CN105810910B - A kind of Na2‑2xFe1+xP2O7/ carbon composite and its preparation method and application - Google Patents

Abstract

The invention discloses a Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material and its preparation method and application. The material is composed of Na _2-2x Fe _{1+ x} P ₂ O ₇ particle surface coated carbon Composite material formed from mesh layers. The synthesis method of the invention is simple, the conditions are mild, and the yield is high. The prepared composite material has high specific capacity, high working voltage, good cycle stability and excellent rate performance when applied as a sodium ion positive electrode material.

Description

A kind of Na2-2xFe1+xP2O7/carbon composite material and its preparation method and application

technical field

The invention relates to a Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material and a preparation method and application thereof, belonging to the field of sodium ion batteries.

Background technique

With the rapid development of the Internet era, since the commercial production of lithium-ion batteries in the 1990s, lithium-ion batteries have achieved rapid development in the field of 3C products and electric vehicles, and have shown good development prospects. However, due to the shortage of lithium metal resources in the world, the manufacturing cost of lithium-ion batteries is on the rise. At the same time, due to the poor safety of lithium-ion batteries, their development in the field of electric vehicles and large-scale energy storage has been greatly restricted. However, sodium, which is in the same main group as lithium in the periodic table, has very similar properties to lithium. And compared with the scarce lithium element, the sodium element has abundant reserves and more extensive sources, and the relatively low manufacturing cost makes the sodium-ion battery a battery system with the most potential to realize industrial large-scale energy storage. However, because the ionic radius of sodium ions is larger than that of lithium ions, it is more difficult for sodium ions to intercalate and extract kinetically than lithium ions in electrode materials, and sodium ions have a relatively positive redox potential and a large The atomic mass of the sodium ion battery makes the voltage of the positive electrode material of the sodium ion battery low and the energy density is not high. Therefore, improving the voltage and energy density of cathode materials for sodium-ion batteries has become the focus of research.

Researchers have studied different systems of cathode materials for sodium-ion batteries, among which P2-type and O3-type layered oxide systems are more representative, such as P2-Na _2/3 [Fe _1/2 Mn _1/2 ]O ₂ , O3-NaFe _0.5 Co _0.5 O ₂ , but these materials have short cycle life and low voltage plateau.

Contents of the invention

The purpose of the present invention is to provide a nano-scale Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material coated with a carbon network layer on the surface, the material has controllable morphology, good electrical conductivity, high specific capacity, High working voltage, good cycle stability and excellent rate performance.

Another object of the present invention is to provide a method for preparing Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material with mild reaction conditions, simple synthesis method and low cost.

Another object of the present invention is to provide an application of Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material, using Na _2-2x Fe _{1+ x} P ₂ O ₇ // carbon composite material as sodium ionic cathode material.

The technical solution of the present invention is to provide a Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material, which is a Na _2-2x Fe _1+x P ₂ O ₇ material coated with a carbon network layer on the surface , where x ranges from 0 to 1.

The present invention further includes the following preferred solutions:

In a preferred scheme, the crystal form of the Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material is a manganese-type.

In a preferred solution, the particle size of the composite material is 10-500 nm.

In a preferred solution, the carbon mesh layer has a thickness of 5-20 nm.

The present invention further includes a method for preparing Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material, comprising the following steps:

(1) Dissolve the carbon source in deionized water or alcohol solution; dissolve the iron source, phosphorus source, and sodium source in deionized water respectively, stir evenly, and drop them into the In the solution that is dissolved with carbon source, obtain mixed solution;

(2) Put the obtained mixed solution in a high-pressure reaction kettle, carry out hydrothermal reaction at 100°C to 300°C, cool, separate solid and liquid, wash with absolute ethanol until the eluate is neutral, dry, and the obtained solid product is It is the precursor of Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material;

(3) Sinter the precursor obtained in step (2) at 250-350°C under the protection of an inert atmosphere, and then heat up to 500-700°C to obtain Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material.

