CN100557862C - A kind of method of encapsulating active material for negative pole of Li-ion secondary battery - Google Patents
A kind of method of encapsulating active material for negative pole of Li-ion secondary battery Download PDFInfo
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- CN100557862C CN100557862C CNB2006101673875A CN200610167387A CN100557862C CN 100557862 C CN100557862 C CN 100557862C CN B2006101673875 A CNB2006101673875 A CN B2006101673875A CN 200610167387 A CN200610167387 A CN 200610167387A CN 100557862 C CN100557862 C CN 100557862C
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Abstract
A kind of method of encapsulating active material for negative pole of Li-ion secondary battery, this method is included in and heats the mixture that contains negative electrode active material and covering under the inert gas atmosphere, wherein, comprise also in the described mixture that described initator is for only containing the organic peroxide of C, H, O with initator.Because method of the present invention, not by carrying out heat polymerization after the physical mixed of finishing covering and negative electrode active material again, make covering form coating layer on the negative electrode active material surface, add initator but adopt in the two mixed process, under temperate condition, finish simultaneously and mix and graft reaction, make covering form coating layer on the negative electrode active material surface, therefore caking phenomenon can not take place, need not broken directly charing or graphitization and just can get evenly complete negative electrode active material of coating layer, the battery first charge-discharge efficiency that is made by this negative electrode active material is higher, and cycle performance is better.
Description
Technical field
The invention relates to a kind of method of surface modification battery cathode active substance, especially about a kind of method of coated lithium ion battery negative electrode active material.
Background technology
Lithium rechargeable battery refers to respectively the ion battery that constitutes as both positive and negative polarity with two compounds that can reversibly embed with the removal lithium embedded ion.Because of its specific energy height, operating voltage height, operating temperature range is wide, self-discharge rate is low, have extended cycle life, pollution-free, in light weight, advantage such as security performance is good, thereby application is extensive.
Lithium rechargeable battery generally includes battery container and is sealed in this battery container interior electrode group and electrolyte; Described electrode group comprises positive pole, negative pole and the barrier film between positive pole and negative pole; Described negative pole comprises negative electrode collector and applies negative material on it; Described negative material comprises negative electrode active material and adhesive.
Material with carbon element is the negative electrode active material of lithium rechargeable battery, is fit to deviating from/embedding of lithium ion.Wherein graphitic conductive is good, and the degree of crystallinity height has good layer structure, and reversible charge/discharge capacity can reach more than 300 MAH/grams (mAh/g), the LiC that forms in material with carbon element near lithium
6Theoretical specific capacity 372mAh/g, lithium taking off in graphite/embedding reaction or take off/embedding capacity mainly occurs in (corresponding Li about 0 volt-0.25 volt
+/ Li), have the favorable charge-discharge platform.
But as the material with carbon element of negative electrode active material, especially the compatibility of graphite and electrolyte is poor, and first charge-discharge can form passivating film at carbon material surface, repeatedly occurs in the charge and discharge process peeling off, subsiding, thereby causes the electrode cycle performance sharply to be decayed.The general at present method that the carbon material surface as negative electrode active material is coated that adopts prevents the problems referred to above, described method generally includes mixes negative electrode active material with covering, make the reaction of negative electrode active material and covering generation thermal polycondensation, to product charing or graphitization processing.High temperature carbonization or graphited material with carbon element obviously improve as the cycle performance of lithium ion secondary battery negative pole after coating.
For example, a kind of method for preparing the hud typed carbon cathode material of lithium rechargeable battery is disclosed among the CN 1547278A, this method comprises that the pulverizing with graphite is the micro mist of particle diameter 5-50 micron, with the gained graphite microparticles by weight 0.01-1: 1 is at least a mixing in the mid temperature pitch of pitch and coal measures with ethylene bottom oil, coal tar, oil, carry out thermal polycondensation reaction 0.5-10 hour at 300-500 ℃, the gained product is handled with washing oil, pyridine or toluene wash, the charing that coats the back graphite microparticles.After the hud typed carbon cathode material of gained is made lithium rechargeable battery, first charge-discharge efficiency height, good cycle.
