Study On The Design And Interface Modification Of Advanced Anode For Na/Li-Ion Batteries

Designing and preparing new energy storage materials and studying their electrochemical performance are the key research contents in the development of energy storage devices.Over the past few decades,lithium-ion batteries have become mainstream secondary energy storage batteries due to their high energy density and long-term cycle stability.The energy density of a battery is mainly determined by the performance of the cathode and anode electrode materials.At present,graphite is a widely used negative electrode material,but it has low energy density and safety issues.Sodium-ion batteries are expected to become a substitute for lithium-ion batteries due to their abundant raw material sources,low cost,and high-rate performance,especially in the field of large-scale energy storage.The development of high-performance sodium ion battery electrode materials has become the focus of new research in energy storage materials.The conversion type sodium/lithium ion battery anode material based on the electrochemical mechanism of conversion energy storage has the outstanding advantage of high specific capacity,but has the disadvantages of large volume changes and poor electrical conductivity.This thesis focuses on the main components of the conversion type sodium storage/lithium anode(active material and binder)as the center,designing the micro-nano structure of the active material and the interface structure of the electrode surface,solving the volume expansion and electronic conductivity problems of the materials,and revealing the electrochemical energy storage mechanism for the materials.The main research works are as follows:First,Co-based metal organic frameworks were prepared through a facile method.After successive carbonization and oxidation treatment,the Co₃O₄/Co/carbon nanocages(COCCNCs)with hollow dodecahedral shapes were obtained.Co₃O₄/Co/carbon nanocages with a high surface area(183.9 m²·g^-1)and uniform pore distribution were employed as an anode material for lithium ion batteties and exhibited a high reversible specific capacity(850 m Ah·g^-1at 100 m A·g^-1),improved Coulombic efficiency,superior rate capability(485 m Ah·g^-1at a high current density of 5000 m A·g^-1)and excellent cycling stability(505 m Ah·g^-1can be remained after 600 cycles at 2000 m A·g^-1).Such a superior lithium storage performance is largely ascribed to the unique architecture composed of well-dispersed Co₃O₄(ca.9 nm)and Co(ca.5 nm)nanocrystals embedded in hollow carbon nanocages with graphitic structure.This architecture not only avoids particle aggregation and nanostructure cracking upon cycling,but also provides continuous and flexile conductive carbon frameworks to facilitate the fast ions and electrons transportation.Second,Hierarchical Fe₃O₄hollow nanostructures are synthesized from the phase transition of Fe₂O₃hollow nanostructures,which are prepared through a dissolution-recrystallization process.The hierarchical Fe₃O₄hollow nanostructures,applied as an anode material for Na-ion batteries,display good rate capability and cycling stability.The reversible capacity of 150 m Ah·g^-1at 100 m A·g^-1after 50 cycles can be maintained for Fe₃O₄anode.The superior Na-ion storage properties of hierarchical Fe₃O₄could be largely ascribed to the stable electrode structure during Na-ion insertion and extraction process.On the contrary,Fe₂O₃anode exhibits a high initial discharge capacity(686 m Ah·g^-1),but it suffers from poor cycling stability due to the remarkable pulverization of the electrode.Third,with the aim of enhancing the electrochemical kinetics and capacity of the TiO₂electrode for Na ion batteries,we have designed a hybrid material of carbon-coated TiO₂mesocrystals anchored on reduced graphene oxide(TiO₂@C-r GO).Such hybrid nanostructures are fabricated through a facile one-step route including in situ growth of oriented selfassembly of TiO₂mesocrystals on GO.TiO₂@C-r GO possesses a very large surface area(279 m²·g^-1),mesoporous nature,and single-crystal-like structure.It is also found that the capacity of TiO₂electrode for NIBs could be improved by carbon coating at a low current rate,but pure TiO₂shows better rate performance than that of TiO₂@C.Remarkably,the enhanced electrochemical kinetics and large capacity can be simultaneously achieved by designing hybrid material.The hybrid nanostructures exhibit a highly reversible capacity of 300 m Ah·g^-1at 100 m A·g^-1,superior rate capability,and long-term cycling stability(a stable capacity of 159 m Ah·g^-1can be retained after 1000cycles at 1 A·g^-1).The superior Na ion storage of TiO₂@C-r GO is largely ascribed to the robust architecture of well-dispersed carbon-coated mesoporous TiO₂mesocrystals anchored on conductive graphene network,leading to enhanced electrochemical kinetics and offering enough active sites for the Na ion to locate.Fourth,Electrode pulverization,low electrochemical reaction kinetics and an unstable SEI layer have prevented the application of transition metal oxides with a conversion-type mechanism.Here,we describe gum Arabic(GA)as a green and multi-functional binder for the fabrication of a Ni Fe₂O₄nanotube(NFNT)electrode enabling predominant application in LIBs and NIBs.Firstly,it's revealed that the NFNTs-GA electrode possesses better mechanical properties of a higher friction coefficient,better elastic resilience and higher reduced modulus and hardness compared with a NFNTs-PVDF electrode.Secondly,the NFNTs-GA electrode can restrain the side reactions between the electrode and electrolyte,leading to the formation of a remarkably stable and thin SEI layer during discharge and charge processes.Thirdly,it is demonstrated by KPFM that the NFNTs-GA electrode possesses improved surface electrical properties and lower energy for the escape of electrons.Consequently,the NFNTs-GA electrode demonstrates much improved rate capability,cycling stability and columbic efficiency when used as an anode material for LIBs.It displays a stable capacity of 770 m A h·g^-1which can be retained after 500 cycles at 0.5 A·g^-1.More importantly,the NFNTs-GA electrode exhibits a high initial coulombic efficiency of 73%(only 48%for the NFNTs-PVDF electrode)and enhanced electrochemical reaction kinetics with significantly improved oxidation and reduction peaks in the application of NIBs.Fifth,Development of anode materials with high performance is crucial for the successful application of Na-ion batteries.In this study,we provide a novel type of conversion-type anode materials,transition metal borates,as promising candidates for Na-ion storage.The transition metal borates(Fe₃BO₅and Ni₃(BO₃)₂)are successfully fabricated by a facile sol-gel route.When they are firstly evaluated for Na-ion storage,they deliver remarkably better Na-ion insertion kinetics and high reversible capacity than transition metal oxides.It's notable that the conversion reaction can be thoroughly realized for transition metal borates during sodiation/desodiation process accompanying with the change of B-O coordination.First-principles calculation indicates that Na insertion into transition metal borate are energetically much more favorable compared with transition metal oxides.Furthermore,carbon coated borates are designed and firstly prepared,which exhibit good rate capability and excellent cycling stability.Moreover,the Fe₃BO₅/Na₂V₃(PO₄)₂F₃full cell exhibits a high energy density of 180.3 Wh·kg^-1at a high power density of 150.1 W·kg^-1.This study demonstrates a class of new promising conversion-type anodes and also verifies the practical application in Na-ion batteries with high energy/power density.