Summary of the invention
In view of this, the invention provides a kind of porous carbon silicon composite, it has relatively large specific discharge capacity and has good cyclicity.This porous carbon silicon composite comprises porous carbon and is attached to the silicon grain of the hole wall of described porous carbon, wherein with the total restatement of described porous carbon silicon composite, described porous carbon silicon composite can comprise the silicon of 20-70 % by weight and the porous carbon of 80-30 % by weight, and the BET specific area of described porous carbon silicon composite can be 50-250m
2/ g, pore volume can be 0.2-0.6cc/g.
According to another example of the present invention, the average pore size of the primary granule of described porous carbon silicon composite can be between 20nm-90nm, the particle diameter of described primary granule can be at 1-5 μ m, can be between 5 μ m-100 μ m and assemble the particle diameter of the second particle forming by this primary granule.
According to an example of the present invention, the about 10nm of wall thickness of described porous carbon.The silicon grain of the described hole wall that is attached to described porous carbon can be any one or its combination in following situation: described silicon grain Attachments is in the hole wall of described porous carbon, the discontinuous hole wall that is attached to described porous carbon of described silicon grain.
According to a further aspect of the invention, also provide a kind of method of preparing porous carbon silicon composite, the method comprises: use carbon precursor dipping template; Heat the template of this dipping, and remove this template after heating, thereby form porous carbon; By chemical vapour deposition (CVD), silicon grain is deposited to described porous carbon.
According to example of the present invention, the template of described this dipping of heating comprises: the template of this dipping, at 200oC-300oC heating 1-2 hour, at 400oC-600oC heating 2-4 hour, is removed to this template, form porous carbon; At 700oC-1000oC, this porous carbon is heated to 4-8 hour.
According to example of the present invention, this carbon precursor can be selected from sucrose, glucose, polyvinyl chloride (PVC), pitch and polyacrylonitrile (PAA).This template can be nano-calcium carbonate particles.In the situation that template is nano-calcium carbonate particles, the weight part ratio of this calcium carbonate and this carbon precursor is between 30:70 and 70:30.
The present invention also provides a kind of electrode material, and it comprises carbon-silicon composite material as above, conductive black and adhesive.Preferably, described electrode material comprises carbon-silicon composite material, the conductive carbon black of 0 % by weight-20 % by weight and the adhesive of 5 % by weight-30 % by weight of 50 % by weight-95 % by weight.Preferably, adhesive is polyacrylic acid, can also be sodium carboxymethylcellulose, the mixture of sodium carboxymethylcellulose and butadiene-styrene rubber.
The present invention also provides a kind of electrode of being prepared by above-mentioned electrode material.The present invention also provides a kind of lithium ion battery that comprises kind electrode.
Porous carbon silicon composite provided by the invention is in the time of the electrode as lithium ion battery, there is good stability, and due to porosity characteristic, for the embedding of the lithium ion that occurs in battery charging and discharging process and silicon or the change in volume of deviating to cause provide enough spaces.
Brief description of the drawings
Fig. 1 a is according in porous carbon silicon composite of the present invention to 1c, the schematic flow sheet of grown silicon on porous carbon.
Fig. 2 a is according in porous carbon silicon composite of the present invention to 2c, the SEM photo of the process of grown silicon on porous carbon.
Fig. 3 is according to the flow chart of the method for preparing porous carbon silicon composite of an example of the present invention.
Fig. 4 is the TEM photo of nano-calcium carbonate particles.
Fig. 5 a is the SEM figure of the porous carbon in embodiment 1.
Fig. 5 b be on the porous carbon of Fig. 5 a vapour deposition the SEM figure of porous carbon silicon composite after silicon grain.
Fig. 6 is the XRD collection of illustrative plates of the porous carbon silicon composite in embodiment 1.
Fig. 7 is isothermal nitrogen adsorption desorption and the pore size distribution curve of porous carbon silicon composite prepared in embodiment 1.
Fig. 8 is the grading curve of the porous carbon silicon composite in embodiment 1.
Fig. 9 is the thermal multigraph of nano-calcium carbonate and carbon precursor in embodiment 1.
Figure 10 is the charge and discharge cycles curve under the battery constant current in tested embodiment 1.
