CN101759174B - Process for reducing impacts on LixFeyPzO4 caused by impurity elements in ferrophosphorus - Google Patents

Abstract

The invention relates to a process for reducing the impacts on LixFeyPzO4 caused by impurity elements in ferrophosphorus, which belongs to the field of material chemical industry. The process comprises the following steps: firstly dissolving and filtering products of the ferrophosphorus and lithium salt under the oxidative atmosphere, then obtaining Li3PO4 filtrate and a Fe2O3 filter cake, carrying out concentration and granulation on the filtrate for obtaining high purity spherical Li3PO4, carrying out acid dissolution, filtration and reaction with phosphoric acid or phosphate on the filter cake, then controlling the temperature and the pH value for obtaining FePO4 precipitate, filtering, washing and drying for obtaining high purity FePO4, finally mixing the Li3PO4, the FePO4 and supplementary raw materials, then carrying out reaction under the non-oxidizing atmosphere for obtaining LixFeyPzO4. The method can reduce the impurity elements in the ferrophosphorus, simplify the control of oxygen content and improve the tap density of the product, and the ferrophosphorus can replace carbon.

Description

Reduce the ferrophosphorus impurity element to Li xFe yP zO 4The technology of influence

Technical field

The present invention relates to a kind of reduction ferrophosphorus impurity element to Li _xFe _yP _zO ₄The technology of influence can be applicable to purification and high performance electrode material Li in the ferrophosphorus recycle process _xFe _yP _zO ₄Low cost development.

Background technology

Li _xFe _yP _zO ₄Be the very potential new green power electrode materials of a class, mainly comprise LiFePO ₄, LiFe _2/3PO ₄And Li _4/7Fe _4/7P _8/7O ₄And mixture, the market space is wide.In these electrode materialss, LiFePO ₄Because its particular structure and performance receive much concern, but high preparation cost has hindered its large-scale application in power cell at present, and people reduce cost by all means one after another and improve performance.Yet, owing to limited by the bottleneck of operational path and raw material, business-like LiFePO on the market ₄Need carry out under the reductive atmosphere fully, preparation cost is higher, and output is not very big, still exists selling at exorbitant prices, raw materials cost height (to adopt the H of ferrous salts such as acetic acid or oxalic acid more ₂Reducing atmosphere), product performance instability, electronic conductivity are low by (about 10 ^-9～10 ^-10S/cm[Nature Mat.2, (2002) 123] and the low (about 1.3～1.5g/cm of tap density ³) deficiency that waits, restricted the fast development in its market.The Fe that raw material occurs in the reduction atmosphere of heating ₂P is on good terms and effectively improves LiFePO ₄Electroconductibility [Nature Mat.2, (2002) 123].Because the density of ferrophosphorus is than the height of carbon, Fe ₂P also can improve LiFePO ₄Tap density.Present commercialization Li _xFe _yP _zO ₄Preparation process in a subject matter still existing be: adopt the salt or the metal simple-substance that contain a kind of metal to make reactant; adopt unsettled ferrous salt as raw material; provide protective atmosphere with argon gas, nitrogen, hydrogen or C; relatively stricter to the oxygen quantitative limitation; do not utilize oxygen as reaction raw materials; specially add other yuan doping vario-property raising usually performance in addition, raw material and preparation cost are higher, and the tap density of material is low.

Ferrophosphorus is the intermetallic compound that phosphorus and iron reaction form, and proportion is bigger, wide material sources, and market value is not high, and is different according to the globule size price, about 5000 yuan/ton of present 800 purposes.The composition of ferrophosphorus generally has following several state: FeP, Fe according to different Rock Phosphate (72Min BPL) raw materials and processing condition and different, of a great variety ₂P, Fe ₃P and FeP ₂Deng, chemical property is stable under the normal temperature, and is stainless, nonmagnetic, about 1149 ℃ of fusing point.The ferrophosphorus aboundresources of China not only has a large amount of kakoxene to smelt preparation, and by-product is more in the production processes such as phosphorous chemical industry such as hot method phosphorus or fused(calcium magnesium)phosphate and silicate chemical industry, at present every year only phosphorous chemical industry by-product ferrophosphorus just have 300,000 tons approximately.The present Application Areas of ferrophosphorus is narrow, most of cheap outlet or purchased with crude product by commerce and trade department.Therefore, urgent need will be protected the ferrophosphorus resource of China now, promotes the value of ferrophosphorus.

