Carbon coated ferriferrous oxide/nitrogen-doped graphene composite material and its application and preparation
Technical field
The present invention relates to a kind of composite material and preparation methods, and in particular to a kind of carbon coated ferriferrous oxide/nitrogen is mixed
Miscellaneous graphite composite material and preparation method thereof, belongs to material and electrochemical technology field, and the invention further relates to the composite materials to exist
Application in lithium ion battery negative material.
Background technique
With the exhaustion of petroleum resources, promote the development of renewable energy that there is great social and economic benefit.With
Chemical energy storage is in the energy storage new technology of application background, lithium ion have open-circuit voltage is high, have extended cycle life, energy density is high,
Memory-less effect, it is environmentally friendly the advantages that, cannot with other secondary cells (nickel-metal hydride battery, lead-acid battery, nickel-cadmium cell)
The advantages such as the superior electrical property and external form of analogy be variable have captured rapidly numerous market segments, become various portable electronic products
First choice, and to the new energy fields such as the large and medium-sized energy storage device such as electric car and photovoltaic engineering extend.Commercial at present
Lithium ion battery mainly uses graphite cathode, and the lower theoretical capacity of graphite cathode (372mA h g-1) significantly limit electricity
The promotion of pond whole volume, therefore there is an urgent need to develop the lithium ion battery negative materials of new high capacity.Recent study table
Bright, transition metal oxide is most hopeful that conventional graphite cathode is replaced to become high-capacity cathode material of new generation.
In transition metal oxide, ferroso-ferric oxide abundance is environmental-friendly, and has high theoretical capacity
(924mA h g-1), become the hot spot of research.But ferriferrous oxide material conductivity is lower, and takes off lithium ion is embedding
There are biggish volume changes in journey, cause the failure of material, limit its application significantly.
Carbon coating can improve Fe3O4Chemical property, people use many methods and are modified to it, such as prepare
The Fe of nanosizing3O4, carbon-coated nanometer Fe3O4And nanoscale Fe3O4/ C composite etc..In lithium ion charge and discharge process
In, nano material due to can be absorbed with biggish specific surface area, shorter diffusion path and faster diffusion rate and
A large amount of lithium ion is stored, is conducive to improve its chemical property;Carbon coating layer can prevent active material in battery charging and discharging
Biggish volume change occurs in the process, and avoids the reunion of active material;Also there is carbon base body good electric conductivity, lithium to seep
The features such as saturating rate height and stable electrochemical property.
Currently, carbon coating Fe3O4The preparation method of nanocomposite mainly has hydro-thermal method, thermal decomposition method etc..Such as publication number
For CN102790217B Chinese patent the invention discloses a kind of carbon coated ferriferrous oxide lithium ion battery negative material and
Preparation method;The negative electrode material is carbon coating Fe3O4Composite material, partial size is between 1~100nm;Its preparation process: it adopts
It uses NaCl as dispersing agent and carrier, it is sufficiently mixed with metal oxide source and solid carbon source;Mixed solution vacuum is done
It is dry, obtain mixture;Mixture is put into tube furnace and is calcined under an inert atmosphere, calcined product is obtained;Calcined product is washed
It washs, grinding obtains carbon-clad metal oxide nano particles.For another example the patent application of Publication No. CN103647041A discloses
A kind of carbon coated ferriferrous oxide nano wire and preparation method thereof and its preparing the application in lithium ion battery;Publication No.
The Chinese patent application of CN104993126A discloses a kind of carbon coating Fe3O4The preparation of nano particle lithium ion battery negative material
Method and its application.As it can be seen that in the prior art, most research focuses mostly in carbon coating Fe3O4The system of nanocomposite
In Preparation Method.
Summary of the invention
The purpose of the present invention is to provide a kind of composite materials, and the material is by carbon coated ferriferrous oxide and N doping graphite
Alkene composite material composition, the composite material are used as in lithium ion battery negative material use process, with excellent circulation and again
Rate performance.
Technical solution of the present invention:
The invention solves first technical problem be to provide a kind of composite material, the composite material is by carbon coating four
Fe 3 O and nitrogen-doped graphene form, and in the composite material, ferroso-ferric oxide is evenly distributed in graphene sheet layer
Surface.
