Design And Lithium Storage Property Of Photovoltaic Waste Silicon-based Battery Anode

Silicon（Si）is widely considered as the most promising anode material for the next generation lithium-ion batteries due to its high specific capacity,low potential and abundant reserves.However,the problems of poor electronic conductivity,large volume variation during the discharge/charge processes and interface instability lead to the poor electrochemical performance of Si anodes.In addition,most of the past researches used high-cost nanosized Si raw material and complex technological processes to prepare silicon-based anode materials,which were unfit for further industrial application.In photovoltaic（PV）industry,a large amount of cutting wastes were generated during the manufacturing process of polysilicon wafers,causing serious environment pollution and resources waste.Based on the above analysis,two kinds of Si-based anode materials with good electrochemical performance were prepared taking low-cost PV waste Si as the raw material through reasonable material design and simple experiment processes.The specific research contents are as follows:（1）We used PV waste Si and lignin wastes as the raw materials to prepare the Si/lignin-based carbon（Si/C）composite by a simple co-precipitation method and studied its electrochemical properties.The elastic carbon frame can effectively alleviate the volume variation of Si during the（de）lithium processes and improve the electronic conductivity.At the same time,the carbon coating structure can block the direct contact between the active Si and the electrolyte,reduce the side reaction and stabilize the electrode interface.The as-achieved Si/C anode showed a high charge capacity of 706.8 mAh g^-1 at 0.2 A g^-1 after 100cycles,which nearly doubled the capacity of the existing commercial graphite anode.What’s more,the Si/C anode delivered capacities of 907.9 and 575.9 mAh g^-1 at 0.2 and 2A g^-1,respectively,indicating good rate capability.（2）From a practical point of view,in order to improve the cyclic stability,pressing density and volumetric capacity of the Si-based anodes,we prepared a Si/reduced graphene oxide/hard carbon（Si/rGO/C）composite with particle size of～10μm and investigated its electrochemical properties.In the hierarchical structure of Si/rGO/C,the three-dimensional conductive network composed of rGO and hard carbon ensures the high electron conduction and full utilization of active Si in the large particles.The rGO can act as the mechanical support to relieve the stress generated from the volume variation of Si,so that the large-scale secondary particles can remain stable during the discharge/charge processes.The prepared Si/rGO/C anode showed mass and volumetric capacities of 780.0 mAh g^-1 and858.0 mAh cm^-3 under a pressing density of 1.1 g cm^-3,respectively,which are higher than those of the commercial graphite anode.After 200 cycles,the capacity retention was 83.6%.At an areal capacity of 2.7 mAh cm^-2 close to that of the commercial batteries,the capacity retention was 84.8%after 100 cycles.In addition,the capacity retention of the Si/rGO/C||NCM622 full cell was up to 90.8%after 50 cycles under an areal current of 0.17 mA cm^-2.The above two kinds of anode materials prepared from the PV waste Si effectively solve the problems of Si and improve the electrochemical performance of the Si-based anodes.The designs have the advantages of simple process and low cost,providing a green and economic way for the recycling of PV waste Si.