CN101209822A - Preparation method for lithium ion secondary battery positive pole active substance lithium iron phosphate - Google Patents
Preparation method for lithium ion secondary battery positive pole active substance lithium iron phosphate Download PDFInfo
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- CN101209822A CN101209822A CNA2006101673911A CN200610167391A CN101209822A CN 101209822 A CN101209822 A CN 101209822A CN A2006101673911 A CNA2006101673911 A CN A2006101673911A CN 200610167391 A CN200610167391 A CN 200610167391A CN 101209822 A CN101209822 A CN 101209822A
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Abstract
The invention relates to a preparation method of lithium iron phosphate, an active substance applied in the anode of lithium-ion secondary batteries. The method comprises that a mixture that contains lithium compound, iron compound, phosphorus compound and carbon source additive is sintered and cooled to obtain a sintering product; wherein, the iron compound is ferric iron compound; the sintering method is carried out in inert atmosphere or reducing atmosphere; the mixture is sintered at a first constant sintering temperature to get the sintering product; the sintering product acquired from the first sintering temperature is cooled to room temperature and mixed with the dispersant and ground; the mixture is sintered at a second constant sintering temperature, and is cooled to room temperature in inert atmosphere or reducing atmosphere; the second sintering temperature is at least 100 DEG C higher than the first sintering temperature. The lithium iron phosphate acquired by the method of the invention has relatively high specific discharge capacity and specific volumetric capacity, and batteries made of lithium iron phosphate have both high capacity and good discharge performance at high current.
Description
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.LiFePO
4It is the research focus of active substance of lithium ion battery anode.LiFePO
4Compare with other battery with positive active material as lithium ion battery and to have good electrochemical, charge and discharge platform is very steady, Stability Analysis of Structures in the charge and discharge process, and having nontoxic, pollution-free, advantage such as safety performance is good, can use under hot environment, starting material wide material sources, is the competitively focus of development research of current battery circle.But LiFePO
4Poor electric conductivity, compare with other active material for anode of Li-ion secondary battery, as cobalt acid lithium (5.1 grams per milliliter), lithium nickelate (4.8 grams per milliliter) and lithium manganate (4.3 grams per milliliter), the density of this material is lower, be 3.6 grams per milliliters, so this has limited the application of LiFePO 4 in practical lithium-ion greatly.
At present, in preparing the method for LiFePO 4, solid phase method technology is simple, and use equipment is realized easily, realizes the earliest in industrialization.Mainly comprising two kinds in the existing solid phase synthesis process, a kind ofly be---the divalence source of iron is as the preparation method of reaction raw materials; Another kind is---ferric iron source is as the preparation method of reaction raw materials.
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, as Ferrox, Iron diacetate, iron protochloride etc., this method comprises that be Li: Fe: P: TR=(1-x) with lithium salts, 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, 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.Adopt ferro-compound as source of iron, and the LiFePO 4 that utilizes the method for secondary clacining to obtain to make the specific discharge capacity of the battery that obtains higher relatively, heavy-current discharge performance is better relatively, but tap density is low, and volume and capacity ratio is low, therefore, the battery volume that makes is bigger.
CN1775665A discloses the method that a kind of solid phase reduction legal system is equipped with LiFePO 4, this method comprise will contain Li source compound, ferric iron source compound, P source compound and organic additive mix, add organic solvent, in ball mill ball milling 1-8 hour; Then 100-120 ℃ of oven dry; Under 500-800 ℃ of constant temperature sintering 4-24 hour again; Last naturally cooling is worn into powder with the LiFePO 4 solid that makes in ball mill.The employing ferric iron compound is big as the tap density of the LiFePO 4 that source of iron prepares, the volume and capacity ratio height, and still, grain graininess is big, and purity is not high, and conductivity of electrolyte materials is lower, and heavy-current discharge performance is undesirable.
Summary of the invention
The objective of the invention is to adopt the LiFePO 4 of prior art for preparing can not take into account high specific discharge capacity and volume and capacity ratio in order to overcome, make the battery for preparing to take into account the defective of heavy body, good heavy-current discharge performance and smaller size smaller, provide a kind of and have high specific discharge capacity and volume and capacity ratio, and make the battery volume less and have the preparation method of the LiFePO 4 of heavy body and good heavy-current discharge performance simultaneously.