Further, in the composite material, carbon coated ferriferrous oxide account for entire composite material gross mass 30~
70wt%.If carbon coated ferriferrous oxide content is less than 30wt%, since activity substance content is too low, gained composite material
Whole specific capacity decline, when its content is greater than 70wt%, the buffer function of graphene weakens, and material circulation performance is poor.
Further, in the composite material, the crystallite dimension of ferroso-ferric oxide is 8~100nm.
The invention solves second technical problem be to provide the preparation method of above-mentioned composite material, including walk as follows
It is rapid:
Step 1: graphene oxide dispersion and divalent source of iron stir and evenly mix to form mixed liquor;Wherein, graphene oxide with
The amount ratio of divalent source of iron are as follows: the divalent source of iron that every 100mg graphene oxide is 1~10mmol using iron content;
Step 2: melamine and formalin are added in the mixed liquor obtained by step 1, in 160~200 DEG C of hydro-thermals
Under the conditions of react at least 3h, so that melamine in-situ polymerization is obtained melamine resin, while redox graphene, obtain oxygen reduction
Graphite alkene/ferrous ion/melamine resin composite material;Wherein, the dosage of melamine is with graphene oxide in step 1
Mass Calculation, the quality of melamine is 0.5~5 times of graphene oxide quality, and the dosage of formalin is 1g melamine
Amine corresponds to 1~5ml formalin;
Step 3: the resulting redox graphene/ferrous ion/melamine resin composite material of step 2 is transferred to
In the strong alkaline aqueous solution of pH > 11,0.5h or more is stood to get compound to ferroso-ferric oxide/graphene of melamine resin cladding
Material, then it is washed, be dried dry melamine resin cladding ferroso-ferric oxide/graphene composite material;
Step 4: by ferroso-ferric oxide/graphene composite material of the dry melamine resin cladding of gained in step 3 in inertia
Under gas shield, high temperature sintering (purpose is carbonization melamine resin) at least 3h (the middle progress in tube furnace at 550~800 DEG C
Sintering), it obtains carbon-coated ferroso-ferric oxide and N doping is carried out to graphene simultaneously, finally obtain the oxidation of carbon coating four three
Iron/nitrogen-doped graphene composite material.
Further, in step 1, the divalent source of iron is frerrous chloride, ferrous nitrate, ferrous sulfate and other divalent
One or more of molysite.In the present invention, source of iron only with ferrous iron as ferroso-ferric oxide is since ferrous iron can be with
Redox graphene under hydrothermal conditions.
In step 1, the graphene oxide dispersion is that graphene oxide passes through stirring with distilled water and is ultrasonically treated
The concentration that (mixing time about 15~25min, preferably 20min) is obtained is the suspension of 8~12mg/mL (preferably 10mg/mL)
Liquid.
Further, it in step 3, adopts and is washed with distilled water, the dry method for using vacuum freeze drying;In the present invention, appoint
Anticipating drying means can be with freeze-drying is more conducive to keep the structure of sample in aqueous solution.
The vacuum freeze-drying method are as follows: carried out very in freeze drier in -55~-45 DEG C (preferably -50 DEG C)
Vacuum freecing-dry.
The invention solves third technical problem be to point out: the present invention gained carbon coated ferriferrous oxide/N doping
Application of the graphene composite material in lithium ion battery anode active material.
The invention solves the 4th technical problem be to provide a kind of lithium ion battery, including positive electrode active materials and negative
Pole active material, the negative electrode active material are carbon coated ferriferrous oxide of the present invention/nitrogen-doped graphene composite wood
Material.
The invention has the following advantages that
1, composite material circulation with higher and high rate performance;Applied to cathode material for high capacity lithium ion battery.
2, carbon coated ferriferrous oxide/nitrogen-doped graphene composite material can not only effectively buffer ferroso-ferric oxide in electrification
The bulk effect in reaction is learned, while also improving the electric conductivity of material, the impedance of battery is substantially reduced, to effectively improve
The chemical property of material.
3, preparation method of the invention is simple, raw material sources are abundant, reaction condition is mild, easy to operate.