The method of prior art encapsulating active material for negative pole of Li-ion secondary battery all is to finish the physical mixed of covering and negative electrode active material earlier, and then make covering and negative electrode active material generation heat polymerization, make covering form coating layer, at last this coating layer is carried out charing or graphitization on the negative electrode active material surface; But the heat polymerization condition is easy to make the negative electrode active material caking after the coating, generally by charing or graphitizing method make the negative electrode active material after the coating reach the particle diameter requirement again after pulverizing, the coating layer on negative electrode active material surface is easy to come off because of Mechanical Crushing in pulverizing heat polymerization product process, cause that coating layer is inhomogeneous, imperfect, make cycle performance of battery can not get improving fully then.
To sum up, there is the inhomogeneous incomplete problem of coating layer in the method for the method encapsulating active material for negative pole of Li-ion secondary battery of prior art.
Summary of the invention
The objective of the invention is inhomogeneous, the incomplete shortcoming of coating layer for the method gained negative electrode active material that overcomes existing encapsulating active material for negative pole of Li-ion secondary battery, a kind of method of encapsulating active material for negative pole of Li-ion secondary battery is provided, and the coating layer of this method gained negative electrode active material is evenly complete.
The present inventor notices, the method of prior art encapsulating active material for negative pole of Li-ion secondary battery all is to finish the physical absorption of covering and negative electrode active material earlier, and then make covering and negative electrode active material generation heat polymerization, make covering form coating layer, at last this coating layer is carried out charing or graphitization on the negative electrode active material surface; But the heat polymerization condition is easy to make the negative electrode active material caking after the coating, generally by charing or graphitizing method make the negative electrode active material after the coating reach the particle diameter requirement again after pulverizing, the coating layer on negative electrode active material surface is easy to come off because of Mechanical Crushing in pulverizing heat polymerization product process, cause that coating is inhomogeneous, imperfect, make cycle performance of battery can not get improving fully then.The present inventor is surprised to find that, not by carrying out heat polymerization after the physical mixed of finishing covering and negative electrode active material again, but in the two mixed process, add initator under temperate condition, finish simultaneously and mix and graft reaction, also can make covering form coating layer on the negative electrode active material surface, and caking phenomenon can not take place, therefore need not just can get evenly complete negative electrode active material of coating layer after broken directly charing or the graphitization.The negative electrode active material coating layer is complete more, and the reversible specific capacity of negative electrode active material and first charge-discharge efficiency are high more, and is good more by the cycle performance of the battery of this negative electrode active material preparation.
The invention provides a kind of method of encapsulating active material for negative pole of Li-ion secondary battery, this method is included in and heats the mixture that contains negative electrode active material and covering under the inert gas atmosphere, wherein, comprise also in the described mixture that with initator described initator is for only containing the organic peroxide of C, H, O.
Because the method for encapsulating active material for negative pole of Li-ion secondary battery of the present invention, not by carrying out heat polymerization after the physical mixed of finishing covering and negative electrode active material again, make covering form coating layer on the negative electrode active material surface, add initator in the two mixed process under temperate condition but adopt, finish simultaneously and mix and graft reaction, make covering form coating layer on the negative electrode active material surface, therefore the negative electrode active material caking phenomenon can not take place, thereby the problem that does not exist the coating layer that causes by fragmentation to come off, need not broken directly charing or graphitization and just can get evenly complete negative electrode active material of coating layer, the battery first charge-discharge efficiency that is made by this negative electrode active material is higher, and cycle performance is better.
Description of drawings
Fig. 1 is the not stereoscan photograph of coated natural graphite of Comparative Examples 1;
Fig. 2 is the stereoscan photograph according to the native graphite after the method coating of Comparative Examples 2;
Fig. 3 is the stereoscan photograph according to the native graphite after the method coating of embodiment 1.
Embodiment
The method of encapsulating active material for negative pole of Li-ion secondary battery provided by the invention is included in and heats the mixture that contains negative electrode active material and covering under the inert gas atmosphere, wherein, comprise also in the described mixture that with initator described initator is for only containing the organic peroxide of C, H, O.
