Ternary transient metal component systems of Li-Ni-Co-Mn-O (NCM; LiNi_xMn_yCo_zO₂ with x + y + z = 1) have advantages of high energy density, lower toxicity, lower cost, and high safety performances. But, NCMs suffer from poor rate capability and cycling performance under high rate charge/discharge conditions due to their low electric conductivities. Constructing well-dispersed conductive network is an important approach to overcome the inherent limits in the performance of the active materials. A variety of carbon materials such as carbon black (Super-P), carbon nanotubes, vapor-grown carbon fibers (VGCFs) have been studied as conductive agents.[1,2] Herein, the effect of different types of conductive agents on the cathode performance of lithium ion batteries is investigated in more detail. Three types of cathode materials (LiCoO₂, LiFePO₄, LiNi_0.6Co_0.2Mn_0.2O₂) which are containing different ratios of VGCFs and Super-P are used.  Pillar-like morphology of the VGCF makes them to efficiently connect to the active materials and therefore, when we use the electrodes composed of primary particles, these achieve the highest electric conductivity for LiCoO₂ (1.721 S cm⁻¹) and LiFePO₄ (1.23 S cm⁻¹). On the contrary, for LiNi_0.6Co_0.2Mn_0.2O₂, consisted of micro-sized secondary particles made up of nano-sized primary particles, a mixture of two kinds of conductive additives shows synergistically improved electric conductivity (1.403 S cm⁻¹). Well-dispersed powdery Super-P can helps electron transfer over the constituent primary particles. For all the studied cathodes, the cathode with a higher electrical conductivity shows improved result for the both cycle performance and rate capability.

References

[1] B. Jin et al., Electrochem. Comm., 2008, 10, 1537

[2] I. Cho et al., RSC Adv., 2015, 5, 95073

Acknowledgements

This work was supported by the Human Resource Training Program for Regional Innovation and Creativity through the Ministry of Education and National Research Foundation of Korea(NRF-2014H1C1A1066977)