The sodium source described in the step (1) is at least one in sodium carbonate, sodium bicarbonate, sodium acetate, sodium oxalate, sodium nitrate, sodium sulfate, sodium citrate or sodium thiosulfate; the iron source is ferric nitrate , ferric chloride, ferrous oxalate, ferrous sulfate, ferric sulfate, ferric citrate, ferric ammonium citrate, ferric ammonium sulfate or ferrous ammonium sulfate; the phosphorus source is ammonium dihydrogen phosphate, phosphoric acid At least one of diammonium hydrogen, phosphoric acid or pyrophosphoric acid; the carbon source is at least one of citric acid, ascorbic acid, glucose, sucrose, polyvinyl alcohol or polyethylene glycol.

The preparation method of the present invention further includes the following preferred options:

In the preferred scheme, the typical but non-limiting examples of the combination of the carbon source are: the combination of citric acid and glucose, the combination of sucrose and glucose, the combination of ascorbic acid, polyvinyl alcohol and glucose, particularly preferably citric acid, glucose, poly at least one of vinyl alcohol.

In a preferred solution, typical but non-limiting examples of the combination of sodium sources include: the combination of sodium carbonate and sodium bicarbonate, the combination of sodium sulfate and sodium carbonate, the combination of sodium acetate, sodium citrate and sodium oxalate. Particularly preferred is at least one of sodium citrate, sodium carbonate, and sodium acetate.

In the preferred scheme, the typical but non-limiting examples of the combination of the iron source are: the combination of ferric nitrate and ferric citrate, the combination of ferric chloride and ferric sulfate, ferrous ammonium sulfate, ferric ammonium citrate and ferric citrate Combinations, particularly preferably at least one of ferric ammonium citrate and ferric ammonium sulfate.

In the preferred scheme, the typical but non-limiting examples of the combination of phosphorus sources are: the combination of ammonium dihydrogen phosphate and diammonium hydrogen phosphate, the combination of phosphoric acid and pyrophosphoric acid, particularly preferably ammonium dihydrogen phosphate, diammonium hydrogen phosphate at least one of .

In a preferred solution, in step (1), the molar ratio of sodium, iron and phosphorus in the sodium source, iron source and phosphorus source is 2-2.2:0.8-1.05:2.0. More preferably, it is 2.05-2.1:0.95:2.0.

In a preferred solution, in step (1), the mass ratio of the carbon source to Na _2-2x Fe _1+x P ₂ O ₇ is 0.05-1.05:1, most preferably 0.05-0.2:1.

In a preferred solution, in step (1), the alcohol solution is at least one of methanol aqueous solution, ethanol aqueous solution, ethylene glycol aqueous solution or glycerol aqueous solution.

In a preferred solution, the volume ratio of alcohol to deionized water in the alcohol solution is 1:0.5-2.

The most preferred is an aqueous solution of ethylene glycol, with a volume ratio of alcohol to deionized water of 1:1.

In a preferred solution, first sinter at 250-350°C for 6-12 hours, and then heat up to 500-700°C for 12-24 hours.

In a preferred scheme, the hydrothermal reaction time in the step (2) is 5-36 hours.

In a preferred scheme, in step (2), the reaction is preferably carried out in a stainless steel reactor. The reactor can be a stand-alone monomer reactor or an integrated temperature-controlled stirring reactor. The stand-alone monomer reactor is placed in a constant temperature vacuum drying oven to maintain the reaction at 100-300°C.

An integrated reaction kettle is preferred, which can realize precise temperature control, and continuous stirring during the reaction process can improve the dispersion uniformity of solute and product, which is beneficial to obtain ultrafine powder with uniform particle size.

In a preferred scheme, in step (2), the method for collecting the product by solid-liquid separation is suction filtration, spray drying, and centrifugation. Among them, the spray drying method can directly obtain dry spherical products with uniform particle size and good dispersion, which can be directly sintered. The suction filtration method is the simplest. After the suction filtration, the product and the solution can be separated, placed in a vacuum oven at 50-100°C, and baked to obtain a dried product. The centrifugation method uses a planetary centrifuge, which rotates at high speed to achieve the separation of the product and the solution. It also needs to be placed in a vacuum oven at 50-100°C and baked for 12-24 hours to obtain the dried product. Preferably, the product is generally collected by suction filtration.

