Editor's note
While it is theoretically possible to extend the driving range of electric vehicles by increasing battery capacity, this approach comes with significant trade-offs. Adding more batteries increases both cost and weight, which can negatively impact economic viability and safety. As a result, simply stacking battery loads is not a practical long-term solution.
Instead, improving the energy density of batteries has become the key focus for enhancing vehicle range. This involves increasing the specific energy of the battery, measured in watt-hours per kilogram (Wh/kg), which directly affects how far an electric vehicle can travel on a single charge.
According to Professor Ai Xinping from Wuhan University, under current vehicle design constraints, a reasonable battery configuration would be around 300 Wh/kg for a 300 km range, 400 Wh/kg for 400 km, and potentially 500 Wh/kg for a 500 km range. These targets are based on advancements in materials like high-nickel cathodes and silicon-carbon anodes.
In the short term, the industry aims to achieve 300 Wh/kg using high-nickel ternary cathodes and silicon-carbon anodes. For the medium term (by 2025), the goal is to reach 400 Wh/kg through lithium-rich manganese-based cathodes combined with high-capacity Si-C anodes. In the long run, researchers are looking into next-generation technologies such as lithium-sulfur and lithium-air batteries, which could potentially offer specific energies exceeding 500 Wh/kg.
Ai Xinping noted that by 2020, achieving 300 Wh/kg was feasible without major technical risks—except for safety concerns. For the 400 Wh/kg target, the required cathode and anode capacities are already within reach with existing materials. However, the long-term vision faces significant challenges, particularly with lithium-air and lithium-sulfur batteries.
Lithium-air batteries, which use oxygen from the air as the cathode and metallic lithium as the anode, have a theoretical energy density of up to 11,000 Wh/kg. However, several critical issues remain unresolved, including moisture control, oxygen reduction catalysis, and the stability of the lithium anode. The presence of water in the air makes it difficult to prevent unwanted reactions with lithium, while the slow oxygen reaction rate requires expensive catalysts. Additionally, lithium dendrites formed during charging pose serious safety risks.
Lithium-sulfur batteries also show promise, with a theoretical energy density of 2,600 Wh/kg. They use sulfur as the cathode and metallic lithium as the anode, offering high capacity due to sulfur’s ability to store a large number of electrons. However, they face their own set of challenges. One major issue is the formation of lithium polysulfides during discharge, which dissolve in the electrolyte and lead to a "shuttle effect," reducing efficiency and causing self-discharge.
Another problem is the poor cycle life of sulfur electrodes. Even though lab-scale tests may show good performance, real-world applications often fall short due to the high sulfur loading and thick electrode structures. For example, in the 863 Project on lithium-sulfur batteries led by Ai Xinping, lab results showed over 1,000 cycles, but real-world batteries struggle to exceed a few cycles.
Moreover, the lithium anode in these batteries is prone to dendrite growth, which can cause internal short circuits and reduce lifespan. This issue remains unsolved despite decades of research. Additionally, the low volumetric energy density of lithium-sulfur batteries limits their applicability in automotive settings, where space is at a premium.
Given these challenges, it seems unlikely that lithium-sulfur or lithium-air batteries will be widely used in power applications, especially for passenger vehicles. While they hold great potential for future development, the path to commercialization is still long and filled with technical hurdles.
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