As the global demand for electric vehicles (EVs) accelerates, the race is on to develop batteries that offer higher energy density, lower costs and reduced reliance on scarce resources like cobalt. Spinel LiNi0.5Mn1.5O4 (LNMO) has emerged as a top contender for next-generation cathodes due to its high operating voltage (4.7 V vs. Li+/Li) and cobalt-free composition. However, its commercial adoption has been stalled by a critical flaw: electrochemical instability. Standard carbonate-based electrolytes break down under the high-voltage conditions required by LNMO, leading to rapid performance fading.
Now, a team of researchers led by Huolin Xin from University of California, Irvine has developed a solution: an all-fluorinated electrolyte (AFE) that acts as a stabilizer for these high-voltage systems. Their findings were published in the journal Energy Materials and Devices on December 1, 2025.
"To boost the energy density of batteries, we need to push the voltage limits. But conventional electrolytes are like using an oil that burns off when the engine gets too hot—they simply oxidize and decompose at voltages above 4.2 V," said Peichao Zou, a former postdoctoral researcher in the research group. "Our goal was to design an electrolyte that could withstand the aggressive 4.7 V environment of LNMO cathodes."
The team's solution involves replacing traditional solvents with fluorinated counterparts combined with a boron-containing additive (TMSB). Fluorinated solvents have special chemical properties that make them resistant to oxidation. In testing, the new AFE demonstrated an impressive stability window, enduring voltages up to 6.5 V without decomposing.
The secret to this enhanced performance lies in the interface. The study reveals that the AFE promotes the formation of a robust Cathode-Electrolyte Interphase (CEI) layer rich in fluorine and boron.
"Think of the CEI layer as a protective skin that forms on the cathode," explained Peichao Zou. "With standard electrolytes, this skin is weak and keeps breaking, consuming the battery's fluid. Our fluorinated electrolyte builds a tough, stable armor that stops side reactions and prevents the metal structure of the cathode from dissolving."
The results are significant for the future of battery longevity. In comparative tests, Li//LNMO cells using the new AFE retained 84.1% of their capacity after 250 cycles at a high cut-off voltage of 4.9 V, significantly outperforming cells with standard electrolytes. Furthermore, the battery showed remarkable resilience at elevated temperatures (50°C), a common condition in real-world EV usage, where standard batteries typically degrade fastest.
While the study marks a major step forward, the team acknowledges that challenges remain, particularly regarding operation in freezing conditions. The fluorinated electrolyte currently exhibits higher viscosity, which can slow down ion movement at temperatures like -10°C.
"This study presents a facile and effective approach to promoting the commercialization of high-voltage LNMO cathodes," said Lulu Ren, a former postdoctoral researcher in the research group. "Our next steps involve optimizing the formula to improve low-temperature conductivity and fast-charging capabilities, ensuring these batteries are ready for all-climate applications."
