WO2013056543A1

WO2013056543A1 - Complete cycle preparation method for producing lithium iron phosphate by using lithium ore as lithium source

Info

Publication number: WO2013056543A1
Application number: PCT/CN2012/074336
Authority: WO
Inventors: 王平; 黄春莲; 金鹏; 高宜宝
Original assignee: 四川天齐锂业股份有限公司
Priority date: 2011-10-20
Filing date: 2012-04-19
Publication date: 2013-04-25
Also published as: CN102311110B; CN102311110A

Abstract

The present invention relates to a complete cycle preparation method for producing lithium iron phosphate by using lithium ore as a lithium source, comprising: carrying out calcining, acidifying, leaching and purifying separation on lithium ore to obtain a primary lithium liquid, carrying out converting and refrigerating, filtering and washing, and evaporating and concentrating on the primary lithium liquid to obtain a lithium liquid for a synthesis reaction, letting the lithium liquid for the synthesis reaction, ferrite solution, and phosphor source solution be subject to a liquid phase synthesis reaction, and calcining the solution, to obtain carbon-coated lithium iron phosphate. According to the method of the present invention, steps such as cooling and crystallizing, separating, drying in the preparation of lithium salt solution with lithium ore as the lithium source are omitted, and byproducts obtained by evaporating and concentrating and filtering separation are recycled, so that the utilization rate of resources is increased, and the cost is saved; and the prepared lithium iron phosphate has characteristics such as high purity, excellent electrochemical performance and the like, and the recycling economy is achieved.

Description

Complete cycle preparation method for producing lithium iron phosphate by using lithium ore as lithium source

TECHNICAL FIELD The present invention relates to the field of lithium ion battery materials, and in particular to a complete cycle preparation method for producing lithium iron phosphate using lithium ore as a lithium source.

Background technique

Since 1994, Goodenough's research team has discovered lithium metal phosphate. In 1997, AkPadhi reported for the first time that olivine-type lithium iron phosphate has lithium removal function. Lithium iron phosphate has high specific capacity, long cycle life, safety, and raw material source. The advantages of richness, low cost and environmental friendliness have been extensively studied and become an ideal cathode material for the production of lithium ion batteries. In recent years, with the strong support of governments, the commercial application of lithium iron phosphate battery has been increasing.

Existing preparation methods of lithium iron phosphate include high temperature solid phase synthesis (for example, AK Padhi, KS Nanj u ndaswam y, JB Goodenough, Phospho- Olivi nes as Positive- Elect rode Materials for Rechargeable Lithi um Batteries, J. EIect rochem Soc. , 1 997, 1 44, 1 1 88- 1 1 94 ), low-temperature liquid phase synthesis method (such as CN03102665.6), liquid phase co-precipitation method, hydrothermal synthesis method, etc. Among them, in the high-temperature solid-phase production process, ferrous ions are easily oxidized, Fe ³⁺ is not easily reduced to Fe ²⁺ , and thus there are defects such as high resistance of lithium iron phosphate, poor consistency and stability of the product. Further, the starting material for preparing lithium iron phosphate used in these synthetic methods is usually a lithium salt. For example, CN200510132431.4 discloses a method for preparing a lithium-rich lithium iron phosphate powder, which is lithium carbonate, lithium oxalate, Lithium acetate or lithium nitrate is a lithium source; ZL200410017382.5 discloses a preparation method of a lithium ion battery positive electrode composite material containing lithium iron phosphate-carbon, which is lithium carbonate, lithium hydroxide, lithium oxalate, lithium acetate or lithium phosphate. Lithium source; CN200610136737.1 discloses a method for synthesizing nanometer lithium iron phosphate powder, using lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride or lithium dihydrogen phosphate as lithium source; CN200610035986.1 discloses high temperature A method for solid phase synthesis of lithium iron phosphate cathode material, using lithium carbonate, lithium fluoride, lithium acetate, lithium hydroxide or lithium nitrate as a lithium source. However, the production of lithium iron phosphate using lithium salt as a lithium source is very expensive, and requires independent lithium salt processing, purification, purification, circulation, storage, etc., and further processing of lithium salt and lithium iron phosphate production is required. The by-products in the process not only increase the production cost, but also the resource utilization rate is not high, and bring environmental pollution, and can not well integrate the production of lithium source for lithium production with the production of lithium iron phosphate, and make full use of it. The by-products in the production of lithium source from lithium ore and the by-products in the production of lithium iron phosphate are recycled in a complete set to realize a circular economy. At present, lithium for production at home and abroad, in addition to lithium in the salt lake, mainly extracts the lithium salt required from the pegmatite-type spodumene. Industrial processes for preparing lithium salts from lithium ores include: potassium sulfate method, lime method, sulfuric acid method, and soda ash hot leaching method. Lithium extraction from ore in China mainly uses lithium sulfate to prepare lithium salt from spodumene. The preparation process includes calcination, acidification, leaching, neutralization, conversion, evaporation, crystallization, filtration and the like. Moreover, in the prior art, limestone (CaC0 ₃ ) is used to adjust the pH value, so that a large amount of Ca ²⁺ plasma is generated in the neutralized slurry, and a Li ₂ C0 ₃ precipitate is partially formed to lose part of Li+. In addition, a large amount of by-products such as condensed water generated during the evaporation and concentration process are not comprehensively utilized, resulting in high production costs.

To this end, the art needs to find a more economical and effective method for preparing lithium iron phosphate, which can effectively reduce the production cost of lithium iron phosphate and ensure the excellent performance of the product.

Summary of the invention

The object of the present invention is to provide a complete cycle preparation method for producing lithium iron phosphate by using lithium ore as a lithium source. The complete cycle preparation method of the present invention does not require complicated lithium salt purification and purification treatment, and partially omits the sulfuric acid method. Preparing a step of cooling crystallization, separation, impurity removal, drying, etc. in the lithium salt; and circulating the condensed water by-product generated during the preparation of the lithium source for preparing the ferrous salt solution or the phosphorus source solution, and the lithium iron phosphate production Lithium by-products are recycled for the process of preparing lithium sources for lithium mines, turning waste products into treasures and realizing a circular economy, which is both cost-effective and environmentally friendly.

