CN114759173A - Trivalent chromium ion doped modified mixed ferric sodium pyrophosphate positive electrode material, preparation and application - Google Patents

Abstract

The invention discloses a trivalent chromium ion doped modified mixed sodium ferric pyrophosphate cathode material, which has the following characteristics: the trivalent chromium ion doped modified mixed ferric sodium pyrophosphate cathode material comprises trivalent chromium ion doped mixed ferric sodium pyrophosphate and in-situ carbon, wherein the trivalent chromium ion doped mixed ferric sodium pyrophosphate is obtained by doping trivalent chromium ions into crystal cells of a crystal material to replace part of divalent iron ions, and the in-situ carbon is uniformly coated on the surface of the trivalent chromium ion doped mixed ferric sodium pyrophosphate. The material has the characteristics of higher voltage, high charge-discharge specific capacity, good cycling stability, low cost of raw materials, abundant reserves, environmental friendliness and the like. The invention also discloses a preparation method of the trivalent chromium ion doped modified mixed sodium ferric pyrophosphate cathode material. The invention also discloses application of the trivalent chromium ion doped modified mixed sodium ferric pyrophosphate positive material in a sodium ion battery, and the trivalent chromium ion doped modified mixed sodium ferric pyrophosphate positive material has a certain promotion effect on development of the positive material of the sodium ion battery.

Description

Trivalent chromium ion doping modified mixed sodium iron pyrophosphate cathode material, preparation and application

technical field

The invention relates to the field of energy storage material sodium ion battery positive electrode materials, in particular to trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode materials, preparation and application.

Background technique

In recent years, environmental problems have received extensive attention from all over the world. On the one hand, the use of traditional fossil energy will cause environmental pollution, and on the other hand, its non-renewable excessive use will cause an energy crisis. Therefore, the development and utilization of new energy has become the first choice for people. However, the generation of new energy is easily restricted by climate and environment, and the energy produced by it is unstable. Energy storage batteries can store clean energy, and then perform stable output and utilization, which solves the problem of clean energy instability.

Compared with lithium-ion battery (LIB), sodium-ion battery (SIB), as an energy storage battery, has the characteristics of abundant sodium resources, low price, high operating voltage and high safety. application prospects. In the research of cathode materials for sodium-ion batteries, people are devoted to finding a cathode material with high energy density, good stability, environmental friendliness and resource saving. Most of the polyanion cathode materials have an open three-dimensional framework, good rate performance and good cycle performance, but the conductivity of such compounds is generally poor. In order to improve their electronic and ionic conductivity, doping and carbon Coating, etc.

SUMMARY OF THE INVENTION

The present invention is carried out in order to solve the above problems, and the purpose is to provide trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material, preparation and application.

The invention provides a trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material, which has the following characteristics: the trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material comprises a trivalent chromium ion doping mixed Sodium iron pyrophosphate and in-situ carbon, trivalent chromium ion doping mixed sodium iron pyrophosphate is obtained by doping trivalent chromium ions into the unit cell of the crystal material to replace part of the divalent iron ions, and the in-situ carbon is uniformly coated on the three Chromium ion-doped mixed sodium iron pyrophosphate surface.

The trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material provided by the present invention may also have the following characteristics: wherein, the chemical equation of the trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material is: : Na _3-x Fe _{2- x} Cr _x (PO ₄ )P ₂ O ₇ @C or Na _4-x Fe _3-x Cr _x (PO ₄ ) ₂ P ₂ O ₇ @C, where 0.01≤x ≤1.

The invention provides a preparation method of a trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material, which has the following characteristics: comprising the following steps: step 1, mixing iron source, chromium source, sodium source, phosphorus source and The reducing agent is dissolved in water to obtain a uniformly dispersed precursor solution. In step 2, the precursor solution is stirred, dried and calcined to obtain a trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material, and the trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material is the present invention. Trivalent chromium ion doping modified mixed sodium iron pyrophosphate cathode material.

In the preparation method of the trivalent chromium ion doping modified mixed sodium iron pyrophosphate cathode material provided by the present invention, it may also have the following characteristics: wherein, in step 1, the iron source, the chromium source, the sodium source, the phosphorus source, the And the molar ratio of the reducing agent is: (1-2):(0.01-1):(1-3):(1-3):(1-3).

