Isotropic Microstrain Relaxation in Ni-Rich Cathodes for Long Cycling Lithium Ion Batteries

Abstract

Developing isotropic-dominated microstrain relaxation is a vital step toward the enhancement of cyclic performance and thermal stability for high-energydensity Ni-rich cathodes. Here, a microstructure engineering strategy is employed for synthesizing the elongated primary particles radially aligned Ni-rich cathodes only by regulating the precipitation rates of cations and the distributions of flow field. The asobtained cathode also exhibits an enlarged lattice distance and highly exposed (003) plane. The high aspect ratio and favorable atomic arrangement of primary particles not only enable isotropic strain relaxation for effectively suppressing microcrack formation and propagation, but also facilitate Li-ion diffusion with greatly reduced Li/Ni mixing. Consequently, it shows obvious superiority in the high-rate, long-cycle life, and thermal stability compared with the conventional counterparts. After modification, an exceptionally long life is achieved with a capacity retention of 90.1% at 1C and 84.3% at 5C after 1500 cycles within 3.0−4.3 V in a 1.5-Ah pouch cell. This work offers a universal strategy to achieve isotropic strain distribution for conveniently enhancing the durability of Ni-rich cathodes.

Revealing the Nanoscopic Corrosive Degradation Mechanism of Nickel-Rich Layered Oxide Cathodes at Low State-of-Charge Levels: Corrosion Cracking and Pitting

“…Low magnification cross-sectional SEM images of NCM811 powders aged in LiClO 4 in EC/DEC and LiPF 6 in EC/DEC were presented in Figure S2 (Supporting Information). Since isotropic lattice collapse between H2 and H3 phases during cycling is known to give rise to crack formation, cracks are frequently observed at high SOC levels in previous literature. , This reveals that the crack formation of fully lithiated NCM811 during aging in LiPF 6 in EC/DEC was due to chemical corrosion rather than a volume mismatch between H2 and H3 phases, which is distinct from the typical electrochemical degradation behavior of NCM811 during cycling. This phenomenon is similar to intergranular stress corrosion cracking in corrosion science …”

“…The increased Ni content in layered oxides enables the attainment of higher energy densities . Contrary to their advantages, Ni-rich layered oxides exhibit rapid performance deterioration during cycling and raise concerns regarding thermal stability due to structural instability at delithiated states. , Specifically, during cycling, intergranular cracks develop along the grain boundaries between primary particles at high state-of-charge (SOC) levels that exceed 4.2 V (vs. Li/Li + ). , This phenomenon is attributed to the substantial volume change resulting from a phase transition between H2 and H3 phases during the delithiation process. , The repetitive volume changes during cycling, coupled with the abrupt contraction of the c -lattice of a unit cell, lead to the propagation of microcracks and, in some cases, the complete pulverization of individual particles. , Microcracking has been recognized as one of the primary degradation mechanisms of Ni-rich layered oxides. These microcracks facilitate the swelling of the electrolyte, which, in turn, leads to significant electrolyte decomposition on the newly exposed surfaces of Ni-rich layered oxides .…”

Architecting Robust Full Concentration Gradient NCM712 Cathodes for High-Energy Li-Ion Batteries

“…According to the GITT results (Figure 4a) and the fitting straight line between the peak current (i p ) and the square root of the scan rate (v 1/2 ) from the CV curves at various scan rates from 0.2 to 1.0 mV s −1 (Figure S7), WF-GNCM712 delivers slightly better Li + diffusion kinetics than WF-NCM712 during the cycling processes. 41 Significantly, only a slight decrease of the Li + diffusion coefficient is observed for WF-GNCM712 after 100 cycles, while WF-NCM712 shows an evident decline. There is a similar trend in impedance changes for the two samples.…”

“…To fully comprehend the mechanism of WF-GNCM712’s superior structural stability, we investigate Li + diffusion kinetics and resistance values at various cycles. According to the GITT results (Figure a) and the fitting straight line between the peak current ( i p ) and the square root of the scan rate ( v 1/2 ) from the CV curves at various scan rates from 0.2 to 1.0 mV s –1 (Figure S7), WF-GNCM712 delivers slightly better Li + diffusion kinetics than WF-NCM712 during the cycling processes . Significantly, only a slight decrease of the Li + diffusion coefficient is observed for WF-GNCM712 after 100 cycles, while WF-NCM712 shows an evident decline.…”

Construction of Selective Ion Transport Polymer at Anode–Electrolyte Interface for Stable Aqueous Zinc-Ion Batteries

“…The capacity retention rate of DA-PPy@Zn∥V 2 O 5 is 5 times higher than that of Zn∥V 2 O 5 (Figure c). From the galvanostatic charge/discharge (GCD) curves (Figure S10) and medium-voltage vibration (Figure d), the average voltage of AZIBs based on the DA-PPy@Zn anode remains stable upon cycling, whereas that of bare Zn changes significantly, which indicates the serious polarization in Zn∥V 2 O 5 . − According to the EIS tests (Figure S11), the Warburg coefficient (δ ω ) of DA-PPy@Zn∥V 2 O 5 after 200 cycles is 20.8, which is much lower than that of Zn∥V 2 O 5 (40.0) (Figure e). It corresponds to faster zinc ion diffusion on the electrode surface after introducing the DA-PPy layer (eq S4).…”