In order to reduce Li _xFe _yP _zO ₄Preparation cost and expand the Application Areas of ferrophosphorus, we have taken the lead in proposing utilizing the abundant inexpensive ferrophosphorus in source to prepare the new approaches [Chinese patent CN101219783A] of electrode materials in the world, set forth and utilized ferrophosphorus preparation phosphorous simultaneously and the positive electrode material of elemental lithium and the method for negative material, carried out and utilized ferrophosphorus to prepare Li ₃PO ₄And Fe ₂O ₃The research of [Chinese patent 200910059920.X] and tertiary iron phosphate [Chinese patent 2009101677564] is at causing difficult the reaching of reaction raw materials proportioning to prepare Li by ferrophosphorus because ferrophosphorus is formed variation _xFe _yP _zO ₄Process in concrete technical problem such as batch mixing, precursor processing, temperature of reaction, reaction times, proposed to prepare Li by ferrophosphorus _xFe _yP _zO ₄Special implementing process [Chinese patent 2009101677579], with present preparation LiFePO ₄Process different fully, utilize ferrophosphorus and airborne oxygen to be raw material, can effectively reduce Li _xFe _yP _zO ₄Preparation cost.

The purity of ferrophosphorus and the composition of raw material and technology are closely related, in order to impel the phosphorus in the calcium phosphate to utilize fully, often add excessive a little SiO in the production of electric heating process phosphorus ₂React with C, except slag making, the iron that contains in the calcium phosphate can generate ferrophosphorus～1300 ℃ of reactions with the phosphorus that generates.Therefore, in the ferrophosphorus except principal element Fe and P, also contain Si, Mn, S, impurity elements such as C, these impurity elements are the reaction raw materials except Si and C, remaining all is that raw material is self-contained, and in slagging process, removed the impurity element of being with in the part material, so the impurity content in the ferrophosphorus except that Si and C is lower, the exemplary impurity element and the content of report and the discovery of our laboratory are as follows both at home and abroad: Si＜15.0%, Mn＜2.5%, C＜5.0%, S＜1.078%, Ti＜2.5%, Ni＜1.5%, V＜1.5%, Cr＜1.5%, Cu＜1.5%, Al＜1.5%, Ca＜1.5%.Be not difficult to find that except Si, Mn, C, Ti element, the content of other impurity element is all lower.These impurity elements may have influence on the chemical property of material, how to purify by methods such as mechanical treatment, zone melting, recrystallizations at present, need finish under the inert atmosphere of comparatively high temps, and technology is complicated, and the cost of removal of impurities is higher.

For this reason, in this application, based on the patent of our former first to file and new experimental result, utilize reaction process ferrophosphorus to be purified and precursor is carried out granulation, creationaryly proposed a kind of technological process of utilizing cascade filtration and reduce the impurity content in the ferrophosphorus and raw material carried out preparing Li after the granulation by simple filtering _xFe _yP _zO ₄Novel process.

Summary of the invention

The objective of the invention is to adopt liquid phase process that the impurity element in the ferrophosphorus is purified, reduce the Li of impurity element in the ferrophosphorus preparing in order to address the above problem _xFe _yP _zO ₄Influence, solve that the oxygen amount is difficult to the accurately difficult problem of control in the reaction process, creationaryly proposed a kind of technological process of utilizing cascade filtration and reduce the impurity content in the ferrophosphorus and raw material carried out preparing Li after the granulation _xFe _yP _zO ₄Novel process.

