How Strategic Metals Could Drive Next-Gen Li-Ion Batteries
This story is contributed by Guilherme Luís Cordeiro
· With the goal of further reducing ─ or even eliminating ─ cobalt and moving beyond the energy limits of the present cathode generation, Group 5 metals could enable battery electrode designs with demonstrated capacities in excess of 250 mAh/g in the next ten years.
· Group 5 metals excel at safety and power density beyond extending the lifespan of the electrochemical system.
· Group 5 metals may advance nickel-rich cathodes for batteries and lead the way to charging EVs as fast as filling up conventional cars.
Vanadium, niobium and tantalum may find their way into more vehicle batteries to boost performance.
Lithium-ion batteries are at the heart of the electric vehicle (EV) revolution. As such, they are a critical component in reducing carbon footprint from transportation. But how do we move around in a low-carbon world without relying heavily on batteries that need cobalt — a key ingredient that has been linked to human rights abuses, corruption, environmental destruction, and child labor?
Given the metal’s advantages in cycle life and specific power, eliminating cobalt is not the first choice for most battery component manufacturers. Although there is a broad consensus toward the reduction of cobalt in batteries, the demand continues to rise steadily: an estimate by Benchmark Minerals suggested that cobalt consumption would reach 300,000 tons in 2029 compared to the 70,000 tons in 2019. These numbers remind us that much innovation is still needed to shift to batteries with less cobalt or none at all.
The solution to moving around with less (or zero) cobalt is not simple. But here is one potential pathway: use electrochemically inactive strategic metals from Group 5 of the periodic table (vanadium, niobium and tantalum) to design improved battery products. This article will provide insight into how strategic minerals could drive next-generation cathode active materials. In particular, researchers at companies like Sumitomo Metal Mining, Samsung and Volkswagen have suggested incorporating these inactive metals into nickel- and lithium-rich cathodes, as detailed below.
Advancing Positive Electrodes
Let’s start with the nickel-rich materials. The good news about nickel-rich formulations of battery cathodes is that we have been making significant progress on energy density. These high-energy materials evolved from the lithium cobalt oxide (LCO, LiCoO2) chemistry, the cathode active material used by Sony in the first commercial lithium-ion batteries for portable electronics in 1991.
Let’s recall that for practical application, the quantity of lithium ions and electrons to be reversibly cycled in Li1-xCoO2//C Li-ion cells is limited to x=0.5 due to structural instability, which means that only 50% (∼140 mAh/g) of the total LCO capacity (275 mAh/g) can be used. Attempts to push this limit further have led to the partial substitution of cobalt by nickel, as well as other elements such as manganese and aluminum, resulting in the development of the NCM (LiNixCoyMnzO2) and NCA (LiNixCoyAlzO2) cathodes that power EVs today. While manganese and aluminum act primarily as stabilizing agents, nickel provides the additional capacity needed to cure our range anxiety. After all, the greater the amount of nickel, the more lithium ions and electrons can be cycled into and out of the cathode, and the higher the energy density.
As a result, NCM and NCA have been the leading chemistries for EVs. An analysis by the consultancy firm ICCSINO found that Chinese consumption of nickel-rich NCM, for example, was at least 90% of NCM and NCA as of 2020. The NCM and NCA market share statistics estimated that 59% of their demand is for NCM 523 (LiNi0.5Co0.2Mn0.3O2), 21% for NCM 811 (LiNi0.8Co0.1Mn0.1O2) and 14% for NCM 622 (LiNi0.6Co0.2Mn0.2O2).
Outside China, several companies are developing high-nickel formulations to increase energy density. According to Battery Power Magazine and Roskill market news, players such as BASF, EcoPro BM, LG Chem and Umicore are also focusing their future strategy on nickel-rich cathodes. BASF is planning go-to-market versions of NCM with 75%, 80%, and 90% nickel and NCA with more than 90% nickel. EcoPro BM sells products with at least 80% nickel — in addition to recycling materials from used cells and transforming them into raw materials for manufacturing their own cathode products. LG Chem and Umicore, in turn, have already invested in materials with 70% and 80% nickel, specifically NCM-712 and NCM-811.
Of course, increasing the amount of nickel helps reduce cobalt dependency, although the low cobalt content limits the cathode’s ability to retain energy during charge/discharge cycles. Since the current market standard for EVs is a retention of 80% of the original capacity of the battery over an eight-year warranty, high nickel cathodes can pose warranty risks. In addition, reducing the quantity of cobalt may lead to problems meeting specific power requirements. If the ability of the battery cells to deliver high current is compromised, fast charge may lead to rapid degradation.
Harnessing Group 5 Metals
Efforts towards zero-cobalt batteries in the next five years have led to a reexamination of alternate chemical substitution strategies. This is where high-valence metals come in. There are several different types, such as vanadium, niobium and tantalum (Group 5 metals).
