Nitrile Electrolyte Strategy for 4.9 V‐Class Lithium‐Metal Batteries Operating in Flame

Abstract

Lithium (Li)-metal batteries have garnered considerable attention as a promising high-energy-density power source beyond commercial Liion batteries. [1][2][3][4] In order to achieve the ultimate goal of high-energydensity, Li-metal anodes should be preferentially coupled with highvoltage/high-capacity cathodes. [5,6] However, the catalytic reactivity of high-voltage cathode materials leads to undesired interfacial side reactions with electrolytes, resulting in electrolyte decomposition and capacity decay upon cycling. [7,8] This issue of the high-voltage cathodes, together with strong reducing nature of Li-metal anodes, poses an obstacle to practical applications of Li-metal batteries. Besides these energy-density and longevity issues, another formidable problem of Li-metal batteries is their safety; Li dendrites grown from Li-metal anodes vigorously react with liquid electrolytes and can trigger internal short-circuit failures, leading to cell fire or explosion through uncontrolled thermal runaway. [9][10][11] The aforementioned challenges of Limetal batteries often stem from liquid electrolytes and their interfacial instability with electrodes. Conventional carbonate-based liquid electrolytes, widely used in commercial Li-ion batteries, are not stable with Limetal anodes [12] and show a limited electrochemical stability window (<4.4 V). [13,14] Ether-based (localized) high-concentration electrolytes were suggested to improve cycling performance of Li-metal batteries. However, their insufficient oxidation stability limited a cell voltage to 4.5 V. [15,16] Recently, nonflammable fluorinated electrolytes have been explored to widen electrochemical stability window and mitigate reactivity of Li-metal anodes. [17,18] However, these electrolytes contain volatile solvents with low boiling points, which thus hinders the application of resulting Li-metal batteries in hightemperature environments.In contrast to the previous studies mostly focusing on carbonate-or ether-based electrolytes that have shown the limitations in thermal tolerance and operating voltage window, herein, we propose a new class of nitrile electrolytes based on concentrated nitrile electrolytes (CNEs) containing co-additives (Li nitrate (LiNO 3 ) and indium fluoride (InF 3 )). This new nitrile electrolyte enables the stable operation of high-voltage (4.9 V-class) Li-metal cells over wide range of temperatures and even under exposure to flame. The CNE is composed of high-concentration lithium bis(fluorosulfonyl) imide (LiFSI) in a solvent mixture of succinonitrile (SN)/acetonitrile (AN). SN is known to show high oxidation stability (a prerequisite for high-voltage cells), along with ion-dissociating capability, thermal stability (boiling point of 266 °C), and nonflammability. [19][20][21] However, its poor reduction stability against Li metals leads to undesired electrochemical polymerization that forms a thick passivation layer, thereby hampering ion transport toward Li metals. [22,23] To resolve this issue, we exploit a concept of concentrated elect...

Concentrated electrolytes for rechargeable lithium metal batteries

“…However, traditional commercial electrolytes have poor tolerance to high voltage, and the CEI formed by free solvent molecules on the cathode surface has a high internal resistance, which is not conducive to long-term battery cycling [49][50][51]. At the same time, it cannot prevent the transition metal (TM) dissolution of the cathode at high voltage, which not only destroys the structure of the cathode but also causes the dissolved TM cations to be solvated in the electrolyte and migrate to the anode surface, destroying the SEI layer [40,52]. This will eventually lead to the irreversible decay of battery capacity.…”

“…The concentrated electrolyte can also inhibit the dissolution of cathodic TMs [31,52]. TM dissolution can be roughly divided into three steps.…”

Boosting the Temperature Adaptability of Lithium Metal Batteries via a Moisture/Acid‐Purified, Ion‐Diffusion Accelerated Separator

“…Figure 5i exhibits the Ragone plot of the NCM811|MS|PE|Ag 2 S|Li prototype in comparison with previously reported NCM811|Li cell models, all values were calculated based on the mass of electrode material. [21,[44][45][46][47][48][49][50] The NCM811|Li cell with MS|PE|Ag 2 S separator shows the highest power output of 2040 W kg −1 with the energy density of 408 Wh kg −1 at 5 C, which surpass the most values of the previously reported NCM811|Li metal batteries. Furthermore, the cycling stability of cell assembled with MS|PE|Ag 2 S separators is also superior to most previously reported metal batteries with other modified separators under lean electrolyte condition (Table S4, Supporting Information).…”

Critical Review on cathode–electrolyte Interphase Toward High-Voltage Cathodes for Li-Ion Batteries

“…A uniform, N-containing CEI layer was also observed on the LiNi 0.5 Co 0.2 Mn 0.3 O 2 for electrolyte with succinonitrile and fluoroethylene carbonate simultaneously as solvents [ 113 ]. Concentrated nitrile electrolyte consisting of a solvent mixture of succinonitrile and acetonitrile exhibits interfacial stability at a high cutoff voltage of 4.9 V due to the formation of uniform CEI layers [ 114 ].…”