Synthesis,Energy Storage And Intelligent Sensing Application Of Two-Dimensional Black Phosphorus Composites

In recent years,with the rapid development of technologies and industries such as new energy,new sensing,flexible electronics,and intelligent wearable for the human body,the old materials are increasingly unable to meet people’s needs for performance and function,so it is urgent to find the functional materials or new composite materials with better performance.With the research and exploration of new materials,more and more two-dimensional materials have been widely used in electronics,chemistry,physics,biology,and other fields due to their unique structural characteristics,showing a variety of excellent material properties,which has aroused the attention of researchers.As a new two-dimensional semiconductor material,black phosphorus（BP）not only has an adjustable band gap lamellar structure but shows great potential for electronic sensing.And it has an ultra-high theoretical capacity,showing strong potential for chemical energy storage.At the same time,the less-layer two-dimensional black phosphorus structure prepared by liquid phase stripping has been applied to energy storage,medicine,optoelectronics,sensing,and other fields due to its excellent physical properties such as higher carrier mobility,adjustable direct band gap,unique anisotropy and so on.However,two-dimensional black phosphorus is easy oxidation degradation in the environment,destroying the lamellar structure,which greatly limits its excellent performance,especially reduces the structural stability and service life of materials,brings many limitations and adverse effects on the large-scale preparation of two-dimensional black phosphorus materials,long-term and stable storage and widely practical application,etc.In addition,when two-dimensional black phosphorus material is applied to secondary battery energy storage,it is often accompanied by continuous volume expansion and contraction,which not only makes the two-dimensional black phosphorus electrode structure easy to be destroyed,leading to irreversible conductivity decline but also greatly reduces the specific capacity of energy storage device and shortens its service life.At present,the structure of two-dimensional black phosphorus shows poor stability and the application performance is not excellent.Through experimental research,we summarized and improved the original preparation method of black phosphorus and successfully produced high-quality black phosphorus through the optimization of the high-energy ball mill process.The thin-layer black phosphorus was successfully prepared by liquid phase stripping and black phosphorus quantum dots were successfully prepared by acoustic degradation.On this basis,according to the performance characteristics of black phosphorus,we carried out targeted improvement and optimization of the structure and performance of black phosphorus,which not only overcame the disadvantages of easy oxidation and hydrolysis of black phosphorus,but also successfully improved the electrochemical performance of two-dimensional black phosphorus,and prepared a variety of new two-dimensional black phosphorus composite materials,which were successfully applied in energy storage devices such as supercapacitors,lithium-ion batteries,pressure sensors,vibration sound sensors and successfully realized the functional applications of multiple intelligent sensing systems by using flexible integration technology.In addition to improving the performance of two-dimensional black phosphorus-based materials,their multi-functional applications of them are broadened.Combined with a variety of theoretical model calculations and quantitative analysis,the experimental principle,material structure,and deep reasons for performance advantages are studied and summarized in detail.Therefore,this paper has important research significance in theoretical analysis and practical application development of black phosphorus materials and the main conclusions are as follows:（1）This paper successfully optimized the preparation method of two-dimensional black phosphorus and its composite materials.Although the large two-dimensional black phosphorus crystals can be synthesized by chemical vapor deposition（CVD）,the higher synthesis conditions greatly increase the experimental cost,and the introduction of catalysts not only has toxicity but also brings many potential environmental hazards.Two-dimensional black phosphorus crystals can be rapidly synthesized by the high temperature and pressure method,but the synthesis conditions are demanding and the yield is low,which brings difficulties to the extensive research and application of two-dimensional black phosphorus.To solve these problems,we adopt the improved high-energy ball milling method,which can directly transform the abundant and cheap red phosphorus into two-dimensional black phosphorus with high purity and high quality at room temperature.The optimized high-energy ball milling method shows obvious advantages:the synthesis conditions are easy to meet,the experiment repeatability is high,and the cost of producing two-dimensional black phosphorus is greatly reduced.And no catalyst and other materials introduced will not produce experimental waste,which can achieve green environmental protection.In addition,in this paper,the liquid phase stripping method was used to successfully prepare the thin-layer black phosphorus,showing good lamellar structure and crystallinity.At the same time,we further studied the nano-scale black phosphorus materials and successfully prepared black phosphorus quantum dots with uniform particle size distribution by acoustic degradation method,which laid a foundation for an in-depth study on the properties and applications of black phosphorus.