Figure 11 is the charging and discharging curve under the different electric currents of the battery in tested embodiment 1.
Figure 12 a be the SEM figure of porous carbon in embodiment 2 and Figure 12 b be on this porous carbon vapour deposition the SEM of porous carbon silicon composite after silicon grain scheme.
Figure 13 is the XRD collection of illustrative plates of the porous carbon silicon composite in embodiment 2.
Figure 14 is isothermal nitrogen adsorption desorption and the pore size distribution curve of the porous carbon silicon composite in embodiment 2.
Figure 15 is the battery of the tested embodiment 2 charge and discharge cycles curve under constant current.
Figure 16 a be the SEM figure of porous carbon in embodiment 3 and Figure 16 b be on this porous carbon vapour deposition the SEM of porous carbon silicon composite after silicon grain scheme.
Figure 17 is the XRD collection of illustrative plates of the porous carbon silicon composite in embodiment 3.
Figure 18 is isothermal nitrogen adsorption desorption and the pore size distribution curve of the porous carbon silicon composite in embodiment 3.
Figure 19 is the battery of the tested embodiment 3 charge and discharge cycles curve under constant current.
Figure 20 a be the SEM figure of porous carbon in embodiment 4 and Figure 20 b be on this porous carbon vapour deposition the SEM of porous carbon silicon composite after silicon grain scheme.
Figure 21 is the XRD collection of illustrative plates of the porous carbon silicon composite in embodiment 4.
Figure 22 is isothermal nitrogen adsorption desorption and the pore size distribution curve of the porous carbon silicon composite in embodiment 4.
Figure 23 is the battery of the tested embodiment 4 charge and discharge cycles curve under constant current.
Figure 24 is that the PAN of embodiment 5 is as the XRD collection of illustrative plates of the porous carbon silicon composite of porous carbon carbon source.
Figure 25 a is the TEM shape appearance figure of porous carbon that the PAN of embodiment 5 forms as porous carbon carbon source, and Figure 25 b is the TEM shape appearance figure that has deposited the porous carbon silicon composite after silicon nanoparticle on this porous carbon.
Figure 26 a is that the PAN of embodiment 5 is as isothermal nitrogen adsorption desorption and the pore size distribution curve of the porous carbon of porous carbon carbon source formation.
Figure 26 b is isothermal nitrogen adsorption desorption and the pore size distribution curve of the porous carbon silicon composite of embodiment 5.
Figure 27 is the battery of the tested embodiment 5 charge and discharge cycles curve under constant current.
Embodiment
Before describing the present invention in detail, first explanation, in all descriptions about number range of the present invention, statement " in the scope of A-B " and " between A and B " comprises the numerical value and A and the B itself that are greater than A and are less than B.
The porous carbon silicon composite that provided according to an aspect of the present invention comprises porous carbon and is attached to the silicon grain of the hole wall of this porous carbon.Using porous carbon silicon composite 100 % by weight as reference basis, in this porous carbon silicon composite, silicone content can be in 20 % by weight between 70 % by weight, and the content of porous carbon in 80 % by weight between 30 % by weight, preferably the weight ratio of silicon and porous carbon is 50:50.This carbon-silicon composite material of Different Weight ratio based on to(for) silicon, BET test result shows that specific area scope is 50-250m
2/ g, pore volume scope is 0.2-0.6cc/g.
In all examples of the present invention, BET test adopts static capacity method, taking nitrogen as adsorbed gas, at relative pressure scope (P/P
0) be 0.05-0.99, liquid nitrogen temperature under the condition of 77K, use the NOVA 4000 of Quantachrome company to test to obtain isothermal adsorption desorption curve.In the scope that specific area is 0.05-0.3 by multiple spot Brunauer-Emmett-Teller method at relative pressure, calculate and obtain, pore-size distribution calculates desorption curve by Barrett-Joyner-Halenda method and obtains.
Table 1 is BET specific area and the pore volume of the silicon weight ratio test based on different.
