Research in the field of battery electric cars focuses mainly on accumulators, aiming to extend the vehicle’s autonomy through the creation of cells with a higher energy density, but also by improving internal efficiency in order to reduce dissipation and increase the energy useful to the world. Of equal significance it is the attention paid to extending the life of the batteries themselves, also aiming to establish a circular process in which accumulators can be recycled and reused at the end of their primary use. There Society of Automotive Engineers reports how ultrasound technology shows encouraging signs in this regard, with potential benefits during the cell production process, in use on board the vehicle and at the end of its life.
With ultrasound they identify themselves sound waves characterized by a frequency lower than 20 kHz. They find application in various industrial and scientific fields, including the medical one, being the basis of the well-known ultrasound scans. Just as ultrasound allows us to look inside the human body, for example to monitor children before their birth, the basic idea is that they can be used in a similar way to observe inside the cells of high-performance batteries. voltage, with the possibility of even carrying out analyzes at the molecular level.
Traditionally, the failures and reliability problems experienced with the accumulators of electric cars derive from an electrical, mechanical or thermal overload, phenomena however often attributable to production defects of the cell itself. During the production process, therefore, ultrasound would allow for more effective quality controlfor example on any imperfections in the assembly of the electrodes or in the arrangement of the electrolyte, facilitating interventions where necessary, reducing waste and decreasing the failures that subsequently emerged during use. Furthermore, this technology would prove to be much cheaper than current computed tomographybased on the use of electromagnetic waves.
Once in the vehicle, battery monitoring is traditionally done by the BMS, which stands for Battery Management System. The BMS is essential for example to prevent phenomena of Thermal Runaway, events in which in the cell, once a limit temperature is exceeded, exothermic chemical reactions are triggered, which release heat and give rise to a self-powered overheating process. Through the sensors available also the Battery Management System monitor battery current, voltage and temperature profiles, exploiting them to indirectly estimate SoC and SoHacronyms respectively of State of Charge And State of Health, as well as indices of residual energy and accumulator deterioration. With traditional technologies, however, it is possible to obtain only estimates of these parameters and averages relating to the battery, without the possibility of carrying out direct measurements on the individual cells, thus neglecting any imbalances in the accumulator that undermine its optimal performance.
However, these aspects would no longer constitute a limitation for ultrasound technology. Through the use of ultrasonic transducers known as CMUTs, Capacity Micromachined Ultrasonic Transducers, a sound wave travels inside the cell and is received after having completely crossed it or after having been reflected at the source. The CMUTs thus generate an electronic signal which is analyzed by algorithms of Machine Learning, able to compare the input data with thousands of battery cycles at different temperatures and operating conditions previously experienced. By doing so, we obtain a real-time measurement of the SoC and SoH of the single cell, as well as an indication of the capacity and remaining life of the battery. The ultrasound technology thus allows a simplification of the traditional BMS architectures, but not only. It is in fact possible to detect possible deviations of the signals from those normally expected, which thus become clues of potential phenomena of Thermal Runaway. In this case, the BMS takes action to correct the behavior of the battery and eventually stop it immediately, also ensuring sufficient advance to prevent damage to passengers, as established by the regulatory bodies.
However, the potential benefits of ultrasound monitoring do not end there. In fact, tests are currently at a cost to exploit this technology in order to monitor and prevent the deleterious phenomena that limit the charging speed. Among these stands out the lithium plating, i.e. the deposition of metallic lithium on the anode. Finally, with a view to the end of life, ultrasound analyzes open up to a deeper understanding of the state of health of the cell, facilitating decisions about an extension of its use or its use in other contexts. There Titan Advanced Energy Solutions is among the companies that are carrying out research on ultrasound in the field of high voltage accumulators. The technology is still in an experimental state, but promising signs indicate that ultrasound may soon find its place in battery-powered vehicles.
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