Constructions And Li-Storage Mechanisms Of Novel Multinary Al-Si-P Based Anode Materials

Anode,as a key component of lithium-ion batteries（LIBs）,its characteristics directly affect the performance and safety of the full battery.Among them,silicon（Si）is one of the most promising new-generation anode materials due to its large capacity,low operating potential,high abundance and large production capacity.However,the poor electrical conductivity and Li-ionic conductivity as well as the huge volume expansion（>300%）during lithiation,limit the practical application of Sianodes.In the thesis,with the purpose of enhancing the electronic and Li-ionic conductivities,as well as anti-volume expansion capability of Sianode,we construct diamond-like structure AlSi_xP（x=2/3,2,6）samples and cation-disordered zinc-blende ZnAlSiP₃ compound though a simple mechanical ball milling method.By controlling Li-reactive components and structure,above series multinary silicon-based anodes can not only improve the electronic conductivity,Li-ionic conductivity and structural flexibility,but also generates electronic and Li-ionic conductors during the charge and discharge process,which is expected to improve the electrochemical performance and lithiation reaction kinetics of Si-based anode,and further to alleviate electrode volume expansion.The main research contents of this thesis are as follows:（1）Through a simple high-energy ball milling method,the highly Li-reactive elements P and metal Alare simultaneously introduced into the structure of silicon to form a ternary AlSi_xP（x=2/3,2,6）compounds.Through theoretical calculation and experimental measurements,it is demonstrated that AlSi₆P has the faster electronic and Li-ionic conductivities than Si,Al₃Si₂P₃and Al₂Si₄P₂,thus offering the best Li-storage performances of large reversible capacity,long cycling life and fast rate capability.Combined with crystallographic and spectrographic characterizations,it is concluded that AlSi₆P endogenously produces abundant Li-ionic conductors and electronic conductors during the whole cycling,such as Li-ionic conductors（Li Si₂P₃）and electronic conductors(Li₁₂Al₃Si₄and Li₁₅Si₄),which imporves the electronic conductivities and Li-ions transport kinetics of silicon-based anode.Further,AlSi₆P/C fabricated by two-step ball milling method exhibited excellent cycling stability(the reversible capacity of AlSi₆P/C was 1496 m Ah g^-1 for 100cycles at 0.5 A g^-1)and outstanding rate capability(1159 m Ah g^-1 specific capacity released at 10 A g^-1).The above strategy can be extended to construct a series of Si-based materials such as Ge Si₆P,GaSi₆P,BSi₆P and ZnSi₆S,which all provide excellent Li-storage properties.（2）Based on the research of AlSi_xP,we further construct cation-disordered ZnAlSiP₃compound by introducing Li-reactive metal Zninto the more flexible zinc-blende structure through Li-reactive components and structure controlling.EIS and GITT tests show that ZnAlSiP₃ has faster electronic and Li-ionic conductivities compared with Si.In addition,the crystallographic,spectrographic and electrochemical characterizations demonstrate that the cation-disordered ZnAlSiP₃ sample stores Li-ions by a reversible process of Li-intercalation and then conversion reactions where both electronic conductors Li₂ZnSi,Li₈Al₃Si₅ and Li₃AlP₂and Li-ionic conductors of Li₃P were produced simultaneously,thus delivering excellent Li-storage performances.Further,through a simple ball milling,the ZnAlSiP₃/C composite achieves the optimization of electrochemical performance.At a large current density of 2 A g^-1,the reversible specific capacity of ZnAlSiP₃/C is 947 m Ah g^-1 after 600cycles,showing excellent capacity retention.