The application's basic design is: utilize the technological process of cascade filtration to reduce impurity content in the ferrophosphorus, at first with ferrophosphorus and contain the lithium material in oxidizing atmosphere fully reaction generate Li ₃PO ₄And Fe ₂O ₃, then product is dissolved, after filtering, obtain the higher Li of purity ₃PO ₄Filtrate and Fe ₂O ₃Filter residue obtains high pure spherical Li after concentrating filter liquor, the granulation ₃PO ₄Raw material, filter residue and a certain amount of acid-respons form iron salt solutions, obtain the higher molysite filtrate of purity after filtering, remove impurity element for the first time, will obtain FePO by controlled temperature and pH value behind molysite filtrate and phosphoric acid or the phosphate reaction ₄Precipitation obtains the higher FePO of purity after filtering ₄Filter cake is removed impurity element for the second time, to FePO ₄Filter cake washs, obtain high-purity FePO after the drying ₄Raw material is removed impurity element for the third time, at last with the high pure spherical Li that obtains ₃PO ₄Raw material, FePO ₄Under non-oxidizing atmosphere, react after raw material and the phosphorus source that replenishes or source of iron or the lithium source batch mixes and obtain Li _xFe _yP _zO ₄, it is characterized in that employed processing step is:

(1) be 1.0 with ferrophosphorus and lithium salts according to the mol ratio of phosphoric and elemental lithium: (1.1～4.0) carry out mix, and roasting formed intermediate product Li in 2～30 hours in 400～1000 ℃ oxidizing atmosphere then ₃PO ₄And Fe ₂O ₃

(2) product with step (1) dissolves, filters;

(3) filtrate with step (2) concentrates, forms after the granulation the higher Li of purity ₃PO ₄Raw material;

(4) filter residue with step (2) carries out forming iron salt solutions after the acidleach, removes by filter insoluble substance, removes the impurity element in the ferrophosphorus for the first time;

(5) the molysite filtrate with step (4) forms FePO with phosphoric acid that replenishes or phosphate reaction ₄Precipitation is filtered once more, obtains FePO ₄Filter cake and filtrate are removed the impurity element in the ferrophosphorus for the second time;

(6) with FePO ₄Filter cake washs, and removes the impurity element in the ferrophosphorus for the third time, obtains the higher FePO of purity ₄Raw material;

(7) mol ratio according to total phosphoric, total ferro element and total elemental lithium is 1.0: (0.2～5.0): the ratio of (0.2～1.5), after the product of step (3) and (6) and the source of iron of replenishing or phosphorus source or lithium source carried out mix, roasting is 0.2～30 hour under 400～900 ℃ non-oxidizing atmosphere, obtains Li _xFe _yP _zO ₄

Among the present invention, described additional source of iron or phosphorus source or lithium source not necessarily add in step (7) fully, can add in a certain technological process of reaction.

Among the present invention, described phosphoric acid or phosphoric acid salt can be by the oxidation products P of ferrophosphorus ₂O ₅With H ₂The O reaction obtains, and its concentration and amount are according to ferrophosphorus and Li _xFe _yP _zO ₄In the phosphorus amount and the pH value and the concentration of solution determine.

Among the present invention, described acidleach refers to mineral acids such as sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid dipping.

Among the present invention, described oxidizing atmosphere is the atmosphere that contains oxidizing substance, especially refers to air and oxygen.

Among the present invention, described non-oxidizing atmosphere is the atmosphere of oxygen-free voltinism material, especially refers to N ₂, Ar, H ₂, C, CO.

Among the present invention, described Li _xFe _yP _zO ₄In, 0＜x≤1.5,0.2≤y≤1.5,0.2≤z≤2.0 especially refer to LiFePO ₄, LiFe _2/3PO ₄, Li _4/7Fe _4/7P _8/7O ₄

Among the present invention, described lithium salts is from LiH ₂PO ₄, Li ₂HPO ₄, Li ₃PO ₄, Li ₂O, Li ₂O ₂, LiOH, Li ₂CO ₃, LiNO ₃, Lithium Acetate, tetra-sodium lithium.

Among the present invention, doped element, conductive agent can add at a certain process section of reaction.

The Li of the present invention's preparation _xFe _yP _zO ₄Electrode materials is not limited to LiFePO ₄, LiFe _2/3PO ₄, Li _4/7Fe _4/7P _8/7O ₄, ferro element wherein or phosphoric can be all from ferrophosphorus.

Among the present invention, pattern, degree of crystallinity and the size and the distribution thereof etc. of product be can control, also can ball milling or processing such as comminution by gas stream, modification be carried out to product as required by processing condition.