To illustrate the capability of Group 5 elements, researchers have conducted various investigations. First, niobium is reported to serve as a stabilizing element in cathode active materials. A study by the Battery Research Laboratories at the Sumitomo Metal Mining Co., Ltd. showed that adding 3% niobium into Li3NbO4-coated NCM 622 crystals had a significant impact on the full cell battery cycling performance. The Li(Ni0.6Co0.2Mn0.2)0.97Nb0.03O2//C Li-ion laminate cell achieved a capacity retention of around 91% of its initial capacity after 500 cycles at a current rate of 2C. In comparison, the cell battery with the non-modified cathode material showed serious capacity fade, retaining only 70% of its original capacity under the same cycling conditions.
Group 5 metals excel at safety and power density beyond extending the lifespan of the electrochemical system. As niobium-oxygen (Nb-O) chemical bonds are even stronger than Mn-O in NCM or Al-O in NCA oxides, Nb can serve as the safe element in low-cobalt formulations. The study by Sumitomo Metal Mining Co. also demonstrated the ability of niobium to minimize oxygen gas evolution when cycling to high voltages (4.5 V).
Group 5 metals may advance nickel-rich cathodes for batteries and lead the way to charging EVs as fast as filling up conventional cars. Their relatively large size, compared to smaller nickel (Ni3+), cobalt (Co3+), manganese (Mn4+) and aluminum (Al3+) ions, promotes a distortion of the active material crystal structure that opens pathways for rapid lithium diffusion in battery electrode materials. While electric car owners would benefit from faster charging, the impact could be particularly significant in terms of extracting lithium from the cathode without rapid degradation.
Enabling High-Capacity Cathodes
With the goal of further reducing ─ or even eliminating ─ cobalt and moving beyond the energy limits of the present cathode generation, Group 5 metals could enable battery electrode designs with demonstrated capacities in excess of 250 mAh/g in the next ten years. While development of nickel-rich cathodes continues, innovation is heading in the direction of oxide materials known as lithium-rich disordered compounds.
In today’s batteries, the cathodes are striated materials of Li-ion layers alternating with metal oxides known as layered lithium metal oxides (LiMO2). Traditionally, cobalt has helped stabilize the layered framework and provide a pathway for lithium ions to be cycled in and out of the cathodes without bumping into the metal oxide layer. Progressive substitutions of Li for M in the [MO2] layer lead to deviations from that perfect order, resulting in certain kinds of disorder that could provide a significant boost in cathode performance with, surprisingly, low or even no cobalt.
Many M elements may also be progressively replaced by the stabilizing Group 5 metals. This approach, however, actually requires putting extra Li and other electrochemically active elements into disordered oxides in order to form stable formulations of cathodes. Since the chemistry of the Group 5 strategic metals is dominated by high oxidation states, charge compensation in these complex materials requires an excess of electroactive Li and M elements. While Li-rich disordered cathodes can hold and release more lithium ions and electrons than nickel-rich ordered ones, they also operate at lower voltages, and further innovation is needed before they become a realistic option for Li-ion batteries.
Weaning Batteries Off Cobalt
The promise that a long-lifetime, high-energy battery holds for the EV sector is huge. Consumers will be able to move around with low- or zero-cobalt batteries thanks to companies like Samsung and Volkswagen, just to name a few. A study by the Samsung Advanced Institute of Technology has demonstrated the advantage in reducing voltage degradation when cycling 2032 coin-type cells manufactured with a vanadium-modified Li1.48Ni0.225Co0.15Mn0.625O2 cathode formulation. And as for the Li-ion technology in R&D at the Volkswagen labs, the target includes a cell energy density of around 800 Wh/L with a Li-rich NVM (N: nickel, V: vanadium, M: manganese) battery cathode by 2025.
The outlook is optimistic for these strategic metals. Although these solutions are not yet ready to be deployed at the scale we need, more companies exploring advanced materials and accelerating their development from the laboratory to commercial application would greatly increase market acceptance of strategic metals and also boost transparency in battery minerals mining. Countries with political instability exacerbated by conflict minerals often dominate headlines about strategic metals, but outside of the media spotlight, Brazil is the world’s first niobium, third tantalum, and fourth vanadium mineral producer. Given the prevalence of conflict-free strategic metals, the nation may be a destination for battery materials manufacturers to consider.
Bio Guilherme Luís Cordeiro
Guilherme Luís Cordeiro brings over five years of experience as a materials scientist in the Research, Development and Innovation area. He helps start-ups and established chemical and auto-parts manufacturers “verticalize” electrode active materials for battery components and mineral fillers for high-performance structural composites. He is a consultant in nanotechnology and new automotive materials with a passion for developing products that help companies build brand equity and make people’s lives happier and more comfortable.
For more information about the author, contact at:
Guilherme Luís Cordeiro
guilherme@guilhermelcordeiro.com.br
+55 (31) 999 350 255
