Editor's Note
The impact of low temperatures on lithium-ion power batteries and proton exchange membrane fuel cell (PEMFC) stacks differs significantly. In general, low temperatures have a more severe negative effect on the performance of lithium-ion batteries compared to PEMFCs.
2.4 Comparison of Low-Temperature Performance Between Lithium Batteries and Fuel Cells
Low-temperature performance is a critical technical parameter for power batteries, especially in automotive applications. The performance of lithium-ion batteries is heavily influenced by temperature, particularly on the conductivity of electrode materials, ion diffusion coefficients, and electrolyte conductivity. At low temperatures, the viscosity of the electrolyte increases, leading to reduced ionic conductivity and higher cell polarization. As a result, the performance of lithium-ion batteries drops sharply near zero degrees Celsius, and at -20°C, they often fail to operate properly. Frequent charge and discharge cycles under such conditions can significantly degrade battery life and may lead to lithium plating on the anode, posing serious safety risks. Improving low-temperature performance usually comes at the cost of other key parameters like cycle life and energy density, which can also increase manufacturing costs.
In contrast, the main challenge for PEMFCs in cold environments is the so-called "cold start." This refers to the ability of a fuel cell electric vehicle (FC-EV) to restart within a short time after being turned off. Ice formation inside the PEMFC stack can hinder electrochemical reactions, making cold starts difficult. However, once the system is started, the heat generated during operation quickly brings the stack to its normal operating temperature range of 80–90°C, giving PEMFCs a clear advantage over lithium-ion batteries in this regard.
Extensive research has been conducted on PEMFC cold start performance below freezing. Currently, Daimler-Benz has achieved cold starts at -25°C, while Toyota, Nissan, and Honda have reached -30°C. The target for standard vehicles is around -40°C, indicating that FC-EVs still need further improvements in this area.
From the above analysis, it is evident that low temperatures affect lithium-ion batteries and PEMFC stacks differently. In particular, the negative impact on lithium-ion batteries is more pronounced.
2.5 Reliability Comparison Between Lithium-Ion Batteries and Fuel Cells
Reliability of a battery refers to its ability to consistently store electrical energy over time. While safety is closely related to reliability, the two are not the same. A safety incident in a lithium-ion battery will inevitably lead to loss of energy storage capacity. However, capacity degradation can also occur due to factors other than safety issues, such as "capacity fading" or internal failures.
Lithium-ion battery systems consist of hundreds of individual cells connected in series and parallel, meaning that the reliability of the entire system is amplified. Limited data from domestic electric vehicles suggest that the reliability of large-scale power battery systems remains unsatisfactory. The root cause of these reliability issues lies in the inherent safety concerns associated with the technology, which are determined by the fundamental characteristics of the chemical processes involved.
Before discussing PEMFC reliability, it’s worth noting that fuel cells have a long history of reliable use. PEMFCs evolved from alkaline fuel cell (AFC) technology, which was originally developed for aerospace applications. In the 1970s, United Technologies Corporation (UTC) successfully implemented AFC stacks in the U.S. space shuttle, demonstrating the high reliability of fuel cell technology.
Military applications also highlight the importance of reliability. Conventional submarines, for example, rely heavily on battery systems to extend their underwater endurance. Most current submarines use lead-acid batteries, while no major military powers have adopted lithium-ion batteries as primary power sources—especially in nuclear submarines. This is largely due to concerns about the safety and reliability of large lithium-ion battery systems in extreme environments.
In contrast, many modern conventional submarines now use PEMFC-based AIP (Air Independent Propulsion) systems. Germany, for instance, has successfully deployed PEMFCs in its 212 and 214-class submarines. These systems are designed for high reliability and have proven effective in demanding conditions. The development of PEMFCs has followed a different path compared to secondary batteries, evolving from small-scale devices to large power sources suitable for high-demand applications.
In summary, lithium-ion batteries and fuel cells serve different roles in energy storage and power generation. While lithium-ion batteries are better suited for medium and small power applications, fuel cells are ideal for high-power systems. This distinction is reflected in their design, performance, and application fields.
Based on this analysis, the author believes that lithium-ion batteries are best suited as auxiliary power sources in passenger cars, primarily used in hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and small pure electric vehicles. On the other hand, PEMFCs were developed from the beginning as large-scale power sources and are truly "power batteries," suitable for high-power applications such as FC-EVs and submarine propulsion systems.
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