In order to reduce the ferrophosphorus impurity element to Li _xFe _yP _zO ₄Influence, physicochemical property and phosphatic different solubility thereof according to the different impurities element, make impurity element form precipitation or solution by control reaction temperature and pH value, also can or add complexing agent by electrolysis, redox reagent is removed the impurity element in the ferrophosphorus, the solution of intermediate product obtains the Li of higher degree through extraction, after filtering ₃PO ₄And FePO ₄Precursor, thus the impurity element in the reduction ferrophosphorus is to Li _xFe _yP _zO ₄Influence.

In order to improve Li _xFe _yP _zO ₄Tap density, obtain the precursor of special appearance, with Li ₃PO ₄Filtrate concentrates, granulation, thereby obtains the high-purity Li of size-controllable spherical ₃PO ₄Raw material.

Accurately control difficult problem in order to solve the oxygen amount, the present invention adopts fully reaction under the initial oxidation atmosphere, and the two-stage process route that reacts in non-oxidizing atmosphere has more well solved the oxygen amount and has been difficult to the accurately technical problem of control.In addition, described oxidizing atmosphere and non-oxidizing atmosphere realize that easily the former mainly refers to air and oxygen, and the latter mainly refers to N ₂, Ar, H ₂, C, CO.

The present invention compared with prior art, this technology utilization reaction process has solved in the ferrophosphorus impurity element to the Li of preparation _xFe _yP _zO ₄Influence, prepare Li by ferrophosphorus _xFe _yP _zO ₄The oxygen amount is difficult to accurately control and product Li in the process _xFe _yP _zO ₄The technical barrier that tap density is low adopts the simple process removal of impurities of cascade filtration, has the following advantages and the high-lighting effect: utilize reaction process to reduce in the ferrophosphorus impurity element to Li _xFe _yP _zO ₄Influence and precursor carried out granulation, earlier with ferrophosphorus and lithium salts abundant reaction generation Li under oxidizing atmosphere ₃PO ₄And Fe ₂O ₃Then product is dissolved, physicochemical property and oxide compound or phosphatic dissolubility difference according to impurity element, by filtering or adding certain complexing agent or precipitation agent or redox agent and remove ferrophosphorus impurities in raw materials element, gained solution is filtered obtain the higher Li of purity ₃PO ₄Filtrate and Fe ₂O ₃Filter residue is with Li ₃PO ₄Filtrate concentrates, obtain the spherical Li of the controlled high purity of particle diameter after the granulation ₃PO ₄, Fe ₂O ₃The mineral acid reaction of filter residue and a certain amount of non-phosphoric acid forms iron salt solutions, obtains the higher molysite filtrate of purity after filtering, removes impurity element for the first time, will obtain FePO by controlled temperature and pH value behind molysite filtrate and phosphoric acid or the phosphate reaction ₄Precipitation obtains the higher FePO of purity after filtering ₄Filter cake is removed impurity element for the second time, to FePO ₄Filter cake washs, obtain high-purity FePO after the drying ₄Raw material is removed impurity element for the third time, at last with the high pure spherical Li that obtains ₃PO ₄Raw material, FePO ₄Under non-oxidizing atmosphere, react after raw material and the phosphorus source that replenishes or source of iron or the lithium source batch mixes and obtain Li _xFe _yP _zO ₄By the spherical Li of high purity ₃PO ₄And FePO ₄Make spherical Li easily _xFe _yP _zO ₄Product, thus Li can be improved _xFe _yP _zO ₄Tap density; The reaction process uniqueness utilizes simple cascade filtration technology to effectively reduce the impurity content in the ferrophosphorus, thereby has reduced the impurity element in the ferrophosphorus to Li _xFe _yP _zO ₄The influence of product; Earlier ferrophosphorus and lithium salts are fully reacted generation Li under oxidizing atmosphere ₃PO ₄And Fe ₂O ₃, again with the Li of special appearance ₃PO ₄And FePO ₄React under non-oxidizing atmosphere with the phosphorus source that replenishes or source of iron or lithium source and to obtain Li _xFe _yP _zO ₄, utilize first complete oxidation, fully the two-stage process of nonoxidizing atmosphere has effectively solved by ferrophosphorus and prepares Li again _xFe _yP _zO ₄The oxygen amount is difficult to the accurately technical problem of control in the process, and the oxygen amount is easy to control, easily realizes industrialization; The phosphorus source or the source of iron of replenishing can be from the oxidation productss of ferrophosphorus; Can reduce the CO that generates by carbonaceous material with the carbonaceous material of ferrophosphorus replacement under non-oxidizing atmosphere ₂Discharging; By to reaction design and raw material combination, with by product CO ₂And H ₂The O recycle can realize the process for cleanly preparing of zero release; Requirement to equipment is lower, and production technique is simple, and reaction is operation easily, impurity element is removed easily, and the oxygen amount is controlled easily, and particle diameter and pattern are adjusted easily, production cost is low, and each processing step organically combines, and realizes self circulation, there is not waste liquid to discharge, less investment, profitable, easily realize industrialization, have good using value, be suitable for by the low-cost scale operation high-performance of ferrophosphorus Li _xFe _yP _zO ₄。

