A kind of carbon cathode material and preparation method thereof
Technical field
The present invention relates to a kind of carbon cathode material and preparation method thereof, relate in particular to a kind of plumbago-carbon negative pole material that contains coating layer and preparation method thereof.
Background technology
The raw material of wood-charcoal material has higher electronic conductivity because its stable chemical performance, but intercalation and form the intercalation compound characteristic also has characteristics such as heat-resisting, resistance to sudden heating, height ratio are strong simultaneously, is widely used in a lot of fields.Especially in recent years, carbon negative electrode material of lithium ion cell exploitation was active, having of being applied in the commercialization battery (comprises MCMB and whole middle powder mutually) in the middle of native graphite, Delanium and special Delanium-graphitization mutually a few class raw material of wood-charcoal material.Native graphite has desirable layer structure, have very high capacitance (>350mAh/g), be easy to compacting (>1.60g/cm
3), but there is structural instability in it, easily causes the common insertion of solvent molecule, and its synusia in charge and discharge process is come off, and causes cycle performance of battery poor, poor stability.Common graphous graphite powder out-of-shape, specific area is big (common>5m
2/ g), causing the materials processing poor performance, efficient is low first.Phase in the middle of special Delanium-graphitization, Stability Analysis of Structures, the little (<2.0m of specific area
2/ g), and good cycle, fail safe is good, but has capacity lower (about about 320mAh/g), and compacted density is undesirable (common<1.55g/cm
3) etc. problem.
At the deficiency of each material, there are many people to adopt different means to propose to improve one's methods.Such as: Chinese patent CN1585172 discloses the method for graphite granule surface coating pitch, and coating layer has the low-crystallinity Turbostratic; U.S. Pat 6156432 is to coat the low-crystallinity charcoal at graphite surface, sees close with CN1585172 from method for coating; The preparation method of the disclosed carbon coated graphite microparticles of Chinese patent CN1397598 after resin-coating, handles through 700~1200 ℃ of charings, can obtain having the graphite microparticles that low-crystallinity Turbostratic charcoal coats.The low-crystallinity charcoal that above-mentioned each patent coats still belongs to disorderly layer stacking states because treatment temperature is lower, and the crystallite of order state is less in the structure, and the strength of materials is big, and toughness is relatively poor, when compacted density is higher, coating layer is broken, and causes the exposed of internal material.U.S. Pat 20040023115 has proposed spherical natural graphite and has used with the middle micro mist blending mutually of graphitization, obtains graphite material and is easy to the high density roll extrusion, can prepare the high-energy-density lithium battery, but the weakness of native graphite can't overcome also.And phase charcoal degree of crystallinity height in the middle of the graphitization, has laminated structure, help the turnover of lithium ion, the applicant's Chinese patent application 200310108982.8 disclosed native graphite surfaces obtain the middle phase coating layer of graphitization of microencapsulation, because this microencapsulation coating layer thin (generally below 500 nanometers) can not solve material and electrolyte consistency problem fully, the improvement of cycle life is subjected to certain influence.And do not having under the additive situation, if phase coating thickness in the middle of increasing can produce particle agglomeration, can not get the middle layer mutually of ideal thickness.
Summary of the invention
The objective of the invention is provides a kind of new carbon cathode material in order to solve above-mentioned problem.
Carbon cathode material of the present invention comprises the middle coating layer mutually of the outer graphitization of graphite microparticles and graphite, it is characterized in that the average thickness of the middle phase coating layer of described graphitization is 0.5~8 μ m.Because the native graphite surface is wrapped up mutually by the centre fully, so this negative material has good compatibility in electrolyte.
Wherein, the average thickness of phase coating layer preferably is 0.5~6 μ m in the middle of the described graphitization, more preferably is 1-5 μ m, is 3 μ m best.
The weight of phase coating layer preferably is 50~200% of graphite in the middle of the described graphitization, more preferably is 80-100%.
Another object of the present invention provides a kind of preparation method of above-mentioned carbon cathode material, it can comprise the steps: 1. 5~45% graphite microparticles and 95~55% pitches to be mixed, and be added with and account for the poly-agent of pressing down of graphite microparticles and pitch total weight 0.5~5%, at 380~480 ℃ of following polymerization reaction take places; 2. separate; 3. dry; 4. charing; 5. graphitization.
