CN101847711A - Porous carbon coated ferrous silicate lithium anode material and preparation method thereof - Google Patents

Abstract

The invention relates to a porous carbon coated ferrous silicate lithium anode material and a preparation method thereof. Polyethylene glycol is adopted as a pore forming agent, gel is formed by the hydrolytic condensation of tetraethoxysilane, and the polyethylene glycol is pyrolyzed to form continuous frames and penetrated macropore/mesoporous port channels in the calcining process of a precursor, wherein the average pore size of the macropore is within 0.5 to 3.9mu m, the average pore size of the mesopore is within 18 to 40nm, and the average porosity is within 57.2 to 71.9 percent. A three-dimensional network structure is formed by the hydrolytic condensation of the tetraethoxysilane, thereby reducing the migration distance in the crystal lattice recombination process and the activation energy required by migration, being beneficial to reducing the reaction temperature and shortening the reaction time and producing the product which has high phase purity and accords with the stoichiometric ratio. The porous structure increases the specific surface area of the material, not only is beneficial to the infiltration of electrolyte in particles, improves the deintercalation probability of lithium ions inside crystals and the utilization ratio of the lithium ions, but also prevents the crystal grains from growing in the calcining process and aggregating in the charging and discharging process and improves the electrochemical property of the anode material.

Description

Porous carbon coated ferrous silicate lithium anode material and preparation method

Technical field

The present invention relates to a kind of porous carbon coated ferrous silicate lithium anode material and preparation method, belong to the energy and material preparing technical field.

Background technology

Human demand to the energy rapidly increases, and the energy becomes the major issue that the countries in the world economic development runs into, and causes problem demanding prompt solutions such as energy crisis and environmental pollution thus.In energy development, it is significant to make full use of natural force such as wind energy, tidal energy, solar energy etc., because these energy effects is discontinuous, utilize these natural energies on a large scale, needs supporting with it energy storage device.Lithium ion battery is a kind of novel secondary cell, little, in light weight owing to its voltage height, capacity height, volume, have extended cycle life, advantages such as security performance is good, memory-less effect become the object that countries in the world fall over each other to develop.Li ₂FeSiO ₄Have advantages such as specific capacity higher (theoretical capacity is 166mAh/g), fail safe are good, nontoxic, cheap, aboundresources, be considered to have in the iron-based positive electrode anode material for lithium-ion batteries of development potentiality.

