Non‐Flammable Electrolyte with Lithium Nitrate as the Only Lithium Salt for Boosting Ultra‐Stable Cycling and Fire‐Safety Lithium Metal Batteries

Abstract

Lithium metal batteries (LMBs) attract considerable attention for their incomparable energy density. However, safety issues caused by uncontrollable lithium dendrites and highly flammable electrolyte limit large-scale LMBs applications. Herein, a low-cost, thermally stable, and low environmentallysensitive lithium nitrate (LiNO 3 ) is proposed as the only lithium salt to incorporate with nonflammable triethyl phosphate and fluoroethylene carbonate (FEC) co-solvent as the electrolyte anticipated to enhance the performance of LMBs. Benefiting from the presence of NO 3 − and FEC with strong solvation effect and easily reduced ability, a Li 3 N-LiF-rich stable solid electrolyte interphase is constructed. Compared to commercial electrolytes, the proposed electrolyte has a high Coulombic efficiency of 98.31% in Li-Cu test at 1 mA cm −2 of 1.0 mAh cm −2 with dendrite-free morphology. Additionally, the electrolyte system shows high voltage stability and cathode electrolyte interphase film-forming properties with stable cycling performances, which exhibit outstanding capacity retention rates of 96.39% and 83.74% after 1000 cycles for LFP//Li and NCM811//Li, respectively. Importantly, the non-flammable electrolyte delays the onset of combustion in lithium metal soft pack batteries by 255 s and reduces the peak heat release by 21.02% under the continuous external high-temperature heating condition. The novel electrolyte can contribute immensely to developing high-electrochemical-performance and high-safety LMBs.

Single‐Solvent‐Based Electrolyte Enabling a High‐Voltage Lithium‐Metal Battery with Long Cycle Life

“…A plethora of prior research has demonstrated that the development of SEI films abundant in LiF and Li 3 N on the surface of lithium metal can significantly enhance the stability of the interface of lithium metal. [57][58][59][60] Therefore, the presence of higher amounts of LiF and Li 3 N in the SEI film may serve as a fundamental factor contributing to the superior performance of FMS-based electrolyte on lithiummetal anode compared to carbonates. In the aforementioned references, Li 3 N was generated through the addition of LiNO 3 as a film-forming additive.…”

Liquid electrolyte chemistries for solid electrolyte interphase construction on silicon and lithium-metal anodes

“…101,102 To take advantage of nitrogen-containing SEI formation on the lithium-metal anode, one should pair the use of LiNO 3 as an electrolyte additive with the use of high-donor number (high-DN) ethereal solvents such as 1,2-dimethoxyethane and tetraethylene glycol dimethyl ether. 103–105 However, as the DN (21.1 kcal mol −1 ) of the NO 3 − anion exceeds those of carbonate solvents (16.4 kcal mol −1 for EC, 17 kcal mol −1 for dimethyl carbonate, 16.0 kcal mol −1 for diethyl carbonate (DEC), and 9.1 kcal mol −1 for FEC), LiNO 3 is insufficiently dissociated in conventional carbonate-based electrolytes. 61,105 This limited dissociation can be enhanced through the use of solubilizers such as tris(pentafluorophenyl)borane, indium trifluoromethanesulfonate, and lithium tetrafluoroborate, additives with different cations, and organic nitrates such as isosorbide dinitrate.…”

“…101,102 To take advantage of nitrogencontaining SEI formation on the lithium-metal anode, one should pair the use of LiNO 3 as an electrolyte additive with the use of high-donor number (high-DN) ethereal solvents such as 1,2-dimethoxyethane and tetraethylene glycol dimethyl ether. [103][104][105] However, as the DN (21.1 kcal mol −1 ) of the NO 3…”

Recent progress in nonflammable electrolytes and cell design for safe Li-ion batteries

“…76 Jiang et al 77 employed FEC as the sacrificial additive to inhibit the decomposition of TEP, which effectively extended the cycle life of the LFP‖Li cell to 900 cycles at 1C employing 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in TEP with 2% FEC as the electrolyte. Liao et al 78 developed 1.5 M LiNO 3 TEP/FEC (3 : 1) that could form a stable Li 3 N–LiF-rich SEI on the Li anode owing to the higher binding energy of FEC with Li + than TEP (−2.01 eV vs. −2.66 eV) and the lower LUMO of NO 3 − compared to TEP. The LIBs exhibited a superior capacity retention of 96.39% and 83.74% after 1000 cycles at 1C for LFP‖Li and NCM811‖Li, respectively.…”

“…161 In addition, utilizing LiNO 3 as a lithium salt leads to an ultra-stable organic–inorganic hybrid SEI film enriched with high ionic conductivity Li 3 N and LiF components, which can considerably enhance the anode stability for LIBs. 78…”