V_(2)O_(5)/rGO复合材料的电化学性能和储锂机理

Electrochemical performance and lithium storage mechanism of V_(2)O_(5)/rGO composite

为研究V_(2)O_(5)/rGO复合材料作为锂离子电池负极的循环稳定性、导电性以及锂离子在其中的迁移机理,通过实验和第一性原理计算相结合的方式,利用水热法制备了V_(2)O_(5)/rGO复合材料。实验研究发现,V_(2)O_(5)/rGO复合材料的首次放电比容量为943.4 mA·h/g,高于V_(2)O_(5)(约为849.7 mA·h/g),经过150圈循环后其放电比容量保持率为65.2%,也高于V_(2)O_(5)(40.4%),说明V_(2)O_(5)/rGO具有更高的比容量和更优异的循环稳定性。电化学阻抗测试发现,V_(2)O_(5)/rGO高频区的半圆小于V_(2)O_(5),说明其导电性更佳。通过基于态密泛函理论的第一原理计算发现,V_(2)O_(5)/rGO在嵌锂之后,在费米能级处d轨道提供的电子数增加,而V_(2)O_(5)却略微减少,说明V_(2)O_(5)/rGO的导电性优于V_(2)O_(5);V_(2)O_(5)/rGO的迁移势垒低于V_(2)O_(5),表明锂离子在V_(2)O_(5)/rGO中更易发生迁移。

The cycling stability,conductivity and the migration mechanism of lithium ions in V_(2)O_(5)/rGO composites as negative electrodes of lithium-ion batteries were studied through experiments and first principle calculations.It is found that the first discharge specific capacity of V_(2)O_(5)/rGO composite was 943.4 mA·h/g,which was higher than that of V_(2)O_(5)(about 849.7 mA·h/g).After 150 cycles,its discharge specific capacity retention rate was 65.2%,which was also higher than that of V_(2)O_(5)(40.4%).V_(2)O_(5)/rGO had higher specific capacity and better cycle stability.Electrochemical impedance test shows that the semicircle of V_(2)O_(5)/rGO high-frequency region was smaller than V_(2)O_(5),indicating that its conductivity was better.According to the first principle calculation based on the state density functional theory,it is found that the number of electrons provided by the d orbital at the Fermi level increased after the intercalation of V_(2)O_(5)/rGO with lithium,but V_(2)O_(5) decreased slightly,indicating that the conductivity of V_(2)O_(5)/rGO was better than V_(2)O_(5);The migration barrier of V_(2)O_(5)/rGO was lower than V_(2)O_(5),indicating that lithium ions were more likely to migrate in V_(2)O_(5)/rGO.