The peroxide radical of described initator can make the C-C key of covering that fracture takes place and the activation free-end occur, the free-end of this activation need not heating condition just can with graphite generation graft reaction.When mixing covering, initator and negative electrode active material, existing physical absorption between negative electrode active material and the covering has chemical bonding again like this, and the physical absorption that the interaction force rate is simple is stronger.In general, the time of covering, initator and the combined material continuous mixing of negative electrode active material is long more, covering and negative electrode active material surface combination are more all even closely, and for the consideration of energy consumption, the time that preferred initator, covering and negative electrode active material mix was generally 0.5-8 hour.The activation free-end that the weight specific energy of described initator and covering effectively increases covering gets final product, and the weight ratio of preferred described initator and covering is 0.05: 10 to 1: 10, more preferably 0.1: 10 to 0.5: 10.
Because covering of the present invention can be selected from organic polymer, according to the similar principle that mixes, therefore described initator is for only containing the organic peroxide of C, H, O, under the preferable case, described initator is selected from one or more in the organic peroxide shown in formula (1), formula (2), the formula (3)
Formula (1)
In the formula (1), R
1For carbon number is not more than the alkyl of 20 (preferably being not more than 16) or the alkoxyl that carbon number is not more than 20 (preferably being not more than 16), R
2Alkyl, H or the carbon number that is not more than 20 (preferably being not more than 16) for carbon number is not more than the ester group of 20 (preferably being not more than 16), R
3And R
4Be that H or carbon number are not more than the alkyl of 20 (preferably being not more than 16), n=1-5 independently;
In the formula (2), X
1For carbon number is not more than the alkyl of 20 (preferably being not more than 16) or the alkoxyl that carbon number is not more than 20 (preferably being not more than 16), X
2Alkyl, H or the carbon number that is not more than 20 (preferably being not more than 16) for carbon number is not more than the ester group of 20 (preferably being not more than 16);
In the formula (3), Y
1For carbon number is not more than the alkylene oxide group that 20 alkylene or carbon number are not more than 20 (preferably being not more than 16), Y
2And Y
2' be not more than the alkyl of 20 (preferably being not more than 16) or the ester group that carbon number is not more than 20 (preferably being not more than 16) for H, carbon number independently.
Described initator is dilauroyl peroxide, dibenzoyl peroxide, new peroxide tert-butyl caprate, tert-butyl hydroperoxide isobutyrate, 1 more preferably, one or more in 1-cyclohexane di-tert-butyl peroxide, dicumyl peroxide and the peroxidating cyclohexane.
This area can may be used to the present invention as the material with carbon element of active material for negative pole of Li-ion secondary battery especially graphite, reaches goal of the invention of the present invention.Described graphite can be divided into native graphite and Delanium.Native graphite comprises types such as amorphous graphite and flaky graphite, and Delanium then is that some easy graphited material with carbon element such as coke, pitch etc. are carried out pulverizing, screening and the material of formation after the graphitization.Described negative electrode active material is selected from one or more in natural flake graphite, natural micro crystal graphite and the Delanium.General by median particle diameter D
50The particle size distribution situation that reflects material with carbon element.Described herein average grain diameter D
50Be by being particle diameter with transverse axis a, longitudinal axis b is that the particle size distribution of the volume reference represented of the a-b coordinate system of population is tried to achieve.In above-mentioned particle size distribution, begin the accumulative total volume from the little particle diameter of a value, a value that the accumulative total volume reaches 50% o'clock correspondence of integral body is particle diameter D
50The median particle diameter D of preferred described negative electrode active material
50Be the 4-50 micron, microcrystalline coating interplanar distance d002 is the 0.3354-0.3390 nanometer, and specific area is the 0.5-6 meters squared per gram, more preferably the median particle diameter D of described negative electrode active material
50Be the 10-25 micron, microcrystalline coating interplanar distance d002 is the 0.3354-0.3370 nanometer, and specific area is the 1-4 meters squared per gram.