Wherein, the graphite microparticles of step described in 1. can be in the prior art any graphite microparticles as carbon cathode material, its particle diameter (D
50) be about 8~40 μ m; The preferred D of the present invention
50Be the graphite of 10-30 μ m, and said graphite is selected from natural micro crystal graphite, natural flake graphite, electrographite (also claiming Delanium) and the graphitization MCMB one or more, preferred micro crystal graphite of the present invention and/or crystalline flake graphite.
And described pitch is petroleum asphalt and/or coal tar pitch, preferred coal tar pitch.
But the press down poly-agent of step of the present invention described in 1. is meant the inhibitory reaction raw material, it is the material that reunion takes place between the graphite microparticles, it preferably is carbon black, as acetylene black, furnace black or conductive black, and vapor-grown carbon fibers, as in the nanometer carbon fiber bar one or more, the preferred acetylene black of the present invention and vapor-grown carbon fibers, more preferably acetylene black.The described consumption that presses down poly-agent preferably accounts for 0.5~2.5% of graphite microparticles and pitch total weight, more preferably accounts for 1.0~1.5%.
The above-mentioned graphite microparticles and the percentage by weight of pitch preferably are respectively 20~40% and 80~60%.
The reaction temperature of polymerization reaction of the present invention preferably is 410~440 ℃, more preferably is 420~430 ℃; Reaction time preferably is 3.5~7 hours usually 3~10 hours scopes, more preferably is 4~5 hours; The same with charcoal preparation methods in the prior art, polymerization reaction of the present invention can be carried out under logical inert gas shielding, prevents the reaction mass oxidation, and the present invention selects nitrogen for use with routine.
2.~5. step among the preparation method of the present invention all can be prior art, as selects disclosed various steps in the above-mentioned patent application for use.
Wherein, step of the present invention separation 2. is that the product that 1. step obtains is carried out conventional liquid-solid separation, isolate solid phase particles as methods such as extraction (solvent) separation, centrifugation or precipitate and separate from reaction system, said solvent can be the solvents stronger to the pitch solvability such as carbolineum, washing oil, diesel oil, pyridine, quinoline, dimethylbenzene, toluene.
And step drying 3. can be and dynamically down heating, and remains in the solvent in the material when removing separation.
In addition, step 4. the carbonization temperature that adopts of charing be controlled at 800~1300 ℃.
The step 5. graphitization temperature of graphitization employing is controlled at greater than 2800 ℃.
Positive progressive effect of the present invention is: carbon cathode material of the present invention compared with prior art, by outside graphite, coating the middle layer mutually of certain thickness graphitization, reduce the specific surface of material, increase structural stability, improve tap density, improve compacted density, helped pole piece processing, preferable by its battery combination property of making; The present invention adds additive in material thus, has suppressed the solid phase particles reunion, can control the sphere diameter size well, obtains the coating layer of desired thickness, realizes raw material of wood-charcoal material Stability Analysis of Structuresization, the form optimization.
Description of drawings
Fig. 1 is raw material natural flake graphite photo (500 *, cross-polarized light).
Fig. 2 is one embodiment of the invention carbon cathode material photo (500 *, cross-polarized light).
Fig. 3 is the compacted density comparison diagram of one embodiment of the invention and contrast.
Embodiment
Further specify the present invention with embodiment below, but the present invention is not limited to this.
Adopt graphite particulate physical property and chemical property in conventional determining method mensuration the following example, relevant assay method is summarized as follows:
1. the observation of middle phase coating layer: step 1 gained polymerization sample cooling back is taken out one, polishes polishing, the anisotropic middle phase (seeing Fig. 1 and Fig. 2) of viewing optics under optical microphotograph mirroring cross-polarized light on sand paper.
2. particle diameter (D
50) and the mensuration of average coating thickness: the sample that takes a morsel joins in the beaker, splash into 1~2 1% surfactant, stirring into pasty state adds a small amount of distilled water again and continues to stir, the ultrasonic concussion of sample is about 3 minutes, measure on Britain Ma Erwen product MS2000 laser particle size distribution instrument, obtaining corresponding to 50% volume part particle diameter is D
50Mean particle dia.The average packet coating thickness is by D before and after coating
50Particle diameter difference and getting.
