The search for new chemical composition options for power batteries is primarily aimed at improving charge storage density, but some research is focused on increasing their service life. At least, Japanese scientists discovered Graphite anode additive for lithium-ion batteries can maintain 95.6% of its remaining capacity after 1,000 charges.
Image source: Unsplash, Igor Omilaev
The degradation of power batteries during operation is a well-known problem, although in modern electric vehicles, this problem is not serious enough to seriously affect the life of the first owner. Experts from the Japanese research institute JAIST have successfully developed an additive to the chemical composition of graphite anodes that forms a protective film on its surface during the first few charging cycles, thus preventing degradation at the same rate. The substance was named pentafluorophenylthiophene imine (FPTI).
This protective layer allows lithium ions to move between the electrolyte and anode without unwanted chemical reactions. The instability of this layer leads to increased consumption of active lithium and increased resistance, accelerating the loss of remaining capacity of the battery cell. During the experiment, FPTI was added to the electrolyte of the lithium-ion battery at a concentration of 2 to 4 mg per milliliter. This additive leads to the formation of a more stable and at the same time conductive coating on the surface of the graphite anode.
The complex molecular composition of additives has different effects on changing the performance of power batteries. Sulfur- and imine-based components are part of the protective layer, and fluorine enriches lithium compounds on the surface. Together, this reduces stray chemical reactions and promotes smoother movement of ions and lithium across the electrode-electrolyte interface. Graphite cells with an FPTI concentration of 2 mg per milliliter retained 89.4% of their initial capacity after 1000 charge cycles. Increasing the concentration to 4 mg increases the residual resource to 95.6%. The control sample without added PFTI retained only 62.7% of the initial capacity after 1000 charge cycles and already showed obvious negative dynamics after 350 charge cycles.
However, adding PFTI directly to the electrolyte increases the cathode resistance and reduces the performance of NMC cells. The researchers found that the additive only works effectively during the preparation stage of the graphite anode. Only after this do you need to start assembling the battery using standard electrolyte compositions.
The sample cell with a PFTI concentration of 4 mg/mL showed an increase in charge storage density from a baseline of 130 Wh/kg to 233 Wh/kg. Reducing the additive concentration to 2 mg/ml limits the increase in charge storage density to 192 Wh/kg. Of course, extensive testing will be needed to successfully introduce this additive into mass-produced batteries, but the experiments themselves show that classic lithium-ion batteries have good potential for further performance improvements.
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