NIE 2024 | Professor Wei Xuezhe, a doctoral supervisor at the School of Automotive Engineering at Tongji University: Towards Zero-Carbon Transportation—Electrochemical Power Systems and Their Digitization

The key points of Professor Wei Xuezhe's speech are as follows:

Since the mid-19th century, the Second Industrial Revolution brought motor and internal combustion engine technologies, promoting a major transformation in global energy use. As the practical application of scientific theories such as electromagnetism and thermodynamics, motor and internal combustion engine technologies have promoted the deep integration of science, technology and engineering, successfully establishing an energy supply system centered on electricity and oil and gas, which strongly supported the huge industrial production scale. However, it cannot be ignored that this process has also brought many adverse effects on the environment, among which the carbon emission problem has become increasingly prominent. Facing this severe challenge, countries around the world, including China, have actively taken countermeasures, especially vigorously promoting in key fields such as transportation, electricity and industry, striving to control and reduce carbon emissions in order to achieve the grand goal of sustainable development.

The low-carbonization of transportation should be carried out from two links: W2T (Well to Tank, energy end) and T2W (Tank to Wheel, power end), forming a closed-loop of W2W (Well to Tank, from energy end to power end). Electrochemical power sources are the core technology for energy and power transformation. Electrochemical power sources not only drive the zero-carbonization of the transportation energy end but also the zero-carbonization of the transportation power end. Over the past two decades or so, the exploration of three main technical routes (electronic control, motor and control, and battery and management) and three sub-routes (from hybrid power to pure electric energy and finally to fuel cells) has kicked off the power transformation. At the same time, renewable energy power generation technology has officially kicked off the energy transformation. Wind and photovoltaics have achieved parity grid connection in most areas, but consumption remains the biggest problem. Professor Wei pointed out that there are currently huge bottlenecks between energy transformation and power transformation. Although the current consensus is to promote the development of energy storage to solve this bottleneck, there are still significant differences in specific technical routes in China. Professor Wei believes that energy transformation and power transformation are scientifically speaking the integration of electrochemistry on the basis of electromagnetism and thermodynamics. At the same time, electrochemical power sources such as power batteries and fuel cells are the main energy and power combinations in the 21st century.

Professor Wei pointed out that from the perspectives of user use and vehicle design, on-board electrochemical power sources, especially lithium-ion batteries, are key independent variables in the development of power system technical routes. The progress of battery technology can drive electric vehicles to continue developing forward. In the future, the products and technical routes developed by different enterprises largely depend on their understanding of batteries. With the continuous improvement of lithium battery technology, such as adopting high-nickel plus-silicon materials, realizing large cell size and carrying out C2X design of battery packs, however, the range anxiety problem still exists, especially prominent in medium and large-sized vehicles, making it difficult to achieve full electrification. The energy density of current-generation lithium-ion batteries has approached the theoretical upper limit, and the focus of technical competition has shifted from energy density to energy replenishment speed. Different fast energy replenishment methods (fast charging, battery swapping and range extender) face different technical and commercial challenges. Under the constraint of 'zero carbon', PEMFC (Proton Exchange Membrane Fuel Cell) is the preferred option for range extender power sources for passenger cars.

Professor Wei introduced that to achieve zero carbon emissions in the transportation field, we must raise our perspective from a single terminal problem to the level of the entire energy system. At present, about 60% of China's power supply depends on thermal power generation. Against the background of achieving the goals of 'carbon peak' and 'carbon neutrality', it is expected that the proportion of renewable energy power generation in China will increase significantly. However, the wide application of renewable energy faces two major challenges: First, the spatial distribution of renewable energy is extremely uneven, and there are significant geographical differences between energy production areas and consumption areas; second, the output of renewable energy is affected by natural conditions and has large time fluctuations, which puts forward higher requirements for the stability of the power grid and the regulation ability of the power generation side. Solving these challenges is crucial for promoting the optimization of the energy structure and achieving sustainable development. In China's traditional energy system, the oil and gas architecture adjusts with 'network' (storage), and the power architecture adjusts with 'source' (power generation) to solve their respective fluctuation challenges. Considering that hydrogen energy storage has low cost but slow response speed, and battery energy storage has high cost but fast response speed, the new energy system can draw on the characteristics of both to build a hydrogen-electric complementary energy storage system to solve the previous two major challenges.

Professor Wei also pointed out that as the core technology for energy and power transformation, electrochemical power source systems themselves are sensitive, and the complexity of the application environment constitutes a contradiction. At the practical application level, we must fully consider the sensitivity of electrochemical power sources themselves and the complex characteristics of the environment, such as power control problems, power source state control problems, life prediction and optimization, and high and low temperature adaptability. And digitization is the core methodology to solve this basic contradiction between the sensitivity of electrochemical power sources and the complexity of the application environment. PEMFC and LIB, as typical electrochemical power sources, have basically the same electrochemical characteristic equations, material transport equations and heat equations. Therefore, PEMFC and LIB have the possibility of modeling integration, as well as good prospects for unified design, development, optimization and management after modeling integration. Since electrochemical power sources have similar electrochemical mechanisms and material transport mechanisms, they can be optimized under a unified multi-scale model.

Professor Wei introduced that the core methodology of digitalization becoming a full-function electrochemical power source system includes four points: 1. Digital modeling starts from the electrode mechanism down to the cloud twin; 2. Digital measurement, including in-depth measurement inside the battery and non-destructive measurement outside; 3. Digital design, covering multi-scale virtual simulation and multi-objective optimization design; 4. Digital control and management to achieve precise state optimization and active management of vehicle-network interaction.

Professor Wei believes that looking ahead, by integrating electrochemistry, information technology and power electronics technology, a new energy system that can achieve hydrogen-electric decoupling and interconnection in the future will also be an important energy system towards zero-carbon transportation. Among them, hydrogen-electric energy storage and conversion based on electrochemical principles and technology are the key technologies for W2W zero-carbonization.