Cycling Stability Of Cathode Materials Research Articles

Study on the impact of cutoff voltage on structural and electrochemical stability of sodium-ion layered cathodes

NaNi1/3Fe1/3Mn1/3O2 is recognized for its relatively high theoretical specific capacity and operating voltage, rendering it a sodium-ion cathode material with significant commercial potential. A higher cutoff voltage typically enables more sodium ion deintercalation, thereby achieving higher capacity. However, this increased deintercalation can introduce challenges such as structural instability and side reactions with the electrolyte, leading to electrochemical performance degradation. This study focuses on the migration process of transition metal ions under conditions of high charging cutoff voltage and high sodium removal. At a voltage of 4.3 V, the migration of Ni ions facilitates more charge compensation but is accompanied by irreversible Ni migration, inducing an irreversible phase transition to the O’ phase. Conversely, at a cutoff voltage of 4.1 V, the P3 and O3 phases with high sodium removal demonstrate excellent cycling stability. The specific capacities before and after 150 cycles (at 0.5C) are 142.3 and 113.7 mAh/g, respectively, indicating a tolerable internal structural stress within these high sodium removal phases. This contrasts with the differentiated internal structural stresses generated by the P3, O3, and O’ phases during phase transitions at a cutoff voltage of 4.3 V. The research underscores the importance of regulating reversible crystal phases within the tolerance range of internal stress and avoiding irreversible crystal phases to enhance the cycling stability of cathode materials. These findings provide crucial insights for optimizing NNFMO cathode materials and hold significant implications for the design of high-performance, long-life sodium-ion batteries.

Boosting ultrafast Li storage kinetics of conductive Nb-doped TiO2 functional layer coated on LiMn2O4

Interface engineering of LiMn2O4 (LMO) is a promising strategy to enhance the lithium storage capability and cycling stability of cathode materials in Li-ion batteries (LIBs). This is because the strategy prevents structural degradation; however, Li storage kinetics remains unsatisfactory, resulting in poor ultrafast cycling performance. Therefore, we fabricated an Nb-doped TiO2 (NTO) functional layer as a conductive passivation layer on the LMO surface by horizontal ultrasonic spray pyrolysis deposition. The NTO functional layer suppressed the volume expansion of LMO and exhibited high electrical and ionic conductivity, which resulted in improved structural stability of LMO (related to cycling stability) and increased electron/ion transfer rate (related to ultrafast cycling performance). In the TiO2 structure, Ti4+ ions were replaced by Nb5+ ions, which possess high electrical conductivity and a wide c-axis as a Li-ion diffusion route. As a result, the NTO-coated LMO cathode material showed an outstanding specific capacity of 112.7 mAh/g with a remarkable capacity retention of 96.2% after 100 cycles at a current density of 1 C and excellent ultrafast cycling capacity and stability of 70.0 mAh/g after 500 cycles at a current density of 10 C.

Boosting the Cycling Stability of Aqueous Flexible Zn Batteries via F Doping in Nickel-Cobalt Carbonate Hydroxide Cathode.

Cathodes of rechargeable Zn batteries typically face the issues of irreversible phase transformation, structure collapse, and volume expansion during repeated charge/discharge cycles, which result in an increased transfer resistance and poor long-term cycling stability. Herein, a facile F doping strategy is developed to boost the cycling stability of nickel cobalt carbonate hydroxide (NiCo-CH) cathode. Benefiting from the extremely high electronegativity, the phase and morphology stabilities as well as the electrical conductivity of NiCo-CH are remarkably enhanced by F incorporation (NiCo-CH-F). Phase interface and amorphous microdomains are also introduced, which are favorable for the electrochemical performance of cathode. Benefiting from these features, NiCo-CH-F delivers a high capacity (245 mA h g-1 ), excellent rate capability (64% retention at 8 A g-1 ), and outstanding cycling stability (maintains 90% after 10 000 cycles). Moreover, the quasi-solid-state battery also manifests superior cycling stability (maintains 90% after 7200 cycles) and desirable flexibility. This work offers a general strategy to boost the cycling stability of cathode materials for aqueous Zn batteries.