The present inventor finds, prepare by existing solid phase method that we recognize in the technology of LiFePO 4, mainly comprise in the existing solid phase synthesis process and adopt the divalence source of iron as the preparation method of reaction raw materials with adopt the preparation method of ferric iron source as reaction raw materials.For adopting the divalence source of iron all to adopt the technology of secondary clacining as the method for reaction raw materials, purpose is to make the bigger ferrous salt of grain graininess carry out pyrolytic decomposition in the time of the first step incinerating, and then in secondary clacining, can prepare the less LiFePO 4 particle of grain graininess, therefore, specific discharge capacity is higher relatively, in addition, when battery carries out heavy-current discharge, lithium ion takes off embedding and embedding in solid particulate distance shortens, therefore, the heavy-current discharge performance of battery is better relatively.But, in the first step calcination process of pretreatment stage, make oarse-grained ferrous salt, when carrying out pyrolytic decomposition, can emit a large amount of gas, as ammonia, carbonic acid gas etc. as Ferrox, can cause the material mesoporosity to increase, short texture, tap density is low, and accumulation property is poor, therefore, the LiFePO 4 granular size irregularity that obtains behind the secondary clacining, though can obtain the ferrous phosphate particle of relative small particle size by two-section calcining,, because granular size irregularity, cause tap density low, accumulation property is poor, so volume and capacity ratio is low.The existing employing in the technology of ferric iron as the feedstock production LiFePO 4, because the difference of source of iron, therefore, only need to adopt one-step calcination just can obtain the relatively large LiFePO 4 particle of tap density, the volume and capacity ratio of the lithium ion battery that the LiFePO 4 that therefore adopts this method to obtain prepares is higher relatively, but the electric conductivity of LiFePO 4 is low, and cell container is not high.
The invention provides a kind of preparation method of active material for anode of Li-ion secondary battery LiFePO 4, this method comprises and will contain the mixture sintering of lithium compound, iron cpd, phosphorus compound and carbon source additive, the sintered product that cooling obtains, wherein, described iron cpd is a ferric iron compound; Described agglomerating method is in inertia or reducing atmosphere, and the constant temperature sintering obtains sintered product under first sintering temperature, and the product that the first sintering temperature sintering is obtained is reduced to room temperature then, with dispersant and grinding; Constant temperature sintering under second sintering temperature, and in inertia or reducing atmosphere, reduce to room temperature, second sintering temperature is higher than at least 100 ℃ of first sintering temperatures.
The present inventor finds unexpectedly, adopt the ferric iron source compound as raw material, and mix with Li source compound, P source compound and carbon source additive, the specific discharge capacity and the volume and capacity ratio that carry out the LiFePO 4 that obtains behind the two-step sintering are all higher, after this LiFePO 4 is prepared into battery, the capacity and the heavy-current discharge performance of battery all are significantly improved, make battery can take into account heavy body and preferable heavy-current discharge performance simultaneously and the battery volume for preparing less.The reason of inferring may be, when adopting ferric iron source to carry out the first step incinerating, under the temperature that is fit to, be preferably under 250-400 ℃, at first be to allow raw material fully react, and there is the part LiFePO 4 to generate, but complete crystallization not, before the second step sintering, grind with first sintered product and dispersant and to material again, be preferably ball milling, can make the particle of material thinner, size is more even, reaches at ball milling necessarily to require laggard second step of row sintering, can eliminate because the short texture in the first step sintering process, and make material carry out secondary crystal, thus can reform to the LiFePO 4 crystallization, reach the further material pattern that improves, the purpose that size distribution and further crystallization are handled.In addition, according to of the present invention one preferred embodiment, after with first sintered product and dispersant and ball milling, carry out compressing tablet again, can allow raw material that decomposition reaction takes place fully, described compressing tablet can make the diffusion length of various ions between solid phase material that participates in reaction shorten, when second goes on foot sintering, can make material carry out secondary crystal more fully, thereby can reform to the LiFePO 4 crystallization, make the material that obtains adopt ferric one-step calcination technology relatively with existing, the grain diameter of the LiFePO 4 that obtains is little, pattern is regular, crystal formation is grown, be evenly distributed and tap density big, therefore, when battery charging and discharging, help shortening lithium ion taking off embedding and embedding diffusion length in LiFePO 4, improved the conductivity of material.Therefore, adopt the specific discharge capacity and the volume and capacity ratio of the LiFePO 4 that such method obtains all higher, therefore can take into account the advantage of the LiFePO 4 that is prepared as source of iron respectively by ferrous iron and ferric iron, improved performance is remarkable.
