Study Of Germanium-phosphorus As Anode For Lithium/Sodium-ion Batteries

Although lithium ion batteries（LIBs） have been widely using in the mobile communications and digital products, also occupying a great market share due to its advantages of small size, light weight and high energy density, it can’t be able to satisfy the ever-increasing demand with the rapid development of emerging fields such as electric vehicles, energy storage solutions. Therefore, to develop new LIBs of lower cost, higher capacity and higher security has become a crucial task. As the key component of LIBs, the electrode materials will directly determine the performance of LIBs. Among the existing anode materials, both phosphorus and germanium possess the ability of lithium storage.But when they used individually, phosphorus could contribute high capacity but poor electrical conductivity, as well as germanium had good electrical conductivity but a large volume change during lithium storage and resulted in poor cycling performance. Here, by introducing P and Ge into the one compound, a series of germanium-phosphorus and its carbon-containing composites with double activity and high energy density have been synthesized successfully, and its composition, structure along with the change of synthesis condition, the relationship between their electrochemical properties were performed.The GeP_x（x=1, 2, 3, 4, 5, 6） powders were obtained via a facile and simple high energy ball milling process using commercial red phosphorus and germanium powder with different composition. Except GeP belonging to monoclinic structure, GeP_x（x=2, 3, 4, 5, 6）correspond to rhombohedral GeP₅, but the diffraction peaks gradually shift to the low angle direction with the increasing proportion of Ge/P. And all the GeP_x materials are the aggregates composed of nanoparticles.The electrochemical performance of GeP_x and GeP_x/C was evaluated. GeP_x exhibited high specific capacity and first coulombic efficiency, but the cycle life was short. After contained with carbon, GeP_x/C composites could effectively suppress the volume change,maintained the high specific capacity and first coulombic efficiency, and its cycleperformance had been improved significantly. Both Ge and P showed excellent lithium storage activity, and the capacity contribution of Ge increased while the capacity contribution of P decreased with the increasing proportion of Ge/P.Taking GeP₅/C as an example, its sodium storage property was studied. The results showed that GeP₅/C showed a low operating voltage, high specific capacity and stable cycle performance as a anode for sodium ion batteries. To explore the possibility of its application in lithium/sodium ion full cells, GeP₅/C was assembled into full cells with different cathode(LiF PO₄, LiCoO₂, Na₃V₂（PO₄）₃/C and Na_0.8Ni_0.4Ti_0.6O₂). LiFePO₄ and GeP₅/C lithium ion full cell showed high capacity and poor cycle performance, whereas LiCoO₂ and GeP₅/C lithium ion full cell showed high voltage platform and poor reversible capacity. Meanwhile, Na₃V₂（PO₄）₃/C and GeP₅/C sodium ion full cell delivered low first coulombic efficiency, but possessed high capacity and excellent cycle performance,Na_0.8Ni_0.4Ti_0.6O₂ and GeP₅/C sodium ion full cell have high voltage and good cycle performance, as well as poor capacity and low first coulombic efficiency.