Doubling Reversible Capacities in Epitaxial Li₄Ti₅O₁₂ Thin Film Anodes for Microbatteries

Abstract

Despite the lower gravimetric capacity, Li4Ti5O12 is an important alternative to graphite anodes, owing to its excellent high temperature stability, high rate capability, and negligible volume change. Although surfaces with lithium compositions exceeding Li7Ti5O12 were observed previously during the first charge–discharge cycles, no stable reversible capacities were achieved during prolonged cycling. Here, structural engineering has been applied to enhance the electrochemical performance of epitaxial Li4Ti5O12 thin films as compared to polycrystalline samples. Variation in the crystal orientation of the Li4Ti5O12 thin films led to distinct differences in surface morphology with pyramidal, rooftop, or flat nanostructures for respectively (100), (110), and (111) orientations. High discharge capacities of 280–310 mAh·g–1 were achieved due to significant surface contributions in lithium storage. The lithiation mechanism of bulk Li4Ti5O12 thin films was analyzed by a phase-field model, which indicated the lithiation wave to be moving faster along the grain boundaries before moving inward to the bulk of the grains. The (100)-oriented Li4Ti5O12 films exhibited the highest capacities, the best rate performance up to 30C, and good cyclability, demonstrating enhanced cycle life and doubling of reversible capacities in contrast to previous polycrystalline studies.

Pulsed Laser Deposited Films for Microbatteries

“…Recently, PLD LTO films grown on Nd-doped oriented STO substrates at T s = 700 • C under P O 2 = 20 Pa showed high discharge capacities of 280 to 310 mAh·g −1 . The best rate performance of 30C was obtained for the (100)-oriented Li 4 Ti 5 O 12 films[319].…”

Miniaturized Energy Storage Devices Based on Two‐Dimensional Materials

“…fabricated MSCs through plasma micropatterning of GO films on both rigid and flexible substrates; these MSCs showed an area capacitance of 80.7 μF cm −2 , a stacked capacitance of 17.9 F cm −3 , and a cycling stability of 98.3 % capacitance retention after 100 000 cycles . Due to the high electrical conductivity (345 S cm −1 ), they also exhibited a power density of 495 W cm −3 and an energy density of 2.5 mWh cm −3 , which was comparable to that of thin‐film lithium batteries . Additionally, graphene quantum dots (GQDs) with novel chemical/physical properties, such as ultrasmall size, abundant edge exposure and defects, solution processable, and rich surface chemistry, are also an attractive member of the graphene family in MEMS studies .…”

“…[93] Due to the high electrical conductivity (345 Scm À1 ), they also exhibited ap ower density of 495 Wcm À3 and an energy density of 2.5 mWh cm À3 , which was comparable to that of thin-film lithium batteries. [94][95][96][97] Additionally,g raphene quantum dots (GQDs)w ith novel chemical/physical properties, such as ultrasmall size, abundant edge exposure and defects, solution processable, and rich surfacec hemistry,a re also an attractive member of the graphene family in MEMS studies. [98] Liu et al showeda GQD//GQD symmetric MSC constructed through electrodeposition on interdigital finger electrodes that possessed as uperior rate capability with as canningr ate up to 1000 Vs À1 ,e xcellent power response with as mall RC time constant (103.6 ms), a high areal specific capacitance (4.68 mF cm À2 ), and outstanding cycling stabilityi na0.5 m aqueous solution of Na 2 SO 4 .…”

Surface Evolution of Lithium Titanate upon Electrochemical Cycling Using a Combination of Surface Specific Characterization Techniques

“…[ 58 ] Pagani et al studied the conductivity on epitaxial LTO without grain boundaries, [ 59 ] while Cunha and collaborators studied the effect of the LTO surface termination on the electrochemical performance. [ 60 ] Kitta et al described the possible formation of α‐Li 2 TiO 3 phase on the surface of LTO upon first Li ion insertion‐extraction along with an increase of the surface corrugation, on the grounds of a TEM, EELS and atomic force microscopy (AFM) investigation, suggesting that it could work as a protective layer. [ 61 ] Recent ab initio calculations suggest that the formation of this lithium metatitanate phase on top of the lithium titanate could occur under certain conditions; starting from Li 4 Ti 5 O 12 , the α‐Li 2 TiO 3 phase could be formed either a) during the 1st Li‐insertion or b) during the 1st Li‐extraction, following reaction with Li 2 O formed during the 1st Li‐insertion.…”