Description of drawings
Fig. 1 is the XRD diffractogram of the LiFePO 4 that adopts method of the present invention and prepare;
Fig. 2 schemes for the SEM of the LiFePO 4 that employing method of the present invention prepares.
Embodiment
According to the present invention, this method comprises and will contain the mixture sintering of lithium compound, iron cpd, phosphorus compound and carbon source additive, the sintered product that cooling obtains, and wherein, described iron cpd is a ferric iron compound; Described agglomerating method is in inertia or reducing atmosphere, and the constant temperature sintering obtains sintered product under first sintering temperature, and the product that the first sintering temperature sintering is obtained is reduced to room temperature then, with dispersant and grinding; Constant temperature sintering under second sintering temperature, and in inertia or reducing atmosphere, reduce to room temperature, second sintering temperature is higher than at least 100 ℃ of first sintering temperatures.
Described ferric iron compound can be selected from various ferric iron source compound as the preparation LiFePO 4 well known in the art, as, can be selected from Fe
2O
3, Fe
3O
4And FePO
4In one or more.
Described 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
4, CH
3COOLi, LiH
2PO
4And Li
3PO
4In one or more.
Described 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, FePO
4, LiH
2PO
4, Li
3PO
4(NH
4)
3PO
4In one or more.
Described monometallic (LiH
2PO
4) both can be used as the lithium source and also can be used as the phosphorus source, lithium and phosphorus can be provided simultaneously, not only greatly reduce cost, also reduce the generation of waste gas in the reaction process, be easy to obtain the LiFePO 4 of pure phase, the therefore preferred compound that adopts the monometallic conduct that lithium source and phosphorus source are provided.
According to the present invention, the mol ratio of Li in described lithium compound, ferric iron compound and the phosphorus compound: Fe: P is (0.9-1.2): 1: 1, it is 1-10 weight % that the consumption of described carbon source additive makes the carbon content in the LiFePO 4 of generation, the product that obtains of the first sintering temperature sintering with respect to 100 grams, the add-on of dispersion agent is the 500-800 milliliter, is preferably the 600-700 milliliter.
According to the present invention, described dispersion agent can be selected from one or more in ethanol, propyl alcohol, ethyl ketone, acetone and the tetrahydrofuran (THF).
Described carbon source additive can be selected from and well known to a person skilled in the art the additive that can play electric action, 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, poly-in benzene, Zulkovsky starch, polyvinyl alcohol, sucrose, glucose, resol, furfuryl resin, synthetic graphite, natural graphite, superconduction acetylene black, acetylene black, carbon black and the mesocarbon bead one or more.
According to method of the present invention, in order further to improve the electroconductibility of material, also contain compounds of metal M in the described mixture that contains lithium compound, iron cpd, phosphorus compound and carbon source additive.Described compounds of metal M can be selected from various compounds of metal M as the preparation LiFePO 4s well known in the art, as, can be selected from oxide compound, oxyhydroxide and the carbonate of Mg, Mn, Ca, Sn, Co, Ni, Mo one or more; As in magnesium oxide, Manganse Dioxide, lime carbonate, tindioxide, tricobalt tetroxide, nickel protoxide and the molybdenum oxide one or more.The mol ratio of Li in described lithium compound, ferric iron compound, phosphorus compound and the compounds of metal M: M: Fe: P is (0.9-1.2): x: (1-x): 1, and in the formula, M is a metal, 0＜x≤0.3.
The described mixture that contains the compounds of metal M that lithium compound, ferric iron compound, phosphorus compound and carbon source additive and selectivity add can be by mechanically mixing, grind the mode that is preferably ball milling mixes and obtains.The method of described ball milling comprises mixes ball milling then with the compounds of metal M of lithium compound, ferric iron compound, phosphorus compound, carbon source additive and selectivity adding with organic solvent, the kind of described organic solvent and consumption are conventionally known to one of skill in the art, as ethanol and/or propyl alcohol, the consumption of organic solvent and the weight ratio of described mixture can be 1-5: 1.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, can adopt the method for this area routine.
Described first sintering temperature is 250-400 ℃, in order more to help allowing raw material fully react, the part LiFePO 4 is generated, but can not complete crystallization, therefore, under the preferable case, described first sintering temperature is 300-400 ℃, the constant temperature agglomerating time is 2-10 hour, is preferably 5-10 hour.
Described second sintering temperature be 600-less than 900 ℃, be preferably 650-800 ℃, the constant temperature agglomerating time is 5-40 hour, is preferably 10-20 hour.