In the preparation method of the trivalent chromium ion doping modified mixed sodium ferric pyrophosphate cathode material provided by the present invention, it can also have the following characteristics: wherein, in step 1, the iron source is ferric nitrate nonahydrate, ferric oxalate and lemon any one in ferrous acid, chromium source is any one in nonahydrate chromium nitrate, chromium acetate, sodium source is any one in sodium dihydrogen phosphate, sodium nitrate and anhydrous sodium acetate, phosphorus source is phosphoric acid Any one of ammonium dihydrogen and hydroxyethylidene diphosphoric acid, and the reducing agent is any one of oxalic acid, citric acid, ascorbic acid and tartaric acid.

The invention provides an application of a trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material in a sodium ion battery, and has the following characteristics: the trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material is As a positive electrode of a sodium ion battery, when applied to a sodium ion battery, the trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material is the trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material of the present invention.

In the application of the trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material in the sodium ion battery provided by the present invention, it also has the following characteristics: the preparation method of the sodium ion battery positive electrode is as follows: The hetero-modified mixed sodium iron pyrophosphate positive electrode material is mixed and slurried with a binder and a conductive agent, and is coated on the current collector and cured to obtain a sodium ion battery positive electrode.

The role and effect of the invention

According to the trivalent chromium ion doped modified mixed sodium iron pyrophosphate cathode material involved in the present invention, because the trivalent chromium ion doped modified mixed sodium iron pyrophosphate cathode material includes trivalent chromium ion doped mixed sodium iron pyrophosphate And in-situ carbon, trivalent chromium ion-doped mixed sodium iron pyrophosphate is obtained by doping trivalent chromium ions into the unit cell of the crystal material to replace part of the divalent iron ions, and the in-situ carbon is uniformly coated on the trivalent chromium ions doped. Hybrid mixed sodium ferric pyrophosphate surface.

Because the trivalent chromium ion can form a strong bond with phosphate and pyrophosphate, it can suppress the change of the unit cell volume during the charging and discharging process, so it has chemical and thermal stability. On the other hand, trivalent chromium ions will expand the lattice volume, widen the space, and promote the diffusion of sodium ions. At the same time, the incorporation of trivalent chromium ions will also generate a certain amount of sodium vacancies, which can improve the sodium ions to a certain extent. The transfer rate during rate charge and discharge. Among them, ascorbic acid is both a reducing agent and a carbon source. In the precursor dispersion, ascorbic acid can reduce the ferric ions in the solution to ferrous ions, and act as a chelating agent and combine with ferrous ions to form chelates. compound. In the final calcination process in an inert atmosphere, ascorbic acid will form in-situ carbon and evenly coat the surface of the material, which greatly improves the electrical conductivity of the material.

The preparation method of the trivalent chromium ion-doped modified mixed sodium iron pyrophosphate positive electrode material involved in the present invention has wide raw material sources, simple operation and large-scale production. The modified mixed polyanion compound cathode material prepared by this method has the characteristics of high electronic conductivity, high reversible discharge capacity and high energy density, which lays a good foundation for the further development of sodium-ion batteries.

Description of drawings

Fig. 1 is the X-ray diffraction pattern (XRD figure) of trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material and undoped mixed sodium iron pyrophosphate positive electrode material in the embodiment of the present invention;

2 is a charge-discharge curve diagram of a trivalent chromium ion-doped modified mixed sodium iron pyrophosphate cathode material at a rate of 0.1C in an embodiment of the present invention;

3 is a charge-discharge curve diagram of an undoped mixed sodium iron pyrophosphate cathode material in a comparative example of the present invention at a rate of 0.1C;

4 is a cycle diagram of the mixed sodium ferric pyrophosphate positive electrode material in the embodiment of the present invention and the comparative example circulating 2000 cycles at a rate of 10C;

5 is a scanning electron microscope image of a trivalent chromium ion doping modified mixed sodium iron pyrophosphate cathode material in an embodiment of the present invention.

Detailed ways

In order to make the technical means, creative features, goals and effects realized by the present invention easy to understand, the following examples are combined with the accompanying drawings to describe the trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material, preparation and application in detail. .

<Example>

In this embodiment, a trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material is provided.

Trivalent chromium ion doped mixed sodium iron pyrophosphate cathode materials include trivalent chromium ion doped mixed sodium iron pyrophosphate and in-situ carbon, trivalent chromium ion doped mixed sodium iron pyrophosphate is trivalent chromium ion doped It is obtained by replacing part of divalent iron ions in the unit cell of the crystal material, and the in-situ carbon is uniformly coated on the surface of the trivalent chromium ion-doped mixed sodium iron pyrophosphate.