Orthosilicate Li ₂FeSiO ₄Have and low temperature li ₃PO ₄Similar structure belongs to rhombic system, and space group is Pmn2 ₁, wherein oxygen atom is arranged in the tightly packed mode of positive tetrahedron, and Fe and Si are in oxygen atom tetrahedron center separately.The Li of present report ₂FeSiO ₄The preparation method mainly contains: (1) high temperature solid-state method: people such as A.Nyten are raw material with lithium metasilicate, ferrous oxalate and tetraethoxysilane, after the abundant ground and mixed of C gel, at CO/CO ₂Air-flow (50: 50) is heated to 750 ℃ and be incubated the synthetic Li of 24h ₂FeSiO ₄Electrochemical results shows: at 60 ℃, and the C/16 multiplying power, under 2.0～3.7V voltage range condition, discharge capacity is stabilized in about 130mAh/g, has presented the favorable charge-discharge invertibity, and circulating, capability retention is 84% after 10 times.Chinese patent CN101582495A adopts microwave process for synthesizing to prepare anode material for lithium-ion batteries Li ₂FeSiO ₄, obtained Li ₂FeSiO ₄/ C composite positive pole, specific discharge capacity is respectively 119.6mAh/g and 103.7mAh/g under 10mA/g and 30mA/g.Japan Patent JP2001266882 (A) adopts FeO and Li ₂SiO ₃Be raw material, behind the ball milling 4h, calcine 4h down, obtain target product Li for 800 ℃ ₂FeSiO ₄But this method is because raw material is a mechanical mixture, needs calcining for a long time under the high temperature, causes the product granularity thicker, and particle size distribution range is wide, and dephasign is more, the electro-chemical activity deficiency.(2) hydrothermal synthesis method: people such as R.Dominko are with lithium hydroxide, and colloidal silica and Iron dichloride tetrahydrate are raw material, and lithium hydroxide and colloidal silica are dispersed in the solution of ferrous chloride, are transferred to then in the airtight autoclave of stainless steel, at N ₂In 150 ℃ of isothermal reaction 14d, then the green powder that obtains is used the distilled water cyclic washing under argon gas atmosphere under the atmosphere, dry 1d obtains Li under 50 ℃ again ₂FeSiO ₄Powder.C/30 multiplying power under the room temperature, 2.0～4.2V voltage range condition discharges and recharges, and reversible capacity is about 91mAh/g.The product chemical property that this method makes is relatively poor, and the reaction time is longer, and is unfavorable for the ion doping modification.(3) sol-gal process: it is 1: 1 the ironic citrate and mixture, lithium acetate and the colloidal state SiO of ferric nitrate that people such as R.Dominko propose with molar ratio ₂Be raw material, lithium acetate and iron (III) ion mixture are dissolved in water respectively after, the three mixed stirs 1h, preserve and make it form colloidal sol.With the colloidal sol that obtains more than 60 ℃ of dry 24h.Obtain Li through after grinding the powder that obtains being cooled to room temperature behind reaction 1h under 700 ℃ the inert atmosphere ₂FeSiO ₄At 60 ℃, under the condition of C/2 multiplying power the circulation 10 times after the reversible capacity conservation rate be 75%.The relevant patent of people such as Yang Yong application proposes: with lithium acetate, ferrous oxalate and tetraethoxysilane join in the 150ml ethanol, react 20h under 80 ℃ of oil bath conditions, transfer to 100 ℃ of oven dry in the evaporating dish.The mixture that obtains being transferred in the agate jar, added sucrose, is dispersant with acetone, ball milling 5h.After treating acetone volatilization, transfer in the porcelain boat in tube type resistance furnace at N ₂Under the protection, 650 ℃ of heat treatment 10h naturally cool to room temperature, promptly obtain Li ₂FeSiO ₄Composite material.In addition, Chinese patent CN101499527A at first prepares the ferrosilicon blend with the precipitation method, oven dry after washing, and then with Li source compound, the organic carbon source mixing and ball milling gets Li after the drying ₂FeSiO ₄Persursor material, low-temperature bake gets Li under protective atmosphere then ₂FeSiO ₄Positive electrode.This method inevitably with the soluble ion flush away in the ferrosilicon blend, causes the mismatch of stoichiometric proportion in washing process, thereby influences the chemical property of product.

The main cause that the restriction ferrosilicon silicate of lithium is done the positive electrode development is lower electronic conductivity of ferrous metasilicate lithium material itself and less lithium ion diffusion coefficient, have a strong impact on material charging and discharging currents density and specific capacity, limited the practical application of ferrosilicon silicate of lithium.Improving the ferrosilicon silicate of lithium conductivity method at present comprises: doping, surface carbon coating and refining grain size etc., these methods can both be improved the chemical property of ferrosilicon silicate of lithium to a certain extent.In addition, if ferrosilicon silicate of lithium is made porous material, loose structure has increased the specific area of material, not only help the infiltration of electrolyte in particle, increased solid-liquid contact interface area, that has improved the crystals lithium ion take off the embedding probability, also avoided crystal grain in calcination process grow up with charge and discharge process in gathering, thereby obviously improve the chemical property of positive electrode.

Summary of the invention

The present invention adopts polyethylene glycol as pore creating material, hydrolytic condensation by tetraethoxysilane forms gel, in the presoma calcination process, form the macroporous/mesoporous duct of continuous skeleton and perforation owing to the polyethylene glycol pyrolysis, the macropore average pore size is between 0.5～3.9 μ m, mesoporous average pore size is between 18～40nm, and mean porosities is between 57.2～71.9%.

