Vanadium, titanium ion codope LiFePO 4 material and preparation method thereof
Technical field
The present invention relates to the lithium ion battery material field, particularly relate to LiFePO 4 material of a kind of vanadium, titanium ion codope and preparation method thereof.This material can be used for lithium ion battery, at used for electric vehicle high power capacity, high power battery potential using value is arranged.
Background technology
Lithium ion battery have voltage height, specific capacity high, discharge and recharge that life-span length, memory-less effect, environmental pollution are few, the advantage such as quick charge, self-discharge rate are low.At present, lithium ion battery progressively moves towards the electric powered motor field by mobile phone, notebook computer, digital camera and the used battery of portable small-sized electrical equipment and submarine, space flight, the used battery of aviation field.Face at human society in the situation of more and more severeer energy and environment problem, lithium ion battery is as desirable environmental protection power supply, and it is more wide that application prospect becomes.Positive electrode is an important component part of lithium ion battery, in the lithium ion charge and discharge process, not only to be provided in the positive and negative lithium intercalation compound the needed lithium of back and forth embedding/take off, form the needed lithium of SEI film but also will bear the negative material surface, therefore, research and develop the key point that high performance positive electrode has become the lithium ion battery development.
1997, J. B. Goodnough developed a kind of LiFePO4 (LiFePO with regular olivine crystal structure
4) positive electrode.As a kind of polyanion phosphate, LiFePO
4P-O key bond energy very strong, Li-O key bond energy then relatively a little less than, the polyanion (PO of regular arrangement
4 3-) given material and taking off/embedding lithium process in the stability of crystal structure.Studies show that, take off lithium fully in electrochemistry and form and LiFePO
4Belong to the FePO of rhombic system
4The time, lattice a, the b direction of principal axis shrinks respectively 5% and 3.6%, c-axis direction elongation 2%, the distortion of lattice volume is less, and about 6.6%.Stable olivine structural is so that LiFePO
4Have the following advantages:
(3.4V is with respect to Li for higher theoretical specific capacity (170mAh/g) and operating voltage
+/ Li); 2. good cycle performance and security performance; 3. World Iron aboundresources, inexpensive and nontoxic, LiFePO
4Be considered to a kind of environmentally friendly positive electrode.
Yet, LiFePO
4Congenital lower electronic conductivity and ionic conduction speed have greatly limited its practical application in the lithium-ion-power cell field.In order to overcome the above shortcoming of LiFePO4, researchers both domestic and external have carried out a large amount of research work to it.It mainly contains: 1. conductive doped dose, such as conductive carbon, conducting metal particles and conducting metal oxide etc., in order to the surface of improving lithium iron phosphate particles and the conductance between the particle; 2. the particle diameter of controlling material try one's best little shorten the LiFePO4 body mutually in the evolving path of lithium ion, thereby improve its ionic conduction speed; 3. foreign cation improves its ionic conduction speed or electronic conductivity; 4. the chemical property that the anion that mixes improves LiFePO4 is multiplying power discharging property especially.
At present, to the research report titanium doped, that vanadium mixes and few.Studies show that the Doped with Titanium ion Li-O key bond distance of can effectively extending in LiFePO4 improves Li
+Taking off in lattice/embedding speed helps the further optimization [Electrochim. Acta, 78 (2012) 576] of material high rate performance and specific capacity.Simultaneously, the LiFePO 4 material of Doped with Titanium ion has good p-type semiconduction, electron transfer rate is so that material still can keep excellent chemical property [J. Electrochem. Soc., 153 (2006) A25] under high power charging-discharging faster.Chinese invention patent CN102013489A utilizes TiO exactly
2As the titanium source, obtained the lithium iron phosphate cathode material that a kind of Titanium mixes, show that by result's contrast the LiFePO 4 material of doping metals titanium is that capacity, multiplying power or cycle performance have all obtained improving greatly.The vanadium ion doping is mainly reflected in the effect of LiFePO 4 material chemical property: low concentration doping can form has the active V of high conduction
2O
3And VO
2Nanocrystal; When doping content can generate the Li with electro-chemical activity when critical concentration is above
3V
2(PO4)
3Phase, and promotion coats degree of graphitization [J. Phys. Chem. C, 115 (2011) 13520 of carbon-coating; J. Electrochem. Soc., 158 (2011) A26; J.Power Sources, 196 (2011) 5623; ].China national patent of invention [CN102447096A; CN102299303A; CN102306769A] show that the LiFePO 4 material cycle performance of doping suitable concn vanadium ion is good, the granule-morphology of material and particle diameter distribute and also are improved effect simultaneously.
