Improved electrochemical performance of LiMn2O4 surface-modified by a Mn4+-rich phase for rechargeable lithium-ion batteries

Synthesis and Surface Coating of LiMn₂O₄ Nanorods for the Cathode of the Lithium-Ion Battery

MnO₂ nanorods are prepared using a hydrothermal method, and used as precursors for the synthesis of LiMn₂O₄ nanorod-based active material for the cathode of lithium-ion batteries. The effects of additives, pressure, reactant concentration in the solution, and reaction time during the hydrothermal synthesis on the morphology of MnO₂ are examined. For the synthesis of the LiMn₂O₄ nanorods, two synthetic methods, hydrothermal processing of the MnO₂ precursor in a Li-containing solution, and the solid-state reaction of the precursor with LiOH·H₂O powder are tested. The morphological and electrochemical properties of the resulting materials are then analyzed. The rate and cycle performances of the LiMn₂O₄ nanorods are considerably improved by a composite coating of Li-ion-conductive Li₂O-2B₂O₃ and electrically conductive carbon. Because the conductive properties of these coating materials can be obtained with low crystallinity of them, superior coating performance is attainable with relatively low-temperature of after heating, which is advantageous in preserving the morphology of LiMn₂O₄ nanorods.

Facile combustion synthesis of amorphous Al2O3-coated LiMn2O4 cathode materials for high-performance Li-ion batteries

The unique Al₂O₃-coating layer can suppress the Mn dissolution and resist HF corrosion, hence stabilizing the crystal structure of spinel LiMn₂O₄ cathode materials.

Effect of Combined Conductive Polymer Binder on the Electrochemical Performance of Electrode Materials for Lithium-Ion Batteries

The electrodes of lithium-ion batteries (LIBs) are multicomponent systems and their electrochemical properties are influenced by each component, therefore the composition of electrodes should be properly balanced. At the beginning of lithium-ion battery research, most attention was paid to the nature, size, and morphology peculiarities of inorganic active components as the main components which determine the functional properties of electrode materials. Over the past decade, considerable attention has been paid to development of new binders, as the binders have shown great effect on the electrochemical performance of electrodes in LIBs. The study of new conductive binders, in particular water-based binders with enhanced electronic and ionic conductivity, has become a trend in the development of new electrode materials, especially the conversion/alloying-type anodes. This mini-review provides a summary on the progress of current research of the effects of binders on the electrochemical properties of intercalation electrodes, with particular attention to the mechanisms of binder effects. The comparative analysis of effects of three different binders (PEDOT:PSS/CMC, CMC, and PVDF) for a number of oxide-based and phosphate-based positive and negative electrodes for lithium-ion batteries was performed based on literature and our own published research data. It reveals that the combined PEDOT:PSS/CMC binder can be considered as a versatile component of lithium-ion battery electrode materials (for both positive and negative electrodes), effective in the wide range of electrode potentials.

Mn Ion Dissolution Mechanism for Lithium-Ion Battery with LiMn2O4 Cathode: In Situ Ultraviolet-Visible Spectroscopy and Ab Initio Molecular Dynamics Simulations

The dissolution of transition-metal (TM) cations into a liquid electrolyte from cathode material, such as Mn ion dissolution from LiMn₂O₄ (LMO), is detrimental to the cycling performance of Li-ion batteries (LIBs). Though much attention has been paid to this issue, the behavior of Mn dissolution has not been clearly revealed. In this work, by using a refined in situ ultraviolet-visible (UV-vis) spectroscopy technique, we monitored the concentration changes of dissolved Mn ions in liquid electrolyte from LMO at different state of charge (SOC), confirming the maximum dissolution concentration and rate at 4.3 V charged state and Mn²⁺ as the main species in the electrolyte. Through ab initio molecular dynamics (AIMD) simulations, we revealed that the Mn dissolution process is highly related to surface structure evolution, solvent decomposition, and lithium salt. These results will contribute to understanding TM dissolution mechanisms at working conditions as well as the design of stable cathodes.

