Dual-anion ionic liquid electrolyte enables stable Ni-rich cathodes in lithium-metal batteries

•Co-poor Ni-rich layered cathodes (NCM88) for LMBs•Application of a highly stable ILE in LMBs•Long-term performance high-energy positive-electrode material ILE•Performance Li|NCM88|ILE cells employing thin Li electrode High-energy batteries, particular lithium are the key to achieve carbon-neutral mobility. Current lithium-ion batteries have already enabled fast-growing electric vehicles market. However, it is foreseen that fully electrified mobility and transportation can only be achieved by development metal as negative while still granting long-term cycling safety. In this work, outstanding Li-metal battery Co-poor (LiNi0.88Co0.09Mn0.03O2, NCM88) demonstrated via use dual-anion ionic liquid electrolyte (0.8Pyr14FSI-0.2LiTFSI, ILE). This enables initial specific capacity 214 mAh g−1 retention 88% over 1,000 cycles with an average Coulombic efficiency 99.94%. The Li|ILE|NCM88 energy above 560 Wh kg−1 based on combined active masses. High-energy-density lithium-metal face challenge developing functional electrolytes enabling both stabilization high-voltage positive electrodes (> 4 V versus Li+/Li). Herein, low-volatility non-flammable (ILE) incorporating two anions, bis(fluorosulfonyl) imide (FSI) bis(trifluoromethanesulfonyl)imide (TFSI), successfully applied overcome challenge, high-energy, low-Co, material, LiNi0.88Co0.09Mn0.03O2 (NCM88), batteries. With electrolyte, cathode exhibits remarkable electrochemical performance, achieving cycles. More importantly, excellent compatibility (50 μm) realization energies more than their great research efforts (LIBs) been further amplified market.1Li W. Erickson E.M. Manthiram A. High-nickel oxide lithium-based automotive batteries.Nat. Energy. 2020; 5: 26-34https://doi.org/10.1038/s41560-019-0513-0Crossref Scopus (301) Google Scholar Among investigated chemistries, nickel-rich, transition oxides appear very promising owing high capacity2Liu Oh P. Liu X. Lee M.J. 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Qin Alwast Jusys Behm R.J. al.Reducing Co-free 1.2 0.2 Mn 0.6 O 2 liquid-based electrolyte.Adv. 2001830https://doi.org/10.1002/aenm.202001830Crossref (10) distinctive way limitations instability. synergistic interplay FSI− TFSI− provides favorable interfacial passivation layers electrodes, thereby dramatically improved through effectively mitigating deterioration evidenced in-depth morphological characterization detailed CEI formed. pristine NCM88 powder together model used Rietveld refinement X-ray diffraction (XRD) pattern reported Figures 1A 1B (Rwp = 0.03963; RF 0.08328; RF2 0.13505). features hexagonal α-NaFeO2 structure9Wu (space group: R-3m) parameters: b 2.87280(6) Å; c 14.1937(4) Å. refined atomic parameters Table S1. Here, atom labeled “Li1” located interslab layer, whereas atoms “Ni1,” “Co1,” “Mn1” intralayer. slight cation mixing was allowed constraining total amount each element 1.00 0.88, respectively. no detected either letting occupancy values float changing them manually, fit goodness did not improve. morphology characterized scanning electron microscopy (SEM) revealing particles diameter 10–30 μm smaller approximately 5 (Figure 1C), consist numerous primary S1). corresponding dispersive (EDX) elemental mapping demonstrates uniform distribution elements (Ni, Co, Mn) types sizes, ICP-OES result confirms composition as-synthesized close targeted stoichiometry (Table S2). For Li||NCM88 cells, employed, contains imide-based anions.26Montanino Alessandrini Appetecchi G.B. Water-based hydrophobic liquids devices.Electrochim. 