The object of the present invention is to provide a kind of porous Li ₂FeSiO ₄/ C method for preparing anode material, according to the porous carbon coated ferrous silicate lithium powder of this method preparation, crystal grain has the macroporous/mesoporous duct of continuous skeleton and perforation.This structure has improved the porosity of material, increased the specific area of material, not only help the infiltration of electrolyte in particle, also avoided crystal grain in calcination process grow up with charge and discharge process in gathering, thereby improve the chemical property of positive electrode.

The present invention is realized by the following technical programs:

Porous carbon coated ferrous silicate lithium anode material of the present invention, form the continuous skeleton and the macroporous/mesoporous duct of perforation, the macropore average pore size is between 0.5～3.9 μ m, mesoporous average pore size is between 18～40nm, mean porosities is between 57.2～71.9%, calcining heat is lower in the building-up process, and 600 ℃ get final product down, and the product stoichiometric proportion is accurate.

The preparation method of porous carbon coated ferrous silicate lithium anode material of the present invention, step is as follows:

1) be raw material with acetate dihydrate lithium, ferrous acetate, tetraethoxysilane, take by weighing respective substance by the amount ratio, make Li: Fe: Si amount ratio is 2: 1: 1; With ethanol is solvent, and the concentration of tetraethoxysilane is 0.5～0.8mol/L; The additives polyethylene glycol pore creating material, acetic acid or ammonia-catalyzed agent, ascorbic acid are antioxidant, wherein reasonable 10%～30% of the ferrous lithium quality of synthetic silicic acid of discussing of polyethylene glycol, 3% of the ferrous lithium quality of antioxidant reasonable opinion synthetic silicic acid, catalyst is made into the aqueous solution of 0.1～0.3mol/L; Lithium salts, tetraethoxysilane and polyethylene glycol are dissolved in the ethanol, mix, add ferrous acetate and ascorbic acid to mixed liquor again, stirring and dissolving adds catalyst regulator solution system pH between 2～7;

2) mixed liquor with step 1) is transferred to reactor, reactor is put into insulating box react 12～20h down at 120～180 ℃, and the gel mixture that obtains obtains xerogel after 60～100 ℃ of oven dry in drying box;

3) with step 2) the xerogel porphyrize after be transferred in the tube furnace of temperature programmed control, under argon gas atmosphere with 10 ℃ of min ^-1Speed be warming up to 600～750 ℃ and constant temperature 7～10h, cool to room temperature with the furnace, obtain porous Li ₂FeSiO ₄/ C powder.

The invention has the advantages that the hydrolytic condensation by tetraethoxysilane forms three-dimensional net structure, various ions in the reactant are fixed in the network configuration, reached the mixing of molecular level, thereby distance and the necessary activation energy of migration that ion moves have been reduced when crystal lattice recombination, help reducing reaction temperature and shorten the reaction time, product phase purity height, meet the product of stoichiometric proportion.In addition, with polyethylene glycol as pore creating material, the crystal grain that forms has the macroporous/mesoporous duct of continuous skeleton and perforation, and can pass through the conditioned reaction substrate concentration, the distribution and the size of the addition control hole of pH and polyethylene glycol, this loose structure has increased the specific area of material, not only help the infiltration of electrolyte in particle, increased solid-liquid contact interface area, that has improved the crystals lithium ion takes off the embedding probability, improved the lithium ion utilance, help improving the specific capacity of material, also avoided crystal grain in calcination process grow up with charge and discharge process in gathering, thereby improve the chemical property of positive electrode.

Description of drawings

The Li that Fig. 1 embodiment one synthesizes ₂FeSiO ₄The XRD figure spectrum of/C;

The Li that Fig. 2 embodiment one synthesizes ₂FeSiO ₄The SEM figure of/C;

The Li that Fig. 3 embodiment one synthesizes ₂FeSiO ₄The charging and discharging curve of/C;

The Li that Fig. 4 embodiment one synthesizes ₂FeSiO ₄The cycle performance curve of/C.