The invention discloses a kind of carbon coated ferriferrous oxide/nitrogen-doped graphene composite material and preparation methods and its
Application as high capacity lithium ion cells cathode active material.The negative electrode material is by carbon coated ferriferrous oxide and N doping stone
Black alkene composition, using gained melamine resin after melamine in-situ polymerization as the carbon source of carbon coated ferriferrous oxide and N doping stone
The nitrogen source of black alkene;Carbon coated ferriferrous oxide is obtained by high temperature sintering in-situ carburization melamine resin, to improve ferroso-ferric oxide
The electric conductivity of material;Meanwhile N doping is carried out to graphene in high-temperature sintering process, additional defect is introduced to be more
The deintercalation of lithium ion provides site.When the composite material is used as electrode material, battery shows excellent cycle performance, tests number
It was demonstrated that with 1000mA g-1Relatively high charge-discharge rate under, composite material charge/discharge capacity can be stablized in 400mA h g-1。
In addition, the method that the present invention prepares lithium ion battery negative material, simple process is easy to operate, and process safety, environmentally protective,
With industrialization potential.
Detailed description of the invention
Fig. 1 is the XRD (a) and XPS (b) figure of the sintering of embodiment 2 front and back.
Fig. 2 is the N1s swarming spectrogram that embodiment 2 is sintered front and back sample XPS.
Fig. 3 is the SEM figure of (a) and (b) after sintering before embodiment 2 is sintered.
Fig. 4 is embodiment figure compared with the cycle performance of comparative example, and charging and discharging currents density is 1000mA h g-1。
Specific embodiment
The present invention is in aqueous solution, using the home position polymerization reaction of melamine, stone to be formed in situ in melamine resin
Black alkene sheet surfaces, while wrapping up a large amount of iron ion;By the pH value of regulation system, make iron ion that four oxidations three be formed in situ
Iron obtains melamine resin/ferroso-ferric oxide/graphene composite material, after then composite material is lyophilized, under inert gas atmosphere
Sintering melamine resin obtains carbon coated ferriferrous oxide/nitrogen-doped graphene composite material, and melamine resin is used as carbon packet simultaneously
Cover the carbon source of ferroso-ferric oxide and the nitrogen source of nitrogen-doped graphene.
In the present invention, the graphite alkenes Carbon Materials with bigger serface are introduced in ferroso-ferric oxide, therefore not only mention
The high conductivity of composite material, while can highly desirable buffer volume of ferroso-ferric oxide during lithium ion is embedding de-
Variation, avoids the collapsing of electrode material, improves the cyclical stability of composite material.In addition, the present invention carries out ferroso-ferric oxide
Carbon coating can be improved its interaction between graphene, and carbon coated ferriferrous oxide can effectively avoid four oxidations three
The reunion of iron nano-particle itself facilitates its and uniform and stable is dispersed in graphene film layer surface, while the carbon-coating energy coated
The charge transmission between ferroso-ferric oxide and graphene is enough improved, further increasing for conductivity of composite material energy is conducive to.
Embodiment 1
Graphene oxide is prepared using traditional Hummers method.250ml reaction flask is assembled in ice-water bath, is added
The 23ml concentrated sulfuric acid, is added with stirring 2g natural flake graphite powder and 1g sodium nitrate, and the control of whole process temperature is reacted at 4 DEG C or less
2h, then it is gradually added 6g potassium permanganate, control reaction temperature is no more than 20 DEG C, is stirred to react 1h, is then warming up to 35 DEG C or so
Continue to stir 30min, be slow added into 60ml deionized water, after stirring 20min, and it is anti-that 25ml hydrogen peroxide (30Vol%) is added
It answers 15min that solution is made to become glassy yellow, and is dissolved with 40ml HCl solution (10Vol%), be centrifugated and be washed with deionized water
It washs until the close neutrality of pH value, the graphene oxide water solution freeze-drying (vacuum, -50 DEG C) of acquisition is finally obtained into graphite oxide
Alkene.
Step 1: graphene oxide 300mg is taken to be dissolved in 30mL distilled water, simultaneously ultrasound 20min is stirred, even suspension is obtained
Liquid;
Step 2: Iron dichloride tetrahydrate 1g (5mmol) is added in the resulting suspension of step 1,10min is stirred;
Step 3: 0.5g melamine is added in the mixed liquor obtained by step 2,30min is stirred, it is molten to add 1ml formaldehyde
Mixed solution is transferred to 100ml polytetrafluoroethylene bushing by liquid, 180 DEG C of reaction 8h in water heating kettle;
Step 4: being filtered to reaction product obtained by step 3, filtered solid product is transferred to 200mL concentration
In 30wt% ammonium hydroxide (pH > 12), to stand 1h to get ferroso-ferric oxide/melamine resin/graphene composite material is arrived, by material
Carry out frozen dried.