The technical solution of the present invention to solve the above problems: After the following steps:

(1) calcining, acidifying, leaching, purifying, and separating the lithium ore, and evaporating and concentrating the filtrate to obtain a primary lithium liquid;

(2) The primary lithium liquid is subjected to conversion freezing, filtration, washing, and the filtrate is concentrated by evaporation to obtain a lithium liquid for reaction; (3) liquid phase synthesis reaction is carried out by reacting lithium liquid with ferrous salt solution and phosphorus source solution. After lithium iron phosphate, it is filtered, washed, and no lithium ions are detected in the filter cake washing liquid. An appropriate amount of water is added to the filter cake, which is diluted into a slurry, and the sugar raw material is added to be calcined to obtain carbon-coated phosphoric acid. Ferrous lithium material;

Wherein, the condensed water cycle generated in the evaporation concentration process in the step (1) and the step (2) is used to prepare at least one of a phosphorus source solution and a ferrous salt solution; the filtrate and the filter cake in the collecting step (3) are washed. a liquid, that is, a solution containing a lithium salt or a recovered filtrate, which is returned to the leaching step of the step (1) and recycled;

The "conversion freezing" in the step (2) means that a sodium salt is added to the primary lithium liquid, Li ₂ S0 ₄ in the primary lithium liquid is reacted with the sodium salt, and another lithium salt and Na ₂ S0 _{4 are} produced, and the resulting The reaction solution was cooled, whereby the resulting sodium sulfate crystallized and separated by filtration.

In a preferred embodiment of the present invention, the lithium ore is selected from any one or a combination of spodumene, lithium aluminite, diaspore, lithium mica, and lithium feldspar. In a preferred embodiment of the present invention, the lithium content in the lithium liquid for reaction described in the step (2) is 25 to 27 g/L, preferably 26.2 g/L.

In a preferred embodiment of the present invention, the content of any one of Ca ²⁺ , Mg ²⁺ , Cl —, K ⁺ , Cu ²⁺ , and Pb ²⁺ in the lithium liquid for the reaction described in the step (2) is not high. At 0.01%.

In a preferred embodiment of the present invention, the Fe ²⁺ concentration in the ferrous salt solution is 54-59 g/L, preferably 55.8 g/L. In a preferred embodiment of the present invention, the P0 ₄ ³ degree of the phosphorus source solution is 680 to 800 g/L, preferably in the preferred embodiment of the present invention, the lithium solution, the ferrous salt solution, and the phosphorus involved in the liquid phase reaction. The volume ratio between the source solutions is 2.5 to 3.5: 3 to 4: 0.3 to 0.7, preferably a volume ratio of 3: 3.5: 0.5.

In a preferred embodiment of the present invention, in the step (3), the metal salt solution for doping is uniformly mixed with the lithium solution, the ferrous salt solution and the phosphorus source solution to carry out a liquid phase synthesis reaction.

In a preferred embodiment of the present invention, the metal salt solution for doping is selected from any one or a combination of metal salt solutions of Co, Ni, Al, Zr.

In a preferred embodiment of the present invention, the ferrous salt raw material for preparing the ferrous salt solution is selected from any one of ferrous bromide, ferrous chloride, ferrous sulfate, ferrous perchlorate, and ferrous nitrate. Its combination.

In a preferred embodiment of the present invention, the phosphorus source material for formulating the phosphorus source solution is selected from the group consisting of ammonium phosphate, phosphoric acid, lithium phosphate, ammonium dihydrogen phosphate, or a combination thereof.

Step (2) When the conversion is frozen, the sodium salt added to the primary lithium liquid is selected from any one of sodium carbonate, sodium hydroxide, sodium dihydrogen phosphate, sodium phosphate, sodium chloride, sodium oxalate, sodium nitrate or a combination thereof. ; preferably any one of sodium chloride, sodium hydroxide or a combination thereof. Accordingly, another lithium salt produced is any one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium phosphate, lithium chloride, lithium oxalate, lithium nitrate, or a combination thereof. In a preferred embodiment of the present invention, the sugar raw material of the step (3) is selected from the group consisting of sucrose, glucose, and lactose, or a combination thereof.

In a preferred embodiment of the present invention, the filtrate in the step (3) is a solution containing a lithium salt, and the solution containing the lithium salt is selected from the group consisting of a lithium sulfate solution, a lithium carbonate solution, a lithium hydroxide solution, a lithium dihydrogen phosphate solution, and a lithium phosphate. Any one of a solution, a lithium chloride solution, a lithium oxalate solution, a lithium nitrate solution, or a combination thereof.

In a preferred embodiment of the present invention, the preparation process of the primary lithium liquid includes the following steps:

A. After the lithium ore is calcined at 1100~1380 °C, acidification is carried out by adding sulfuric acid to the calcined lithium ore according to the acid ratio of 1:4~7 (w/w); For the ore meter, according to the liquid-solid ratio of 2-3:1 (w/w), add water or recover the filtrate in the acidification treatment solution, adjust the pH value to 5.7~6.2, let stand, filter, and obtain the mother liquor 1;

B, adjust the mother liquor 1 ρ Η 8.5~9.7, let stand, filter, get the mother liquor 2; C, adjusting the mother liquor 2 pH 10~10.8, standing, filtering, to get the mother liquor 3;

D, detecting the concentration of Ca ^{2+ in the} mother liquor 3, adding an equimolar amount of Na ₂ C0 ₃ , stirring, standing, filtering, to obtain a mother liquor 4;

E. Evaporate and concentrate the mother liquid 4 to a Li ⁺ concentration of 65 to 75 g/L, and filter to obtain a mother liquid 5, wherein the condensed water generated during the evaporation concentration process is used for formulating the ferrous salt solution and the phosphorus source solution. One or a combination thereof.

In a preferred embodiment of the present invention, the preparation process of the lithium liquid for reaction comprises the following steps:

a, detecting the concentration of S0 ₄ ² in the mother liquor 5, adding an appropriate amount of sodium salt, converting all of the S0 ₄ ² in the mother liquor 5 into Na ₂ S0 ₄ , stirring, cooling the crystal, filtering, and obtaining the mother liquor 6, wherein The sodium salt is selected from the group consisting of sodium carbonate, sodium chloride, sodium dihydrogen phosphate, sodium phosphate, sodium hydroxide, sodium oxalate, sodium nitrate or a combination thereof, preferably any of sodium chloride and sodium hydroxide. One or a combination thereof, preferably a cooling temperature of -15 ° C ~ 0 ° C;

b. Evaporating and concentrating the mother liquid 6 to a lithium content of 25-27 g/L, preferably having a lithium content of 26.2 g/L, to obtain a lithium solution for the reaction, wherein the condensed water generated during the evaporation concentration process is used. For formulating any one or a combination of a ferrous salt solution, a phosphorus source solution.

