High‐Voltage‐Driven Surface Structuring and Electrochemical Stabilization of Ni‐Rich Layered Cathode Materials for Li Rechargeable Batteries

Abstract

Layered lithium–nickel–cobalt–manganese oxide (NCM) materials have emerged as promising alternative cathode materials owing to their high energy density and electrochemical stability. Although high reversible capacity has been achieved for Ni‐rich NCM materials when charged beyond 4.2 V versus Li+/Li, full lithium utilization is hindered by the pronounced structural degradation and electrolyte decomposition. Herein, the unexpected realization of sustained working voltage as well as improved electrochemical performance upon electrochemical cycling at a high operating voltage of 4.9 V in the Ni‐rich NCM LiNi0.895Co0.085Mn0.02O2 is presented. The improved electrochemical performance at a high working voltage at 4.9 V is attributed to the removal of the resistive Ni2+O rock‐salt surface layer, which stabilizes the voltage profile and improves retention of the energy density during electrochemical cycling. The manifestation of the layered Ni2+O rock‐salt phase along with the structural evolution related to the metal dissolution are probed using in situ X‐ray diffraction, neutron diffraction, transmission electron microscopy, and X‐ray absorption spectroscopy. The findings help unravel the structural complexities associated with high working voltages and offer insight for the design of advanced battery materials, enabling the realization of fully reversible lithium extraction in Ni‐rich NCM materials.

Cross‐Talk‐Suppressing Electrolyte Additive Enabling High Voltage Performance of Ni‐Rich Layered Oxides in Li‐Ion Batteries

“…After cycling in the standard electrolyte, significant shifts of the (003), (104), and (108)/(110) peaks to lower and higher 2θ angles [Figure 4b(ii),c(ii)], as well as the disappearance of the (106) peak, were observed [Figure S8a(ii), black], indicating severe degradation of the layered structure of NCM851005. [50][51][52] This is consistent with the weakening of redox peaks in the dQ/dV plots (Figure 2b) after long-term cycling, which also well correlates with the rapid capacity fading (Figure 2g). At the same time, cathode, cycled with AEDB in electrolyte, exhibited significantly reduced shifts for the (003) and (104) reflections [Figure 4b(iii),c(iii), blue], as well as smaller interval distance for the (108)/(110) split peaks [Figure S8b(iii)].…”

Recent advance in structure regulation of high‐capacity Ni‐rich layered oxide cathodes

“…46,55,56 In these structural changes, Sun et al exposed that the H2-H3 structure transition which happened at about 4.2 V for the content of Ni more than 80%, was regarded as the most drastic and caused vast cracks pervade the whole particles. 57,58 Especially, the destruction is significant different when Ni-based positive materials are cycled under different cut-off voltages: the upper limit of voltage is 4.1 V, the capacity retention of cathodes up to 95% and there is no obvious crack in the particle, nevertheless, the upper limit of voltage is 4.3 V, their capacity retention is only 75% and abundant cracks appear after 100 cycles. 59 To suppress cracks, Watanabe et al suggested that the positive cycling should be limited to 60% depth-of-discharge (DOD) overlooked the particular voltage range.…”

Native lattice strain induced structural earthquake in sodium layered oxide cathodes

“…To further increase the energy density, a prevailing approach is to push the charging voltage limit to simultaneously attain higher specific capacity and increase the average working voltage 4 . However, these layered cathodes undergo universal capacity drop and voltage decay during high-voltage operation 5 – 7 . Over several decades, extensive fundamental understanding and material development have been carried out to reveal the underlying failure mechanism and mitigate the structural degradation at elevated voltage.…”