The weight ratio that described negative electrode active material mixes with covering can make the existing various weight ratios in this area, as long as covering is excessive in the graft reaction of covering and negative electrode active material.Under the preferable case, the weight ratio that described negative electrode active material mixes with covering is 100: 0.5 to 100: 30.Described covering can be selected from can with the organic substance of the activation free-end generation graft reaction of negative electrode active material, be preferably selected from styrene, polystyrene, polyethylene, polypropylene, furfural resin, Lauxite, epoxy resin, polyvinyl alcohol, polymethyl methacrylate, polyacrylonitrile, coal tar pitch and the petroleum asphalt one or more.
The hybrid mode of described negative electrode active material, covering mixture can be this area various hybrid modes commonly used, such as ball milling, vibrate, stir mill, the collision, mixing can improve the surface energy of negative electrode active material, in general the time of Hun Heing long approximately, easy more generation graft reaction.Preferred high-energy ball milling or stir mill, the time of mixing is 0.5-8 hour.More preferably negative electrode active material carried out earlier pre-grinding 0.5-4 hour, added covering and initator then and mixed afterwards.Also covering, initator can be mixed simultaneously with mixing of negative electrode active material.Preferred earlier negative electrode active material being carried out earlier mixing after the pre-grinding.The mode of described mixing can make the various hybrid modes of this area routine, stirs, shakes mill, ball mill ball milling etc. such as stirring grinding machine, preferably uses high energy ball mill to carry out ball milling and mixes.
Described inert gas atmosphere is the atmosphere that contains one or more gases in nitrogen, helium, neon, argon gas, krypton gas, xenon and the radon gas.Preferred described inert gas atmosphere is a nitrogen atmosphere.
Described heating can make the coating layer coalization or the graphitization of negative electrode active material, and the temperature of described heating is 500-3500 ℃, and the time of heating is 1-480 hour, and the temperature of preferred described heating is 1000-3000 ℃, and the time of heating is 4-300 hour.More preferably describedly be heated to be 1000 ℃-1500 ℃ and finished charing in constant temperature 4-12 hour, or carried out graphitization in constant temperature 50-300 hour at 2500 ℃-3000 ℃.
Unless stated otherwise, all kinds of solvents of the present invention and reagent are commercially available analytical reagent.
The present invention is described further below in conjunction with embodiment.
Embodiment 1
The method of present embodiment explanation encapsulating active material for negative pole of Li-ion secondary battery of the present invention.
With 2 kilograms of median particle diameter D
50Be that 17.54 microns, microcrystalline coating interplanar distance d002 corrected value are that 0.33650 nanometer, specific area are that the native graphite of 3.2 meters squared per gram is at XQM frequency conversion planetary ball mill, the middle ball milling of experimental study institute (high energy ball mill) was analysed after 1 hour by Nanjing section, add 0.1 kilogram of polystyrene, 10 gram dilauroyl peroxides, continue ball milling 3 hours, and obtained the natural graphite particles that grafting coats.The graphite that grafting is coated was handled 2 hours in 1200 ℃ of charings under nitrogen atmosphere, obtained the native graphite of coating layer charing.The median particle diameter D of the native graphite of this coating layer charing
50Be 17.23 microns, microcrystalline coating interplanar distance d002 corrected value is 0.33652 nanometer, and specific area is 1.3 meters squared per gram.Graphite after the coating amplifies 1000 times of observed photos with JSM-5610LV type ESEM (JEOL company, Japan) and sees Fig. 3, the spherical in shape or elliposoidal of graphite after coating as seen from Figure 3, smooth surface.
Comparative Examples 1
As reference, native graphite amplifies 1000 times of observed photos with JSM-5610LV type ESEM (JEOL company, Japan) and sees Fig. 1 this Comparative Examples with the natural flake graphite that do not coat, and the visible graphite shape that does not coat is irregular, rough surface.
Comparative Examples 2
The method of this Comparative Examples explanation prior art encapsulating active material for negative pole of Li-ion secondary battery.
