As a replacement for highly flammable and volatile organic liquid electrolyte, solid polymer electrolyte shows attractive practical prospect in high-energy lithium metal batteries. However, unsatisfied interface performance and ionic conductivities are two critical challenges. A common strategy involves introducing organic solvents or plasticizers, but this violates the original intention of security design. Here, an electrolyte concept called liquid polymer electrolyte without any small molecular solvents is proposed for safe and high-performance batteries, based on the design of a room-temperature liquid-state brush-like polymer as the sole solvent of lithium salts. This liquid polymer electrolyte is non-flammable and exhibits high ionic conductivity (1.09 \(\times\) 10 −4 S cm −1 at 25 °C), significant lithium dendrite suppression, and stable long-term cycling over a wide operating temperature range ( ≥ 1000 cycles at 60 °C and 90 °C). Moreover, the pouch cell can resist thermal abuse, vacuum environment, and mechanical abuse. This electrolyte and design strategy are expected to provide enlightening ideas for the development of safe and high-performance polymer electrolytes.
Constraining the electrochemical reactivity of free solvent molecules is pivotal for developing high-voltage lithium metal batteries, especially for ether solvents with high Li metal compatibility but low oxidation stability ( <4.0 V vs Li + /Li). The typical high concentration electrolyte approach relies on nearly saturated Li + coordination to ether molecules, which is confronted with severe side reactions under high voltages ( >4.4 V) and extensive exothermic reactions between Li metal and reactive anions. Herein, we propose a molecular anchoring approach to restrict the interfacial reactivity of free ether solvents in diluted electrolytes. The hydrogen-bonding interactions from the anchoring solvent effectively suppress excessive ether side reactions and enhances the stability of nickel rich cathodes at 4.7 V, despite the extremely low Li + /ether molar ratio (1:9) and the absence of typical anion-derived interphase. Furthermore, the exothermic processes under thermal abuse conditions are mitigated due to the reduced reactivity of anions, which effectively postpones the battery thermal runaway.
Polymer electrolytes with high safety and high performance are considered to be one of the most promising candidates to upgrade the traditional organic-solvent-based lithium-ion batteries. However, unlimited thermal runaway and incompatibility between electrolyte and electrode greatly limit the development of advanced polymer electrolytes. In this work, we fabricated bilayer polymer electrolytes (DLMs) with a multilevel heterostructure to achieve high-temperature self-shutdown functionality and uniform Li-ion flux. The double-layer heterostructure consists of a self-shutdown layer in contact with the cathode and an ionic liquid composite polymer layer in contact with the anode, which can achieve effective electrode–electrolyte interface contact, fast self-shutdown, and more than 900 h of stable lithium plating/stripping. In addition, the NCM523/DLM/Li battery exhibits a high reversible capacity of 129.7 mAh g −1 at 0.5 C and maintains high-capacity retention (> 89%) after 200 charge–discharge cycles. This study shows a great advantage in handling thermal abuse and a stable lithium anode, suggesting a promising approach to the high-safety lithium metal batteries.
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