Description of drawings

Fig. 1 by ferrophosphorus through FePO ₄Precipitation preparation Li _xFe _yP _zO ₄A kind of process flow sheet.

Fig. 2 is by Fe ₂The LiFePO of P preparation ₄XRD figure.

Embodiment

The invention will be further described below in conjunction with embodiment and accompanying drawing; described content only is the basic explanation of the present invention under conceiving; but the present invention is not limited to following example, and any equivalent transformation according to technical scheme of the present invention is done all belongs to protection scope of the present invention.

Embodiment 1

With ferrophosphorus Fe ₂P and Quilonum Retard are feedstock production LiFePO ₄, with chloroazotic acid ferrophosphorus is dissolved laggard row element analysis, contain 67.7% Fe in the ferrophosphorus raw material, 18.9% P, 6.3% Si, 2.1% Mn, 1.3% Ti, 1.2% V, 1.2% C, all the other insoluble impurities content are 1.3%, according to calculating, the composition of ferrophosphorus is approximately Fe ₂P is because C burning-off in reaction process so real impurity element is Si, Mn, Ti, V and insoluble impurities, be it should be noted that: help improving LiFePO according to bibliographical information Si, Mn, Ti and V ₄The chemical property of positive electrode material, and impurity element Si, Mn, Ti and V in the real reaction process can be to LiFePO ₄Carry out the original position auto-doping.At this, might as well establish Si, Mn, Ti, V and insoluble impurities are the impurity elements that will remove in the ferrophosphorus, according to their physicochemical property and phosphatic different solubility, adopt reaction process as shown in Figure 1, be to carry out mix at 1: 3 by the mol ratio of phosphorus and lithium earlier with the Quilonum Retard of 4 moles ferrophosphorus and 6 moles, roasting 6～9 hours in 400～800 ℃ air behind the mixing, control by temperature, has only the reaction of ferrophosphorus and Quilonum Retard in the reaction, and Si, Mn, oxidizing reaction takes place in Ti and V, not with the Quilonum Retard reaction, after testing, insoluble impurities does not react, and the reaction that is taken place under the oxidizing atmosphere is as follows:

4Fe ₂P+6Li ₂CO ₃+11O ₂→4Li ₃PO ₄+4Fe ₂O ₃+6CO ₂

Si+O ₂→SiO ₂

Mn+O ₂→MnO ₂

Ti+O ₂→TiO ₂

4V+5O ₂→2V ₂O ₅

In order to realize cleaner production, with the by product CO that generates ₂After centrifugation, absorb in the feeding LiOH solution, after concentrated, crystallization, drying, make Li ₂CO ₃Raw material, the water condensation recovery back of evaporation is standby, following reaction takes place:

