Enhanced Electrochemical Performance of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ Cathode with an Ionic Conductive LiVO₃ Coating Layer

With the aim to enhance the Li⁺ ion conductivity, an ionic conductor, LiVO₃, has been successfully coated on the surface of lithium-rich layered Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode materials for the first time. After combining with LiVO₃, significantly improved high-rate capability and cyclic stability of the Li-rich cathode have been achieved due to the enhanced lithium ion diffusion and stabilized electrode/electrolyte interface. Moreover, a stable three-dimensional spinel phase has been generated in the surface region during the coating process, which mitigates the structure deterioration and suppresses the voltage decay and energy density degradation. After optimization, 5 wt % LiVO₃-coated–Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ exhibits superior electrochemical performance with a higher reversible capacity of 272 mA h g^–1, increased initial Coulombic efficiency of 92.6%, and an excellent high-rate capability of 135 mA h g^–1 at 5 C, respectively. The coexistence of an ionic conductor coating layer and the locally transformed spinel structure generated in a one-step approach provides a novel design concept for surface modification on Li-rich Mn-based cathode materials toward high-performance lithium-ion batteries

In Situ Thermal Polymerization of a Succinonitrile-Based Gel Polymer Electrolyte for Lithium-Oxygen Batteries

For lithium-oxygen batteries (LOBs), the leakage and volatilization of a liquid electrolyte and its poor electrochemical performance are the main reasons for the slow industrial advancement. Searching for more stable electrolyte substrates and reducing the use of liquid solvents are crucial to the development of LOBs. In this work, a well-designed succinonitrile-based (SN) gel polymer electrolyte (GPE-SLFE) is prepared by in situ thermal cross-linking of an ethoxylate trimethylolpropane triacrylate (ETPTA) monomer. The continuous Li+ transfer channel, formed by the synergistic effect of an SN-based plastic crystal electrolyte and an ETPTA polymer network, endows the GPE-SLFE with a high room-temperature ionic conductivity (1.61 mS cm–1 at 25 °C), a high lithium-ion transference number (tLi+ = 0.489), and excellent long-term stability of the Li/GPE-SLFE/Li symmetric cell at a current density of 0.1 mA cm–2 for over 220 h. Furthermore, cells with the GPE-SLFE exhibit a high discharge specific capacity of 4629.7 mAh g–1 and achieve 40 cycles

Enhancing Electrochemical Performance of LiMn₂O₄ Cathode Material at Elevated Temperature by Uniform Nanosized TiO₂ Coating

The severe capacity fading of LiMn₂O₄ at elevated temperature hinders its wide application in lithium ion batteries despite several advantages over present cathode materials in terms of cost, rate capability, and environmental benignity. In this study, porous nanosized TiO₂-coated LiMn₂O₄ is prepared via a modified sol–gel process of controlling hydrolysis and condensation of titanium tetrabutoxide in ethanol/ammonia mixtures, and the phenomenon of homogeneous nucleation has been almost entirely avoided. The X-ray diffraction patterns and transmission electron microscopy images show that a porous nanosized TiO₂ layer is uniformly coated on the surface of spinel LiMn₂O₄. Electrochemical tests reveal that the optimal coating content is 3 wt % which shows remarkably improved capacity retentions at both room temperature of 25 °C and elevated temperature of 55 °C. Even after long-term charge and discharge cycles, the TiO₂ layer is still robust enough to prevent LiMn₂O₄ particles from the attack of electrolyte. The inductively coupled plasma-atomic emission spectrometry, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy results indicate that the obvious improvement of TiO₂-coated LiMn₂O₄ electrodes is attributed to the suppression of Mn dissolution, as well as the enhancement of kinetics of Li⁺ diffusion

Three-Dimensional Porous Si and SiO₂ with In Situ Decorated Carbon Nanotubes As Anode Materials for Li-ion Batteries

A high-capacity Si anode is always accompanied by very large volume expansion and structural collapse during the lithium-ion insertion/extraction process. To stabilize the structure of the Si anode, magnesium vapor thermal reduction has been used to synthesize porous Si and SiO₂ (pSS) particles, followed by in situ growth of carbon nanotubes (CNTs) in pSS pores through a chemical vapor deposition (CVD) process. Field-emission scanning electron microscopy and high-resolution transmission electron microscopy have shown that the final product (pSS/CNTs) possesses adequate void space intertwined by uniformly distributed CNTs and inactive silica in particle form. pSS/CNTs with such an elaborate structural design deliver improved electrochemical performance, with better coulombic efficiency (70% at the first cycle), cycling capability (1200 mAh g^–1 at 0.5 A g^–1 after 200 cycles), and rate capability (1984, 1654, 1385, 1072, and 800 mAh g^–1 at current densities of 0.1, 0.2, 0.5, 1, and 2 A g^–1, respectively), compared to pSS and porous Si/CNTs. These merits of pSS/CNTs are attributed to the capability of void space to absorb the volume changes and that of the silica to confine the excessive lithiation expansion of the Si anode. In addition, CNTs have interwound the particles, leading to significant enhancement of electronic conductivity before and after Si-anode pulverization. This simple and scalable strategy makes it easy to expand the application to manufacturing other alloy anode materials

Sulfur Encapsulated in Mo₄O₁₁-Anchored Ultralight Graphene for High-Energy Lithium Sulfur Batteries

Mo₄O₁₁ nanoparticles were decorated onto ultralight graphene sheets (HRG) to form a Mo₄O₁₁/HRG precursor. Sulfur was then homogeneously dispersed onto the surface of Mo₄O₁₁/HRG by self-assembly from a sulfur/carbon disulfide solution to obtain a Mo₄O₁₁–HRG/S composite, which was used as the cathode material for a lithium sulfur battery. The morphologies and microstructures of the as-synthesized composites were characterized by electron microscopy and X-ray diffraction/photoelectron spectroscopy. Mo₄O₁₁ nanoparticles not only have a strong ability to adsorb to lithium polysulfides but also lead to a high Coulombic efficiency (96%). Furthermore, the incorporation of Mo₄O₁₁ on graphene improves the utilization of sulfur and enhances the cycling stability and rate capability of a Li–S battery

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

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_<i>x</i>F_<i>y</i> layers can inhibit Mn dissolution and electrolyte decomposition