Although above method has all improved the chemical property of LiFePO4 aspect to a great extent, following existing problems are arranged still:
Although 1, titanium doped high rate performance that can the Effective Raise LiFePO4, the increase of titanium ion also can form impurity such as the LiTi with low electro-chemical activity
2(PO
4)
3And Ti
2P
2O
7, and then affect specific energy and the specific power of battery, still can not satisfy the requirement of lithium-ion-power cell.
Although 2, vanadium mix can the Effective Raise LiFePO4 discharge potential, not obvious to the effect of the ionic conductance of raising LiFePO4, can not satisfy well the requirement of lithium-ion-power cell.
3, single titanium doped or single vanadium mixes and all is difficult to reach the high rate performance that improves simultaneously LiFePO4 and the purpose of specific capacity, thus limited it in, application in the high-power type power consumption equipment.
Summary of the invention
First purpose of the present invention is for existing problem in the above-mentioned prior art, provide a kind of and can improve simultaneously the titanium of high rate performance, cycle performance and the specific capacity of LiFePO4, the LiFePO 4 material of vanadium ion-doped, to satisfy lithium-ion-power cell to the performance requirement of LiFePO 4 material.For this reason, the present invention is by the following technical solutions:
The LiFePO 4 material of a kind of titanium, vanadium ion-doped, the LiFePO 4 material chemical general formula of this titanium, vanadium ion-doped is LiFe
1-x-yTi
xV
y(PO
4)/C, wherein 0.005≤x≤0.01,0.005≤y≤0.02,0.01≤x+y≤0.03.
Another object of the present invention provides a kind of preparation method of above-mentioned LiFePO 4 material.For this reason, the present invention is by the following technical solutions:
Lithium source, source of iron, phosphorus source and dopant are pressed the mol ratio Li of ion
+: iron ion: Ti
4+: V
5+: PO
4 3-=1:1-x-y:x:y:1 weighing, 0.005≤x≤0.01 wherein, 0.005≤y≤0.02,0.01≤x+y≤0.03 adds carbon source and blending agent, adopt the liquid phase ball milling to mix, place nitrogen or argon gas atmosphere, be warming up to 350-450 ℃ and carry out presintering, be incubated 4-6 hour, be warming up to 650-750 ℃ and calcine, be incubated 8-12 hour; Be cooled to room temperature, grind, namely get the LiFePO 4 material of titanium, vanadium ion-doped; Wherein, described iron ion is Fe
3+Or Fe
2+
On the basis of adopting technique scheme, the present invention also can adopt following further technical scheme:
Described lithium source is one or more in lithium carbonate, lithium oxalate, lithium hydroxide, lithium acetate and the lithium nitrate.
Described source of iron is one or more in ferrous oxalate, ferrous acetate, di-iron trioxide, ferric phosphate, ferric nitrate and the ironic citrate.
Described phosphorus source is one or more in phosphoric acid, ammonium phosphate, diammonium hydrogen phosphate and the ammonium dihydrogen phosphate.
Described dopant is titaniferous compound and vanadium compounds; Described titaniferous compound is titanium dioxide and/or metatitanic acid tetramethyl ester; Described vanadium compounds is vanadic oxide and/or ammonium metavanadate.
Described carbon source is one or more in soluble starch, glucose, sucrose, citric acid, polypropylene, polyacrylamide, polyvinyl alcohol, acetylene black and the carbon black.
Described blending agent is deionized water, absolute ethyl alcohol, acetone or industrial alcohol.
The addition of described blending agent is the 80-150% of lithium source, source of iron, phosphorus source, dopant and carbon source gross mass.
