Revisited Ti2Nb2O9 as an Anode Material for Advanced Li-Ion Batteries

A3Ti5NbO14 (A = H, Li and K) family: ionic exchange, physical and electrochemical properties

A new layered titanoniobate, Li3Ti5NbO14, a member of the AxM2nO4n+2 family, has been synthesized using a molten salt reaction between H3Ti5NbO14 and an eutectic mixture of LiOH and LiNO3. This compound crystallizes in the P21/m space group with a = 9.273(15) Å, b = 3.788(6) Å, c = 8.871(3) Å, and β = 114.33(1)°, as determined by 3D electron diffraction single crystal analysis. It exhibits [Ti5NbO14]3- layers similar to K3Ti5NbO14, but differs from the latter by a 'parallel configuration' of its [Ti5NbO5]3- ribbons between the two successive layers. The topotactic character of the reaction suggests that exfoliation plays a prominent role in the synthesis of this new form. This new phase intercalates reversibly 2 lithium through a first-order transformation leading to a capacity of 100 mA h g-1 at a potential of 1.67 V vs. Li/Li+.

Structural and electrochemical insights into novel Wadsley Roth Nb7Ti1.5Mo1.5O25 and Ta7Ti1.5Mo1.5O25 anodes for Li-ion battery application

Niobium based anodes are gaining increasing popularity for application in high-power lithium-ion batteries, due to their high theoretical capacities, inherent safety at high current densities, and long-term stability. Here, we report the discovery and characterisation of a new Wadsley Roth niobate system, Nb7Ti1.5Mo1.5O25, showing that it is isostructural with known systems: Nb9PO25 and Nb9VO25. To evaluate the material's electrochemical performance, including performance at high current densities (for potential high power applications), and long-term stability, Li half-coin cells were prepared. The material showed an initial capacity of 268(9) mA h g-1 at 0.01 A g-1 (voltage range of 2.5-1.0 V). However, in subsequent cycles, some of this initial capacity is lost, which is attributed to Li trapping associated with the presence of reducible MoO4 units, similar to the situation observed for isostructural Nb9VO25. After this initial irreversible capacity loss, the material showed good performance at high current density rates, such that at 2 A g-1 and 4 A g-1 respective capacities of 132(10) mA h g-1 and 115(14) mA g-1 were delivered. Moreover, the material showed respectable capacity retention (97%) after being cycled for 100 cycles at 0.2 A g-1. In order to identify the different Nb, Ti, Mo redox couples involved in this system, a Ta analogue was also synthesized (Ta7Ti1.5Mo1.5O25) and the electrochemical performance for this phase is also reported. This phase shows a lower initial capacity at 0.01 A g-1 (140(3) mA h g-1) than the Nb analogue in the same voltage range, which can be increased (225 mA h g-1) if a lower cutoff voltage (0.5 V) is applied. The capacity retention for this Ta system after 100 cycles at 0.2 A g-1 is similar to the Nb analogue (97%). Further work has explored whether the Nb-Ti-Mo contents could be varied, and these results showed that single phase Nb10-2xTixMoxO25 samples could be prepared for 1.5 ≤ x ≤ 1.75, and electrochemical testing results for the x = 1.75 endmember are also reported. Overall, this research highlights the synthesis and electrochemical characterisation of two new Wadsley Roth phases, and further highlights the challenges associated with the presence of reducible cations in tetrahedral sites in such structures with respect to minimising initial irreversible capacity loss.

Screening of electrode materials for ammonium ion batteries by high throughput calculation

Ammonium-ion batteries (AIBs) have attracted intense interest lately as promising energy storage systems due to their light weight, safe, inexpensive, and widely available advantages. It is of great significance to find a fast ammonium ion conductor for the electrode of AIBs that directly affects the electrochemical performance of the battery. Using high-throughput bond-valence calculation, we screened the electrode materials of AIBs with a low diffusion barrier from more than 8000 compounds in the ICSD database. Twenty-seven candidate materials were finally identified by the bond-valence sum method and density functional theory. Their electrochemical properties were further analyzed. Our results, which give the relationship between the structure and electrochemical properties of various important electrode materials which are suitable for AIBs development, may pave the way for next-generation energy storage systems.

Synergy of oxygen defects and structural modulation on titanium niobium oxide with a constructed conductive network for high-rate lithium-ion half/full batteries

Titanium niobium oxide as an electrode material for lithium-ion batteries (LIBs) has relatively high working potential and theoretical capacity, which is expected to replace a graphite anode.