Facile One-Step Dynamic Hydrothermal Synthesis of Spinel LiMn2O4/Carbon Nanotubes Composite as Cathode Material for Lithium-Ion Batteries

Nano-sized spinel LiMn2O4/carbon nanotubes (LMO/CNTs) composite is facilely synthesized via a one-step dynamic hydrothermal approach. The characterizations and electrochemical measurements reveal that LiMn2O4 particles with narrow size distribution are well dispersed with CNTs in the composite. The LMO/CNTs nanocomposite with 5 wt % CNTs displays a high specific discharge capacity of 114 mAh g-1 at 1C rate, and the retention rate after 180 cycles at room temperature reaches 94.5% in the potential window of 3.3 to 4.3 V vs. Li/Li+. Furthermore, the electrochemical performance of the composite with 5 wt % CNTs at elevated temperature (55 °C) is also impressive, 90% discharging capacity could be maintained after 100 cycles at 1C. Such excellent electrochemical performance of the final product is attributed to the content of CNTs added in the hydrothermal process and small particle size inherited from pretreated MnO2 precursor.

Improved Electrochemical Properties of LiMn2O4-Based Cathode Material Co-Modified by Mg-Doping and Octahedral Morphology

In this work, the spinel LiMn₂O₄ cathode material was prepared by high-temperature solid-phase method and further optimized by co-modification strategy based on the Mg-doping and octahedral morphology. The octahedral LiMn_1.95Mg_0.05O₄ sample belongs to the spinel cubic structure with the space group of Fd3m, and no other impurities are presented in the XRD patterns. The octahedral LiMn_1.95Mg_0.05O₄ particles show narrow size distribution with regular morphology. When used as cathode material, the obtained LiMn_1.95Mg_0.05O₄ octahedra shows excellent electrochemical properties. This material can exhibit high capacity retention of 96.8% with 100th discharge capacity of 111.6 mAh g⁻¹ at 1.0 C. Moreover, the rate performance and high-temperature cycling stability of LiMn₂O₄ are effectively improved by the co-modification strategy based on Mg-doping and octahedral morphology. These results are mostly given to the fact that the addition of magnesium ions can suppress the Jahn–Teller effect and the octahedral morphology contributes to the Mn dissolution, which can improve the structural stability of LiMn₂O₄.

Enhanced Cycling Stability through Erbium Doping of LiMn₂O₄ Cathode Material Synthesized by Sol-Gel Technique

In this work, LiMn_2−xEr_xO₄ (x ≤ 0.05) samples were obtained by sol-gel processing with erbium nitrate as the erbium source. XRD measurements showed that the Er-doping had no substantial impact on the crystalline structure of the sample. The optimal LiMn_1.97Er_0.03O₄ sample exhibited an intrinsic spinel structure and a narrow particle size distribution. The introduction of Er³⁺ ions reduced the content of Mn³⁺ ions, which seemed to efficiently suppress the Jahn–Teller distortion. Moreover, the decreased lattice parameters suggested that a more stable spinel structure was obtained, because the Er³⁺ ions in a ErO₆ octahedra have stronger bonding energy (615 kJ/mol) than that of the Mn³⁺ ions in a MnO₆ octahedra (402 kJ/mol). The present results suggest that the excellent cycling life of the optimal LiMn_1.97Er_0.03O₄ sample is because of the inhibition of the Jahn-Teller distortion and the improvement of the structural stability. When cycled at 0.5 C, the optimal LiMn_1.97Er_0.03O₄ sample exhibited a high initial capacity of 130.2 mAh g⁻¹ with an excellent retention of 95.2% after 100 cycles. More significantly, this sample showed 83.1 mAh g⁻¹ at 10 C, while the undoped sample showed a much lower capacity. Additionally, when cycled at 55 °C, a satisfactory retention of 91.4% could be achieved at 0.5 C after 100 cycles with a first reversible capacity of 130.1 mAh g⁻¹.