Synthesis And Electrochemical Properties Studies Of Phosphorus/Carbon Anode Materials

The tense shortage of global energy resources promotes the vigorous development of various new energy storage technologies.Owing to the abundance and low price of potassium resource,as well as the low standard electrode potential of potassium,potassium-ion batteries(PIBs)have become a promising energy storage technology in recent years.However,when the traditional intercalation anode materials represented by graphite used as PIBs anode,PIBs often confront with those problems,including low theoretical capacity and the damage and collapse of electrode structure caused by repeating insertion/removal of large radius K⁺.Alloy anode materials follow the multi-electron transfer electrode reaction and often has a high theoretical capacity,which means it is the preferred anode material for high energy density PIBs.Among the alloy anode materials,red phosphorus has the highest theoretical capacity,but the cycling performance of phosphorus-based anode is poor due to the drastic volume fluctuation during the potassiation/depotassiation process.In this paper,carbon-based materials with good mechanical properties and stability were used as carbon matrix to synthesis phosphorus/carbon anode materials with high potassium storage capacity and excellent cycling performance.The specific works were listed as follow:(1)Three kinds of phosphorus/carbon composites with different chemical bonding states were prepared by using carboxylic carbon nanotubes(CGCNT),carbon nanotubes(CNT)and reduced Carboxylic Carbon Nanotubes(RCGCNT)as carbon matrix.When P-CGCNT was used as anode of PIBs,the cycling performance of P-CGCNT was the most stable(the reversible capacity was 402.6 m Ah g^-1 after 110cycles),which was much higher than that of P-CNT under the same test conditions.According to the results of X-ray photoelectron spectroscopy and electrochemical properties,we think that the existence of carboxyl functional group is helpful to the formation of P-O-C bond.More importantly,the excellent cycle stability of P-CGCNT anode is due to the higher bond energy of P-O-C bond(585 KJ mol^-1)than that of P-C bond(264k KJ mol^-1).(2)Corrugated carbon nanosheets(CCN)were prepared by the method of crystallization induction with the KCl crystal as template and PEG as carbon source.The characterization results show oxygen-containing functional groups on the surface of CCN,the internal defects are abundant,and the microstructure is disordered.The wavy-like 2-D structure of CCN increases the specific surface area and brings abundant pore structure.When used as anodes of sodium and potassium ion batteries,the capacity of sodium and potassium storage of CCN electrode is 265 and 252.7 m Ah g^-1respectively after 400 cycles at 0.5 A g^-1.The results of cyclic voltammetry show that the dominant factor of the storage of Na⁺and K⁺in CCN anode is diffusion behavior when the current value is small,but with the increase of current value,the capacitance contribution rate of Na⁺storage in CCN is much greater than that of K⁺storage.(3)Using CCN as carbon matrix,phosphorus/corrugated carbon nanosheets composite(P/CCN-F)and phosphorus/corrugated carbon nanosheets mixture(P/CCN-H)were prepared by mechanical ball milling and manual grinding.When P/CCN-F was used as the anode of PIBs,the reversible capacity was maintained at 466.9 m Ah g^-1after 60 cycles at a current density of 0.1 A g^-1.The results of ex-situ SEM,electrochemical impedance and galvanostatic intermittent titration showed that P/CCN-F could maintain a more stable electrode structure during repeating charge/discharge processes.Due to the abundant oxygen-containing functional groups on the surface of CCN matrix,there are lots of P-O-C bonds between P and CCN in P/CCN-F,which increases the overall conductivity and makes P/CCN-F maintain a more stable structure during the repeating alloying process.There are 44 pictures,2 tables and 128 references in this paper.