Table 1
Silicon weight ratio (wt%) |
BET specific area (m
2/g)
|
Pore volume (cc/g) |
48.3 |
211.2 |
0.52 |
53.1 |
153.1 |
0.39 |
67.6 |
48.3 |
0.21 |
As can be seen from Table 1, porous silicon carbon composite, in the time having the silicon of Different Weight ratio, has different specific areas and pore volume.Inventor's discovery, BET specific area is at 50-250m
2between/g, pore volume can produce good cycle performance at the porous carbon silicon composite of 0.2-0.6cc/g as electrode material.With regard to the data in table 1, silicon weight ratio is 48.3, specific area is 211.2m
2the porous carbon silicon composite that/g, pore volume are 0.52cc/g and silicon weight ratio are 53.1, specific area is 153.1m
2the porous carbon silicon composite that/g, pore volume are 0.39cc/g has more good capacitance and cycle performance.
According to example of the present invention, the size of porous carbon silicon composite primary granule is between 1-5 μ m.Assembled the size of the second particle forming by this primary granule between 5 μ m-100 μ m.In the present invention, term " primary granule " refers to the primary granule of porous carbon silicon composite, and term " second particle " refers to by the primary granule particle forming of reuniting.At observed under electron microscope porous carbon silicon composite of the present invention, can see that a lot of little primary granules are agglomerated into larger second particle.
The average pore size scope of this porous carbon silicon composite is between 20nm-90nm, and about 10nm is thick for hole wall.The silicon grain that is attached to these hole walls is the crystalline silicon of size between 5nm-10nm.Fig. 1 a is according in porous carbon silicon composite of the present invention to 1c, the schematic flow sheet of grown silicon on porous carbon.If Fig. 1 a is to as shown in 1c, silicon grain is distributed on the hole wall of porous carbon.Silicon grain can be Attachments in porous carbon carbon wall, can be also dispersedly, that is discontinuous note be in porous carbon carbon wall, can also be that some place is for Attachments is in some local discontinuous note of porous carbon carbon wall in porous carbon carbon wall.At Attachments, in the place of porous carbon carbon wall, silicon grain has formed layer, and the thickness of this layer is approximately 10nm-50nm.Fig. 2 a is according to the SEM photo of the silicon grain growth course of the porous carbon silicon composite of one exemplary embodiment of the present invention to Fig. 2 c.
According to an example of the present invention, can prepare above-mentioned porous carbon silicon composite according to method as shown in Figure 3.In step 10, by carbon precursor dipping template.In step 12, the template of this dipping of heat treatment is to form porous carbon.In step 14, by chemical vapour deposition (CVD), silicon nanoparticle is deposited on the porous carbon that step 12 forms.
The carbon precursor using in step 10 can be any one in sucrose, glucose, PVC, pitch and polyacrylonitrile (PAN); Template can be other particles such as nano-calcium carbonate particles or nanometer titanium sulfide.Select the benefit of nano-calcium carbonate particles to be its easily acquisition and cheap on market.In this step, the weight ratio of carbon precursor and template in the scope of 70:30, is sucrose and template be calcium carbonate granule in the situation that at carbon precursor at 30:70, and the weight ratio of carbon precursor and template is 60:40.Preferably, the particle size range of selected calcium carbonate granule is between 20nm-80nm.Fig. 4 is the TEM photo of nano-calcium carbonate particles.
In step 12, by the template with carbon precursor dipping obtaining in step 10 middle temperature heating 3 to 6 hours, preferably heat in 200oC-300oC 1 to 2 hours and heat 2 to 4 hours at 400oC-600oC.After so middle temperature heating, template is removed, form porous carbon.And then at high-temperature heating 4-8 hour, preferably 700oC-1000oC heating 4 to 8 hours, so so that the porous carbon forming is more firm.
According to a preferred example, the calcium carbonate template of sucrose dipping, 225oC continuous heating 1 hour, subsequently 500oC continuous heating 2 hours, is then removed template with 8% hydrochloric acid, then 900oC continuous heating 4 hours.In heating process, calcium carbonate granule has formed porous in the sucrose of carbonization.Select calcium carbonate to be that as another favourable part of template calcium carbonate template is easy to remove by acid such as hydrochloric acid after middle temperature heating.In the actual selection process of template, the material of preferably easily removing after heat treated.