Zeolitic imidazolate framework-8 modified LiNi1/3Co1/3Mn1/3O2: A durable cathode showing excellent electrochemical performances in Li-ion batteries

Surface coating is a useful strategy to enhance the cycling stability of cathode materials. Achieving superior rate capability at the same time, however, is still a challenge. In this work, the zeolitic imidazolate framework-8 (ZIF-8), one of metal-organic framework material, is initially coated on the surface of LiNi1/3Co1/3Mn1/3O2 (NCM333). After ZIF-8 coating, the cycling stability and rate capability of NCM333@ZIF-8 are simultaneously improved in comparison with that of NCM333. A high capacity retention ratio of 81.4% is achieved after 300 cycles at 800 mA g−1, which is much larger than that of NCM333 (41.2%). Even at an elevated temperature (55 °C), the cycling stability of NCM333@ZIF-8 is still excellent. In addition, a high capacity of 122 mA h g−1 is obtained at a high current density of 1200 mA g−1. The enhanced performances are highly related with the unique properties of permanent porosity, exceptional thermal and chemical stability and the high ionic conductivity (3.16 × 10−4 S cm−1) of ZIF-8 that not only acts as a shield for NCM333 against the electrolyte corrosion, but also enables faster lithium-ion transfer at the interfacial regions. The current work offers guidance for improving the overall electrochemical performance of electrode materials in lithium-ion batteries.

Deciphering the Cathode–Electrolyte Interfacial Chemistry in Sodium Layered Cathode Materials

AbstractThe ever‐increasing demand for stationary energy storage has driven the prosperous investigation of low‐cost sodium ion batteries. The inferior long‐term cycling stability of cathode materials is a significant roadblock toward the wide commercialization of sodium ion batteries. This study enlightens a path toward empowering stable sodium ion batteries through incisive diagnostics of the multiscale surface chemical processes in layered oxide materials (e.g., O3‐NaNi1/3Fe1/3Mn1/3O2). The major challenges are unraveled in a promising sodium layered cathode material using a range of complementary advanced spectroscopic and imaging diagnostic techniques. It is discovered that the cathode–electrolyte interfacial reaction triggers transition metal reduction, heterogeneous surface reconstruction, metal dissolution, and formation of intragranular nanocracks. These surface chemistry driven processes are partly responsible for significant performance decay. This diagnostic study also rationalizes the elemental substitution and surface passivation methods that are widely applied in the field. The prepassivated and Ti‐substituted cathode materials allow for significantly improved cycling stability by inhibiting the metal dissolution. Therefore, incisively diagnosing the interfacial chemistry not only creates scientific insights into understanding sodium cathode chemistry, but also represents an advance toward establishing universal interfacial design principles for all alkali metal ion cathode materials.

The Capturing of Ionized Oxygen in Sodium Vanadium Oxide Nanorods Cathodes under Operando Conditions

The control of voltage window has been considered as a universal strategy in improving the cycling stability of cathode materials, which is supposed and explained by avoiding side reactions. To address the conjecture, the detailed structure evolution of Na0.76V6O15 nanorods is investigated with different electrochemical reaction voltage windows. High time resolution in situ X‐ray diffraction, ex situ X‐ray photoelectron spectroscopy, ex situ Raman spectroscopy, and transmission electron microscopy demonstrate the amorphization of Na0.76V6O15 nanorods and formation of ionized oxygen in nanorods, leading to the increased polarization voltage and fast capacity fading. The amorphization and diffusion of ionized oxygen in nanorods is controlled by optimizing the voltage window, resulting in the great increase of capacity retention from 26% to 80%. It is demonstrated that controlling the voltage window and corresponding ionized oxygen diffusion can mitigate the fast capacity fading to achieve long lasting lithium ion batteries.