CN101428782A - Coprecipitation process for producing lithium cell anode material of lithium iron phosphate - Google Patents

Abstract

The invention relates to a coprecipitation preparation method of phosphoric lithium iron for the positive material of a lithium battery, which is characterized in that the coprecipitation preparation method comprises the following steps: mixing and synthesizing a ferrous iron brine solution, a phosphor source aqueous solution, a lithium source aqueous solution and a manganese salt aqueous solution doped with metal according to the stoichiometric proportion into a coprecipitation precursor; and then baking the precursor for 8 to 36 hours under the protection of inert gas at the high temperature of 600 to 800 DEG C, so as to obtain doping-shaped phosphoric lithium iron.

Description

A kind of co-precipitation preparation method of lithium cell anode material of lithium iron phosphate

Technical field

The invention belongs to the new energy materials technical field, relate to a kind of method of utilizing co-precipitation and prepare lithium ion battery anode material lithium iron phosphate with the method for manganese ion doping modification.

Background technology

Reported first such as Goodenough in 1997 have the LiFePO of olivine-type structure ₄Can reversibly embed and the removal lithium embedded ion, consider that it is nontoxic, environmentally friendly, raw material sources abundant, high, the good cycle of specific storage, thinking to become the desirable positive electrode material of lithium ion battery.Having obtained the patent No. again up to this research group in 1999 is the patent right of US 591382 lithium cell anode material of lithium iron phosphate.Particularly report such as Chiang in 2002 is by since lithium position or iron position doped metal ion can 8 orders of magnitude of electronic conductivity raising with it, and its research is reached unprecedented temperature.

LiFePO ₄Have higher current potential and theoretical specific capacity, better cycle performance, environmental friendliness, but pure LiFePO ₄Ionic conductance and electron conductivity all lower, only be adapted at discharging and recharging under the low current density.So, how to improve LiFePO ₄Conductivity and to improve the travelling speed of lithium ion between material body and solid-liquid interface be the key that can such material practical application.

Improve LiFePO ₄The specific conductivity usual method is sample to be carried out carbon mix.Patent CN1 401559 heats certain hour after a certain proportion of P source compound, Fe source compound, Li source compound and carbon containing conductive agent ball milling are mixed under inert atmosphere, obtain the LiFePO of pure phase ₄Sample.Patent CN1775666A mixes the LiFePO that back employing microwave heating technique obtains carbon dope with a certain amount of Quilonum Retard, Ferrox and primary ammonium phosphate and conductive agent ₄Sample.Though the carbon method for coating can improve the conductivity between the material granule, powerless to the conductivity that improves intracell, cause the tap density of material to reduce and (in general only be 1.0-1.35g/cm ³), and then having reduced the volume of battery specific storage, this practicability for high power battery is disadvantageous.

CN1255888C disclose a kind of with phosphorus source, source of iron lithium source and doped metal ion under the solid phase ball milling condition, roasting obtains modification LiFePO ₄The method of sample.Metal ion mixing is a kind of approach of effectively regulating material electrochemical performance by the manufactured materials lattice imperfection, in the modification of various electrode materialss, be subjected to great attention, according to the materials chemistry principle, under the situation of basic material better performances, can further improve the performance of material by element substitution, the bulk phase-doped disordering degree that not only can improve lattice, the strongthener structural stability, and doping can cause defective usually, improve the electronic conductivity of material, thereby improving the charge-discharge performance of material, and don't influence other physical and chemical performance of material, is that a kind of ideal improves LiFePO ₄The mode of chemical property.

In the method for doped metal ion, Mn ²⁺Doping is more special a kind of.LiMnPO ₄With LiFePO ₄Belong to the Pnmb spacer together, has similar structure, and manganese and iron atom structural similitude, radius are approaching, meet the formation sosoloid condition of dissolving each other fully, CN1632970A discloses the preparation method of a kind of high-density spherical ferric lithium phosphate and iron manganese phosphate for lithium, this method is a raw material with ferrous sulfate, phosphorus source complexing agent and manganous sulfate, with ammonia soln control pH value, gets the higher sphere of density at last and mixes manganese iron lithium phosphate sample again.The little metal ion doping influences LiFePO hardly ₄Actual density, compare with doping carbon, more can improve the electrical property of material.

Summary of the invention

The purpose of this invention is to provide and a kind of lithium iron phosphate positive material is carried out the method for doping vario-property, make LiFePO 4 material under the prerequisite that does not reduce its tap density, obtain higher ionic conduction speed and bigger loading capacity.

The present invention is a kind of co-precipitation preparation method of lithium cell anode material of lithium iron phosphate; It is characterized in that:

Earlier the divalent iron salt aqueous solution, the phosphorus source aqueous solution, the lithium source aqueous solution and doping metals salt brine solution are synthesized the co-precipitation presoma according to stoichiometric ratio; Then with presoma under protection of inert gas, obtained the iron lithium phosphate sample of doping type in 8-36 hour through 600-800 ℃ of high-temperature roasting thermal treatment, electroconductibility is better, volume ratio is higher.

