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Register a new userDesign Principles for Self-forming Interfaces Enabling Stable Lithium Metal Anodes
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Added by
Venkatasubramanian Viswanathan
Publication date
2019
fields
Physics
and research's language is
English
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The path toward Li-ion batteries with higher energy-densities will likely involve use of thin lithium metal (Li) anode (<50 $mu$m in thickness), whose cyclability today remains limited by dendrite formation and low Coulombic efficiency. Previous studies have shown that the solid-electrolyte-interface (SEI) of Li metal plays a crucial role in Li electrodeposition and stripping. However, design rules for optimal SEIs on lithium metal are not well-established. Here, using integrated experimental and modeling studies on a series of structurally-similar SEI-modifying compounds as model systems, we reveal the relationship between SEI compositions, Li deposition morphology and coulombic efficiency, and identify two key descriptors (ionicity and compactness) for high performance SEIs through integrated experimental and modeling studies. Using this understanding, we design a highly ionic and compact SEI that shows excellent cycling performance in LiCoO$_2$-Li full cells at practical current densities. Our results provide guidance for the rational selection and optimization of SEI modifiers to further improve Li metal anodes.
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Lithium metal cells are key towards achieving high specific energy and energy density for electrification of transportation and aviation. Anode-free cells are the limiting case of lithium metal cells involving no excess lithium and the highest possible specific energy. In addition, anode-free cells are easier, cheaper and safer as they avoid handling and manufacturing of lithium metal foils. Issues related to dendrite growth and poor cycling are magnified in anode-free cells due to lack of excess lithium. Electrolyte and current collector surface play a crucial role in affecting the cycling performance of anode-free cells. In this work, we have computationally screened for candidate current collectors that can nucleate lithium effectively and allow uniform growth. These are determined by the free energy of lithium adsorption and lithium surface diffusion barrier on candidate current collectors. Using density functional theory calculations, we show that Li-alloys possess ideal characteristics for Li nucleation and growth. These can lead to vastly improved specific energy compared to current transition metal current collectors.
A porous electrode resulting from unregulated Li growth is the major cause of the low Coulombic efficiency and potential safety hazards of rechargeable Li metal batteries. Strategies aiming to achieve large granular Li deposits have been extensively explored; yet, the ideal Li deposits, which consist of large Li particles that are seamlessly packed on the electrode and can be reversibly deposited and stripped, have never been achieved. Here, by controlling the uniaxial stack pressure during battery operation, a dense Li deposition (99.49% electrode density) with an ideal columnar structure has been achieved. Using multi-scale characterization and simulation, we elucidated the critical role of stack pressure on Li nucleation, growth and dissolution processes, and developed innovative strategies to maintain the ideal Li morphology during extended cycling. The precision manipulation of Li deposition and dissolution is a critical step to enable fast charging and low temperature operation for Li metal batteries.
A new class of high-performance pyrrolidinium cation based ionanofluid electrolytes with higher lithium salt concentration are developed. The electrolytes are formed by dispersing imidazolium ionic liquid functionalized TiO2 nanoparticles in low conducting, 0.6 M lithium salt doped N-alkyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr14TFSI) ionic liquid (IL) hosted electrolyte. Viscosity, ionic conductivity and thermal properties of these electrolytes are compared with well studied 0.2 M salt doped Pyr14TFSI IL-based electrolyte. The highly crystalline 0.6 M lithium salt dissolved IL-based electrolytes gradually become amorphous with the increasing dispersion of surface functionalized nanoparticles within it. The ionic conductivity of the electrolytes shows unusual viscosity decoupled characteristics and at the 5.0 wt% nanoparticle dispersion it attains a maximum value, higher than that of pure IL host. As compared to pure IL-based electrolytes, the ionanofluid electrolyte also possesses a significantly higher value of lithium ion transference number. The Li/LiMn2O4 cell with the best conducting ionanofluid electrolyte delivers a discharge capacity of about 131 mAh g-1 at 25 degree C at a current density of 24 mA g-1, much higher than that obtained in 0.2 M Li salt dissociated Pyr14TFSI electrolyte (87 mAh g-1). Superior interfacial compatibility between ionanofluid electrolyte and electrodes as indicated by the excellent rate performance with outstanding capacity retention of the cell as compared to pure IL-based analogue, further establish great application potentiality of this optimized newly developed electrolyte for safer LMBs.
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