In a preferred embodiment of the present invention, the liquid phase synthesis condition is that a reaction solution is required to add a lithium solution, a ferrous salt solution, and a phosphorus source solution to the reaction vessel, and the temperature is raised to 150 to 220 ° C, and the temperature is maintained. After 220 to 720 minutes, after cooling, filter, take the filter cake, and set aside. At the same time, the collected filtrate is returned to the primary lithium liquid leaching step and recycled.

In a preferred embodiment of the present invention, the washing in the step (3) refers to washing to the filter cake washing liquid, no lithium ions are detected, the filter cake is taken, and the leaching step of returning the filtrate to the primary lithium liquid is performed. Recycling.

The "no lithium ion detected in the filter cake washing liquid" according to the present invention means that the lithium ion content in the filter cake washing liquid is not more than 0.01%.

In a preferred embodiment of the present invention, the amount of the sugar raw material added to the filter cake in the step (3) is 5 to 20% by weight, preferably 10% by weight, based on the solid content of the washed cake.

In a preferred embodiment of the present invention, the calcination in the step (3) is to uniformly knead the dried sugar material and the filter cake under the protection of a protective gas at 650 to 1000 ° C to obtain a carbon package. Covered lithium iron phosphate.

In a preferred embodiment of the present invention, the protective gas of the present invention is selected from any one or a combination of argon gas, nitrogen gas, and hydrogen gas.

In a preferred embodiment of the present invention, the preparation process of the mother liquor 1 comprises the following steps: calcining the lithium ore at 1100 to 1380 ° C for 50 to 300 minutes, cooling, grinding, in terms of lithium ore, according to an acid ratio of 1:4 ~7 (w/w) Adding sulfuric acid to the calcined lithium ore for acidification for 50-200 minutes; based on lithium ore, based on liquid to solid ratio of 2~3:1 (w/w) Add water or recover the filtrate, adjust the pH to 5.7~6.2, stir for 35~50 minutes, let stand, filter, and collect the filtrate to obtain the mother liquor 1.

In a preferred embodiment of the present invention, the calcination time under the protective action of the protective gas is 3 to 15 hours. In a preferred embodiment of the present invention, the substance for adjusting _P H is selected from any one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate or a combination thereof, preferably any one of sodium hydroxide and sodium carbonate or combination.

In a preferred embodiment of the present invention, the liquid phase synthesis reaction is carried out under a sealed condition to effectively prevent oxidation of Fe ²⁺ .

Another object of the present invention is to provide a carbon-coated lithium iron phosphate prepared by the cycle preparation method of the present invention.

In a preferred embodiment of the present invention, the carbon-coated lithium iron phosphate has a purity of not less than 99.97%, preferably

1C specific capacity is not lower than 141mAh/g, more preferably carbon-coated lithium iron phosphate in Ca ²⁺ , Mg ²⁺ , S04 ² - , CI-, Na ⁺ , K ⁺ , Cu ²⁺ , Pb ²⁺ One content is not more than 0.01%.

Another object of the present invention is to use the carbon-coated lithium iron phosphate produced by the present invention for the preparation of lithium ion battery materials, preferably for the preparation of lithium ion power battery materials.

In order to clearly illustrate the scope of protection of the present invention, the present invention is explained as follows: The "primary lithium liquid" as used in the present invention refers to a lithium solution prepared by preliminary purification and separation obtained from a lithium ore. The "reaction lithium liquid" described in the present invention is also referred to as "reaction-reactive lithium liquid" and "reaction-grade lithium liquid", and refers to a lithium solution directly used for participating in a liquid phase synthesis reaction.

The "recycled filtrate" in the present invention refers to the filtrate collected during the liquid phase synthesis of lithium iron phosphate, or the washing filtrate collected during the washing process of the lithium iron phosphate filter cake, and the collected "recycled filtrate" can be returned to the primary lithium. The liquid leaching step is recycled.

The "smooth raw material and the filter cake uniformly mixed and dried" according to the present invention means that an appropriate amount of water is added to the washed lithium iron phosphate filter cake, and the mixture is diluted into a slurry, and then the filter cake solid content is added to 5~ 20 wt.% of the sugar raw material, uniformly mixed, and dried to obtain a uniform dry mixture, wherein preferably, the sugar raw material is added in an amount of 10 wt.%.

The "solution containing lithium salt" as used in the present invention refers to a lithium salt solution formed during the production of lithium iron phosphate, wherein the lithium salt solution is selected from the group consisting of lithium sulfate solution, lithium carbonate solution, lithium hydroxide solution, and phosphoric acid. Any one or a combination of a lithium dihydrogen solution, a lithium phosphate solution, a lithium chloride solution, a lithium oxalate solution, or a lithium nitrate solution.

The "conversion freezing" described in the step (2) of the present invention means that a sodium salt is added to the primary lithium liquid to react Li ₂ SO ₄ in the primary lithium liquid with the sodium salt to produce another lithium salt and Na ₂ S0. ₄ , the resulting reaction solution is cooled, so that the formed sodium sulfate crystallizes and is separated and removed by filtration to obtain a lithium-containing mother liquid (ie, mother liquid 6), wherein The sodium salt is selected from the group consisting of sodium carbonate, sodium hydroxide, sodium dihydrogen phosphate, sodium phosphate, sodium chloride, sodium oxalate, sodium nitrate or a combination thereof, preferably sodium chloride or sodium hydroxide. Any one or a combination thereof; the other lithium salt includes any one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium phosphate, lithium chloride, lithium oxalate, lithium nitrate, or a combination thereof.

The percentages stated herein are by weight unless otherwise indicated.

The invention uses other pH adjusting substances (such as any one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate or a combination thereof) instead of CaC0 ₃ to avoid carrying a large amount of Ca ²⁺ in the reaction system. The grading and adjusting the pH value for the static precipitation can effectively remove Ca ²⁺ , Mg ²⁺ , S04 ² - and the like.