Described divalent iron salt is one or both in ferrous sulfate, the ferrous ammonium sulphate;

Described phosphorus source is one or more in primary ammonium phosphate, phosphoric acid and the Secondary ammonium phosphate;

Described lithium source is one or more in lithium hydroxide, monometallic and phosphoric acid hydrogen two lithiums;

Described doped metal ion is Mn ²⁺, the manganese salt of employing is manganous sulfate;

Its processing step comprises:

1. prepare the aqueous solution of lithium hydroxide, ferrous ammonium sulphate, phosphoric acid and manganous sulfate respectively;

2. with the aqueous solution of ferrous ammonium sulphate, phosphoric acid and manganous sulfate, make stoichiometric ratio (Fe+Mn): P=1:1, and Fe:Mn=4:1 (being mol ratio);

3. the lithium hydroxide Fe+Mn:P:Li=1:1:1.05 aqueous solution is slowly dropped in the above-mentioned mixing solutions (rate of addition 0.3ml/min) and guarantee constant temperature 30-50 ℃;

4. after reaction finishes precipitation left standstill, filters and with the continuous washing precipitation of deionized water until using BaCl ₂Can not detect the SO in the filtrate ₄ ^2-Till;

5. precipitation is placed tube type resistance furnace, and is placed with the reductive agent gac, under the purity nitrogen atmosphere protection, 100-250 ℃ dry 1-5 hour, 300-450 ℃ the insulation 6-10 hour, obtain presoma;

6. behind the furnace cooling, presoma taken out grinds and place once more in the tube type resistance furnace, under the purity nitrogen atmosphere 600-800 ℃ roasting 8-36 hour, furnace cooling is crossed 200 mesh sieves and is promptly got anode material for lithium-ion batteries LiFePO ₄

The invention has the beneficial effects as follows and adopt coprecipitation method to prepare LiFe _0.8Mn _0.2PO ₄Thereby, when improving product loading capacity (loading capacity first of product is 135.2mAh/g under the room temperature), guaranteed higher tap density (〉=1.5g/cm ³).The present invention adopts divalent iron salt as reaction raw materials, has avoided adopting reducing atmosphere in roasting process, makes reaction system more gentle, has also improved the practical value of this method simultaneously greatly.

Description of drawings

Fig. 1 obtains the XRD test curve of sample for preparation method of the present invention;

Fig. 2 obtains LiFePO for preparation method of the present invention ₄The SEM photo;

Fig. 3 obtains LiFe for preparation method of the present invention _0.8Mn _0.2PO ₄The SEM photo;

Fig. 4 obtains LiFePO for preparation method of the present invention ₄First charge-discharge curve at room temperature;

Fig. 5 obtains LiFe for preparation method of the present invention _0.8Mn _0.2PO ₄First charge-discharge curve at room temperature;

Embodiment

Embodiment 1,

With ferrous ammonium sulphate, phosphoric acid and manganous sulfate (Fe+Mn): P=1:1 (mol ratio), wherein Fe:Mn=4:1 is mixed with mixing solutions, and with lithium hydroxide source wiring solution-forming drop to obtain in the above-mentioned mixing solutions precipitation (Fe+Mn:P:Li=1:1:1.05), with washing of precipitate to using BaCl ₂Can not detect the SO in the filtrate ₄ ^2-Till, and (100-250 ℃ dry 1-5 hour, 300-450 ℃ insulation 6-10 hour) drying obtains presoma under nitrogen atmosphere protection; Presoma is ground, continue under nitrogen protection 600-800 ℃ and obtained LiFe in roasting 8-36 hour _0.8Mn _0.2PO ₄0.1C loading capacity 135.2mAh/g first under the sample room temperature that this method obtains, tap density is 1.72g/cm ³

Positive active material, conductive agent (acetylene black) and polyvinylidene difluoride (PVDF) (PVDF) caking agent are compared uniform mixing by the quality of 80:13:7, be dissolved in the solvent N-Methyl pyrrolidone (NMP), mix, vacuumize and remove the gas that mixes in the slurry, be evenly coated on the thick aluminium foil of 15 μ m, in 100 ℃ of down oven dry, under 15MPa pressure, roll, to be die-cut into diameter be that the disk of 20mm is as positive plate with justifying.In the middle of the preparation process, strict control batch mixing and coated weight, avoid of the influence of these factors test result.