For the reaction that makes material more abundant, make the pattern of the LiFePO 4 that obtains better, described agglomerating method is preferably in inertia or reducing atmosphere, be warming up to the first sintering temperature constant temperature sintering with 2-10 ℃/minute speed, obtain sintered product, the product that the first sintering temperature sintering is obtained is reduced to room temperature with 2-10 ℃/minute speed then, with dispersant and grinding; Be warming up to the second sintering temperature constant temperature sintering with 2-10 ℃/minute speed again, in inertia or reducing atmosphere, reduce to room temperature or naturally cool to room temperature then with 2-10 ℃/minute speed.
Before constant temperature sintering under second sintering temperature, the product that the first sintering temperature sintering obtains is reduced to room temperature, with dispersant and grinding, be preferably ball milling.
Add and to adopt behind the dispersion agent low speed ball milling just can make the grain graininess of the material that ball milling obtains thinner again, granular size is more even, and therefore, the condition of described ball milling can make the median particle diameter D of the product that the first sintering temperature sintering obtains
50Less than 3 microns, be preferably the 0.8-2.8 micron; D
95Less than 10 microns, be preferably the 4-8 micron.The condition of described ball milling comprises the time of the rotating speed and the ball milling of ball milling, and the rotating speed of described ball milling is generally the low speed ball milling and gets final product, and as being 350-500 rev/min, the time of ball milling is not particularly limited, and can be 3-10 hour.The present invention only needs to adopt low speed and the ball milling of short period of time just to can be good at controlling the material particle size that obtains after with first sintered product and dispersant, make the material of short texture be ground into small-particle, fill up in the macrobead gap, increased the accumulation of material, thereby further improve the tap density of material, the sintering that was second step is laid good basis, the crystal shape of the LiFePO 4 that obtains after making the employing ferric iron compound as source of iron process two-step sintering is regular, even particle size distribution, tap density is big.In addition, reach the step that need not to sieve again after the above-mentioned particle diameter requirement, can directly carry out the second step sintering step, therefore, simplified technology, saved starting material through this step ball milling.For the ease of the second step sintering, under the preferable case, this method also comprises the step of dry this grinding back material, and exsiccant method and condition are conventionally known to one of skill in the art, can adopt the method for this area routine.
Under the preferable case, this method also comprise product that the first sintering temperature sintering is obtained and dispersant and grind after the material compressing tablet, it is the 2.0-3.5 gram per centimeter that the condition of compressing tablet makes the compacted density of the material that obtains
3, be preferably the 2.5-3 gram per centimeter
3Described compressing tablet can reduce hole between the material, increase the accumulation of material; Get rid of the air in the material, prevent that material is oxidized in sintering process; Make easier the reaching unanimity property of material reaction.
Described inertia or reducing atmosphere refer to not any one gas or the gaseous mixture with reactant and product generation chemical reaction, as in hydrogen, nitrogen, carbon monoxide, decomposed ammonia and the periodic table of elements zero group gas one or more.This inertia or reducing atmosphere can be static atmosphere, be preferably gas flow rate and be the 2-50 liter/minute mobile atmosphere.
To do further specific descriptions to the present invention by specific embodiment below.
Embodiment 1
This embodiment illustrates the preparation of positive active material LiFePO 4 provided by the invention
(1) with 103.93 gram LiH
2PO
4, 79.85 the gram Fe
2O
3Mix (Li: Fe: the P mol ratio is 1: 1: 1) with 1250 milliliters of dehydrated alcohols with 33.02 gram glucose, with 300 rev/mins speed ball millings 10 hours, taking-up, 70 ℃ of oven dry;
(2) under flow velocity is 10 liters/minute argon shield, the mixture of step (1) is risen to 350 ℃ with 2 ℃/minute speed, constant temperature sintering 6 hours is reduced to room temperature with 2 ℃/minute speed again;
(3) first sintered product that step (2) is obtained mixes (the alcoholic acid amount that adds with respect to 100 grams, first sintered product is 625 milliliters) with dispersion agent ethanol, and with 350 rev/mins rotating speed ball milling 6 hours, and 70 ℃ of oven dry, the median particle diameter D of the sintered product that obtains
50It is 2.285 microns; D
95It is 8.842 microns; Then with above-mentioned materials at 10 MPa pressure lower sheetings, the compacted density of the material that obtains is 2.8 gram per centimeters
3Continuation is under 10 liters/minute the argon shield at flow velocity, and above-mentioned materials is warming up to 700 ℃ with 2 ℃/minute speed, and constant temperature sintering 15 hours obtains the active material for anode of Li-ion secondary battery LiFePO 4 after reducing to room temperature with 2 ℃/minute speed again.It is 3.79 weight % that the consumption of described glucose makes the carbon content in the LiFePO 4 of generation.This LiFePO 4 particulate median particle diameter D that obtains
50It is 1.030 microns; D
95It is 5.153 microns; The tap density of this LiFePO 4 is 1.407 grams per milliliters.
