Contributed Commentary by Vladimir Yufit, CTO & co-founder, Addionics
December 8, 2021 | As investment in electrification as a decarbonization strategy has rapidly developed over the last two decades, so has the lithium-ion battery. This now prevailing chemistry has existed since the early 1990s, but continued demand and R&D has resulted in significant performance improvements and cost reductions. However, today’s supply chain challenges and higher performance requirements for EVs and energy storage have many wondering if lithium-ion has reached its limit. For example, many of the world’s accessible mineral deposits for nickel and cobalt—the metals found in lithium-ion batteries—are becoming limited in supply, resulting in higher procurement costs. China’s monopoly on cobalt is another huge issue for other countries aiming to scale up battery production. As a result, several promising new chemistries within the lithium family have emerged in recent years, such as sodium-ion batteries for certain applications.
While there are many advantages to these new chemistries, they all come with tradeoffs. But not all is lost. While much attention has been paid to chemistry, the battery cell and electrode design (the physics, as it can also be understood) has not been sufficiently considered.
Let’s explore some of today’s trending chemistries and how design can help.
NMC batteries are a popular choice for power tools, energy storage systems, and the automotive industry, for which they have become one of the most commonly used chemistries. NMC cells offer a long life cycle, high energy density, and are cost-effective. However, the nickel and cobalt in the cathode make these batteries less safe due to unwanted reactions that can release oxygen that can then react with the electrolyte. High temperatures developed during battery operation contribute to the risk of accelerated chemical and mechanical degradation of NMC batteries, and therefore improving the heat dissipation and mechanical stability of the electrodes is a critical task.
Much work has gone into reducing the ratio of cobalt to increase cathode energy and alleviate dependence on cobalt supply. LG recently introduced a battery with a cathode composed primarily of nickel with only 10% cobalt. However, industry concerns around the decreasing supply of nickel pose another challenge to the future of this particular NMC configuration.
Lithium Iron Phosphate (LFP)
The LFP battery uses lithium iron phosphate as the cathode material and a graphitic carbon electrode as the anode. This chemistry has high thermal and mechanical stability, making it much safer than alternatives, and because it doesn’t require nickel or cobalt, cost and material availability are less of an issue. The primary disadvantage with LFP is low energy density, but that hasn’t kept Tesla from recently announcing that it is switching to LFP batteries for its standard-range vehicles. However, as electrification becomes mainstream, LFP batteries simply won’t be able to address the energy demands of all electric vehicles, particularly the ones requiring high energy density.
There’s much debate about the merits of NMC vs. LFP. While LFP batteries ($80/kWh in 2020) are less expensive than NMC, costs for both are expected to fall below $100/kWh by 2024. With its higher energy density, many analysts expect NMC to stick around as one of the most preferred chemistries for the transportation sector.
Many battery makers are looking to silicon to partially or even fully replace graphite in battery anodes, which have hit a ceiling in terms of power and energy density (in vehicles this translates to drive range and charging speeds). Silicon is a highly abundant material, and when used in the anode, it offers potentially 10x more capacity than graphite, translating to much higher energy per weight and volume.
It’s no wonder the world’s leading automakers including Ford, Porsche, GM, BMW, and Tesla are all doubling down on silicon battery development. Of course, there is a downside. Silicon batteries are less stable and have a shorter battery life due to the swelling and contraction of material that occurs during battery operation. We’re seeing more manufacturers partner with material scientists to create advanced technologies that help mitigate swelling, with encouraging support from government agencies such as the DOE. Tesla has been working on its own solution that it claims is six to ten times cheaper than current methods used to date. Using an “elastic binder and electrode design” and an “elastic, ion-conducting, polymer coating,” the battery is designed to accommodate swelling, but not entirely prevent it. However, not much information is available on Tesla’s progress since that announcement.
Solid-state has become the darling of the battery world over the last year, with many well-funded new entrants such as QuantumScape and SolidPower claiming to offer the next step-change in battery performance required for an all-electric future. The world’s leading OEMs and even Bill Gates have bought in, investing millions.
Instead of using traditional liquid electrolytes, solid-state batteries utilize safer, non-flammable solid electrolytes and replace the battery anode with very light and highly energetic lithium metal. This leads to very high energy density batteries, allowing for faster charging, greater range, and safer battery operation. They also handle heat better while operating at extremely cold temperatures. So what’s the catch? Well, this technology is very expensive to manufacture and scale up, which will extend the time to commercialization. Research estimates that solid-state technology will cost ~$400-$800/kWh by 2026, a far cry from the auto industry’s goal to reach $50/kWh in the coming years.
Another barrier to solid-state batteries is the amount of total energy density that can be stored in the cathodes per unit of volume. If you try to solve this with thicker cathodes, it may reduce the mechanical and thermal stability of the battery, leading to battery degradation and premature failure. Furthermore, thicker cathodes limit diffusion and decrease power, meaning solid-state still doesn’t crack the code for a perfectly optimized power to energy ratio, which is one of the primary end goals for all battery innovation.
Lastly, we come to a new chemistry outside the lithium-ion family that, like silicon, aims to use one of the most abundant, cheap, and benign materials on earth—sodium. Sodium-ion batteries are more stable and safer than lithium-ion. Although having lower energy density similar to LFP, sodium-ion batteries are expected to replace some of LFP’s share of the passenger EV and energy storage markets due to significant cost savings for the materials involved.
Chinese battery maker CATL recently made headlines for its solution improving the energy density of sodium-ion batteries, which normally offer approximately half the density of lithium-ion. CATL combines sodium-ion and lithium-ion batteries in a specific proportion and integrates them into one case, which is then controlled by a battery management system (BMS) algorithm. Although not a pure sodium-ion solution, this method achieves significant cost and safety benefits while maintaining performance.
Improving Buzzworthy Battery Chemistries Through Electrode Design
While the recent wave of battery innovation has undoubtedly produced many exciting improvements, none come without disadvantages. Enhancing energy density, mechanical stability, heat dissipation, charge time, and battery life are still needed to various degrees. All of this can be achieved, for any chemistry, at the electrode level.
Traditionally, all batteries have a 2D electrode structure composed of a flat metal foil coated with active chemical materials. In contrast, 3D electrodes use a porous metal structure with the active chemical material embedded inside during the coating process. This structural update modifies physical phenomena (e.g., diffusion) in the battery cell resulting in significant improvements for all the aforementioned key performance metrics.
As the world races toward electrification to mitigate the impacts of climate change, it’s critical that the industry takes a holistic approach, innovating batteries with both chemistry and physics in mind. New chemistry configurations are still required, but design enhancements will help make them more commercially viable, faster.
Vladimir Yufit is a battery expert with more than 20 years of experience in the field. He is a co-author of more than 70 papers in peer-reviewed journals and 15 patent applications. His research has led to the formation of a spin-out company developing energy devices for long-duration storage. He has co-founded Addionics and helped grow the company from 3 to a team of 17 people located in two different countries. He can be reached at https://www.linkedin.com/in/vladimir-yufit/