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Structural defects, e.g. Mn 3+ /oxygen non-stoichiometry, largely affect the electrochemical performance of both Li 2 MnO 3 and lithium-rich manganese-rich (LMR) layered oxides with Li 2 MnO 3 as one of the key components. Herein, Li 2 MnO 3 samples with different amount of structural defects of Mn 3+ /oxygen non-stoichiometry are prepared. The results clearly demonstrate that the annealed Li 2 MnO 3 (ALMO), quenched Li 2 MnO 3 (QLMO), and quenched Li 2 MnO 3 milled with Super P (MLMO) all show pure C2/m monoclinic phase with stacking faults. MLMO shows the largest amount of Mn 3+ , followed by the QLMO and then the ALMO. The increased amount of Mn 3+ in Li 2 MnO 3 (such as sample MLMO) facilitates the activation of Li 2 MnO 3 and leads to the highest initial discharge specific capacity of 167.7 mA h g −1 among the samples investigated in this work. However, accelerated activation of Li 2 MnO 3 also results in faster structural transformation to spinel-like phase, leading to rapid capacity degradation. Therefore, the amount of Mn 3+ needs to be well controlled during synthesis of LMR cathode in order to reach a reasonable compromise between the initial activity and long-term cycling stability. The findings of this work could be widely applied to explain the effects of Mn 3+ on different kinds of LMR cathodes. [ABSTRACT FROM AUTHOR]

Lithium-sulfur (Li-S) redox flow battery (RFB) is a promising candidate for high energy large-scale energy storage application due to good solubility of long-chain polysulfide species and low cost of sulfur. Here, the fundamental understanding and control of lithium polysulfide chemistry are studied to enable the development of liquid phase Li-S redox flow prototype cells. These differ significantly from conventional static Li-S batteries targeting for vehicle electrification. A high solubility of the different lithium polysulfides generated at different depths of discharge and states of charge is required for a flow battery in order to take full advantage of the multiple electron transitions. A new dimethyl sulfoxide based electrolyte is proposed for Li-S RFBs, which not only enables the high solubility of lithium polysulfide species, especially for the short-chain species, but also results in excellent cycling with a high Coulombic efficiency. The challenges and opportunities for the Li-S redox flow concept have also been discussed in depth. [ABSTRACT FROM AUTHOR]

In recent years, the Li metal anode has regained a position of paramount research interest because of the necessity for employing Li metal in next-generation battery technologies such as Li-S and Li-O2. Severely limiting this utilization, however, are the rapid capacity degradation and safety issues associated with rechargeable Li metal anodes. A fundamental understanding of the failure mechanism of Li metal at high charge rates has remained elusive due to the complicated interfacial chemistry that occurs between Li metal and liquid electrolytes. Here, it is demonstrated that at high current density the quick formation of a highly resistive solid electrolyte interphase (SEI) entangled with Li metal, which grows towards the bulk Li, dramatically increases up the cell impedance and this is the actual origin of the onset of cell degradation and failure. This is instead of dendritic or mossy Li growing outwards from the metal surface towards/through the separator and/or the consumption of the Li and electrolyte through side reactions. Interphase, in this context, refers to a substantive layer rather than a thin interfacial layer. Discerning the mechanisms and consequences for this interphase formation is crucial for resolving the stability and safety issues associated with Li metal anodes. [ABSTRACT FROM AUTHOR]

Dendrimer-encapsulated ruthenium oxide nanoparticles (DEN-RuO2) have been used as catalysts in lithium-oxygen (Li-O2) batteries for the first time. The results obtained from ultraviolet-visible spectroscopy, electron microscopy and X-ray photoelectron spectroscopy show that the nanoparticles synthesized by the dendrimer template method are ruthenium oxide, not metallic ruthenium as reported by other groups. The DEN-RuO2 significantly improves the cycling stability of Li-O2 batteries with carbon electrodes and decreases the charging potential even at ten times less catalyst loading than those reported previously. The monodispersity, porosity, and large number of surface functionalities of the dendrimer template prevent the aggregation of the RuO2 nanoparticles, making their entire surface area available for catalysis. The potential of using DEN-RuO2 as a standalone cathode material for Li-O2 batteries is also explored. [ABSTRACT FROM AUTHOR]

Rechargeable lithium (Li) metal batteries with conventional LiPF 6 -carbonate electrolytes have been reported to fail quickly at charging current densities of about 1.0 mA cm −2 and above. In this work, we demonstrate the rapid charging capability of Li||LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) cells can be enabled by a dual-salt electrolyte of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(oxalato)borate (LiBOB) in a carbonate solvent mixture. The cells using the LiTFSI-LiBOB dual-salt electrolyte significantly outperform those using the LiPF 6 electrolyte at high charging current densities. At the charging current density of 1.50 mA cm −2 , the Li||NCA cells with the dual-salt electrolyte can still deliver a discharge capacity of 131 mAh g −1 and a capacity retention of 80% after 100 cycles. The Li||NCA cells with the LiPF 6 electrolyte start to show fast capacity fading after the 30th cycle and only exhibit a low capacity of 25 mAh g −1 and a low retention of 15% after 100 cycles. The reasons for the good chargeability and cycling stability of the cells using the LiTFSI-LiBOB dual-salt electrolyte can be attributed to the good film-formation ability of the electrolyte on the Li metal anode and the highly conductive nature of the sulfur-rich interphase layer. [ABSTRACT FROM AUTHOR]