Gradient Solid Electrolyte Interphase and Lithium‐Ion Solvation Regulated by Bisfluoroacetamide for Stable Lithium Metal Batteries

Solvation Structure Tuning Induces LiF/Li3 N-Rich CEI and SEI Interfaces for Superior Li/CFx Batteries

The electrode/electrolyte interfaces play an important role in the electrochemical reaction kinetics to alleviate the severe polarization and voltage hysteresis in lithium primary batteries. Herein, C5 F5 N is proposed as an electrolyte additive to tune the characteristics of the electrode/electrolyte interfaces. The Li/CFx primary battery with C5 F5 N additive exhibits an excellent discharge-specific capacity of 981.4 mAh g-1 (0.1 C), a remarkable high-rate capability of 598 mAh g-1 (15 C), and an outstanding energy/power density of 1068.7 Wh kg-1 /24362.5 W kg-1 . It also shows remarkable storage performance with 717.2 mAh g-1 at 0.1 C after storage at 55 °C for 2 months. The excellent performance of the Li/CFx batteries is closely related to the improved and stable Li3 N/LiF-rich homogeneous interfaces induced by the C5 F5 N additive, which results in uniform distribution of Li+ flux, facilitated electrochemical kinetics, and increased rate capability of Li/CFx battery. Therefore, C5 F5 N is expected to be a promising electrolyte additive, and the related electrode/electrolyte interface engineering provides an effective and facile strategy to increase the performance of the lithium primary battery.

The Anionic Chemistry in Regulating the Reductive Stability of Electrolytes for Lithium Metal Batteries

Advanced electrolyte design is essential for building high-energy-density lithium (Li) batteries, and introducing anions into the Li⁺ solvation sheaths has been widely demonstrated as a promising strategy. However, a fundamental understanding of the critical role of anions in such electrolytes is very lacking. Herein, the anionic chemistry in regulating the electrolyte structure and stability is probed by combining computational and experimental approaches. Based on a comprehensive analysis of the lowest unoccupied molecular orbitals, the solvents and anions in Li⁺ solvation sheaths exhibit enhanced and decreased reductive stability compared with free counterparts, respectively, which agrees with both calculated and experimental results of reduction potentials. Accordingly, new strategies are proposed to build stable electrolytes based on the established anionic chemistry. This work unveils the mysterious anionic chemistry in regulating the structure-function relationship of electrolytes and contributes to a rational design of advanced electrolytes for practical Li metal batteries.

Formation of NaF-rich Solid Electrolyte Interphase on Na Anode through Additive Induced Anion-enriched Structure of Na+ Solvation

High-capacity sodium (Na) anode suffer from the trouble of dendrite growth due to high reactivity, which can be overcome through inducing stable NaF-rich solid electrolyte interphase (SEI). Herein, we propose an additive strategy for realizing the anion-enriched structure of Na+ solvation to obtain NaF-rich SEI. The electron withdrawing acetyl group in 4-acetylpyridine (4-APD) increases the coordination number of PF6- in Na+ solvation sheath to facilitate PF6- decompose to NaF. Thus, the NaF-rich SEI with high mechanical stability and interfacial energy is formed to repress the growth of Na dendrites. With the 4-APD-contained electrolyte, the symmetric Na||Na cells show excellent cycling performance over 360 h at 1.0 mA cm-2. Meanwhile, enhanced stability is also achieved of Na||Na3V2(PO4)2O2F full cells with high Coulombic efficiency (97%) and capacity retention (91%) after 200 cycles.

Additive-Assisted Hydrophobic Li+ -Solvated Structure for Stabilizing Dual Electrode Electrolyte Interphases through Suppressing LiPF6 Hydrolysis

Lithium-metal batteries have attracted much attention due to their high energy density. However, the hydrolysis of LiPF₆ leads to uncontrollable Li dendrites growth and fast capacity fading. Herein, a hydrophobic Li⁺ -solvated structure is designed by inducing the hexafluoroisopropyl acrylate into the electrolyte system. Due to the alkene groups and non-polar perfluorocarbon (-CF₂ CF₂ CF₃ ) chain, a hydrophobic surface around Li-ion solvated aggregates can be obtained to protect the LiPF₆ against the attack from trace H₂ O. Moreover, the additive could also help to form an organic solid electrolyte interphase with rich polar C-F bonds, which can capture Li ions to restrain the dendrite growth. Therefore, the Li||Li symmetric cells show a stable cycling performance up to 500 h at a current density of 1 mA cm^-2 . The Li||LiNi_0.6 Co_0.2 Mn_0.2 O₂ cells show good cycling stability, exhibiting a specific capacity of 111 mAh g^-1 at 1 C with a capacity retention of 74 % after 200 cycles.

Reclaiming Inactive Lithium with a Triiodide/Iodide Redox Couple for Practical Lithium Metal Batteries

High-energy-density lithium (Li) metal batteries suffer from a short lifespan owing to apparently ceaseless inactive Li accumulation, which is accompanied by the consumption of electrolyte and active Li reservoir, seriously deteriorating the cyclability of batteries. Herein, a triiodide/iodide (I₃ ^- /I^- ) redox couple initiated by stannic iodide (SnI₄ ) is demonstrated to reclaim inactive Li. The reduction of I₃ ^- converts inactive Li into soluble LiI, which then diffuses to the cathode side. The oxidation of LiI by the delithiated cathode transforms cathode into the lithiation state and regenerates I₃ ^- , reclaiming Li ion from inactive Li. The regenerated I₃ ^- engages the further redox reactions. Furthermore, the formation of Sn mitigates the corrosion of I₃ ^- on active Li reservoir sacrificially. In working Li | LiNi_0.5 Co_0.2 Mn_0.3 O₂ batteries, the accumulated inactive Li is significantly reclaimed by the reversible I₃ ^- /I^- redox couple, improving the lifespan of batteries by twice. This work initiates a creative solution to reclaim inactive Li for prolonging the lifespan of practical Li metal batteries.

Optimizing Electrode/Electrolyte Interphases and Li-Ion Flux/Solvation for Lithium-Metal Batteries with Qua-Functional Heptafluorobutyric Anhydride

The safety and electrochemical performance of rechargeable lithium-metal batteries (LMBs) are primarily influenced by the additives in the organic liquid electrolytes. However, multi-functional additives are still rarely reported. Herein, we proposed heptafluorobutyric anhydride (HFA) as a qua-functional additive to optimize the composition and structure of the solid electrolyte interphase (SEI) at the electrode/electrolyte interface. The reduction/oxidation decomposition of the fluorine-rich HFA facilitate uniform inorganic-rich SEI and compact cathode electrolyte interphase (CEI) formation, which enables stable lithium plating during charge and suppresses the dissolution of transition-metal ions. Moreover, HFA optimizes the Li-ion solvation for stable Li plating/stripping and serves as the surfactant to enhance the wettability of the separator by the electrolyte to increase Li-ion flux. The symmetric Li∥Li cell with 1.0 wt % HFA electrolyte had an excellent cycling performance over 340 h at 1.0 mA cm^-2 with a capacity of 0.5 mAh cm^-2 while the Li∥NCM622 cell maintained high capacity retention after 250 cycles and outstanding rate performance even at 15 C.