Thuy Duong Pham

The LiTFSI/LiDFP-based PDS MMA/BA copolymer electrolyte enables stable Li‖LFP cycling with >99% coulombic efficiency and uniform Li ⁺ transport, resulting in dendrite-free lithium deposition.

Despite the reported benefits of lithium difluorophosphate (LiDFP), studies on its physical and electrochemical properties remain limited. This work systematically investigates LiDFP and its potential for lithium metal battery (LMB) electrolytes using a combined experimental and theoretical approach. Solubility, ionic conductivity, viscosity, lithium‐ion transference number, diffusion coefficient, and contact angle are experimentally evaluated to provide a comprehensive understanding of its behavior. A key finding is the decoupling of ionic conductivity and viscosity at high concentrations. Additionally, Raman and nuclear magnetic resonance spectroscopy, along with molecular dynamics simulations, reveal the formation of large cation–anion aggregates at high concentrations, which facilitate lithium‐ion transport and contribute to the stabilization of the solid electrolyte interphase. The results reported herein emphasize the potential of LiDFP as an attractive component for advanced electrolyte formulations in energy storage, providing new insights into optimizing LMB performance.

Challenging the preference for bulky anions due to low binding energy with Li⁺ ion, the lithium thiocyanate‐polyethylene carbonate (LiSCN‐PEC) solid polymer electrolyte (SPE) demonstrates higher ionic conductivities (3.16 × 10⁻⁵ S cm⁻¹) at polymer‐in‐salt concentration (100 mol%) compared to those with lithium bis(fluorosulfonyl)imide (LiFSI, 1.01 × 10⁻⁵ S cm⁻¹) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 1.72 × 10⁻⁷ S cm⁻¹). Through the careful selection of PEC and LiSCN as components of SPE, the carbonyl stretching of PEC and the SCN⁻ stretching band as vibrational reporters provide detailed structural insights into the Li⁺ ion transport channel. Spectroscopic investigations reveal that enhanced ion aggregation alters the solvation structure around the Li⁺ and diminishes the interaction between Li⁺ and polymer (PEC) with increasing LiSCN concentrations, promoting faster segmental motion as a major transport mechanism. However, the transition observed from subionic to superionic behavior in the Walden plot indicates the onset of segmental motion decoupled charge transport pathway. The SCN⁻ vibrational spectrum elucidates the evolution from a Li–SCN–Li type chain‐like structure to a Li₂ > SCN < Li₂ type extended ion network with increasing LiSCN concentration, revealing that the ion network provides an alternative channel for Li⁺ ion transfer at higher concentrations, enhancing conductivity.

The stability of high‐energy‐density lithium metal batteries (LMBs) heavily relies on the composition of the solid electrolyte interphase (SEI) formed on lithium metal anodes. In this study, the inorganic‐rich SEI layer was achieved by incorporating bisalts additives into carbonate‐based electrolytes. Within this SEI layer, the presence of LiF, polythionate, and Li₃N was observed, generated by combining 1.0 м lithium bis(trifluoromethanesulfonyl)imide in ethylene carbonate: ethyl methyl carbonate:dimethyl carbonate in a 1 : 1 : 1 volume ratio, with the addition of 2 wt% lithium difluorophosphate and 2 wt% lithium difluoro(oxalato)borate additives (EL‐DO). Furthermore, this formulation effectively mitigated corrosion of aluminum current collectors. EL‐DO exhibited outstanding performance, including an average coulombic efficiency of 98.2 % in Li||Cu cells and a stable discharge capacity of approximately 162 mAh g⁻¹ after 200 cycles in a Li||LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) configuration. Moreover, EL‐DO displayed the potential to enhance the performance not only of LMBs but also of lithium‐ion batteries. In the case of Gr||NCM811 cell using EL‐DO, it consistently maintained high discharge capacities, even achieving around 135 mAh g⁻¹ after the 100^th cycle, surpassing the performance of other electrolytes. This study underscores the synergistic impact of bisalts additives in elevating the performance of lithium batteries.

