Kinetic Control of Long‐Range Cationic Ordering in the Synthesis of Layered Ni‐Rich Oxides

Abstract

Deciphering the sophisticated interplay between thermodynamics and kinetics of high‐temperature lithiation reaction is fundamentally significant for designing and preparing cathode materials. Here, the formation pathway of Ni‐rich layered ordered LiNi0.6Co0.2Mn0.2O2 (O‐LNCM622O) is carefully characterized using in situ synchrotron radiation diffraction. A fast nonequilibrium phase transition from the reactants to a metastable disordered Li1−x(Ni0.6Co0.2Mn0.2)1+xO2 (D‐LNCM622O, 0 < x < 0.95) takes place while lithium/oxygen is incorporated during heating before the generation of the equilibrium phase (O‐LNCM622O). The time evolution of the lattice parameters for layered nonstoichiometric D‐LNCM622O is well‐fitted to a model of first‐order disorder‐to‐order transition. The long‐range cation disordering parameter, Li/TM (TM = Ni, Co, Mn) ion exchange, decreases exponentially and finally reaches a steady‐state as a function of heating time at selected temperatures. The dominant kinetic pathways revealed here will be instrumental in achieving high‐performance cathode materials. Importantly, the O‐LNCM622O tends to form the D‐LNCM622O with Li/O loss above 850 °C. In situ XRD results exhibit that the long‐range cationic (dis)ordering in the Ni‐rich cathodes could affect the structural evolution during cycling and thus their electrochemical properties. These insights may open a new avenue for the kinetic control of the synthesis of advanced electrode materials.

A Review of Degradation Mechanisms and Recent Achievements for Ni‐Rich Cathode‐Based Li‐Ion Batteries

“…Liu and co‐workers employed in situ high‐temperature synchrotron radiation diffraction (HTSRD) to systematically investigate the nonequilibrium formation of layered NCM622 (Figure 6c). [ 37 ] The starting reactants are the TM‐hydroxide Ni 0.6 Co 0.2 Mn 0.2 (OH) 2 (NCM622OH) precursor with trigonal layered structure ( P m 1, T1 phase), and lithium source LiOH·H 2 O. The in situ HTSRD pattern shows that the characterized reflections of NCM622OH gradually disappear when the temperature increases to 300 °C.…”

Structural Origin of Suppressed Voltage Decay in Single‐Crystalline Li‐Rich Layered Li[Li0.2Ni0.2Mn0.6]O2 Cathodes

“…Generally, the layered transition metal oxides, including NCM and LMLOs, are synthesized by using a co-precipitation method followed by a high-temperature solid-state reaction. [23][24][25][26][27] The nano-sized primary particles tend to agglomerate to form micron-sized spherical secondary particles during the co-precipitation process, concomitant with the formation of voids inside the secondary particles. [28,29] The agglomerates provide a reduced diffusion length for Li-ions within their primary particles and an increased number of pores, which facilitate the transport of Li-ions and enhance the rate capability of cathode materials.…”

A multipurpose laboratory diffractometer for operando powder X-ray diffraction investigations of energy materials

“…In contrast to quartz capillaries, where molten LiOH (m.p. 735 K at 1 atm) (1 atm = 101 325 Pa) reacts with SiO 2 to yield side products such as Li 2 SiO 3 or Li 4 SiO 4 , (Bianchini et al, 2020;Wang et al, 2021), no additional peaks were observed in the PXRD measured in sapphire capillaries. Alkaline earth silicate wool was used as a plug material instead of quartz.…”

“…Thus, it is crucial to understand the interplay of thermodynamics and kinetics to engineer the materials' crystallinity and primary particle size. Two recent studies of the formation of LiNiO 2 (Bianchini et al, 2020) and LiNi 0.6 Co 0.2 Mn 0.2 O 2 (Wang et al, 2021) showed that the reaction proceeds from a layered TM hydroxide through a 3D condensed intermediate phase to the final layered structure. Additionally, there is a strong correlation between easily observed lattice parameters and crystallite size, as well as chemical processes such as Ni 2+ to Ni 3+ oxidation or site ordering inside the unit cell.…”

“…Aside from these electrochemical operando experiments, the understanding and optimization of time-and cost-intensive synthesis processes of advanced battery materials attract the focus of academic and industrial research. Non-ambient in situ diffraction is the method of choice and gives important insights on the reaction pathways and kinetics of phase transformations during synthesis (Wang et al, 2021;Bianchini et al, 2020).…”