Amidst the search for solutions, the Lithium Titanate Oxide (LTO) battery stands out. These batteries are renowned for their exceptional performance, extended lifespan, and enhanced safety features, making them a promising contender in the world of energy storage.
Toshiba’s General Manager for Battery Sales Volker Schumann spoke to Battey Technology about the use of Toshiba’s SCiB batteries in heavy-duty applications. Schumann will be a speaker at the Battery Show Europe 2023, with a presentation on the same topic.
What are the key factors driving the demand for batteries in various industries, and how is Toshiba Electronics Europe positioning itself to meet those demands?
Schumann: Electrification and decarbonization are clear driving forces behind the strong battery-demand growth. Toshiba’s SCiB batteries are mainly used in “heavy-duty” applications, such as rail, marine, off-highway commercial vehicles, trams, and buses. These applications typically require long operating hours with challenging requirements for the battery regarding operating conditions, power, lifetime, and safety. The battery has to be recharged very quickly, several times per day. Efficiency and the total cost of ownership over its lifetime are critical factors for selecting the most suitable battery technology.
For example, an electric ferry crossing a lake 20 times per day could be equipped with a huge battery that provides enough energy for the whole day and is recharged rather slowly overnight. However, an alternative approach is to use a much smaller battery that is recharged during each regular stop. The smaller capacity not only reduces the initial investment for the battery but also enables more space for passengers and increases the efficiency of the vessel by carrying less weight. But this battery will have to be able to be recharged in a few minutes and will have to last many more cycles. This is what we call “heavy-duty,” which is perfectly possible with our SCiB batteries.
The reason is that SCiB batteries use Lithium Titanium Oxide (LTO) as an active material for the anode. Toshiba is the world leader in LTO batteries, with a proven track record of more than ten years of experience in the field. LTO are the most powerful, robust, and safest Lithium-ion batteries. For the abovementioned applications, reducing the battery's size and avoiding replacements over a lifetime are more important factors for the total cost of ownership than energy density.
Can you discuss some of the battery technology innovations that Toshiba Electronics Europe offers and how they address customers’ evolving needs in terms of performance, reliability, and sustainability?
Schumann: Conventional lithium ion chemistries use graphite as the active material of the negative electrode. Fast and reversible insertion of lithium ions into the layered structure of the graphite is the key challenge for these batteries. If the ions cannot be inserted fast enough, there is a risk that they will instead form metallic lithium. Such plating will happen if the battery is charged at too high of a current or at low temperatures. The risk increases with a higher state of charge (SoC). This is the limiting factor of conventional lithium-ion batteries for fast charging and an essential factor for their capacity degradation.
In Toshiba’s SCiB battery cells, the layered graphite is replaced with Lithium Titanium Oxide (LTO), which instead has a crystalline spinel structure. In this structure, there are certain voids into which the lithium ions can be inserted and easily extracted. Therefore, SCiB batteries can be charged up to 80% in just 3 minutes—which means a charging current of 20C!—and that’s why they can be charged even at -20 degrees C. Furthermore, the crystal structure of LTO shows no volume change during charge and discharge. This “zero-strain” characteristic makes it very robust, and Toshiba’s high-power cells keeps 90% of their initial capacity even after more than 20,000 cycles with 5C/5C load profile. Finally, the higher electrochemical potential of LTO prevents the formation of lithium dendrites, minimizing the risk of internal short circuits, which could lead to thermal runaway. This makes LTO a very safe and reliable technology, one often used in critical safety applications like trains or passenger ferries.
Toshiba's SCiB contributes to the realization of a sustainable society in various ways. The electrification of many applications enables the usage of renewable energy sources. The use of LTO technology, in particular, can avoid the “oversizing” of the battery in case of demanding load profiles and hence minimize the consumption of scarce resources for their production. Additionally, the smaller battery increases the efficiency of the application, and therefore, less energy will be required in operation.
