Boosting the high-rate performance of lithium-ion battery anodes using MnCo2O4/Co3O4 nanocomposite interfaces.

Herein, a mesoporous MnCo2O4/Co3O4 nanocomposite was fabricated using a polyvinylpyrrolidone (PVP)-assisted hydrothermal synthesis method by maintaining only the non-stoichiometric ratio of Mn and Co (2 : 6), leading to an extra phase of Co3O4 coupled with MnCo2O4. Microstructural analysis showed that the obtained sample has a uniform nanowire-like morphology composed of interconnected nanoparticles. The stoichiometric ratio (2 : 4) was maintained to synthesize pure MnCo2O4 for comparative analysis. However, the obtained structure of pure MnCo2O4 was found to be irregular and fragile. After their employment as anode-active materials, the nanocomposite electrode showed superior high rate capability (1043.8 mA h g-1 at 5C) and long-term cycling stability (773.6 mA h g-1 after 500 cycles at 0.5C) in comparison to the pure MnCo2O4 electrode (771.5 mA h g-1 at 5C and 638.9 mA h g-1 at 0.5C after 500 cycles). It was believed that the extra phase of Co3O4 may also participate in the electrochemical reactions due to its high electrochemically active nature. Benefiting from the appealing architectural features and striking synergistic effect, the integrated MnCo2O4/Co3O4 nanocomposite anode exhibits excellent electrochemical properties and high cycle stability for LIBs.

Synergistic effect between ZnCo2O4 and Co3O4 induces superior electrochemical performance as anodes for lithium-ion batteries.

The current work describes a facile synthesis of spinel-type ZnCo2O4 along with an additional phase, Co3O4, by simply maintaining a non-stoichiometric ratio of Zn and Co precursors. Pure ZnCo2O4 and Co3O4 were also synthesized using the same method to compare results. The obtained morphologies of samples show that small-sized nanoparticles are interconnected and form a porous nanosheet-like structure. When used as anode materials for Li-ion batteries, the ZnCo2O4/Co3O4 nanocomposite electrode exhibits a highly stable charge capacity of 1146.2 mA h g-1 at 0.5C after 350 cycles, which is superior to those of other two pure electrodes, which can be attributed to its optimum porosity, synergistic effect of ZnCo2O4 and Co3O4, increased active sites for Li+ ion diffusion, and higher electrical conductivity. Although the pure Co3O4 electrode displayed a much higher rate capability than the ZnCo2O4/Co3O4 nanocomposite electrode at all investigated current rates, the Co3O4 morphology apparently could not withstand long-term cycling, and the electrode became pulverized due to the repeated volume expansion/contraction, resulting in a rapid decrease in the capacity.

Boosting Cycling Stability of Polymer Sodium Battery by "Rigid-Flexible" Coupled Interfacial Stress Modulation.

The discontinuous interfacial contact of solid-state polymer metal batteries is due to the stress changes in the electrode structure during cycling, resulting in poor ion transport. Herein, a rigid-flexible coupled interface stress modulation strategy is developed to solve the above issues, which is to design a rigid cathode with enhanced solid-solution behavior to guide the uniform distribution of ions and electric field. Meanwhile, the polymer components are optimized to build an organic-inorganic blended flexible interfacial film to relieve the change of interfacial stress and ensure rapid ion transmission. The fabricated battery comprising a Co-modulated P2-type layered cathode (Na0.67Mn2/3Co1/3O2) and a high ion conductive polymer could deliver good cycling stability without distinct capacity fading (72.8 mAh g-1 over 350 cycles at 1 C), outperforming those without Co modulation or interfacial film construction. This work demonstrates a promising rigid-flexible coupled interfacial stress modulation strategy for polymer-metal batteries with excellent cycling stability.

A highly stable δ-MnO2 cathode with superior electrochemical performance for rechargeable aqueous zinc ion batteries.

Recently, aqueous zinc ion batteries (AZIBs) have attracted significant attention owing to their high safety, low cost, and abundant raw materials. However, finding an affordable and stable cathode, which can reversibly store a substantial amount of Zn2+ ions without damaging the original crystal structure, is still a major challenge for the practical application of ZIBs. It has already been demonstrated that δ-MnO2 is a promising cathode for AZIBs owing to its layered structure and superior electrochemical performance; however, the reported results are still unsatisfactory (especially cyclability). Thus, using an oil bath method, we have fabricated a δ-MnO2 cathode that exhibits a unique mixed phase morphology of mostly spherical nanoparticles and a few nanorods. It is believed that some of the nanoparticles are agglomerated to form nanorods, which may eventually help to offer numerous active sites for Zn2+ diffusion, enhancing the electrolyte osmosis and the contact area between the electrode and electrolyte. The obtained cathode delivers a high reversible capacity of ∼204 mA h g-1 for the 100th cycle and ∼75 mA h g-1 over 1000 cycles at a high current density of 3000 mA g-1 with stable long-range cycling. Ex situ results indicate the mechanism of formation of ZnMn2O4 during discharge, followed by the evolution of the layered δ-MnO2 during charge.

Effect of vanadium doping on the electrochemical performances of sodium titanate anode for sodium ion battery application.

In this study, V5+ doped sodium titanate nanorods were successfully synthesized by a sol-gel method with different optimized vanadium concentrations. Before testing as a promising anode material for sodium ion battery (SIB) application, the samples were systematically characterized. It was clearly observed that V5+ doping significantly affects the phase formation of sodium titanate samples and leads to the alteration of the major phase of Na2Ti3O7 to a single Na2Ti6O13 phase with increasing doping concentrations. Electrochemical investigations clearly showed that the optimized 15 wt% V5+ doped sample exhibits the highest capacity of 136 mA h g-1 at 100 mA g-1 after 900 cycles as well as better rate capability than the undoped sample by delivering 101 mA h g-1 capacity at a high current density of 1000 mA g-1. It is believed that the incorporation of highly charged V5+ in sodium titanate produces oxygen vacancies along with partial reduction of Ti4+ to Ti3+, resulting in improved electronic conductivity. The utilization of oxygen vacancies also preserves the integrity of the electrode, giving rise to long term cycling. Thereby, V5+ doping was found to be an effective strategy to enhance the electrochemical performance of the sodium titanate anode for SIBs.

Carbon Coated CoO Electrode Synthesized by Urea-Assisted Auto Combustion for Rechargeable Lithium Battery.

A simple and low cost urea-assisted auto-combustion route was investigated for the synthesis of carbon coated CoO nanocomposite. CHN analysis determined the carbon content in CoO/C nanocomposite to be very low as 0.27 wt%. The results show that the CoO/C nanocomposite electrode displays marked lower charge transfer resistance, high lithium storage capacity, and much better rate capability than original CoO nanoparticles electrode.