Constructing a Thin Disordered Self‐Protective Layer on the LiNiO₂ Primary Particles Against Oxygen Release

Abstract

One of the major challenges facing the application of layered LiNiO 2 (LNO) cathode materials is the oxygen release upon electrochemical cycling. Here it is shown that tailoring the provided lithium content during synthesis process can create a disordered layered Li 1-x Ni 1+x O 2 phase at the primary particle surface. The disordered surface, which serves as a self-protective layer to alleviate the oxygen loss, possesses the same layered rhombohedral structure (R3m) as the inner core of primary particles of the Li 1-x Ni 1+x O 2 (x ≈ 0). With advanced synchrotron-based x-ray 3D imaging and spectroscopic techniques, a macroporous architecture within the agglomerates of LNO with ordered surface (LNO-OS) is revealed after only 40 cycles, concomitant with the reduction of nickel on the primary particle surface throughout the whole secondary particles. Such chemomechanical degradation accelerates the deterioration of LNO-OS cathodes. Comparably, there are only slight changes in the nickel valence state and interior architecture of LNO with a thin disordered surface layer (LNO-DS) after cycling, mainly arising from an improved robustness of the oxygen framework on the surface. More importantly, the disordered surface can suppress the detrimental H2 ⇋ H3 phase transition upon cycling compared to the ordered one.

Cobalt‐Free LiNiO2 with a Selenium Coating as a High‐Energy Layered Cathode Material for Lithium‐Ion Batteries

“…Both samples exhibited typical α ‐NaFeO 2 layered structures in the R‐3 m space group, indicating the successful synthesis of LNO. [ 14,39 ] Additionally, three low‐intensity peaks of Se (PDF#38‐0768) were observed in the 2 θ range of 20°–50° in the XRD pattern of Se–LNO, indicating the successful coating of Se onto the surface of LNO. Concurrently, two pairs of split peaks, (006)/(102) and (108)/(110), clearly appeared, indicating that layered structures of the two materials were successfully formed.…”

“…[11][12][13] Among these cathode materials, Co-free layered lithium nickel oxide (LiNiO 2 ) is undoubtedly the most distinctive, with a maximum theoretical specific capacity of 270 mAh g À1 at a higher-voltage plateau (3.8 V vs Li/Li þ ). [14][15][16][17][18][19][20] However, LiNiO 2 cathodes suffer from deterioration of the material surface and physical structure during cycling due to several reasons. During the synthesis of LiNiO 2 , a large amount of Ni 2þ cannot be oxidized to Ni 3þ .…”

Durable and Adjustable Interfacial Engineering of Polymeric Electrolytes for Both Stable Ni‐Rich Cathodes and High‐Energy Metal Anodes

“…Figure 4j presents that both samples with and without the SIP show a representative signal for the spin states of the polyether. [61] At the high temperature, the peak intensity in the TiP case decreases continuously, showing the poor interfacial stability. By contrast, the characteristic peaks in SIP-NCM cathode show a slight attenuation and further remain almost unchanged for several minutes, demonstrating the high-voltage and high-temperature tolerance of the SIP-derived coating.…”

“…The inhomogeneous CEI and severe phase transformation could cause aggressive high-valence Ni to be exposed on the surface of NCM cathodes, resulting to the continuous electrolyte decomposition. [60] Therefore, electron paramagnetic spectrometer (EPR) measurements were conducted to survey the stability of polyether electrolytes on NCM cathodes at a high delithiation state of 4.2 V. [61,62] The decomposition products could consume the labeling reagent, resulting to the weakening of the signal intensity in the EPR spectra. The high temperature of 60 °C was held for 5 min to accelerate the reaction.…”

Accumulated Lattice Strain as an Intrinsic Trigger for the First-Cycle Voltage Decay in Li-Rich 3d Layered Oxides

“…It is well known that the grain size and the microstrain of crystals can be indirectly determined from the analysis of the X-ray Bragg peak broadening. , As the synchrotron radiation technology has developed by leaps and bounds, acquiring hundreds of high-resolution synchrotron-based X-ray radiation diffraction (SXRD) patterns within a short time period becomes a reality. ,− In situ or operando high-resolution SXRD is becoming a powerful method for monitoring the changes of the lattice parameter and microstructure in the electrode materials during electrochemical cycling. − In this study, a hydroxide coprecipitation route coupled with an annealing process was used to synthesize Li­[Li 0.2 Ni 0.2 Mn 0.6 ]­O 2 (LLNMO). The relationship between the microstrain and its roles in the first-cycle voltage fade of LLNMO was investigated by the operando high-resolution SXRD technique.…”