Synthesis And Lithium Storage Property Of Transition Metal Oxides With Nanostructure

Transition metal oxides（TMOs）have become a promising anode material due to high theoretical specific capacity and abundant sources.However,volume expansion occurs in the process of lithiation and delithiation,resulting in electrode pulverization and capacity fading.In order to solve this problem,constructing hierarchical structure for TMOs is a rational and effective strategy.In this paper,TMOs with hierarchical structure were synthesized.The prepared TMOs materials combined with optimized binder possess excellent lithium storage properties.Specifically,this thesis includes the following three parts:（1）CuO microspheres with porous structure were synthesized by coprecipitation method using citric acid as chelating agent.The size of CuO porous microspheres was3-4μm.As anode material,its electrochemical properties were tested.The results showed high reversible discharge capacity(623 mAh g^-1 at the current density of 0.2 A g^-1),stable cycle performance and good rate performance.After 200 cycles at current density of 2 A g^-1,the reversible capacity remains 77.9%.Such excellent electrochemical performance is due to the micro-nano structure and porous structure characteristics of CuO microspheres.（2）Five kinds of mixed TMOs microspheres with core-shell hollow structure were synthesized by co-precipitation method.The size of as-prepared microspheres was 4-5μm.The synthesis method is simple,mild and general,which can be used for the synthesis of other materials.Taking ZnCo₂O₄ as an example,the electrochemical properties were tested,and the effects of two different binders,carboxymethyl cellulose（CMC）and polyvinylidene fluoride（PVDF）,on the battery performance were compared.The results show that electrode with CMC displays better reversible capacity of 1063 mAh g^-1after 50 cycles at 200 mA g^-1,good rate performance(486mAh g^-1 even at 10 A g^-1)and long cycle stability.（3）The micron ZnCo₂O₄ cube was synthesized by hydrothermal method.And biopolymer guar gum（GG）was used as binder to construct ZnCo₂O₄ anode electrode with high areal capacity and high volumetric capacity for the first time.Resulting from its robust mechanical properties and strong interactions with ZnCo₂O₄,the cycling stability of ZnCo₂O₄ anode has been improved with a capacity of 412 mAh g^-1 after600 cycles at 1200 mA g^-1.More importantly,ZnCo₂O₄ can act as crosslinking agent to in-situ form a robust network with GG,which is beneficial to stabilize the electrode structure.Hence,ultrahigh loading of 6.73 mg cm^-2 can be achieved and deliver a high areal capacity of 5.6 mAh cm^-2.Meanwhile,the volumetric capacity was up to 1179mAh cm^-3due to high tap density of ZnCo₂O₄ materials.