The Preparation And Electrochemical Properties Of Tin-based Anode Materials For Lithium/sodium Batterries

Li-ion batteries are the most frequently used energy storage devices, while Na-ion batteries are very promising candidates for electrical energy storage, owing to the natural abundance, cost-effectiveness and environmental friendliness of sodium. Herein, we employed easily synthesized Cu Sn（OH）₆ submicron spheres as precursors for the development of new Sn-based materials for sodium batteries, such as Cu Sn O₃ microspheres、Cu Sn O₃@C microspheres、Cu₃Sn/Sn O composite microspheres and Cu₃Sn/Sn O@G materials. The electrochemical performances of these anode materials were investigated in this thesis. The differences of these electrode materials in Li-ion and Na-ion reactions have also been investigated.（1） Composite oxide materials Cu Sn O₃ as anode materials for Lithium-ion batteries and sodium-ion batteries were synthesized by calcination under air atmosphere at 350 ℃. The Cu Sn O₃ anode materials were investigated comparatively by galvanostatic charge-discharge experiments. Tin oxide anode has attracted much attention due to its high specific capacity, which is about twice that of graphite, and has been considered the best candidate for lithium-ion battery anode material. This material shows moderate capacity fading with cycling, which may result from the decreased mass of active material. Further work is needed to fully study the mechanism so as to improve the cycle life.（2） After annealed in acetylene atmosphere at 350 ℃, the Cu Sn O₃ was transformed to Cu Sn O₃@C. Cu Sn O₃@C showed better capacity and capacity retention compared with Cu Sn O₃. These materials also present better rate performance with fairly stable capacity retention at different current densities. The enhanced rate capability of the electrode material is achieved by improving the electronic conductivity using a carbon buffer. The carbon not only provides excellent conductivity for this material, but also buffers the volume expansion-related cracking.（3） After annealed in hydrogen atmosphere at 350 ℃, the hydroxide was transformed to Cu₃Sn/Sn O. The multiple phased materials still kept sphere morphology which may be more suitable for electrode fabrication. On one hand, oxygen in Sn O leads to the formation of Na₂ O which act a buffer for Sn volume expansion. As a result, a more stable cycling performance can be expected. On the other hand, Cu is formed after 1st discharge process due to the existence of Cu₃ Sn. For this reason, rate capability of the composite anode was also enhanced compared with Cu Sn O₃ counterparts.（4） An elastic Cu₃Sn/Sn O@G anode material was designed and fabricated without any polymer binders or additives. It is demonstrated that an enhanced cycle performance can be acquired because grapheme can accelerate the electron diffusion among Cu₃Sn/Sn O active particles. The two dimentional graphene layer prevents the aggregation of Cu₃Sn/Sn O submicrosphere, as well as buffers the expension of Cu₃Sn/Sn O submicrosphere which maintain a well structural integrity. As the graphene layer structure has a great influence on the transport speed of Li⁺/Na⁺ ions, the rate performances of such batteries need to be further improved.