（2）This paper successfully overcomes the shortcomings of two-dimensional black phosphorus,which is prone to structural oxidative degradation and poor stability.For the first time,we successfully prepared MXene/BP self-supporting flexible thin films with periodic layered stable structure by the method of layered vacuum extraction and filtration.Through experiments,it is found that thin-layer two-dimensional black phosphorus and thin-layer Ti₃C₂T_X MXene can stably compound in the composite film structure.MXene can wrap and protect the BP lamellar structure while closely bonding with BP through the chemical bond（P-O-Ti）,which effectively overcomes the defect of poor stability caused by easy degradation of the two-dimensional black phosphorus structure.Flexible supercapacitor prepared using MXene/BP film as electrode,shows ultra-high volume ratio capacitance（896.87 F/cm³,0.69 A/cm³）,excellent rate performance（241.2 F/cm³,6.94 A/cm³）and long-term cycle stability（capacitance retention rate 91.74%,1 A/cm³,10,000 cycles）.Meanwhile,MXene/BP film is used as a pressure-sensitive layer to prepare the flexible pressure sensor,which has a sensitivity of 78.18 k Pa^-1,fast response/recovery time（10.9/12.9 ms）,and wide pressure-sensitive operating range（0-200 k Pa）.The flexible integrated design of MXene/BP thin-film flexible supercapacitor and flexible pressure sensor was carried out,and the flexible intelligent bracelet was successfully assembled by combining the flexible solar cell module.It can not only accurately monitor the pulse signal of the human body and reflect the health status of the human body,but also realize the collection,storage,and recycling of green energy.（3）This paper successfully solved the problem of rapid performance decline caused by structural fragmentation accompanied by volume expansion and contraction and irreversible generation of phospho-lithium when two-dimensional black phosphorus material is applied to lithium-ion batteries.BP@CNTs composites with the stable three-dimensional crosslinking structure were successfully prepared by the chemical crosslinking method.We use the urea decomposition process to introduce a variety of functional groups,two-dimensional black phosphorus,and nitrogen-doped carbon nanotubes（N-CNT）through the chemical bond（P-C,P-O-C）to form a stable three-dimensional composite structure BP@CNTs.Lithium-ion batteries assembled with BP@CNTs composites as anode materials for lithium-ion batteries show high discharge specific capacity（1088 m Ah/g,0.1 A/g）,low resistance（88.9Ω）,long-term cycle stability（757.3 m Ah/g,0.5 A/g,650 cycles）,excellent rate performance（552m Ah/g,2.5 A/g）and high energy density（543 Wh/kg）.At the same time,we use density functional theory to calculate and compare the numerical value of binding energy between multi-phosphide（Li _XP）and（N-）CNT generated in the process of lithium storage,which explains the deep reasons of BP@CNTs composite can keep the stability of energy storage structure for a long time and the favorable effect of nitrogen doping on the composite structure.We extend the operating voltage window by connecting BP@CNTs-based lithium-ion batteries in series and use them to provide a long-term stable power supply for patterned LEDs.Compared with the performance of the same type of lithium-ion batteries,BP@CNTs composite material shows the advantage of excellent energy storage performance,which provides a new idea for the optimization design of two-dimensional black phosphorus material as the electrode performance of the lithium-ion battery.（4）In this paper,a CNT-BP@MXene-based flexible lithium-ion battery with both flexibility and high energy storage stability was successfully produced,which overcomes the problems of electrode structure destruction and rapid performance decline of flexible lithium-ion battery in the process of energy storage.At the same time,we successfully prepared high flexibility CNT-BP@MXene-PVDF composite film-based pressure sensing film,showing excellent pressure-sensitive performance.We have prepared CNT-BP@MXene composite with stable structure by ball milling method as the flexible electrode material of flexible lithium-ion battery,which not only shows excellent flexibility.Moreover,it has a high discharge capacity（1349 m Ah/g）,strong conductivity（105.8Ω）,excellent rate performance（384.67 m Ah/g,10 A/g）,and long cycle life（750 m Ah/g,2000 cycles）.Through density functional theory calculation,it is confirmed that the CNT-BP@MXene composite has a stronger adsorption capacity for lithium-ion.The reaction process and mechanism of lithium storage in composites were investigated in detail by in-situ X-ray diffraction.At the same time,we obtained CNT-BP@MXene-PVDF flexible composite film with high strength and self-supporting structure by adding PVDF and using the wet ball milling method and applied it to the flexible pressure sensor,showing fast response speed（8.94 ms）and excellent pressure-sensitive stability（pressure sensitive retention rate of 110%,over 10000cycles）.We integrated CNT-BP@MXene composite flexible lithium-ion battery,CNT-BP@MXene-PVDF composite thin film flexible pressure sensor,flexible solar cell,micro-processor,voltage control module,and Bluetooth module,which were successfully prepared intelligent wireless human health monitoring bracelet and foot pad.It can not only monitor the pulse and various motion signals of the human body in real-time but also realize the real-time wireless data transmission function.These works show the great significance of the application of two-dimensional black phosphorus composite materials in flexible lithium batteries and intelligent sensing systems.（5）In this paper,a vibration sound sensor based on two-dimensional black phosphorus composite material is successfully prepared,which expands the acoustic application field of 2D BP.We integrate BP/MXene composite film with periodic layered structure and vibration coil to obtain BP/MXene@Vibration coil magnetic vibration sound device,showing a wide range of sound frequency response（20 Hz-20k Hz）.In addition,we have successfully prepared BP/MXene@AAO and BP/MXene@PI thermoacoustic devices by using the layered spin coating method,which uniformly coated the 2D BP and MXene thickening layers on the anodic alumina（AAO）and polyimide（PI）substrates,and show excellent sound performance（68.2 d B,f=15 k Hz）.Finally,we simulate the bionic artificial throat structure with a 2D BP-based vibration sound sensor and integrate it with a voice-controlled LED to form an intelligent voice robot,which provides a new method for the exploration of new functions and intelligent sensing applications of 2D BP-based materials.