◎ Reporter Zhang Jiaxin

With the increasing concern about environmental protection and climate change, more and more people are choosing electric vehicles as a means of transportation. However, range anxiety is still a "heart disease" for car owners. However, breakthroughs in the field of quantum technology have opened up more possibilities to solve the problem of electric vehicle range.

According to a recent report by the Nihon Keizai Shimbun, the diamond quantum sensor developed by scientists at Tokyo Institute of Technology in Japan can increase the range of electric vehicles by about 10%. The technology maximizes the performance of on-board batteries by accurately measuring the amount of stored power, and they aim to put the technology into practical use as early as 2030.

There is an error in the measurement of the electric vehicle battery

Typically, EV batteries can reach hundreds of amps, but because it is difficult to accurately measure the amount of charge, the battery is set to about 10% less than the actual amount of power that can be stored.

Liu Xiaobing, a professor at the School of Physics and Engineering of Qufu Normal University, said in an interview with a reporter from Science and Technology Daily that there are many reasons why it is difficult to measure the battery power of electric vehicles.

For example, small changes in battery voltage and current will obviously affect the detection of electric power, especially for lithium iron phosphate LiFePO4 battery, its discharge curve is gentle, the cell voltage measurement accuracy is difficult to accurately control, and any small amplitude error of the sensor may lead to a large electric power measurement error.

Second, a battery pack is usually composed of dozens of cells, and the overall performance is determined by the weakest cell. Accurate assessment of battery level requires real-time monitoring of each cell, which poses a huge challenge for space placement and cost control.

In addition, as the battery is in a constantly changing state of charge and discharge during the operation of electric vehicles, sensors are required to be able to accurately monitor these changes in real time. However, fast charge-discharge cycles and dynamic load changes can exceed the sensor's fast response capability.

"Therefore, if there is a sensor that can measure the amount of charge with high accuracy, it will be possible to make full use of the performance of the on-board battery." Liu Xiaobing said.

Diamonds are highly sought after in the field of quantum sensing

Diamonds have long been favored in the field of quantum sensing for their coherent nitrogen-vacancy (NV) centers, tunable spin, magnetic field sensitivity, and ability to operate at room temperature. Liu Xiaobing said that diamond itself has extremely high chemical stability and physical durability, and is the material with the highest hardness and best thermal conductivity in the world, which also makes diamond quantum sensors very suitable for long-term applications in harsh environments.

Tokyo Institute of Technology and Yazaki Corporation, an auto parts manufacturer, have set their sights on diamond quantum sensors. They designed a special structure in the partial crystallization of the diamond that gave it the property of fluoresceing red when irradiated with a green laser. Depending on the quantum state of the electrons inside, the intensity of the fluorescence changes. The quantum state of electrons changes due to the influence of the surrounding electric current, magnetic force, and temperature, so the magnetic force can be calculated based on the fluorescence intensity.

The sensor can reportedly be mounted on a metal part known as a "busbar". The "busbar" is the channel through which the battery transmits electricity. Conventional sensors measure current in units of 1 ampere, while newly developed sensors measure current in units of 10 milliamps, improving accuracy by a factor of 100. As a result, the battery can be charged close to what the battery can actually store, without having to reserve 10% of the space, thus extending the battery's range.

Liu Xiaobing further explained the scientific principles of diamond quantum sensors. He said that the NV center is a composite defect formed by the replacement of a carbon atom by a nitrogen atom in the diamond lattice, accompanied by a vacancy in an adjacent position, with a manipulable and readable electron spin state. Through optical excitation, the spin state can be read, and then the external environment information can be obtained. The NV center is extremely sensitive to the external environment, has nanometer spatial resolution, and has significant advantages in detecting changes in the weak electric and magnetic fields of the environment, which makes diamond quantum sensors have great potential for measuring the amount of charge.

Countries are vying for the Quantum Diamond Heights

Compared with the superconducting quantum interferometer that has been put into use, the diamond quantum sensor has higher detection sensitivity and spatial resolution, and has many advantages such as simple operation, strong environmental adaptability, and wider application range.

At present, diamond quantum sensors have also become one of the frontier fields of international quantum competition. The United States, the United Kingdom, the European Union and other Western countries have taken the NV center quantum control and quantum sensor application as the key support direction.

Yazaki Corporation aims to commercialize diamond quantum sensors for automakers and parts manufacturers by 2030 at the earliest. Although the peripherals are now larger, the size of the quantum sensor can be reduced to 10 cubic centimeters by using a small diode laser, etc., and the cost is comparable to that of conventional current sensors.

However, Muiko Hatano, a professor at Tokyo Institute of Technology, said that the biggest cost factor is diamonds. The diamonds used to make the quantum sensors are synthetic, unlike natural diamonds that are mined from mines and used in jewelry. The use of low-cost circuit boards and the mass production method of extracting diamonds from biogas can significantly reduce manufacturing costs.

Liu Xiaobing said that as a major country in the production and consumption of electric vehicles, China's quantum-level diamonds are still heavily dependent on foreign imports, which has also become an important problem in the development of new energy vehicles. At present, the team led by him has cooperated with other universities and scientific research institutions to successfully prepare artificial quantum diamonds, and China's Shandong Supercrystal New Materials Company has realized the large-scale production of centimeter-level quantum diamonds.

Liu Xiaobing believes that although diamond quantum sensors are currently facing cost challenges, considering their unique performance and potential applications, as well as the cost reduction brought about by later technological advances, the future market prospects are very worth looking forward to.