Synthesis of highly crystalline LiMn2O4/multiwalled carbon nanotube composite material with high performance as lithium-ion battery cathode via an improved two-step approach

Spectroscopic and Electrochemical Exploration of Carbon-Infused Intercalation-Type Spinel Composite for Aqueous Systems

Lithium-manganese-based compounds are promising intercalation host materials for aqueous battery systems due to their synergy with high ionic conductive aqueous electrolytes, safety, eco-friendliness, and low cost. Yet, due to poor electrical conductivity and trapping of diffused electrolyte cations within its crystal formation, achieving optimum cycle stability and rate capability remains a challenge. This unfortunately limits their use in modern day high-powered devices, which require quality output with high reliability. Here, the authors propose a facile method to produce LiMn₂O₄ and LiFe_0.5Mn_0.5PO₄ and compare their structural stability and corresponding electrochemical performance by controlling the interfacial layer through multi-walled carbon nanotubes’ (MWCNTs) infusion. High-resolution scanning electron microscopy results revealed that the active particles were connected by MWCNT via the formation of a three-dimensional wiring network, suggesting that stronger interfacial bonding exists within the composite. As a result, the conducting composite decreases the electron transport distance with an increased number of active sites, thus accelerating the lithium ion intercalation/de-intercalation process. Compared to C/LMO with a R_ct of 226.3 Ω and change transfer (i_o) of 2.75 × 10⁻³, the C/LFMPO-composite has a reduced R_ct of 138 Ω and enhanced rate of 1.86 × 10⁻⁴ A cm⁻². The faster kinetics can be attributed to the unique synergy between the conductive MWCNTs and the contribution of both single-phase and two-phase regions in Li_1-x(Fe,Mn)PO₄ during Li⁺ extraction and insertion. The electrochemical features before and after modification correlate well with the interplanar distance of the expanded manganese and manganese phosphate layers shown by their unique surface features, as analyzed by advanced spectroscopy techniques. The results reveal that MWCNTs facilitate faster electron transmission whilst maintaining the stability of the host framework, which makes them favorable as next generation cathode materials.

CNT-Strung LiMn2 O4 for Lithium Extraction with High Selectivity and Stability

LiMn₂ O₄ is of great potential for selectively extracting Li⁺ from brines and seawater, yet its application is hindered by its poor cycle stability and conductivity. Herein a two-step strategy to fabricate highly conductive and stable CNT-strung LiMn₂ O₄ (CNT-s-LMO) is reported, by first stringing Mn₃ O₄ particles with multiwalled carbon nanotube (CNT), then converting the hybrids into CNT-s-LMO through hydrothermal lithiation. The as-synthesized CNT-s-LMO materials have a net-like structure with CNTs threading through LMO particles. This unique structure has endowed the CNT-s-LMO electrode with excellent conductivity, high specific capacitance, and enhanced rate performance. Because of this, the CNT-s-LMO electrode in the hybrid capacitive deionization cell (HCDI) can deliver a high Li⁺ extraction percentage (≈84%) in brine and an outstanding lithium selectivity with a separation factor of ≈181 at the Mg²⁺ /Li⁺ molar ratio of 60. Significantly, the CNT-s-LMO-based HCDI cell has a high stability, evidenced by 90% capacity retention and negligible Mn loss in 100 cycles. This method has paved a new way to fabricate carbon-enabled LMO-based absorbents with tuned structure and superior capacity for electrochemical lithium extraction with high Li⁺ selectivity and exceptional cycling stability, which may help to tackle the shortage in supply of Li-ion batteries in industry in the future.

Surface Modification of Nanocrystalline LiMn2O4 Using Graphene Oxide Flakes

In this work, a facile, wet chemical synthesis was utilized to achieve a series of lithium manganese oxide (LiMn₂O₄, (LMO) with 1–5%wt. graphene oxide (GO) composites. The average crystallite sizes estimated by the Rietveld method of LMO/GO nanocomposites were in the range of 18–27 nm. The electrochemical performance was studied using CR2013 coin-type cell batteries prepared from pristine LMO material and LMO modified with 5%wt. GO. Synthesized materials were tested as positive electrodes for Li-ion batteries in the voltage range between 3.0 and 4.3 V at room temperature. The specific discharge capacity after 100 cycles for LMO and LMO/5%wt. GO were 84 and 83 mAh g⁻¹, respectively. The LMO material modified with 5%wt. of graphene oxide flakes retained more than 91% of its initial specific capacity, as compared with the 86% of pristine LMO material.