12LiOH+6CO ₂→6Li ₂CO ₃+6H ₂O

Element Li, Fe in the product of above-mentioned generation, the mol ratio of P are 3: 2: 1, in order to generate LiFePO ₄, need to replenish phosphorus source and source of iron.Oxidation products with ferrophosphorus is additional phosphorus source and source of iron, gets ferrophosphorus fully reaction in dry air of 2 moles again, and ferrophosphorus roasting in dry oxygen-containing atmosphere obtains Fe ₂O ₃, SiO ₂, MnO ₂, TiO ₂, V ₂O ₅, insoluble impurities solid and P ₂O ₅Gas is with ferrophosphorus oxidation products P ₂O ₅Gas feeds and obtains the additional phosphorus source of high purity phosphoric acid in the cold water.The product of roasting of above-mentioned ferrophosphorus and Quilonum Retard is shifted in the entry, after stirring, dissolving, filtering separation, obtain Li ₃PO ₄Filtrate and Fe ₂O ₃With SiO ₂, MnO ₂, TiO ₂, V ₂O ₅, insoluble impurities filter cake, with Li ₃PO ₄Filtrate concentrates, obtain after the granulation～the spherical Li of 50nm ₃PO ₄Raw material.Like this, after filtering, impurity element is transferred to Fe ₂O ₃In, with the oxidation products Fe of ferrophosphorus ₂O ₃, SiO ₂, MnO ₂, TiO ₂, V ₂O ₅, the Fe that obtains of insoluble impurities solid and filtration ₂O ₃, SiO ₂, MnO ₂, TiO ₂, V ₂O ₅, insoluble impurities filter cake and interpolation additional source of iron be dipped in fully reaction in the boiling hydrochloric acid because SiO ₂, TiO ₂With insoluble impurities not with hydrochloric acid reaction, so obtain containing the FeCl of Mn and V after filtering ₃Filtrate, and Si, Ti and insoluble impurities enter filter residue and remove, toward the FeCl that contains Mn and V ₃Drop in the filtrate and replenish phosphorus source (NH ₄) ₃PO ₄, obtain FePO by adjusting temperature and pH=5～6 ₄Precipitation obtains FePO after the filtration ₄Filter cake, and Mn and V enter filtrate, this filtrate is as ferrophosphorus oxidation products P ₂O ₅Absorption agent carry out recycle, with FePO ₄After filter cake repeatedly washs, can remove the impurity element of surface adsorption, thereby obtain highly purified FePO ₄Following reaction, take place in raw material:

P ₂O ₅+3H ₂O→2H ₃PO ₄

4Fe ₂O ₃+2Fe ₂O ₃+36HCl→12FeCl ₃+18H ₂O

12FeCl ₃+12(NH ₄) ₃PO ₄→12FePO ₄↓+36NH ₄Cl

Because FePO ₄Solubleness minimum when pH=5.5 makes generation FePO by control reaction temperature and pH value ₄Precipitation directly just can be removed Si, Mn, Ti, V impurity by filtering, washing, and obtains the higher FePO of purity ₄Raw material.Analyze Li according to corresponding standard ₃PO ₄Purity be 99.6%, FePO ₄Purity be 99.2%, wherein the content of Si, Mn, Ti, V reaches 0.3%, 0.1%, 0.1% and 0.1% respectively, can satisfy the requirement of cell-grade raw material.With gained Li ₃PO ₄And FePO ₄After precursor and source of iron ferric oxide that replenishes and the lithium source LiOH batch mixes of replenishing, content requirement according to carbon in the product, add certain carbon,, obtain LiFePO in roasting 18～21 hours in the anoxybiotic closed system at 400～900 ℃ again after 100～300 ℃ of oven dry ₄, the reaction of generation is as follows:

4Li ₃PO ₄+12FePO ₄+4LiOH+2Fe ₂O ₃+8C→16LiFePO ₄+8CO↑+2H ₂O

Organically each technological process is coupled together, the CO that generates is blasted reaction obtains CO in the warm air ₂, can make Li after in LiOH solution, absorbing ₂CO ₃Raw material, the water of filtering filtrate and washing can circulate and be used for ferrophosphorus oxidation products P ₂O ₅Absorption, recycle after forming phosphoric acid, do not have waste liquid to discharge, realize green cleaning procedure production.The LiFePO of preparation ₄Product is more loose, and peridotites crystal formation is preferably arranged, and as shown in Figure 2, particle diameter is less, reaches～60nm.

