Effect of Nb and F Co-doping on Li1.2Mn0.54Ni0.13Co0.13O2 Cathode Material for High-Performance Lithium-Ion Batteries

Enhanced Performance of Li-Rich Manganese Oxide Cathode Synergistically Modificated by F-Doping and Oleic Acid Treatment

Even lithium-rich manganese oxides (LRMOs) are considered as promising cathode materials for next-generation lithium-ion batteries, their commercialization is hindered mainly by the low initial Coulombic efficiency, poor cyclability and unexpected capacity fade. Here, a synergistic modification strategy by using both F doping and weak organic acid surface treatment is proposed to improve the electrochemical performances of LRMOs significantly. Optimized Li1.2 Mn0.54 Ni0.13 Co0.13 O1.95 F0.05 sample with surface oxygen vacancy defects and thin carbon coating layer exhibits profound electrochemical performances, for example, discharging capacities of 298.6 and 212.5 mAh g-1 at 0.1 C and 1 C rate, respectively. In addition, it can own an initial Coulombic efficiency of 84.4%, which is much higher than that of untreated sample. In situ X-ray diffraction analysis implies that synergistic modification can enhance the skeleton stability of LRMOs , especially at a high state of charge. Galvanostatic intermittent titration technique analysis suggests that as-developed synergistic modification can accelerate the lithium ions diffusion. Theoretical calculations reveal that substituted F and oxygen vacancy defects can diminish the diffusion energy barrier of Li+ ions. This work provides a new synergistic modification strategy to improve the comprehensive properties of LRMO cathode effectively.

Improve the Midpoint Voltage and Structural Stability of Li-Rich Manganese-Based Cathode Material by Increasing the Nickel Content

Lithium-rich manganese is a promising new-generation cathode material for lithium-ion batteries. However, it has the common problems of serious discharge capacity decline, poor rate performance, and faster midpoint voltage decay. In this experiment, a sol-gel method was used to synthesize a high-nickel, lithium-rich layered oxide (1 − x)Li1.2Mn0.54Co0.13Ni0.13O2 − xLiNiO2 (x = 0, 1.0, 2.0, 3.0 and 4.0) that was characterized by XRD, SEM, XPS, TEM, and charge-discharge performance tests. The research results show that increasing Ni content can improve the stability of the material structure and enhance the electrochemical performance of the cathode material. When the LiNiO2 is 0.3, the electrochemical performance is better, the capacity retention rate is 100.3% after 60 cycles at a current density of 0.2 C, and the capacity retention rate for 100 cycles at 0.5 C is 99.0%.

Recent Developments of Nanomaterials and Nanostructures for High-Rate Lithium Ion Batteries

Lithium ion batteries have been considered as a promising energy-storage solution, the performance of which depends on the electrochemical properties of each component, including cathode, anode, electrolyte and separator. Currently, fast charging is becoming an attractive research field due to the widespread application of batteries in electric vehicles, which are designated to replace conventional diesel automobiles in the future. In these batteries, rate capability, which is closely linked to the topology and morphology of electrode materials, is one of the determining parameters of interest. It has been revealed that nanotechnology is an exceptional tool in designing and preparing cathodes and anodes with outstanding electrochemical kinetics due to the well-known nanosizing effect. Nevertheless, the negative effects of applying nanomaterials in electrodes sometimes outweigh the benefits. To better understand the exact function of nanostructures in solid-state electrodes, herein, a comprehensive review is provided beginning with the fundamental theory of lithium ion transport in solids, which is then followed by a detailed analysis of several major factors affecting the migration of lithium ions in solid-state electrodes. The latest developments in characterisation techniques, based on either electrochemical or radiology methodologies, are covered as well. In addition, state-of-the-art research findings are provided to illustrate the effect of nanomaterials and nanostructures in promoting the rate performance of lithium ion batteries. Finally, several challenges and shortcomings of applying nanotechnology in fabricating high-rate lithium ion batteries are summarised.

