Improving Lifetime of Lithium-Ion Cells with Electrolyte Additives

Abstract

Lithium-ion batteries are the dominant technology for electric vehicles and grid energy storage, yet improvements in lifetime across wide voltage and temperature ranges remain essential for next-generation applications. Electrolyte additives improve cell lifetime by modifying the electrode–electrolyte interphases, which govern degradation processes including lithium inventory loss, transition metal dissolution, impedance growth, and electrolyte decomposition.

In this work, nearly 25 novel additives and more than 100 additive combinations were evaluated in lithium-ion pouch cells containing layered oxide cathodes (LiNixMnyCozO2 or NMC) and olivine cathodes (LiFePO4 or LFP). Cells were tested under demanding conditions including high voltage operation up to 4.4 V and elevated temperatures up to 70 °C.

For LFP/graphite cells cycled at 70 °C, 4% vinylene carbonate (VC) emerged as an effective additive formulation. The improved performance is attributed to residual VC in the electrolyte, which suppresses the formation of lithium alkoxide species that promote Fe dissolution from the LFP positive electrode and accelerate solid electrolyte interphase growth and lithium inventory loss. While cells containing 4% VC achieved about 1500 cycles at 70 °C, they failed at room temperature due to the formation of a highly resistive negative electrode surface impedance.

To overcome this limitation, a novel additive, bis(1,3,2-dioxathiolane-2,2-dioxide) (bis-DTD), was synthesized by the author and investigated as a co-additive with lower VC concentrations. In LFP/graphite cells, the combination of 2% VC + 2% bis-DTD delivered a lifetime at 70 °C comparable to that obtained with 4% VC, while maintaining stable cycling at room temperature due to lower charge transfer resistance. This formulation enables LFP/graphite cells to operate over a wider temperature range.

Bis-DTD also dramatically improved lifetime of LiNi0.65Mn0.3Co0.05O2/graphite pouch cells cycled to 4.4 V, where electrolytes containing 2% bis-DTD retained more than 80% capacity after over 2500 cycles at 40 °C and over 5000 cycles at 20 °C. In sodium-ion cells using layered oxide cathodes paired with hard carbon, bis-DTD improved capacity retention to more than 92% after about 1100 cycles at 40 °C.

This single electrolyte additive has demonstrated significant lifetime improvements across diverse lithium-ion and sodium-ion chemistries, highlighting the potential of rational electrolyte additive design for next-generation energy storage systems.