Embodiment 2

With ferrophosphorus FeP and lithium hydroxide is feedstock production LiFePO ₄Through ultimate analysis, contain 54.1% Fe in the ferrophosphorus raw material, 29.8% P, 7.3% Si, 2.1% Mn, 1.5% Ti, 1.5% V, 2.2% C, all the other insoluble impurities content are 1.5%, and according to calculating, the composition of ferrophosphorus is approximately FeP, because C burning-off in reaction process, and other impurity of 0.3% allows to exist in the cell-grade raw material, so real impurity element is Si, Mn, Ti, V and insoluble impurities, it should be noted that: help improving LiFePO according to bibliographical information Si, Mn, Ti and V ₄The chemical property of positive electrode material, and impurity element Si, Mn, Ti and V in the real reaction process can be to LiFePO ₄Carry out the original position auto-doping.At this, might as well establish Si, Mn, Ti, V and insoluble impurities is the impurity element that will remove in the ferrophosphorus, according to their physicochemical property and phosphatic different solubility, be to carry out mix at 1: 3 by the mol ratio of phosphorus and lithium earlier with the Quilonum Retard of 4 moles ferrophosphorus and 6 moles, roasting 6～9 hours in 400～800 ℃ air behind the mixing, control by temperature, has only the reaction of ferrophosphorus and Quilonum Retard in the reaction, and oxidizing reaction takes place in Si, Mn, Ti and V, with the Quilonum Retard reaction, the reaction that is taken place under the oxidizing atmosphere is not as follows:

2FeP+6LiOH+4O ₂→2Li ₃PO ₄+Fe ₂O ₃+3H ₂O

Si+O ₂→SiO ₂

Mn+O ₂→MnO ₂

Ti+O ₂→TiO ₂

4V+5O ₂→2V ₂O ₅

Except water, there is not deleterious by product to generate in the reaction process.

Element Li, Fe in the product of above-mentioned generation, the mol ratio of P are 3: 1: 1, in order to generate LiFePO ₄, need to replenish phosphorus source and source of iron.Oxidation products with ferrophosphorus is additional phosphorus source and source of iron, gets ferrophosphorus fully reaction in dry air of 2 moles again, and ferrophosphorus roasting in dry oxygen-containing atmosphere obtains Fe ₂O ₃, SiO ₂, MnO ₂, TiO ₂, V ₂O ₅, insoluble impurities solid and P ₂O ₅Gas is with ferrophosphorus oxidation products P ₂O ₅Gas feeds and obtains the additional phosphorus source of high purity phosphoric acid in the cold water.The product of roasting of above-mentioned ferrophosphorus and Quilonum Retard is shifted in the entry, after stirring, dissolving, filtering separation, obtain Li ₃PO ₄Filtrate and Fe ₂O ₃With SiO ₂, MnO ₂, TiO ₂, V ₂O ₅, insoluble impurities filter cake, with Li ₃PO ₄Filtrate concentrates, obtain after the granulation～the spherical Li of 50nm ₃PO ₄Raw material.Like this, after filtering, impurity element is transferred to Fe ₂O ₃In, with the oxidation products Fe of ferrophosphorus ₂O ₃, SiO ₂, MnO ₂, TiO ₂, V ₂O ₅, the Fe that obtains of insoluble impurities solid and filtration ₂O ₃, SiO ₂, MnO ₂, TiO ₂, V ₂O ₅, insoluble impurities filter cake and interpolation additional source of iron be dipped in fully reaction in the boiling sulfuric acid because SiO ₂, TiO ₂With insoluble impurities not with sulfuric acid reaction, so obtain containing the Fe of Mn and V after filtering ₂(SO ₄) ₃Filtrate, and Si, Ti and insoluble impurities enter filter residue and remove, toward the FeCl that contains Mn and V ₃Drop into above-mentioned gained H in the filtrate ₃PO ₄With additional NH ₄H ₂PO ₄In, by adjusting temperature and transferring pH=5～6 to obtain FePO with ammoniacal liquor ₄Precipitation obtains FePO after the filtration ₄Filter cake, and Mn and V enter filtrate, this filtrate is as ferrophosphorus oxidation products P ₂O ₅Absorption agent carry out recycle, with FePO ₄After filter cake repeatedly washs, can remove the impurity element of surface adsorption, thereby obtain highly purified FePO ₄Following reaction, take place in raw material:

