Technical background
The problems such as nowadays world environments pollution, greenhouse effect, energy crisis are day by day serious.The secondary cell with high-energy-density has very important significance for solving the outstanding energy and environmental problem.Wherein lithium ion battery is one of battery that in secondary cell, specific energy is the highest.But in lithium rechargeable battery system, specific capacity, the cycle performance of positive electrode all need to be optimized.Traditional positive electrode is as LiCoO
2/ graphite and LiFePO
4the theoretical energy density of/graphite system is all about 400Wh/kg.Due to the restriction of its theoretical energy density, even if determined, these positive electrodes are formed with the improvement of process aspect and are also difficult to lithium ion battery is made a breakthrough in energy density.Therefore, develop new there is high-energy-density, long circulation life, energy storage material that cost is low is imperative.Wherein elemental sulfur has the highest theoretical specific discharge capacity: 1675mAh/g, and taking elemental sulfur as anodal, lithium metal as the theoretical energy density of the lithium-sulfur cell of negative pole can reach 2600Wh/kg, its theoretical energy density is LiCoO
2/ graphite and LiFePO
4more than 6 times of/graphite system, are far longer than the business-like secondary cell that present stage is used.In addition sulphur simple substance also has the advantage of the great commercial value such as with low cost, environmental friendliness.
But the poor problem of cycle performance that lithium-sulfur cell exists has seriously hindered its commercialization process.The problem that the capacity existing in circulating battery process is decayed fast mainly following several factor causes: the many lithium sulfide (Li of intermediate product that (1) lithium-sulfur cell produces in charge and discharge process
2s
x, 4≤x≤8) and be soluble in organic electrolyte, the active material on positive pole is reduced gradually, and owing to flying shuttle effect, many lithium sulfides of dissolving can be diffused on the negative pole lithium sheet of battery through barrier film, the Li of generation
2s
2and Li
2s precipitates poorly conductive, thereby has caused the corrosion of battery cathode and the increase of the internal resistance of cell.And fly shuttle effect and also can cause Li
2s
2and Li
2s is deposited on anodal surface, thereby causes the remarkable change of electrode pattern.And then cause the quick decay of capacity.(2) in cyclic process, in lithium-sulfur cell, the cubical expansivity of sulfur electrode is up to 80%, and this may cause sulfur electrode inside to crack, the existence of this crackle and nonconducting Li
2s
2and Li
2s has destroyed anodal globality in the generation of cracks, finally causes the quick decay of capacity.(3) all very poor (conductivity is 5 ' 10 25 DEG C time for the electron conduction of elemental sulfur and ionic conductivity
-30s/cm), cause the problems such as the chemical property of elemental sulfur is not good and utilance is low.
Graphene is a kind of new material of the individual layer laminated structure being made up of carbon atom.Be a kind ofly to form with sp2 hybridized orbit the flat film that hexangle type is honeycomb lattice by carbon atom, only have the two-dimensional material of a carbon atom thickness.Under normal temperature, its electron mobility exceedes 15000cm
2/ Vs, even than carbon nano-tube and silicon wafer height, and only about 10-6 Ω cm of resistivity is lower than copper or silver, is the material of resistivity minimum in the world so far.Therefore adopt redox graphene to be conducive to improve anodal conductivity as lithium sulfur battery anode material.And this two-dimensional structure of Graphene is conducive to the fixing of many lithium sulfides.
Many lithium sulfides that lithium-sulfur cell produces in charge and discharge process are soluble in organic electrolyte, and this is the most important factor that affects lithium-sulfur cell cycle performance.And nano-metal-oxide has large specific area and strong absorption property, can hinder the polysulfide generating and be dissolved in electrolyte.Therefore, in lithium-sulfur cell, dopen Nano metal oxide is conducive to the raising of circulating battery stability.
This two-dimensional network structure of Graphene provides unimpeded transmission channel for electric transmission, but the graphene platelet of layering is easily stacked into the structure of multilayer again, so just cause Graphene to lose high-specific surface area and some its intrinsic physicochemical properties.But, if this nano-metal-oxide nano particle is fixed on graphene sheet layer, just can effectively suppress serious stacking problem again between graphene sheet layer.Thereby be conducive to obtain having more fold and the Graphene of large interlamellar spacing more.
Because ultraviolet catalytic redox graphene can't be removed the functional group above Graphene completely, therefore the dispersion that nano particle can be stable, and nano particle can and redox graphene lamella between form stronger chemical bond, thereby be conducive to the formation of Graphene-nano-metal-oxide.And, using uv irradiation method redox graphene, without any poisonous and harmful reagent, pollution-free, environmentally friendly in preparation method, method is convenient, easy to learn, favorable reproducibility, and low cost of manufacture, efficiency is high.
