Haoxiang Yu

Effect of Sodium-Site Doping on Enhancing the Lithium Storage Performance of Sodium Lithium Titanate.

Via Li(+), Cu(2+), Y(3+), Ce(4+), and Nb(5+) dopings, a series of Na-site-substituted Na1.9M0.1Li2Ti6O14 are prepared and evaluated as lithium storage host materials. Structural and electrochemical analyses suggest that Na-site substitution by high-valent metal ions can effectively enhance the ionic and electronic conductivities of Na2Li2Ti6O14. As a result, Cu(2+)-, Y(3+)-, Ce(4+)-, and Nb(5+)-doped samples reveal better electrochemical performance than bare Na2Li2Ti6O14, especially for Na1.9Nb0.1Li2Ti6O14, which can deliver the highest reversible charge capacity of 259.4 mAh g(-1) at 100 mA g(-1) among all samples. Even when cycled at higher rates, Na1.9Nb0.1Li2Ti6O14 still can maintain excellent lithium storage capability with the reversible charge capacities of 242.9 mAh g(-1) at 700 mA g(-1), 216.4 mAh g(-1) at 900 mA g(-1), and 190.5 mAh g(-1) at 1100 mA g(-1). In addition, ex situ and in situ observations demonstrate that the zero-strain characteristic should also be responsible for the outstanding lithium storage capability of Na1.9Nb0.1Li2Ti6O14. All of this evidence indicates that Na1.9Nb0.1Li2Ti6O14 is a high-performance anode material for rechargeable lithium ion batteries.

Electrospun WNb12O33 nanowires: superior lithium storage capability and their working mechanism

In this study, WNb12O33 with different morphologies were fabricated using various sample collectors through a facile electrospinning method. The WNb12O33 nanorods (NR-WNb12O33) were synthesized using a rounded roller as the sample collector, and the WNb12O33 nanowires (NW-WNb12O33) were prepared using a stainless steel net as a sample collector for the first time. The possible formation process of different morphologies may depend on the self-aggregation of the precursor. Evaluated as a lithium storage anode, NW-WNb12O33 exhibited higher reversible capacity, longer cycle life, and superior rate performance than NR-WNb12O33. Even when cycled at 700 mA g−1, NW-WNb12O33 could retain capacity retention as high as 86.1% after 700 cycles (only 78.9% for NR-WNb12O33). Moreover, the structural change and lithium storage mechanism were studied via in situ X-ray diffraction. It was found that lithium ions insert into the WNb12O33 structure via three steps, and the total volume change is only 1.55%. In addition, in situ observation results also demonstrated that the lithiation/delithiation behavior of NW-WNb12O33 is highly reversible, which makes it a potential candidate for probable high-rate and long-life anode for lithium-ion batteries.

High-Rate Long-Life Pored Nanoribbon VNb9O25 Built by Interconnected Ultrafine Nanoparticles as Anode for Lithium-Ion Batteries

VNb9O25 is a novel lithium storage material, which has not been systematically investigated so far. Via electrospinning technology, VNb9O25 samples with two different morphologies, pored nanoribbon and rodlike nanoparticles, are prepared in relatively low temperature and time-saving calcination conditions. It is found that the formation process of different morphologies depends on the control of self-aggregation of the precursor by using different sample collectors. Compared with rodlike VNb9O25 (RL-VNb9O25), pored nanoribbon VNb9O25 (PR-VNb9O25) can deliver a higher specific capacity, lower capacity loss, and better cyclability. Even cycled at 1000 mA g-1, the reversible capacity of 132.3 mAh g-1 is maintained by PR-VNb9O25 after 500 cycles, whereas RL-VNb9O25 only exhibits a capacity of 102.7 mAh g-1. The enhancement should be attributed to the pored nanoribbon structure with large specific surface area and shorter pathway for lithium ions transport. Furthermore, the lithium ions insertion/extraction process is verified from refinement results of in situ X-ray diffraction data, which is associated with a lithium occupation process in type III and VI cavities through tunnels I, II, and III. In addition, high structural stability and electrochemical reversibility are also demonstrated. All of these advantages suggest that PR-VNb9O25 is a promising anode material for lithium-ion batteries.

K2Nb8O21 nanotubes with superior electrochemical performance for ultrastable lithium storage

High-performance lithium-ion batteries are important for developing sustainable energy. However, there is a shortage of advanced energy storage materials. K2Nb8O21 is a novel material for lithium storage which has not been investigated systematically. In this work, K2Nb8O21 nanotubes and microtubes were prepared facilely using electrospinning under different conditions. As an anode host, K2Nb8O21 nanotubes showed better long-term cycling, superior rate performance, and higher structural stability compared with microtubes. Electrochemical results showed that K2Nb8O21 nanotubes delivered a considerable lithium storage capacity of 213 mA h g−1 after 5000 cycles at 1000 mA g−1 with outstanding capacity retention of 80.3%. The nano/micro structured host could increase Li-ion transport to render high-rate capability and excellent cycling stability. In situ XRD, ex situ XPS and ex situ TEM revealed K2Nb8O21 nanotubes had high structural stability and reversibility as lithium storage anode materials. All of these advantages suggest that K2Nb8O21 nanotubes may be promising anode material for lithium-ion batteries.

Rapid and durable electrochemical storage behavior enabled by V4Nb18O55 beaded nanofibers: a joint theoretical and experimental study

A relatively thermodynamically stable phase in the V2O5–Nb2O5 system, namely, V4Nb18O55, was prepared and then structurally and electrochemically characterized. Theoretical calculations show that the crystal structure of V4Nb18O55 allows the rapid diffusion of lithium ions in three directions in the open structure, which ensures a high diffusion coefficient at crystal structure horizon. V4Nb18O55 synthesized by a sol–gel method exhibited a reversible specific capacity of 226.8 mA h g−1. A significant enhancement in electrochemical properties can be delivered by the electrospun V4Nb18O55 beaded nanofibers due to the shorter pathways in the spheres, leading to an improved capacity of 251.6 mA h g−1 between 1 V and 3 V with 92.54% capacity retention. According to the results of the theoretical calculations, we can find that electrochemical energy storage in V4Nb18O55 arises from the occupation by lithium ions in 8q, 4g, 4h and 4j sites in the structure. The in situ X-ray diffraction study further confirmed that the open structure of V4Nb18O55 not only ensures the highly reversible storage and transport of lithium ions in these cavities, but also provides a stable framework during repeated charge/discharge cycles.

Sol–Gel Synthesis and in Situ X-ray Diffraction Study of Li3Nd3W2O12 as a Lithium Container

In this work, garnet-framework Li3Nd3W2O12 as a novel insertion-type anode material has been prepared via a facile sol-gel method and examined as a lithium container for lithium ion batteries (LIBs). Li3Nd3W2O12 shows a charge capacity of 225 mA h g-1 at 50 mA g-1, and with the current density increasing up to 500 mA g-1, the charge capacity can still be maintained at 186 mA h g-1. After cycling at 500 mA g-1 for 500 cycles, Li3Nd3W2O12 retains about 85% of its first charge capacity changed from 190.2 to 161 mA h g-1. Furthermore, in situ X-ray diffraction technique is adopted for the understanding of the insertion/extraction mechanism of Li3Nd3W2O12. The full-cell configuration LiFePO4/Li3Nd3W2O12 is also assembled to evaluate the potential of Li3Nd3W2O12 for practical application. These results show that Li3Nd3W2O12 is such a promising anode material for LIBs with excellent electrochemical performance and stable structure.