CN107863530B

CN107863530B - A method for preparing high-density lithium iron phosphate by using siderite

Info

Publication number: CN107863530B
Application number: CN201711070611.3A
Authority: CN
Inventors: 谷亦杰; 秦文娟; 陈蕴博; 刘成全; 王海峰; 刘洪权; 陈林; 王萌
Original assignee: Shandong University of Science and Technology
Current assignee: Shandong University of Science and Technology
Priority date: 2017-11-03
Filing date: 2017-11-03
Publication date: 2020-04-28
Anticipated expiration: 2037-11-03
Also published as: CN107863530A

Abstract

The invention discloses a method for preparing high-density lithium iron phosphate by using siderite. First, phosphoric acid is directly added to siderite to obtain an iron solution, and the iron solution is mixed with polymer copolymer P (DMDAAC-AM), Hydrogen peroxide is added to the mixed solution to fully react to obtain iron phosphate dihydrate, a precursor of lithium iron phosphate, and the iron phosphate dihydrate is mixed with lithium carbonate and glucose to obtain lithium iron phosphate after sintering. The raw material used in the invention is siderite, which is a widely distributed mineral and can be used as iron ore to extract iron, and the precursor iron phosphate dihydrate is directly synthesized with siderite, which not only saves iron ore The energy-consuming step of extracting iron from stone realizes the purpose that the cathode material of lithium ion battery is directly obtained from nature, and siderite is easier to react with phosphoric acid than iron powder, which improves the feasibility of the reaction.

Description

Method for preparing high-density lithium iron phosphate by adopting siderite

Technical Field

The invention belongs to the field of electrochemistry, and particularly relates to a method for preparing a lithium ion battery anode material by utilizing siderite.

Background

The lithium ion battery is a new generation of green high-energy battery with excellent performance, and has become one of the key points of the development of high and new technologies, and the synthesis method of lithium iron phosphate as the anode material of the lithium ion battery is the central importance in the development. The method for synthesizing the lithium iron phosphate battery by utilizing the siderite at present comprises the steps of dissolving the siderite by sulfuric acid, hydrochloric acid or nitric acid, adding an oxidant and phosphoric acid or phosphate to react to generate precursor iron phosphate of a lithium ion battery positive electrode material, and sintering the iron phosphate with lithium carbonate and C to synthesize the lithium iron phosphate. Such as:

chinese patent application No. 201210591476.8 discloses a preparation method of a lithium iron phosphate precursor of a lithium ion battery anode material, which comprises the steps of leaching siderite by sulfuric acid or hydrochloric acid, adjusting the concentration of the solution, adding hydrogen peroxide or an ozone oxidant and a precipitator, selectively precipitating elements in the siderite which are beneficial to the electrochemical performance of lithium iron phosphate by controlling the synthesis conditions, and drying to obtain the lithium iron phosphate precursor.

Chinese patent application No. 200810031119.3 discloses a method for preparing a lithium iron phosphate precursor by comprehensively utilizing ilmenite: leaching titanic iron ore with acid, filtering to obtain filtrate, and dissolving a certain amount of other iron sources in the filtrate to ensure that the concentration of Fe in the mixed solution is 0.01-3mol/L and the molar ratio of Ti to Fe is 0.0005-0.5; adding a proper amount of oxidant into the mixed solution, adjusting the pH value of the system to be 1.5-6.0 by using an aqueous solution of alkali to ensure that part of iron and certain impurity ions are coprecipitated, and filtering to obtain filtrate; adding a precipitator (0.01-6mol/L) into the filtrate, adjusting the pH value of the system to be 4.0-14.0 by using an aqueous solution of alkali, reacting in a stirring reactor at 10-90 ℃ for 10min-24h, filtering, washing, drying the precipitate at 50-150 ℃, and calcining in the air at 300-800 ℃ for 1-24h to obtain the ferric oxide of the doped metal element, which is the precursor of the lithium iron phosphate of the lithium ion battery anode material.

The lithium iron phosphate prepared by the methods described in the two documents has good electrochemical performance, but has the following defects that firstly, the process is long and the synthesis efficiency is low because acid is required to be added to leach iron in siderite; secondly, because of adding sulfuric acid, hydrochloric acid or nitric acid, impurity element SO which influences the performance of the battery is introduced₄ ^2-、CL^-And NO₃ ^-And the like.

At present, ferric phosphate lithium is synthesized by directly using ferric salt, lithium salt and phosphoric acid under hydrothermal conditions without adding sulfuric acid, hydrochloric acid or nitric acid, such as Chinese patent applicationNo. 201110045252.2 discloses a method for greatly improving the performance of LiFePO which is a cathode material of a lithium ion battery prepared by low-temperature hydrothermal synthesis₄A method with excellent electrochemical performance comprises the steps of preparing a slurry precursor in water through lithium salt, ferric salt and phosphoric acid according to a certain adding sequence and proportion, then adding a certain amount of organic solvent, and preparing nano LiFePO with excellent electrochemical performance under hydrothermal conditions₄And (3) a positive electrode material. The raw material of the patent uses soluble ferric salt, and the preparation of the soluble ferric salt consumes a large amount of energy and increases reaction steps.