In a preferred scheme, in step (3), the inert atmosphere is argon or nitrogen.

The present invention further includes applying the Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material as a sodium ion cathode material.

Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material performance test method for sodium ion battery prepared by the present invention: take the above-mentioned Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material, add 10wt .% Conductive carbon black is used as a conductive agent, 10wt.% PVDF is used as a binder, after grinding fully, a small amount of deionized water is added to mix to form a uniform black paste slurry, which is coated on an aluminum foil current collector as a test The electrode is assembled into a button battery with a metal sodium sheet as a counter electrode, and the electrolyte system is 1M NaClO ₄ /EC:PC (1:1). The charge and discharge current density used to test the cycle performance is 100mAh g ^-1 (1C rate).

The invention adopts a hydrothermal method, the obtained material has less impurity phases, and the calcination temperature of the synthesized precursor is lower.

Compared with prior art, the advantage of the present invention is:

(1) Using cheap sodium sources, iron sources, and carbon sources as raw materials reduces costs, and the present invention can prevent ferrous ions from being oxidized in the material preparation process to cause heterogeneous phases. The formed carbon network coating structure improves the electrical conductivity of the material and improves the electrochemical performance of the material.

(2) After the raw materials used in the present invention are dissolved respectively, by strictly controlling the dripping sequence, not only avoiding premature precipitation and reducing the generation of impurity phases, but also through the synergistic cooperation controlled by other parameters, the control of crystal formation is achieved. The speed of nucleation and growth, modulates the beneficial effect of topography.

(3) The precursor prepared by the present invention has less impurity phase and high activity. Compared with the existing method, it can be sintered at a lower temperature to obtain pure phase Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material.

(4) The carbon conductive network formed in the present invention greatly improves the conductivity of the material, reduces the polarization, and improves the rate performance.

(5) The Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material obtained in the present invention has excellent electrochemical properties, and the discharge specific capacity reaches 95mAh g ^-1 at a discharge rate of 1C.

(6) The present invention overcomes that the voltage platform of Na _2+2x Fe _2-x (SO ₄ ) ₃ prepared in this laboratory is unstable, has hygroscopicity, and is very sensitive to the moisture content of the production environment in the actual production process. It is prone to "poisoning", has poor thermal stability, and is easy to decompose to generate sulfur dioxide and other defects. The present invention is a further optimization of the previous scheme. The Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material obtained by the present invention has moderate voltage (up to 3.0V), stable voltage platform, good cycle performance, and chemical stability Better performance and thermal stability, energy saving and environmental protection in the preparation process, easy industrialization and other advantages.

Description of drawings

[FIG. 1] is an X-ray diffraction pattern prepared in Example 1.

[ FIG. 2 ] is a scanning electron micrograph of the Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material prepared in Example 1.

[ Fig. 3 ] is the charge-discharge curve of the Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material prepared in Example 1.

[ Fig. 4 ] is a charge-discharge efficiency diagram of the Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material prepared in Example 1 at a discharge rate of 1C.

[ Fig. 5 ] is a scanning electron micrograph of Na _2-2x Fe _1+x P ₂ O ₇ prepared in Comparative Example 2.

detailed description

The following examples are intended to further describe the content of the present invention in detail; and the protection scope of the claims of the present invention is not limited by the examples.

Example 1

This embodiment includes the following steps:

(1) This embodiment is designed to generate 0.03mol of the target product Na _2-2x Fe _1+x P ₂ O ₇ , and prepare a solution of 100mL: weigh 0.827 g of glucose and dissolve it in 40mL of ethylene glycol solution (ethylene glycol and deionized The ratio of water is 1:1), weigh 0.06mol of ammonium dihydrogen phosphate, 0.03mol of ferric nitrate, and 0.0315mol of sodium carbonate, respectively, dissolve them in 20mL of deionized water, and stir to dissolve. According to the sequence of phosphorus source, iron source and sodium source, it was added dropwise to the alcohol solution of glucose at a rate of 15 mL/min, supplemented by vigorous stirring, and left to stand for 24 hours after the addition was completed;