2013; 96: 124-133https://doi.org/10.1016/j.electacta.2013.02.082Crossref (61) displays verified galvanostatic stripping-plating symmetrical Li/ILE/Li S2), broad window (∼5 V) measured carbon (Super C65) working scan speed 0.1 mV s−1 S3), well rather S4). Additionally, aluminum current collector upon repeated CV scans S5). Thus, contrast LiTFSI-based organic carbonate solvents, corrosion observed Al S6).27Kühnel R.-S. Lübke Winter Balducci Suppression containing electrolytes.J. 214: 178-184https://doi.org/10.1016/j.jpowsour.2012.04.054Crossref benchmark Figure conventional commercially available solvent-based (LP30, 1M LiPF6 ethylene [EC]/DMC,1:1 volume). Both exhibit discharge greater 210 0.1C rate (1C corresponds 200 mA g−1, 2A). Whereas gradual decrease apparent LP30 90.8% after 50 cycles, 99.3% almost visible fade. 2B compares 0.3C initial-activation 0.1C. Again, 0.1C, extremely shows 97.5%, much (74.7%). insight difference given evolution profiles during (Figures 2C 2D). When LP30, evident continuously severely contrast, drop hardly noticeable Only fade curve tail, practically potential profiles. To understand reasons cycled (ILE LP30), before 3). low-magnification SEM images 3A–3C) show cracks coated edges, cycling. expected swelled might occur sample handling preparation. high-resolution micrographs clearly reveal dramatic strain generated H2-H3 high-charge cycling, especially LP30. Several seriously damaged, seen 3E, broken several parts. phenomenon essentially fresh (compare 3D 3F). addition, shown S7. presents thick mossy photographs images. appears mostly undamaged (except dendrites around edge). Its smooth clean, indicating robust solid surface. identify reason change electrolytes, inner acquiring cross-sectional focused ion-beam (FIB) possesses well-structured shape without any microcrack 3G). severe 3H) penetrating along grain particles. vertical crack likely caused mechanical stress preparation (pressing under load), then starting point offering channels penetration interior particle.28Kim U.-H. Kuo L.-Y. Kaghazchi Quaternary NCMA batteries.ACS 576-582https://doi.org/10.1021/acsenergylett.8b02499Crossref (92) turn, micrograph 3I less pronounced cracking particle. origin investigated. fact, subjected compression open porosity optimize electronic among collector. verify if merely induced pressing, set non-pressed deep (dis-)charge 3J–3L). micrographs, major indeed perfectly resemble structure those electrode, showing damage. Overall, FIB-SEM investigation indicates superior reduced (if suppressed) resulting slower aging absence implies does because broken. Indeed, case develop, leading additional degradation suspectedly, electrochemically inactive rock-salt proceeding fading impedance increase.29Yoon Kang K.H. Ryu ni-rich Li[NixCoyMn1−x−y]O2 compositional partitioning vehicles.Chem. 29: 10436-10445https://doi.org/10.1021/acs.chemmater.7b04047Crossref (134) Scholar,30Kim J.-H. S.J. Yuk Variation within capacity-fading mechanism cathode.ACS 3002-3007https://doi.org/10.1021/acsenergylett.8b02043Crossref (37) highlight tremendous difference, average-charge -discharge voltages 4A. 3.893 3.933 0.20 per cycle, buildup resistive film increases polarization taking place state, promotes decomposition.5Heist inside known another factor contributing increasing impedance.28Kim Although, severely, decreased 3.840 3.716 V, 0.63 directly translates loss stored cell, results serious crystal charge exceptionally being initially slightly viscous ion-conductive steady lines dis/charge cross de/inclining ones making system terms energy-storage capability. overall hysteresis (ΔV) calculated voltages31Li Downie L.E. Ma Qiu Dahn J.R. Study failure mechanisms LiNi0.8Mn0.1Co0.1O2 162: A1401-A1408https://doi.org/10.1149/2.1011507jesCrossref (271) 4B. Initially, ΔV (0.053 (0.118 V). 0.217 resembles line formed suggests structure. differences differential-capacity curves 5. Each distinct pe