In addition, the capacity of the storage battery is an important index for measuring the performance of the storage battery, and lithium iron phosphate has some performance defects, and the energy density of the lithium iron phosphate battery is low due to the fact that the tap density and the compaction density are low due to the fact that the existing synthesized lithium iron phosphate particles are small.

Chinese patent publication No. CN104817059A discloses a method for preparing battery-grade iron phosphate by reacting iron powder with phosphoric acid, which comprises mixing iron powder with diluted phosphoric acid, and reacting to generate Fe (H)₂PO₄)₂Then adding an oxidant to oxidize to generate iron phosphate precipitate, and filtering and drying to obtain high-purity battery-grade iron phosphate, namely dihydrate iron phosphate; ferric phosphate dihydrate is a nano-flaky crystal of a quasi-red iron phosphate ore (phosphosiderite) crystal form. The disclosed technology has the following defects: firstly, because the main raw material is iron powder, the common knowledge that the iron powder does not naturally exist in the nature, is a regenerated substance and needs to be made by steel making, the steel making is a more complicated process and consumes a large amount of electric energy, and if the regenerated substance is used for synthesizing the anode material of the lithium ion battery, the method is certainly not a good method which is worth recommending; secondly, hydrogen is generated in the reaction process, the hydrogen is flammable and explosive, and when the hydrogen reaches a certain proportion in the air, the hydrogen can explode when exposed to fire, which not only brings harmfulness to the whole process, but also requires that an operator has high operation skill. Therefore, the technology disclosed in the document cannot be popularized and industrialized in a large scale, and does not meet the current policy of energy conservation and environmental protection.

Disclosure of Invention

The invention provides a method for preparing a lithium ion battery anode material by siderite, aiming at overcoming the technical defects of long process, low synthesis efficiency, high danger coefficient, difficult operation and impurity element content in the existing lithium iron phosphate preparation technology and improving the density of lithium iron phosphate so as to improve the capacity of a lithium ion battery.

In order to achieve the purpose, the invention adopts the technical scheme that:

a method for preparing a high-density lithium ion battery anode material by siderite, which is characterized in that,

the first step is as follows: dissolving siderite

Directly adding phosphoric acid into siderite, wherein the concentration of the phosphoric acid is required to be 0.2-0.3mol/L, the molar ratio of iron to pure phosphoric acid is required to be 2 (4-8), the reaction temperature is 0-100 ℃, the reaction time is 1-5h, after full reaction, filtering to obtain an iron solution, and the chemical reaction formula is as follows:

FeCO₃+2H₃PO₄＝Fe²⁺+2(H₂PO₄)^-+H₂O+CO₂

in the second step, the solution of iron is mixed with the high molecular copolymer P (DMDAAC-AM)

Adding the iron solution obtained in the first step into a P (DMDAAC-AM) solution, and fully stirring to uniformly mix the solution and the solution, wherein the mass ratio of the P (DMDAAC-AM) to siderite is required to be 1: 10-1: 50;

thirdly, reacting the mixed solution of iron and P (DMDAAC-AM) with hydrogen peroxide

Adding hydrogen peroxide into the mixed solution in the second step, wherein the concentration of the hydrogen peroxide is 5-30wt%, the molar ratio of iron to pure hydrogen peroxide is required to be 2 (1-1.5), the reaction temperature is 50-100 ℃, the reaction time is 1-5h, after full reaction, filtering, washing with deionized water, and drying to obtain the ferric phosphate dihydrate as the precursor of the lithium iron phosphate, and the chemical reaction formula is as follows:

2Fe²⁺+4(H₂PO₄)^-+H₂O₂+2H₂O＝2FePO₄·2H₂O↓+2H₃PO₄

the fourth step: and (3) mixing and sintering the ferric phosphate dihydrate prepared in the third step with lithium carbonate and glucose to obtain lithium iron phosphate, wherein the mixing molar ratio of lithium phosphate to lithium carbonate to glucose (calculated by carbon) is 2 (1-1.1): 0.5-0.8), the reaction is carried out in a protective atmosphere, the reaction temperature is 600-800 ℃, and the reaction time is 5-15 hours.

The chemical reaction formula is as follows:

2FePO₄·2H₂O↓+Li₂CO₃+0.5C＝2LiFePO₄+1.5CO₂+2H₂O。

the lithium iron phosphate material prepared by the process is used as the anode, and the graphite is used as the cathode to manufacture the lithium ion battery.