2FeP+4O ₂→Fe ₂O ₃+P ₂O ₅

P ₂O ₅+3H ₂O→2H ₃PO ₄

Fe ₂O ₃+Fe ₂O ₃+6H ₂SO ₄→2Fe ₂(SO ₄) ₃+6H ₂O

2Fe ₂(SO) ₄) ₃+2H ₃PO ₄+2NH ₄H ₂PO ₄+10NH ₃→4FePO ₄↓+6(NH ₄) ₂SO ₄

Because FePO ₄Solubleness minimum when pH=5.5 makes generation FePO by control reaction temperature and pH value ₄Precipitation directly just can be removed Si, Mn, Ti, V impurity by filtering, washing, and obtains the higher FePO of purity ₄Raw material.Analyze Li according to corresponding standard ₃PO ₄Purity be 99.5%, FePO ₄Purity be 99.1%, wherein the content of Si, Mn, Ti, V reaches 0.4%, 0.1%, 0.1% and 0.1% respectively, can satisfy the requirement of cell-grade raw material.With gained Li ₃PO ₄And FePO ₄After precursor and the source of iron iron powder batch mixes of replenishing,, can add certain carbonaceous material,, obtain LiFePO in roasting 18～21 hours in the anoxybiotic closed system at 400～900 ℃ again after 100～300 ℃ of oven dry according to the content requirement of carbon in the product ₄, the reaction of generation is as follows:

2Li ₃PO ₄+4FePO ₄+2Fe→6LiFePO ₄

Organically each technological process is coupled together, the water of filtering filtrate and washing can circulate and be used for ferrophosphorus oxidation products P ₂O ₅Absorption, recycle after forming phosphoric acid, do not have waste liquid to discharge, realize green cleaning procedure production.The LiFePO of preparation ₄Product is more loose, and peridotites crystal formation is preferably arranged, and particle diameter is less, reaches～70nm.

Claims (4)

1. a reduction ferrophosphorus impurity element prepares Li _xFe _yP _zO ₄Technology, with to contain the lithium material be raw material, utilize reaction process to reduce the impurity element influence with ferrophosphorus, x, y, z are that different chemical is formed determined coefficient, 0＜x≤1.5,0.2≤y≤1.5,0.2＜z＜2.0 is characterized in that employed processing step is:

(1) be 1.0 with ferrophosphorus and lithium salts according to the mol ratio of phosphoric and elemental lithium: (1.1～4.0) carry out mix, and roasting formed intermediate product Li in 2～30 hours in 400～1000 ℃ oxidizing atmosphere then ₃PO ₄And Fe ₂O ₃, product is dissolved, filters;

(2) filtrate with step (1) concentrates, forms after the granulation the higher Li of purity ₃PO ₄Raw material;

(3) filter residue with step (1) carries out forming iron salt solutions after the acidleach, removes by filter insoluble substance, removes the impurity element in the ferrophosphorus for the first time;

(4) the molysite filtrate with step (3) forms FePO with phosphoric acid that replenishes or phosphate reaction ₄Precipitation is filtered once more, obtains FePO ₄Filter cake and filtrate are removed the impurity element in the ferrophosphorus for the second time;

(5) with FePO ₄Filter cake washs, and removes the impurity element in the ferrophosphorus for the third time, obtains the higher FePO of purity ₄Raw material;

(6) mol ratio according to total phosphoric, total ferro element and total elemental lithium is 1.0: (0.2～5.0): the ratio of (0.2～1.5), after the product of step (2) and (5) and the source of iron of replenishing or phosphorus source or lithium source carried out mix, roasting is 0.2～30 hour under 400～900 ℃ non-oxidizing atmosphere, obtains Li _xFe _yP _zO ₄

2. technology according to claim 1 is characterized in that: described oxidizing atmosphere refers to air and oxygen.

3. technology according to claim 1 is characterized in that: described non-oxidizing atmosphere refers to N ₂, Ar, H ₂, CO.

4. technology according to claim 1 is characterized in that: described additional phosphorus source or source of iron are from the oxidation products of ferrophosphorus.

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