Immersive Imagery/Shuttlestock
In many respects, niobium’s properties resemble those of its chemical cousin tantalum, but nearly always in a way that disappoints. Niobium is chemically resistant to mineral acids, it can act as a capacitor anode, and it can add high-temperature strength to nickel alloys. Unfortunately, it just isn’t as effective in these applications as tantalum.
Part of the problem is that niobium just has a lower melting point than tantalum. However, the greater issue is that it exhibits numerous oxide forms and can readily transition between them. The ability of the metal to move from one oxidation state to another greatly undermines its effectiveness, in harsh environments and especially in capacitors.
Paradoxically, niobium’s fickle oxides are today promising growth in niobium demand, in the field of lithium-ion batteries, precisely because of the element’s easy transitions between oxidation states.
In a lithium-ion battery, the anode acts as a reservoir for lithium atoms. On discharge, lithium atoms give up an electron, migrate through the battery’s electrolyte, and bond with the battery cathode. At present almost all anodes are graphite, while most cathodes are made from compounds based on nickel manganese cobalt (NMC) in various ratios, or lithium iron phosphate (LFP) compounds, again with various additives and adjustments.
Each cathode material has its deficiencies. For example, NMC cathode materials typically lose around 15% of their storage capacity on the first charge-discharge cycle, while LFP cathodes suffer from low conductivity. These compounds are also prone to degradation over time thanks to undesirable side reactions.
Battery makers have expended considerable effort to address these cathode deficiencies, and it turns out that one of the most promising approaches is to incorporate niobium oxide into the cathode compound, either as a dopant or as a coating for cathode particles. Adding around 1% by weight of niobium oxide can dramatically improve the conductivity of LFP cathodes while it also can all but eliminate the first-cycle capacity loss of NMC cathodes.
On the anode side of the battery, almost all lithium batteries today use graphitic carbon as the anode. Carbon stores lithium atoms in a process called intercalation, where the lithium atoms sit between the graphitic layers and flow in and out as the battery charges and discharges. Unfortunately, charge cycling leads to damage to the anode due to swelling and contraction over time, while too-rapid charging can cause the lithium to plate out as a metal and to threaten the integrity (and safety) of the battery.
One way to resolve the anode challenges of lithium batteries is to introduce silicon. Silicon stores lithium within the crystal lattice of the metal. However, this process causes very large volume increases in the silicon, and if there are grain boundaries, bulk silicon will quickly disintegrate at them. As a result, making a silicon-rich anode is a goal that today remains elusive, albeit that some progress has been made.
Niobium compounds offer an alternative, and represent in some respects an upgrade on existing lithium titanium oxide (LTO) anode materials. Toshiba has marketed LTO-based batteries since 2008, and although they command only a tiny share (about 3%) of the battery market, these anodes are characterised by high charge rates, durability over thousands of life cycles, and good environmental stability.
Materials that exhibit what is known as Wadsley Roth (WR) shear structure have been known since at least the early 1980s to be excellent reservoirs for lithium atoms. In WR compounds, mixed oxides undergo a physical shape change at elevated temperatures (typically above 1,000°C), leading to lattice realignments that open macroscopic channels through which lithium ions can move extremely rapidly and with little pressure to swell the lattice. The absence of substantial lattice distortion means WR compounds can retain their storage capacity over tens of thousands of charge-discharge cycles, even when charging at rates approaching 10x what is safe with graphitic anode materials.
Many WR materials are based on niobium. Niobium is especially effective as an anode because it can frequently store two lithium atoms per niobium atom. In lower oxidation states, niobium oxide becomes conducting (there are niobium capacitors produced by Kyocera-AVX that use niobium monoxide, NbO, as the anode material).
Leading firms in this area include Toshiba, and also Nyobolt and Echion of the UK. Nyobolt appears (based on published patents) to use oxide alloys of tungsten and niobium, while Echion (again looking at patents) appears to use a majority of niobium plus some titanium. Both firms have claims to additional additives and dopants.
CPM has written before about the supply chain barriers to widespread niobium adoption in batteries. These obstacles remain (and are discussed in CPM’s forthcoming Niobium Market Review & Outlook) but there are other, more prosaic concerns that CPM believes will limit at least for now the growth of niobium in batteries, particularly in anodes.
Cost is a paramount concern in the automotive industry, which will argue over pennies. Spot ferroniobium prices today are in the range of US$45/kg Nb, as are prices for technical grade niobium oxide. Capacity, especially as a function of weight, is a second concern – lithium-ion battery packs can weigh several hundred kilogrammes. As much as niobium anode compounds are likely to increase performance, it is hard to see them reaching the level of performance promised by lithium metal and silicon anodes.
So, for anodes, stationary storage and high life-cycle mobile applications are stronger candidate markets for niobium, although one should recognise adoption cycles here will be lengthy. Cathode markets are likely to adopt niobium sooner, to address current shortcomings, although probably not in meaningful volume prior to 2025. And cathode chemistries remain fluid, with recipes evolving as market prices move and as consumer preferences influence the share of various formulations.
In addition to these issues, there is the prospect of sodium-ion batteries. These are early stage and low energy density, while current cathode compounds are directed at layered oxide structures. Nonetheless, research suggests WR compounds can work with sodium ions. Given the demands for grid-scale storage, this is a potential long-term driver for niobium demand.
To sum up, niobium usage in lithium-ion (and sodium-ion) batteries may grow dramatically in the next decades, as the global economy electrifies. However, niobium demand is likely to be concentrated in storage and in long-life transportation markets (trucks, buses, trains) where battery longevity is a value customers will pay for.
By Andrew Matheson and Patrick Stratton, CPM Group
About the authors
CPM Group is an independent commodities research, consulting, and investment banking advisory company headquartered in New York. The company is considered the foremost authority on markets for precious metals, along with high purity manganese, molybdenum, tantalum, and other metals.
Andrew Matheson and Patrick Stratton are recognised experts in tantalum and niobium markets.
Andrew Matheson, the founder and principal of OnG Commodities LLC, has 25 years of experience in the tantalum industry, leading Cabot Corporation’s tantalum ore procurement and mineral development activities, as general manager of Cabot’s sputtering target business and serving as director of R&D. His experience includes a range of other specialty materials including niobium, scandium, and rare earth metals.
Patrick Stratton spent 16 years with Roskill, where he led the tantalum and niobium research. His experience also covers gallium, magnesium metal, and titanium. In addition to being the lead author of published research reports on these commodities, he has also undertaken many consulting assignments for producers, project developers, financial institutions and government bodies.
