RESUMEN
The interfacial instability of high-nickel layered oxides severely plagues practical application of high-energy quasi-solid-state lithium metal batteries (LMBs). Herein, a uniform and highly oxidation-resistant polymer layer within inner Helmholtz plane is engineered by in situ polymerizing 1-vinyl-3-ethylimidazolium (VEIM) cations preferentially adsorbed on LiNi0.83Co0.11Mn0.06O2 (NCM83) surface, inducing the formation of anion-derived cathode electrolyte interphase with fast interfacial kinetics. Meanwhile, the copolymerization of [VEIM][BF4] and vinyl ethylene carbonate (VEC) endows P(VEC-IL) copolymer with the positively-charged imidazolium moieties, providing positive electric fields to facilitate Li+ transport and desolvation process. Consequently, the Li||NCM83 cells with a cut-off voltage up to 4.5â V exhibit excellent reversible capacity of 130â mAh g-1 after 1000â cycles at 25 °C and considerable discharge capacity of 134â mAh g-1 without capacity decay after 100â cycles at -20 °C. This work provides deep understanding on tailoring electric double layer by cation specific adsorption for high-voltage quasi-solid-state LMBs.
RESUMEN
Considering practical viability, Li-metal battery electrolytes should be formulated by tuning solvent composition similar to electrolyte systems for Li-ion batteries to enable the facile salt-dissociation, ion-conduction, and introduction of sacrificial additives for building stable electrode-electrolyte interfaces. Although 1,2-dimethoxyethane with a high-donor number enables the implementation of ionic compounds as effective interface modifiers, its ubiquitous usage is limited by its low-oxidation durability and high-volatility. Regulation of the solvation structure and construction of well-structured interfacial layers ensure the potential strength of electrolytes in both Li-metal and LiNi0.8Co0.1Mn0.1O2 (NCM811). This study reports the build-up of multilayer solid-electrolyte interphase by utilizing different electron-accepting tendencies of lithium difluoro(bisoxalato) phosphate (LiDFBP), lithium nitrate, and synthetic 1-((trifluoromethyl)sulfonyl)piperidine. Furthermore, a well-structured cathode-electrolyte interface from LiDFBP effectively addresses the issues with NCM811. The developed electrolyte based on a framework of highly- and weakly-solvating solvents with interface modifiers enables the operation of Li|NCM811 cells with a high areal capacity cathode (4.3 mAh cm-2) at 4.4 V versus Li/Li+.
RESUMEN
Solid-state polymer electrolytes (SPEs) are deemed as a class of sought-after candidates for high-safety and high-energy-density solid-state lithium metal batteries, but their low ionic conductivity, narrow electrochemical windows, and severe interfacial deterioration limit their practical implementations. Herein, an organoboron- and cyano-grafted polymer electrolyte (PVNB) was designed using vinylene carbonate as the polymer backbone and organoboron-modified poly(ethylene glycol) methacrylate and acrylonitrile as the grafted phases, which may facilitate Li-ion transport, immobilize the anions, and enlarge the oxidation voltage window; therefore, the well-tailored PVNB exhibits a high Li-ion transference number (tLi+ = 0.86), a wide electrochemical window (>5 V), and a high ionic conductivity (σ = 9.24 × 10-4 S cm-1) at room temperature (RT). As a result, the electrochemical cyclability and safety of the Li|LiFePO4 and Li|LiNi0.8Co0.1Mn0.1O2 cells with in situ polymerization of PVNB are substantially improved by forming the stable organic-inorganic composite cathode electrolyte interphase (CEI) and the Li3N-LiF-rich solid electrolyte interphase (SEI).
RESUMEN
To guide the selection of a suitable fluorinated ether (FE) co-solvent for lithium metal batteries, it is crucial to understand the relationship between the organic structures of the FEs and the electrochemical performance of an FE-containing electrolyte. In this work, 1,1,2,2-tetrafluoro-1-(2,2,2-trifluoroethoxy)ethane (FEE), 1,1,2,2-tetrafluoro-3-(1,1,2,2-tetrafluoroethoxy)propane (TTE), and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (OFDEE) were chosen as representative FE co-solvents because of their distinct structural properties. The structure-activity relationship between the FEs and the electrochemical performance of Li||LiNi0.6Mn0.2Co0.2O2 (Li||NMC622) cells was correlated and quantified by Fourier-transform infrared and multi-dimensional nuclear magnetic resonance techniques. Sand's model was also employed to assess the extent of lithium dendrite formation in the cells using various FE electrolytes. The cycling performance of Li||NMC622 cells using different FE co-solvents follows the order FEE > TTE > OFDEE. Since the direct measurement of Sand's time is difficult, we introduced relative Sand's time to probe the diffusion behavior of each electrolyte, and the results showed that the best performance was obtained in the electrolyte with the longest relative Sand's time. Moreover, the lithium metal cell using the electrolyte with FEE co-solvent showed similar capacity retention compared with the baseline electrolyte at room temperature, but it demonstrated significantly improved low-temperature performance. The results indicate that FEE is a promising co-solvent candidate for improving the low-temperature performance of lithium metal batteries because it possesses not only non-solvating behavior but also very low viscosity and non-flammability. The advanced electrolyte LiPF6-FEC-DMC-FEE enables very stable cycling of lithium metal batteries at various temperatures.
RESUMEN
Electrode (including cathode and anode) /electrolyte interfaces play a vital role in determining battery performance. Especially, high-voltage lithium metal batteries (HVLMBs) with the Ni-rich layered oxide ternary cathode (NCM) can be considered a promising energy storage technology due to their outstanding energy density. However, it is still extremely challenging to address the unstable electrode/electrolyte interface and structural collapse of polycrystalline NCM at high voltage, greatly restraining its practical applications. In this work, a novel electrolyte additive, tris(2-cyanoethyl) borate (TCEB), has been used to construct the robust nitrogen (N) and boron (B)-rich protective films on single-crystal LiNi0.6Co0.1Mn0.3O2 (SNCM) cathode and lithium metal anode surfaces, which could effectively mitigate parasitic reactions against electrolyte corrosion and retain the structural integrity of electrode. Remarkably, the SNCM||Li metal cell using TCEB-containing electrolyte maintains unprecedentedly superb capacity retention of 80% after 100 cycles at an ultrahigh charging voltage of 4.7 V (versus Li/Li+). This finding provides a valuable reference to construct a stable electrode/electrolyte interface for the HVLMBs with achieving high-energy density.