Carbonate deprotonation on an Ni-rich layered cathode: development of a new cis-oligomer as an organic coverage †

Abstract

Ni-rich layered cathodes have a high practical capacity (>200 mA h g⁻¹) and tapped density (>3.6 mg cm⁻²) and have thus attracted widespread attention in significant applications such as electric vehicles and energy storage. However, the high surface reactivity of these cathodes promotes the decomposition of carbonate solvents, which contributes to the growth of the cathode–electrolyte interphase (CEI) as well as rapid fading of the battery's capacity during long-term cycling. Carbonates are favorable for the deprotonation reaction by the oxygen atom in the Ni-rich layered cathode and in the formation of the CEI. In this study, the deprotonation mechanism of cyclic and linear carbonates on a Ni-rich layered cathode was thoroughly investigated using operando Fourier-transfer infrared spectroscopy, and the reasons for cathode fading could be confirmed in terms of carbonate structures. In addition, a new maleimide oligomer was developed and coated on a Ni-rich layered cathode to inhibit the deprotonation of the carbonates. The maleimide oligomer acts as a cis isomer that provides a bridge function for reacting with oxygen on the cathode surface through its cis configuration. Moreover, this bridge function will keep the carbonates away from the cathode surface for further decomposition during cycling. On the contrary, battery performance exhibited a cycling ability at a high rate, and the new cis–maleimide oligomer helped improve rate capability. A full-cell (>3 A h) containing graphite as the anode coated with the maleimide oligomer in its cis form was fabricated.