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Small: high performance sodium phosphate cathode materials with isomorphic anion substitution

wallpapers News 2020-12-13

sodium ion battery has the advantages of abundant sodium in nature which makes it one of the best battery systems with low cost large-scale energy storage. In order to develop excellent sodium ion batteries the design preparation of high-performance cathode materials is the key which determines the main energy storage parameters such as energy density power density cycle life. Among all kinds of cathode materials sodium vanadate (molecular formula is na3v2 (PO4) 3) is the crystal structure of sodium superionic conductor (NASICON) which contains open three-dimensional Na transport channels stable crystal framework. With moderate average voltage high energy density it has become a star material in the research of sodium ion battery cathode. However as a typical polyanion material na3v2 (PO4) 3 also has poor electronic conductivity due to the separation of vo6 octahedron by PO4 tetrahedron in the structure Na also shows slow dynamic characteristics in the transport process. Therefore the common na3v2 (PO4) 3 cathode materials usually show poor rate cycling performance which is difficult to reach the practical level. In order to solve this problem the research group of Professor Wu Xinglong of Northeast Normal University developed the anion doped high-performance na3.1v2 (PO4) 2.9 (SiO4) 0.1 sodium cathode material by using high valence isomorphic anion sio44 - to replace PO43 - in na3v2 (PO4) 3 without reducing the active transition metal sites

for phosphate cathode materials previous researchers have proposed a variety of modification strategies including: (1) nano materials to reduce the ion transmission distance; (2) composite with high conductivity carbon other materials to improve the electronic conductivity of phosphate based composite cathode materials; (3) ion doping or substitution to change the internal characteristics of the materials to improve the electronic conductivity Electrochemical performance. However the cost of nano fabrication is high. A large amount of carbon composite or cation site doping will reduce the proportion of active phosphate or the number of active sites (Na site V site) in the composites respectively thus reducing the theoretical capacity. In contrast it is easier to achieve precise regulation without reducing the theoretical capacity by substituting inactive anions. A series of na3 xv2 (PO4) 3-x (SiO4) x (nvpsix x = 0 0.05 0.1 0.15) sodium cathode materials were synthesized by using high valence sio44 - with the same spatial configuration as inactive PO43 - to control the crystal structure of na3v2 (PO4) 3 materials. It is found that the high valence sio44 - is embedded in the NVP lattice which increases the active Na content the specific capacity of the material. Compared with the NVP parent material the a value in the nvpsix cell decreases the C value increases which together with the higher Na diffusion coefficient measured in the experiment proves that the poor dynamic characteristics of the NVP material are effectively improved by sio44 substitution. In addition the calculated density of States experimental results also show that the electronic conductivity of nvpsix material is improved after sio44 substitution. Therefore the comprehensive electrochemical performance of NVP based phosphate cathode materials was effectively improved. Compared with the discharge capacity of 99 MAH g − 1 49 MAH g − 1 at 0.2 C 20 C the discharge capacity of nvpsi0.1 can reach 109 MAH g − 1 82.5 MAH g − 1 at the same rate the capacity retention rate increases from 75% to 98% after 500 cycles at 1 C. Furthermore nvpsi0.1 anode carbon cloth anode were matched to assemble develop a high performance sodium ion battery. This work provides a new idea for the design modification of polyanionic cathode materials.

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