Step 5: by ferroso-ferric oxide/melamine resin/graphene composite material after freeze-drying with 600 DEG C in tube furnace,
It is sintered 5h under nitrogen protection and mixes graphene composite material to get to carbon coated ferriferrous oxide/nitrogen.
Embodiment 2
Step 1: graphene oxide 300mg is taken to be dissolved in 30mL distilled water, simultaneously ultrasound 20min is stirred, even suspension is obtained
Liquid;
Step 2: Iron dichloride tetrahydrate 1g (5mmol) is added in the resulting suspension of step 1,10min is stirred;
Step 3: 1.0g melamine is added in the mixed liquor obtained by step 2,30min is stirred, it is molten to add 2ml formaldehyde
Mixed solution is transferred to 100ml polytetrafluoroethylene bushing by liquid, 190 DEG C of reaction 5h in water heating kettle.
Step 4: being filtered to reaction product obtained by step 3, filtered solid product is transferred to 200mL
In 30wt% ammonium hydroxide, 1h is stood to get ferroso-ferric oxide/melamine resin/graphene composite material is arrived, material is carried out at freeze-drying
Reason.
Step 5: by ferroso-ferric oxide/melamine resin/graphene composite material after freeze-drying with 700 DEG C in tube furnace,
It is sintered 3h under nitrogen protection and mixes graphene composite material to get to carbon coated ferriferrous oxide/nitrogen.
Comparative example 1
Step 1: graphene oxide 300mg is taken to be dissolved in 30mL distilled water, simultaneously ultrasound 20min is stirred, even suspension is obtained
Liquid;
Step 2: Iron dichloride tetrahydrate 1g (5mmol) is added in the resulting suspension of step 1,10min is stirred;
Step 3: 2.0g melamine is added in the mixed liquor obtained by step 2,30min is stirred, it is molten to add 4ml formaldehyde
Mixed solution is transferred to 100ml polytetrafluoroethylene bushing by liquid, 200 DEG C of reaction 3h in water heating kettle.
Step 4: being filtered to reaction product obtained by step 3, filtered solid product is transferred to 200mL
In 30% ammonium hydroxide, 1h is stood to get ferroso-ferric oxide/melamine resin/graphene composite material is arrived, material is carried out at freeze-drying
Reason.
Step 5: by ferroso-ferric oxide/melamine resin/graphene composite material after freeze-drying with 800 DEG C in tube furnace,
It is sintered 3h under nitrogen protection and mixes graphene composite material to get to carbon coated ferriferrous oxide/nitrogen.
Comparative example 2
Step 1: taking graphene oxide dispersion 30mL, contain about 300mg graphene oxide, stir simultaneously ultrasound 20min,
Obtain unit for uniform suspension;
Step 2: Iron dichloride tetrahydrate 1g (5mmol) is added in the resulting suspension of step 1,10min is stirred;
Step 3: mixed solution is transferred to 100ml polytetrafluoroethylene bushing, 180 DEG C of reaction 10h in water heating kettle.
Step 4: being filtered to reaction product obtained by step 3, filtered solid product is transferred to 200mL
In 30wt% ammonium hydroxide, 1h is stood to get ferroso-ferric oxide/graphene composite material is arrived, material is subjected to frozen dried.
Step 5: by ferroso-ferric oxide/graphene composite material after freeze-drying with 700 DEG C in tube furnace, nitrogen protection
Lower sintering 3h.