The chemical vapor deposition (CVD) adopting in step 14 is conventional CVD technology, can simply be described as entering reative cell by current-carrying gas with the source steam of one or several gases, at substrate surface generation chemical change, and on substrate, deposit required solid matter.For the present invention, in CVD process using in step 12 generate porous carbon in substrate is placed into horizontal tube furnace, then by siliceous deposits to this substrate.The internal diameter of this horizontal tube furnace is preferably 60mm.Carry high-purity silane by the inert gas of for example argon gas, the silane that preferably purity is 99.999% enters in the horizontal tube furnace that is heated to 400oC-500oC 1.5 hours-2 hours with the speed within the scope of 80-120 standard cubic centimeters per minute, silane is decomposed into compared with the silicon grain of small particle diameter and hydrogen, and silicon grain finally deposits to the hole wall of porous silicon substrate.Preferably, the mixed weight of silane and argon gas is than being 5:95.
Porous carbon is as substrate, and it has larger specific area and pore volume.Larger specific area shows that porous carbon has larger silicon adsorption capacity.According to the present invention, at the porous carbon of rear formed the not depositing silicon of above-mentioned steps 14, in an exemplary embodiment, a test number of its BET specific area is 650.4m
2/ g, pore volume are 1.32cc/g.
In chemical vapor deposition processes, at identical temperature and flow velocity, can obtain by controlling sedimentation time the carbon-silicon composite material of Different Weight ratio.Generally speaking, the weight ratio of silicon and porous carbon is too small, carbon-silicon composite material cannot have been given play to the high power capacity of silicon completely, weight ratio is too high, likely make silicon grain reunite change greatly, thereby affect the cyclicity of material, therefore, preferably the weight ratio of silicon in 20 % by weight between 70 % by weight, and the weight ratio of porous carbon in 80 % by weight between 30 % by weight.
According to an aspect of the present invention, also provide a kind of electrode material for lithium ion battery.This electrode material comprises carbon-silicon composite material, the conductive carbon black of 0 % by weight-20 % by weight and the adhesive of 5 % by weight-30 % by weight of 50 % by weight-95 % by weight.This carbon-silicon composite material is preferably according to porous carbon silicon composite of the present invention, and preferably include 60 % by weight according to carbon-silicon composite material of the present invention, the adhesive of the conductive black of 20 % by weight and 20 % by weight.Adhesive is preferably polyacrylic acid (PAA), can be also the mixture of sodium carboxymethylcellulose (CMC) or sodium carboxymethylcellulose and butadiene-styrene rubber (SBR).According to a concrete example, be that 60:20:20 stirs and makes the electrode material of pulp-like by carbon-silicon composite material, conductive black and polyacrylic acid according to weight ratio.Illustratively, the electrode material of making pulp-like is poured on the Copper Foil of horizontal positioned, carries out film with the wet film preparing device that is preferably 150 μ m and make pole piece.After film, pole piece is dried naturally, then under the pressure environment of for example 8MPa, carry out compressing tablet processing.After compressing tablet, put into vacuum drying oven overnight dry at the temperature that is preferably 80 DEG C, finally form electrode.Can be using the electrode as above forming electrode pair as lithium ion battery together with metal lithium sheet, selecting weight ratio is that the 1mol/L LiPF6/EC:DMC:EMC of 1:1:1 is as electrolyte again, making case is as button cell thus, wherein EC is ethylene (propylene) carbonate, DMC is dimethyl carbonate, and EMC is methyl ethyl carbonate.
embodiment 1
Select sucrose as carbon precursor, select nano-calcium carbonate particles as template.According to the weight ratio of 60:40, flood this nano-calcium carbonate particles with sucrose.The template of this dipping of 225oC continuous heating 1 hour, then, 500oC continuous heating 2 hours, the hydrochloric acid with 8% removed calcium carbonate template, finally, 900oC continuous heating 4 hours, obtained thus the porous carbon for depositing silicon particle.Fig. 5 a is the SEM image of this porous carbon.In above-mentioned continuous heating process, sucrose carbonization, Fig. 9 is the template 1 hour of this dipping of 225oC continuous heating, the then thermal multigraph after 2 hours at 500oC continuous heating.
