A New Insight into the Capacity Decay Mechanism of Ni‐Rich Layered Oxide Cathode for Lithium‐Ion Batteries

Abstract

Understanding the mapping relationship between electrochemical characteristics and physicochemical properties of layered LiNi0.80Co0.15Al0.05O2 (NCA) cathodes is important to develop high energy density lithium‐ion batteries (LIBs). Combining in situ and ex situ characterization, the effect of the H2‐H3 phase transition on the capacity decay and aging mechanism of NCA materials are systematically investigated. With the increase of cut‐off voltage, the cathode electrolyte interphase (CEI) on the NCA interface shows an evolutionary path of formation‐thickening‐rupture. This phenomenon is closely related to the H2‐H3 phase transition. The volumetric stresses and strains caused by the H2‐H3 phase transition accelerate the formation and expansion of secondary particle microcracks in the electrode material, leading to the growth of interfacial CEI variations. The capacity of the electrode material can decrease even if the material does not experience the H2‐H3 phase transition due to the persistence of interfacial side reactions with calendar aging from long cycles. This work opens up a valuable perspective for the study of the mapping relationship between phase transition and electrochemical properties in Ni‐rich layered oxide cathodes and provides guidance for developing high capacity and long cycle life LIBs.

In Situ Constructing Ultrastable Mechanical Integrity of Single‐Crystalline LiNi0.9Co0.05Mn0.05O2 Cathode by Interior and Exterior Decoration Strategy

“…There are three pairs of dominant reduction‐oxidation peaks at ≈3.7, 4.0, and 4.2 V during the cycling reaction, [ 23 ] corresponding to the phase conversion from the hexagonal H1 phase to the monoclinic M phase, monoclinic M phase to hexagonal H2 phase, and hexagonal H2 phase to hexagonal H3 phase, respectively. [ 24 ] Notably, the peak intensity of the SC90@MTO‐0 cathode decreases significantly in the H2–H3 transformation, demonstrating the continuous stress accumulation and structural degradation (Figure 3b,e; Figure S6b, Supporting Information). As a comparison, such phase conversion for the SC90@MTO‐9 cathode shows a slight reduction in intensity (Figure 3c,f; Figure S6c, Supporting Information), suggesting an immensely reversible process of H2→H3 phase conversion.…”

Construction of Planar Gliding Restriction Buffer and Kinetic Self-Accelerator Stabilizing Single-Crystalline LiNi0.9Co0.05Mn0.05O2 Cathode

“…Note that SC90@LSTP-10 exhibits an outstanding discharge capacity of 192.6 mAh g –1 with a reversible capacity retention of 95.6% after 100 cycles at 0.5C (Figure S6a), while the pristine SC90@LSTP-0 cathode maintains only 147.4 mAh g –1 after 100 cycles, corresponding to 72.1% capacity retention at a capacity of 0.5 C (Figure S6b). Higher requirements of the operating voltage of Ni-rich cathodes are put forward to obtain higher energy density LIBs; however, the surface and bulk of single-crystal Ni-rich cathodes are more vulnerable to undergo irreversible structure deterioration at a high cutoff voltage. , To evaluate whether the LSTP protective coating is still effective under a high cutoff voltage, the cycle performance of SC90@LSTP-0 and SC90@LSTP-10 was examined at 2.8–4.5 V. Inspiringly, SC90@LSTP-10 still sustains a desirable specific capacity of 196.6 mAh g –1 after 100 cycles (Figure d and Figure S6c), which retains 87.3% capacity retention. In contrast, the specific capacity of SC90@LSTP-0 leads to a rapid attenuation after 100 cycles (Figure S6d), displaying a lower capacity retention of 63.2%.…”

Inverse Spinel-Structured Mg2MnO4 Coating to Enable Superior Thermal Stability of LiNi0.83Co0.12Mn0.05O2 Cathodes for Lithium-Ion Batteries

“…Ni-rich cathode materials often pulverize during the charge/discharge process due to the intergranular cracks caused by lithium-ion deintercalation. , The microstructural change and phase transition of pristine NCM and NCM-1.0% MMO particles after long-term cycling with a voltage of 2.7–4.3 V at different temperatures were observed by SEM and TEM, for investigating the influence of MMO coating deeply. Comparing cross-sectional SEM images of the cathodes (Figure a,e,i,m), due to anisotropic strain during cycling, the pristine NCM samples, both at room temperature and high temperature, shows huge microcracks that extend from the interior to the surface, and the phenomenon is worse at high temperatures.…”