The present embodiment also provides a preparation method of a trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material, comprising the following steps:

Step S1, in a 100ml beaker, mix 3.636g of ferric nitrate nonahydrate, 0.4002g of chromium nitrate nonahydrate, 3g of ascorbic acid, 1.7255g of ammonium dihydrogen phosphate, 1.1899g of sodium nitrate, 0.05g of sodium dodecyl sulfate and 5ml of ethylenediol The alcohol was dissolved in 50 mL of deionized water and stirred for 1 h to obtain a uniformly dispersed precursor solution.

In step S2, the uniformly dispersed precursor solution is placed in a constant temperature oil bath, and the water in the solution is evaporated to dryness under the condition of an oil bath at 80°C, and then vacuum dried at 90°C for 8 hours. The dried raw material was heated to 500°C at a heating rate of 2°C/min in an atmosphere of 5% hydrogen + 95% argon, and kept for 10 hours to obtain a trivalent chromium ion-doped modified mixed sodium iron pyrophosphate cathode. Material Na _2.8 Fe _1.8 Cr _0.2 (PO ₄ )P ₂ O ₇ .

This embodiment also provides an application of a trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material in a sodium ion battery:

The trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material is used as the positive electrode of the sodium ion battery and applied to the sodium ion battery. The trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material in this embodiment Trivalent chromium ion doping modified mixed sodium iron pyrophosphate cathode material.

The preparation method of the positive electrode of the sodium ion battery is as follows: the positive electrode material of trivalent chromium ion doped and modified mixed sodium iron pyrophosphate is mixed and slurried, and the binder and the conductive agent are mixed and slurried, coated on the current collector, and cured to obtain the positive electrode of the sodium ion battery. .

<Comparative example>

The present comparative example provides a mixed sodium iron pyrophosphate cathode material and a preparation method thereof.

The preparation method of the mixed sodium ferric pyrophosphate cathode material in this comparative example is similar to the embodiment, the difference is:

Step S1, in a 100ml beaker, dissolve 4.04g ferric nitrate nonahydrate, 3g ascorbic acid, 1.7255g ammonium dihydrogen phosphate, 1.2749g sodium nitrate, 0.05g sodium dodecyl sulfate and 5ml ethylene glycol in 50mL deionized water , and stirred for 1 h to obtain a uniformly dispersed precursor solution.

The rest of the steps are the same as in the embodiment.

FIG. 1 is the X-ray diffraction pattern (XRD pattern) of the trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material in the present embodiment and the undoped mixed sodium iron pyrophosphate positive electrode material in the comparative example.

As shown in Figure 1, the diffraction peaks of the XRD images of the material before and after doping modification with trivalent chromium ions did not change significantly. It can be seen that a small amount of doping has no effect on the purity of the material.

In this example, the charge-discharge cycle test at a rate of 0.1C was also performed on the trivalent chromium ion-doped modified mixed sodium iron pyrophosphate positive electrode material obtained in the comparative example and the example.

FIG. 2 is a charge-discharge curve diagram of a trivalent chromium ion-doped modified mixed sodium iron pyrophosphate positive electrode material at a rate of 0.1 C in the embodiment.

FIG. 3 is a charge-discharge curve diagram of the mixed sodium iron pyrophosphate cathode material in the comparative example at a rate of 0.1C.

FIG. 4 is a cycle diagram of the mixed sodium iron pyrophosphate cathode material in the example and the comparative example cycled for 2000 cycles at a rate of 10C.

As shown in Figures 2 to 4, the discharge capacity of the trivalent chromium ion-doped modified mixed sodium iron pyrophosphate cathode material prepared in the Example is 113mAh·g ^-1 at 0.1C, which is close to the theoretical capacity of 119mAh·g ^{- 1.} It is better than the mixed sodium iron pyrophosphate cathode material (before modification) in the comparative example, indicating that the doping of trivalent chromium ions has a positive effect on the improvement of the material capacity. It can be seen from the cycle diagram below that the capacity and cycle stability of the material are improved after doping with trivalent chromium ions.

5 is a scanning electron microscope image of a trivalent chromium ion doping modified mixed sodium iron pyrophosphate cathode material in the embodiment.

As shown in Figure 5, the morphology of the modified mixed sodium iron pyrophosphate cathode material doped with trivalent chromium ions is relatively dispersed, and no large aggregation occurs, which is conducive to the full contact of the electrolyte and the rapid diffusion of sodium ions.

