In the near term, quantum sensors are being developed that can more accurately measure electric vehicle (EV) battery capacity, assess battery safety, and reduce vehicle weight. In the longer term, quantum batteries have been proposed that could dramatically improve the speed and efficiency of battery charging.
The energy remaining in an EV battery has been estimated using nitrogen-vacancy (NV) centers in diamond crystals to measure current flows. An NV center occurs when a single nitrogen atom and an adjacent empty space replace two carbon atoms in a diamond lattice. An NV center is extremely sensitive to external magnetic fields, which can be measured precisely using light and microwaves. The much higher accuracy of the quantum sensors is expected to help improve EV range estimations and reduce range anxiety.
The accuracy of existing current measurement sensors is limited due to the need to measure currents from a few amps up to hundreds of amps. That makes the sensors susceptible to noise and limits their accuracy to about 10%. As a result, current battery monitoring systems assume the batteries are drained when the charge level reaches about 10%. That safety margin effectively reduces the achievable driving range.
To improve battery capacity monitoring, a pair of NV center sensors were placed on either side of an EV battery pack busbar. The sensors react to the magnetic field created by current flowing through the busbar. One sensor measures a positive value of the magnetic field, and the other, on the opposite side, measures a negative value (Figure 1).
Since both sensors are subjected to the same level of ambient noise, subtracting the measurements eliminates the effect of the noise and improves sensitivity. The differential NV center sensors could accurately measure currents from 130 A to 10 mA over a temperature range of -45° to 85° C.
Figure 1. Prototype busbar current differential detection system showing the 2 × 2 × 1 mm NV center diamond sensor adhered to the end of a fiber (left) and the arrangement of two sensors on opposite sides of the busbar for differential measurements (right). (Image: Scientific Reports).
End-of-line testing
Quantum sensors are also being developed to speed up production line testing of EV batteries. Cell age testing is currently used where the batteries are charged and stored for up to two weeks prior to testing to identify good and bad cells. That increases costs and consumes a lot of energy.
A pilot-scale system has been developed using optically pumped quantum magnetometers (OPMs) for continuous end-of-line testing. The system has an array of OPMs to detect the small variations in the magnetic fields between good and bad battery cells. It’s been estimated that the use of quantum OPMs could save millions of dollars in a battery Gigafactory, reducing production costs by up to 30% and increasing production capacity by eliminating the need for time-consuming battery storage.
Quantum batteries
A quantum battery has been proposed that stores energy in the form of photons instead of using electrochemical reactions. The quantum battery would be charged using the phenomena of quantum entanglement and superposition.
In an electrochemical battery, the cells are charged independently. In a quantum battery, the cells are collectively charged (Figure 2). The improved performance of collective versus parallel charging is called the quantum charging advantage. For example, in a battery pack with 200 cells, quantum charging would be 200 times faster than conventional charging. Using the same power level available with a small home charger that takes ten hours to charge an electrochemical battery pack could charge a quantum battery pack in about three minutes.
Figure 2. The cells in an electrochemical battery charge independently (left) while the cells in a quantum battery are entangled and collectively charged (right). (Image: APS Physics).
Summary
The use of quantum mechanical principles can result in EV battery state of charge sensors with much higher accuracies, reducing range anxiety and other types of quantum sensors can be used for end-of-line testing of batteries in a Gigafactory, speeding production and reducing costs. Further in the future, quantum batteries have been proposed that can be charged significantly faster than electrochemical batteries further increasing the utility of EVs.
- References
Battery camera developed using quantum technology launches in key milestone for transport electrification, University of Sussex
- High‑precision robust monitoring of charge/discharge current over a wide dynamic range for electric vehicle batteries using diamond quantum sensors, Scientific Reports
- Non-invasive Current Density Imaging of Lithium-Ion Batteries, arVix
- Quantum Charging Advantage Cannot Be Extensive Without Global Operations, arVix
- Quantum sensors for end-of-line battery testing, UK Research and Innovation
- Sizing Up the Potential of Quantum Batteries, APS Physics
- Wide temperature operation of diamond quantum sensor for electric vehicle battery monitoring, Science Direct
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