Embodiment

Embodiment 1:

With lithium acetate, ferrous acetate, tetraethoxysilane is raw material, take by weighing respective substance by the amount of substance ratio, make Li: Fe: Si amount ratio is 2: 1: 1, accurately take by weighing the 1.640g lithium acetate, 1.8ml tetraethoxysilane and 0.399g polyethylene glycol, above-mentioned substance is dissolved in 13.3ml ethanol, makes that the concentration of tetraethoxysilane is 0.6mol/L.The gained solution system fully stirs 10min and mixes.Accurately take by weighing the 1.391g ferrous acetate, accurately take by weighing the 0.039g ascorbic acid, it is joined in the above-mentioned solution, stirring and dissolving is regulated pH value to 7 with the ammoniacal liquor of 0.3mol/L as catalyst.Mixed liquor is transferred to reactor, places insulating box to react 20h down at 120 ℃ reactor, the gel mixture that obtains obtains xerogel after 60 ℃ of oven dry in vacuum drying chamber.

At N ₂Under the atmosphere protection, above-mentioned ferrosilicon silicate of lithium presoma is calcined 10h down at 600 ℃, obtain the porous silicon ferrous silicate lithium powder that carbon coats.The about 3.9 μ m of macropore average pore size, and wider distribution, mesoporous average pore size is 30nm, mean porosities is 71.9%.Li ₂FeSiO ₄The XRD figure of/C is composed as shown in Figure 1, the characteristic peak of XRD and standard Li among the figure ₂FeSiO ₄The XRD figure spectrum diffraction maximum correspondence of powder shows that synthetic powder is Li ₂FeSiO ₄Li ₂FeSiO ₄SEM as shown in Figure 2, product has continuous skeleton and connects porous duct, the about 3.9 μ m of macropore average pore size.Under 60 ℃, the charging and discharging curve under the C/10 multiplying power as shown in Figure 3, the Li that is synthesized ₂FeSiO ₄/ C positive electrode first charge-discharge capacity is for being respectively 142.2mAh/g and 138.7mAh/g.The cycle performance curve as shown in Figure 4, Li ₂FeSiO ₄Capacity remains on 128.3mAh/g after the/C circulation 20 times, and it is less to decay.

Embodiment 2:

With lithium acetate, ferrous acetate, tetraethoxysilane is raw material, take by weighing respective substance by the amount of substance ratio, make Li: Fe: Si amount ratio is 2: 1: 1, accurately take by weighing the 1.640g lithium acetate, 1.8ml tetraethoxysilane and 0.129g polyethylene glycol, above-mentioned substance is dissolved in 10.0ml ethanol, makes that the concentration of tetraethoxysilane is 0.8mol/L.The gained solution system fully stirs 10min and mixes.Accurately take by weighing the 1.391g ferrous acetate, accurately take by weighing the 0.039g ascorbic acid, it is joined in the above-mentioned solution, stirring and dissolving is regulated pH value to 6 with the ammoniacal liquor of 0.2mol/L as catalyst.Mixed liquor is transferred to reactor, places insulating box to react 17h down at 140 ℃ reactor, the gel mixture that obtains obtains xerogel after 70 ℃ of oven dry in vacuum drying chamber.

At N ₂Under the atmosphere protection, above-mentioned ferrosilicon silicate of lithium presoma is calcined 9h down at 650 ℃, obtain the porous silicon ferrous silicate lithium powder that carbon coats.The about 0.5 μ m of macropore average pore size, and narrow distribution, mesoporous average pore size is 40nm, mean porosities is 57.2%.

Embodiment 3:

With lithium acetate, ferrous acetate, tetraethoxysilane is raw material, take by weighing respective substance by the amount of substance ratio, make Li: Fe: Si amount ratio is 2: 1: 1, accurately take by weighing the 1.640g lithium acetate, 1.8ml tetraethoxysilane and 0.399g polyethylene glycol, above-mentioned substance is dissolved in 16.0ml ethanol, makes that the concentration of tetraethoxysilane is 0.53mol/L.The gained solution system fully stirs 10min and mixes.Accurately take by weighing the 1.391g ferrous acetate, accurately take by weighing the 0.039g ascorbic acid, it is joined in the above-mentioned solution, stirring and dissolving is regulated pH value to 4 with the ammoniacal liquor of 0.3mol/L as catalyst.Mixed liquor is transferred to reactor, places insulating box to react 15h down at 160 ℃ reactor, the gel mixture that obtains obtains xerogel after 80 ℃ of oven dry in vacuum drying chamber.