In the present invention, impurities such as Ca ²⁺ and Mg ²⁺ in the solution are precipitated by sodium carbonate, and are thoroughly filtered and removed to obtain a lithium solution for reaction.

The invention controls the lithium ion concentration and the impurity content in the lithium solution for reaction, and according to the preparation composition of the lithium iron phosphate, the lithium ion concentration in the lithium solution for reaction and the concentration of the phosphoric acid solution participating in the liquid phase synthesis reaction The organically matching between the concentrations of the ferrous solution can effectively reduce the production cost increased by the purification, refining and evaporation concentration in the process of preparing the lithium solution for the reaction using the lithium ore as a lithium source.

Compared with the prior art, the complete cycle preparation method for producing lithium iron phosphate using lithium ore as a lithium source has the following advantages:

1. The cycle complete process of the present invention can control the lithium ion concentration or its impurity content in the lithium solution for reaction according to the preparation composition of lithium iron phosphate, partially omitting the cooling crystallization, separation and drying of the lithium salt preparation process by the sulfuric acid method. The process, and shortening the evaporation concentration time of the mother liquor, saving the marketing cost of the lithium salt, reducing the difficulty of purifying and purifying the lithium salt, and significantly reducing the production cost;

2. The by-products in the complete cycle process (condensed water from evaporation concentration, lithium-containing solution by-products from liquid phase synthesis, etc.) are recycled, omitting the recycling process of by-products, reducing or even avoiding wastewater discharge, saving wastewater Processing costs, significantly improving resource utilization, significantly reducing production costs, while achieving a circular economy;

3. The invention uses other pH adjusting substances (such as any one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate or a combination thereof) instead of CaC0 ₃ to avoid carrying a large amount of Ca ² in the reaction system. ⁺ , and adopting graded pH adjustment for graded static precipitation, which can effectively remove Ca ²⁺ , Mg ²⁺ , S04 ² -, etc.;

4. The present invention preliminarily removes impurities such as Ca ²⁺ and Mg ²⁺ in a solution by using sodium carbonate to obtain a lithium solution for reaction;

5. This cycle complete process removes and controls Ca ²⁺ , Mg ²⁺ , S04 ² - , Cl- in lithium iron phosphate. The content of impurities such as Na+, K+, Cu ²⁺ and Pb ²⁺ has the advantages of high purity, excellent electrochemical performance, stability and good consistency, and the 1C discharge capacity can reach 140 mAh/g or more;

6. The complete cycle process of the invention can save the comprehensive cost of lithium iron phosphate up to 12,000 yuan / ton. DRAWINGS

Fig. 1 is a schematic diagram of a complete cycle preparation process for producing lithium iron phosphate from lithium ore as a lithium source.

Fig. 2 Detailed process flow diagram of a complete cycle preparation process for producing lithium iron phosphate from lithium ore as a lithium source.

Fig. 3 X-ray diffraction pattern of the lithium iron phosphate-carbon composite positive electrode material prepared in Example 2. detailed description

The technical solution of the present invention specifically goes through the following steps:

(2) The primary lithium liquid is subjected to conversion freezing, filtration, washing, and the filtrate is concentrated by evaporation to obtain a lithium liquid for reaction;

(3) The liquid lithium reaction solution is reacted with a ferrous salt solution and a phosphorus source solution to obtain lithium iron phosphate, which is filtered, washed, and no lithium ions are detected in the filter cake washing liquid, and added to the filter cake. Appropriate amount of water, dilute it into a slurry, add sugar raw materials, calcined, that is, carbon-coated lithium iron phosphate material;

In a preferred embodiment of the present invention, the lithium ore is selected from any one or a combination of spodumene, lithium aluminite, diaspore, lithium mica, and lithium feldspar.

In a preferred embodiment of the present invention, the lithium content in the lithium liquid for reaction described in the step (2) is 25 to 27 g/L, preferably 26.2 g/L. In a preferred embodiment of the present invention, the content of any one of Ca ²⁺ , Mg ²⁺ , Cl —, K ⁺ , Cu ²⁺ , and Pb ²⁺ in the lithium liquid for the reaction described in the step (2) is not high. At 0.01%.

In a preferred embodiment of the present invention, the Fe ²⁺ concentration in the ferrous salt solution is 54-59 g/L, preferably 55.8 g/L. Preferred aspect of the present invention, the phosphorous source solution P0 ₄ ³ agricultural degree 680~800g / L, preferably of 719.2g / L.

In a preferred embodiment of the present invention, the volume ratio between the lithium solution, the ferrous salt solution, and the phosphorus source solution participating in the liquid phase reaction is 2.5 to 3.5: 3 to 4: 0.3 to 0.7, preferably the volume ratio is 3: 3.5: 0.5.

Step (2) When the conversion is frozen, the sodium salt added to the primary lithium liquid is selected from any one of sodium carbonate, sodium hydroxide, sodium dihydrogen phosphate, sodium phosphate, sodium chloride, sodium oxalate, sodium nitrate or a combination thereof. ; preferably any one of sodium chloride, sodium hydroxide or a combination thereof. Accordingly, another lithium salt produced is any one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium phosphate, lithium chloride, lithium oxalate, lithium nitrate, or a combination thereof. In a preferred embodiment of the invention, the sugar material is selected from the group consisting of sucrose, glucose, lactose or a combination thereof.

B, adjust the mother liquor 1 ρ Η 8.5~9.7, let stand, filter, get the mother liquor 2;

C, adjusting the mother liquor 2 pH 10~10.8, standing, filtering, to get the mother liquor 3;

D, detecting the concentration of Ca ^{2+ in the} mother liquor 3, adding an equimolar amount of Na ₂ C0 ₃ , stirring, standing, filtering, to obtain a mother liquor 4; E. Evaporate and concentrate the mother liquid 4 to a Li ⁺ concentration of 65 to 75 g/L, and filter to obtain a mother liquid 5, wherein the condensed water generated during the evaporation concentration process is used for formulating the ferrous salt solution and the phosphorus source solution. One or a combination thereof.