The XRD diffractogram of this LiFePO 4 that the D/MAX-2200/PC type x-ray powder diffraction instrument of employing Rigaku company records as shown in Figure 1; The SEM that adopts day SSX-550 type scanning electron microscope of island proper Tianjin company (Shimadzu) production to record this LiFePO 4 schemes as shown in Figure 2.
Embodiment 2
This embodiment illustrates the preparation of positive active material LiFePO 4 provided by the invention
Method according to embodiment 1 prepares LiFePO 4, different is, after the product that the first sintering temperature sintering is obtained and dispersant and ball milling, oven dry, do not carry out compressing tablet, directly carry out the sintering second time, other condition is identical with embodiment 1 with step, this LiFePO 4 particulate median particle diameter D that obtains
50It is 1.587 microns; D
95It is 8.363 microns; The tap density of this LiFePO 4 is 1.124 grams per milliliters.
Embodiment 3
This embodiment illustrates the preparation of positive active material LiFePO 4 provided by the invention
(1) with 103.93 gram LiH
2PO
4, 79.85 the gram Fe
2O
3Mix (Li: Fe: the P mol ratio is 1: 1: 1) with 1250 milliliters of dehydrated alcohols with 28.52 gram sucrose, with 450 rev/mins speed ball millings 10 hours, taking-up, 70 ℃ of oven dry;
(2) under flow velocity is 10 liters/minute argon shield, the mixture of step (1) is risen to 400 ℃ with 3 ℃/minute speed, constant temperature sintering 6 hours is reduced to room temperature with 3 ℃/minute speed again;
(3) first sintered product that step (2) is obtained mixes (is 600 milliliters with respect to 100 amounts that restrain the acetone of first sintered product adding) with dispersion agent acetone, and with 450 rev/mins rotating speed ball milling 6 hours, and 70 ℃ of oven dry, the median particle diameter D of the sintered product that obtains
50It is 2.047 microns; D
95It is 7.986 microns; Then with above-mentioned materials at 10 MPa pressure lower sheetings, the compacted density of the material that obtains is 2.62 gram per centimeters
3Continuation is under 10 liters/minute the argon shield at flow velocity, and above-mentioned materials is warming up to 800 ℃ with 3 ℃/minute speed, and constant temperature sintering 15 hours obtains the active material for anode of Li-ion secondary battery LiFePO 4 after reducing to room temperature with 3 ℃/minute speed again.It is 3.79 weight % that the consumption of described sucrose makes the carbon content in the LiFePO 4 of generation.This LiFePO 4 particulate median particle diameter D that obtains
50It is 1.009 microns; D
95It is 5.046 microns; The tap density of this LiFePO 4 is 1.353 grams per milliliters.
Embodiment 4
This embodiment illustrates the preparation of positive active material LiFePO 4 provided by the invention
Method according to embodiment 3 prepares LiFePO 4, different is, after the product that the first sintering temperature sintering is obtained and dispersant and ball milling, oven dry, do not carry out compressing tablet, directly carry out the sintering second time, other condition is identical with embodiment 3 with step, this LiFePO 4 particulate median particle diameter D that obtains
50It is 1.835 microns; D
95It is 5.091 microns; The tap density of the LiFePO 4 that obtains is 1.102 grams per milliliters.
