Lithium-ion batteries (LIB) are becoming increasingly important in energy storage, electric vehicles and portable electronics due to their high energy density and long cycle life. The demand for more environmentally friendly LIB chemistries and lower production costs brought cobalt free cathode materials to the forefront of battery research. LiNi0.5Mn1.5O4 (LNMO) is a potential Co-free high voltage cathode material, due to its outstanding high voltage plateau, high theoretical energy density of 650 Wh kg-1, high specific capacity of 147 mAh g-1 and low cost. [1] In combination with silicon-based electrodes and its approximately ten-fold increase in specific capacity compared to the state-of-the-art graphite analogue, the energy density of the resulting cell chemistry can be considerably improved. [2]
The objective of this work is to develop and optimize a high voltage electrolyte formulation for LNMO||SiGr pouch cells with 250 mAh capacity that is not only stable up to 5.0 V vs. Li|Li+, but further enables HF scavenging and suppression of Mn and Ni dissolution while simultaneously forming effective SEI and CEI layers on corresponding electrodes. By using fluorinated solvents, a high oxidative stability of up to 5.0 V vs. Li|Li+ and effective interphase formation were achieved. Compared to non-fluorinated solvents, galvanostatic cycling performance was increased and achievable cycle life doubled. In addition, the accumulated discharge energy was almost tripled while the roll over failure was suppressed for more than 500 cycles. Various complementary analytical techniques have been used to study the interphase of the cathode and the anode in more detail.