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Nanometer‐sized rutile shows much higher electroactivity towards Li insertion than micrometer‐sized rutile. Up to 0.8 mol of Li per mole of TiO2 can be inserted into nanometer‐sized rutile at room temperature (see figure), which is able to reversibly accommodate Li up to Li0.5TiO2 with excellent capacity retention and high rate capability on cycling, rendering it a promising anode material for high‐power lithium‐ion batteries.

In the fi eld of energy storage, lithium (Li)-ion batteries dominate the portable consumer electronic market because of their high energy density. Recently, however, the sodium (Na)-ion battery has again aroused interest for large-scale energy storage due to Na abundance. [1][2][3][4][5][6] Conventionally, the chemistry behind Li-ion and Na-ion batteries involves transition metal elements, [ 4 , 6 ] thus giving rise to problems of cost and environmental concern. Therefore, intensive efforts have been aimed at the development of new Li storage materials shifting from inorganic to organic compounds. [ 7 ] Numerous advantages exist in using organic materials as electrodes for energy storage, such as their tremendous chemical compounds, the tuning of the redox potential in a wide range, possible multi-electron reactions, the abundant resources from biomass, and ease in recycling. [7][8][9][10][11][12] A number of Li-containing organic compounds have been demonstrated to have high lithium storage capacity, good cycleability, and moderate rate capability, making them promising applications in Li-ion batteries. [ 7 , 10-12 ] However, there is no report on the use of such organic compounds in Na-ion batteries.In this contribution, a carboxylate-based organic material, disodium terephthalate (Na 2 C 8 H 4 O 4 ), is introduced as a novel anode material for low-cost room-temperature Na-ion batteries. To the best of our knowledge, this is the fi rst time that an organic compound is reported for the use as an anode material for Na-ion batteries. This material exhibits a low Na insertion voltage at 0.29 V vs. Na + /Na and a high reversible capacity of 250 mAh/g with excellent cycleability. It is found that Na storage performance can be further improved by a thin layer of Al 2 O 3 coating on the Na 2 C 8 H 4 O 4 electrode surface.Scheme 1 shows the molecular structure of Na 2 C 8 H 4 O 4 . The existence of two carbonyl groups allows for the insertion and deinsertion of two Na ions, corresponding to a theoretical capacity of 255 mAh/g. In order to confi rm the purity of the as-received Na 2 C 8 H 4 O 4 , nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) measurements were performed. Both NMR and FTIR results as shown in Figures S1 and S2 reveal the high purity of the sample. The Na 2 C 8 H 4 O 4 has an orthorhombic structure and can be indexed in space group Pbc21, according to JCPDS card No. 00-052-2146 ( Figure S3). [ 13 ] The lattice constants of Na 2 C 8 H 4 O 4 are a = 3.5480 Å, b = 10.8160 Å, and c = 18.9943 Å, and its lattice volume is V = 728.92 Å 3 . The XRD pattern of as-received Na 2 C 8 H 4 O 4 showed preferentially oriented (006) and (008) planes. Thus, refi ning the structure is diffi cult. This can be evidenced by the scanning electron microscopy (SEM) image in Figure 1 b, where the as-received sample is shown to have a fl ake-like structure with very large size near 100 μ m. To reduce the particle size and increase electronic conductivity, the sample wa...

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Layered sodium titanium oxide, Na2Ti3O7, is synthesized by a solid‐state reaction method as a potential anode for sodium‐ion batteries. Through optimization of the electrolyte and binder, the microsized Na2Ti3O7 electrode delivers a reversible capacity of 188 mA h g−1 in 1 M NaFSI/PC electrolyte at a current rate of 0.1C in a voltage range of 0.0–3.0 V, with sodium alginate as binder. The average Na storage voltage plateau is found at ca. 0.3 V vs. Na+/Na, in good agreement with a first‐principles prediction of 0.35 V. The Na storage properties in Na2Ti3O7 are investigated from thermodynamic and kinetic aspects. By reducing particle size, the nanosized Na2Ti3O7 exhibits much higher capacity, but still with unsatisfied cyclic properties. The solid‐state interphase layer on Na2Ti3O7 electrode is analyzed. A zero‐current overpotential related to thermodynamic factors is observed for both nano‐ and microsized Na2Ti3O7. The electronic structure, Na+ ion transport and conductivity are investigated by the combination of first‐principles calculation and electrochemical characterizations. On the basis of the vacancy‐hopping mechanism, a quasi‐3D energy favorable trajectory is proposed for Na2Ti3O7. The Na+ ions diffuse between the TiO6 octahedron layers with pretty low activation energy of 0.186 eV.

Replacing organic liquid electrolyte with inorganic solid electrolytes (SE) can potentially address the inherent safety problems in conventional rechargeable batteries. However, solid-state batteries (SSBs) have been plagued by the relatively low ionic conductivity of SEs and large charge-transfer resistance between electrode and SE. Here, a new design strategy is reported for improving the ionic conductivity of SE by self-forming a composite material. An optimized Na + ion conducting composite electrolyte derived from the Na 1+n Zr 2 Si n P 3−n O 12 NASICON (Na Super Ionic Conductor) structure is successfully synthesized, yielding ultrahigh ionic conductivity of 3.4 mS cm −1 at 25 °C and 14 mS cm −1 at 80 °C. On the other hand, in order to enhance the charge-transfer rate at the electrode/electrolyte interface, an interface modification strategy is demonstrated by utilization of a small amount of nonflammable and nonvolatile ionic liquid (IL) at the cathode side in SSBs. The IL acts as a wetting agent, enabling a favorable interface kinetic in SSBs. The Na 3 V 2 (PO 4 ) 3 /IL/SE/Na SSB exhibits excellent cycle performance and rate capability. A specific capacity of ≈90 mA h g −1 is maintained after 10 000 cycles without capacity decay under 10 C rate at room temperature. This provides a new perspective to design fast ion conductors and fabricate long life SSBs.

An air‐stable copper‐based P2‐Na7/9Cu2/9Fe1/9Mn2/3O2 is designed and synthesized by a simple solid‐state method and investigated as a positive electrode material for sodium‐ion batteries. The attractive long cycling stability is demonstrated by the capacity retention of 85% after 150 cycles at 1 C rate without phase transformation. The reversible Cu2+/Cu3+ redox couple in P2 phase oxides is proved for the first time.

A series of hard-soft carbon composite materials is produced from biomass and oil waste and applied as low-cost anodes for sodium-ion batteries to study the fundamentals behind the dependence of Na storage on their structural features. A good reversible capacity of 282 mAh g −1 is obtained at a current density of 30 mA g −1 with a high initial Coulombic efficiency of 80% at a carbonization temperature of only 1000 °C by adjusting the ratio of hard to soft carbon. The performance is superior to the pure hard or soft carbon anodes produced at the same temperatures. This synergy between hard and soft carbon resulting in an excellent performance is due to the blockage of some open pores in hard carbon by the soft carbon, which suppresses the solid electro lyte interface formation and increases the reversible sodium storage capacity.