Summary of the invention
Many lithium sulfide (the Li of intermediate product that produce in charge and discharge process in order to solve lithium-sulfur cell
2s
x, 4≤x≤8) be soluble in organic electrolyte, easily fly shuttle effect, sulfur electrode volumetric expansion, elemental sulfur conduct electricity sub-property and lead ionic poor, thereby cause the poor problem of circulating battery.
For achieving the above object, the technical solution used in the present invention is as follows:
Graphene-nano metal oxide composite material is applied in lithium-sulfur cell, and described Graphene-nano metal oxide composite material is used for lithium-sulfur cell as the positive electrode of lithium-sulfur cell.
The preferred 0.2:0.08 of mass ratio 0.1-5:0.01-0.3(of nano-metal-oxide and Graphene in Graphene-nano metal oxide composite material).
Graphene-nano metal oxide composite material preparation process is as follows,
Preparation process can list of references Hao Zhang, Xiao jun Lv, Yueming Li, etal.P25-Graphene Composite as a High Performance Photocatalyst.ACS NANO, 2009,4 (1): 380-387
(1) by graphene oxide ultrasonic dispersion in ethanol solution, graphene oxide ethanolic solution concentration is 0.1-3mg/mL;
(2) nano-metal-oxide is added in above-mentioned graphene oxide ethanolic solution, nano-metal-oxide addition 0.1-5g in every 100ml graphene oxide ethanolic solution, mix and blend 0.5-4h, obtains graphene oxide-nano metal oxide composite material suspension;
(3) at UV-irradiation (100-750 μ W/cm
2) under, continue to stir (10-600min) suspension redox graphene-nano metal oxide composite material, obtain redox graphene-nano metal oxide composite material suspension;
(4) by washing with deionized water after above-mentioned suspension centrifugation, at-20~-70 DEG C, by sample freeze drying 2-120h, obtain redox graphene-nano-metal-oxide composite positive pole.
Nano-metal-oxide is TiO
2nano particle, TiO
2nano wire, TiO
2nanometer rods, TiO
2nanometer film, three-dimensional TiO
2the mixture of one or two or more kinds in nano material, ZnO nano particle, ZnO nano-wire, ZnO nanorod, ZnO nano film or three-dimensional ZnO nano material.Described centrifugal speed is 6000-18000rpm, and centrifugation time is 3-60min.
Described ultrasonic power is 100-500W, and ultrasonic time is 0.5-3h.
Beneficial effect
1. doped with nanometer particle is conducive to reduce between graphene sheet layer serious stacking again.There is more fold and larger interlamellar spacing.
2. nano-metal-oxide has large specific area and strong absorption property, can hinder the polysulfide generating and be dissolved in electrolyte.
3. adopt redox graphene to be conducive to improve anodal conductivity as lithium sulfur battery anode material.
4. this two-dimensional structure of Graphene is conducive to the fixing of many lithium sulfides.
5. use uv irradiation method redox graphene, without any poisonous and harmful reagent, pollution-free, environmentally friendly in preparation method, method is convenient, easy to learn, favorable reproducibility, and low cost of manufacture, and efficiency is high.
Embodiment:
Embodiment 1:
A is by the ultrasonic dispersion in 50ml ethanol solution of 0.04g graphene oxide.
B is by 0.1g nano-TiO
2add in graphite oxide aqueous solution, mix and blend 3h, obtains graphene oxide-nano metal oxide composite material suspension.
C, under UV-irradiation, continues stirred suspension redox graphene-nano metal oxide composite material, obtains redox graphene-nano metal oxide composite material suspension.
The centrifugation of d suspension, deionized water washing 5 times, by sample freeze drying, obtain redox graphene-nano metal oxide composite material.
E nanofiber sulfurizing: the two ends that the redox graphene-nano metal oxide composite material making and elemental sulfur are placed in respectively to glass tube, then glass tube is put into tube furnace, pass into inert gas, at 400 DEG C, heat 2h, make sulphur-Graphene-nano metal oxide composite material.
F prepares slurry: by the sulphur-Graphene-nano metal oxide composite material making, binding agent, solvent, three's mix and blend is made slurry.The mass ratio of sulphur-Graphene-nano metal oxide composite material and binding agent is 9:1.
The preparation of g electrode: slurry is coated on collector uniformly, and vacuumize 36h, obtains lithium-sulphur cell positive electrode at 60 DEG C.
Described nano-TiO
2granular size is 21nm.TiO2 crystal formation is anatase.
Described centrifugal speed is 16000rpm, and centrifugation time is 5min.
Described ultrasonic power is 200W, and ultrasonic time is 3h.
Described collector is aluminium foil.
