Electric vehicles (EVs) are at the forefront of the shift toward sustainable transportation, but effective battery management remains a key challenge. A recent breakthrough in diamond quantum sensor technology enables larger, high-quality substrates, improving battery monitoring accuracy and industrial viability.
Heteroepitaxial diamond growth on a non-diamond substrate enables industrial-scale production of diamond quantum sensors for EV battery monitoring. Image Credit: Science Tokyo
Traditional monitoring techniques often struggle with precision and resistance to noise. Diamond quantum sensors offer a promising solution, leveraging nitrogen-vacancy (NV) centers to detect even the slightest changes in magnetic fields, making them well-suited for battery monitoring. Despite this potential, large-scale industrial adoption requires further optimization and seamless integration into manufacturing processes.
Diamond quantum sensors are gaining recognition for their high sensitivity in measuring magnetic and electric fields, temperature, and pressure. Their biocompatibility also makes them valuable for applications beyond energy systems. However, a major limitation has been the small size of available diamond crystal substrates—typically only a few millimeters in diameter—due to manufacturing constraints.
A recent study led by Professors Mutsuko Hatano and Takayuki Iwasaki from the Department of Electrical and Electronic Engineering at Science Tokyo, Japan, tackled this size limitation using heteroepitaxial growth technology.
Their research focuses on developing heteroepitaxial (111) diamond quantum sensors with preferentially aligned NV centers on larger substrates, a breakthrough that could enhance EV battery monitoring.
The team collaborated with Shin-Etsu Chemical Co., Ltd. and the National Institute of Advanced Industrial Science and Technology (AIST) to fabricate the diamond crystal substrates. Their findings, published in Advanced Quantum Technologies on January 18, 2025, demonstrate how diamond growth on non-diamond substrates can improve material quality and sensor performance.
The researchers successfully developed a self-standing heteroepitaxial chemical vapor deposition (CVD) diamond film with a (111) orientation, measuring 150 μm thick. This film was separated from the substrate to ensure high uniformity and crystallinity, improving industrial productivity.
A 150-μm thick NV-diamond layer was then deposited on the heteroepitaxial diamond, achieving a T2 (spin coherence time) value of 20 μs, with a substitutional nitrogen defect concentration of 8 ppm. To address the inherent miscut angle in CVD substrates, the team introduced a tilt correction mechanism, enhancing sensor performance to levels comparable to conventional substrates.
Using continuous-wave optically detected magnetic resonance spectroscopy in a fiber-top sensor setup; the team measured the NV concentration and T2* (decoherence time) at 0.05 ppm and 0.05 μs, respectively. Their gradiometer configuration, with two sensors positioned on either side of the busbar, achieved a noise floor of less than 20 nT/Hz0.5 without magnetic shielding. Additionally, the Allan deviation of magnetic field noise remained below 0.3 μT, enabling the detection of busbar currents as low as 10 mA over an accumulation time of 10 milliseconds to 100 seconds.
The ability to measure currents accurately while minimizing interference makes this sensor a promising candidate for monitoring battery systems in electric vehicles, where precision and reliability are paramount.
Mutsuko Hatano, Professor, Department of Electrical and Electronic Engineering, School of Engineering, Institute of Science Tokyo
To further enhance detection in noisy automotive environments, the team aims to increase NV center density through electron beam irradiation, improving sensitivity. They also plan to enhance fluorescence collection efficiency and extend coherence time using advanced quantum protocols for more accurate and long-lasting current detection.
This study highlights the industrial viability of quantum-grade diamond substrates and their broader applications in quantum technologies, including EV battery monitoring, medical diagnostics, and energy devices.
Hatano concluded, “This success contributes to the acceleration of quantum technologies, particularly in sectors related to sustainable development goals and well-being.”
Journal Reference:
Kajiyama, K. et. al. (2025) Heteroepitaxial (111) Diamond Quantum Sensors with Preferentially Aligned Nitrogen-Vacancy Centers for an Electric Vehicle Battery Monitor. Advanced Quantum Technologies. doi.org/10.1002/qute.202400400