An official website of the United States government
Abstract A dual‐layer interphase that consists of an in‐situ‐formed lithium carboxylate organic layer and a thin BF3‐doped monolayer Ti3C2MXene on Li metal is reported. The honeycomb‐structured organic layer increases the wetting of electrolyte, leading to a thin solid electrolyte interface (SEI). While the BF3‐doped monolayer MXene provides abundant active sites for lithium homogeneous nucleation and growth, resulting in about 50% reduced thickness of inorganic‐rich components among the SEI layer. A low overpotential of less than 30 mV over 1000 h cycling in symmetric cells is received. The functional BF3 groups, along with the excellent electronic conductivity and smooth surface of the MXene, greatly reduce the lithium plating/stripping energy barrier, enabling a dendrite‐free lithium‐metal anode. The battery with this dual‐layer coated lithium metal as the anode displays greatly improved electrochemical performance. A high capacity‐retention of 175.4 mAh g−1at 1.0 C is achieved after 350 cycles. In a pouch cell with a capacity of 475 mAh, the battery still exhibits a high discharge capacity of 165.6 mAh g−1with a capacity retention of 90.2% after 200 cycles. In contrast to the fast capacity decay of pure Li metal, the battery using NCA as the cathode also displays excellent capacity retention in both coin and pouch cells. The dual‐layer modified surface provides an effective approach in stabilizing the Li‐metal anode.
more »
« less
Cryo‐Electron Tomography of Highly Deformable and Adherent Solid‐Electrolyte Interphase Exoskeleton in Li‐Metal Batteries with Ether‐Based Electrolyte
Abstract The 3D nanocomposite structure of plated lithium (LiMetal) and solid electrolyte interphases (SEI), including a polymer‐rich surficial passivation layer (SEI exoskeleton) and inorganic SEI “fossils” buried inside amorphous Li matrix, is resolved using cryogenic transmission electron microscopy. With ether‐based DOLDME‐LiTFSI electrolyte, LiF and Li2O nanocrystals are formed and embedded in a thin but tough amorphous polymer in the SEI exoskeleton. The fast Li‐stripping directions are along or , which produces eight exposed {111} planes at halfway charging. Full Li stripping produces completely sagging, empty SEI husks that can sustain large bending and buckling, with the smallest bending radius of curvature observed approaching tens of nanometers without apparent damage. In the 2nd round of Li plating, a thin LiBCCsheet first nucleates at the current collector, extends to the top end of the deflated SEI husk, and then expands its thickness. The apparent zero wetting angle between LiBCCand the SEI interior means that the heterogeneous nucleation energy barrier is zero. Due to its complete‐wetting property and chemo‐mechanical stability, the SEI largely prevents further reactions between the Li metal and the electrolyte, which explains the superior performance of Li‐metal batteries with ether‐based electrolytes. However, uneven refilling of the SEI husks results in dendrite protrusions and some new SEI formation during the 2nd plating. A strategy to form bigger SEI capsules during the initial cycle with higher energy density than the following cycles enables further enhanced Coulombic efficiency to above 99%.
