Preparation And Properties Of Alginate-Prussian Blue Analogs Aqueous Binder For Silicon Anodes In Lithium-Ion Batteries

Silicon anode with a high theoretical specific capacity and a relatively low operating voltage is one of most potential anode materials for lithium-ion batteries.However,due to the huge volume change of Silicon in the process of lithiation/delithiation process,its electrochemical performance rapidly decays,which limits its commercial application.Aiming at the problem of poor cycling stability of silicon anode,alginate-metal ion binders with a three-dimensional network structure were designed and prepared in this paper.The volume expansion of the silicon nanoparticles is limited by the strong surface-contact interaction between the binder network and the silicon nanoparticles,and the cycling stability of the silicon anode is improved.Moreover,Alginate-Metal ion-Prussian blue binders with better thermal stability and strong mechanical properties has been designed and prepared by introducing cyanide ions into the alginate-metal ion network to furtherly improve the cycle stability of the silicon anodes.The specific research contents are as follows:（1）Based on the chelation reaction between alginate and polyvalent metal ions,alginate-metal ion hydrogel binders（Alg-Ni/Cu/Zn）with a three-dimensional network structure were prepared to improve mechanical its properties and thermal stabilities.Moreover,the mechanism of lithium ion migration of alginatemetal binder has also been investigated.The results showed that the alginate hydrogel cross-linked with different metal ions exhibited porous network structure with different tensile strength.Among them,the tensile strength of Alg-Ni reached 27.88 MPa.Furthermore,using alginate-metal ion hydrogel as a binder,the electrochemical performance of the silicon anode was tested.The Si@Alg-Ni electrode could retain a high reversible capacity of1851.6 m Ah g^-1 with a capacity retention of 66.09%at a current density of 0.84 A g^-1after 200 cycles,which was much higher than thaf of the Si@Alg-Na electrode(377.5m Ah g^-1,18.37%).Furthermore,at a current density of 8.4 A g^-1,the discharge specific capacity of Si@Alg-Ni was 892.3 m Ah g^-1,while the discharge specific capacity of Si@Alg-Na was reduced to 22.7 m Ah g^-1,showing an excellent rate performance.Therefore,the construction of alginate-metal binders has three-dimensional network structure and promising properties,which is of great significance for improving the electrochemical performance of silicon anodes.（2）Using transition divalent metal ions as"bridges"and ferrocyanide ions,Prussian blue was in-situ synthesized in the network of alginate-metal ions to form alginate-metal ion-Prussian blue hydrogel binder.The obtained alginate-metal ion-Prussian blue hydrogel binders（Alg-Ni/Zn/Cu-PBAs）were constructed by the cross-linking reaction of alginate chain with divalent metal ions as the main body and the coordination reaction of ferrocyanide with divalent metal ions as Prussian blue nanoparticles for lithium ion transport.The results showed that the mechanical properties and thermal stability of the binder had been significantly improved.Among them,the tensile strength of Alg-Ni-PBAs reached 25.60 MPa.Furthermore,using alginate-metal ion-Prussian blue hydrogel as a binder,the electrochemical performance of the silicon anode was tested.After 200 cycles,the specific capacities of Si@Alg-Ni-PBAs,Si@Alg-Zn-PBAs,Si@Alg-Cu-PBAs,Si@Alg-Na and Si@CMC-SBR were 1157.2,1372.9,1265.1 377.5 m Ah g^-1 and 905.4 m Ah g^-1,the capacity retention were 41.08%,58.66%,57.93%,18.37%and 30.16%,respectively.