Enhancing Lithium Manganese Oxide Electrochemical Behavior by Doping and Surface Modifications

Lithium manganese oxide is regarded as a capable cathode material for lithium-ion batteries, but it suffers from relative low conductivity, manganese dissolution in electrolyte and structural distortion from cubic to tetragonal during elevated temperature tests. This review covers a comprehensive study about the main directions taken into consideration to supress the drawbacks of lithium manganese oxide: structure doping and surface modification by coating. Regarding the doping of LiMn2O4, several perspectives are studied, which include doping with single or multiple cations, only anions and combined doping with cations and anions. Surface modification approach consists in coating with different materials like carbonaceous compounds, oxides, phosphates and solid electrolyte solutions. The modified lithium manganese oxide performs better than pristine samples, showing improved cyclability, better behaviour at high discharge c-rates and elevated temperate and improves lithium ions diffusion coefficient.

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.

Preparation of the CNTs/AG/ITO electrode with high electro-catalytic activity for 2-chlorophenol degradation and the potential risks from intermediates

A novel carbon nanotubes (CNTs)/agarose (AG)/ITO electrode with high electro-catalytic activity was prepared using a simple sol-gel method. Characterization results showed that the prepared CNTs/AG membrane, coated on the ITO conductive glass, was consisted of C and O. The electro-catalytic degradation for 2-chlorophenol (2-CP) and the influence factors were investigated. The results meant that electro-catalytic degradation for 2-CP was highly dependent on pH, bias voltage, and catalyst dosage. At pH 2, 4 V bias voltage, and 5 wt% CNTs dosage, the electro-catalytic efficiency of CNTs/AG/ITO electrode for 2-CP (20 mg/L) achieved 98% within 180 min. Afterwards, the electro-catalytic properties of recycling electrode, roles of the generated reactive oxygen species, and the reaction pathways were also investigated and proposed. In addition, the toxicities of the generated intermediates from the electro-catalytic degradation were calculated by easy methods. The results indicated that the toxicities of some intermediates were higher than the parent pollutant, especially the formation of 2-CP dimer which was seldom reported in the advanced oxidation process. The findings of using AG as the carrier and conductive adhesive for catalytic material and the assessment methods for the possible increasing risks from the intermediates were reported firstly in this paper.

Artificial solid electrolyte interphase for aqueous lithium energy storage systems

Aqueous lithium energy storage systems address environmental sustainability and safety issues. However, significant capacity fading after repeated cycles of charge-discharge and during float charge limit their practical application compared to their nonaqueous counterparts. We introduce an artificial solid electrolyte interphase (SEI) to the aqueous systems and report the use of graphene films as an artificial SEI (G-SEI) that substantially enhance the overall performance of an aqueous lithium battery and a supercapacitor. The thickness (1 to 50 nm) and the surface area (1 cm2 to 1 m2) of the G-SEI are precisely controlled on the LiMn2O4-based cathode using the Langmuir trough-based techniques. The aqueous battery with a 10-nm-thick G-SEI exhibits a discharge capacity as high as 104 mA·hour g-1 after 600 cycles and a float charge current density as low as 1.03 mA g-1 after 1 day, 26% higher (74 mA·hour g-1) and 54% lower (1.88 mA g-1) than the battery without the G-SEI, respectively. We propose that the G-SEI on the cathode surface simultaneously suppress the structural distortion of the LiMn2O4 (the Jahn-Teller distortion) and the oxidation of conductive carbon through controlled diffusion of Li+ and restricted permeation of gases (O2 and CO x ), respectively. The G-SEI on both small (~1 cm2 in 1.15 mA·hour cell) and large (~9 cm2 in 7 mA·hour cell) cathodes exhibit similar property enhancement, demonstrating excellent potential for scale-up and manufacturing.

High-performance carbon-coated mesoporous LiMn2O4 cathode materials synthesized from a novel hydrated layered-spinel lithium manganate composite

High-performance carbon-coated mesoporous LiMn₂O₄ cathode materials have been synthesized from a novel hydrated layered-spinel lithium manganate composite.

MnO2 nanotubes with a water soluble binder as high performance sodium storage materials

Well dispersed MnO₂ nanotubes were synthesized via a hydrothermal method.

Aerosol construction of multi-shelled LiMn2O4 hollow microspheres as a cathode in lithium ion batteries

Novel multi-shelled LiMn₂O₄ hollow microspheres have been successfully prepared by a facile aerosol spray pyrolysis route through the controlled combustion of carbon species. These microspheres show a superior specific capacity and a good rate capacity in LIBs.

Research progress on design strategies, synthesis and performance of LiMn2O4-based cathodes

In this work, we review recent progress in structural design, designing composites with graphene/carbon nanotubes, crystalline doping, and coatings for improving the electrochemical performance of LiMn₂O₄-based cathode materials.