In a preferred embodiment of the present invention, the preparation process of the mother liquor 1 comprises the following steps: calcining the lithium ore at 1100 to 1380 ° C for 50 to 300 minutes, cooling, grinding, in terms of lithium ore, according to an acid ratio of 1:4 ~7 (w/w) Adding sulfuric acid to the calcined lithium ore for acidification for 50-200 minutes; in terms of lithium ore, according to the liquid-solid ratio of 2~3:1 (w/w), adding water or recovering the filtrate, adjusting The pH is adjusted to 5.7 to 6.2, stirred for 35 to 50 minutes, allowed to stand, filtered, and the filtrate is collected to obtain a mother liquor 1. In a preferred embodiment of the present invention, the calcination time under the protective action of the protective gas is 3 to 15 hours. In a preferred embodiment of the present invention, the substance for adjusting _P H is selected from any one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate or a combination thereof, preferably any one of sodium hydroxide and sodium carbonate or combination.

In a preferred embodiment of the present invention, the carbon-coated lithium iron phosphate has a purity of not less than 99.97%, preferably a 1C specific capacity of not less than 141 mAh/g, more preferably a carbon-coated lithium iron phosphate in Ca ^{2 . The content of +} , Mg ²⁺ , S04 ² - , CI—, Na ⁺ , K ⁺ , Cu ²⁺ , and Pb ^{2+ is} not more than 0.01%.

The "conversion freezing" described in the step (2) of the present invention means that a sodium salt is added to the primary lithium liquid to react Li ₂ SO ₄ in the primary lithium liquid with the sodium salt to produce another lithium salt and Na ₂ S0. ₄ , the resulting reaction solution is cooled, so that the formed sodium sulfate crystallizes and is separated and removed by filtration to obtain a lithium-containing mother liquor (ie, mother liquor 6), wherein the sodium salt is selected from the group consisting of sodium carbonate, sodium hydroxide, Any one or a combination of sodium dihydrogen phosphate, sodium phosphate, sodium chloride, sodium oxalate, sodium nitrate, or a combination thereof, preferably any one of sodium chloride and sodium hydroxide, or a combination thereof; Salt It includes any one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium phosphate, lithium chloride, lithium oxalate, and lithium nitrate, or a combination thereof.

The percentages stated herein are by weight unless otherwise indicated.

The method for detecting the purity of lithium iron phosphate according to the present invention is a combination of an X-ray diffraction analysis method and a chemical composition analysis method, wherein the X-ray diffraction analysis method is extracted from the instrument information network "XRD powder X-ray analysis method", http:// www.instrument.com.cn/download/DownLoadFile.asp? id=1673 48&huodong=3; The chemical analysis method of ferrous citrate is extracted from China Standard Quality Network.

Http://hi.baidu.com/795007/blog/item/018fbcd3132e5531970al6ac.html) o

The method for determining the specific capacity (mAh/g) of the present invention and the detection methods of Ca ²⁺ , Mg ²⁺ , Cl — , Na ⁺ , K ⁺ , Cu ²⁺ , Pb ^{2+ ,} etc. are extracted from the 863 Modernization of the Ministry of Science and Technology. The "Technical Specifications for Testing Key Materials for Lithium-Ion Power Battery" issued by the Transportation Technology Office on March 31, 2010,

Http:〃 doc.mbalib.com/view/2679ed041 aa01 e1 ad4401643428c6f43. html ).

Among them, the 1C specific capacity is determined as follows:

Cathode material: Conductive agent (SP): PVDF ( HSV900 ) = 83: 10: 7; Negative electrode: Metal Li; Electrolyte: l . lM LiPF6, EC: DEC: DMC = 1: 1: 1; Separator: Celgard 2325 Button battery (2430).

At 25 °C ± 2 °C, the half-cell is charged to the charge cut-off voltage (3.9V) with a constant current of 1C, then discharged to a discharge cut-off voltage (2.0V) with a constant current of 1C, and cycled three times. The specific capacity of the positive electrode material was calculated from the average of the three discharge capacities. Five samples of the half-cell were tested in parallel, and after the abnormal value was removed, the average value was taken.

C=C average discharge /[(M electrode -M aluminum foil) *0·83]

Where C: specific capacity of the positive electrode material mAh/g; C average discharge: average value of three discharge capacities of the half cell mAh; M electrode: mass of the positive electrode sheet g; M aluminum foil: mass of the aluminum foil g.

The invention uses other pH adjusting substances (such as any one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate or a combination thereof) instead of CaC0 ₃ to avoid carrying a large amount of Ca ²⁺ in the reaction system. The grading and adjusting the pH value for the static precipitation can effectively remove Ca ²⁺ , Mg ² S04 ² - and the like.

The invention controls the lithium ion concentration and the impurity content in the lithium solution for reaction, and according to the preparation composition of the lithium iron phosphate, the lithium ion concentration in the lithium solution for reaction and the concentration of the phosphoric acid solution participating in the liquid phase synthesis reaction The organically matching between the concentrations of the ferrous solution can effectively reduce the production cost increased by the purification, refining and evaporation concentration in the process of preparing the lithium solution for the reaction using the lithium ore as a lithium source. The invention adopts lithium ore as a lithium source for the complete cycle preparation method for producing lithium iron phosphate, and does not need to carry out complicated refining and purification treatment of the prepared lithium liquid, and partially omits the cooling crystallization in the lithium salt prepared by the sulfuric acid method. , separation, impurity removal, drying, etc., and shortening the evaporation concentration time of the mother liquor, saving the marketing cost of lithium salt, and circulating the condensed water by-product generated during the preparation of the lithium source for preparing the ferrous salt solution or phosphorus The source solution, the lithium-containing by-product in the production of lithium iron phosphate, is recycled to the lithium source for the preparation of a lithium source. Therefore, the recycling process of the invention has the advantages of short process flow, low energy consumption, high comprehensive benefit, and realization of circular economy, etc., not only can greatly reduce production cost, improve resource utilization rate, realize circular economy, and according to phosphoric acid The preparation composition of iron lithium is required to control the concentration of lithium ions in the lithium solution for reaction or the content of impurities thereof, and the lithium ion concentration in the lithium solution for reaction is made between the concentration of the lithium ion solution in the liquid phase synthesis reaction and the concentration of the ferrous solution. Organically matched, and the obtained lithium iron phosphate has the advantages of high purity, excellent electrochemical performance, stability, and good consistency, and the 1C discharge capacity can reach 140 mAh/g or more.