Described binding agent is Kynoar, and solvent is METHYLPYRROLIDONE.
Embodiment 2:
A is by the ultrasonic dispersion in 50ml ethanol solution of 0.04g graphene oxide.
B is by 0.2g nano-TiO
2add in graphite oxide aqueous solution, mix and blend 3h, obtains graphene oxide-nano metal oxide composite material suspension.
C, under UV-irradiation, continues stirred suspension redox graphene-nano-metal-oxide composite wood
Material, obtains redox graphene-nano metal oxide composite material suspension.
The centrifugation of d suspension, deionized water washing 5 times, by sample freeze drying, obtain redox graphene-nano metal oxide composite material.
E nanofiber sulfurizing: the two ends that the redox graphene-nano metal oxide composite material making and elemental sulfur are placed in respectively to glass tube, then glass tube is put into tube furnace, pass into inert gas, at 400 DEG C, heat 2h, make sulphur-Graphene-nano metal oxide composite material.
F prepares slurry: by the sulphur-Graphene-nano metal oxide composite material making, binding agent, solvent, three's mix and blend is made slurry.The mass ratio of sulphur-Graphene-nano metal oxide composite material and binding agent is 9:1.
The preparation of g electrode: slurry is coated on collector uniformly, and vacuumize 36h, obtains lithium-sulphur cell positive electrode at 60 DEG C.
Described nano-TiO
2granular size is 21nm.TiO
2crystal formation is anatase.
Described centrifugal speed is 16000rpm, and centrifugation time is 5min.
Described ultrasonic power is 200W, and ultrasonic time is 3h.
Described collector is aluminium foil.
Described binding agent is Kynoar, and solvent is METHYLPYRROLIDONE.
Embodiment 3:
A is by the ultrasonic dispersion in 50ml ethanol solution of 0.04g graphene oxide.
B is by 0.3g nano-TiO
2add in graphite oxide aqueous solution, mix and blend 3h, obtains graphene oxide-nano metal oxide composite material suspension.
C, under UV-irradiation, continues stirred suspension redox graphene-nano-metal-oxide composite wood
Material, obtains redox graphene-nano metal oxide composite material suspension.
The centrifugation of d suspension, deionized water washing 5 times, by sample freeze drying, obtain redox graphene-nano metal oxide composite material.
E nanofiber sulfurizing: the two ends that the redox graphene-nano metal oxide composite material making and elemental sulfur are placed in respectively to glass tube, then glass tube is put into tube furnace, pass into inert gas, at 400 DEG C, heat 2h, make sulphur-Graphene-nano metal oxide composite material.
F prepares slurry: by the sulphur-Graphene-nano metal oxide composite material making, binding agent, solvent, three's mix and blend is made slurry.The mass ratio of sulphur-Graphene-nano metal oxide composite material and binding agent is 9:1.
The preparation of g electrode: slurry is coated on collector uniformly, and vacuumize 36h, obtains lithium-sulphur cell positive electrode at 60 DEG C.
Described nano-TiO
2granular size is 21nm.TiO
2crystal formation is anatase.
Described centrifugal speed is 16000rpm, and centrifugation time is 5min.
Described ultrasonic power is 200W, and ultrasonic time is 3h.
Described collector is aluminium foil.
Described binding agent is Kynoar, and solvent is METHYLPYRROLIDONE.
Embodiment 4:
A is by the ultrasonic dispersion in 50ml ethanol solution of 0.04g graphene oxide.
B is by 0.4g nano-TiO
2add in graphite oxide aqueous solution, mix and blend 3h, obtains graphene oxide-nano metal oxide composite material suspension.
C, under UV-irradiation, continues stirred suspension redox graphene-nano-metal-oxide composite wood
Material, obtains redox graphene-nano metal oxide composite material suspension.
The centrifugation of d suspension, deionized water washing 5 times, by sample freeze drying, obtain redox graphene-nano metal oxide composite material.
E nanofiber sulfurizing: the two ends that the redox graphene-nano metal oxide composite material making and elemental sulfur are placed in respectively to glass tube, then glass tube is put into tube furnace, pass into inert gas, at 400 DEG C, heat 2h, make sulphur-Graphene-nano metal oxide composite material.
F prepares slurry: by the sulphur-Graphene-nano metal oxide composite material making, binding agent, solvent, three's mix and blend is made slurry.The mass ratio of sulphur-Graphene-nano metal oxide composite material and binding agent is 9:1.
The preparation of g electrode: slurry is coated on collector uniformly, and vacuumize 36h, obtains lithium-sulphur cell positive electrode at 60 DEG C.
Described nano-TiO
2granular size is 21nm.TiO
2crystal formation is anatase.
Described centrifugal speed is 16000rpm, and centrifugation time is 5min.