According to 1 disclosed method of the embodiment among the CN 1547278A, taking by weighing the 76 grams native graphite identical with the embodiment of the invention 1 and 120 restrains medium temperature coal pitch and places autoclave jointly and mix, under sealing state, be warming up to 410 ℃ and isothermal reaction after 1 hour, in reactor, add the light component of an amount of coal tar with unreacted pitch dissolving completely, heat filtering obtains the graphite that the surface chemistry deposition coats, and then with pyridine in Soxhlet extractor further the washing back at last the material that obtains was obtained the native graphite of coating layer charing in 1 hour in 1000 ℃ of charings in 60 ℃ of dryings 24 hours in the tubular type retort.Then this graphite is obtained the median particle diameter D of the native graphite of coating layer charing through fragmentation, sorting
50Be 18.24 microns, microcrystalline coating interplanar distance d002 corrected value is 0.33658 nanometer, and specific area is 2.7 meters squared per gram.Graphite after the coating amplifies 1000 times of observed photos with JSM-5610LV type ESEM (JEOL company, Japan) and sees Fig. 2, and the graphite surface after visible the coating is smooth than Comparative Examples 1.
Embodiment 2-6
According to the method encapsulating active material for negative pole of Li-ion secondary battery of embodiment 1, difference is, the negative electrode active material and the median particle diameter D thereof that are coated
50, microcrystalline coating interplanar distance d002 value, specific area, the weight ratio of initator and covering thereof, covering and with the weight ratio of negative electrode active material, heating condition, coat median particle diameter D50, microcrystalline coating interplanar distance d002, the specific area of back negative electrode active material.Concrete difference sees Table 1.
Table 1
| Embodiment | Embodiment 2 | Embodiment 3 | Embodiment 4 | Embodiment 5 | Embodiment 6 |
| Negative electrode active material | Natural flake graphite | Natural flake graphite | Natural flake graphite | Natural micro crystal graphite | Delanium |
| Negative electrode active material median particle diameter D 50(micron) | 45.0 | 20.1 | 25.9 | 8.4 | 15.1 |
| Negative electrode active material microcrystalline coating interplanar distance d002 value (nanometer) | 0.33629 | 0.33657 | 0.33670 | 0.33776 | 0.33725 |
| Negative electrode active material specific area (meters squared per gram) | 2.8 | 3.6 | 3.5 | 5.8 | 3.2 |
| Initator | The peroxidating cyclohexane | The butyl peroxy cyclohexane | New peroxide tert-butyl caprate | New peroxide tert-butyl caprate | Dibenzoyl peroxide |
| The weight ratio of initator and covering | 0.1∶10 | 0.2∶10 | 0.4∶10 | 0.6∶10 | 0.8∶10 |
| Covering | Polyethylene | Polypropylene | Furfural resin | Polymethyl methacrylate | Coal tar pitch |
| The weight ratio of the solution of negative electrode active material and covering | 100∶30 | 100∶15 | 100∶8 | 100∶5 | 100∶3 |
| Heating-up temperature (℃) | 3200 | 3000 | 1200 | 700 | 1500 |
| Heating time (hour) | 240 | 180 | 8 | 8 | 6 |
| Coat the median particle diameter D of back negative electrode active material 50(micron) | 26.2 | 19.6 | 22.3 | 8.5 | 15.0 |
| Coat the microcrystalline coating interplanar distance d002 value (nanometer) of back negative electrode active material | 0.33631 | 0.33660 | 0.33674 | 0.33779 | 0.33727 |
| Coat the specific area (meters squared per gram) of back negative electrode active material | 1.8 | 1.9 | 1.4 | 1.7 | 1.5 |
Battery performance test:
(1) preparation of button cell
Get surface modified graphite that the foregoing description 1-6 and Comparative Examples 1-2 obtain as negative electrode active material, under the pressure of 4 MPas, be on 15 millimeters the nickel screen negative material of the above-mentioned oven dry of 0.025 gram to be pressed into pie at diameter, make diameter and be 15 millimeters button cell pole piece.Contain 0.022 gram negative electrode active material on the pole piece.