In the context of the growing electrification trend, what opportunities and challenges do you see for battery sales in the European market, and how is Toshiba Electronics Europe adapting its strategies to capitalize on these opportunities?
Schumann: Europe is particularly strong in the electrification of several specific markets. For example, Europe leads in replacing diesel engines of regional trains to cover areas without catenary by batteries. Many of these trains already use Toshiba’s SCiB battery cells, as they can meet the requirements for a long lifetime and very high safety standards. In fact, in 2018, it was the first lithium-ion battery to be approved anywhere in the world for usage in railway vehicles, meeting the highest safety integrity-level of the European Norm standards. Similarly, Europe is leading the electrification of marine vessels. And again, SCiB is already used in many electric ferries, water buses, and tugboats. It was the first lithium-ion battery to acquire certification from Nippon Kaiji Kyokai in Japan, approving it to be used in marine vessels.
Besides the pure battery-driven applications, we see more and more opportunities for vehicles with hydrogen fuel cells. For example, hydrogen buses are now scaling up in Europe. Next to the fuel cell, these buses also require a battery to buffer power peaks and enable the fuel cell to run at maximum efficiency. The high power density of LTO makes it the ideal technology for such applications. And we already see similar trends for other commercial vehicles, trucks, and maritime vessels powered by hydrogen.
Another opportunity for electrification is off-highway vehicles like the huge mining haul trucks. Mine operators are strongly motivated to replace diesel engines to reduce CO2 emissions and energy consumption. Only one of these vehicles already consumes about 350 liters of Diesel per hour. The challenge is that these trucks usually operate 24/7, leaving no time for lengthy battery recharges. Using Toshiba’s SCiB allows installing a battery that is not too big and heavy, can be recharged in a few minutes, and still enables a long lifetime without needing replacement.
Regarding your presentation, can you highlight the unique features and advantages of NTO? What potential benefits does NTO offer in terms of energy density and theoretical capacity compared to LTO?
Schumann: LTO batteries are very powerful, robust, and safe but have a lower energy density than other chemistries with a graphite anode. Niobium Titanium Oxide (NTO) keeps most of these positive characteristics, but it can offer a higher energy density.
At first glance, this is surprising. Because of its higher mass, the gravimetric capacity of Niobium (Nb) should be less. But this disadvantage is more than fully compensated by an accessible two-electron reduction to Nb(III). Hence, a key difference is that Niobium can release two electrons in the reduction, and therefore two Li+ Ions can be accommodated per Nb Atom. As a result, the gravimetric capacity of NTO is much higher than LTO and basically at the level of graphite anodes. And because NTO is more dense than graphite, the volumetric capacity is even higher. The theoretical capacity of TiNb2O7 (NTO) is 1,680 mAh/cm³ compared to 837 mAh/cm³ in the case of graphite.
What is the current status of Toshiba's development of NTO as a new anode material, from laboratory prototypes to industrial-scale products? Are there any notable milestones, challenges, or timelines in the journey towards the commercialization of NTO technology?
Schumann: NTO has many characteristics, making it a good candidate as anode material. But it isn’t easy to bring such new materials from the first test samples in the lab to commercial products. Researchers have to develop and screen hundreds to thousands of material composition candidates to find the right combination that meets the many conflicting targets. Long evaluation, especially the lifetime testing, makes this a very time-consuming effort.
For example, in the case of NTO, highly crystallized nanoparticles show the highest reversible capacity. But to enable manufacturing on a commercial scale, Toshiba first had to develop a new synthesis method. Other challenges are, e.g., the poor electric conductivity of NTO. These are just two examples that have to be overcome on the way commercialization. Since 2010, Toshiba has filed more than 90 patent families worldwide for titanium niobium oxide-related materials and battery systems.
On prototypes, Toshiba could already prove the cycle life, fast charge/discharge rate performance, and power capability of NTO cells. I expect samples of the first commercial product by next year.