Using fast time-resolved in situ X-ray diffraction, charge-rate dependent phase transition processes of layer structured cathode material LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC) for lithium-ion batteries are studied. During first charge, intermediate phases emerge at high rates of 10C, 30C and 60C, but not at low rates of 0.1C and 1C. These intermediate phases can be continuously observed during relaxation after the charging current was switched off. After half-way charging at high rate, sample studied by scanning transmission electron microscopy shows Li-rich and Li-poor phases coexistence with tetrahedral occupation of Li in Li-poor phase. The high rate induced over-potential is thought to be the driving force for the

A Cu2Se electrode on a copper grid substrate has been directly fabricated by a facile post-selenized method and tested as a positive material for sodium ion batteries. Cu2Se exhibits large reversible capacities (about 250 mA h g(-1)), good cyclic stabilities and low polarization. These results indicate that Cu2Se is a promising candidate as a cathode material for sodium ion batteries.

The electrochemical performance of most transition metal oxides based on the conversion mechanism is greatly restricted by inferior cycling stability, rate capability, high overpotential induced by the serious irreversible reactions, low electrical conductivity, and poor ion diffusivity. To mitigate these problems, highly porous Mn O micro/nanocuboids with in situ formed carbon matrix (denoted as Mn O @C micro/nanocuboids) are designed and synthesized via a one-pot hydrothermal method, in which glucose plays the roles of a reductive agent and a carbon source simultaneously. The carbon content, particle size, and pore structure in the composite can be facilely controlled, resulting in continuous carbon matrix with abundant pores in the cuboids. The as-fabricated Mn O @C micro/nanocuboids exhibit large reversible specific capacity (879 mAh g at the current density of 100 mA g ) as well as outstanding cycling stability (86% capacity retention after 500 cycles) and rate capability, making it a potential candidate as anode material for lithium-ion batteries. Moreover, this facile and effective synthetic strategy can be further explored as a universal approach for the synthesis of other hierarchical transition metal oxides and carbon hybrids with subtle structure engineering.

High rate capability and long cycle life are challenging goals for the development of room temperature sodium-ion batteries. Here we report a new single phase quaternary O3-type layer-structured transition metal oxide Na(NiCoFeTi)1/4O2 synthesized by a simple solid-state reaction as a new cathode material for sodium-ion batteries. It can deliver a reversible capacity of 90.6 mAh g -1 at a rate as high as 20C. At 5C, 75.0% of the initial specific capacity can be maintained after 400 cycles with a capacity-decay rate of 0.07% per cycle, demonstrating a superior long-term cyclability at high current density. X-ray diffraction and absorption characterizations revealed reversible phase transformations and electronic structural changes during the Na + deintercalation/intercalation process. Ni, Co and Fe ions contribute to the charge compensations during charge and discharge. Although Ti ions do not contribute to the charge transfer, it plays a very important role to stabilize the structure during charge and discharge by suppressing the Fe migration. In addition, Ti substitution can also smooth the charge-discharge plateaus effectively, which provides a potential advantage for the commercialization of this material for room temperature sodium-ion batteries.Please do not adjust margins Please do not adjust margins GRAPHICAL ABSTRACTA new single phase quaternary O3-type layer-structured transition metal oxide Na(NiCoFeTi) 1/4 O 2 was successfully synthesized. It can deliver a reversible capacity of 90.6 mAh g -1 at a rate as high as 20C. At 5C, 75.0% of the initial specific capacity can be maintained after 400 cycles with a capacity-decay rate of 0.07% per cycle.

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