In a recent breakthrough, researchers from iChEM, led by Professor Wang Yonggang from Fudan University, have developed a novel lithium-ion battery system using a simple pre-lithiation method. The system consists of Li₂V₂(PO₄)₃ as the cathode and a pre-lithiated hard carbon anode (LixC), demonstrating remarkable high power, long cycle life, and excellent low-temperature performance.
With the rapid growth of electric vehicles powered by lithium-ion batteries, their performance under cold conditions remains a major challenge. As temperatures drop, the capacity and efficiency of conventional lithium-ion batteries significantly decrease, limiting their use in colder climates or mountainous regions.
This decline is mainly due to two factors: the reduced ionic conductivity of the electrolyte at low temperatures and the difficulty of lithium ions to intercalate into and deintercalate from graphite anodes. To address this issue, the research team replaced the traditional graphite anode with a pre-lithiated hard carbon anode, paired with a lithium vanadium phosphate (Li₂V₂(PO₄)₃) cathode, creating a new battery system that overcomes these limitations.
Previously, pre-lithiated hard carbon has been used in hybrid lithium-ion capacitors, showing promising electrochemical properties. However, the traditional pre-lithiation process is complex, expensive, and involves the use of metallic lithium, which poses safety risks. In this study, the team cleverly utilized the multi-step delithiation process of the Li₃V₂(PO₄)₃ cathode material to achieve pre-lithiation of the hard carbon anode without the need for pure lithium electrodes.
During the initial charging cycle, lithium ions are extracted from the cathode, forming Li₂V₂(PO₄)₃, while the released lithium ions are embedded into the hard carbon anode, resulting in a pre-lithiated hard carbon electrode (LixC). This setup forms a stable lithium-ion battery system. When charged at 4.3 V, the battery exhibits characteristics similar to those of a supercapacitor, with high power density and long cycle life.
Even with the use of a conventional electrolyte (LB303), the battery shows outstanding low-temperature performance. At -40°C, it retains about 67% of its normal temperature capacity, far exceeding that of traditional lithium-ion batteries. This is attributed to the good low-temperature performance of the nano-carbon-coated Li₂V₂(PO₄)₃ cathode and the fast kinetics of the pre-lithiated hard carbon anode at low temperatures.
However, there are still challenges. Only a portion of the Li₃V₂(PO₄)₃ capacity is utilized in the system, limiting the energy density, making it more suitable for start-stop applications. Additionally, as the temperature decreases, the electrolyte's ionic conductivity drops rapidly, increasing internal resistance and causing significant polarization. Future research should focus on developing advanced low-temperature electrolytes to further enhance the performance of such batteries in extreme conditions.
This innovation marks a significant step forward in the development of reliable and efficient energy storage systems for electric vehicles and other low-temperature applications.
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