The addition of described carbon source is the 30-75% of lithium source quality.
The incorporation time of described liquid phase ball milling is preferably 4-10 hour; The described 350-450 of being warming up to ℃ of heating rate that carries out presintering is preferably 1-5 ℃/min; The described 650-750 of the being warming up to ℃ of heating rate of calcining is preferably 1-5 ℃/min.
The present invention compared with prior art has following advantage:
1, the LiFePO 4 material of employing titanium, the preparation of vanadium ion-doped method has higher specific discharge capacity, more superior multiplying power discharging property and cyclical stability than the material of independent doping vanadium ion or titanium ion.
2, the present invention can obtain crystallization perfection, titanium, vanadium ion-doped LiFePO 4 material that particle diameter is less by adjusting the technological parameters such as calcining heat, temperature retention time.Can also reach by the relative doping of regulating and controlling titanium, vanadium ion lay particular emphasis on improve LiFePO 4 material high rate capability also or improve material specific capacity.
3, lower, the raw material of simple, the processing ease of preparation method's technique of the present invention, energy consumption cheaply are easy to get, and the chemical property of resulting materials is superior, Modulatory character is strong, and is convenient to carry out industrialized production.
Description of drawings
Fig. 1 is the X ray diffracting spectrum (XRD) of prepared titanium, vanadium ion-doped LiFePO 4 material (a) and plain LiFePO 4 material (b) of the embodiment of the invention 1.
Fig. 2 is prepared titanium, vanadium ion-doped LiFePO 4 material scanning electron microscope (SEM) photograph (SEM) of the embodiment of the invention 1.
Fig. 3 is prepared titanium, vanadium ion-doped LiFePO 4 material (a) of the embodiment of the invention 1, titanium ion doped iron lithium phosphate material (b), vanadium ion doped iron lithium phosphate material (c) and plain LiFePO 4 material (d) are assembled into the 0.2C discharge curve behind the button cell, wherein: rate of charge is 0.2C, the charging/discharging voltage scope is 2.0-4.0V, and electrolyte is 1mol/L LiPF
6/ ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1).
Fig. 4 is prepared titanium, vanadium ion-doped LiFePO 4 material (a) of the embodiment of the invention 1, titanium ion doped iron lithium phosphate material (b), vanadium ion doped iron lithium phosphate material (c) and plain LiFePO 4 material (d) are assembled into the 2C discharge curve behind the button cell, wherein: rate of charge is 0.2C, the charging/discharging voltage scope is 2.0-4.0V, and electrolyte is 1mol/L LiPF
6/ ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1).
Fig. 5 is that the embodiment of the invention 1 prepared titanium, vanadium ion-doped LiFePO 4 material is assembled into the cycle performance curve behind the button cell, and wherein: charge-discharge magnification is 2C, and charging/discharging voltage is 2.0-4.0V, and electrolyte is 1mol/L LiPF
6/ ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1).
Embodiment
For better understanding the present invention, the invention will be further described below in conjunction with drawings and Examples, but embodiments of the present invention are not limited to this.
Embodiment 1
Preparation process is as follows: the mol ratio Li that lithium carbonate, ferrous oxalate, ammonium dihydrogen phosphate, ammonium metavanadate and titanium dioxide is pressed ion
+: Fe
2+: Ti
4+: V
5+: PO
4 3-=1.00:0.975:0.005:0.02:1.00 weighing, press 35% of lithium carbonate quality and add glucose, add absolute ethyl alcohol by 80% of reactant materials gross mass again, ball milling mixed 4 hours, the slurry that obtains mixing, then be placed in the tube furnace of nitrogen atmosphere protection, be warming up to 400 ℃ with the programming rate of 2 ℃/min and carry out presintering, be incubated 4 hours; Then be warming up to 700 ℃ with 2 ℃/min again and calcine, be incubated 10 hours.Naturally cool to room temperature with stove, namely get the LiFePO 4 material of titanium, vanadium ion-doped, molecular formula is LiFe
1-x-yTi
xV
y(PO
4)/C, x=0.005 wherein, y=0.02.