At N ₂Under the atmosphere protection, above-mentioned ferrosilicon silicate of lithium presoma is calcined 8h down at 700 ℃, obtain the porous silicon ferrous silicate lithium powder that carbon coats.The about 3.4 μ m of macropore average pore size, mesoporous average pore size is 33nm, mean porosities is 68.5%.

Embodiment 4:

With lithium acetate, ferrous acetate, tetraethoxysilane is raw material, take by weighing respective substance by the amount of substance ratio, make Li: Fe: Si amount ratio is 2: 1: 1, accurately take by weighing the 1.640g lithium acetate, 1.8ml tetraethoxysilane and 0.258g polyethylene glycol, above-mentioned substance is dissolved in 11.4ml ethanol, makes that the concentration of tetraethoxysilane is 0.53mol/L.The gained solution system fully stirs 10min and mixes.Accurately take by weighing the 1.391g ferrous acetate, accurately take by weighing the 0.039g ascorbic acid, it is joined in the above-mentioned solution, stirring and dissolving is regulated pH value to 2 with the acetic acid of 0.1mol/L as catalyst.Mixed liquor is transferred to reactor, places insulating box to react 12h down at 180 ℃ reactor, the gel mixture that obtains obtains xerogel after 100 ℃ of oven dry in vacuum drying chamber.

At N ₂Under the atmosphere protection, above-mentioned ferrosilicon silicate of lithium presoma is calcined 7h down at 750 ℃, obtain the porous silicon ferrous silicate lithium powder that carbon coats.The about 2.0 μ m of macropore average pore size, mesoporous average pore size is 18nm, mean porosities is 63.4%.

Claims (2)

1. porous carbon coated ferrous silicate lithium anode material, it is characterized in that forming the macroporous/mesoporous duct of continuous skeleton and perforation, three-dimensional net structure, the macropore average pore size is between 0.5～3.9 μ m, mesoporous average pore size is between 18～40nm, and mean porosities is between 57.2～71.9%.

2. the preparation method of porous carbon coated ferrous silicate lithium anode material is characterized in that step is as follows:

1) be raw material with acetate dihydrate lithium, ferrous acetate, tetraethoxysilane, take by weighing respective substance by the amount ratio, make Li: Fe: Si amount ratio is 2: 1: 1; With ethanol is solvent, and the concentration of tetraethoxysilane is 0.5～0.8mol/L; The additives polyethylene glycol pore creating material, acetic acid or ammonia-catalyzed agent, ascorbic acid are antioxidant, wherein reasonable 10%～30% of the ferrous lithium quality of synthetic silicic acid of discussing of polyethylene glycol, 3% of the ferrous lithium quality of antioxidant reasonable opinion synthetic silicic acid, catalyst is made into the aqueous solution of 0.1～0.3mol/L; Lithium salts, tetraethoxysilane and polyethylene glycol are dissolved in the ethanol, mix, add ferrous acetate and ascorbic acid to mixed liquor again, stirring and dissolving adds catalyst regulator solution system pH between 2～7;

2) mixed liquor with step 1) is transferred to reactor, reactor is put into insulating box react 12～20h down at 120～180 ℃, and the gel mixture that obtains obtains xerogel after 60～100 ℃ of oven dry in drying box;

3) with step 2) the xerogel porphyrize after be transferred in the tube furnace of temperature programmed control, under argon gas atmosphere with 10 ℃ of min ^-1Speed be warming up to 600～750 ℃ and constant temperature 7～10h, cool to room temperature with the furnace, obtain porous Li ₂FeSiO ₄/ C powder.

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