CN101407318B

CN101407318B - Method for preparing lithium iron phosphate as positive electrode active material of lithium ion secondary battery

Info

Publication number: CN101407318B
Application number: CN2007101525721A
Authority: CN
Inventors: 席小兵; 荣强; 廖华栋; 韦建群
Original assignee: BYD Co Ltd
Current assignee: BYD Co Ltd
Priority date: 2007-10-11
Filing date: 2007-10-11
Publication date: 2012-05-02
Anticipated expiration: 2027-10-11
Also published as: CN101407318A

Abstract

A preparation method of lithium iron phosphate as a positive electrode active material of a lithium ion secondary battery comprises the steps of sintering a mixture containing a lithium compound, a ferrous compound, a phosphorus compound and a carbon source additive in an inert atmosphere, and cooling the obtained sintered product, wherein the inert atmosphere is a static inert atmosphere during sintering, and the pressure of the inert atmosphere is normal pressure. The lithium iron phosphate prepared by the method of the invention does not contain Fe₂P mixed phase, and the battery prepared from the lithium iron phosphate has high capacity, low internal resistance and good cycle performance.

Description

The preparation method of active material for anode of Li-ion secondary battery LiFePO 4

Technical field

The invention relates to a kind of preparation method of battery positive electrode active material, more particularly, is the preparation method about a kind of active material for anode of Li-ion secondary battery LiFePO 4.

Background technology

Lithium ion battery has been widely used in fields such as mobile communication, notebook computer, pick up camera, photographic camera, portable instrument as the high-energy-density chemical power source; Also be the electromobile studied energetically of various countries, the first-selected supporting power supply of space power system, become the first-selection of the alternative energy.Commercial LiCoO ₂The positive active material capacity is higher, have extended cycle life; But, thereby seek the research direction that low price, dependable performance, eco-friendly positive active material become lithium ion battery owing to the poorness of cobalt resource, cost an arm and a leg and certain toxicity is arranged.LiNiO ₂, LiNi _xCo _1-xO ₂Deng layered oxide and with LiMnO ₄For the spinel type positive active material of representing has obtained extensive studies in more than ten years in the past, but because LiNiO ₂, LiNi _xCo _1-xO ₂The problem of synthetic difficulty and security does not drop into practical application; Though spinel LiMn ₂O ₄Specific storage height, aboundresources, low price, but because at high temperature, the cycle charge-discharge capacity attenuation is fast, also influences its practical application.Goodenough in 1997 etc. discover the LiFePO of olivine structural ₄Can be used as anode material for lithium-ion batteries and have high theoretical specific storage (170 MAH/gram).Discharge voltage plateau, low price are arranged about 3.4 volts stably and environmental protection is arranged and safety performance is good etc. that advantage caused widely pays close attention to.But pure LiFePO ₄Ionic conductance and electron conductivity all lower, when charge and discharge, Li ⁺Ion is at LiFePO ₄-FePO ₄Spread coefficient between two phases is also little, causes LiFePO ₄In commercialization, have certain difficulty, this big limitations the application of LiFePO 4 in practical lithium-ion.Utilize the carbon thermal response at LiFePO at present ₄Coated with carbon is processed LiFePO ₄/ C matrix material, thus LiFePO solved basically ₄The problem of poorly conductive.

CN1785799A discloses a kind of preparation method of solid phase synthesis LiFePO 4; The source of iron that this method adopts is a ferrous salt, and like Ferrox, Iron diacetate and iron protochloride etc., the phosphorus source is ammonium phosphate, Secondary ammonium phosphate and primary ammonium phosphate etc.; This method comprises that be Li: Fe: P: TR=(1-x) with lithium salts, above-mentioned ferrous salt and phosphoric acid salt and transition element doped thing by atomic ratio: 1: 1: weighing charging of the mol ratio of x; Add the mix grinding medium, 6-12 hour ball milling time is 40-70 ℃ of oven dry down; Oven dry back powder heats 400-550 ℃ under inert atmosphere or reducing atmosphere, be incubated 5-10 hour and carry out precalcining; Secondary ball milling 6-12 hour, 40-70 ℃ of oven dry down, under inert atmosphere or reducing atmosphere, 550-850 ℃ of following secondary clacining obtained transition element doped LiFePO 4 powder then.