Described ultrasonic power is 200W, and ultrasonic time is 3h.
Described collector is aluminium foil.
Described binding agent is Kynoar, and solvent is METHYLPYRROLIDONE.
Embodiment 5:
A is by the ultrasonic dispersion in 50ml ethanol solution of 0.04g graphene oxide.
B is by 0.5g nano-TiO
2add in graphite oxide aqueous solution, mix and blend 3h, obtains graphene oxide-nano metal oxide composite material suspension.
C, under UV-irradiation, continues stirred suspension redox graphene-nano metal oxide composite material, obtains redox graphene-nano metal oxide composite material suspension.
The centrifugation of d suspension, deionized water washing 5 times, by sample freeze drying, obtain redox graphene-nano metal oxide composite material.
E nanofiber sulfurizing: the two ends that the redox graphene-nano metal oxide composite material making and elemental sulfur are placed in respectively to glass tube, then glass tube is put into tube furnace, pass into inert gas, at 400 DEG C, heat 2h, make sulphur-Graphene-nano metal oxide composite material.
F prepares slurry: by the sulphur-Graphene-nano metal oxide composite material making, binding agent, solvent, three's mix and blend is made slurry.The mass ratio of sulphur-Graphene-nano metal oxide composite material and binding agent is 9:1.
The preparation of g electrode: slurry is coated on collector uniformly, and vacuumize 36h, obtains lithium-sulphur cell positive electrode at 60 DEG C.
Described nano-TiO
2granular size is 21nm.TiO
2crystal formation is anatase.
Described centrifugal speed is 16000rpm, and centrifugation time is 5min.
Described ultrasonic power is 200W, and ultrasonic time is 3h.
Described collector is aluminium foil.
Described binding agent is Kynoar, and solvent is METHYLPYRROLIDONE.
Comparative example 1:
A nanofiber sulfurizing: graphene powder and elemental sulfur are placed in respectively to the two ends of glass tube, then glass tube are put into tube furnace, pass into inert gas, heat 2h at 400 DEG C, make sulphur-graphene composite material.
B prepares slurry: by the sulphur-graphene composite material making, binding agent, solvent, three's mix and blend is made slurry.The mass ratio of sulphur-Graphene-nano metal oxide composite material and binding agent is 9:1.
The preparation of c electrode: slurry is coated on collector uniformly, and vacuumize 36h, obtains lithium-sulphur cell positive electrode at 60 DEG C.
Described collector is aluminium foil.
Described binding agent is Kynoar, and solvent is METHYLPYRROLIDONE.
Comparative example 2:
A nanofiber sulfurizing: KB600 carbon dust and elemental sulfur are placed in respectively to the two ends of glass tube, then glass tube are put into tube furnace, pass into inert gas, heat 2h at 400 DEG C, make sulphur-KB600 composite material.
B prepares slurry: by the sulphur-Graphene-nano metal oxide composite material making, binding agent, solvent, three's mix and blend is made slurry.The mass ratio of sulphur-KB600 composite material and binding agent is 9:1.
The preparation of c electrode: slurry is coated on collector uniformly, and vacuumize 36h, obtains lithium-sulphur cell positive electrode at 60 DEG C.
Described collector is aluminium foil.
Described binding agent is Kynoar, and solvent is METHYLPYRROLIDONE.
The preparation of battery:
In argon shield, water content is in the glove box below 1ppm, and with the above-mentioned electrode slice preparing, as positive pole, metal lithium sheet, as negative pole, adopts Guotai Huarong Chemical New Material Co., Ltd., Zhangjiagang City's lithium battery electrolytes: 1mol/L LiClO
4/ DOL+DME(1:1, by volume), Celgard2325 barrier film, is assembled into CR2016 type button cell, and carries out charge-discharge test.
The battery of making in embodiment 1-5 and comparative example 1-2 is at room temperature carried out to charge-discharge test, and deboost is 2.8V to 1.5V, and charging and discharging currents density is 0.1mAh/cm
2.
The electrode that comparative example 1-2 obtains with embodiment 1-5 is according to identical mode assembled battery, and measures the capability retention after first charge-discharge capacity and 100 circulations of battery according to identical mode.Measurement result is as shown in table 1.
As shown in table 1: after 100 circulations, Graphene-nano-TiO
2the capability retention of electrode is higher than the capability retention of Graphene electrodes.Along with nano-TiO
2the increase of quality in reaction system, the first charge-discharge capacity of battery presents first increases the trend reducing afterwards, and after 100 circulations, the capability retention of batteries is also and first increases the trend reducing afterwards.As compared with anodal battery, after the first charge-discharge capacity of the battery that contains Graphene and 100 circulations, capability retention is all higher with KB600-sulphur composite material.