With the above-mentioned negative plate that makes, diameter is that 15 millimeters, the metal lithium sheet of purity 99.9% are as the polypropylene diaphragm paper composition battery battery core that is 15 millimeters to electrode and diameter, add 0.15 milliliter of electrolyte, make CR2016 type button cell, its normal capacity is 7.0 milliampere-hours.
(2) preparation of rectangular cell
Get the negative electrode active material after the coating that the foregoing description 1-6 and Comparative Examples 1-2 obtain, be prepared into square lithium ion secondary battery according to the following step respectively.
60 gram polyvinylidene fluoride (PVDF) are dissolved in 770 gram N-methyl pyrrolidone (NMP) solvents make binder solution, the 2000 gram lithium cobalt oxygen that will mix in advance then join in the above-mentioned solution, add 200 gram N-methyl pyrrolidones (NMP) again, fully mix and make anode sizing agent; With tensile pulp machine this anode sizing agent is coated to thick 18 microns aluminium foil two sides equably, through 125 ℃ of vacuum and heating dryings 2 hours, roll-in, cut-parts make the positive pole of millimeter (wide) * 130,550 millimeters (length) * 43.8 micron (thick), contain the positive active material that 7.9-8.1 restrains on the every positive pole.
950 gram negative electrode active materials, 20 gram carbon fibers and 30 gram butadiene-styrene rubber (SBR) are mixed.Adding 1500 milliliters water stirs and is made into cathode size, evenly be applied to 12 microns Copper Foil two sides with tensile pulp machine, through 125 ℃ of vacuum and heating dryings 1 hour, roll-in, cut-parts make the negative pole of millimeter (wide) * 130,515 millimeters (length) * 44.5 micron (thick), contain the graphite that 3.8-4.1 restrains on the every negative pole.
With LiPF
6Be configured to LiPF with ethylene carbonate (EC) and dimethyl carbonate (DMC)
6Concentration is the solution (volume ratio of EC/DMC is 1: 1) of 1 mol, obtains electrolyte.
The positive pole that above-mentioned (1) is made, the negative pole that (2) make are wound into the electrode group of a square shaped lithium ion secondary battery with three layers of composite diaphragm of 20 microns polypropylene, polyethylene/polypropylene, and this electrode group included in 6 millimeters * 34 millimeters * 50 millimeters the rectangular cell aluminum hull, about 2.8 milliliters of the electrolyte that manual injection above-mentioned (3) makes in ar gas environment in glove box, lithium rechargeable battery LP 063450 is made in sealing.
(3) button cell graphite initial capacity, reversible capacity of graphite and first charge-discharge efficiency
Above-mentioned steps (1) is used graphite initial capacity, reversible capacity of graphite and the first charge-discharge efficiency of the battery that embodiment 1-6 and Comparative Examples 1-2 positive active material make, under normal temperature, relative humidity 25-85% environmental condition, measure respectively.Measure 15 batteries for every kind.Assay method is as follows:
After the button cell for preparing shelved 60 minutes, use button secondary cell device for detecting performance (model BK6016R, Guangzhou Lan Qi company), change into to 0.2 volt of voltage with 0.2 milliampere of electric current, then with 0.2 milliampere of constant current discharge to 0.005 volt, write down the time A of this discharge process, after shelving 30 minutes, again with 0.5 milliampere, constant current charge to 2.0 volt, write down the time B of this discharge process, graphite initial capacity, reversible capacity of graphite and first charge-discharge efficiency according to following formula calculating button cell the results are shown in Table 2.
Graphite initial weight specific capacity (MAH/gram)=0.2 milliampere * time A (hour)/0.022;
The reversible weight ratio capacity of graphite (MAH/gram)=0.5 milliampere * time B (hour)/0.022;
First charge-discharge efficiency=100% * reversible capacity/initial capacity.