Prior art be that reaction raw materials prepares in the reaction process of LiFePO 4 with the divalent iron salt; Wanting all the time successive to feed rare gas element protects; Oxidized to prevent divalent iron salt, so not only the labor rare gas element also makes doped F e in the LiFePO 4 that makes easily ₂The P dephasign, the internal resistance of the battery that causes being prepared by this LiFePO 4 is higher, specific storage is lower.

Summary of the invention

The objective of the invention is the internal resistance of cell height for preparing for the LiFePO 4 that overcomes the employing prior art for preparing, the defective that specific storage is low, a kind of preparation method who makes battery have the LiFePO 4 of low internal resistance and height ratio capacity is provided.

Contriver of the present invention finds; Existing with ferrous salt, like in Ferrox, Iron diacetate and the iron protochloride one or more, microcosmic salt; One or more and lithium salts as in ammonium phosphate, Secondary ammonium phosphate and the primary ammonium phosphate are that reaction raw materials prepares in the entire reaction course of iron lithium phosphate; Want all the time successive to feed rare gas element and protect, oxidized to prevent divalent iron salt, and in the process of reaction, generate Fe easily ₂The P dephasign, the internal resistance of the battery that causes being prepared by this ferrousphosphate lithium material is higher, specific storage is lower.

The invention provides a kind of preparation method of active material for anode of Li-ion secondary battery LiFePO 4; This method comprises the mixture that contains lithium compound, ferro-compound, phosphorus compound and carbon source additive sintering in inert atmosphere; The sintered product that cooling obtains, wherein, in the agglomerating process; Said inert atmosphere is static inert atmosphere, and the pressure of said inert atmosphere is normal pressure; Said inert atmosphere is one or more in nitrogen, carbon monoxide, carbonic acid gas, ammonia and the periodic table of elements zero group gas.

Among the preparation method of LiFePO 4 provided by the invention, in the agglomerating process, said inert atmosphere is static atmosphere, and the pressure of said inert atmosphere is normal pressure.That is, in roasting process, no longer feed rare gas element, the non-oxidizing gas that only relies on reaction raw materials decomposition generation in preceding rare gas element that is charged into of roasting and the roasting process is protected Fe as shielding gas ²⁺Not oxidized one-tenth Fe ³⁺, do not have Fe in the LiFePO 4 for preparing by method of the present invention ₂The P dephasign, the battery that is prepared by this LiFePO 4 has heavy body, low internal resistance and excellent cycle performance.The first discharge specific capacity of the battery that the LiFePO 4 that is made by the method for the embodiment of the invention 1 prepares is up to 150 MAH/grams, and the internal resistance of battery is lower, is merely the 25-30 milliohm.And the first discharge specific capacity of the battery that is prepared by the LiFePO 4 that the method for Comparative Examples 1 makes is merely 112 MAH/grams, and the internal resistance of battery is the 200-300 milliohm.

Description of drawings

Fig. 1 is the XRD diffractogram of the LiFePO 4 that adopts the inventive method and obtain;

Fig. 2 is the XRD diffractogram of the LiFePO 4 that adopts the inventive method and obtain;

Fig. 3 is the XRD diffractogram of the LiFePO 4 that adopts existing method and obtain;

Fig. 4 is the XRD diffractogram of the LiFePO 4 that adopts existing method and obtain.

Embodiment

According to the present invention; This method comprises the mixture that contains lithium compound, ferro-compound, phosphorus compound and carbon source additive sintering in inert atmosphere; The sintered product that cooling obtains, wherein, in the agglomerating process; Said inert atmosphere is static inert atmosphere, and the pressure of said inert atmosphere is normal pressure; Said inert atmosphere is one or more in nitrogen, carbon monoxide, carbonic acid gas, ammonia and the periodic table of elements zero group gas.