The composite material that the present embodiment obtains is carbon coated ferriferrous oxide/nitrogen-doped graphene composite material, is being sintered
In composite material before and after carbonization melamine resin, by taking embodiment 2 as an example, XRD spectra (Fig. 1 (a)) all shows the four of standard
Size of the ferroferric oxide nano granules before high temperature sintering is calculated 8 according to XRD result in Fe 3 O crystal diffraction peak
~10nm, ferroferric oxide nano granules crystallite dimension is between 20~25nm after being sintered carbonization melamine resin.Mainly due to
After high-temperature maturing is handled, the crystallization further growth of ferroso-ferric oxide is crystallized more perfect.Meanwhile the sample before and after being sintered
XPS (Fig. 1 (the b)) data of product are it is found that essential element is C, O, Fe, N, N element in the sample after burning in the sample of sintering front and back
Relative amount reduce, mainly since melamine resin decomposes at high temperature.Peak-fit processing is carried out to the N1s of sintering front and back sample
Determine the different Covalent bonding together forms of nitrogen, shown in Fig. 2, N1s spectrogram is mainly by being located in the sample before sintering
Pyrroles's type nitrogen at 400.0eV and the pyridine type nitrogen composition at 398.2eV, and sintered sample is in addition to containing the above two classes nitrogen
Other than element, there is also the graphitization nitrogen at 401.0eV, form nitrogen-doped graphene after illustrating sintering.
From scanning electron microscope (SEM) test result of embodiment 2 it is obvious that sintering before sample in, in-situ polymerization
Obtained melamine resin is uniformly coated on the surface (Fig. 3 (a)) of graphene sheet layer, by high temperature sintering carbonization melamine resin
Afterwards, the lamellar structure of graphene can be observed directly, and the nano particle that can see ferroso-ferric oxide is uniformly distributed
On the surface (Fig. 3 (b)) of entire graphene sheet layer.
Using the material of embodiment and comparative example preparation as lithium ion battery anode active material, the preparation of lithium ion battery
Remaining step of method is identical as common preparation method.Negative electrode tab the production method is as follows be respectively adopted embodiment and comparative example
The material of preparation is active material, and acetylene black is conductive agent, and PVDF is bonding agent.The quality of active material, conductive agent, bonding agent
Than in NMP (N-methyl pyrrolidones) solvent after mixing by them being coated uniformly on copper foil for 80:10:10, and
It is dried in vacuo at 120 DEG C for 24 hours, is cut into disk with slicer.With 1M LiPF6It is dissolved in vinyl carbonate (EC) and carbonic acid two
Electrolyte is used as in methyl esters (DMC), for lithium piece as anode, Celgard2320 is diaphragm, is assembled into the progress of CR2030 button cell
Test.
1 embodiment of table (charging and discharging currents density=1C (1000mA g compared with comparative example cycle performance-1))
|
1st time |
20th time |
40th time |
60th time |
80th time |
100th time |
(the mA h g of embodiment 1-1) |
550 |
420 |
300 |
250 |
200 |
150 |
(the mA h g of embodiment 2-1) |
420 |
420 |
400 |
400 |
380 |
350 |
(the mA h g of comparative example 1-1) |
300 |
200 |
170 |
150 |
140 |
140 |
Comparative example (mA h g-1) |
420 |
300 |
250 |
200 |
190 |
140 |
As shown in table 1, embodiment and comparative example are in 1C (1000mA g-1) constant current charge-discharge survey is carried out under current density
Resulting specific capacity is tried, the results show that embodiment 2 has most stable of cycle performance, the cyclic specific capacity in charge and discharge process
Always higher level is maintained;1 gained sample of embodiment shows higher first charge-discharge capacity, however as circulation time
Several increases, cyclic specific capacity show significantly to decay, mainly since the content of ferroso-ferric oxide in system is more;It is real
It applies example 3 and shows lower first charge-discharge capacity, and as cycle-index increase also shows the trend of capacity attenuation, a side
Face is to lead to its lower cyclic specific capacity for the first time since ferroso-ferric oxide content is lower, is on the other hand due to 1 sample of comparative example
Product introduce more melamine resin before sintering, and after melamine resin removes, the connection between ferroso-ferric oxide and graphene is broken
It is bad, cause grapheme material to weaken the volume buffering effect of ferroso-ferric oxide, therefore cyclical stability declines, therefore melamine
Additive amount no more than 5 times of graphene oxide content.2 sample of comparative example is the sample for being not added with melamine, but is passed through
Experimentation identical with embodiment sample is said the results show that 2 sample of comparative example shows the trend of apparent capacity attenuation
The bright cyclicity that ferroso-ferric oxide/graphene composite material is carried out to effectively improve material after carbon coating and nitrogen cladding
Energy.