The present invention will be specifically described with reference to the embodiments, which are merely illustrative of the technical solutions of the present invention and are not intended to limit the scope of the invention.

Example 1 Preparation of lithium iron phosphate

(1) Weigh 50kg of spodumene, calcined at 110CTC for 50 minutes, cool, grind, add 7.1kg of sulfuric acid

(acid ratio 1:7) After 50 minutes of treatment, the spodumene powder added with sulfuric acid was poured into 114 kg (liquid-solid ratio 2:1) water under stirring, and the pH was adjusted to 5.7 with NaOH, and stirred for 35 minutes. Allow to stand, filter, and get mother liquor 1;

(2) Adjust the mother liquor Ι Η to 8.5 with NaOH, stir the reaction for 5 minutes, let stand, filter, and obtain the mother liquor 2; then adjust the pH of the mother liquor 2 to 10.8 with NaOH, stir the reaction for 5 minutes, let stand, filter, and obtain 3 mother liquor; 3 was added in the mother liquor 236.6 g Na ₂ C0 _3, the reaction stirred for 30 minutes, allowed to stand and filtered to give 4 mother liquor;

(3) Evaporating and concentrating the mother liquid 4 to a lithium content of 65 g/L, allowing to stand and filtering to obtain a mother liquor 5, wherein the condensed water obtained by evaporation and concentration is used to prepare a ferrous salt solution or a phosphorus source solution;

(4) Add 5.46 kg of NaOH to the mother liquor 5, stir, cool to -15-0 ° C, crystallize, and filter to obtain mother liquor.

6;

(5) evaporating and concentrating the mother liquid 6, to a lithium content of 25.34 g/L, to obtain a lithium solution for reaction, wherein the condensed water obtained by evaporation and concentration is used for preparing a ferrous salt solution or a phosphorus source solution;

(6) Weigh 5531.0 g of 62.0% ferrous chloride, add water, and prepare it into a ferrous salt solution of 36 liters (Fe ²⁺ concentration: 58.3 g / L);

(7) Weigh 14071.6 g of 98.0% ammonium phosphate trihydrate, add water, and prepare it into a phosphorus source solution 5 liters (P0 ₄ ³ - concentration: 685.9 g / L); (8) Measure 3 liters of lithium solution, 3.5 liters of ferrous salt solution and 0.5 liter of phosphorus source solution, add to the reactor under stirring, continue stirring, heat to 150 ° C, heat for 720 minutes, cool, and then filter , the filter cake is obtained, and the filtrate is collected, and the collected filtrate is returned to the step (1) for recycling;

(9) washing the filter cake twice, until no lithium ions are detected in the filter cake washing liquid, and the filter cake is obtained, and the filtrate is collected, and the collected filtrate is returned to the step (1) for recycling; an appropriate amount of water is added to the filter cake. Diluted into a slurry, and then added 27.5 g of sucrose (5%), uniformly mixed, and dried to obtain a uniform dry mixture of the sugar raw material and the filter cake;

(10) Under the protection of argon, the uniformly mixed dried sugar material and the filter cake were calcined at 65 CTC for 12 hours to obtain carbon-coated lithium iron phosphate.

According to the measuring method of the present invention, the carbon-coated lithium iron phosphate obtained by the preparation of Example 1 was found to have a purity of 99.99%, a specific capacity (mAh/g) of 141 mAh/g, and Ca ²⁺ , The content of any one of Mg ²⁺ , S04 ² - , Cl—, Na+, K ⁺ , Cu ²⁺ , and Pb ^{2+ is} not more than 0.01%.

Lithium raw material cost required to produce 1 ton of carbon-coated lithium iron phosphate from different lithium sources

Explanation: The expression in Table 1 is absent, "+" indicates an increase in cost, and the "lithium raw material cost" is the cost of obtaining the lithium liquid for reaction from the lithium source described in Table 1.

It can be seen from Table 1 that the invention has a very significant cost advantage for preparing lithium iron phosphate by using lithium ore as a lithium source, compared with a method for preparing carbon-coated lithium iron phosphate using a lithium salt as a lithium source, and The comprehensive cost can save more than RMB 12,000/ton.

Example 2 Preparation of lithium iron phosphate

(1) Weigh 50kg of lithium phosphite, calcined at 138CTC for 300 minutes, cool, grind, add 12.5kg of sulfuric acid (according to acid ratio 1:4) for 200 minutes, under stirring, add acid Spodum pumice powder poured into 187.5kg The filtrate was recovered (liquid-solid ratio 3:1), the pH was adjusted to 6.2 with NaOH, stirred for 50 minutes, allowed to stand, and filtered to obtain mother liquor 1;

(2) Adjust the mother liquor Ι Η value to 9.7 with NaOH, stir the reaction for 12 minutes, let stand, filter, and obtain the mother liquor 2; then adjust the pH of the mother liquor 2 to 10 with NaOH, stir the reaction for 12 minutes, let stand, filter, and obtain 3 mother liquor; 3 was added in the mother liquor 240.5 g Na ₂ C0 _3, the reaction stirred for 10 minutes, allowed to stand and filtered to give 4 mother liquor;

(3) Evaporating and concentrating the mother liquid 4 to a lithium content of 75 g/L, allowing to stand and filtering to obtain a mother liquid 5, wherein the condensed water obtained by evaporation and concentration is used for preparing a ferrous salt solution or a phosphorus source solution;

(4) Add 5.45kg NaOH to the mother liquor 5, stir, cool to 0 ° C, crystallize, filter, to get the mother liquor 6;

(5) evaporating and concentrating the mother liquid 6, to a lithium content of 26.95 g/L, to obtain a lithium solution for reaction, wherein the condensed water obtained by evaporation and concentration is used for preparing a ferrous salt solution or a phosphorus source solution;

(6) Weigh 3568.6 g of 98.3% ferrous sulfate salt, add water, and prepare it into 35 liters of ferrous solution (Fe ²⁺ concentration is 54.8 g / L);

(7) Weigh 4825.3 g of 85.3% phosphoric acid, add water, and prepare it into 5 liters of phosphorus source solution (P0 ₄ ³ - concentration 798.0 g / L);

(8) Measure 3 liters of lithium solution, 3.5 liters of ferrous salt solution and 0.5 liter of phosphorus source solution, add it to the reaction kettle under stirring, continue stirring, heat to 220 ° C, heat for 220 minutes, after cooling , standing, filtering, obtaining a filter cake, returning the collected filtrate to the leaching step of step (1), and recycling;

(9) washing the filter cake 5 times until the lithium ion is not detected in the filter cake washing liquid, obtaining a filter cake, returning the collected filtrate to the leaching step of the step (1), and recycling; adding an appropriate amount of water to the filter cake, Dilute it into a slurry, add 110 g of glucose (20%), mix well, and dry to obtain a uniform mixture of the sugar material and the filter cake;

(10) Under the protection of nitrogen, the uniformly mixed dried sugar material and the filter cake were calcined at 65 CTC for 3 hours to obtain a carbon-coated lithium iron phosphate product, and the X-ray diffraction spectrum thereof is shown in Fig. 3.