According to the present invention, said agglomerating process can be carried out in various conversion units, as long as guarantee in the agglomerating process, said inert atmosphere is static inert atmosphere, and the pressure of said inert atmosphere is that normal pressure gets final product.For example; Said sintering carries out in the reaction vessel that is provided with inlet mouth and air outlet, before sintering, rare gas element is fed in the reaction vessel; With the air displacement in the reaction vessel; Inlet mouth keeps shut in sintering process, and with an end airtight be connected of air outlet with conduit, the other end of this conduit places hydraulic fluid.In sintering process of the present invention; No longer in reaction vessel, feed rare gas element; But with the air outlet of said reaction vessel and airtight connection of an end of conduit, the other end of this conduit places hydraulic fluid, and the gas that can guarantee in sintering process, to produce is being discharged through behind the hydraulic fluid; Satisfy inert atmosphere described in the sintering process and be static inert atmosphere, the pressure that can guarantee said inert atmosphere again is normal pressure.

Normal pressure of the present invention refers to a standard atmospheric pressure, that is, and and 1.01 * 10 ⁵Handkerchief.Each is local owing to differences such as geographical position, sea level elevation, temperature, and local real atmosphere is pressed with standard atmospheric pressure also incomplete same, but for simplicity, normal pressure according to the invention refers to a standard atmospheric pressure.

The inert atmosphere of static state according to the invention refers to immobilising atmosphere,, in sintering process, stops to feed rare gas element that is.

According to the present invention; In sintering process, through conduit the air outlet being communicated with hydraulic fluid is in order to prevent to make in the air admission reaction vessel LiFePO 4 oxidized and keep the atmospheric pressure state in the reaction vessel; Therefore; Under the preferable case, the mode that said air outlet is communicated with hydraulic fluid through conduit is for to place hydraulic fluid with conduit, make conduit under the liquid level of hydraulic fluid 5-8 centimetre be most preferred mode.

Saidly be arranged on the quantity of inlet mouth and air outlet on the reaction vessel and the position is not special limits; As long as can guarantee said rare gas element is fed in the reaction vessel; With the air displacement in the reaction vessel, the reactant gases discharge is guaranteed that the pressure of said inert atmosphere is that normal pressure gets final product through the air outlet.Under the preferable case, for the ease of displaced air, and the discharge that in sintering process, produces gas, said inlet mouth and air outlet are arranged on the same side of reaction vessel, and more preferably on the same vertical surface of the same side, inlet mouth is following, and the air outlet is last.When feeding said rare gas element in the reaction vessel, the flow velocity of said rare gas element is not special to be limited, be generally the 5-20 liter/minute.

Volume and material to said reaction vessel also are not particularly limited, and those skilled in the art can be according to the material and the specification of the needs choice reaction vessel of producing.

Because in reaction process; The mixture that contains lithium compound, ferro-compound, phosphorus compound and carbon source additive can produce gases such as hydrogen, ammonia, carbon monoxide and carbonic acid gas during the constant temperature sintering in inert atmosphere; And the agglomerating temperature is higher, under the preferable case, in order to prevent the hydraulic fluid suck-back; Said hydraulic fluid for not with sintering process in the boiling point of the gas reaction that produces be not less than 140 ℃ liquid, a kind of as in hydraulicefficiency oil, quenching oil and the high temperature resistant luboil.

According to the present invention, said inert atmosphere refers to not any one gas or the gaseous mixture with reactant and product generation chemical reaction, like in nitrogen, carbon monoxide, carbonic acid gas, ammonia and the periodic table of elements zero group gas one or more.The mol ratio of Li in said lithium compound, ferro-compound, tertiary iron phosphate and the phosphorus compound: Fe: P is (0.9-1.2): 1: 1.