(2) Pour the mixed emulsion treated in step (1) into a stainless steel reaction kettle with a volume of 150mL and a filling capacity of 66.67%. Put the stainless steel reaction kettle into a 150°C constant temperature drying oven for 18 hours. Naturally cool to room temperature, take out the reactor, and use a sand core funnel for solid-liquid separation. The obtained solid powder is the precursor product of Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material;

(3) Place the obtained precursor solid-phase product in a constant temperature drying oven at 80°C to obtain dry powder, transfer the powdery product to a crucible, raise the temperature to 300°C under the protection of an argon atmosphere, and sinter for 6 hours, Then raise the temperature to 600°C and sinter for 12 hours at a heating rate of 5°C/min to obtain a Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material.

The sodium ion battery composite positive electrode material prepared in this example is assembled into a button battery with sodium sheets, and its material characterization and electrochemical performance are shown in the figure:

Figure 1 shows the successful synthesis of Na _2-2x Fe _1+x P ₂ O ₇ /carbon composites.

Figure 2 shows that the synthesized Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material has uniform particle size distribution and good dispersion. The particle size is 200nm, and the carbon network thickness is 10nm.

Figure 3 shows that the Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material and the sodium sheet are assembled into a button battery, and the first charge specific capacity is 94mAh g ^-1 , and the discharge specific capacity is 95mAh g ^-1 .

Figure 4 shows that the charge-discharge efficiency of the button battery assembled by Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material and sodium sheet at 1C rate for 10 cycles is maintained at about 96%.

Example 2

This embodiment includes the following steps:

(1) This embodiment is designed to generate 0.03mol target product Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material, and prepare 100mL of solution: weigh 1.634g of citric acid and dissolve it in 40mL of ethylene glycol solution (B The ratio of diol to deionized water is 1:1), respectively weigh 0.06mol of ammonium dihydrogen phosphate, 0.03mol of ferric nitrate, and 0.0315mol of sodium carbonate, dissolve them in 20mL of deionized water, and stir to dissolve. According to the order of phosphorus source, iron source and sodium source, add it dropwise to the alcohol solution of citric acid at a rate of 15mL/min, supplemented by vigorous stirring. After the addition is completed, let stand and age for 24 hours;

(2) Pour the mixed emulsion treated in step (1) into a stainless steel reaction kettle with a volume of 150mL and a filling capacity of 66.67%. Put the stainless steel reaction kettle into a 150°C constant temperature drying oven for 18 hours. Naturally cool to room temperature, take out the reactor, and use a sand core funnel for solid-liquid separation. The obtained solid powder is the precursor product of Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material;

(3) Place the obtained precursor solid-phase product in a constant temperature drying oven at 80°C to obtain dry powder, transfer the powdery product to a crucible, raise the temperature to 300°C under the protection of an argon atmosphere, and sinter for 6 hours, Then raise the temperature to 600°C and sinter for 12 hours at a heating rate of 5°C/min to obtain a Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material.

The battery assembly and testing methods of the material obtained in this example are the same as those in Example 1. The particle size of the Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material is 250nm, and the thickness of the carbon network is 15nm. The first charge specific capacity is 93mAh g ^-1 , the discharge specific capacity is 92mAh g ^-1 , and the charge and discharge efficiency of 10 cycles at 1C rate is maintained at about 94%.

Example 3

This embodiment includes the following steps:

(1) This embodiment is designed to generate 0.03mol of the target product Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material, and prepare a solution of 100mL: weigh 1.634g of glucose and dissolve it in 40mL of ethylene glycol solution (ethylene glycol The ratio of alcohol to deionized water is 1:1), weigh 0.06mol of ammonium dihydrogen phosphate, 0.03mol of ferric nitrate, and 0.0315mol of sodium carbonate, respectively, dissolve them in 20mL of deionized water, and stir to dissolve. According to the order of phosphorus source, iron source, and sodium source, add it dropwise to the alcohol solution of glucose at a rate of 15mL/min, supplemented by vigorous stirring, and leave it to stand for 24 hours after the addition is completed;

