Preparation Of Phosphorene And Its Electrochemical And Carrier Transport Properties

Since the successfully preparation of graphene,two-dimensional materials have attracted extensive attention due to their atomic-scale thickness,excellent flexibility,and exotic properties different from those of bulk materials.Therefore,they are widely used in energy storage devices,microelectronic devices,optoelectronic devices,thermoelectric devices,and biomaterials.Especially,black phosphorus（BP）,as a layered semiconductor material with a direct band gap structure,receives extensive attention from researchers due to itsexcellent lithium storage capacity and high carrier mobility.However,in practical applications,the poor structure stability and atmospheric degradation make the actual performance of BP much lower than the theoretical prediction value.Therefore,this paper focuses on the preparation and modification of two-dimensional BP to solve the problems existing in practical applications and give full play to the excellent electrochemical and electrical transport properties of BP,which promotes its further development and application.To realize the controllable preparation of two-dimensional BP,while ensuring the small thickness and large lateral size,BP nanosheets with antioxidation capacity were prepared by ultrasonic-assisted liquid-phase exfoliation,with an average thickness of 3.6 nm,and the lateral size of 1μm.The larger lateral size could provide more active sites and facilitate the deintercalation of lithium ions,giving full play to the excellent electrochemical properties of BP.At a current density of 0.1 A g^-1,the few-layer BP electrode exhibits an initial discharging specific capacity of 2210 m Ah g^-1,which was better than that of the bulk BP electrode(1528 m Ah g^-1).Aiming at the problem of particle fragmentation during cycling,graphite and amorphous TiO_x were introduced into the prepared two-dimensional BP by mechanical milling and anhydrosol-gel method,and the BP–C@TiO_x composite electrode was constructed to optimize the cycle stability of BP.Benefiting from the stable P–C bond between BP and graphite and the in-situ electrochemical induction of TiO_x into a Li_yTiO_x layer,the huge volume expansion during cycling was relieved and the stability of electrode structure was improved.A t a current density of 0.1 A g^-1,the BP–C@TiO_x electrode exhibited an initial charging specific capacity of 875m Ah g^-1,and could still maintain a reversible specific capacity of 702 m Ah g^-1 after50 cycles.After 1000 cycles at a rate of 2 A g^-1,the capacity retention rate reached79.3%.To further improve the rate performance of BP electrodes,polyaniline（PANI）was in-situ coated on the surface of BP–graphene oxide（GO）to obtain BP–GO–PANI ternary composites.As a typical conductive polymer,PANI could enhance the conductivity of electrode materials.Furthermore,it could prevent the formation of non-conductive impurities such as Li F on the electrode surface,ensuring the smooth pathways of Li⁺to achieve rapid storage at high rates.The reversible specific capacity of 334 m Ah g^-1 can still be maintained at a current density of 5 A g^-1,which is much higher than that of BP(19 m Ah g^-1)and BP–GO(104 m Ah g^-1)electrode.To give full play to the excellent electrical transport properties of BP,clean and complete BP nanosheets with large size and high crystal quality were obtained by mechanical exfoliation.Based on the unique electrical anisotropy of BP,the Armchair direction of BP was identified by angle-resolved Raman spectroscopy,and field effect transistors with controllable channel orientation were fabricated to improve the carrier mobility of devices.At a channel thickness of 28 nm,whe mobility increased from 172.2 cm² V^-1s^-1（along the Zigzag direction）to 637.1 cm² V^-1s^-1（along the Armchair direction）.In addition,with the change of channel thickness,both the impurity scattering of the substrate and the interlayer resistance would affect the movement of carriers,so the carrier mobility of the device increased first and then decreased with the increase of the channel thickness.In this thesis,few-layer black phosphorus with controllable thickness were prepared by liquid-phase exfoliation method,and the electrochemical performance of BP was optimized by means of in-situ electrochemical induction of Li_yTiO_x and organic-inorganic hybrid coating.In addition,clean and complete BP nanosheets were obtained by mechanical exfoliation,and the carrier transport performance of the device was improved by controlling the orientation of the channel.This work provides theoretical and experimental basis for the practical application of BP.