While abbreviations for Li-ion cell chemistries – NMC, NCA, LFP, etc. – typically refer to the cathode’s elements, ‘LTO’ refers to a cell with a lithium titanate oxide anode that replaces graphite. LTO brings unique high-power cell characteristics, more comparable to a supercapacitor than a battery, creating new electrification opportunities for train OEMs.
The advantages of LTO are derived from a fundamentally different charge and discharge process – a phase transition rather than intercalation. This brings fundamental advantages: high power charging up to 20C (vs. 1-6C for NMC/g), low-temperature operation (-20°C), and a cycle life of over 20,000 cycles (vs. 2000-3000 for NMC/g). There is also little evidence of thermal runaway, cell swelling, or dendrite growth compared to NMC/g – safety features which are particularly attractive for heavy-duty sectors where batteries are subject to harsher environments.
Despite the advantages, LTO batteries have not yet had a meaningful impact on electric vehicle markets. For consumers, EV range is often the deciding factor, and the Achilles heel of LTO has always been low energy density – typically less than half that of NMC/g. This reduces the pure electric range that can be provided and drives a high upfront cost (typically ~$1000/kWh), limiting LTO to niche, low-volume applications such as electric bus prototypes and automotive stop-start systems.
In the rail sector, battery electrification will initially be led by multiple units (MU), which are trains used for passenger operations. Battery MUs often rely on overhead catenary systems, whereby the catenary directly powers the train for long stretches of track, and a battery (replacing an engine) is used to connect any gaps. This presents the ideal use case for an LTO battery – short ranges alongside fast charging and frequent cycling requirements for intermittent catenary connections throughout the day.
Indeed, emerging electric MU models are opting for LTO battery propulsion systems. In 2019, Siemens Mobility and Austrian Federal Railways (ÖBB) operated the Desiro ML ÖBB CityJet Eco with a 528kWh LTO system installed on the roof. This technology was extensively tested for over one year and evolved into the Mireo Plus B – a two-car trainset that can accommodate 120 seated passengers, travel up to 140kmph, and has a range of around 80km with battery operation. The batteries can be charged via 25kV overhead lines and by recuperating the train’s braking energy.
Siemens is already an orderbook leader with the Mireo B Plus and has 52 deliveries planned, providing LTO with at least 50% market share by 2024. The short-term potential is also high, with battery MUs emerging as the low-hanging fruit for train electrification, particularly in Europe, reflecting that LTO may finally have found its electric vehicle market.