Said ferro-compound can be selected from various ferrous iron source compound as the preparation LiFePO 4 well known in the art, as, can be selected from FeC ₂O ₄, Fe (CH ₃COO) ₂And FeCO ₃In one or more.

Said lithium compound can be selected from various lithium compound as the preparation LiFePO 4 well known in the art, as, can be selected from Li ₂CO ₃, LiOH, Li ₂C ₂O ₄And CH ₃Among the COOLi one or more.

Said phosphorus compound can be selected from various phosphorus compound as the preparation LiFePO 4 well known in the art, as, can be selected from NH ₄H ₂PO ₄, (NH ₄) ₂HPO ₄, LiH ₂PO ₄(NH ₄) ₃PO ₄In one or more.

Said carbon source additive can be the additive that can play electric action well known in the art; As, can be selected from the luxuriant and rich with fragrance terpolymer of benzene naphthalene, the luxuriant and rich with fragrance copolymer of benzene, benzene anthracene copolymer, Zulkovsky starch, Z 150PH, sucrose, glucose, Hydrocerol A, starch, dextrin, resol, furfuryl resin, synthetic graphite, natural graphite, carbon black and the mesocarbon bead one or more; Wherein, said carbon black can be acetylene black, and said acetylene black can be superconduction acetylene black.Said carbon source additive becomes carbon monoxide, carbonic acid gas etc. after part is at high temperature decomposed and is released in the agglomerating process, and part is entrained in the LiFePO 4 of generation, to improve the electroconductibility of LiFePO 4.It is 1-10 weight % that the consumption of said carbon source additive makes the carbon content in the LiFePO 4 of generation, is preferably 3-5 weight %.

The said mixture that contains lithium compound, ferro-compound, phosphorus compound and carbon source additive can be through mechanically mixing, grind the mode that is preferably ball milling mixes and obtains.The method of said ball milling comprises mixes ball milling then with lithium compound, ferro-compound, phosphorus compound and carbon source additive with organic solvent; The kind of said organic solvent and consumption are conventionally known to one of skill in the art; Like ethanol and/or propyl alcohol, the consumption of organic solvent and the weight ratio of said mixture can be 1-5: 1.The rotating speed of ball milling and time do not have special qualification, can granularity as requested need to set.Under the preferable case, adopt the step that also comprises dry this mixture behind this method ball milling, exsiccant method and condition are conventionally known to one of skill in the art.

Said agglomerating method can be for well known to a person skilled in the art various sintering methods, like the method for once sintered or double sintering, under the preferable case; In order to shorten process step, enhance productivity, the present invention adopts constant temperature agglomerating method one time; A said constant temperature agglomerating sintering temperature is 500-750 ℃; Be preferably 700-750 ℃, the constant temperature agglomerating time is 2-20 hour, is preferably 10-20 hour.In order further to control the LiFePO 4 granule-morphology; It is more complete that the LiFePO 4 crystal formation is grown; Under the preferable case; A constant temperature agglomerating method according to the invention is the speed with 5-20 ℃/minute, and the speed that is preferably 10-15 ℃/minute is warming up to the constant temperature sintering temperature, then sintering under this constant temperature sintering temperature.

Said refrigerative method can adopt the various known methods of this area, and is oxidized for the LiFePO 4 that further prevents to generate like naturally cooling, preferably under inert atmosphere, sintered product is cooled to room temperature.This inert atmosphere can be static atmosphere, be preferably gas flow rate and be the 2-20 liter/minute mobile atmosphere.

To do further specific descriptions to the present invention through specific embodiment below.