The advantages of the present invention are illustrated below based on the reaction mechanism:

1. the invention directly adds phosphoric acid into siderite, leaches iron in siderite to obtain iron solution by controlling the concentration of phosphoric acid and the reaction temperature and time, then adds high molecular copolymer P (DMDAAC-AM) into the iron solution, because P (DMDAAC-AM) is the copolymer of dimethyl diallyl ammonium chloride and acrylamide, it is a glassy solid, easy to absorb water, it is an important water-soluble polymer, and it has flocculation and thickening properties, when adding hydrogen peroxide into the mixed solution of iron and P (DMDAAC-AM), because of the delayed precipitation of P (DMDAAC-AM), the particle size of iron phosphate after reaction is large, and finally the sintered lithium iron phosphate particles are controlled to about 10um, and the tap density reaches 1.5-2 g/cm³Thereby improving the energy density of the lithium iron phosphate battery.

2. The invention directly reacts to obtain the ferric phosphate dihydrate of the precursor of the lithium iron phosphate by controlling the concentration of the phosphoric acid and the reaction temperature and time, the reacted ferric phosphate dihydrate exists in the phosphoric acid in a precipitation form, and the pure precursor ferric phosphate dihydrate is obtained by direct filtration, thereby not only omitting the process of leaching iron in siderite by hydrochloric acid or sulfuric acid in advance, reducing the cost, but also not introducing other impurities which are not beneficial to the performance of the battery, and improving the conductivity of the battery.

3. The siderite is a mineral with wide distribution and can be used as iron ore to refine iron, and the siderite is directly used for synthesizing the precursor ferric phosphate dihydrate, so that the energy consumption step of extracting iron from the iron ore is omitted, the aim of directly obtaining the anode material of the lithium ion battery from the nature is fulfilled, and the siderite is easier to react with phosphoric acid compared with iron powder, and the feasibility of the reaction is improved.

4. The gas generated in the reaction process is colorless, tasteless and odorless CO at normal temperature₂Gas, CO₂The gas has no harm to human body, no flammability, easy operation, and generated CO₂Plays a role of stirring the solution, increases the activity of the siderite and further improves the feasibility of the reaction

In a word, the invention is a method for preparing the lithium ion battery anode material, which has low energy consumption and high safety factor and is convenient to popularize.

Drawings

Fig. 1 is a Scanning Electron Microscope (SEM) image of lithium iron phosphate prepared in example 1 of the present invention.

Fig. 2 is an X-ray powder diffraction (XRD) pattern of lithium iron phosphate prepared in example 1 of the present invention.

Fig. 3 is a Scanning Electron Microscope (SEM) image of lithium iron phosphate prepared in example 2 of the present invention.

Fig. 4 is an X-ray powder diffraction (XRD) pattern of lithium iron phosphate prepared in example 2 of the present invention.

The technical scheme of the invention is further illustrated by combining the specific examples.

In the first embodiment, taking siderite containing 1mol of iron carbonate as an example, the concentration of phosphoric acid is 0.2mol/L, and the concentration of hydrogen peroxide is 10 wt%, and the specific preparation method comprises the following steps:

the first step is as follows: dissolving siderite

According to the mol ratio of iron to pure phosphoric acid of 2:7, H is directly added into siderite₃PO is 3.5mol of phosphoric acid, the reaction temperature is 40 ℃, the reaction time is 5 hours, and after full reaction, an iron solution is obtained;

in the second step, the solution of iron is mixed with P (DMDAAC-AM)

Adding the iron solution obtained in the first step into a P (DMDAAC-AM) solution, and fully stirring to uniformly mix the solution and the solution, wherein the mass ratio of siderite to P (DMDAAC-AM) is 10: 1;

thirdly, reacting the iron solution with hydrogen peroxide

Adding H into the iron solution according to the molar ratio of iron to pure hydrogen peroxide of 2:1₂O₂0.5mol of hydrogen peroxide, wherein the concentration of the hydrogen peroxide is 10 wt%, the reaction temperature is 70 ℃, the reaction time is 3 hours, and after full reaction, the mixture is filtered, washed by deionized water and dried to obtain a precursor ferric phosphate dihydrate;

the fourth step: and mixing and sintering the ferric phosphate dihydrate prepared in the first step, lithium carbonate and glucose to obtain lithium iron phosphate, wherein the mixing molar ratio of the ferric phosphate, the lithium carbonate and the glucose (calculated by carbon) is 2:1:0.6, and the reaction is carried out in a protective atmosphere, wherein the reaction temperature is 700 ℃ and the reaction time is 10 hours. The scanning electron microscope image and the X-ray powder diffraction image of the prepared lithium iron phosphate are respectively shown in the figures 1-2.