By chemical vapour deposition (CVD) by siliceous deposits to this porous carbon.Particularly, obtained porous carbon is placed in horizontal tube furnace, carrying purity by argon gas is 99.999% silane, continue to enter with the speed of 100 standard cubic centimeters per minute for 2 hours the horizontal tube furnace that is heated to 450oC, obtain thus porous carbon silicon composite, wherein the mixed weight of silane and argon gas is than being 5:95.
The SEM image of prepared porous carbon silicon composite can be referring to Fig. 5 b thus, XRD collection of illustrative plates is referring to Fig. 6, Fig. 7 is shown in by nitrogen adsorption and desorption isothermal curve and pore-size distribution, the particle diameter of primary granule and second particle distributes referring to Fig. 8, and wherein primary granule obtains by the broken second particle of method grinding.
With reference to Fig. 8, the particle diameter that front and back are ground in contrast distributes known, the meso-position radius D50 of second particle is 36.741 um before grinding, after grinding, be 25.806 um, decline obviously, especially, after grinding, 1-5um scope endoparticle volumn concentration is increased to 14.7% by 4.4%, increase obviously, this illustrates this carbon-silicon composite material second particle short texture, is easy to be separated into the primary granule of smaller szie.As is known to the person skilled in the art, D50 is commonly used to represent the average grain diameter of powder, the accumulative total particle diameter that the represents sample corresponding particle diameter while reaching 50% that distributes, and the particle that particle diameter is greater than it accounts for 50%, and the particle that is less than it also accounts for 50%.
Accordingly, can show that the particle diameter of the second particle of porous carbon silicon composite in the present embodiment, between 5 μ m-100 μ m, is mainly distributed in 20 μ m-60 μ m, the pore diameter range of primary granule is between 1 μ m-5 μ m, and pore diameter range is at 20nm-90nm.In the present embodiment, BET specific area is 153.1m
2/ g, pore volume is 0.39cc/g.As is known to the person skilled in the art, " particle diameter " can be used to the size of characterizing particles.
Adopt according to a conventional method this porous carbon silicon composite to prepare electrode.Using prepared electrode as test battery positive pole, lithium metal is as test battery negative pole, 1 mol/l LiPF
6/ EC:DMC:EMC, as electrolyte, makes button cell.
This battery is tested, and test result is referring to Figure 10 and Figure 11.Figure 10 is charge-discharge performance curve under constant current.Visible according to figure, under 100mA/g current density, discharge capacity reaches 2404mAh/g and initial charge capacity reaches 1541mAh/g first.Electric current is increased to 500mA/g, and after 200 cycle periods, reversible capacity is still greater than 850mAh/g, approaches 70% of three charging capacity 1280mAh/g.In follow-up circulation, the coulomb efficiency of battery maintains more than 98%.Above data show that this battery has extraordinary cycle performance.Figure 11 be cycle performance of battery curve under different electric currents as seen from the figure, in the time that current density is increased to 2A/g from 0.1A/g, keep specific capacity more than 500mAh/g.
embodiment 2
The difference of the present embodiment and embodiment 1 is that the time that chemical vapour deposition (CVD) is carried out is 1.75 hours, that is it is silane that argon gas carries purity, continues to enter in the horizontal tube furnace that is heated to 450oC with the speed of 100 standard cubic centimeters per minute for 1.75 hours.The porous carbon silicon composite pore diameter range of preparation is at 20-90nm thus, and pore volume is 0.52cc/g, and BET specific area is 211.2m
2/ g.
Adopt according to a conventional method this porous carbon silicon composite to prepare electrode.Using prepared electrode as test battery positive pole, lithium metal is as test battery negative pole, 1 mol/l LiPF
6/ EC:DMC:EMC, as electrolyte, makes button cell.Figure 15 is charge-discharge performance curve under tested this battery constant current.
embodiment 3
The difference of the present embodiment and embodiment 1 is that time that chemical vapour deposition (CVD) is carried out is that to carry the speed that high-purity silane enters horizontal tube furnace be 120 standard cubic centimeters per minute for 2 hours and argon gas, that is, it is silane that argon gas carries purity, continues to enter in the horizontal tube furnace that is heated to 450oC with the speed of 120 standard cubic centimeters per minute for 2 hours.The porous carbon silicon composite pore diameter range of preparation is at 20-90nm thus, and pore volume is 0.21cc/g, and BET specific area is 48.3m
2/ g.