Embodiment 1

This embodiment explains the preparation of positive active material LiFePO 4 provided by the invention

(1) with 369 gram Li ₂CO ₃, 1799 the gram FeC ₂O ₄2H ₂O, 1150 gram NH ₄H ₂PO ₄Mix (Li: Fe: the P mol ratio is 1: 1: 1) with 300 gram glucose with 3000 gram alcohol, with 300 rev/mins rotating speed ball millings 10 hours, taking-up, 80 ℃ of oven dry;

(2) with the mixture of step (1) place one be provided with an inlet mouth and air outlet reaction vessel (inlet mouth and air outlet are in same vertical surface, and inlet mouth is down, and the air outlet is last); Open air outlet and inlet mouth; Feed argon gas with 5 liters/minute flow velocitys, with the air displacement in the reaction vessel, then with inlet close; And the air outlet is connected with conduit and conduit put into 25 ℃ hydraulicefficiency oil (Jia Deshi; Superfine hydraulicefficiency oil 460) in (conduit mouth under the hydraulicefficiency oil liquid level 5 centimetres), be warming up to 750 ℃ of constant temperature sintering 20 hours with 10 ℃/minute heat-up rate then, open inlet mouth then; Feed argon gas with 5 liters/minute flow velocitys and make product be cooled to room temperature, obtain the active material for anode of Li-ion secondary battery LiFePO 4; Carbon content in the LiFePO 4 that generates is that 3.52 weight % (adopt infrared carbon sulfur analyzer to measure (production of Wuxi Ying Zhicheng company); Measuring method is: take by weighing 0.03-0.5 gram sample and put in the special copple; And the tungsten particle of pure iron solubility promoter, 1.8-1.9 gram that adds the 0.6-0.7 gram is as ignition dope; Put in the high frequency, utilize oxygen to do ignition dope and carrier gas, with the burning CO of generation later ₂Take in the carbon analysis cell, determine the carbon content in the LiFePO 4) through instrumental analysis.

The XRD diffractogram of this LiFePO 4 that the D/MAX-2200/PC type x-ray powder diffraction instrument of employing Rigaku company records is as shown in Figure 1.

Embodiment 2

(1) with 239.5 gram LiOH, 1158.6 gram FeCO ₃, 1319.7 the gram (NH ₄) ₂HPO ₄Mix (Li: Fe: the P mol ratio is 1: 1: 1) with 320 gram glucose with 2700 gram alcohol, with 300 rev/mins rotating speed ball millings 10 hours, taking-up, 80 ℃ of oven dry;

(2) place one to be provided with the reaction vessel of an inlet mouth and air outlet (inlet mouth and air outlet are in same vertical surface in the mixture of step (1); And inlet mouth is following, and the air outlet is last), open air outlet and inlet mouth; Feed argon gas with 5 liters/minute flow velocitys; With the air displacement in the reaction vessel,, and the air outlet is connected with conduit and conduit put into 25 ℃ hydraulicefficiency oil (conduit mouth under the hydraulicefficiency oil liquid level 5 centimetres) then with inlet close; Be warming up to 700 ℃ of constant temperature sintering 20 hours with 5 ℃/minute heat-up rate then; Open inlet mouth then, feed argon gas with 5 liters/minute flow velocitys and make product be cooled to room temperature, obtain the active material for anode of Li-ion secondary battery LiFePO 4; Carbon content in the LiFePO 4 that generates is 3.47 weight %.

The XRD diffractogram of this LiFePO 4 that the D/MAX-2200/PC type x-ray powder diffraction instrument of employing Rigaku company records is as shown in Figure 2.

Embodiment 3

(1) with 369 gram Li ₂CO ₃, 1799 the gram FeC ₂O ₄2H ₂O, 1150 gram NH ₄H ₂PO ₄Mix (Li: Fe: the P mol ratio is 1: 1: 1) with 310 gram sucrose with 3000 gram alcohol, with 300 rev/mins rotating speed ball millings 10 hours, taking-up, 80 ℃ of oven dry;

(2) place one to be provided with the reaction vessel of an inlet mouth and air outlet (inlet mouth and air outlet are in same vertical surface in the mixture of step (1); And inlet mouth is following, and the air outlet is last), open air outlet and inlet mouth; Feed argon gas with 5 liters/minute flow velocitys; With the air displacement in the reaction vessel,, and the air outlet is connected with conduit and conduit put into 25 ℃ hydraulicefficiency oil (conduit mouth under the hydraulicefficiency oil liquid level 5 centimetres) then with inlet close; Be warming up to 750 ℃ of constant temperature sintering 20 hours with 15 ℃/minute heat-up rate then; Open inlet mouth then, feed argon gas with 5 liters/minute flow velocitys and make product be cooled to room temperature, obtain the active material for anode of Li-ion secondary battery LiFePO 4; Carbon content in the LiFePO 4 that generates is 3.8 weight %.

