Preparation And Application Of Polypyrene-derived Conductive Binders For Silicon Anodes In Lithium-ion Batteries

Silicon?Si?anodes,with high theoretical specific capacity,have the potential to achieve high-energy-density lithium-ion batteries.However,during the charge/discharge process,the large volume change of Si destroys the contact between Si and conductive additive whose interaction force is weak,which reduces the cycling and rate performance of Si anodes.In recent years,researchers have replace the traditional binders and conductive agents with conductive binders,which can not only improve the stability of the structure and conductive network of Si anodes,but also increase the content of Si in anodes to increase the energy density of batteries.Among the conductive binders,polypyrene-derived conductive binders have potential for scale-up because they are easier to prepare and modify.However,the conductive network of rigid poly?1-pyrenemethyl methacrylate??PPy?is easy to destroy due to the stress concentration during the charge/discharge process.Therefore,this paper aims to improve the performance of PPy from two aspects:improving flexibility and endowing self-healing ability of PPy.The main contents of this paper are as follows:1.From the point of view of improving the flexibility of PPy,a polypyrene-derived multi-block conductive binder?PPy-b-PB?,modified by polybutadiene?PB?,was prepared,which is the first conductive binder with multi-block structure in the field of the researches of binders in Si anodes so far.Compared with PPy,the multi-block PPy-b-PB,with higher flexibility,reversible deformation ability,and molecular weight,is beneficial to the decrease of the impedance and increase of mechanical stability,lithium-ion diffusion rate,and reconstruction ability of the conductive network of Si anode,which can improve the cycling and rate performance of the anode.With mass ratio of Si to conductive binder of 2:1 and the Si loading of 0.24 mg·cm^-2,the average delithiation specific capacity of the PPy-b-PB/Si anode at the charge/discharge rate of 1 C is 570 mAh·g^-1,which is 4.07 times as high as that of the PPy/Si anode.At the rate of 0.2 C,the initial coulombic efficiency of PPy-b-PB/Si anode is 77.9%and the delithiation specific capacity of the PPy-b-PB/Si anode after 200charge/discharge cycles is 2270 mAh·g^-1,which is 29.7%higher than that of the PPy/Si anode.When the Si loading increases to 0.60 mg·cm^-2,the delithiation specific capacity of the PPy-b-PB/Si anode after 200 charge/discharge cycles is 2050 mAh·g^-11 which is better than most of Si anodes prepared by other n-type conductive binders.2.From the point of view of endowing PPy with self-healing ability,polypyrene-derived self-healing conductive binder?PPU?,modified by ureido-pyrimidinone?UPy?,was prepared,which is the first conductive binder with self-healing ability in the field of the researches of binders in Si anodes so far.Compared with PPy,PPU with stronger polarity and self-healing performance can not only slow down the increase of impedance,improve the mechanical stability and the lithium-ion diffusion rate of the anode,but also significantly enhance the reconstruction ability of conductive network and repair the cracks in the anode,which contributes to the improvement the cycling and rate performance of the anode.With mass ratio of Si to conductive binder of 2:1 and Si loading of 0.24 mg·cm^-2,the average delithiation specific capacity of the PPU/Si anode at the charge/discharge rate of 1 C is 820 mAh·g^-1,which is 5.86 times as high as that of the PPy/Si anode.At the rate of 0.2 C,initial coulombic efficiency of the PPU/Si anode is 78.2%,while the delithiation specific capacity of the PPU/Si anode after 200 charge/discharge cycles is 2570 mAh·g^-1,which is 46.9%higher than that of the PPy/Si anode.When the Si loading increases to 0.60 mg·cm^-2,the delithiation specific capacity of the PPU/Si anode after 200 charge/discharge cycles is 2100 mAh·g^-1,which is better than most of Si anodes prepared by other n-type conductive binders.In addition,when the mass ratio of Si to conductive binder,Si loading,and the charge/discharge rate are increased to 4:1,1.24 mg·cm^-2,and 0.5 C,respectively,the cyclic stability of the PPU/Si anode has become favorable since 21^th cycle.The average delithiation specific losses per cycle from 21^th to 200^th cycle of PPU/Si anodes is as low as 0.12%.