Table 2
| Embodiment or Comparative Examples | Initial weight specific capacity (MAH/gram) | Reversible weight ratio capacity (MAH/gram) | First charge-discharge efficiency (%) |
| Embodiment 1 | 382 | 358 | 93.7 |
| Embodiment 2 | 381 | 357 | 93.7 |
| Embodiment 3 | 376 | 354 | 94.1 |
| Embodiment 4 | 378 | 355 | 93.9 |
| Embodiment 5 | 373 | 350 | 93.8 |
| Embodiment 6 | 375 | 351 | 93.6 |
| Comparative Examples 1 | 396 | 349 | 88.1 |
| Comparative Examples 2 | 382 | 350 | 91.6 |
From the result shown in the table 2 as can be seen: use method provided by the invention to coat the lithium rechargeable battery of negative electrode active material, compare as the Comparative Examples 1 of negative electrode active material with the graphite that uses not coating, graphite initial capacity Comparative Examples 1 is higher than the present invention, but reversible capacity of graphite of the present invention and first charge-discharge efficiency obviously improve than Comparative Examples 1.The Comparative Examples 2 that coats negative electrode active material with the method for using prior art is compared, the graphite initial capacity is suitable, reversible capacity of graphite and first charge-discharge efficiency have also had tangible improvement, illustrate that from macroscopic view the coating situation of negative pole of the present invention is significantly better than prior art.
(4) rectangular cell cycle performance test
Above-mentioned steps (2) is used the cycle performance of the battery that embodiment 1-6 and Comparative Examples 1-2 positive active material make, under normal temperature, relative humidity 25-85% environmental condition, measure respectively.Measure 15 batteries for every kind.Assay method is as follows:
At first, use BS-9300 (R) secondary cell device for detecting performance, electric current with 200 milliamperes (0.2C) charges to 3.8 volts to mesuring battary, shelved 5 minutes, be discharged to 3.0 volts in order to 1000 milliamperes (1C) then, shelved 0.5C constant voltage charge to 4.2 volt, 20 milliamperes of charging cut-off currents again 5 minutes.With electric current constant-current discharge to 3.0 volt of 0.5C, measure the initial capacity that obtains battery discharge then.Circulation repeats to lie prostrate with 1C constant current charge to 4.2; Be discharged to 3.0 volts charge and discharge process again with 1C, write down the loop ends capacity of the 1st time and the 500th time, and be calculated as follows battery capacity surplus ratio and average time attenuation rate:
Capacity surplus ratio=loop ends capacity/initial capacity * 100%.
Measurement result is as shown in table 3.
Table 3
| Embodiment or Comparative Examples | The 1st cyclic discharge capacity (milliampere-hour) | The 500th cyclic discharge capacity (milliampere-hour) | 500 circulation back capacity surplus ratios (%) |
| Embodiment 1 | 1122 | 948 | 84.5％ |
| Embodiment 2 | 1123 | 941 | 83.8％ |
| Embodiment 3 | 1125 | 952 | 84.6％ |
| Embodiment 4 | 1120 | 955 | 85.3％ |
| Embodiment 5 | 1115 | 931 | 83.5％ |
| Embodiment 6 | 1118 | 949 | 84.9％ |
| Comparative Examples 1 | 1016 | 572 | 56.3％ |
| Comparative Examples 2 | 1081 | 849 | 78.5％ |
From the result shown in the table 3 as can be seen: use method provided by the invention to coat the lithium rechargeable battery of negative electrode active material, compare as the Comparative Examples 1 of negative electrode active material with the graphite that uses not coating, initial capacity and cycle performance have had large increase, the Comparative Examples 2 that coats negative electrode active material with the method for using prior art is compared, and initial capacity and cycle performance have also had tangible improvement.As after adopting the battery circulation 500 times of positive active material preparation of embodiment 1, capability retention is 84.5%; And after adopting the battery circulation 500 times of positive active material preparation of Comparative Examples 1, capability retention only is 56.3%; After the battery circulation of the positive active material preparation of employing Comparative Examples 2 500 times, capability retention only is 78.5%.The lithium rechargeable battery cycle performance that uses method provided by the invention to coat negative electrode active material significantly improves, and illustrates that from macroscopic view the coating situation of graphite of the present invention is significantly better than prior art.