Embodiment 4

(1) with 369 gram Li ₂CO ₃, 1799 the gram FeC ₂O ₄2H ₂O, 1319.7 gram (NH ₄) ₂HPO ₄Mix (Li: Fe: the P mol ratio is 1: 1: 1) with 310 gram sucrose with 3000 gram alcohol, with 300 rev/mins rotating speed ball millings 10 hours, taking-up, 80 ℃ of oven dry;

(2) place one to be provided with the reaction vessel of an inlet mouth and air outlet (inlet mouth and air outlet are in same vertical surface in the mixture of step (1); And inlet mouth is following, and the air outlet is last), open air outlet and inlet mouth; Feed argon gas with 5 liters/minute flow velocitys; With the air displacement in the reaction vessel,, and the air outlet is connected with conduit and conduit put into 25 ℃ hydraulicefficiency oil (conduit mouth under the hydraulicefficiency oil liquid level 5 centimetres) then with inlet close; Be warming up to 700 ℃ of constant temperature sintering 20 hours with 10 ℃/minute heat-up rate then; Open inlet mouth then, feed argon gas with 5 liters/minute flow velocitys and make product be cooled to room temperature, obtain the active material for anode of Li-ion secondary battery LiFePO 4; Carbon content in the LiFePO 4 that generates is 3.56 weight %.

Comparative Examples 1

The preparation method of the positive active material LiFePO 4 of this Comparative Examples explanation prior art

Method according to embodiment 1 prepares LiFePO 4, and different is, in step (2); The mixture with step (1) place one be provided with an inlet mouth and air outlet reaction vessel (inlet mouth and air outlet are in same vertical surface, and inlet mouth is down, and the air outlet is last); Open inlet mouth and air outlet; Feed argon gas with 5 liters/minute flow velocitys,, continue to feed argon gas then the air displacement in the reaction vessel; The flow of regulating argon gas is 2 liters/minute; Be warming up to 750 ℃ of constant temperature sintering 20 hours with 10 ℃/minute heat-up rate then, continue to feed argon gas then and make product be cooled to room temperature, obtain the active material for anode of Li-ion secondary battery LiFePO 4.Carbon content in the LiFePO 4 that generates is 3.57 weight %.

The XRD diffractogram of this LiFePO 4 that the D/MAX-2200/PC type x-ray powder diffraction instrument of employing Rigaku company records is as shown in Figure 3.

Comparative Examples 2

Method according to embodiment 1 prepares LiFePO 4, and different is, in step (2); The mixture with step (1) place one be provided with an inlet mouth and air outlet reaction vessel (inlet mouth and air outlet are in same vertical surface, and inlet mouth is down, and the air outlet is last); Open inlet mouth and air outlet, feed carbon monoxide with 5 liters/minute flow velocitys, the air displacement in the reaction vessel; Continue to feed carbon monoxide then; Be warming up to 750 ℃ of constant temperature sintering 20 hours with 10 ℃/minute heat-up rate then, continue to feed carbon monoxide then and make product be cooled to room temperature, obtain the active material for anode of Li-ion secondary battery LiFePO 4.Carbon content in the LiFePO 4 that generates is 3.62 weight %.

The XRD diffractogram of this LiFePO 4 that the D/MAX-2200/PC type x-ray powder diffraction instrument of employing Rigaku company records is as shown in Figure 4.

Embodiment 5-8

Following embodiment carries out performance test to battery after explaining and adopting positive active material LiFePO 4 provided by the invention to be prepared into battery.