(2) Pour the mixed emulsion treated in step (1) into a stainless steel reaction kettle with a volume of 150mL and a filling capacity of 66.67%. Put the stainless steel reaction kettle into a 150°C constant temperature drying oven for 18 hours. Naturally cool to room temperature, take out the reactor, and use a sand core funnel for solid-liquid separation. The obtained solid powder is the precursor product of Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material;

(3) Place the obtained precursor solid-phase product in a constant temperature drying oven at 80°C to obtain dry powder, transfer the powdery product to a crucible, raise the temperature to 300°C under the protection of an argon atmosphere, and sinter for 6 hours, Then raise the temperature to 650°C and sinter for 12 hours at a heating rate of 5°C/min to obtain a Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material.

The battery assembly and testing methods of the material obtained in this example are the same as those in Example 1. The Na2FeP2O7/carbon composite material has a particle size of 220nm and a carbon network thickness of 20nm. The first charge specific capacity is 94mAh g ^-1 , the discharge specific capacity is 93mAh g ^-1 , and the charge and discharge efficiency of 10 cycles at 1C rate is maintained at about 96%.

Example 4

This embodiment includes the following steps:

(1) This embodiment is designed to generate 0.03mol of the target product Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material, and prepare a solution of 100mL: weigh 1.634g of glucose and dissolve it in 40mL of glycerol solution (glycerin The ratio of alcohol to deionized water is 1:1), respectively weigh 0.06mol of ammonium dihydrogen phosphate, 0.03mol of ferric nitrate, and 0.0315mol of sodium bicarbonate, dissolve them in 20mL of deionized water, and stir to dissolve. According to the sequence of phosphorus source, iron source, and sodium source, add it dropwise to the alcohol solution of glucose at a rate of 20mL/min, supplemented by vigorous stirring, and leave it to stand for 24 hours after the addition is completed;

(2) Pour the mixed emulsion treated in step (1) into a stainless steel reaction kettle with a volume of 150mL and a filling capacity of 66.67%. Put the stainless steel reaction kettle into a 150°C constant temperature drying oven for 18 hours. Naturally cool to room temperature, take out the reactor, and use a sand core funnel for solid-liquid separation. The obtained solid powder is the precursor product of Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material;

(3) Place the obtained precursor solid-phase product in a constant temperature drying oven at 80°C to obtain dry powder, transfer the powdery product to a crucible, raise the temperature to 300°C under the protection of an argon atmosphere, and sinter for 6 hours, Then raise the temperature to 620°C and sinter for 12 hours at a heating rate of 5°C/min to obtain Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material.

The battery assembly and testing methods of the material obtained in this example are the same as those in Example 1. The Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material has a particle size of 250nm and a carbon network thickness of 10nm. The first charge specific capacity is 96mAh g ^-1 , the discharge specific capacity is 93mAh g ^-1 , and the charge and discharge efficiency of 10 cycles at 1C rate is maintained at about 93%.

Example 5

This embodiment includes the following steps:

(1) This embodiment is designed to generate 0.03mol of the target product Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material, and prepare a solution of 100mL: weigh 1.634g of glucose and dissolve it in 40mL of glycerol solution (glycerin The ratio of alcohol to deionized water is 1:1), weigh 0.06mol of ammonium dihydrogen phosphate, 0.03mol of ferric sulfate, and 0.0315mol of sodium bicarbonate, dissolve them in 20mL of deionized water, and stir to dissolve. According to the sequence of phosphorus source, iron source, and sodium source, add it dropwise to the alcohol solution of glucose at a rate of 20mL/min, supplemented by vigorous stirring, and leave it to stand for 24 hours after the addition is completed;

(2) Pour the mixed emulsion treated in step (1) into a stainless steel reaction kettle with a volume of 150mL and a filling capacity of 66.67%. Put the stainless steel reaction kettle into a 150°C constant temperature drying oven for 18 hours. Naturally cool to room temperature, take out the reactor, and use a sand core funnel for solid-liquid separation. The obtained solid powder is the precursor product of Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material;

(3) Place the obtained precursor solid-phase product in a constant temperature drying oven at 80°C to obtain dry powder, transfer the powdery product to a crucible, raise the temperature to 300°C under the protection of an argon atmosphere, and sinter for 6 hours, Then raise the temperature to 600°C and sinter for 12 hours at a heating rate of 5°C/min to obtain a Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material.

