Microstructure Effects on the Electrochemical Kinetics of Vanadium Pentoxide Thin-Film Cathodes

Abstract

The relationship between microstructure and electrochemical performance was investigated in sputter-deposited V 2 O 5 thin-film cathodes. As-deposited and heat-treated films in unlithiated and lithiated states were studied by transmission electron microscopy, X-ray diffraction, and secondary ion mass spectroscopy. Film properties including orientation, grain size, and morphology were found to be strongly dependent on the heating rate during annealing. Large enhancements in the capacity-rate performance of coarser grained over nanocrystalline grained films were observed, contrary to expectations. Potential transient methods were used to investigate the mass-transport differences between these two distinct microstructures. Slow transport phenomena during phase transformation and interfacial impedances linked to differences in grain orientation and/or grain boundary content are proposed to explain the observed performance.

Determination of Li+ Diffusion Coefficients in the LixV2O5 (x = 0 − 1) Nanocrystals of Composite Film Cathodes

“…The severe loss of capacity usually observed for the V2O5 powder cathodes during repeated discharging/charging processes is considered to be correlated with several steps of irreversible structural modification induced by extensive Li insertion into/extraction from the LixV2O5 lattice (1 << x). [3][4][5][6][7][8][9][10][11][12][13][14] For the nanobeam-V2O5/PEDOT composite film cathode, there appears to be a voltage deflection at about 2.2 V, in addition to the voltage plateaus and deflections above 3 V. This particular contribution from the redox reaction of PEDOT in the V2O5/ PEDOT composite-film-cathode, was confirmed by a discharge/ charge cycling experiment of a Li battery assembled with a PEDOT-only film cathode (Fig. 3).…”

“…In the case of a cathode made from V2O5 powder, however, voltage plateaus only appeared during the first discharge curve, disappearing during subsequent charging/discharging cycles with a severe loss of specific capacity. [6][7][8][9] The potential change generated by Li-ion intercalation in V2O5 is known to be caused by phase transformation, and the shape of the discharging voltage curve as a function of composition can be used to obtain detailed phase diagrams. [13][14][15][16]24 Distinct voltage plateaus at voltages above 3 V are produced by structural modifications of V2O5 to LixV2O5 (x = 1.1) through α-, ε-, to δ-LixV2O5 intermediate phases.…”

“…The diffusion properties of the Li ions determine some of the key battery-performances, including the charge and discharge rates, practical capacity, and cycling stability. [5][6][7][8][9][10][16][17][18][21][22][23][24][25][26][27] GITT combines transient and steady-state electrochemical measurements, which have been widely applied for the characterization of the diffusion kinetics of Li ions into various electrode materials including graphite anodes and transition-metal-oxide cathodes. [21][22][23][24][25][26][27] Although the intercalation diffusion kinetics are complicated by first-order phase transitions, GITT provides valuable information on the chemical diffusion coefficient, even at the starting point of the two-phase coexistence region (i.e., at the very beginning and the very end of a two-phase domain).…”

“…1,2 Layered V2O5 demonstrates a high capacity and structural flexibility for the reversible insertion and release of Li ions as a novel cathode material. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The crystallinity and morphology of V2O5 can play a key role in determining the electrochemical properties of this material. [3][4][5][6][7][8][9][10][11][12][13][14][15] Elongated-rectangular-plate-shape (beam-shaped) V2O5 crystals were prepared by a hydrothermal method and the plate-like morphology reflects the intrinsic properties of layered structure.…”

Three-dimensional self-supported metal oxides as cathodes for microbatteries

“…However, Li metal is the only anode choice for such Li-free metal oxide cathodes, which limits their applications in microbatteries. 42 …”