Study On Preparation And Electrochemical Properties Of Sodium Ion Battery Cathode Materials With Nano-microstructure

Due to the low cost and the widespread distribution of sodium resources,sodium-ion batteries are expected to be used in the large-scale energy storage in the future.Similar to the development of next-generation lithium-ion batteries,the development of practical sodium-ion batteries is also limited by the lack of suitable cathode materials.The Na+ radius is larger than Li+,that larger ion channels are needed during the process of ion insertion and extraction,and higher requirement for the material structure stability.Therefore,the material selection for sodium-ion batteries is more demanding.In this dissertation,two kinds of high-performance sodium cathode materials with micro-nanocomposite structure were designed and synthesized,and their related physicochemical structure characteristics and electrochemical performance of sodium cathode were tested.The main research contents and innovations are as follows:(1)The microsphere precursor was synthesized using a simple carbonate coprecipitation method and then calcined at high temperature to obtain a pure phase P2 phase layered metal oxide product,Na0.67Ni0.33Mn0.67O2.The uniform microspheres have a particle size of 10-25 ?m,and the primary particles are about 200 nm nanocrystals.The electrochemical performance of P2-Nao.67Nio.33Mno.67O2 as a sodium cathode electrode material was tested,with a high specific capacity(108 mA h/g),stable cycling characteristics(capacity retention after 91 cycles of 91%),and excellent rate characteristics(up to 80 mA h/g at 15C high current).This material will be used as a choice of sodium positive electrode during the industrialization of sodium electricity.The method of shape regulation will also provide a solution strategy for the optimization of sodium cathode material in the future.(2)In order to improve the ion and electron conductivity and to exert its electrochemical performance,the novel nano-micro composite NaFePO4@nanoporous carbon matrix was designed and constructed.Among them,nano-sized NaFePO4 particles are uniformly embedded in a carbon-matrix having both a three-dimensional electronically conductive network and a mesoporous network.Electrochemical test results show that when used as a cathode material for sodium-ion batteries,nano-structured NaFePO4@ nanoporous carbon matrix exhibit a capacity of 96%of theoretical capacity and excellent high rate performance.The nano-NaFePO4@ porous carbon substrate composites exhibited good electrochemical performance,mainly due to:(i)NaFePO4 particles were nanoscale,favoring the shuttle of sodium ions in the Maricite structure;(ii)NaFePO4 possessed under low temperature calcination conditions.The lower crystallinity is also beneficial to break through the blockage of the sodium-ion transport path in the Maricite structure;(iii)The amorphous porous carbon substrate enables the composite to have a three-dimensional high-efficiency electron and ion transport network.