The battery assembly and testing methods of the material obtained in this example are the same as in Example 1. The particle size of the Na _2-2x Fe _1+x P ₂ O ₇ /carbon composite material is 230nm, and the thickness of the carbon network is 13nm. The first charge specific capacity is 94mAh g ^-1 , the discharge specific capacity is 92mAh g ^-1 , and the charge and discharge efficiency of 10 cycles at 1C rate is maintained at about 92%.

Comparative example 1

This comparative example is designed to generate 0.03mol of the target product Na _2-2x Fe _1+x P ₂ O ₇ , using the traditional solid-phase synthesis method: Weigh 0.06mol of ammonium dihydrogen phosphate, 0.03mol of ferric nitrate, and 0.0315mol of Sodium carbonate, put each raw material into a ball mill tank, the ball-to-material ratio is 6:1, use acetone as the grinding medium, ball mill for 6 hours under the condition of 550r/min, and the obtained slurry is dried in an oven at 80°C, and ground After sieving, transfer to a crucible, heat up to 660°C and sinter for 12 hours, and the obtained black powder is Na _{2- 2x} Fe _1+x P ₂ O ₇ .

The battery assembly and testing methods of the material obtained in this comparative example are the same as those in Example 1, and the particle size of the obtained material is 400 nm. The initial charge specific capacity is 60mAh g ^-1 , the discharge specific capacity is 65mAh g ^-1 , and the charge-discharge efficiency of 10 cycles at 1C rate is maintained at about 91%.

Comparative example 2

(1) This control example is designed to generate 0.03mol of the target product Na _2-2x Fe _1+x P ₂ O ₇ , and prepare a solution of 100mL: weigh 0.06mol of ammonium dihydrogen phosphate, 0.03mol of ferric nitrate, and 0.0315mol of carbonic acid Sodium, were dissolved in 20mL of deionized water, stirred to dissolve. Add the phosphorus source and sodium source solutions drop by drop to the iron source solution in turn, and set the volume to 100mL with vigorous stirring. After the addition is completed, let stand and age for 24 hours;

(2) Pour the mixed emulsion treated in step (1) into a stainless steel reaction kettle with a volume of 150mL and a filling capacity of 66.67%. Put the stainless steel reaction kettle into a 150°C constant temperature drying oven for 18 hours. Naturally cool to room temperature, take out the reactor, and use a sand core funnel for solid-liquid separation.

(3) Place the obtained precursor solid-phase product in a constant temperature drying oven at 80°C to obtain dry powder, transfer the powdery product to a crucible, raise the temperature to 300°C under the protection of an argon atmosphere, and sinter for 6 hours, Then raise the temperature to 600°C, sinter for 12 hours, and heat up at a rate of 5°C/min.

The battery assembly and testing methods of the material obtained in this comparative example are the same as those in Example 1, and the particle size of the obtained material is 400 nm. The first charge specific capacity is 65mAh g ^-1 , the discharge specific capacity is 50mAh g ^-1 , and the charge-discharge efficiency of 10 cycles at 1C rate is maintained at about 80%.

Comparative example 3

This comparative example includes the following steps:

(1) This embodiment is designed to generate 0.03mol of the target product Na _2-2x Fe _1+x P ₂ O ₇ , and prepare a solution of 100mL: weigh 0.827 g of glucose and dissolve it in 40mL of ethylene glycol solution (ethylene glycol and deionized The ratio of water is 1:1), weigh 0.06mol of ammonium dihydrogen phosphate, 0.03mol of ferric nitrate, and 0.0315mol of sodium carbonate, respectively, dissolve them in 20mL of deionized water, and stir to dissolve. According to the order of sodium source, iron source, and phosphorus source, add it dropwise to the alcohol solution of glucose at a rate of 15 mL/min, supplemented by vigorous stirring, and leave it to stand for 24 hours after the addition is completed;

(2) Pour the mixed emulsion treated in step (1) into a stainless steel reaction kettle with a volume of 150mL and a filling capacity of 66.67%. Put the stainless steel reaction kettle into a 150°C constant temperature drying oven for 18 hours. Naturally cool to room temperature, take out the reactor, and use a sand core funnel for solid-liquid separation.

