The Origin of High‐Voltage Stability in Single‐Crystal Layered Ni‐Rich Cathode Materials

Abstract

Compared with the polycrystal (PC) Ni-rich cathode materials, the single-crystal (SC) counterpart displayed excellent structural stability, high reversible capacity and limited voltage decay during cycling, which received great attention from academics and industry. However, the origin of fascinating high-voltage stability within SC is poorly understood yet. Herein, we tracked the evolution of phase transitions, in which the destructive volume change and H3 phase formation presented in PC, are effectively suppressed in SC when cycling at a high cut-off voltage of 4.6 V, further clarifying the origin of high-voltage stability in SC cathode. Moreover, SC electrode displayed crack-free morphology, and excellent electrochemical stability during long-term cycling, whereas PC suffered severe capacity and voltage fade because of the spinel-like phase, decoding the failure mechanisms of PC and SC during cycling at high cut-off voltages. This finding provides universal insights into high-voltage stability and failure mechanisms of layered Ni-rich cathode materials.

Enhanced Cyclability of LiNi0.6Co0.2Mn0.2O2 Cathodes by Integrating a Spinel Interphase in the Grain Boundary

“…The pristine NCM shows severe voltage decay and capacity loss in the d Q /d V curves in which the peak intensities were obviously weakened during cycling. Moreover, during cycling, the oxidation peaks for the pristine NCM cathode visibly shifted to a high potential, which illustrated that the electrode exhibited serious polarization . However, the severe polarization and irreversible electrochemical failure were significantly inhibited in NCM@LMO-1.…”

“…Moreover, during cycling, the oxidation peaks for the pristine NCM cathode visibly shifted to a high potential, which illustrated that the electrode exhibited serious polarization. 49 However, the severe polarization and irreversible electrochemical failure were significantly inhibited in NCM@LMO-1. A GITT measurement was performed to estimate the diffusion coefficient of lithium ions for the NCM and NCM@LMO-1 samples, as shown in Figure 4c,d.…”

Quantifying the Influence of Li Plating on a Graphite Anode by Mass Spectrometry

“…Graphite (Gr) is still a major and irreplaceable commercial anode of lithium-ion batteries due to the advantages of low cost, low operating voltage (∼0.1 V vs Li/Li + ), and stable cycling. In past decades, the corresponding reaction mechanisms of solid electrolyte interface (SEI) formation and Li + intercalation–deintercalation processes have been thoroughly studied. − With the diversification of application scenarios (e.g., fast-charging) and continuous upgrading of matching cathodes (e.g., Ni-rich and/or high-voltage cathodes), the development of Gr anode faces many unprecedented new challenges. , Among them, the most prominent issue in practical applications is unwanted Li plating. Under certain conditions of fast charging, low temperatures, or overcharging, the large overpotential drives the voltage of the local Gr electrode below 0 V vs Li/Li + .…”

Titration Mass Spectroscopy (TMS): A Quantitative Analytical Technology for Rechargeable Batteries

“…For the typical layered LiTMO 2 cathode (TM: Ni/Co/Mn), extending the depth of charge (DoC%) would harvest more capacity and simultaneously trigger more irreversible loss, including TM migration, lattice oxygen loss (structural distortion), and electrolyte decomposition (interfacial degradation). 33 Currently, researchers have developed thousands of corresponding doping and coating strategies to modify the TM-O covalency and interface passivated protection layer. However, there are still pairs of core issues, which remain uncertain but essential for making assessments on these material modifications: (1) How many decomposition products have been deposited onto the surface of a cathode (cathode electrolyte interface, CEI content) at each stage of DoC%?…”

“…For the typical layered LiTMO 2 cathode (TM: Ni/Co/Mn), extending the depth of charge (DoC%) would harvest more capacity and simultaneously trigger more irreversible loss, including TM migration, lattice oxygen loss (structural distortion), and electrolyte decomposition (interfacial degradation) . Currently, researchers have developed thousands of corresponding doping and coating strategies to modify the TM-O covalency and interface passivated protection layer.…”