3.BET specific area measuring: adopt U.S. health tower NOVA2000e type specific surface area measuring instrument, graphite powder stopped 15 minutes under 300 ℃ of nitrogen current, adopted the specific area of nitrogen absorption BET multipoint method working sample.
4. chemical property is measured: graphite sample, the N-methyl pyrrolidone that contains 6~7% Kynoar and 2% conductive black mix, and are applied on the Copper Foil, and it is that 110 ℃ of vacuum drying chamber vacuumizes 4 hours are standby that the pole piece that coats is put into temperature.Simulated battery is assemblied in the German Braun glove box of applying argon gas and carries out, and electrolyte is 1M LiPF
6+ EC: DEC: DMC=1: 1: 1 (volume ratio), metal lithium sheet are to electrode, and electrochemical property test carries out on U.S. ArbinBT2000 type cell tester, and the charging/discharging voltage scope is 0.005 to 1.0V, and charge-discharge velocity is 0.1C.
5. compacted density condition determination:
To roller slit spacing 80~90 μ m (1), 60~70 μ m (2), 30~40 μ m (3),<10 μ m (4).
6. embodiment 1,2,4 and comparative example's 3 negative material is made the battery design condition
Battery design capacity: 810mAh, negative pole list gram volume design: 330mAh/g,
Anodal single gram volume design: 140mAh/g, compacted density is 1.60g/cm
3
Embodiment 1~9
Comparative example's (comparative example) 1~3
The step of each embodiment and comparative example 1-2 1. in relevant raw material and content thereof, and the relevant reaction condition of polymerization reaction is as shown in table 1 below, all the other are referring to the prior art of above-mentioned document.
Comparative example 1 is the raw material native graphite, and comparative example 2 is the MCMB of preparation, and comparative example 3 is to be the carbon cathode material that raw material adopts the method for CN200310108982.8 embodiment 3 to make with 17 μ m crystalline flake graphites and coal tar pitch equally.
Table 1
Embodiment |
Graphite microparticles (D50) μ m |
Pitch |
Press down poly-agent (%) |
Graphite microparticles/pitch (%) |
Temperature (℃) |
Time (branch) |
1 |
Crystalline flake graphite 17 |
Coal tar pitch |
Nanometer carbon fiber bar 0.5 |
10/90 |
420 |
330 |
2 |
Crystalline flake graphite 17 |
Coal tar pitch |
Acetylene black 1.5 |
20/80 |
430 |
295 |
3 |
Crystalline flake graphite 17 |
Coal tar pitch |
Acetylene black 2.5 |
30/70 |
440 |
275 |
4 |
Crystalline flake graphite 17 |
Petroleum asphalt |
Acetylene black 1 |
5/95 |
440 |
380 |
5 |
Micro crystal graphite 13 |
Coal tar pitch |
Acetylene black 1 |
20/80 |
430 |
305 |
6 |
Micro crystal graphite 13 |
Petroleum asphalt |
Nanometer carbon fiber bar 0.5 |
10/90 |
410 |
375 |
7 |
Delanium 20 |
Coal tar pitch |
Acetylene black 0.5 |
20/80 |
440 |
200 |
8 |
Delanium 30 |
Coal tar pitch |
Furnace black 5 |
45/55 |
380 |
600 |
9 |
Crystalline flake graphite 15 |
Coal tar pitch |
Conductive black 1.2 |
40/60 |
480 |
300 |
Comparative example 1 |
Crystalline flake graphite 17 |
|
|
|
|
|
Comparative example 2 |
|
Coal tar pitch |
|
|
430 |
230 |
Comparative example 3 |
Crystalline flake graphite 17 |
Coal tar pitch |
|
20/80 |
450 |
180 |
Percentage in the above-mentioned table all is weight percentage, and the percentage that wherein presses down poly-agent is for pressing down the percentage by weight that poly-agent accounts for graphite microparticles and pitch total weight.