more »
« less
- PAR ID:
- 10446314
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 34
- Issue:
- 13
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The utilization of alkali metal anodes is hindered by an inherent instability in organic electrolytes. Sodium is of growing interest due to its high natural abundance, but the carbonate electrolytes popular in lithium systems cannot form a stable solid electrolyte interphase (SEI) with a sodium electrode. Using half-cell and symmetric-cell analysis, we identify specific glyme (chain ether) electrolytes that produce thin, predominantly inorganic SEI at the sodium metal interface, and we study the effect of ethylene carbonate and fluoroethylene carbonate (FEC) additives on the SEI formed in these systems via X-ray photoelectron spectroscopy. Through in situ optical microscopy, we observe the onset and growth of sodium dendrites in these electrolytes. We determine that the SEI formed by glyme alone may not support extensive or extreme cycling conditions, but the addition of FEC provides a more robust SEI to facilitate numerous consistent sodium plating and stripping cycles.more » « less
-
Abstract This is the first report of a multifunctional separator for potassium‐metal batteries (KMBs). Double‐coated tape‐cast microscale AlF3on polypropylene (AlF3@PP) yields state‐of‐the‐art electrochemical performance: symmetric cells are stable after 1000 cycles (2000 h) at 0.5 mA cm−2and 0.5 mAh cm−2, with 0.042 V overpotential. Stability is maintained at 5.0 mA cm−2for 600 cycles (240 h), with 0.138 V overpotential. Postcycled plated surface is dendrite‐free, while stripped surface contains smooth solid electrolyte interphase (SEI). Conventional PP cells fail rapidly, with dendrites at plating, and “dead metal” and SEI clumps at stripping. Potassium hexacyanoferrate(III) cathode KMBs with AlF3@PP display enhanced capacity retention (91% at 100 cycles vs 58%). AlF3partially reacts with K to form an artificial SEI containing KF, AlF3, and Al2O3phases. The AlF3@PP promotes complete electrolyte wetting and enhances uptake, improves ion conductivity, and increases ion transference number. The higher of K+transference number is ascribed to the strong interaction between AlF3and FSI−anions, as revealed through19F NMR. The enhancement in wetting and performance is general, being demonstrated with ester‐ and ether‐based solvents, with K‐, Na‐, or Li‐ salts, and with different commercial separators. In full batteries, AlF3prevents Fe crossover and cycling‐induced cathode pulverization.more » « less
-
Abstract The solid electrolyte interphase (SEI) dictates the cycling stability of lithium‐metal batteries. Here, direct atomic imaging of the SEI's phase components and their spatial arrangement is achieved, using ultralow‐dosage cryogenic transmission electron microscopy. The results show that, surprisingly, a lot of the deposited Li metal has amorphous atomic structure, likely due to carbon and oxygen impurities, and that crystalline lithium carbonate is not stable and readily decomposes when contacting the lithium metal. Lithium carbonate distributed in the outer SEI also continuously reacts with the electrolyte to produce gas, resulting in a dynamically evolving and porous SEI. Sulfur‐containing additives cause the SEI to preferentially generate Li2SO4and overlithiated lithium sulfate and lithium oxide, which encapsulate lithium carbonate in the middle, limiting SEI thickening and enhancing battery life by a factor of ten. The spatial mapping of the SEI gradient amorphous (polymeric → inorganic → metallic) and crystalline phase components provides guidance for designing electrolyte additives.more » « less
-
Abstract All‐solid‐state batteries with metallic lithium (LiBCC) anode and solid electrolyte (SE) are under active development. However, an unstable SE/LiBCCinterface due to electrochemical and mechanical instabilities hinders their operation. Herein, an ultra‐thin nanoporous mixed ionic and electronic conductor (MIEC) interlayer (≈3.25 µm), which regulates LiBCCdeposition and stripping, serving as a 3D scaffold for Li0ad‐atom formation, LiBCCnucleation, and long‐range transport of ions and electrons at SE/LiBCCinterface is demonstrated. Consisting of lithium silicide and carbon nanotubes, the MIEC interlayer is thermodynamically stable against LiBCCand highly lithiophilic. Moreover, its nanopores (<100 nm) confine the deposited LiBCCto the size regime where LiBCCexhibits “smaller is much softer” size‐dependent plasticity governed by diffusive deformation mechanisms. The LiBCCthus remains soft enough not to mechanically penetrate SE in contact. Upon further plating, LiBCCgrows in between the current collector and the MIEC interlayer, not directly contacting the SE. As a result, a full‐cell having Li3.75Si‐CNT/LiBCCfoil as an anode and LiNi0.8Co0.1Mn0.1O2as a cathode displays a high specific capacity of 207.8 mAh g−1, 92.0% initial Coulombic efficiency, 88.9% capacity retention after 200 cycles (Coulombic efficiency reaches 99.9% after tens of cycles), and excellent rate capability (76% at 5 C).more » « less
