Fluorine-free water-in-ionomer electrolytes for sustainable lithium-ion batteries

Abstract

The continuously increasing number and size of lithium-based batteries developed for large-scale applications raise serious environmental concerns. Herein, we address the issues related to electrolyte toxicity and safety by proposing a “water-in-ionomer” type of electrolyte which replaces organic solvents by water and expensive and toxic fluorinated lithium salts by a non-fluorinated, inexpensive and non-toxic superabsorbing ionomer, lithium polyacrylate. Interestingly, the electrochemical stability window of this electrolyte is extended greatly, even for high water contents. Particularly, the gel with 50 wt% ionomer exhibits an electrochemical stability window of 2.6 V vs. platinum and a conductivity of 6.5 mS cm−1 at 20 °C. Structural investigations suggest that the electrolytes locally self-organize and most likely switch local structures with the change of water content, leading to a 50% gel with good conductivity and elastic properties. A LiTi2(PO4)3/LiMn2O4 lithium-ion cell incorporating this electrolyte provided an average discharge voltage > 1.5 V and a specific energy of 77 Wh kg−1, while for an alternative cell chemistry, i.e., TiO2/LiMn2O4, a further enhanced average output voltage of 2.1 V and an initial specific energy of 124.2 Wh kg−1 are achieved.

Development of Safe and Sustainable Dual‐Ion Batteries Through Hybrid Aqueous/Nonaqueous Electrolytes

“…Particularly noteworthy in this context are the pioneering works of Xu and co‐workers, presenting encouraging approaches to expand the (electro‐)chemical stability window (ESW) of water‐based electrolytes against decomposition by proposing a “water‐in‐salt” electrolyte (WiSE) with a 21 m (mol [salt] kg −1 [solvent]) solution of LiTFSI in water for high‐voltage aqueous LIBs . This concept has been continuously developed into “hydrate‐melt electrolytes,” “water‐in‐bisalt (WiBS),” “water‐in‐ionomer,” and “hybrid aqueous/non‐aqueous electrolytes (HANE),” yielding outstanding ESWs up to 4.1 V ( Figure 1 ) and enabling a 3.2 V battery output voltage using Li 4 Ti 5 O 12 (LTO) and LiNi 0.5 Mn 1.5 O 4 (LNMO) as active electrode materials . By following an “inhomogeneous additive” approach, even 4.0 V aqueous LIBs were realized and further combined with a new halogen conversion–intercalation chemistry in graphite .…”

Recyclable High‐Performance Polymer Electrolyte Based on a Modified Methyl Cellulose–Lithium Trifluoromethanesulfonate Salt Composite for Sustainable Energy Systems

“…If we consider the scarcity of Li and the environmental impact of Li‐containing waste, electrolyte recycling can be extremely beneficial. Research toward environmentally friendly electrolytes for sustainable energy systems is not a new concept, but the idea of a perfectly recyclable electrolyte or energy‐storage devices is rather new. The recycling of materials can increase their lifespan substantially and can be advantageous in economic aspects, which depends on the complexity of the recycling/reuse processes.…”

Thermal safety study of Li‐ion batteries under limited overcharge abuse based on coupled electrochemical‐thermal model

“…The internal resistance test proceeded until the battery voltage attends 5 V or the battery fails. Eventually, R ohm and R pol can be, respectively, calculated by Equations (1) and (2), where I represents overcharge current, U(t 1 ) is the voltage at the last sampling moment before charge termination, U(t 2 ) is the voltage at the first sampling moment after charge termination, and U(t 3 ) is the voltage after shelving for 10 minutes.…”

“…During the past few decades, Li‐ion batteries (LIBs) have gained enormous popularity with the advantages of high energy, density, no memory effect, environmentally friendly, and extended cycle life. The application of LIBs has expanded from information industry (mobile phones, personal digital assistants (PDAs), and laptops) to energy transportation (electric vehicles and solar) …”

“…The application of LIBs has expanded from information industry (mobile phones, personal digital assistants (PDAs), and laptops) to energy transportation (electric vehicles and solar). [1][2][3][4][5] However, due to the poor thermal stability of materials in LIBs, serious hazards may be induced when LIBs are under unexpected abuse conditions such as extrusion, penetration, overheat, and overcharge. [6][7][8][9][10] Thermal runaway caused by the above abuse conditions can be attributed to a series of side reaction heat generation inside the battery.…”