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Sodium ion batteries are one of most promising alternatives to lithium ion batteries for large-scale energy storage, due to the high abundance and low cost of sodium in the earth. However, the lack of advanced electrode materials greatly affects their applications. Here, layeredstructure SbPO 4 is explored as an anode material for sodium ion batteries in terms of SbPO 4 nanorods on reduced graphene oxide (SbPO 4 /rGO). In situ transmission electron microscopy images reveal the preferential expansion along the transverse direction of the nanorods upon the first discharging, which arises from the reduction of SbPO 4 to Sb and the subsequent alloying of Sb as supported by in situ X-ray diffraction and selected area electron diffraction patterns. SbPO 4 /rGO exhibits a capacity retention of 99% after 100 cycles at 0.5 A g −1 both in half cells and in full cells. Its specific capacity at 5 A g −1 is 214 mA h g −1 in half cells or 134 mA h g −1 in full cells. Moreover, the energy density of the full cells at 1.2 kW kg −1 total is still 99.8 W h kg −1 total , very promising as an advanced electrode material.

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SnP 2 O 7 attached to reduced graphene oxide (rGO) is synthesized by a solvothermal reaction, followed by a mild annealing in Ar/H 2 . As an anode material for sodium-ion batteries, this composite is associated with the conversion reaction between Sn and SnP 2 O 7 and the alloy reaction between Sn and Na x Sn, as evidenced by ex situ techniques, such as high-resolution transmission electron microscope images, selected area electron diffraction patterns, and X-ray diffraction patterns. The close contact between SnP 2 O 7 and rGO facilitates the charge transfer upon cycling and benefits the preservation of SnP 2 O 7 on rGO even after pulverization. Therefore, this composite exhibits an extraordinary cycling stability. 99% of the initial capacity is remained after 200 cycles at 0.2 A g −1 and also 99% is kept after 1000 cycles at 1.0 A g −1 . The similar results are also observed in full cells. Quantitative kinetic analysis confirms that sodium storage in this composite is governed by pseudocapacitance, especially at high rates. These results indicate the promising potential of metal pyrophosphates in sodium-ion batteries.

Summary Oxide-based resistive switching devices, including ferroelectric tunnel junctions and resistance random access memory, are promising candidates for the next-generation non-volatile memory technology. In this work, we propose a ferroionic tunnel junction to realize a giant electroresistance. It functions as a ferroelectric tunnel junction at low resistance state and as a Schottky junction at high resistance state, due to interface engineering through the field-induced migration of oxygen vacancies. An extremely large electroresistance with ON/OFF ratios of 5.1×10 7 at room temperature and 2.1×10 9 at 10 K is achieved, using an ultrathin BaTiO 3-δ layer as the ferroelectric barrier and a semiconducting Nb-doped SrTiO 3 substrate as the bottom electrode. The results point toward an appealing way for the design of high-performance resistive switching devices based on ultrathin oxide heterostructures by ionic controlled interface engineering.