Adopt according to a conventional method this porous carbon silicon composite to prepare electrode.Using prepared electrode as test battery positive pole, lithium metal is as test battery negative pole, 1 mol/l LiPF
6/ EC:DMC:EMC, as electrolyte, makes button cell.Figure 19 is charge-discharge performance curve under tested this battery constant current.
embodiment 4
The difference of the present embodiment and embodiment 1 be time that chemical vapour deposition (CVD) is carried out be 2 hours and argon gas to carry the speed that high-purity silane enters horizontal tube furnace be 120 standard cubic centimeters per minute, in addition, horizontal tube furnace is heated to 500oC.That is, that is it is silane that argon gas carries purity, continues to enter in the horizontal tube furnace that is heated to 500oC with the speed of 120 standard cubic centimeters per minute for 2 hours.The porous carbon silicon composite pore diameter range of preparation is at 20-90nm thus, and pore volume is 0.16cc/g, and BET specific area is 33.0m
2/ g.
Adopt according to a conventional method this porous carbon silicon composite to prepare electrode.Using prepared electrode as test battery positive pole, lithium metal is as test battery negative pole, 1 mol/l LiPF
6/ EC:DMC:EMC, as electrolyte, makes button cell.Figure 23 is charge-discharge performance curve under tested this battery constant current.
embodiment 5
Select polyacrylonitrile (PAN) as carbon precursor, select nano-calcium carbonate particles as template.According to the weight ratio of 60:40, flood this nano-calcium carbonate template with polyacrylonitrile.In 290oC air atmosphere, the nano-calcium carbonate 2 hours of continuous heating polyacrylonitrile (PAN) dipping, then removes calcium carbonate template with 8% hydrochloric acid, finally, 1050oC continuous heating 4 hours, obtains thus porous carbon.Pore volume is 0.71cc/g after measured, and BET specific area is 92.1 m
2/ g.Figure 25 a shows the TEM shape appearance figure of this porous carbon, and Figure 26 a shows nitrogen adsorption and desorption isothermal curve and the pore-size distribution of this porous carbon.
By chemical vapour deposition (CVD), silicon grain is deposited in this porous carbon.Particularly, obtained porous carbon is placed in horizontal tube furnace, carrying purity by argon gas is 99.999% silane, continue to enter with the speed of 100 standard cubic centimeters per minute in the horizontal tube furnace that is heated to 450oC for 2 hours, obtain thus porous carbon silicon composite, wherein the mixed weight of silane and argon gas is than being 5:95.
The pore volume of prepared porous carbon silicon composite is 0.23cc/g, and BET specific area is 32.0 m
2/ g.About prepared porous carbon silicon composite, its TEM shape appearance figure is referring to Figure 25 b, and XRD collection of illustrative plates is referring to Figure 24, and Figure 26 b is shown in by nitrogen adsorption and desorption isothermal curve and pore-size distribution.
Adopt according to a conventional method this porous carbon silicon composite to prepare electrode.Using prepared electrode as test battery positive pole, lithium metal is as test battery negative pole, and 1 mol/l LiPF6/EC:DMC:EMC, as electrolyte, makes button cell.
Figure 27 is charge-discharge performance curve under tested this battery constant current.Visible according to figure, under 100mA/g current density, discharge capacity reaches 1565mAh/g and initial charge capacity reaches 1022mAh/g first, electric current is increased to 500mA/g, after 100 cycle periods, reversible capacity is 450mAh/g, approaches 70% of three charging capacity 1280mAh/g, in follow-up circulation, the coulomb efficiency of battery, in 100% fluctuation up and down, shows that this battery has good cycle performance.
Although in description above, disclose specific embodiments of the invention by reference to the accompanying drawings, it will be appreciated by those skilled in the art that, can, in the situation that not departing from spirit of the present invention, disclosed specific embodiment be out of shape or be revised.Embodiments of the invention are only not limited to the present invention for signal.