Temperature-Controlled Synthesis of Li- and Mn-Rich Li1.2Mn0.54Ni0.13Co0.13O2 Hollow Nano/Sub-Microsphere Electrodes for High-Performance Lithium-Ion Battery

The calcination temperature plays a significant role in the structural, textural, and energy-storage performance of metal oxide nanomaterials in Li-ion battery application. Here, we report the formation of well-crystallized homogeneously dispersed Li1.2Mn0.54Ni0.13Co0.13O2 hollow nano/sub-microsphere architectures through a simple cost-effective coprecipitation and chemical mixing route without surface modification for improving the efficiency of energy storage devices. The synthesized Li1.2Mn0.54Ni0.13Co0.13O2 hollow nano/sub-microsphere cathode materials are calcined at 800, 900, 950, and 1000 °C. Among them, Li1.2Mn0.54Ni0.13Co0.13O2 calcined at 950 °C exhibits a high discharge capacity (277 mAh g-1 at 0.1C rate) and excellent capacity retention (88%) after 50 cycles and also delivers an excellent discharge capacity of >172 mAh g-1 at 5C rate. Good electrochemical performance of Li1.2Mn0.54Ni0.13Co0.13O2-950 is directly related to the optimized size of its primary particles (85 nm) (which constitute the spherical secondary particle, ∼720 nm) and homogeneous cation mixing. Higher calcination temperature (≥950 °C) leads to an increase of the primary particle size, poor cycling stability, and inferior rate capacity of Li1.2Mn0.54Ni0.13Co0.13O2 due to smashing of quasi-hollow spheres upon repeated lithium ion intercalations/deintercalations. Therefore, Li1.2Mn0.54Ni0.13Co0.13O2-950 is a promising electrode for the next-generation high-voltage and high-capacity Li-ion battery application.

Enhanced Electrochemical Performance of the Lithium-Manganese-Rich Cathode for Li-Ion Batteries with Na and F CoDoping

The lithium-manganese-rich layered oxide cathode (LMR-NMC), xLi₂MnO₃·(1 - x)LiMO₂ (M = Co, Ni, and Mn), is on demand because of its high specific capacity of over 250 mA h g^-1 between the voltage range 2.0-4.8 V (vs Li/Li⁺). Because of the requirement of activating the Li₂MnO₃ phase in the first cycle, oxygen extraction from the lattice structure occurs. Consequently, capacity fading and voltage fading during cycling are still major obstacles to the commercialization of LMR-NMC in battery applications. Here, codoping Na and F into LMR-NMC via facile hydroxide coprecipitation followed by solid-state reaction is introduced. Na and F are partially substituted into Li and O sites, respectively. These dopant ions enlarge the Li slab, which in turn eases Li diffusion and minimizes oxygen loss, thereby stabilizing the structure. The codoped sample exhibits both high capacity retention (97%) and high voltage retention (91%) over 100 cycles with an initial discharge capacity of 260 mA h g^-1 at 0.1 C. Compared to other reports on LMR-NMC as obtained by coprecipitation, results from this study show the best capacity retention. The developed codoping approach may provide a new strategy for designing high-performance LMR-NMC cathodes for next-generation lithium ion batteries.

Chemical, Structural, and Electronic Aspects of Formation and Degradation Behavior on Different Length Scales of Ni-Rich NCM and Li-Rich HE-NCM Cathode Materials in Li-Ion Batteries

In order to satisfy the energy demands of the electromobility market, both Ni-rich and Li-rich layered oxides of NCM type are receiving much attention as high-energy-density cathode materials for application in Li-ion batteries. However, due to different stability issues, their longevity is limited. During formation and continuous cycling, especially the electronic and crystal structure suffers from various changes, eventually leading to fatigue and mechanical degradation. In recent years, comprehensive battery research has been conducted at Karlsruhe Institute of Technology, mainly aiming at better understanding the primary degradation processes occurring in these layered transition metal oxides. The characteristic process of formation and mechanisms of fatigue are fundamentally characterized and the effect of chemical composition on cell chemistry, electrochemistry, and cycling stability is addressed on different length scales by use of state-of-the-art analytical techniques, ranging from "standard" characterization tools to combinations of advanced in situ and operando methods. Here, the results are presented and discussed within a broader scientific context.