A Novel Multifunctional Additive Tripropargyl Phosphate for Lithium-ion battery

Lithium-ion battery are considered the most promising candidate for high energy density. It was widely applied in digital products, electrical vehicle, energy storage devices and so on. With the increasing demand, the lithium-ion battery with high higher energy density and longer lifespan is the pursuit of  its widely application.

At present, the lithium-ion battery with liquid electrolyte can not satisfy the requirements of high energy density, longer lifespan and safety. So many researcher are dedicated to search different compound as additives to improve the performance of lithium-ion battery. Here, Yang et al. study the tripropargyl phosphate(TPP) as a novel multifunctional additive for 4.5V graphite | LiNi_0.5Mn_0.3Co_0.2O₂ pouch cell. They found that TPP can form beneficial surface films on both electrodes to enhance cycling stability of battery. 

More concretely, they compared the LSV of the baseline electrolyte, 1.0 wt% TPP-containing electrolyte. Although the TPP has an oxidation current peak at around 5.2V, which is earlier than the oxidation of the baseline electrolyte , the oxidation of its bulk electrolyte component is extended to 6.5V. The CV curves of the above electrolytes using NMC532 as the working electrode are also compared. It shows that the cell containg 1.0 wt% TPP shows oxidative current around 3.7 V during the first linear sweeping experiment, the peak is significantly shifted to the lower voltage than that of the baseline electrolyte. 

In the following, the cycling stability of graphite | NMC532 coin cell with TPP additive are studied. The long-term cycling performance of the graphite|NMC532 using base electrolyte and TPP-containing electrolyte are compared by charging and discharging each cell at a current density of 175 mA/g between 3V and 4.5V. The initial 150 cycles were conducted at 25 degrees centigrade,and afterwards the cells were cycled at 55 degrees centigrade for an additional 250 times.Small capacity decay is observed in the baseline cell after 150 cycles, the TPP cell show slightly better capacity rentention that the baseline at 25 degrees centigrade. However, the baseline cell experiences a capacity degrades rapidly at the elevated temperature and its capacity retention is just 27.6% after only 125 cycles at 55 degrees centigrade. The experiment showed that TPP-containg electrolyte demonstrate more cycling stability.

In addition, TPP can form SEI film at the graphite anode surface via polymerization of TPP, which serves as a protective layer for defending the attacks from the hydrogen ions. Moreover, the TPP additive erases the degradation of the electrolyte.  

In summary, the TPP was employed into the graphite|NMC532 full cell as a novel multifunctional additive, which significantly enhances the cycle life of the full cell at 55 degrees centigrade due to forming protective films on both electrodes.  

Reference:

W. Zhao, B. Zheng, H. Liu, et al. DOI: 10.1016/j.nanoen.2019.06.011. 

Edited by Suzhou Yacoo Science Co., Ltd.