(1) preparation of battery

The anodal preparation

The positive active material LiFePO that respectively 90 grams is made by embodiment 1-4 ₄, 5 gram sticker pvdf (PVDF) join in the 50 gram N-Methyl pyrrolidone with 5 gram static eliminator acetylene blacks, in vacuum mixer, stir the uniform anode sizing agent of formation then.This anode sizing agent is coated on the both sides that thickness is 20 microns aluminium foil equably, 150 ℃ of following oven dry, roll-ins then, cuts to make and be of a size of 540 * 43.5 millimeters positive pole, wherein contain the 5.2 gram activeconstituents LiFePO that have an appointment ₄

The preparation of negative pole

90 gram negative electrode active composition natural graphites, 5 gram caking agent pvdf, 5 gram static eliminator carbon blacks are joined in the 100 gram N-Methyl pyrrolidone, in vacuum mixer, stir then and form uniform cathode size.This cathode size is coated on the both sides that thickness is 12 microns Copper Foil equably, then in 90 ℃ of following oven dry, roll-in, cut to make and be of a size of 500 * 44 millimeters negative pole, wherein contain the 3.8 gram activeconstituents natural graphites of having an appointment.

The assembling of battery

Respectively above-mentioned positive and negative electrode and polypropylene screen are wound into the pole piece of a square lithium ion battery, subsequently with LiPF ₆Concentration by 1 mol is dissolved in EC/EMC/DEC=1: form nonaqueous electrolytic solution in 1: 1 the mixed solvent, this electrolytic solution is injected the battery aluminum hull with the amount of 3.8g/Ah, lithium-ion secondary cell A1-A4 is processed in sealing respectively.

(2) battery performance test

The above-mentioned lithium ion A1-A4 battery that makes is placed on test respectively cashier's office in a shop, carries out constant-current constant-voltage charging with 0.2C earlier, be limited to 4.2 volts in the charging; After shelving 20 minutes, be discharged to 2.5 volts from 4.2 volts with the electric current of 0.2C, the loading capacity first of recording cell, and calculate the specific discharge capacity of battery according to the following equation;

Specific discharge capacity=battery is loading capacity (MAH)/positive electrode material weight (gram) first

After repeating above-mentioned steps 30 times and 50 times then, obtain the capacity behind the battery 30 times and 50 times respectively, the loading capacity of recording cell.By presented higher holdup before and after the computes circulation:

Presented higher holdup=(the N time cyclic discharge capacity/cyclic discharge capacity) first * 100%

The result is as shown in table 1 below.

(3) internal resistance of cell test

The above-mentioned lithium ion A1-A4 battery that makes is placed on respectively on the BS-VR3 Intelligentized battery internal resistance test device (Qingtian Industry Co., Ltd., Guangzhou), measurand is applied the 1KHz AC signal, obtain its internal resistance through measuring its interchange pressure drop.

Comparative Examples 3-4

After the positive active material LiFePO 4 that following Comparative Examples explanation adopts prior art to obtain is prepared into battery battery is carried out performance test.

Method according to embodiment 5-8 prepares reference cell AC1-AC2; And the loading capacity first of test battery and the cycle performance of battery; And the specific discharge capacity of calculating battery; Different is the reference positive active material LiFePO 4 that the positive active material of preparation used in battery obtains for Comparative Examples 1-2.

The result is as shown in table 1 below.

Table 1

Is example with embodiment 1 with embodiment 2, the XRD diffractogram of the LiFePO 4 that the XRD diffractogram of the LiFePO 4 that Fig. 1 obtains for the method that adopts embodiments of the invention 1, Fig. 2 obtain for the method that adopts embodiments of the invention 2.As can be seen from the figure, olivine-type structure and crystal formation that this LiFePO 4 has standard physically well develop, and do not have dephasign.

