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Herein, sol–gel-synthesized α-Li2TiO3 was evaluated as a new promising anode material for lithium-ion batteries. The results show ultrastable release of discharge capacity within the range of 290–350 mA h g−1 in 400 cycles. Decent rate performances were also observed. A capacity of ca. 113 mA h g−1 was retained at a current density of 3 C. A 2 × 2 × 1 supercell of the lowest energy ordering structure was used in density functional theory simulations. The calculations show that in the intercalation process, Li+ preferentially enters the tetrahedral voids, leading to the activation of lithium-ion diffusion on the a–b plane with a minimal energy barrier of 0.06 eV (compared with 0.82 eV for the fully charged state). The activation of cation mobility at Li+ intercalation and insulator–conductor transition both contribute significantly to the ultrastability of the material. However, Li+ propagation along the c-axis is highly limited during the whole intercalation process. The enumeration of all the ordering structures on the tetrahedral sites shows two intermediate phases, α-Li2.25TiO3 and α-Li3.0TiO3, as observed from the formation energy convex hull. [ABSTRACT FROM AUTHOR]

With the development of electric vehicles, more and more attention has been paid to the kinetic performance of batteries, which is related to rapid charge/discharge and safety issues. To improve this aspect, Cu2Nb34O87 nanowires covered by nitrogen and sulfur co-doped carbon (Cu2Nb34O87/NSC nanowires) are prepared by electrospinning combined with surface coating. As-prepared Cu2Nb34O87/NSC nanowires present a high ion diffusion coefficient and electronic conductivity, showing good a kinetic performance. Specifically, they deliver a splendid capacity of 311.2 mA h g−1 at 1 C and a superior cycling stability with a capacity fading of 0.031% per cycle upon 1000 cycles. At the same time, the electrochemical and structural reversibility is fully discussed and demonstrated by ex situ XRD, ex situ SEM and ex situ XPS based on the redox couples of Cu2+/Cu+, Nb5+/Nb4+, and Nb4+/Nb3+. Contributing to peculiar physico-chemical properties, Cu2Nb34O87/NSC nanowires are expected to be a candidate material for the anode in lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) together with the first principles method (DFT) reveal that Na+ is capable of migrating three dimensionally in a Na2Mn2Si2O7 cathode material. Migration along the a-axis and c-axis have the same mechanism, that is, alternating between the Na1 and Na2 route with a similar local environment and distance. Long-distance hopping between two Na2 atoms or between Na1 and Na2 atoms is crucial for continuous migration along the b-axis. Also, the anti-site phenomenon is identified, and it facilitates the migration of the Na ions. Four intermediate phases are determined according to the formation energy curve and, as a result, the voltage profile is predicted accurately. The state of charge (SOC) dependency of the Na+ energy shows that the mobility of Na+ is highly inhibited in the fully discharged state. Upon the deintercalation of sodium ions, Na+ is activated immediately. A maximal DNa+ value of 3.6 × 10−9 cm2 s−1 and a low energy barrier of ca. 0.26 eV at the deintercalation level of x = 0.25 are observed. Because of the scarcity of Na+, DNa+ experiences a sharp decrease at the end of deintercalation. Despite the low level of Na+ mobility in the range of 0.25 < x < 1, Na2Mn2Si2O7 is still a potential cathode material for use in sodium ion batteries (SIBs). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Herein, sol-gel-synthesized α-Li 2 TiO 3 was evaluated as a new promising anode material for lithium-ion batteries. The results show ultrastable release of discharge capacity within the range of 290-350 mA h g -1 in 400 cycles. Decent rate performances were also observed. A capacity of ca . 113 mA h g -1 was retained at a current density of 3 C. A 2 × 2 × 1 supercell of the lowest energy ordering structure was used in density functional theory simulations. The calculations show that in the intercalation process, Li + preferentially enters the tetrahedral voids, leading to the activation of lithium-ion diffusion on the a - b plane with a minimal energy barrier of 0.06 eV (compared with 0.82 eV for the fully charged state). The activation of cation mobility at Li + intercalation and insulator-conductor transition both contribute significantly to the ultrastability of the material. However, Li + propagation along the c -axis is highly limited during the whole intercalation process. The enumeration of all the ordering structures on the tetrahedral sites shows two intermediate phases, α-Li 2.25 TiO 3 and α-Li 3.0 TiO 3 , as observed from the formation energy convex hull.

With the development of electric vehicles, more and more attention has been paid to the kinetic performance of batteries, which is related to rapid charge/discharge and safety issues. To improve this aspect, Cu 2 Nb 34 O 87 nanowires covered by nitrogen and sulfur co-doped carbon (Cu 2 Nb 34 O 87 /NSC nanowires) are prepared by electrospinning combined with surface coating. As-prepared Cu 2 Nb 34 O 87 /NSC nanowires present a high ion diffusion coefficient and electronic conductivity, showing good a kinetic performance. Specifically, they deliver a splendid capacity of 311.2 mA h g -1 at 1 C and a superior cycling stability with a capacity fading of 0.031% per cycle upon 1000 cycles. At the same time, the electrochemical and structural reversibility is fully discussed and demonstrated by ex situ XRD, ex situ SEM and ex situ XPS based on the redox couples of Cu 2+ /Cu + , Nb 5+ /Nb 4+ , and Nb 4+ /Nb 3+ . Contributing to peculiar physico-chemical properties, Cu 2 Nb 34 O 87 /NSC nanowires are expected to be a candidate material for the anode in lithium-ion batteries.

Molecular dynamics (MD) together with the first principles method (DFT) reveal that Na+ is capable of migrating three dimensionally in a Na2Mn2Si2O7 cathode material. Migration along the a-axis and c-axis have the same mechanism, that is, alternating between the Na1 and Na2 route with a similar local environment and distance. Long-distance hopping between two Na2 atoms or between Na1 and Na2 atoms is crucial for continuous migration along the b-axis. Also, the anti-site phenomenon is identified, and it facilitates the migration of the Na ions. Four intermediate phases are determined according to the formation energy curve and, as a result, the voltage profile is predicted accurately. The state of charge (SOC) dependency of the Na+ energy shows that the mobility of Na+ is highly inhibited in the fully discharged state. Upon the deintercalation of sodium ions, Na+ is activated immediately. A maximal DNa+ value of 3.6 × 10-9 cm2 s-1 and a low energy barrier of ca. 0.26 eV at the deintercalation level of x = 0.25 are observed. Because of the scarcity of Na+, DNa+ experiences a sharp decrease at the end of deintercalation. Despite the low level of Na+ mobility in the range of 0.25 < x < 1, Na2Mn2Si2O7 is still a potential cathode material for use in sodium ion batteries (SIBs).