Action and effect of the embodiment

According to the trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material, preparation method and application in sodium ion battery involved in this embodiment, because the trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode The material includes trivalent chromium ion doped mixed sodium iron pyrophosphate and in-situ carbon, trivalent chromium ion doped mixed sodium iron pyrophosphate is obtained by doped trivalent chromium ion into the unit cell of the crystal material to replace part of the divalent iron ion , the in situ carbon is uniformly coated on the surface of trivalent chromium ion-doped mixed sodium iron pyrophosphate.

Therefore, trivalent chromium ions can form strong bonds with phosphate and pyrophosphate, which can suppress the change of unit cell volume during charging and discharging, so it has chemical and thermal stability. On the other hand, trivalent chromium ions will expand the lattice volume, widen the space, and promote the diffusion of sodium ions. At the same time, the incorporation of trivalent chromium ions will also generate a certain amount of sodium vacancies, which can improve the sodium ions to a certain extent. The transfer rate during rate charge and discharge. Among them, ascorbic acid is both a reducing agent and a carbon source. In the precursor dispersion, ascorbic acid can reduce the ferric ions in the solution to ferrous ions, and act as a chelating agent and combine with ferrous ions to form chelates. compound. In the final calcination process in an inert atmosphere, ascorbic acid will form in-situ carbon and evenly coat the surface of the material, which greatly improves the electrical conductivity of the material.

The preparation method of the trivalent chromium ion-doped modified mixed sodium ferric pyrophosphate cathode material involved in the above embodiment has a wide range of raw materials, simple operation, and large-scale production. The modified mixed polyanion compound cathode material prepared by this method has the characteristics of high electronic conductivity, high reversible discharge capacity and high energy density, which lays a good foundation for the further development of sodium-ion batteries.

The above embodiments are preferred cases of the present invention, and are not intended to limit the protection scope of the present invention.

Claims (7)

1. a trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material, is characterized in that: The trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material comprises trivalent chromium ion doped mixed sodium iron pyrophosphate and in-situ carbon, The trivalent chromium ion-doped mixed sodium ferric pyrophosphate is obtained by doping trivalent chromium ions into the unit cell of the crystal material to replace part of the divalent iron ions, The in-situ carbon is uniformly coated on the surface of the trivalent chromium ion-doped mixed sodium iron pyrophosphate. 2. a kind of trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material according to claim 1, is characterized in that: Wherein, the chemical equation of the trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material is: Na _3-x Fe _2-x Cr _x (PO ₄ )P ₂ O ₇ @C or Na _4-x Fe _3-x Cr _x (PO ₄ ) ₂ P ₂ O ₇ @C, In the formula, 0.01≤x≤1. 3. a preparation method of trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material, is characterized in that, comprises the following steps: Step 1, dissolving iron source, chromium source, sodium source, phosphorus source and reducing agent in water to obtain a uniformly dispersed precursor solution; Step 2, stirring, drying and calcining the precursor solution to obtain the trivalent chromium ion-doped modified mixed sodium iron pyrophosphate positive electrode material, The trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material is the trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material according to any one of claims 1 to 2. 4. the preparation method of a kind of trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material according to claim 3, is characterized in that: Wherein, in step 1, the molar ratio of the iron source, the chromium source, the sodium source, the phosphorus source, and the reducing agent is: (1～2):(0.01～1):(1 ~3):(1~3):(1~3). 5. the preparation method of a kind of trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material according to claim 3, is characterized in that: Wherein, in step 1, the iron source is any one in ferric nitrate nonahydrate, ferric oxalate and ferrous citrate, Described chromium source is any one in nonahydrate chromium nitrate, chromium acetate, Described sodium source is any one in sodium dihydrogen phosphate, sodium nitrate and anhydrous sodium acetate, Described phosphorus source is any one in ammonium dihydrogen phosphate, hydroxyethylidene diphosphoric acid, The reducing agent is any one of oxalic acid, citric acid, ascorbic acid and tartaric acid. 6. the application of a trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material in a sodium ion battery, is characterized in that: The trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material is used as the positive electrode of the sodium ion battery and applied to the sodium ion battery, The trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material is the trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material according to any one of claims 1-2. 7. the application of a kind of trivalent chromium ion doping modified mixed sodium iron pyrophosphate positive electrode material in sodium ion battery according to claim 6, is characterized in that: The preparation method of the positive electrode of the sodium ion battery is: The trivalent chromium ion doped modified mixed sodium iron pyrophosphate positive electrode material, a binder and a conductive agent are mixed and slurried, coated on the current collector, and cured to obtain the sodium ion battery positive electrode.

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