Ultrasmall TiO_x Nanoparticles Rich in Oxygen Vacancies Synthesized through a Simple Strategy for Ultrahigh‐Rate Lithium‐Ion Batteries

Abstract

Ultrasmall particle size (< 10 nm) and rich oxygen vacancies are two sought-after characteristics for titanium dioxide (TiO 2) to achieve high performance, namely, high rate and high storage capacity, when being used as an anode in lithium-ion batteries (LIBs). However, free TiO 2 particles simultaneously possessing both characteristics have not been reported, owing to the synthetic challenges. In this study, we report novel TiO 2 nanoparticles with ultrasmall size (ca. 5-8 nm) as well as rich oxygen vacancies synthesized through a simple strategy. Specifically, porous carbon nanoparticles were used to confine the TiO 2 precursor in the nanosized pores in the carbon nanoparticles, which were annealed at a high temperature in argon to produce the TiO 2 nanoparticles with ultrasmall size and rich oxygen vacancies and subsequently annealed in air to burn away the carbon nanoparticles to afford the so-called TiO x nanoparticles in a quantitative yield. The obtained anatase TiO x nanoparticles showed an exceptional ultrahigh-rate lithium storage capability. A record reversible specific capacity of 235 mAh g À 1 was achieved at the current density of 0.1 A g À 1. Even at an ultrahigh rate of 10 A g À 1 (ca. 59 C), it still delivered a specific capacity of 90 mAh g À 1 , which is five times that of the electrode made with the commercial anatase TiO 2 nanoparticles. Furthermore, this electrode also showed an excellent cycling performance with capacity retentions of 87 % and 90 % at high rates of 1 A g À 1 and 5 A g À 1 , respectively, after 1000 cycles. The strategy reported in this work can potentially be a universal method for synthesis of other metal oxides with ultrasmall particle size and rich oxygen vacancies.

(N/S)‐TiO2@C‐Nanosphere Anode Materials with Prominent Electrochemistry Performance Synthesized by Pyrolysis of In Situ Coated Polypyrrole

“…On one hand, the carbon nanospheres produced by pyrolysis of polypyrrole coating at high temperatures greatly improve the conductivity of the material. On the other hand, the formation of Ti−N and N−O bonds and oxygen vacancies produced in the pyrolysis of polypyrrole in the N 2 atmosphere are beneficial to increasing the lithium storage capacity [11,28,43] . Additionally, the formation of dense titanium dioxide particles (see Figure 1c) improves the internal contact of titanium dioxide particles and the contact of titanium dioxide particles with copper foil collectors, which finally increases the specific capacity of the (N,S)‐TiO 2 @C‐sphere‐1 anode material to a large extent.…”

“…On the other hand, the formation of TiÀ N and NÀ O bonds and oxygen vacancies produced in the pyrolysis of polypyrrole in the N 2 atmosphere are beneficial to increasing the lithium storage capacity. [11,28,43] Additionally, the formation…”

Effect of the Secondary Rutile Phase in Single‐Step Synthesized Carbon‐Coated Anatase TiO2 Nanoparticles as Lithium‐Ion Anode Material

“…This difference is generally in line with the limited (essentially 1D) Li + diffusion kinetics in bulk rutile TiO 2 (≈10 −6 cm 2 s −1 along the c ‐axis and about 10 −15 cm 2 s −1 along the a‐ and b ‐axis, decreasing with an increasing lithium content [ 56 ] ) compared with the anatase phase (≈10 −12 –10 −16 cm 2 s −1 , no preferential diffusion direction). [ 12,14–16,48,57–61 ] Moreover, the extended presence of phase boundaries in A50R50 might additionally hamper the charge transport along with the aforementioned nanoscale porosity—at least if these pores/defects are not accessible for the electrolyte. Regarding the absolute values, we may note here that these do not directly represent lithium diffusivity within the single TiO 2 nanoparticle(s) but only serve for a direct comparison between the two samples to highlight the impact of the different anatase‐to‐rutile ratios, considering that all external parameters (i.e., the cell setup, electrode composition, mass loading, current collector, electrolytes, separator, etc.)…”

“…This difference is generally in line with the limited (essentially 1D) Li þ diffusion kinetics in bulk rutile TiO 2 (%10 À6 cm 2 s À1 along the c-axis and about 10 À15 cm 2 s À1 along the aand b-axis, decreasing with an increasing lithium content [56] ) compared with the anatase phase (%10 À12 -10 À16 cm 2 s À1 , no preferential diffusion direction). [12,[14][15][16]48,[57][58][59][60][61] Moreover, the extended presence of phase boundaries in A50R50 might additionally hamper the charge transport along with the aforementioned nanoscale porosityat least if these pores/defects are not accessible for the electrolyte.…”

Unleash the Capacity Potential of LiFePO4 through Rocking‐Chair Coordination Chemistry

“…A straightforward way to overcome the problem of low electronic conductivity is to reduce the particle size to the nanometer range. [ 9,10 ] In the presence of conductive additives (commonly carbon black) that bridge LFP nanoparticles, the apparent conductivity of the LFP cathode can be increased several times, which leads to enhanced specific capacity and rate performance. In situ and ex situ coating of a thin layer of conductive materials such as carbon, graphene, and conductive polymers on the surface of LFP particles can further improve the interface contact of LFP particles with conductive additives, thereby increasing the electronic conductivity and capacity of the LFP cathode.…”