The XRD diffractogram of the LiFePO 4 that the XRD diffractogram of the LiFePO 4 that Fig. 3 obtains for the method that adopts Comparative Examples 1, Fig. 4 obtain for the method that adopts Comparative Examples 2 can be found out from Fig. 3 and Fig. 4, is doped with Fe in this LiFePO 4 ₂The P dephasign.(with Fe ₂The PDF standard card (85-1727) of P is compared, and a climax in 2 θ angles are 40 °-41 ° scope, occurs, in 44 °-45 ° scope, occurs the peak one time, and Fe has been described ₂The existence of P can obviously be found out from Fig. 3 and Fig. 4, and the existence of above-mentioned characteristic peak is arranged.)

Data from last table 1 can be found out; The initial discharge specific discharge capacity of the battery A1-A4 that the LiFePO 4 that adopts method of the present invention to prepare prepares all is significantly higher than the reference cell AC1-AC2 of Comparative Examples, and the internal resistance of battery all is significantly less than reference cell; Presented higher holdup after the battery circulation 30 times is more than 98%; Presented higher holdup after the battery circulation 50 times also all reaches more than 97%; And reference cell is merely 92.21%-93.28% and 88.83%-90.85% at the presented higher holdup of circulation after 30 times and 50 times; Therefore explanation, the battery that the LiFePO 4 that adopts method of the present invention to prepare prepares have heavy body, low internal resistance and excellent cycle performance.

Claims

1. the preparation method of an active material for anode of Li-ion secondary battery LiFePO 4; This method comprises the mixture that contains lithium compound, ferro-compound, phosphorus compound and carbon source additive sintering in inert atmosphere; The sintered product that cooling obtains is characterized in that, in the agglomerating process; Said inert atmosphere is static inert atmosphere, and the pressure of said inert atmosphere is normal pressure; Said inert atmosphere is one or more in nitrogen, carbon monoxide, carbonic acid gas, ammonia and the periodic table of elements zero group gas.

2. method according to claim 1, wherein, said sintering carries out in the reaction vessel that is provided with inlet mouth and air outlet; Before sintering; Rare gas element is fed in the reaction vessel, and with the air displacement in the reaction vessel, inlet mouth keeps shut in sintering process; With an end airtight be connected of air outlet with conduit, the other end of this conduit places hydraulic fluid.

3. method according to claim 2, wherein, said hydraulic fluid for not with sintering process in the boiling point of the gas reaction that produces be not less than 140 ℃ liquid.

4. method according to claim 1 and 2, wherein, the said constant temperature sintering that is sintered to a time, the agglomerating method comprises that the speed with 5-20 ℃/minute is warming up to the constant temperature sintering temperature, then sintering under this constant temperature sintering temperature.

5. method according to claim 4, wherein, said constant temperature agglomerating temperature is 500-750 ℃, the agglomerating time is 2-20 hour.

6. method according to claim 1, wherein, said refrigerative method is included in the inert atmosphere sintered product is cooled to room temperature.

7. method according to claim 1; Wherein, The mol ratio of Li in said lithium compound, ferro-compound and the phosphorus compound: Fe: P is 0.9-1.2: 1: 1, it was 1-10 weight % that the consumption of said carbon source additive makes the carbon content in the LiFePO 4 of generation.

8. method according to claim 1, wherein, said lithium compound is selected from Li ₂CO ₃, LiOH, Li ₂C ₂O ₄And CH ₃Among the COOLi one or more; Said ferro-compound is selected from FeC ₂O ₄, Fe (CH ₃COO) ₂And FeCO ₃In one or more; Said phosphorus compound is selected from NH ₄H ₂PO ₄, (NH ₄) ₂HPO ₄(NH ₄) ₃PO ₄In one or more; Said carbon source additive is selected from one or more in the luxuriant and rich with fragrance terpolymer of benzene naphthalene, the luxuriant and rich with fragrance copolymer of benzene, benzene anthracene copolymer, Zulkovsky starch, Z 150PH, sucrose, glucose, Hydrocerol A, starch, dextrin, resol, furfuryl resin, synthetic graphite, natural graphite, carbon black and the mesocarbon bead.

9. method according to claim 8, wherein, said carbon black is an acetylene black.