A New Sodium Calcium Cyclotetravanadate Framework: “Zero‐Strain” during Large‐Capacity Lithium Intercalation

Abstract

Zero-strain" materials with little lattice strain and volume change during long-term cycling are ideal electrode choices for long-life lithium-ion batteries. However, the very limited "zero-strain" materials explored generally show small capacities (<200 mAh g −1 ), and the origin of "zero-strain" is still unclear. Here, Na 2 Ca(VO 3 ) 4 (NCVO) nanowires are explored as a new anode material capable of keeping single-phase-transition "zero-strain" during large-capacity (381 mAh g −1 ) Li + intercalation. NCVO owns a crystal structure with isolated [V 4 O 12 ] 4− tetracycles separated by large-sized NaO 6 octahedra and CaO 8 square antiprism decahedra, generating large-sized quadrilateral and hexagonal channels (≈3.6 Å). During lithiation, two-electron transfer per vanadium is accomplished, introducing a large amount of Li + into interstitial sites and increasing the size of reduced vanadium ions. The former and latter expansion effects are eliminated by the superior volume-buffering capabilities of the sufficiently large interstitial sites and electrochemical inactive Na-/Ca-based polyhedra, respectively, thus achieving "zero-strain" with the maximum volume variation of only 0.039% and mean strain of only 0.060%. Therefore, the NCVO nanowires exhibit exceptional cyclic stability, as demonstrated by 93.8%/93.2%/94.7% capacity retention over 2000/2000/7000 cycles at 1C/2C/10C. The understanding of the crystal-structural features for "zero-strain" provides a guide for the future designs of "zero-strain" energy-storage materials.

A general strategy to enhance the electrochemical activity and energy density of energy-storage materials through using sintering aids with redox activity: a case study of Mo4Nb26O77

“…7d–f (also see the ESI Video†), verifying the high electrochemical activity of the Mo 4 Nb 26 O 77 submicron-sized particles. 47,48 However, the morphology and volume variations are rather small, which confirms the intercalation nature of Mo 4 Nb 26 O 77 with small unit-cell-volume change.…”

Cation‐Vacancy Ordered Superstructure Enhanced Cycling Stability in Tungsten Bronze Anode

“…Generally, the structural variation increases with the number of lithium ions inserted. [16] Hence, the diffraction peaks of BNO@C exhibit more significant change than those of BNO. Nevertheless, the refinement results in Figure 5d show that the unit cell volume of BNO@C expands from 618.081 to 633.878 Å 3 caused by Li + -insertion.…”

Conductive LaCeNb6O18 with a Very Open A‐Site‐Cation‐Deficient Perovskite Structure: A Fast‐ and Stable‐Charging Li+‐Storage Anode Compound in a Wide Temperature Range

“…Additionally, the electrochemical inactive layers constructed by large-sized (vacancy/La/Ce)O 12 dodecahedra own superior volumebuffering capability, which can effectively accommodate the volume changes originated from Nb-ion reduction/oxidation and Li + intercalation/de-intercalation. [8] These two crystal-structure advantages of LCNO work together, leading to its low-and negative-strain characteristics at different temperatures.…”

“…Its maximum unit cell volume layers constructed by large-sized (vacancy/La/Ce)O 12 dodecahedra are expected to have superior volume-buffering capability, which can decrease the maximum unit-cell-volume change. [8] In this work, pure LCNO micrometer-sized particles are successfully prepared through solid-state reaction. Its structures, Li + -storage properties, redox mechanism, electrochemical kinetics, and crystal-structure evolutions at 25 and 60 °C are systematically investigated through various state-of-the-art research methods.…”