Design Of Multifunctional Aqueous Binders And Application In Silicon-based Anodes For Lithium-ion Batteries

Silicon（Si）-based anodes are considered to be one of the most promising candidates for next-generation high-energy-density lithium-ion batteries due to its ultra-high theoretical specific capacity,low lithiation-delithiation potential,and abundant reserves.However,the huge volume expansion of Si-based anodes during the charging and discharging process will destroy electrode structure,which leads to the poor cycle performance.In order to solve these challenges of Si-based anodes,the scientific community has improved the performance of Si-based anodes from many aspects,such as nano-Si-based design,composite material,electrolyte additives,and development of novel binders.Among them,the development of novel binder is considered to be the most economical and effective way to solve these problems of Si-based anodes.In recent years,researchers have successively reported a series of Si-based anode binders and significantly improved the electrochemical performance of Si-based anodes.However,to realize the practical application of silicon-based anodes,the current binders still have a series of deficiencies.In view of the shortcomings of the current binders,the following two binders were prepared:（1）Sericin protein in situ cross-linked citric acid as a high-performance Si O_x anodes.In this work,citric acid（CA）was used as a cross-linking agent to chemically cross-link with sericin（SP）to prepare a composite binder with a three-dimensional network structure（C-SP-CA）.Due to its excellent mechanical properties,adhesion properties,and ion-conducting properties,the Si O_x anode（Si O_x@C-SP-CA）using C-SP-CA binder demonstrated excellent long cycling stability at 500 m A g^-1.Specially,Si O_x@C-SP-CA anode demonstrated a high reversible areal capacity of 4.47 m A h cm^-2and still hold 1.42 m A h cm^-2 after 100 cycles.In addition,the full cell based of Si O_x@C-SP-CA anode exert the cycle retention is 79.1%after100 cycles at 0.2 C.（2）In view of the problems of low mass loading and low ICE of Si-based anodes,this work obtained a universal lithiated-binder（Li_xPAA）for Si-based anodes by regulating the degree of lithiation for polyacrylic acid（PAA）.By introducing Li⁺into the functional groups of PAA,the side reactions of the binder during cycling can be reduced,which is contributed to the formation of a stable SEI layer.In addition,the introduction of Li⁺have significantly improved the ion-conducting of the binder and reduce the polarization effect of the Si-based anode.Next,by controlling the degree of lithiation of the binder,the mechanical properties of the binder can be effectively regulated,thereby ensuring the integrity of the electrode.Benefiting from the excellent mechanical properties,adhesion properties and ion-conducting properties of the binders,Si O_x@Li_0.75PAA,Si@Li_0.75PAA and Si C@Li_0.5PAA achieve ultra-high areal capacities of 3.2 m A h cm^-2,3.48 m A h cm^-2 and 3.41 m A h cm^-2 after l00 cycles,respectively.In addition,the full cell based of Si O_x@Li_0.75PAA anode exert the cycle retention is 77%after 100 cycles at 0.2 C.