The lithium-ion battery system with prelithification shows high power, long life and good low temperature performance!

Recently, iChEM researchers, Professor Wangyonggang of Fudan University and his team used a simple pre-lithification method to construct the Li2V2(PO4) 3/LixC lithium-ion battery system, which shows high power, long life and good cryogenic performance.

In recent years, electric vehicles powered by lithium-ion batteries are developing rapidly. However, it is well known that the performance of lithium-ion batteries rapidly decreases as temperatures decrease. This will greatly limit the use of electric vehicles in winter or in some cold areas.

The previous studies showed that in addition to the low ion conductivity of electrolytes at low temperatures, the low temperature performance of conventional lithium-ion batteries based on graphite negative electrodes is also limited by the dissolvation/solvent of lithium-ion in and out of graphite at low temperatures. In response to this problem, the group used a prelithified hard carbon negative electrode to replace the traditional graphite negative electrode and combined positively with lithium vanadium phosphate(Li2V2(PO4) 3) to form a new battery system.

In recent years, pre-lithium hard carbon(Elithiatedhardcarbon) has been applied to hybrid lithium ion capacitors and has demonstrated excellent electrochemical properties. However, the prelithification process is complex and costly. It involves the use of pure lithium electrodes and has potential security risks. In this study, the researchers cleverly used the multi-step delithium removal process of the Li3V2(PO4) 3 positive electrode material to achieve the pre-lithification of hard carbon.

During the first charging process, lithium ions are removed from the positive pole to form Li2V2(PO4) 3, while the removed lithium ions are embedded in the hard carbon negative electrode and form a prelithium hard carbon negative electrode(LixC). Subsequently, Li2V2(PO4) 3 and LixC formed a lithium-ion battery system. When charged with 4.3 V at 3.5, the battery exhibits high power and long life similar to a supercapacitor.

In addition, although the conventional electrolyte LB303 was used, the battery showed excellent cryogenic performance. At minus 40 degrees Celsius, its capacity can maintain 67 % of room temperature capacity, far better than conventional lithium-ion batteries. This is mainly due to the good low temperature performance of the positive electrode material covered by carbon nanoparticles Li2V2(PO4) 3 and the relatively rapid dynamic process of the prelithified hard carbon negative electrode at low temperatures.

However, it is worth noting that only part of the capacity of Li3V2(PO4) 3 is used in this battery system, and the energy density is limited, making it more suitable for starting batteries. In addition, as the temperature decreases, the Ionic conductivity of the electrolyte rapidly decreases, increasing the internal resistance of the battery, so that the battery exhibits a significant polarization at low temperatures. In the follow-up study, further development of high-performance cryogenic electrolytes is needed to improve the electrochemical performance of such batteries at low temperatures.

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