In order relatively to need, also under identical preparation condition and composition and ratio, prepared respectively titanium doped LiFePO 4 material, LiFePO 4 material and plain LiFePO 4 material that vanadium mixes.
Titanium, vanadium ion-doped LiFePO 4 material and the plain LiFePO 4 material of said method preparation are carried out the powder X-ray diffraction, and its collection of illustrative plates is shown in Fig. 1.As seen from Figure 1, the LiFePO 4 material (a) that vanadium, titanium ion mix is almost identical with the diffraction maximum of the LiFePO 4 material (b) that undopes, show that the titanium of low concentration, the introduction of vanadium ion can not change the crystalline structure of LiFePO4, the doping ion enters LiFePO fully
4In the lattice, avoided LiTi
2(PO
4)
3, Ti
2P
2O
7And Li
3V
2(PO
4)
3Generation Deng impurity phase.Titanium, vanadium ion-doped LiFePO 4 material have been carried out ESEM (SEM) research, its result as shown in Figure 2, powder body material is comprised of class sphere and rod shaped particles not of uniform size, particle size is between 0.2 μ m-1 μ m, less particle diameter helps to improve the migration rate of lithium ion in the LiFePO4 body, and then improves the ionic conduction speed of material.
Adopt the titanium of said method preparation, the LiFePO 4 material of vanadium ion-doped to make cathode film as positive active material, cathode film by active material, acetylene black and polytetrafluoroethylene (solid content) in mass ratio 82:10:8 form; With metal lithium sheet as negative pole; Barrier film is import microporous polypropylene membrane (Celgard 2400); Electrolyte is 1mol/L LiPF6/ ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1), is assembled into button cell in the glove box of applying argon gas.In order relatively to need, titanium doped LiFePO 4 material, vanadium doped iron lithium phosphate material and the plain LiFePO 4 material for preparing under the same terms also is assembled into button cell according to above-mentioned technique.Above battery is carried out 0.2C and 2.0C discharge test under the room temperature, by Fig. 3 and Fig. 4 as can be known, the LiFePO 4 material of titanium, vanadium ion-doped (a), titanium doped LiFePO 4 material (b), vanadium doped iron lithium phosphate material (c) and the first discharge specific capacity of plain LiFePO 4 material (d) under the 0.2C multiplying power are respectively 151.6mAh/g, 137.8mAh/g, 132.2mAh/g and 122.4mAh/g, and the first discharge specific capacity under the 2.0C multiplying power is respectively 132.4mAh/g, 122.5mAh/g, 116.8mAh/g and 89.7mAh/g.This explanation titanium, vanadium ion-doped can improve lithium ion diffusion rate and the electronic conductivity of LiFePO 4 material effectively, and have suppressed electrode polarization, thereby have improved specific discharge capacity, the multiplying power specific capacity of material.Button cell to the preparation of the LiFePO 4 material of titanium, vanadium ion-doped carries out 2.0C rate charge-discharge loop test, the result as shown in Figure 5: material is through 50 weeks of loop test, and capacity is not decay almost.The high rate cyclic stability that higher specific capacity, good multiplying power discharging are especially outstanding is so that the LiFePO 4 material of the titanium that the present invention relates to, vanadium ion-doped has potential using value at battery for electric automobile.
Embodiment 2
Preparation process is as follows: the mol ratio Li that lithium oxalate, iron oxide, diammonium hydrogen phosphate, ammonium metavanadate and metatitanic acid tetramethyl ester is pressed ion
+: Fe
3+: Ti
4+: V
5+: PO
4 3-=1.00:0.98:0.01:0.01:1 weighing, press 30% of lithium oxalate quality and add glucose, add absolute ethyl alcohol by 80% of reactant materials gross mass again, ball milling mixed 6 hours, the slurry that obtains mixing, then be placed in the tube furnace of nitrogen atmosphere protection, be warming up to 400 ℃ with the programming rate of 2 ℃/min and carry out presintering, be incubated 4 hours; Then be warming up to 700 ℃ with 2 ℃/min again and calcine, be incubated 10 hours.Naturally cool to room temperature with stove, namely get the LiFePO 4 material of titanium, vanadium ion-doped, molecular formula is LiFe
1-x-yTi
xV
y(PO
4)/C, x=0.01 wherein, y=0.01.
