Designing Hierarchical Assembly of Carbon-Coated TiO₂ Nanocrystals and Unraveling the Role of TiO₂/Carbon Interface in Lithium-Ion Storage in TiO₂

Abstract

Despite the many benefits of hierarchical nanostructures of oxide-based electrode materials for lithium-ion batteries, it remains a challenging task to fully exploit the advantages of such materials partly because of their intrinsically poor electrical conductivities. The resulting limited electron supply to primary particles inside secondary microparticles gives rise to significant variation in the lithiumion (Li + ) storage capability within the nanostructured particles. To address this, facile annealing, where in situ generated carbon-coated primary particles were assembled into porous microagglomerates, is demonstrated to prepare nanostructured titanium dioxide (TiO 2 ). A systematic study on the effect of the carbon coating reveals that it is exclusively governed by the characteristics of the TiO 2 /carbon interface rather than by the nature of the carbon coating. Depending on their number, oxygen vacancies created by carbothermal reduction on the TiO 2 surface are detrimental to Li + diffusion in the TiO 2 lattice, and structural distortion at the interface profoundly influences the Li + (de)intercalation mechanism. This new insight serves as a stepping stone toward understanding an important yet often overlooked effect of the oxide/carbon interface on Li + storage kinetics, thereby demanding more investigations to establish a new design principle for carbon-coated oxide electrode materials.

Oxygen‐Deficient Blue TiO2 for Ultrastable and Fast Lithium Storage

“…It is clear that the CV curves of B‐TiO 2− δ electrode have larger areas than that of W‐TiO 2 electrode at different sweep rates (Figure S10a, Supporting Information), coinciding well with the rate performance at different current densities (Figure 4a). As presented in Figure 5c, the extra area of B‐TiO 2− δ electrode is mainly contributed from the prominent insertion/extraction process at ≈1.7/2.1 V versus Li + /Li, as the presence of oxygen vacancies provides lower charge‐transfer resistance and effective Li ions diffusion among the crystal lattice to form more lithium‐rich orthorhombic titanate …”

Dynamics of Lithium Insertion in Electrochromic Titanium Dioxide Nanocrystal Ensembles

“…Differences in specific capacity, cycle stability, and energy density have been attributed to the faceting, size, and mesostructure of nanostructured TiO2 electrodes. 10,41,44 However, polydispersity among nanocrystal ensembles can obscure the precise relationship between nanoparticle structure and electrode behavior. Surfactant-mediated colloidal synthesis provides an effective method to control the morphology of TiO2 nanocrystals while limiting polydispersity in the particle ensemble.…”

“…Nanostructured anatase TiO2 is a candidate Li-ion anode with moderate specific capacity and excellent cycle stability at (dis)charging rates relevant to transportation applications. [6][7][8][9][10][11][12][13][14] The rate at which battery electrodes, including nanostructured anatase, can be reliably charged and discharged depends on the kinetics of charging processes, including surface capacitance, phase transformations due to Li-ion intercalation, and conversion reactions. [15][16][17] An assortment of in situ and in operando characterization tools have been developed to observe these processes, and inform developments in mesoscale architecture, electrode particle morphology, composition and surface chemistry of mature and frontier electrode materials.…”

“…Titania and lithium titanate polymorphs, including spinel Li4Ti5O12, [23][24][25][26][27][28] anatase, [6][7][8][9][10][11][12] TiO2-B bronze [29][30][31][32][33] and amorphous phases, [34][35][36][37] are prototypical Li-ion anodes that charge through lithium insertion and surface reactions in nanostructured electrodes. In particular, anatase TiO2 has charge storage densities competitive with conventional graphite electrodes and a small volume change during Li-ion insertion that allows for high cycle and calendar lifetimes at fast charging rates.…”

“…In particular, anatase TiO2 has charge storage densities competitive with conventional graphite electrodes and a small volume change during Li-ion insertion that allows for high cycle and calendar lifetimes at fast charging rates. [6][7][8][9][10][11][12][13][14] However, the broad use of titanium oxide anodes is limited by their relatively high potentials (i.e., low specific energy), slow lithium diffusion and low intrinsic electronic conductivity. Despite these issues, titanium oxide phases have been explored as alternative anode materials in certain battery applications because of their low cost and durability at high cycle rates.…”