Claims (11)
1, a kind of method of encapsulating active material for negative pole of Li-ion secondary battery, this method is included in and heats the mixture that contains negative electrode active material and covering under the inert gas atmosphere, it is characterized in that, described negative electrode active material is a material with carbon element, also comprise initator in the described mixture, described initator is for only containing the organic peroxide of C, H, O, and the hybrid mode of described mixture is ball milling, vibrates, stirs and grind or collision.
2, method according to claim 1, wherein, in described mixture, the weight ratio of described negative electrode active material and covering is 100: 0.5 to 100: 30, the weight ratio of described initator and covering is 0.05: 10 to 1: 10.
3, method according to claim 1 and 2, wherein, described initator is selected from one or more in the organic peroxide shown in formula (1), formula (2), the formula (3),
Formula (1)
In the formula (1), R
1Be not more than 20 alkyl or carbon number for carbon number and be not more than 20 alkoxyl, R
2Be not more than 20 alkyl, H or carbon number for carbon number and be not more than 20 ester group, R
3And R
4Independently for H or carbon number are not more than 20 alkyl, n=1-5;
Formula (2)
In the formula (2), X
1Be not more than 20 alkyl or carbon number for carbon number and be not more than 20 alkoxyl, X
2Be not more than 20 alkyl, H or carbon number for carbon number and be not more than 20 ester group;
Formula (3)
In the formula (3), Y
1Be not more than 20 alkylene or carbon number for carbon number and be not more than 20 alkylene oxide group, Y
2And Y
2' for being not more than 20 alkyl or carbon number, H, carbon number be not more than 20 ester group independently.
4, method according to claim 3, wherein, described initator is selected from dilauroyl peroxide, dibenzoyl peroxide, new peroxide tert-butyl caprate, tert-butyl hydroperoxide isobutyrate, 1, one or more in 1-cyclohexane di-tert-butyl peroxide, dicumyl peroxide and the peroxidating cyclohexane.
5, method according to claim 1, wherein, described negative electrode active material is selected from one or more in natural flake graphite, natural micro crystal graphite and the Delanium, the median particle diameter D of described negative electrode active material
50Be the 4-50 micron, microcrystalline coating interplanar distance d002 is the 0.3354-0.3390 nanometer, and specific area is the 0.5-6 meters squared per gram.
6, method according to claim 5, wherein, described negative electrode active material is a graphite, the median particle diameter D of described graphite
50Be the 10-25 micron, microcrystalline coating interplanar distance d002 is the 0.3354-0.3370 nanometer, and specific area is the 1-4 meters squared per gram.
7, method according to claim 1, wherein, described covering is selected from one or more in styrene, polystyrene, polyethylene, polypropylene, furfural resin, Lauxite, epoxy resin, polyvinyl alcohol, polymethyl methacrylate, polyacrylonitrile, coal tar pitch and the petroleum asphalt.
8, method according to claim 1, wherein, described inert gas atmosphere is the atmosphere that contains one or more gases in nitrogen, helium, neon, argon gas, krypton gas, xenon and the radon gas.
9, method according to claim 1, the hybrid mode of described mixture are high-energy ball milling or stir mill that the time of mixing is 0.5-8 hour.
10, method according to claim 1, wherein, the temperature of described heating is 500-3500 ℃, the time of heating is 1-480 hour.
11, method according to claim 1, wherein, the temperature of described heating is 1000-3000 ℃, the time of heating is 4-300 hour.
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| CN108448097B (en) * | 2017-12-20 | 2020-04-28 | 湖南中科星城石墨有限公司 | Self-coated precursor of lithium ion battery negative electrode material and preparation method thereof |
| CN110993916B (en) * | 2019-12-11 | 2021-07-30 | 内蒙古三信新材料科技有限公司 | Composite graphite negative electrode material and preparation method thereof |
| CN116914125B (en) * | 2023-09-12 | 2023-12-05 | 深圳市贝特瑞新能源技术研究院有限公司 | Micro-expansion modified microcrystalline graphite negative electrode material and preparation method and application thereof |
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