Adopt the titanium of said method preparation, the LiFePO 4 material of vanadium ion-doped to make cathode film as positive active material, cathode film by active material, acetylene black and polytetrafluoroethylene (solid content) in mass ratio 82:10:8 form; With metal lithium sheet as negative pole; Barrier film is import microporous polypropylene membrane (Celgard 2400); Electrolyte is 1mol/L LiPF6/ ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1), is assembled into button cell in the glove box of applying argon gas.The first discharge specific capacity of this material under 0.2C and 2.0C multiplying power is respectively 148.9mAh/g and 128.5mAh/g, and still kept more than 98% of initial specific capacity with the specific capacity behind the 2.0C multiplying power cycle charge-discharge 50 times.
Embodiment 3
Preparation process is as follows: the mol ratio Li that lithium oxalate, ferrous acetate, ammonium phosphate, vanadic oxide and titanium dioxide is pressed ion
+: Fe
2+: Ti
4+: V
5+: PO
4 3-=1.00:0.97:0.01:0.02:1.00 weighing, press 40% of lithium oxalate quality and add sucrose, add acetone by 90% of reactant materials gross mass again, ball milling mixed 6 hours, the slurry that obtains mixing, then be placed in the tube furnace of nitrogen atmosphere protection, be warming up to 350 ℃ with the programming rate of 2 ℃/min and carry out presintering, be incubated 6 hours; Then be warming up to 720 ℃ with 2 ℃/min again and calcine, be incubated 8 hours.Naturally cool to room temperature with stove, namely get the LiFePO 4 material of titanium, vanadium ion-doped, molecular formula is LiFe
1-x-yTi
xV
y(PO
4)/C, x=0.01 wherein, y=0.02.
Adopt the titanium of said method preparation, the LiFePO 4 material of vanadium ion-doped to make cathode film as positive active material, cathode film by active material, acetylene black and polytetrafluoroethylene (solid content) in mass ratio 82:10:8 form; With metal lithium sheet as negative pole; Barrier film is import microporous polypropylene membrane (Celgard 2400); Electrolyte is 1mol/L LiPF6/ ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1), is assembled into button cell in the glove box of applying argon gas.The first discharge specific capacity of this material under 0.2C and 2.0C multiplying power is respectively 147.5mAh/g and 129.5mAh/g, and still kept more than 98% of initial specific capacity with the specific capacity behind the 2.0C multiplying power cycle charge-discharge 50 times.
Embodiment 4
Preparation process is as follows: the mol ratio Li that lithium hydroxide, ferrous oxalate, phosphoric acid, vanadic oxide and metatitanic acid tetramethyl ester is pressed ion
+: Fe
2+: Ti
4+: V
5+: PO
4 3-=1.00:0.975:0.01:0.015:1.00 weighing, press 50% of lithium hydroxide quality and add citric acid, add deionized water by 100% of reactant materials gross mass again, ball milling mixed 6 hours, the slurry that obtains mixing, then be placed in the tube furnace of nitrogen atmosphere protection, be warming up to 450 ℃ with the programming rate of 4 ℃/min and carry out presintering, be incubated 5 hours; Then be warming up to 750 ℃ with 2 ℃/min again and calcine, be incubated 8 hours.Naturally cool to room temperature with stove, namely get the LiFePO 4 material of titanium, vanadium ion-doped, molecular formula is LiFe
1-x-yTi
xV
y(PO
4)/C, x=0.01 wherein, y=0.015.
Adopt the titanium of said method preparation, the LiFePO 4 material of vanadium ion-doped to make cathode film as positive active material, cathode film by active material, acetylene black and polytetrafluoroethylene (solid content) in mass ratio 82:10:8 form; With metal lithium sheet as negative pole; Barrier film is import microporous polypropylene membrane (Celgard 2400); Electrolyte is 1mol/L LiPF6/ ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1), is assembled into button cell in the glove box of applying argon gas.The first discharge specific capacity of this material under 0.2C and 2.0C multiplying power is respectively 150.5mAh/g and 130.5mAh/g, and still kept more than 98% of initial specific capacity with the specific capacity behind the 2.0C multiplying power cycle charge-discharge 50 times.
