Battery technology is evolving rapidly and the goal seems obvious – as much capacity as possible in the smallest space at the lowest cost. While this may sometimes be true, certain applications require a different mindset. which is that.
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In the logistics sector in particular, compact, high-performance batteries enable new mobility and delivery concepts. (Bild: Gorodenkoff @ AdobeStock)
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Environmental protection and dwindling reserves of fossil fuels are driving car manufacturers to replace the internal combustion engine with an electric drive. The battery becomes the crucial element in terms of vehicle range. Developers are forced to To provide batteries that offer more and more capacity per unit volume while further reducing costs, measured in euros/kWh.
This is exactly the right approach for vehicles that have to travel long distances but are charged relatively infrequently. However, for other applications, such as rail vehicles, ships or heavy-duty vehicles, careful consideration of alternative techniques can result in lower costs and higher performance. Rather than maximizing battery capacity at the lowest cost, it is often more beneficial to optimize battery capacity through regular rapid charging – as is possible through the use of LTO technology.
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In this paper, Toshiba looks at Lithium Titanium Oxide (LTO) battery technology and how it offers significant performance and cost benefits in heavy-duty applications where batteries are frequently charged and discharged can. Using driverless transport vehicles (DTS) as an example, it is shown how LTO helps to optimize the battery and reduce the total cost of ownership.
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This is how lithium titanium oxide (LTO) battery technology works
LTO has a fundamentally different chemical structure than other batteries, making it the most powerful and robust Lithium Ion (Li-Ion) technology available today. In LTO batteries, the anode consists of a lithium titanate structure instead of the more common graphite powder.
The surface area of this material is thirty times that of carbon. This avoids the problem of rapid reversible intercalation of lithium ions into the carbon. Instead, the ions can easily occupy the voids in the crystal structure during charging, giving an LTO battery a much lower internal resistance that allows higher currents.
The spinel structure of an LTO anode can be regarded as “dimensionally stable” due to the small, if any, volume change occurring during storage and extraction of the lithium ions. This leads to a high cycle stability of the battery: even after 8000 cycles of continuous charging and discharging at 5 C from From 10 to 90 percent of the full SoC (state of charge) range, Toshiba’s latest high-performance LTO cell retained nearly 100 percent of its rated capacity and showed no noticeable degradation.
LTO has a lower cell voltage of 2.3V compared to the 3.6V of other Li-Ion cells. This results in lower specific energy, and while LTO batteries are capable of exceeding 100 Wh/kg, this is less than a comparable current NMC or LFP cell.
However, the benefit of this lower cell voltage is that it creates a safety margin that largely eliminates the risk of Li metallization. As a result, LTO cells are extremely safe and no Li dendrites are formed even during fast charging at low temperatures. In the unlikely event of an internal short circuit, LTO cells also discharge much more slowly than cells with a carbon anode. The slower chemical reaction means less heat is generated, so the risk of thermal runaway and spread (thermal propagation) is much lower than other types of Li-Ion cells. This is crucial in applications such as passenger ships.
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LTO cells in driverless transport systems
As companies strive for greater efficiency, automation is being driven across all areas of manufacturing. A particular focus is AGVs (automated guided vehicle systems – small electrically powered vehicles that can be used to move materials and goods in factories and warehouses). These are often used around the clock. Looking at the typical working profile of a small AGV, the benefits of LTO battery technology in these applications become apparent.
Around 75 percent of the time they move forward with little power consumption. Raising the load uses the most energy while lowering it Energy is recovered and returned to the battery. On a typical 20-hour day, such an AGV consumes around 4.8 kWh of energy – for around 1,200 journeys.
There are two options for the charging strategy and the selection of the optimal battery. The AGV can operate for a full workday, draining a large battery, which is then recharged in about an hour. Or a much smaller battery is recharged regularly throughout the day. In terms of working time, the two scenarios are the same, charging 60 minutes per day.
The first option with daily charging requires a battery with a capacity of 165 Ah capacity. Even if NMC cells with a very high energy density of 20 Wh/kg were used, the battery would still weigh almost 40 kg. With the second option, a battery with a significantly lower capacity of around 16.5 Ah is recharged ten times a day for six minutes during operation. The challenge is that this operation requires much faster charging – the relative charging power is 10 times higher (6C). This is made possible by the LTO technology, which can be recharged more quickly even at low temperatures without the risk of metallic lithium deposits (“lithium plating”). As a result, this solution weighs less than 10 kg despite the lower energy density, and assuming a factor of two for euros/kWh, the costs for the cells would still only be one-fifth.
Aside from the lower initial cost of the battery, its smaller size and weight will simplify the design and lower the cost of the AGV. The company is shaped by it much more efficient and new applications such as shuttles connected to the storage racks become possible.
The LTO technology can also score in terms of robustness and insensitivity: Not only is the risk of fire minimal – LTO batteries do not have to be heated to charge and during their long service life it is likely that two or three sets of NMC batteries would otherwise be required .
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Toshiba industrial lithium-ion batteries
Toshiba’s range of industrial batteries includes a 24V/22Ah LTO battery which the company developed specifically for applications such as AGVs. The battery can be operated at temperatures from -30 to +45°C and delivers up to 125 A current for 200 seconds. Measuring 247 mm × 188 mm × 165 mm and weighing 8 kg, the batteries can be connected in parallel or in series for 48 V operation. Status and diagnostic data are provided via the CAN bus.
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E-mobility: battery and safety
(Image: AdobeStock_277540900)
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How are better electric car batteries made and are they safe? Proven and new battery technologies from development to recycling, fire protection from simulation to materials to battery management and safety concepts, as well as test procedures from EMC to security. The technologies behind it can be found here.
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Conclusion
AGVs are becoming increasingly popular and to be successful they must be small, agile, reliable and inexpensive to buy and operate. Choosing the right battery technology is crucial. While the tenor for batteries in general is “more capacity at a lower cost”, choosing an LTO battery for such demanding applications can significantly reduce costs while providing a safer and more robust solution. (prm)
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