E-Mobility Engineering 015 l EMotive Scarab off-road truck dossier l In Conversation: Giulio Ornella l Hall effect and magnetic sensors focus l Challenge of batteries for heavy-duty EVs l Alpha Motor Corporation digest l Automated charging insight l HVAC systems focus

Super-fast silicon cell charging Tunnel devices come into the light Enovix has demonstrated 5-minute charging of its prototype silicon battery cells for EVs (writes Nick Flaherty). Tests on the 0.27 Ah cells demonstrate charging from 0 to 80% charge in 5.2 minutes, and achieve a greater than 98% charge capacity in under 10 minutes. The cell uses a 100% silicon anode with an energy density of 1.8 Ah/cm 3 , more than twice the 800 mAh/cm 3 of graphite anodes. “With a lithium cobalt oxide cathode in a 4.1 Ah cell, that gives a volumetric energy density of 900 Wh/litre,” said Ashok Lahiri, chief technology officer of Enovix. “With a higher performance NMC811 cathode with eight parts of nickel to one part of manganese and one part of cobalt, the cell can achieve Murata has launched its first series of high- performance coreless current sensors using tunnel magneto-resistive (TMR) elements (writes Nick Flaherty). The MRD series of open-loop current sensors integrates high-performance TMR elements. These use a magneto-resistive an energy density of 950 Wh/litre in a cell with a capacity of 106 Ah.” A key issue with silicon anodes is that they swell when charging, especially during fast charging, which can split the cell and allow the lithium electrolyte to leak, potentially causing a fire. Enovix uses a steel construction for the cell to prevent that. The 106 Ah cell has a gravimetric energy density of 320 Wh/kg, well above the present energy density of 255 Wh/kg from mainstream cells, indicating that the steel construction has not reduced the performance of the cell. The fact that the silicon anode is half the thickness of a graphite anode also helps to reduce the impact of the swelling. Enovix has also developed an architecture that enables multiple effect that occurs in a magnetic tunnel junction composed of two ferromagnets separated by a thin insulator. The insulator, typically a few nanometres thick, allows electrons to tunnel from one ferromagnet into the other in a magnetic field. In the MRD series, this provides precision measurement of both DC and AC up to 40 A with stability across an extensive temperature range. The series has a full-scale output accuracy of ±1.0% when operating between -40 C and +105 C, with a fast response time of 0.5 µs. The coreless structure of the sensors does not exhibit hysteresis effects or saturation issues, which are typical side- effects with an iron core. It also results parallel cell-to-busbar connections to minimise the impact of damage to the cell. It uses a device called BrakeFlow, a resistor with a set value placed at the busbar junction. Normally, each electrode carries a small current, resulting in negligible energy loss, but in the event of an internal short the BrakeFlow resistor regulates the current flux to the short. This limits the short area from overheating and inhibits thermal runaway. Other Enovix cells, with a 622NMC cathode, have surpassed 1000 cycles while retaining 93% of their capacity. Testing also showed that after 6 months at elevated temperatures, the cells had minimal capacity loss. That would give them a lifetime of more than 10 years. in reduced size and weight, as well as making mounting easier. The proprietary differential measurement with two TMR-based elements gives immunity from external magnetic stray fields. That makes the sensors suitable for use in environments with high levels of electromagnetic noise. Because of the highly accurate current capabilities and fast response, the devices are aimed at photovoltaic inverters, DC- DC converters, EV charging infrastructure and power conditioning systems. The sensors comply with the UL62368- 1 electrical equipment safety standard. They are supplied in SOICW16 packages as well as those with a galvanic isolation of more 4.8 kV. BATTERY CHARGING SENSORS Enovix’s cell has a steel construction to prevent swelling of the silicon anodes The MRD coreless current sensors operate between -40 C and +105 C 10 Autumn 2022 | E-Mobility Engineering