Study On The Biack Phosphorus Based Anode Materials For Lithium Secondary Battery

Diversified application scenarios make higher request on the performance of lithium-ion batteries（LIBs）.The energy density of LIBs needs to be increased continuously.The specific capacity of the anode material greatly affects the energy density of the battery.Therefore,it is imperative to develop high specific capacity anode materials.Black phosphorus（BP）has a folded laminar structure,a low Li⁺diffusion barrier along the Z direction（0.08 e V）,and the theoretical specific capacity of BP(2596 m Ah g^-1)is larger than that of the current commercial graphite cathode(372 mAh g^-1).These make BP a very promising anode material.However,the poor air stability,low conductivity,and volume change during lithium de-embedding process of BP limit the application of BP.According to the limiting factor of poor air stability of BP,in this paper,we first prepared BP electrode sheets under air or argon conditions and investigated the effect of atmosphere on the electrochemical properties of the electrode sheets.It was found that the preparation of BP electrode sheets under air conditions generates part of Cu₃P phase,which helps to improve the electrochemical properties of BP electrode sheets.Thus,Cu₃P materials were prepared and investigated their electrochemical properties.The results show that the Cu₃P negative electrode obtained by ball milling has low specific capacity.In order to improve its electrochemical performance furtherly,the molar ratio of BP is increased in the preparation of Cu₃P and Cu₃P/BP material is prepared.The details of the study are as follows:（1）The BP-Air anode and BP-Ar anode were prepared under air and argon conditions,respectively.The results showed that the BP-Air negative electrode had a discharge specific capacity of 2326 m Ah g^-1 in the first circle and a charging specific capacity of 1780 m Ah g^-1.However,the electrochemical performance of the BP-Ar negative electrode was poor and almost negligible.Through XRD and energy spectrum analysis,it is found that the great difference in electrochemical performance is that Cu₃P phase is formed in BP-Air anode but not in BP-Ar anode.The presence of Cu₃P phase keeps the cycle of BP-Air anode going,which alleviates the fragmentation of active particles to a certain extent.Besides,fine metallic copper was formed during the lithium embedding of Cu₃P,which keeps the electrical contact between active fragment particles.The particle fragmentation and the low electrical conductivity of the electrons of the BP negative electrode material are important factors affecting its high cycling performance.（2）Due to the presence of Cu₃P phase in BP-Air anode can improve its electrochemical performance and mitigate the reversible capacity loss.Using black phosphorus and copper powder as precursors,Cu₃P materials were prepared by ball milling and the electrochemical properties of Cu₃P materials as anode materials were studied.The results show that the Cu₃P material has good cycling and multiplication performance.The discharge specific capacity and charge specific capacity of the first cycle were 1172.3m Ah g^-1 and 452.9 m Ah g^-1 at 0.1 C.After 50 cycles,its reversible capacity was 303.7 m Ah g^-1,and its capacity retention rate was 62.3%compared with the discharge specific capacity of the second week(487.6 m Ah g^-1).（3）Although the Cu₃P material can maintain a certain cycle stability,its specific capacity is still low,and it cannot reach the high cycle capacity of BP-Air electrode sheet,we prepared Cu₃P/BP material by increasing the ratio of BP,expecting to further improve the cycle capacity.The results showed that the initial cycle capacity of Cu₃P/0.367BP material increased.However,due to the increase of BP content,the volume expansion of black phosphorus before and after cycling is large,which leads to the poor structural stability of Cu₃P/BP material and more serious decay of specific capacity after long cycling.