Enabling High-Energy Battery Performance of 4.8 V Li-Rich Layered Oxide Cathode with a High-Voltage Additive

Li-rich layered oxide of xLi₂MnO₃.(1−x)Li(Mn,Ni,Co)O₂ is an attractive cathode material for high-energy density Li-ion batteries because of a possible attainment of high capacity as much as or higher than 250 mAhg⁻¹ on the operation above 4.6 V vs. Li/Li⁺.¹ Its performance however has been limited by high-voltage operation (> 4.3 V), due to anodic instability of conventional electrolyte and interfacial instability of the cathode. Here we report high performance of half-cell and full-cell with Li_1.2Mn_0.525Ni_0.175Co_0.1O₂ cathode and fluorinated linear carbonate (di-(2,2,2 trifluoroethyl)carbonate, DFDEC) as a novel high-voltage electrolyte additive, on the high-voltage operation to 4.8 V.² The full cell consisting of Li_1.2Mn_0.525Ni_0.175Co_0.1O₂ cathode and graphite anode in the electrolyte of 1M LiPF6/EC:EMC only experiences a rapid capacity fade when being operated at 2.5- 4.75V, resulting in just 32 % capacity retention after 60 cycles. Although the performance improves with the use of DFDEC, a notable performance improvement is achieved when using the blended additives of DFDEC and VC, which is a well-known SEI-forming agent for graphite anode,³ delivering high discharge capacities of 231 − 189 mAhg⁻¹ with the capacity retention of 82 % at the 60th cycle. The full-cell demonstrates doubled energy density (~278 Whkg⁻¹) compared to ~136 Whkg⁻¹ of a commercialized cell of graphite//LiCoO₂. Spectroscopic surface chemistry studies indicate that DFDEC plays a critical role in stabilizing the SEI and inhibiting the interfacial degradation of cathode. The details of interfacial reaction (SEI formation) mechanisms, SEI composition and stability, and their relation to high-voltage cycling performance at room and elevated temperatures would be presented in the meeting.

References

1) M. M. Thackeray, S.-H. Kang, C. S. Johnson, J. T. Vaughey, S. A. Hackney, Electrochem. Commun., 8, 1531 (2006).

2) H. Q. Pham, K.-M. Nam, E.-H. Hwang, Y.-G. Kwon, H. M. Jung, S.-W. Song, J. Electrochem. Soc., 161, A2002 (2014).

3) L. El Ouatani, R. DedryveÌre, C. Siret, P. Biensan, S. Reynaud, P. Iratçabal, D. Gonbeau, J. Electrochem. Soc., 156, A103 (2009).

Acknowledgements

This research was financially supported by the Korean Ministry of Trade, Industry & Energy (A0022–00725) and by the Ministry of Education (2012026203).