Significant Improvement on Electrochemical Performance of LiMn₂O₄ at Elevated Temperature by Atomic Layer Deposition of TiO₂ Nanocoating

Abstract

The spinel LiMn2O4 cathode is considered a promising cathode material for lithium ion batteries. Unfortunately, the poor capacity stability, especially at elevated temperature, hinders its practical utilization. In this study, the atomic layer deposition (ALD) technique is employed to deposit a TiO2 nanocoating on a LiMn2O4 electrode. To maintain electrical conductivity, this amorphous coating layer with high uniformity, conformity, and completeness is directly coated on cathode electrodes instead of LiMn2O4 particles. Among all the samples studied, the TiO2-coated sample with 15 ALD cycles exhibits the best cyclability at both room temperature of 25 °C and elevated temperature of 55 °C and has the higher specific capacity of 136.4 mAh g–1 at 0.1 C that is nearly close to the theoretical capacity of LiMn2O4. Meanwhile, this sample realizes lower polarization and less self-discharge. The improved electrochemical performance is ascribed to the high conformal and ultrathin TiO2 coating, which enhances the kinetics of Li+ diffusion and stabilizes the electrode/electrolyte interface. Also, the deconvolution of Ti 2p X-ray photoelectron spectroscopy shows a weaker peak of Ti–O–F after cycling, which indicates that the coexistence of TiO2 and TiO x F y layers can inhibit Mn dissolution and electrolyte decomposition.

A Porous Au@Rh Bimetallic Core–Shell Nanostructure as an H2O2‐Driven Oxygenerator to Alleviate Tumor Hypoxia for Simultaneous Bimodal Imaging and Enhanced Photodynamic Therapy

“…[ 8 ] So far, three major strategies have been taken, including: 1) the use of oxygen‐carrying nanomaterials, based on perfluorocarbon or hemoglobin, for direct delivery of oxygen into tumor sites, [ 9 ] 2) in situ generation of oxygen upon decomposition of chemicals (such as C 3 N 4 and CaO 2 ) carried by nanomaterials to the tumor site, [ 10 ] and 3) in situ conversion of endogenous hydrogen peroxide (H 2 O 2 ) into oxygen using catalytic nanoparticles. [ 11 ] As a result of abnormal pathophysiologic processes in tumors (e.g., overexpression of NADPH oxidase (NOX) enzymes), elevated H 2 O 2 at a typical generation rate of 5 nmol per 10 5 cells h −1 is consistently observed in the tumor microenvironment. [ 12 ] Thus, the strategy to generate oxygen out of elevated endogenous H 2 O 2 will exhibit a good tumor therapeutic efficiency.…”

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

“…All these advantages can promote large-scale applications of LiMn 2 O 4 . It must be noted, however, that the cycling stability and high temperature performance cannot meet the requirement of long endurance mileage [9,10,11,12].…”

“…In recent years, many optimization strategies (doping, coating, morphology control, etc.) have been developed to address these problems [11,15,17,18,19,20,21]. Among them, the doping strategy usually choses other heterogeneous ions (Li + , Mg 2+ , Zn 2+ , Al 3+ , Cr 3+ , Si 4+ , etc.)…”

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

“…The undesirable dissolution of manganese and molecule distortion during charge and discharge limit the application of lithium manganese oxides as a cathode material at high current densities (>500 mA g −1 ) . Substitution of manganese ions with other metal cations was investigated in order to improve the electrochemical stability and rate performance of LMO cathodes . For instance, dual‐doped LMO (LiNi 0.03 Mg 0.05 Mn 1.92 O 4 ) was synthesised by solid‐state combustion by Yu et al., in which citric acid was used as the fuel .…”

“…[310] Substitution of manganese ions with other metal cations was investigated in order to improve the electrochemical stability and rate performance of LMO cathodes. [311] For instance, dual-doped LMO (Li-Ni 0.03 Mg 0.05 Mn 1.92 O 4 ) was synthesised by solid-state combustion by Yu et al, in which citric acid was used as the fuel. [312] Compared to an undoped sample (LiMn 2 O 4 ), the dual-doped cathode has a higher specific capacity at a high current rate (91.2 mAh g À 1 versus~50 mAh g À 1 at 20 C, 1 C = 148 mA g À 1 ), which is partially due to the reduced intercalation/deintercalation energy barrier from 33.88 kJ mol À 1 for LiMn 2 O 4 to 30.60 kJ mol À 1 for LiNi 0.03 Mg 0.05 Mn 1.92 O 4 .…”