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The use of electric-field to manipulate the transport properties of correlated oxides is promising for achieving nano-functional electronic devices. As a typical correlated oxide material, vanadium dioxide (VO2) displays a special metal-insulator transition (MIT) at about 340 K. In this work, we select a water-free electrolyte gel, Li+/propylene carbonate, to achieve a non-volatile and reversible Li-doping and phase modulation in nano-VO2crystal film under gating voltages. Synchrotron characterizations indicate the originally insulating VO2undergoes an effective structure change and an increased V 3d-O 2phybrid t2g-orbital occupancy, which is responsible for the metallic state formation as proved by first-principle calculation. The field-driving Li-doping shows pronounced facet dependence, indicating the existence of energetically favored channels for Li-ions diffusion along V-V chains as proved by dynamic stimulation. Our current findings will supply opportunities for the electric-field control of atomic sieve, correlated ionitronics and synaptic transistor.

Compared with most cathodes for lithium-ion batteries (LIBs), α-MoO3exhibits high specific capacity and therefore receives widespread attention. However, due to its irreversible structural transformation, the capacity of α-MoO3declines rapidly upon discharge-charge process. Herein, via H2plasma etching, oxygen-deficient α-MoO3-xwith improved electrochemical performance is prepared on the basis of pristine α-MoO3(MoO3(I)). The obtained MoO3(II) (10 min etching) and MoO3(III) (20 min etching) have reduced bandgap and expanded van der Waals gap (vdW gap). Electrochemical test results demonstrate MoO3(II) obtains the largest Li+diffusion coefficient, the lowest charge transfer resistance and the slightest polarization. In situ X-ray diffraction characterization further reveals that during cycling, vdW gap of MoO3(II) changes periodically within a small range, indicating a stabilized crystal structure. This work shows that moderate oxygen vacancies can enhance the capacity and stabilize the structure of molybdenum trioxide cathode for LIBs, which has great potential in other cathode materials.

It is of great significance to discover new negative electrode materials featuring a low operating voltage, high capacity and improved initial coulombic efficiency for lithium ion batteries. This is the first report on the use of orthorhombic Li3V(MoO4)3as a promising anode material that exhibits natural advantages over reported traditional metal oxides. High-crystalline Li3V(MoO4)3nanoparticles decorated with carbon are synthesized by a facile mechanochemical route followed by low-temperature (480°C) calcination. The lithium storage ability of the prepared Li3V(MoO4)3anode is fully tapped at 3.0–0.01V vs. Li+/Li, displaying a lower voltage plateau than the conversion-type metal oxides. It delivers a high reversible specific capacity of 999 mAh g−1at 50mAg−1and a high coulombic efficiency of 82.6%. Moreover, it maintains a capacity retention of 92% after 75 cycles at 500mAg−1. The GITT-determined Li+diffusion coefficient ranges from 10−10to 10–13cm2s−1along with the voltage. The lithium storage mechanism indicates that Li3V(MoO4)3can be considered a pre-lithiated material. In-situ XRD testing during the first cycle reflects the conversion reaction of Li3V(MoO4)3. These insights will benefit the discovery of novel anode materials for lithium-ion batteries.

Li3V2(PO4)3(LVP) was evaluated as a promising cathode material for sodium-ion batteries (SIBs). The three-dimensional graphene frameworks wrapped LVP (LVP-G-FD) exhibited high energy density of 501.3Whkg−1, which is almost the highest energy density among the known polyanionic cathodes for SIBs. The enhanced electrochemical performance of LVP-G-FD is attributed to the graphene framework which provides the fast electronic transport network and buffering space. Besides, the sodium-ion storage mechanism of LVP was investigated via in-situXRD and so on. The sodium-ion storage process is composed of the electrochemical topotactic replacement and the subsequent topotactic reaction.

