Structure Design And Performance Optimization Of Silicon-based Anode For Lithium-ion Battery

With high specific capacity and abundant reserves,Si is one of the most promising anode materials for next-generation Li-ion batteries.However,the huge change of Si particle volume during the charging and discharging process hinders its industrialization.The huge volume change makes the Si anode face four major challenges,namely,the crushing of the electrode material,the repeated formation of unstable solid electrolyte interfacial film,the destruction of the conductive network and the electrode structure,which eventually lead to the rapid decay of the battery capacity.Aiming at the four challenges of Si anode,this paper optimizes the performance of silicon-based anodes from three aspects:the preparation of electrode material,the design of electrode structure and the development of flexibility binder.The details are as follows:The Mn4Si7 alloy doped Si-Mn/C composites was prepared for the first time,and the buffering effect and electron transport ability of the Mn4Si7 alloy were used to improve the battery cycle stability.Mn4Si7 doped Si-Mn/C composites were prepared by secondary precipitation and subsequent heat treatment.In the experiment,the 90%Si10%Mn/C composite with the best electrochemical performance was obtained by optimizing the heat treatment temperature and the Si-Mn feeding ratio.The 90%Si10%Mn/C composite exhibits excellent cycling performance and rate capability,with a specific capacity retention of 1281.3 mAh g-1 at a current density of 500 mA g-1 after 100 cycles,and the capacity retention rate is as high as 82.3%;after 300 cycles at a current of 1300 mA g-1,there is still 60%of the specific capacity remaining,and the capacity retention rate of the comparative Si/C electrode is only 38.1%.Compared with the Si/C electrode,the 90%Si10%Mn/C electrode also exhibits better rate capability,exhibiting a specific capacity of 880.6 mAh g-1 even at a high current density of 13 A g-1.Based on the concept of designing the buffering effect and improving the electron transport of the electrode,the experiment went from the preparation of the electrode material to the design of the whole electrode.The Si@C-network electrode with a continuous conductive network was designed by cleverly used the interfacial compatibility between xanthan gum and Si to stabilize the conductive network and electrode structure.The fluffy and porous conductive network provides a certain buffer space for the volume change of the silicon particles,and at the same time improves the overall electron transport of the electrode.Containing a high proportion of active Si(83.4 wt.%),the Si@C-network electrode exhibited long-term cycling stability:the electrode maintains a capacity of 765 mAh g-1 after cycling at a current density of 2100 mA g-1 for 700 cycles;even with the Si loading of 0.8 mg cm-2,the electrode maintains a specific charge capacity of 1707 mAh g-1 after 50 cycles.The Si@C-network electrode with continuous conductive network also exhibits better rate capability,and its specific charge capacity can reach 1460 mAh g-1 when the current density is increased to 8400 mA g-1The integrity of the electrode structure and conductive network under high Si loading needs to be regulated by the flexibility components in the electrode.A flexible multivalent amide-hydrogen-bond supramolecular binder was developed to maintain the stability of the electrode structure in the experiment.Firstly,NAGA monomers containing bis-amide functional groups were prepared by condensation reaction,and then the flexibility PNAGA supramolecular binder were obtained by free radical polymerization.Based on the presence of two amide-hydrogen bonds on each side chain,the PNAGA supramolecular binder contains multiple intermolecular and intramolecular hydrogen bonds when applied to Si anodes.The electrode containing PNAGA binder exhibits better electrochemical performance,with a capacity retention of 84%after 100 cycles at 420 mA g-1 and a 1942.6 mAh g-1 capacity maintained after 400 cycles at 1260 mA g-1 Even with a Si loading of 1.2 mg cm-2,the electrode with PNAGA binder exhibits high initial areal capacity(2.64 mAh cm-2)and good cycling performance(81%capacity retention after 50 cycles).In addition,the PNAGA binder also showed more stable cycling performance when applied to commercial SiC anode.This paper focuses on preparation of Si-Mn/C composites to enhance electron transport and buffering of electrode materials;design of Si@C-network electrode to improve electrode overall electron transport and conductive network integrity;and development of a PNAGA binder to enhance the stability of the conductive network and electrode structure during cycling.The three works sequentially optimize the electrochemical performance of Si-based anodes for lithium-ion batteries,which have reference value for the development of high-energy Li-ion batteries.