It is as follows to be with embodiment 3 that example specifies:
In the container of 5L, add crystalline flake graphite 600 gram of 17 μ m, 1400 grams are crushed to millimetre-sized coal tar pitch, add acetylene black 50 grams again, begin to stir after being heated to the pitch fusion, feed nitrogen, manually are warming up to 440 ℃, and constant temperature 275 minutes stops heating.The cooling back adds conventional solvent (such as quinoline) extraction, and centrifugation goes out micro mist.Again micro mist is put into the dynamic drying oven of MA-102, removed the solvent that remains in when separating in the material.Dry back sample promptly gets above-mentioned lithium ion battery negative material in 800 ℃ of charings, 2800 ℃ of graphitizations after the screening.
Each embodiment and comparative example's performance parameter is as shown in the table:
Embodiment |
Particle diameter (μ m) |
Coating thickness (μ m) |
Weightening finish is (to graphite microparticles, %) |
Specific area (m
2/g)
|
Discharge capacity (mAh/g) |
Efficient (%) first |
1 |
21.5 |
4.5 |
196.2 |
1.2 |
340.2 |
94.8 |
2 |
20.0 |
3.0 |
148.6 |
1.8 |
348.6 |
94.4 |
3 |
18.9 |
1.9 |
101.2 |
2.0 |
351.3 |
95.2 |
4 |
17.6 |
0.6 |
58.3 |
|
|
|
5 |
16.8 |
3.8 |
93.2 |
2.1 |
355.0 |
93.1 |
6 |
15.3 |
2.3 |
132.0 |
|
|
|
7 |
25.2 |
5.2 |
81.3 |
2.4 |
338.1 |
94.5 |
8 |
35.5 |
5.5 |
101.2 |
2.0 |
341.2 |
94.8 |
9 |
19.3 |
4.3 |
112.3 |
1.7 |
343.2 |
95.2 |
Comparative example 1 |
17.0 |
Natural flake graphite |
|
6.6 |
375.8 |
90.2 |
Comparative example 2 |
18.4 |
The graphitization MCMB |
|
1.0 |
319.2 |
95.3 |
Comparative example 3 |
17.4 |
0.4 |
|
1.7 |
355.0 |
94.3 |
From top data as can be seen, raw material natural flake graphite specific area is big, is 6.6m
2/ g, efficient is low first only 90.2%; Graphitization MCMB discharge capacity is low to be 319.2mAh/g; Adopt the negative material of the described method preparation of patent, specific area is reduced in 2.0m greatly
2About/g, capacity is higher than graphitization MCMB 20mAh/g about 340mAh/g.The compacted density of embodiment 3 samples is higher than comparative example 2 at 0.2g/cm
3More than, improved the energy density of battery greatly, as shown in Figure 3.
Application Example 1
With the same crystalline flake graphite with 17 μ m is graphite raw material, the embodiment of the invention 1,2 and 4 of layer mutually in the middle of the coated graphiteization, and the carbon cathode material made of comparative example 3 is made into battery and carries out performance relatively, the results are shown in shown in the following table:
The negative material of the embodiment of the invention and comparative example 3 is made battery performance relatively
The sample title |
Comparative example 3 |
Embodiment 1 |
Embodiment 2 |
Embodiment 4 |
First charge-discharge efficiency (%) |
88.5 |
89.9 |
90.5 |
89.0 |
Internal resistance (m Ω) |
35.9 |
34.5 |
34.3 |
35.2 |
1C platform occupation rate (%) |
83.2 |
85.9 |
86.8 |
84.7 |
1C/0.2C(%) |
98.8 |
99.2 |
99.3 |
98.9 |
2C/0.2C(%) |
96.4 |
97.4 |
97.5 |
97.1 |
3C/0.2C(%) |
92.2 |
94.7 |
94.9 |
93.5 |
As seen from the above table, the battery that adopts the carbon cathode material of embodiment 1,2 and 4 to make is all good than the battery respective performances that comparative example 3 is made in aspect performances such as first charge-discharge efficiency, material platform occupation rate, large current discharging capabilities, these advantages illustrate that all coating thickness increases the further many-sided performance of raising material, satisfied the demand of market simultaneously, so carbon cathode material of the present invention has broad application prospects to the high-performance negative material.On the other hand, by last table as can be seen, the phase coating layer is not thick more good more yet in the middle of the graphitization yet, with best about 3 μ m, this is because it surpasses certain thickness, can reduce material capacity, so control certain thickness scope helps improving the whole synthesis performance of material.