Embodiment 5
Preparation process is as follows: the mol ratio Li that lithium hydroxide, ferric phosphate, ammonium dihydrogen phosphate, ammonium metavanadate and titanium dioxide is pressed ion
+: Fe
3+: Ti
4+: V
5+: PO
4 3-=1.00:0.975:0.005:0.015:1.00 weighing, press 65% of lithium hydroxide quality and add glucose, add industrial alcohol by 80% of reactant materials gross mass again, ball milling mixed 6 hours, the slurry that obtains mixing, then be placed in the tube furnace of nitrogen atmosphere protection, be warming up to 400 ℃ with the programming rate of 2 ℃/min and carry out presintering, be incubated 4 hours; Then be warming up to 720 ℃ with 2 ℃/min again and calcine, be incubated 8 hours.Naturally cool to room temperature with stove, namely get the LiFePO 4 material of titanium, vanadium ion-doped, molecular formula is LiFe
1-x-yTi
xV
y(PO
4)/C, x=0.005 wherein, y=0.015.
Adopt the titanium of said method preparation, the LiFePO 4 material of vanadium ion-doped to make cathode film as positive active material, cathode film by active material, acetylene black and polytetrafluoroethylene (solid content) in mass ratio 82:10:8 form; With metal lithium sheet as negative pole; Barrier film is import microporous polypropylene membrane (Celgard 2400); Electrolyte is 1mol/L LiPF6/ ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1), is assembled into button cell in the glove box of applying argon gas.The first discharge specific capacity of this material under 0.2C and 2.0C multiplying power is respectively 151.5mAh/g and 131.5mAh/g, and still kept more than 98% of initial specific capacity with the specific capacity behind the 2.0C multiplying power cycle charge-discharge 50 times.
Embodiment 6
Preparation process is as follows: the mol ratio Li that lithium nitrate, ferric nitrate, ammonium dihydrogen phosphate, vanadic oxide and metatitanic acid tetramethyl ester is pressed ion
+: Fe
3+: Ti
4+: V
5+: PO
4 3-=1.00:0.99:0.005:0.005:1.00 weighing, press 50% of lithium nitrate quality and add citric acid, add deionized water by 100% of reactant materials gross mass again, ball milling mixed 6 hours, the slurry that obtains mixing, then be placed in the tube furnace of nitrogen atmosphere protection, be warming up to 400 ℃ with the programming rate of 4 ℃/min and carry out presintering, be incubated 6 hours; Then be warming up to 750 ℃ with 2 ℃/min again and calcine, be incubated 10 hours.Naturally cool to room temperature with stove, namely get the LiFePO 4 material of titanium, vanadium ion-doped, molecular formula is LiFe
1-x-yTi
xV
y(PO
4)/C, x=0.005 wherein, y=0.005.
Adopt the titanium of said method preparation, the LiFePO 4 material of vanadium ion-doped to make cathode film as positive active material, cathode film by active material, acetylene black and polytetrafluoroethylene (solid content) in mass ratio 82:10:8 form; With metal lithium sheet as negative pole; Barrier film is import microporous polypropylene membrane (Celgard 2400); Electrolyte is 1mol/L LiPF6/ ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1), is assembled into button cell in the glove box of applying argon gas.The first discharge specific capacity of this material under 0.2C and 2.0C multiplying power is respectively 146.4mAh/g and 127.5mAh/g, and still kept more than 97% of initial specific capacity with the specific capacity behind the 2.0C multiplying power cycle charge-discharge 50 times.
Above-described embodiment is the better execution mode of the present invention; but embodiments of the present invention are not restricted to the described embodiments; other any do not deviate from Spirit Essence of the present invention and principle change, modification, substitute, combination, simplify; all should be the substitute mode of equivalence, be included within protection scope of the present invention.