Example one lithium iron phosphate particle tap density of 1.7g/cm³。

By using the lithium iron phosphate prepared in the first embodiment as a positive electrode and graphite as a negative electrode, a lithium ion battery with a battery voltage of 3V and a 18650 battery capacity of 1300mAh can be prepared.

Example two

In the second embodiment, 1mol of siderite (calculated by iron carbonate) is taken as an example, the concentration of phosphoric acid is 0.3mol/L, and the concentration of hydrogen peroxide is 20 wt%, and the specific preparation method comprises the following steps:

the first step is as follows: dissolving siderite.

According to the mol ratio of iron to pure phosphoric acid of 2:4, H is directly added into siderite₃PO is 2mol of phosphoric acid, the concentration of the phosphoric acid is 0.3mol/L, the reaction temperature is 70 ℃, the reaction time is 3 hours, and after full reaction, an iron solution is obtained;

in the second step, the solution of iron is mixed with P (DMDAAC-AM)

Adding the iron solution obtained in the first step into the P (DMDAAC-AM) solution, and fully stirring to uniformly mix the iron solution and the P (DMDAAC-AM) solution, wherein the mass ratio of the siderite to the P (DMDAAC-AM) is required to be 20: 1.

And thirdly, reacting the iron solution with hydrogen peroxide.

Adding H into the iron solution according to the molar ratio of iron to pure hydrogen peroxide of 2:1.5₂O₂0.75mol of hydrogen peroxide, wherein the reaction temperature is 90 ℃, the reaction time is 1h, and after full reaction, filtering, washing with deionized water and drying to obtain a precursor ferric phosphate dihydrate;

the fourth step: mixing and sintering the ferric phosphate dihydrate prepared in the first step, lithium carbonate and glucose to obtain lithium iron phosphate, wherein the mixing molar ratio of the ferric phosphate to the lithium carbonate to the glucose (calculated by carbon) is 2:1.1: 0.6; the reaction was carried out in a protective atmosphere at a reaction temperature of 650 ℃ for a reaction time of 12 h. The scanning electron microscope image and the X-ray powder diffraction pattern of the prepared lithium iron phosphate are respectively shown in fig. 3-4.

The tap density of the lithium iron phosphate particles prepared in the second embodiment reaches 1.75g/cm³。

The lithium iron phosphate prepared in the second embodiment is used as a positive electrode, graphite is used as a negative electrode, and the battery voltage is 3V, and the 18650 battery capacity is 1300 mAh.

Claims

1. a method utilizing siderite to prepare high-density lithium iron phosphate, is characterized in that,

Step 1: Dissolving siderite

Add phosphoric acid directly to siderite, the concentration of phosphoric acid is required to be 0.2-0.3mol/L, the molar ratio of iron to pure phosphoric acid is required to be 2:(4-8), the reaction temperature is 0-100℃, and the reaction time is 1 -5h, after fully reacted, the iron solution was obtained by filtration. The chemical reaction formula is:

FeCO ₃ +2H ₃ PO ₄ =Fe ²⁺ +2(H ₂ PO ₄ ) ^- +H ₂ O+CO ₂

Step 2: The iron solution is mixed with the polymer copolymer P (DMDAAC-AM)

Add the iron solution obtained in the first step into the P(DMDAAC-AM) solution and stir well to make the two evenly mixed. The mass ratio of P(DMDAAC-AM) to siderite is required to be 1:10～1: 50;

Step 3: The mixed solution of iron and P (DMDAAC-AM) reacts with hydrogen peroxide

In the mixed solution of the second step, add hydrogen peroxide, the concentration of hydrogen peroxide is 5-30wt%, the molar ratio of iron and pure hydrogen peroxide is required to be 2:(1-1.5), the reaction temperature is 50-100 ℃, and the reaction time is 1- 5h, after fully reacting, filtering, washing with deionized water, and drying to obtain iron phosphate dihydrate, the precursor of lithium iron phosphate. The chemical reaction formula is:

2Fe ²⁺ +4(H ₂ PO ₄ ) ^- +H ₂ O ₂ +2H ₂ O =2FePO ₄ ·2H ₂ O↓+2H ₃ PO ₄

The fourth step: the iron phosphate dihydrate prepared in the third step is mixed and sintered with lithium carbonate and glucose to obtain lithium iron phosphate with a tap density of 1.5-2g/ ^cm3 , iron phosphate dihydrate and lithium carbonate and glucose in terms of carbon. The mixing molar ratio is 2:(1-1.1):(0.5-0.8), the reaction is carried out in a protective atmosphere, the reaction temperature is 600-800°C, and the reaction time is 5-15h;

The chemical reaction formula is:

2FePO ₄ ·2H ₂ O↓+Li ₂ CO ₃ +0.5C=2LiFePO ₄ +1.5CO ₂ + 2H ₂ O.