According to the measuring method of the present invention, the carbon-coated lithium iron phosphate prepared in Example 2 has a purity of 99.98%, a specific capacity (mAh/g) of 140 mAh/g, and lithium iron phosphate. The content of any of Ca ²⁺ , Mg ²⁺ , S04 ² — , CI—, Na ⁺ , K ⁺ , Cu ²⁺ , and Pb ^{2+ is} not more than 0.01%.

Example 3-9 Preparation of lithium iron phosphate

The preparation process of Examples 3-9 was the same as that of Example 1, and the required preparation materials and process parameters are shown in Table 2. At the same time, the lithium ore is firstly prepared according to the sulfuric acid method, and then deionized water is added to prepare a lithium solution having a concentration of 25-27 g/L, and the remaining steps of preparing lithium iron phosphate are the same. (6) to (10) of Example 1, but without recycling the preparation method of the recovered filtrate and condensed water" as a comparative example, and the comparative example and the phosphorus obtained by the preparation of Examples 3-9 The production costs of lithium iron hydride are compared, and the results are shown in Table 2.

Table 2 Preparation materials and process parameters of Examples 3-9

It can be seen from Table 2 that the purity of the lithium iron phosphate prepared in Examples 3-9 is not less than 99.97 %, and the lithium iron phosphate is Ca ²⁺ , Mg ² S04 ² — , CI, according to the measurement method of the present invention. - The content of any of Na ⁺ , K + , Cu ²⁺ , and Pb ^{2+ is} not more than 0.01%, and the specific capacity of 1C is 140 mAh/g or more.

In summary, the lithium iron phosphate prepared by the complete cycle process of the invention has the advantages of high purity, excellent electrochemical performance, good stability and consistency.

And, in comparison with the comparative example (that is, the lithium ore is purified and dried to the corresponding lithium salt according to the sulfuric acid method, deionized water is added, and the lithium salt is prepared into a lithium solution having a concentration of 25-27 g/L, and the remaining preparation steps are carried out simultaneously. Compared with the preparation method of (6)-(10) of Example 1, but not recycling the recovered filtrate and the condensed water, the complete cycle process of the present invention can control the lithium in the lithium solution for reaction according to the preparation of lithium iron phosphate. The ion concentration or its impurity content partially omits the processes of cooling crystallization, separation and drying of the lithium salt preparation process by sulfuric acid method, shortens the evaporation concentration time of the mother liquor, saves the marketing cost of lithium salt, and reduces the purification and purification of lithium salt. Miscellaneous difficulty, significantly reducing production costs; At the same time, recycling condensed water and recovering filtrate, reducing the cost of preparing deionized or distilled water, saving the recovery cost of the filtrate, especially the treatment cost of wastewater in the filtrate, the overall cost Can save more than 12,000 yuan / ton.

Claims

Claim

1. A complete cycle preparation method for producing lithium iron phosphate by using lithium ore as a lithium source, comprising the following steps:

(2) The primary lithium liquid is subjected to conversion freezing, filtration, washing, and the filtrate is concentrated by evaporation to obtain a lithium liquid for reaction; (3) liquid phase synthesis reaction is carried out by reacting lithium liquid with ferrous salt solution and phosphorus source solution. After lithium iron phosphate, it is filtered and washed. No lithium ions are detected in the filter cake washing liquid. An appropriate amount of water is added to the filter cake in the filter cake, which is diluted into a slurry, added to the sugar material, dried, and calcined. a carbon coated lithium iron phosphate material;

The "conversion freezing" in the step (2) means that a sodium salt is added to the primary lithium liquid, Li ₂ S0 ₄ in the primary lithium liquid is reacted with the sodium salt, another lithium salt and Na ₂ S0 _{4 are} produced, and the solution is cooled. The resulting sodium sulfate crystallized and was removed by solid-liquid separation.

2. The preparation method according to claim 1, wherein: the lithium ore is selected from the group consisting of spodumene, lithium phosphite, lycopene, lithium mica, and lithium feldspar. Kind or a combination thereof.

The preparation method according to claim 1 or 2, wherein: the lithium content in the lithium liquid for the reaction according to the step (2) is 25 to 27 g/L, preferably 26.2 g/L; The concentration of Fe ^{2+ in the} iron salt solution is 54-59 g/L, preferably 55.8 g/L; the concentration of P0 ₄ ³ in the phosphorus source solution is 680-780 g/L, preferably 719.2 g/L; The volume ratio between the reacted lithium solution, the ferrous salt solution, and the phosphorus source solution is 2.5 to 3.5: 3-4: 0.3-0.7, preferably a volume ratio of 3: 3.5: 0.5.

The preparation method according to any one of claims 1 to 3, wherein the glycogen according to the step (3) is selected from any one of sucrose, glucose, lactose or a combination thereof.

The preparation method according to claim 4, wherein the sugar raw material is added in an amount of 5 to 20% by weight, preferably 10% by weight, based on the solid content of the washed cake.

The preparation method according to any one of claims 1 to 5, wherein: in the step (2), the sodium salt added to the primary lithium liquid is selected from the group consisting of sodium carbonate, sodium chloride, and sodium dihydrogen phosphate. Any one or a combination of sodium phosphate, sodium hydroxide, sodium oxalate or sodium nitrate; preferably any one of sodium chloride and sodium hydroxide or a combination thereof.

