Evolution of Interfacial Phenomena Induced by Electrolyte Formulation and Hot Cycling of Anode-Free Li-Metal Batteries

Abstract

Even though the anode-free lithium metal battery (AFLMB) is the next promising energy-storage device because of its high energy density, the irreversible interfacial phenomena at the Cu/electrolyte interface are the key failure mechanisms of the AFLMBs. To the best of our knowledge, the interfacial phenomena associated with the capacity fading of AFLMBs are not reported yet. Herein, hot cycling combined with electrolyte formulation using 1% tris(trimethylsilyl) phosphite (TMSP) additive has been used as a protocol to systematically investigate the Cu/electrolyte interfacial phenomena of Li nucleation, compactness of deposited Li, inactive Li ("dead Li" and Li for solid−electrolyte interphase (SEI) formation "SEI-Li"), electrolyte decomposition, and SEI layer formation using a scanning electron microscope, scanning electron microscope-focused ion beam, titration gas chromatography, in situ gas chromatography− mass spectroscopy, and X-ray photoelectron spectroscopy, respectively. The synergy of hot cycling and the TMSP additive lowers the nucleation barrier in Li/Cu from 76.2 to 21.7 mV and increases the compactness of deposited Li from 32.3 to 43.8% and decreases "dead Li" from 45.18 to 10.86% and SEI-Li from 31.04 to 12.49% of anode-free Cu/NMC111. Because of the synergy effects, the Cu/NMC111 cell provides over 100 cycles with an average coulombic efficiency (avg. CE) of 98.6% for the first 60 cycles and a capacity retention (CR) of 60.4% at the end of the 60th cycle at 0.2/0.5 mA cm −2 charger/discharge current density, while the cell with 1 M LiPF 6 EC/DEC at 25 °C offers only an avg. CE of 92.8% for the first 15 cycles with a CR of 40.4% at the 15th cycle. The results suggest that the synergy of hot cycling and electrolyte formulation decreases the surface area of deposited Li and stabilizes the interface that suppresses inventory Li loss. This work probes the Cu/electrolyte interfacial phenomena, attributed to the failure mechanisms of AFLMBs. It also sheds light on suitable strategies to stabilize the Cu interface for stable cycling of AFLMBs.

Optimizing Current Collector Interfaces for Efficient “Anode‐Free” Lithium Metal Batteries

“…Highly concentrated ether-based electrolytes (above 4 m), further diluted by non-solvating and low-viscosity solvents, enable highly reversible Li plating with the highest CE (> 99%) and show great promise for improving the cycle life of Li metal anodes. [92,93] J. Dahn's group tested 65 different electrolyte mixtures consisting of various additives or co-solvents that are added to a base electrolyte with a double salt content. [92] For example, one of these electrolytes using a practical anode-free cathode with a high nickel content and bare Cu, tested at 0.2C/0.5C in the potential range of 3.55-4.40 V vs Li/Li + , maintains the total energy delivered for 140 cycles.…”

“…[92,93] J. Dahn's group tested 65 different electrolyte mixtures consisting of various additives or co-solvents that are added to a base electrolyte with a double salt content. [92] For example, one of these electrolytes using a practical anode-free cathode with a high nickel content and bare Cu, tested at 0.2C/0.5C in the potential range of 3.55-4.40 V vs Li/Li + , maintains the total energy delivered for 140 cycles. To increase the CE of the anode-free battery, a new cell configuration was used to properly measure and interpret cycling data.…”

“…For example, LiFSI undergoes decomposition, resulting in the formation of an inorganic LiF layer on the surface of Li into various LE or dual-electrolyte systems leading to the improvement of the CE. [91,92] Li plating can be stabilized by using high-concentration dual salt electrolytes consisting of LiFSI or LiTFSI and LiNO 3 . Recent studies [92,93] have shown that electrolytes with a high concentration of LiNO 3 (up to 2 m) can suppress LiNO 3 and Li dendrite agglomeration by forming a protective SEI layer and electrolyte oxidation of Al corrosion, leading to good cycling performance by reversible Li operation.…”

Reviving Inactive Lithium and Stabilizing Lithium Deposition for Improving the Performance of Anode-Free Lithium–Sulfur Batteries

“…Dead lithium consists of (electro)chemically formed Li-ion compounds in the SEI and electrically isolated lithium metal (Li 0 ). 20,21 Recently, inactive lithium accumulations have been identified as the principal cause for poor reversibility of lithium plating and stripping in AFLMBs. 22 Although AFLSBs show prolonged cycle life 2-fold higher than AFLMBs, they are yet insufficient.…”

“…The electrochemical performance of anode-free batteries depends on the lithium plating and stripping efficiency. − However, lithium plating and stripping are not fully reversible because of inactive lithium (dead lithium) accumulation upon cell operation. Dead lithium consists of (electro)­chemically formed Li-ion compounds in the SEI and electrically isolated lithium metal (Li 0 ). , …”