A Polymerized‐Ionic‐Liquid‐Based Polymer Electrolyte with High Oxidative Stability for 4 and 5 V Class Solid‐State Lithium Metal Batteries

Abstract

the low thermal stability and flammability of liquid electrolytes employed in traditional lithium-ion batteries. Solid electrolytes also promise to enable the use of lithium metal as negative electrode, which exhibits very high specific capacity (3860 mAh g −1 ) and the lowest electrochemical potential (−3.04 V) of all chemistries, offering a pathway to batteries with energy densities of >400 Wh kg −1 and >1200 Wh L −1 on cell level when paired with a high-energy positive electrode. [2][3][4][5][6][7][8][9][10] However, the electrochemical stability window of most solid electrolytes is typically not wide enough to enable stable cycling of lithium metal versus a 4 V-class positive electrode required to reach such high energy density. [11][12][13] Instead, most solid electrolytes tend to either chemically or electrochemically reduce at the interface to lithium metal and/or oxidize at the interface to the positive electrode resulting in poor cycling performance and poor cycle life, if no passivating interphase is formed. [14,15] Furthermore, lithium metal anodes are prone to the formation of socalled lithium metal dendrites upon charging, which can penetrate into the solid electrolyte and can cause the cell to shortcircuit. Voids forming at the interface between lithium metal and solid electrolytes upon battery discharge cause current constrictions and were demonstrated to promote dendrite formation. [16][17][18][19][20] Therefore, a solid electrolyte needs to not only form a stable interface to lithium metal and the positive electrode, but must also enable stable plating and stripping of lithium metal.Compared to inorganic solid electrolytes, polymer solid electrolytes are typically more flexible and able to maintain a much more intimate contact with the electrodes during cycling, which alleviates voids formation at the interface between lithium metal and solid electrolytes. However, the low room-temperature ionic conductivity and narrow electrochemical stability window hinder their application. [21][22][23] Incorporating plasticizers into polymer solid electrolytes helps to boost the ionic conductivity at room temperature while retaining the polymer's flexibility. [24][25][26] Polymer matrices, including poly(ethylene oxide) (PEO), [26][27][28][29] polyacrylonitrile (PAN), [30,31] poly(methyl methacrylate) (PMMA), [32,33] and poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP), [34][35][36][37] and plasticizers, such as carbonates, [38][39][40] Polymer solid electrolytes for solid-state batteries typically suffer from low ionic conductivity and low oxidative stability. Herein, a polymer electrolyte based on a polymerized ionic liquid and an ionic liquid plasticizer offering simultaneously a high room-temperature ionic conductivity of 0.8 mS cm −1 and a high oxidative stability >5.0 V versus Li + /Li, is reported. The electrolyte is compatible with lithium metal and non-flammable upon direct flame exposure. In symmetric lithium metal cells, the electrolyte enables stable lithium plating and stripping at 0.1...

Are Polymer‐Based Electrolytes Ready for High‐Voltage Lithium Battery Applications? An Overview of Degradation Mechanisms and Battery Performance

“…Such ternary systems, have been recently cycled with NMC, NCA, [164,165] and even with LNMO. [166] In context, PAN and PVdF (and its derivates such as P(VdF-HFP) (poly(vinylidene fluoride)-co-hexafluoropropylene) and P(VdF-TrFE) (poly(vinylidene fluoride-co-trifluoroethylene)) were also used in CPEs and HSEs (Table 4). [30,43,[167][168][169][170][171][172][173][174] In GPEs, the electrochemical stability may be limited by the choice of the solvent or plasticizer.…”

A self-healing polymerized-ionic-liquid-based polymer electrolyte enables a long lifespan and dendrite-free solid-state Li metal batteries at room temperature

“…3(c)), which is superior to conventional organic liquid electrolytes with points of flammability near ambient temperature. 22,35 The electrochemical stability of the PIL electrolyte was investigated by the linear sweep voltammetry (LSV) measurement. According to the results in Fig.…”

Working Principles of Lithium Metal Anode in Pouch Cells

“…However, the interface between SSE and Li metal anode is not completely stable, and some SSEs even explode when in contact with molten metallic Li. [206,207] Worse, Li dendrite growth cannot be effectively solved due to the poor solid-solid interfacial contact. These challenges result in poor room-temperature cycling performance of LMBs matching SSE.…”