Electrolytes for Li-Ion Batteries Based on High Voltage Cathodes

The electrolyte is a critical part of today’s Li-ion batteries. The state-of-the-art Li-ion batteries, which are made of cathodes such as 4.1 V LiCoO₂ and 3.4 V LiFePO₄ and graphite anode, function well in the state-of-the-art electrolytes made of LiPF₆ in carbonate solvent mixtures such as EC and EMC with additive such as VC. The reason for this compatibility is attributed to the facts that the cathodes are within the stability range of the electrolytes and the ability of the electrolyte for forming a solid electrolyte interphase (SEI) layer on graphite, protecting the graphite anode from reacting with the electrolytes.

When developing higher energy density Li-ion batteries based on higher voltage cathodes such as 4.7 V LiNi_0.5Mn_1.5O₄ (LNMO) and 4.8 V LiCoPO₄ (LCP), the oxidative stability of the state-of-the-art electrolytes is in question. Furthermore, the stability of the high voltage cathodes themselves is also not certain. Efforts in improving the stability of LNMO and LCP through substitutions have yielded better performing cathodes in terms of improved capacity retention and coulombic efficiency.^{1, 2}

The search for electrolytes that work with the high voltage cathodes has been intensive. Molecular modeling to understand the oxidative stability of Li-ion electrolytes has been active.³ This paper will review our recent efforts on electrolyte development for improving the electrochemical performance of the high voltage cathodes in Li-ion batteries.

References

1. A. Manthiram, Phys.Chem. Lett. 2011, 2, 176-184.
2. J. L. Allen, T. R. Jow, J. Wolfenstine, J. Power Sources 2011, 196, 8656.
3. O. Borodin, W. Behl, T. R. Jow, J. Phys. Chem. C 2013, 117, 8661-8682.