Embodiment 5
This embodiment illustrates the preparation of positive active material LiFePO 4 provided by the invention
(1) with 36.95 gram Li
2CO
3, 150.82 the gram FePO
4Mix (Li: Fe: the P mol ratio is 1: 1: 1) with 1250 milliliters of dehydrated alcohols with 69.5 gram polyvinyl alcohol, with 350 rev/mins speed ball millings 6 hours, taking-up, 70 ℃ of oven dry;
(2) under flow velocity is 10 liters/minute argon shield, the mixture of step (1) is risen to 300 ℃ with 3 ℃/minute speed, constant temperature sintering 8 hours is reduced to room temperature with 3 ℃/minute speed again;
(3) first sintered product that step (2) is obtained mixes (the alcoholic acid amount that adds with respect to 100 grams, first sintered product is 650 milliliters) with dispersion agent ethanol, and with 350 rev/mins rotating speed ball milling 8 hours, 70 ℃ of oven dry, the median particle diameter D of the sintered product that obtains
50It is 2.687 microns; D
95It is 10.041 microns; Then with above-mentioned materials at 10 MPa pressure lower sheetings, the compacted density of the material that obtains is 2.5 gram per centimeters
3Continuation is under 10 liters/minute the argon shield at flow velocity, and above-mentioned materials is warming up to 850 ℃ with 3 ℃/minute speed, and constant temperature sintering 10 hours obtains the active material for anode of Li-ion secondary battery LiFePO 4 after reducing to room temperature with 3 ℃/minute speed again.It is 5 weight % that the consumption of described polyvinyl alcohol makes the carbon content in the LiFePO 4 of generation.This LiFePO 4 particulate median particle diameter D that obtains
50It is 1.924 microns; D
95It is 8.006 microns; The tap density of this LiFePO 4 is 1.364 grams per milliliters.
Embodiment 6
This embodiment illustrates the preparation of positive active material LiFePO 4 provided by the invention
Method according to embodiment 5 prepares LiFePO 4, and different is also to comprise in step (1) 36.95 gram Li
2CO
3, 143.28 the gram FePO
4, 69.5 gram polyvinyl alcohol and 2 gram MgO mix with 1500 milliliters of dehydrated alcohols that (Li: Fe: Mg: the P mol ratio is 1: 0.95: 0.05: 1).Other condition is identical with embodiment 5 with step, this LiFePO 4 particulate median particle diameter D that obtains
50It is 1.236 microns; D
95It is 9.657 microns; The tap density of the LiFePO 4 that obtains is 1.241 grams per milliliters.
Embodiment 7
This embodiment illustrates the preparation of positive active material LiFePO 4 provided by the invention
(1) with 103.93 gram LiH
2PO
4, 79.85 the gram Fe
2O
3Mix (Li: Fe: the P mol ratio is 1: 1: 1) with 1500 milliliters of dehydrated alcohols with 42.65 gram resol, with 500 rev/mins speed ball millings 10 hours, taking-up, 70 ℃ of oven dry;
(2) under flow velocity is 20 liters/minute argon shield, the mixture of step (1) is risen to 350 ℃ with 3 ℃/minute speed, constant temperature sintering 8 hours is reduced to room temperature with 3 ℃/minute speed again;
(3) first sintered product that step (2) is obtained mixes (is 700 milliliters with respect to 100 amounts that restrain the tetrahydrofuran (THF) of first sintered product adding) with the dispersion agent tetrahydrofuran (THF), and with 500 rev/mins rotating speed ball milling 6 hours, and 70 ℃ of oven dry, the median particle diameter D of the sintered product that obtains
50It is 0.957 micron; D
95It is 7.954 microns; Then with above-mentioned materials at 15 MPa pressure lower sheetings, the compacted density of the material that obtains is 2.6 gram per centimeters
3Continuation is under 20 liters/minute the argon shield at flow velocity, and above-mentioned materials is warming up to 800 ℃ with 3 ℃/minute speed, and constant temperature sintering 15 hours obtains the active material for anode of Li-ion secondary battery LiFePO 4 after reducing to room temperature with 3 ℃/minute speed again.It is 7 weight % that the consumption of described resol makes the carbon content in the LiFePO 4 of generation.This LiFePO 4 particulate median particle diameter D that obtains
50It is 0.903 micron; D
95It is 5.351 microns; The tap density of this LiFePO 4 is 1.297 grams per milliliters.
Comparative Examples 1
The reference preparation method of this Comparative Examples explanation positive active material LiFePO 4
Method according to embodiment 1 prepares LiFePO 4, and different is, with LiH
2PO
4, Fe
2O
3Mix with 1250 milliliters of dehydrated alcohols with glucose and with 300 rev/mins speed ball milling 10 hours; and oven dry back is directly under flow velocity is 10 liters/minute argon shield; this mixture is risen to 700 ℃ with 2 ℃/minute speed; constant temperature sintering 15 hours, this LiFePO 4 particulate median particle diameter D that obtains
50It is 3.825 microns; D
95It is 13.672 microns; The tap density of this LiFePO 4 is 0.820 grams per milliliter.
Comparative Examples 2
The preparation method of the positive active material LiFePO 4 of this Comparative Examples explanation prior art
Method according to the disclosed embodiment 1 of CN1775665A prepares the battery positive electrode active material LiFePO 4.The LiFePO 4 particulate average particulate diameter that adopts this method to prepare is the 1-3 micron.