(3) Place the obtained precursor solid-phase product in a constant temperature drying oven at 80°C to obtain dry powder, transfer the powdery product to a crucible, raise the temperature to 300°C under the protection of an argon atmosphere, and sinter for 6 hours, Then raise the temperature to 600°C, sinter for 12 hours, and heat up at a rate of 5°C/min.

The battery assembly and testing method of the material obtained in this comparative example is the same as that in Example 1. The obtained material has many heterogeneous phases, and the first charge specific capacity is 20mAh g ^-1 , and the discharge specific capacity is 10mAh g ^-1 .

Claims (9)

1. A kind of 1. Na_2-2xFe_1+xP₂O₇The preparation method of/carbon composite, it is characterised in that comprise the following steps：

   (1) carbon source is dissolved in deionized water or alcoholic solution；Source of iron, phosphorus source, sodium source are dissolved separately in deionized water, stirred Mix uniformly, be added dropwise to successively according to source of iron, phosphorus source, the order of sodium source in the solution dissolved with carbon source, obtain mixed solution；

   (2) gained mixed solution is placed in autoclave, hydro-thermal reaction, cooling, solid-liquid point is carried out in 100 DEG C~300 DEG C From it is in neutrality to be washed with absolute ethyl alcohol to eluate, is dried, gained solid product is Na_2-2xFe_1+xP₂O₇/ carbon composite Presoma；

   (3) presoma obtained by step (2) is first sintered under inert atmosphere protection at 250~350 DEG C, then is warming up to 500~700 DEG C sintering, produce Na_2-2xFe_1+xP₂O₇/ carbon composite.
2. 2. preparation method according to claim 1, it is characterised in that sodium source described in step (1) is sodium carbonate, bicarbonate At least one of sodium, sodium acetate, sodium oxalate, sodium nitrate, sodium sulphate, sodium citrate or sodium thiosulfate；The source of iron is nitre Sour iron, iron chloride, ferrous oxalate, ferrous sulfate, ferric sulfate, ironic citrate, ferric citrate, ferric ammonium sulfate or ferrous sulfate At least one of ammonium；Phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid or pyrophosphoric acid；It is described Carbon source is at least one of citric acid, ascorbic acid, glucose, sucrose, polyvinyl alcohol or polyethylene glycol.
3. 3. preparation method according to claim 1, it is characterised in that sodium in sodium source, source of iron and phosphorus source described in step (1) The mol ratio of element, ferro element and P elements is 2~2.2:0.8~1.05:2.
4. 4. preparation method according to claim 1, it is characterised in that the quality and Na of the carbon source_2-2xFe_1+xP₂O₇Matter Amount is than being 0.05~0.2:1.
5. 5. preparation method according to claim 1, it is characterised in that alcoholic solution described in step (1) be methanol aqueous solution, At least one of ethanol water, glycol water or glycerin solution；The volume of alcohol and deionized water in alcoholic solution Than for 1:0.5~2.
6. 6. preparation method according to claim 1, it is characterised in that in the step (2) time of hydro-thermal reaction be 5~ 36h。
7. 7. according to the preparation method described in claim 1~6 any one, it is characterised in that the Na_2-2xFe_1+xP₂O₇/ carbon is multiple Condensation material is the Na of coated with carbon stratum reticulare_2-2xFe_1+xP₂O₇The scope of material, wherein x is 0~1.
8. 8. preparation method according to claim 7, it is characterised in that the Na_2-2xFe_1+xP₂O₇/ carbon composite crystal formation For reddingite type, the particle diameter of composite is 10~500nm.
9. 9. preparation method according to claim 7, it is characterised in that the thickness of the carbon stratum reticulare is 5~20nm.