NASICON structured NaTi2(PO4)3with stable and open framework has become a promising electrode material for sodium-ion batteries. However, the intrinsic low electronic conductivity of NaTi2(PO4)3leads to inferior rate capability and poor active material utilization. Herein, we first report the synthesis of carbon-coated hierarchical NaTi2(PO4)3mesoporous microflowers (NTP/C-F), viaa facile and controllable solvothermal method and subsequent annealing treatment. The unique structural features endow the NTP/C-F with excellent structural stability, enhanced charge transfer kinetics, and suppressed polarization. This architecture exhibits superior sodium storage performance: high initial capacity (125mAhg−1at 1C), outstanding rate capability (95mAhg−1at 100C), and ultra-long cycling stability (capacity retention of 77.3% after 10,000 cycles at 20C). Time-resolved in-situX-ray diffraction study reveals a typical two-phase electrochemical reaction with reversible structure change. This work suggests the integration of hierarchical structure and carbon coating provides a promising approach for boosting the electrochemical performances of battery electrode materials.

Three-dimensional (3D) hierarchical heterostructures have been widely studied for energy storage because of their amazing synergistic effect. However, a detailed characterization how the branched structure affects the backbone structure during electrochemical cycling, and the specific relationship between the backbone and the branched heterogeneous structure (namely synergistic effect) have been rarely revealed. In addition, the controllable synthesis of this system still remains a great challenge. Herein, we developed a one-step gradient hydrothermal method to obtain a series of 3D hierarchical heterogeneous nanostructures, including V2O5/NaV6O15, V2O5/ZnV2O6and V2O5/CoV2O6, through controlling the sequence of nucleation and growth processes of different structural units in the same precursor. On the basis of time-resolved in situX-ray diffraction (XRD) characterizations, we clearly elucidated the synergistic effect between the branched and backbone structure. During the synergistic effect, the branched NaV6O15helps to reduce the potential barrier during lithium-ion insertion/extraction, buffers the impact of crystal-system transformations during the charge/discharge process; the backbone V2O5is beneficial to increase the charge/discharge capacity, inhibits the self-aggregation of branched NaV6O15and maintains the stability of 3D structure. Consequently, 3D V2O5/NaV6O15hierarchical heterogeneous microspheres exhibit the best electrochemical performance than pure V2O5and V2O5/NaV6O15physical mixture in lithium-ion batteries (LIBs). When tested at a high rate of 5Ag−1, 92% of the initial capacity can be maintained after 1000 cycles. We believe this method will be in favor of the construction of 3D hierarchical heterostructures and this specific synergistic effect investigated by in situXRD will be significant for the design of better electrodes.

Na+superionic conductor (NASICON) type Fe2(MoO4)3with capacious ion diffusion tunnels and a flat discharge plateau, is a promising cathode material for sodium ion batteries. However, the sluggish electrochemical kinetics limits its further development due to the poor electron conductivity and long Na+diffusion path. In this work, a graphene wrapped Fe2(MoO4)3nanoparticle composite was synthesized viaa micro-emulsion method followed by annealing. The composite exhibits ultra-high rate capability (64.1mAhg−1at 100C, better than all the reported works) and good high-rate cycling stability (76% capacity retention after 100 cycles at 10C). The enhanced electrochemical performances are attributed to the unique composite structure with shortened ion diffusion distance and high electron conductivity. Furthermore, the Na+insertion/extraction mechanism of the composite is systematically investigated, based on in-situX-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Our work demonstrates that the graphene wrapped Fe2(MoO4)3nanoparticle composite has great potential for high-rate sodium ion batteries.

LiFePO4is one of the most outstanding cathodes for the high performance lithium-ion battery, while it is restricted by its unsatisfactory low temperature performance. Here we detect the structural dynamics and reaction routes of LiFePO4via operando condition with high rates, well reproducibility over cycles and low temperature in common laboratory X-ray without the synchrotron light source. The intermediate phases between LiFePO4and FePO4, driven by the overpotential and limited ion transfer rate along the bdirection at low temperature, are captured. Our results demonstrate that the existence of intermediate can greatly improve the diffusion kinetics of LiFePO4. The deep understanding of reaction routes of LiFePO4at low temperature will guide the further material optimization design. Besides LiFePO4, such high time resolution in-situX-ray diffraction testing method with laboratory source is available to understand the reaction mechanisms of other electrochemical reaction system.