Uniform MnS hollow microspheres in situ crystallized on reduced graphene oxide (RGO) nanosheets via a facile hydrothermal method. The MnS/RGO composite material was used as the anode for Na-ion batteries for the first time and exhibited excellent cycling performance, superior specific capacity, and great cycle stability and rate capability for both Li- and Na-ion batteries. Compared with nonencapsulated pure MnS hollow microspheres, these MnS/RGO nanocomposites demonstrated excellent charge-discharge stability and long cycle life. Li-ion storage testing revealed that these MnS/RGO nanocomposites deliver high discharge-charge capacities of 640 mAh g(-1) at 1.0 A g(-1) after 400 cycles and 830 mAh g(-1) at 0.5 A g(-1) after 100 cycles. The MnS/RGO nanocomposites even retained a specific capacity of 308 mAh g(-1) at a current density of 0.1 A g(-1) after 125 cycles as the anode for Na-ion batteries. The outstanding electrochemical performance of the MnS/RGO composite attributed to the RGO nanosheets greatly improved the electronic conductivity and efficiently mitigated the stupendous volume expansion during the progress of charge and discharge.

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Sodium-ion batteries have received great attention because of the abundant sodium resources and low cost. As a typical kind of cathode materials for Na-ion batteries, sodium manganese oxides have shown great potential in cathode application due to their high specific capacity and good rate capability. Herein, we successfully synthesized P2-type Na 0.4 Mn 0.54 Co 0.46 O 2 nanosheets via a two-step annealing route.The morphology and structure information of Na 0.4 Mn 0.54 Co 0.46 O 2 products were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM) technologies. The electrochemical performances of Na 0.4 Mn 0.54 Co 0.46 O 2 were measured by charge-discharge test, cyclic voltammogram (CV) and electrochemical impedance spectrum (EIS). As the cathode for Na-ion batteries, the layered Na 0.4 Mn 0.54 Co 0.46 O 2 nanosheets showed a high second charge capacity of 194 mAh/g and delivered a specific capacity of 125 mAh/g at a current of 20 mA/g after 60 cycles. 100 cycles at a rate of 2C) 30 . The available reversible capacity of P2-Na x [Fe 1/2 Mn 1/2 ]O 2 reaches 190 mAh/g with an average voltage of 2.75 V versus sodium metal 31 . The energy density is estimated to be 520 mWh/g, which is comparable to that of LiFePO 4 (about 530 mWh/g versus Li) and slightly higher than that of LiMn 2 O 4 (about 450mWh/g) 17,31 . The above research progress is proved that layered P2-type Co-doped sodium manganese oxides are promising cathode materials for Na-ion batteries. It is well know that reducing the manganese content and raising the average valence of manganese in the layered manganese-based cathode materials are effective ways to alleviate the manganese dissolution and Jahn-Teller effect. As we known, high sodium contents normally result in O3-type oxide cathodes, while low contents for P2-type ones with a higher capacity than O3-type 26,32,33 . Herein we have designed a layered Na 0.4 Mn 0.54 Co 0.46 O 2 cathode material with low sodium content for superior Na-ion batteries. The P2-Na 0.4 Mn 0.54 Co 0.46 O 2 have a good specific capacity and cycling performance at a current of 20 mA/g, and a specific capacity of 120 mAh/g is still achieved after 67 cycles. Experiment SectionMaterials synthesis： ： ： ：MnCO 3 was synthesized by a precipitation method. In a typical synthesis, 10 mmol Mn(NO 3 ) 2 was dissolved in 200 mL distilled water, then 200 mL of 0.5 mol/L NH 4 HCO 3 was added into the Mn(NO 3 ) 2 solution. Spherical Mn 2 O 3 was synthesized by annealing microsphere MnCO 3 at 400 °C for 10 h in air condition. The P2-Na 0.4 Mn 0.54 Co 0.46 O 2 cathode was synthesized by mixing 5 mmol Mn 2 O 3 , 5 mmol uniformity of spherical morphology. The pure phase of Mn 2 O 3 precursor can be clearly proved by the corresponding XRD patterns (Figure S1 in Supplementary information). The morphology and size of P2-Na 0.4 Mn 0.54 Co 0.46 O 2 particles can be also clearly observed from SEM images (Figure 3c,d), revealing that during the following high-tem...

Iron fluoride cathodes have been attracting considerable interest due to their high electromotive force value of 2.7 V and their high theoretical capacity of 237 mA h g(-1) (1 e(-) transfer). In this study, uniform iron fluoride hollow porous microspheres have been synthesized for the first time by using a facile and scalable solution-phase route. These uniform porous and hollow microspheres show a high specific capacity of 210 mA h g(-1) at 0.1 C, and excellent rate capability (100 mA h g(-1) at 1 C) between 1.7 and 4.5 V versus Li/Li(+) . When in the range of 1.3 to 4.5 V, stable capacity was achieved at 350 mA h g(-1) at a current of 50 mA g(-1) .

A cathode of FeF3/C nanocomposites has been fabricated by a simple vapor-solid fluoridation route which shows superior Na-ion storage performance.

Spinel cathode materials consisting of LiMn2 O4 @LiNi0.5 Mn1.5 O4 hollow microspheres have been synthesized by a facile solution-phase coating and subsequent solid-phase lithiation route in an atmosphere of air. When used as the cathode of lithium-ion batteries, the double-shell LiMn2 O4 @LiNi0.5 Mn1.5 O4 hollow microspheres thus obtained show a high specific capacity of 120 mA h g(-1) at 1 C rate, and excellent rate capability (90 mAhg(-1) at 10 C) over the range of 3.5-5 V versus Li/Li(+) with a retention of 95 % over 500 cycles.

Charged up: A general soft-template route for the synthesis of uniform hollow carbon microspheres embedded with transition-metal oxide nanocrystals (OHCMs) has been developed (see figure). The obtained OHCMs possess a microsized spherical shape, embedded transition-metal oxide nanocrystals, and fully encapsulating conductive carbon shells, which endow the resulting anode materials with high specific capacities, rate capabilities, electrode densities, and cycle stabilities.

An in situ carbon-encapsulating solution route for the synthesis of Li 4 Ti 5 O 12 @C composite hollow microspheres has been developed. The finally obtained Li 4 Ti 5 O 12 @C hollow microspheres possess a microsized spherical shape, embedded Li 4 Ti 5 O 12 nanocrystals, and fully encapsulating conductive carbon shells, which endow this Li 4 Ti 5 O 12 anode material with high specific capacity, rate capability, and cycle sta-[a] Key