The preparation method according to any one of claims 1 to 6, wherein the filtrate in the step (3) is a solution containing a lithium salt, and the solution containing the lithium salt is selected from a lithium sulfate solution and a lithium carbonate. Any one of a solution, a lithium hydroxide solution, a lithium dihydrogen phosphate solution, a lithium phosphate solution, a lithium chloride solution, a lithium oxalate solution, or a lithium nitrate solution Kind or a combination thereof.

The preparation method according to any one of claims 1 to 7, wherein the ferrous component of the ferrous salt solution prepared in the step (3) is selected from the group consisting of ferrous bromide, ferrous chloride and sulfuric acid. Any one or a combination of ferrous iron, ferrous perchlorate, and ferrous nitrate; the phosphorus source material for formulating the phosphorus source solution is selected from any one of ammonium phosphate, phosphoric acid, lithium phosphate, ammonium dihydrogen phosphate or combination.

The preparation method according to any one of claims 1 to 8, characterized in that the preparation process of the primary lithium liquid is carried out as follows:

A. After the lithium ore is calcined at 1100-138CTC, acidification is carried out by adding sulfuric acid to the calcined lithium ore in a ratio of acid to w/w ratio of 1:4 to 7; Calculate, according to the ratio of liquid to solid ratio w / w of 2 ~ 3: 1 in the acidification treatment solution to add water or recover the filtrate, adjust the pH to 5.7 ~ 6.2, let stand, filter, to get the mother liquor 1;

B, adjusting the pH of the mother liquor 1 is 8.5~9.7, standing, filtering, to obtain the mother liquor 2;

C, adjusting the pH of the mother liquor 2 is 10~10.8, standing, filtering, to obtain the mother liquor 3;

D. Detecting the concentration of Ca ^{2+ in the} mother liquor 3, adding an equimolar amount of Na ₂ C0 ₃ , stirring, standing, filtering, to obtain a mother liquor 4; E, evaporating the concentrated mother liquor 4, to a Li ⁺ concentration of 65-75 g/L , filtering, obtaining a mother liquor 5, wherein the condensed water produced during the evaporation concentration process is used to prepare any one of a ferrous salt solution, a phosphorus source solution, or a combination thereof;

The filtrate recovered in the step A is the filtrate or the filter cake washing liquid in the step (3).

The preparation method according to claim 9, wherein the preparation method of the mother liquid 1 comprises the following steps: calcining the lithium ore at 1100 to 1380 ° C for 50 to 300 minutes, cooling, grinding, and measuring with lithium ore According to the acid ratio w/wl: 4~7, the sulfuric acid is added to the calcined lithium ore for acidification for 50-200 minutes; based on the lithium ore, the liquid-solid ratio w/w is 2~3: 1 with water or recycled The filtrate was adjusted to a pH of 5.7 to 6.2, stirred for 35 to 50 minutes, allowed to stand, filtered, and the filtrate was collected to obtain a mother liquor 1.

The preparation method according to claim 9 or 10, wherein the pH is adjusted to use any one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate or a combination thereof, preferably sodium hydroxide or sodium carbonate. Any one or a combination thereof.

12. The preparation method according to claim 9, wherein the preparation process of the lithium liquid for the reaction is carried out by the following steps:

a, detecting the concentration of S0 ₄ ² in the mother liquor 5, adding the sodium salt, converting all of the S0 ₄ ² in the mother liquor 5 into Na ₂ S0 ₄ , stirring, cooling, crystallization, filtering, to obtain the mother liquor 6, wherein The sodium salt is selected from the group consisting of sodium carbonate, sodium chloride, sodium dihydrogen phosphate, sodium phosphate, sodium hydroxide, sodium oxalate, sodium nitrate, or both, preferably sodium chloride, hydrogen and oxygen. Any one or a combination of sodium, preferably a cooling temperature of -15 ° C ~ 0 ° C;

b, evaporating and concentrating the mother liquid 6, to a lithium content of 25~27 g/L, preferably having a lithium content of 26.2 g/L, to obtain a lithium solution for reaction;

The condensed water produced during the evaporation concentration process is used to prepare any one or combination of a ferrous salt solution and a phosphorus source solution.

The preparation method according to any one of claims 1 to 12, wherein the liquid phase synthesis condition in the step (3) is: a reaction solution for a lithium solution, a ferrous salt solution, The phosphorus source solution is added to the reaction vessel, heated to 150~220 ° C, and kept for 220 to 720 minutes. After cooling, it is filtered, and the filter cake is taken for calcination reaction; the filtrate is collected, and the filtrate is returned to the leaching step of the step (1). Recycled.

The preparation method according to any one of claims 1 to 13, wherein: the calcination is carried out under the protection of a protective gas, and the sugar raw material and the filter cake are calcined at 650 to 1000 ° C. The dried product is uniformly mixed to obtain carbon-coated lithium iron phosphate; preferably, the protective gas is selected from any one of argon gas, nitrogen gas, and hydrogen gas or a combination thereof.

The preparation method according to claim 14, wherein the calcination time under the protection of a protective gas is 4 to 15 hours.

The production method according to any one of claims 1 to 15, wherein the liquid phase synthesis reaction in the step (3) is carried out under a sealed condition.

The preparation method according to any one of claims 1 to 16, wherein in step (3), a metal salt solution for doping is added, and a metal salt solution for doping and a lithium solution are used. And performing the liquid phase synthesis reaction together with the ferrous salt solution and the phosphorus source solution, wherein the metal salt solution for doping is selected from any one of a metal salt solution of Co, Ni, Al, Zr or a combination thereof .

A carbon-coated lithium iron phosphate prepared by the production method according to any one of claims 1 to 17.

The lithium iron phosphate according to claim 18, wherein the lithium iron phosphate has a purity of not less than 99.97%; preferably, the lithium iron phosphate has a 1C specific capacity of not less than 141 mAh/g; more preferably phosphoric acid The content of Ca ²⁺ , Mg ²⁺ , S04 ² -, CI—, Na ⁺ , K ⁺ , Cu ²⁺ , and Pb ^{2+ in} lithium ferrous iron is not more than 0.01%.

20. Use of carbon-coated lithium iron phosphate according to claim 18 or 19 for the preparation of lithium ion battery materials; preferably carbon coated lithium iron phosphate for use in the preparation of lithium ion power battery materials.