is tested as C1, the discharge capacity under 0.1 C is tested as C2, and the rate performance is C1 / C2.

[0155] Then, the rate performance test is performed: the charge and discharge cutoff voltage is 2.0-4.5 V, the discharge capacity under 1 C is tested as C1, the discharge capacity under 0.1 C is tested as C2, and the rate performance is C1 / C2.

[0156] The test results are shown in Table 1.

[0157]

[0158] Table 1

[0159] It can be seen that the above examples 1-5 have obviously better electrical performance than the comparative examples 1-5 which omit some elements.

[0160] Test two:

[0161] The above prepared sodium ferric sulfate positive electrode material is vacuum dried at 80°C for 12 hours, ball milled to 325 mesh, mixed with 1% polytetrafluoroethylene (PTFE) as a binder, and a rust steel mold (diameter 10 mm) is selected to prepare a pressed sheet under a pressure of 15 MPa, so as to ensure that the surface of the pressed sheet is flat and crack-free.

[0162] Then, the four-probe test method is used, the pressed sheet is fixed on an insulating substrate, the four probes are vertically contacted with the surface of the pressed sheet at equal intervals, a constant current is applied, the voltage difference is measured, and the electronic conductivity of the material is calculated. The results are shown in Table 2.

[0163] For the same pressed sheet, a small amount of ionic liquid PYR 14The positive electrode sheet made by TFSI reducing interface impedance was assembled into 2032 button cell with metal sodium sheet as negative electrode, PC (propylene carbonate) solution of 1 mol / L NaClO4 as electrolyte, and the ion conductivity of the material was obtained by AC impedance (EIS) ion conductivity test using electrochemical workstation. The results are listed in Table 2.

[0164] Sample Electrical conductivity (S / cm) Ionic conductivity (S / cm) Example 1 3.2 x 10 -4 ]]> 1.2 x 10 -3 ]] Example 2 1.3 x 10 -5 ]] 1.0 x 10 -3 ]] Example 3 6.2 x 10 -5 ]]> 1.1 x 10 -3 ]]> Example 4 1.9 x 10 -4 ]] 9.1 x 10 -4 ]] Example 5 2.4 x 10 -4 ]]> 8.7 x 10 -4 ]]> Comparative Example 1 8.9 x 10 -8 ]] 1.2 x 10 -4 ]]> Comparative Example 2 1.7 x 10 -7 ]]> 7.8 x 10 -4 ]]> Comparative Example 3 1.9 x 10 -4 ]]> 3.5 x 10 -4 ]]> Comparative Example 4 2.1 x 10 -4 ]]> 3.8 x 10 -4 <!-- 9 -->]]> Comparative Example 5 3.6 x 10- 6 ]]> 8.3 x 10 -4 ]]>

[0165] Table 2

[0166] While this application contains many specifics, these should not be construed as limiting the scope of any disclosures or any scope of patent or patent applications herein but for describing a specific embodiment thereof. Some features described in multiple embodiments within this application can also be implemented in a single embodiment. On the other hand, various features described in a single embodiment can also be implemented in multiple embodiments or in any suitable subcombination. Furthermore, while features can be described as being in certain combinations, it is understood that one or more features from a combination can be removed and each subcombination is also contemplated. It is therefore apparent that there is a need for a system and method that addresses the aforementioned problems and others in the art.

[0167] The preferred embodiments of the present application are shown and described above, but the present application is not limited to the above-mentioned embodiments. It will be apparent to those skilled in the art that various modifications and changes can be made thereto without departing from the scope of the present application which is set out in the claims.

Claims

1. A sodium-ion battery cathode material, characterized in that, The sodium ion battery cathode material comprises a sodium iron sulfate precursor and a carbon coating layer coated on the surface of the sodium iron sulfate precursor; The sodium iron sulfate precursor is composed of a sodium source, an iron source, an antioxidant, and a halogenated carboxylic acid; The carbon coating layer is formed by phosphate coating sintering.

2. The sodium-ion battery cathode material of claim 1, wherein, The mass of carbon elements in the halogenated carboxylic acid is between 0.5-15% of the sum of the mass of the sodium source and the iron source; The halogenated carboxylic acid comprises at least one of fluorinated carboxylic acid, chlorinated carboxylic acid, brominated carboxylic acid, or iodinated carboxylic acid.

3. The sodium-ion battery cathode material of claim 1, wherein, The antioxidant comprises at least one of ascorbic acid, citric acid, phytic acid, uric acid, oxalic acid, formic acid, and acetic acid.

4. The sodium-ion battery cathode material of claim 1, wherein, The mass of the phosphate is between 0.1-5% of the mass of the cathode material precursor; The phosphate comprises at least one of sodium phosphate, sodium pyrophosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate.

5. The sodium-ion battery cathode material of claim 1, wherein, The sodium source comprises at least one of sodium sulfate, sodium bisulfate, sodium carbonate, sodium bicarbonate, sodium nitrate, and sodium hydroxide; The iron source comprises at least one of ferrous sulfate, ferrous carbonate, and ferrous oxalate.

6. A method for preparing a sodium-ion battery cathode material, characterized in that, A sodium ion battery cathode material as claimed in any one of claims 1-5; The preparation method comprises: Step S1: Put the sodium source, iron source, antioxidant, and halogenated carboxylic acid into deionized water and mix to form a material solution; Step S2: Spray dry the material solution to obtain a sodium iron sulfate precursor; Step S3: Mix the sodium iron sulfate precursor with a phosphate, and then sinter to obtain the sodium ion battery cathode material.

7. The production method according to claim 6, wherein In the step S1, the solid content of the material solution is between 15-40% of the mass of the solution.

8. The preparation method according to claim 6, characterized in that, The step S1 comprises stirring and mixing the material solution, the stirring speed is 100-500 r / min, and the stirring time is between 0.5-4 h.

9. The preparation method according to claim 6, characterized in that, In the step S2, the inlet air temperature of the spray drying is between 120-300℃, and the outlet air temperature is between 60-180℃.

10. The method of claim 6, wherein, In the step S3, the sintering process comprises a first-stage sintering and a second-stage sintering; The temperature of the first-stage sintering is between 100-300℃, and the time is between 0.1-12 h; the temperature of the second-stage sintering is between 300-420℃, and the time is between 1-24 h.

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