Ready-made positive plate is placed vacuum drying oven, stay after more than 80 ℃ of following vacuum-drying 12h standby.With the metal lithium sheet is counter electrode, and diameter is 24mm, and thickness is 0.30mm, compares the consumption surplus of cathode of lithium with positive active material.Adopt that 20 μ m are thick, diameter is the 28mmCelgard barrier film.Electrolytic solution adopts 1mol/L LiPF ₆, the solvent mixed solution of NSC 11801 (EC) and dimethyl carbonate (DMC) (volume ratio 1:1).Be assembled into CR2430 type button cell at moisture in less than the 5ppm drying room, leave standstill behind the 12h to be tested.0.1C loading capacity 135.2mAh/g first under the sample room temperature that this method obtains, tap density is 1.56g/cm ³

Embodiment 2,

With ferrous sulfate, primary ammonium phosphate and manganous sulfate (Fe+Mn): P=1:1 (mol ratio), wherein Fe:Mn=4:1 is mixed with mixing solutions, and with the lithium hydroxide wiring solution-forming drop to obtain in the above-mentioned mixing solutions precipitation (Fe+Mn:P:Li=1:1:1.05), with washing of precipitate to using BaCl ₂Can not detect the SO in the filtrate ₄ ^2-Till, and (100-250 ℃ dry 1-5 hour, 300-450 ℃ insulation 6-10 hour) drying obtains presoma under nitrogen atmosphere protection; Presoma is ground, continue under nitrogen protection 600-800 ℃ and obtained LiFe in roasting 8-36 hour _0.8Mn _0.2PO ₄, the sample that (as follows embodiment 1) this method obtains, under the room temperature 0.1C first loading capacity be 128.6mAh/g, tap density is 1.52g/cm ³

Embodiment 3

With ferrous sulfate, Secondary ammonium phosphate and manganous sulfate (Fe+Mn): P=1:1 (mol ratio), wherein Fe:Mn=4:1 is mixed with mixing solutions, and with the lithium hydroxide wiring solution-forming drop to obtain in the above-mentioned mixing solutions precipitation (Fe+Mn:P:Li=1:1:1.05), with washing of precipitate to using BaCl ₂Can not detect the SO in the filtrate ₄ ^2-Till, and (100-250 ℃ dry 1-5 hour, 300-450 ℃ insulation 6-10 hour) drying obtains presoma under nitrogen atmosphere protection; Presoma is ground, continue under nitrogen protection 600-800 ℃ and obtained LiFe in roasting 8-36 hour _0.8Mn _0.2PO ₄, the sample that (as follows embodiment 1) this method obtains, under the room temperature 0.1C first loading capacity be 128.6mAh/g, tap density is 1.53g/cm ³

Comparative example 1

Ferrous sulfate and manganous sulfate Fe:Mn=4:1 (mol ratio) are mixed with mixing solutions, and with the monometallic wiring solution-forming drop to obtain in the above-mentioned mixing solutions precipitation (Fe+Mn:P:Li=1:1:1.05), with washing of precipitate to using BaCl ₂Can not detect the SO in the filtrate ₄ ^2-Till, and (100-250 ℃ dry 1-5 hour, 300-450 ℃ insulation 6-10 hour) drying obtains presoma under nitrogen atmosphere protection; Presoma is ground, continue under nitrogen protection 600-800 ℃ and obtained LiFe in roasting 8-36 hour _0.8Mn _0.2PO ₄, the sample that (as follows embodiment 1) this method obtains, under the room temperature first loading capacity be 121mAh/g, tap density is 1.36g/cm ³

Claims (1)

1, a kind of co-precipitation preparation method of lithium cell anode material of lithium iron phosphate; It is characterized in that:

Earlier the divalent iron salt aqueous solution, the phosphorus source aqueous solution, the lithium source aqueous solution and doping metals salt brine solution are synthesized the co-precipitation presoma according to stoichiometric ratio; Then with presoma under protection of inert gas, through 600-800 ℃ of iron lithium phosphate sample that obtained doping type in high-temperature roasting 8-36 hour;

Described divalent iron salt is one or both in ferrous sulfate, the ferrous ammonium sulphate;

Described phosphorus source is one or more in primary ammonium phosphate, phosphoric acid and the Secondary ammonium phosphate;

Described lithium source is one or more in lithium hydroxide, monometallic and phosphoric acid hydrogen two lithiums;

Described doped metal ion is Mn ²⁺, the manganese salt of employing is manganous sulfate;

Its processing step comprises:

1. prepare the aqueous solution of lithium hydroxide, ferrous ammonium sulphate, phosphoric acid and manganous sulfate respectively;

2. with the aqueous solution of ferrous ammonium sulphate, phosphoric acid and manganous sulfate, make the stoichiometric ratio mol ratio be [Fe+Mn]: P=1:1, and Fe:Mn=4:1;

3. with the lithium hydroxide Fe+Mn:P:Li=1:1:1.05 aqueous solution, slowly drop in the above-mentioned mixing solutions, and guarantee 30-50 ℃ of constant temperature with rate of addition 0.3ml/min;

4. after reaction finishes precipitation left standstill, filters and with the continuous washing precipitation of deionized water until using BaCl ₂Can not detect the SO in the filtrate ₄ ^2-Till;

5. precipitation is placed tube type resistance furnace, and is placed with the reductive agent gac, under the purity nitrogen atmosphere protection, 100-250 ℃ dry 1-5 hour, 300-450 ℃ the insulation 6-10 hour, obtain presoma;

6. behind the furnace cooling, presoma taken out grinds and place once more in the tube type resistance furnace, under the purity nitrogen atmosphere 600-800 ℃ roasting 8-36 hour, furnace cooling is crossed 200 mesh sieves and is promptly got anode material for lithium-ion batteries LiFePO ₄

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