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The right chemistry

18 July 2024

SPECIFYING LTO battery cell chemistry can be vital to boosting performance of mobile industrial robots, reports Owen McNally

DEMAND FOR battery-powered products has increased exponentially during our lifetime and in more recent years has been booming in the industrial sector. With more processes relying on battery-powered vehicles and devices that have wide-ranging jobs to do in varied environments, it is inevitable that the design and development of the batteries that power these products has also changed. There are now more considerations than ever when making design decisions during battery pack development, one of the critical decisions is which cell chemistry is best suited to the application of the battery pack.

The knock-on effect is that more OEMs are choosing custom lithium-ion battery pack designs to enhance the performance of their products, because off-the-shelf solutions often don’t meet the specific requirements of their application.

Mobile robotics are a relatively new technology that is in increased use across various industrial sectors and as organisations become more reliant on robots performing crucial roles, getting them to perform to an optimum level has never been more important.

Popular devices include automated guided vehicles (AGVs) used in materials handling and other applications; automated mobile robots (AMRs) for last-mile deliveries: and frame climbers in automated warehouses. This automation of more processes means the robotic devices require portable battery power systems that can maintain a continuous output, without running out of charge, or failing prematurely because of a fault or breakdown. Consequently, battery pack technology is developing at a fast pace to keep up with the development of robotics in the workplace. Choosing the right battery chemistry has become critical to ensuring reliable performance.

Lithium-based batteries are the most common choice for new industrial batteries today, because of their high energy density and capacity, giving much longer run-time between charges than any other battery chemistry. With so many types of lithium chemistries used in battery cells, it is important to consider and specify the correct cell type, pack design, and quality for different environments.

The proliferation of lithium chemistries, and of the components such as battery charge controller ICs that support lithium battery packs, mean that a robot OEM can be faced with a complex set of trade-offs to consider. The decision about the best set of trade-offs needs to be made on an application-by-application basis. A reliable custom battery pack manufacturer, Alexander Battery Technologies, will work in collaboration with OEMs to provide detailed guidance about the these and every other performance attribute of each lithium chemistry, and to advise on the best choice for the OEM’s specific mobile robot application.  For example, when it comes to mobile robotics that are required to perform in extreme temperature ranges, we often tend to turn to one of the older chemistry technologies - lithium titanate (LTO).

Mobile robots that operate in a cold environment, such as a refrigerated warehouse, need to take account of the battery temperature: a lithium cell cannot normally be charged when it is colder than 0°C. This might require the use of active in-pack heating technology to raise cell temperature above 0°C in preparation for charging. In many applications, active heating is a better solution than depositing the pack in a space at room temperature and waiting for it to draw heat from the ambient air.

Strengths and benefits

LTO batteries offer some distinct advantages over traditional lithium-ion batteries, particularly those using lithium cobalt oxide (LCO), lithium manganese oxide (LMO), or lithium iron phosphate (LFP) chemistries. The primary strengths and benefits of LTO batteries stem from their unique electrochemical properties, which provide superior performance in several critical areas.

One of the most notable strengths of LTO batteries is their exceptional safety profile. Unlike other lithium chemistries, LTO batteries exhibit a minimal risk of thermal runaway, a condition that can lead to overheating and potential combustion. This safety advantage arises from the stable LTO anode, which operates at a higher voltage (around 1.55V versus 0.5V for graphite anodes). This higher voltage reduces the risk of lithium plating and dendrite formation, which are common causes of short circuits and battery fires in traditional lithium-ion batteries.

LTO batteries are renowned for their cycle life. They can endure between 7000 to 10,000 charge-discharge cycles or more, significantly surpassing the cycle life of other lithium chemistries. This longevity is due to the minimal volume change in the LTO anode during cycling, reducing mechanical stress and degradation over time. Consequently, LTO batteries offer lower total cost of ownership, especially in applications demanding frequent cycling.

The fast-charging capability of LTO batteries is another key benefit. These batteries can be charged at rates up to 10C, allowing for full recharges in as little as 6 to 10 minutes. This rapid charging is facilitated by the high surface area and excellent conductivity of the LTO anode, which enhances ion transport and reduces resistance. This feature is particularly advantageous in applications where downtime for charging must be minimised.

LTO batteries perform well over a wide temperature range, from as low as -30°C to as high as 55°C. This thermal tolerance makes them suitable for environments where other lithium batteries would struggle, either losing capacity or failing altogether. The stable electrochemical properties of LTO in extreme temperatures ensure consistent performance and reliability.

Industrial automation and environments

In industrial settings, mobile robots are used for tasks such as material handling, inventory management, and assembly line support. The long cycle life of LTO batteries ensures these robots can operate continuously over extended periods, reducing the need for frequent battery replacements and maintenance downtime. Additionally, the rapid charging capability allows robots to quickly recharge during short breaks, maximising operational uptime.

Mobile robots in warehouses and logistics centres often operate in shifts and require batteries that can be quickly recharged between operations. LTO batteries' fast-charging ability ensures robots spend minimal time docked and more time performing tasks such as picking, packing, and transporting goods. The wide temperature tolerance of LTO batteries also allows these robots to function effectively in cold storage environments.

AGVs (autonomous guided vehicles), commonly used in manufacturing and warehouse automation, rely on robust and reliable power sources to navigate complex environments and transport heavy loads. LTO batteries' long cycle life and ability to withstand high discharge rates without significant capacity loss make them ideal for AGVs. The quick recharge capability ensures that AGVs remain operational with minimal downtime, enhancing overall productivity.

In summary

Lithium Titanate (LTO) batteries offer numerous advantages over other lithium chemistries, including superior safety, extended cycle life, rapid charging, and reliable performance across a wide temperature range.

These strengths make LTO batteries an excellent choice for powering mobile robots in industrial and business environments. Their use in industrial automation, warehouse logistics, service robots, and AGVs highlights the practical benefits of LTO batteries in enhancing efficiency, safety, and reliability in various demanding applications.

Owen McNally is principal design engineer at Alexander Battery Technologies