Titanium Niobium Oxide: From Discovery to Application in Fast-Charging Lithium-Ion Batteries

Abstract

Lithium-ion batteries are essential for portable technology and are now poised to disrupt a century of combustion-based transportation. The electrification revolution could eliminate our reliance on fossil fuels and enable a clean energy future; advanced batteries would facilitate this transition. However, owing to the demanding performance, cost, and safety requirements, it is challenging to translate new materials from laboratory prototypes to industrial-scale products. This Perspective describes that journey for a new lithium-ion battery anode material, TiNb2O7 (TNO). TNO is intended as an alternative to graphite or Li4Ti5O12 with better rate and safety characteristics than the former and higher energy density than the latter. The high capacity of TNO stems from the multielectron redox of Nb5+ to Nb3+, its operating voltage window well above the Li+/Li reduction potential prevents lithium dendrite formation, and its open crystal structure leads to high-power performance. Nevertheless, the creation of a practical TNO anode was nonlinear and nontrivial. Its history is built on 30 years of fundamental science that preceded its application as a battery anode, and its battery development included a nearly 30-year gap. The insights and lessons contained in this Perspective, many of them acquired firsthand, serve two purposes: (i) to unite the disparate studies of TiNb2O7 into a coherent modern understanding relevant to its application as a battery material and (ii) to highlight briefly some of the challenges faced when scaling up a new material that affect TiNb2O7 as well as new electrode candidates more generally.

Atomic-resolution STEM-EDS studies of cation ordering in Ti-Nb oxide crystals

“…It is important to know the real crystal structures of any material in order to understand their physical and chemical properties as well as their practical uses. Crystal structures were traditionally analyzed by X-ray or neutron diffraction methods; however, these techniques are not adequate for cases where samples are powder crystals, nanocrystals (commonly used in Li-battery electrodes), or contain crystalline imperfections 1 – 8 . Nevertheless, these crystals can be studied with high-resolution transmission electron microscopy (HRTEM), and the usefulness of this method has been proved over the years 9 .…”

“…One of the present authors successfully imaged the cation arrangements of the orthorhombic Ti 2 Nb 10 O 29 crystal structure for the first time using HRTEM in the 1970s 10 . The research on the ternary Ti-Nb and Ti–W oxide has been resumed and extensively investigated as the candidate electrodes for Li batteries 1 – 8 .…”

“…They concluded the Ti ions were located preferentially near the CS planes, while the Nb ions were located near the center of the ReO 3 -type blocks. More recently, a cation chemical ordering has been discussed for Nb-W oxide crystals using the neutron method via first-principle calculations 8 , 21 . However, the theory and the experiments were not entirely in agreement such as on cation occupancy ratios.…”

Polyoxoniobates as molecular building blocks in thin films

“…Notably, the titanium-niobium oxides are considered as prospective anode materials for lithium-ion batteries, to replace graphite or Li 4 Ti 5 O 12 anodes currently used. 48,49 Studies of the electrochemical properties of Ti 2 Nb 10 O 29 have determined it has a high rate capability and diffusion coefficient, which facilitates Li + and electron transport. 47,50,51 The TiNb 2 O 7 is of particular interest because of its energy density and lithiation properties.…”

“…47,50,51 The TiNb 2 O 7 is of particular interest because of its energy density and lithiation properties. 48 Decaniobate (Nb 10 ) has been used as an aqueous precursor for depositing Nb 2 O 5 and Nb 2 O 5 -ITO thin films on glass to elicit optical, electrochromic and electrochemical properties. [52][53][54] These studies were limited to temperatures below 400 °C in the annealing process of Nb 2 O 5 due the thermal properties of ITO.…”