Adopt 0.3 milliampere of electric current to discharge and recharge experiment.Initial discharge capacity is 152.6 MAH/grams.
Comparative Examples 3
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, different is, described iron cpd is 179.90 gram Ferroxs, and do not add the dispersion agent among the embodiment 1 when before the second step sintering, grinding, other step is identical with embodiment 1 with condition, the LiFePO 4 particulate median particle diameter D that obtains
50It is 2.56 microns; D
95It is 12.62 microns; The tap density of this LiFePO 4 is 0.75 grams per milliliter.
Embodiment 8-14
The following examples explanation is carried out performance test to battery after adopting positive active material LiFePO 4 provided by the invention to be prepared into battery.
(1) preparation of battery
The anodal preparation
Restrain the positive active material LiFePO that makes by embodiment 1-7 with 100 respectively
4, 2 gram binding agent polyvinylidene difluoride (PVDF) (PVDF) and 3 gram conductive agent acetylene blacks join in the 40 gram N-Methyl pyrrolidone, stir the uniform anode sizing agent of formation then in vacuum mixer.
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 5.8 gram activeconstituents LiFePO that have an appointment
4
The preparation of negative pole
100 gram negative electrode active composition natural graphites, 3 gram caking agent polyvinylidene difluoride (PVDF), 3 gram conductive agent 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 2.6 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-A7 is made in sealing respectively.
(2) battery performance test
The above-mentioned lithium ion A1-A7 battery that makes is placed on test respectively cashier's office in a shop, carries out constant current charge with the 0.2C electric current earlier, the charging upper voltage limit is 3.8 volts, and constant voltage charge is 2.5 hours then; After shelving 20 minutes, be discharged to 3.0 volts with the electric current of 0.2C from 3.8 volts again, the loading capacity first of record battery, and calculate the specific discharge capacity and the volume and capacity ratio of battery according to the following equation;
Specific discharge capacity=battery is loading capacity (MAH)/positive electrode material weight (gram) first
Volume and capacity ratio=battery is loading capacity (MAH)/positive electrode material volume (centimetre 3) first
And then carry out constant current charge with the 0.2C electric current, and being limited to 3.8 volts in the charging, constant voltage charge is 2.5 hours then; After shelving 20 minutes, be discharged to 3.0 volts with the electric current of 1C, 2C and 5C from 3.8 volts respectively, the ratio of the loading capacity when writing down the loading capacity of each battery and calculating respectively with the 0.2C discharge, that is:
C
1C/ C
0.2C: the electric current with 1C is discharged to the loading capacity of 3.0V and the ratio that is discharged to the loading capacity of 3.0V with the electric current of 0.2C from 3.8V from 3.8V;
C
2C/ C
0.2C: the electric current with 2C is discharged to the loading capacity of 3.0V and the ratio that is discharged to the loading capacity of 3.0V with the electric current of 0.2C from 3.8V from 3.8V;
C
5C/ C
0.2C: the electric current with 5C is discharged to the loading capacity of 3.0V and the ratio that is discharged to the loading capacity of 3.0V with the electric current of 0.2C from 3.8V from 3.8V.
The result is as shown in table 1 below.
Comparative Examples 4-6
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 8-14 prepares reference cell AC1-AC3, and the loading capacity first of test battery, and calculates the specific discharge capacity and the volume and capacity ratio of battery; And heavy-current discharge performance, different is the reference positive active material LiFePO 4 that the positive active material of preparation used in battery obtains for Comparative Examples 1-3.
The result is as shown in table 1 below.
Table 1
With embodiment 1 is example, and as can be seen from Figure 1, the LiFePO 4 that adopts method of the present invention to prepare has the olivine-type structure of standard, no dephasign, purity height, and crystal formation physically well develops.Fig. 2 serves as reasons and adopts method of the present invention to obtain the stereoscan photograph of 10000 times of the amplifications of LiFePO 4, as can be seen from the figure, the crystalline particle of LiFePO 4 is little, and size is than homogeneous, particle size distribution is even, and most of particulate diameter is between the 0.5-3 micron.