Lithium‐sulfur batteries (LSBs) are considered a highly promising next‐generation energy storage technology due to their exceptional energy density and cost‐effectiveness. However, the practical use of current LSBs is hindered primarily by issues related to the “shuttle effect” of lithium polysulfide (LiPS) intermediates and the growth of lithium dendrites. In strongly solvating electrolytes, the solvent‐derived solid electrolyte interphase (SEI) lacks mechanical strength due to organic components, leading to ineffective lithium dendrite suppression and severe LiPS dissolution and shuttling. In contrast, the weakly solvating electrolyte (WSE) can create an anion‐derived SEI layer which can enhance compatibility with lithium metal anode, and restricting LiPS solubility. Herein, a WSE consisting of 0.4 м LiTFSI in the mixture of 1,4‐dioxane (DX):dimethoxymethane (DMM) is designed to overcome the issues associated with LSB. Surface analyses confirmed the formation of a beneficial SEI layer rich in LiF, enabling homogeneous lithium deposition with an average Coulombic efficiency CE exceeding 99% over 100 cycles. Implementing the low‐concentration WSE in Li||SPAN cells yielded an impressive initial specific capacity of 671 mAh g⁻¹. This research highlights the advantages of WSE and offers the pathway for cost‐effective electrolyte development, enabling the realization of high‐performance LSBs.

Lithium metal batteries (LMBs) have the potential to significantly increase the energy density of advanced batteries in the future. Nonetheless, the dendritic lithium structures and low Coulombic efficiency (CE) of LMBs currently impede their applied implementation. Herein, a sulfite‐based electrolyte (SBE/FEC), including 1.0 m lithium bis(fluorosulfonyl)imide in a blend of ethylene sulfite and diethyl sulfite, and 5 wt% fluoroethylene carbonate is proposed. SBE/FEC is a highly efficient inhibitor against the growth of lithium dendrites through the formation of robust solid electrolyte interphase (SEI) layer. Raman spectroscopy and theoretical calculation indicate that in SBE/FEC, a significant portion of FSI⁻ exists in associated complexes, playing a vital role in the creation of LiF‐rich passivation. Besides, the sulfite solvents decompose and yield polysulfide complexes in the SEI layer. A direct correlation between the proportion of cation–anion complexes and the contact angle between electrolyte and separator is elucidated through molecular dynamics simulations. The SBE/FEC system exhibits high CEs (98.3%) with Li||Cu cells, along with a steady discharge capacity of ≈137 mA h g⁻¹ in Li||LiFePO₄ cell. This study presents an effective approach for enhancing LMBs with sulfite‐based electrolytes, which can lead to high‐energy‐density next‐generation rechargeable batteries.

Li-metal batteries (LMBs) are regarded as next generation storage devices for applications in a wide range of fields, such as electric vehicles and grid-scale energy storage. Unfortunately, their practical applications have been restricted by some defects including safety hazards, low coulombic efficiency (CE), and lithium dendrite growth. Inspired by the low-cost electrolytes in industrial applications, a low concentration bisalt electrolyte (LBE) for practical LMBs is proposed in this work. The synergistic effect of bisalt (0.3 M lithium bis(fluorosulfonyl)imide (LiFSI) and 0.2 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)) and weakly solvating solvent (1,4-dioxane (DX)), provides robust and conductive solid/cathode electrolyte interphase (SEI/CEI) layers on the Li metal anode and LiFePO₄ (LFP) cathode, respectively. The majority of salt anions exist in associated states, such as contact ion pairs (CIPs) and aggregates (AGGs), as observed in highly concentrated electrolytes. These ion associates are involved in the formation of stable and LiF-rich SEI and CEI layers which suppress the dendrite growth on the Li anode and prevent parasitic reactions on the LFP cathode. The average CE of the Li‖Cu cells in the LBE was 99.2%. Furthermore, LBE also improved the cycling stability of a Li‖LiFP cell, with a capacity retention of 78.5% after 400 cycles. These results demonstrate the benefits of LBE, paving way for the industrial application of LCE.