Data from table 1 as can be seen, and are all undesirable by cell container and the heavy-current discharge performance of the AC1 of the reference cell of the LiFePO 4 preparation of Comparative Examples 1 preparation; The heavy-current discharge performance of the AC2 of the reference cell that the LiFePO 4 that is prepared by Comparative Examples 2 prepares is relatively poor; Though D by the LiFePO 4 of Comparative Examples 3 preparation
50Less, cell container is higher relatively, still, the volume of battery specific storage that is prepared by this LiFePO 4 is low, if preparation volume little battery, then can the limit battery positive pole in the content of active substance ferrous lithium phosphate, make the room for promotion of cell container be restricted.
Grain diameter by the positive active material LiFePO 4 of method of the present invention preparation is little, median particle diameter D
50For about 1 micron, and as can be seen from Figure 3, most of particulate diameter is between the 0.5-3 micron, and the crystalline particle of LiFePO 4 size homogeneous, particle size distribution is even, therefore, specific discharge capacity and the volume and capacity ratio of the battery A1-A7 that is prepared by this LiFePO 4 are all higher, and battery is taken into account heavy body and good heavy-current discharge performance.
Claims (9)
1. the preparation method of an active material for anode of Li-ion secondary battery LiFePO 4, this method comprises and will contain the mixture sintering of lithium compound, iron cpd, phosphorus compound and carbon source additive, the sintered product that cooling obtains, it is characterized in that described iron cpd is a ferric iron compound; Described agglomerating method is in inertia or reducing atmosphere, and the constant temperature sintering obtains sintered product under first sintering temperature, and the product that the first sintering temperature sintering is obtained is reduced to room temperature then, with dispersant and grinding; Constant temperature sintering under second sintering temperature, and in inertia or reducing atmosphere, reduce to room temperature, second sintering temperature is higher than at least 100 ℃ of first sintering temperatures.
2. method according to claim 1, wherein, described ferric iron compound is selected from Fe
2O
3, Fe
3O
4And FePO
4In one or more.
3. method according to claim 1, wherein, the condition of described grinding makes the median particle diameter D of material
50Less than 3 microns; D
95Less than 10 microns.
4. method according to claim 1, wherein, described first sintering temperature is 250-400 ℃, the constant temperature agglomerating time is 2-10 hour; Described second sintering temperature be 500-less than 900 ℃, the constant temperature agglomerating time is 5-40 hour.
5. method according to claim 1, wherein, this method also comprise product that the first sintering temperature sintering is obtained and dispersant and grind after the material compressing tablet, it is the 2.0-3.5 gram per centimeter that the condition of compressing tablet makes the density of the material that obtains
3
6. method according to claim 1, wherein, the mol ratio of Li in described lithium compound, ferric iron compound and the phosphorus compound: Fe: P is (0.9-1.2): 1: 1, it is 1-10 weight % that the consumption of described carbon source additive makes the carbon content in the LiFePO 4 of generation, with respect to the product that the 100 first sintering temperature sintering that restrain obtain, the add-on of dispersion agent is the 500-800 milliliter.
7. according to claim 1,5 or 6 described methods, wherein, described dispersion agent is selected from one or more in ethanol, propyl alcohol, ethyl ketone, acetone and the tetrahydrofuran (THF).
8. according to claim 1 or 6 described methods, wherein, described lithium compound is selected from Li
2CO
3, LiOH, Li
2C
2O
4, CH
3COOLi, LiH
2PO
4And Li
3PO
4In one or more; Described phosphorus compound is selected from NH
4H
2PO
4, (NH
4)
2HPO
4, FePO
4, LiH
2PO
4, Li
3PO
4(NH
4)
3PO
4In one or more; Described carbon source additive is selected from the luxuriant and rich with fragrance terpolymer of benzene naphthalene, the luxuriant and rich with fragrance copolymer of benzene, benzene anthracene copolymer, poly-in benzene, Zulkovsky starch, polyvinyl alcohol, sucrose, glucose, resol, furfuryl resin, synthetic graphite, natural graphite, superconduction acetylene black, acetylene black, carbon black and the mesocarbon bead one or more.
9. method according to claim 1 wherein, contains in the mixture of lithium compound, iron cpd, phosphorus compound and carbon source additive and also contains compounds of metal M; Described compounds of metal M is selected from one or more in oxide compound, oxyhydroxide and the carbonate of Mg, Mn, Ca, Sn, Co, Ni, Mo, and the mol ratio of described Li: M: Fe: P is (0.9-1.2): x: (1-x): 1, and in the formula, 0＜x≤0.3.
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| CN108091869A (en) * | 2018-01-10 | 2018-05-29 | 福州大学 | A kind of high jolt ramming lithium iron phosphate positive material and preparation method |
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