Unveiling the Mystery of LiF within Solid Electrolyte Interphase in Lithium Batteries

Accurate prelithiation of lithium ion battery SiOx anodes towards improved initial coulombic efficiency

We propose an accurate prelithiation method for SiOx anodes using ball-milling with LiF. The formation of a LiF-rich SEI layer reduces active lithium loss, resulting in excellent electrochemical performance. This study provides a new approach for developing high-performance silicon-based anodes for lithium-ion batteries.

Synergistic Anion and Solvent-Derived Interphases Enable Lithium-Ion Batteries under Extreme Conditions

Lithium-ion batteries (LIBs) face increasingly stringent demands as their application expands into new areas, including extreme temperatures and fast charging. To meet these demands, the electrolyte should enable fast lithium-ion transport and form stable interphases on electrodes simultaneously. In practice, however, improving one aspect often compromises another. For instance, the trend toward electrolytes forming anion-derived interphases typically reduces transport efficiency due to weak-solvating solvents. We propose that instead of relying on anions to form the interphase, leveraging both solvents and anions to form interphases can potentially lead to a balancing point between robust interphase formation and effective ion transport. Guided by this design principle, 2,2-difluoroethyl ethyl carbonate (DFDEC) was identified as the promising solvent. With the new electrolyte using DFDEC as the major solvent and lithium bis(fluorosulfonyl) imide (LiFSI) as the salt, graphite||LiNi0.8Mn0.1Co0.1O2 (NMC811) full cells are capable of fast charging and demonstrate long-term cycling stability with a cutoff voltage of 4.5 V. Notably, the battery shows a capacity retention of 84.3% after 500 cycles with an average Coulombic efficiency (CE) as high as 99.93%. This new electrolyte also enables stable battery cycling across a wide temperature range (-20 to 60 °C), with excellent capacity retention.

MgF2 Interface Engineering Promotes the Growth and Stability of LiF-Rich Solid-Electrolyte Interphases on Si-C

Volume expansion of the Si-C anode during the charging/discharging process causes continuous fracture/formation of the solid electrolyte interface (SEI), which leads to rapid capacity fading. Here, we designed a MgF2-modified separator (MF-PP) to construct a fluorine-rich SEI layer by generating more LiF. The robust SEI layer formed can alleviate the volume stress and prevent crack growth in Si-C electrodes. After 450 cycles, the Si-C||MF-PP half cell retained a reversible capacity of 543.2 mAh g-1, while the LFP||MF-PP||Si-C full cell maintained a reversible capacity of 103.4 mAh g-1 with high Coulombic efficiency after 100 cycles. This facile and low-cost separator modification strategy provides an easily scalable approach to develop stable Si-based anodes for next-generation high-energy-density systems.

In situ polymerization of 1,3-dioxolane and formation of fluorine/boron-rich interfaces enabled by film-forming additives for long-life lithium metal batteries

In situ polymerized 1,3-dioxolane (PDOL) is widely utilized to construct solid polymer electrolytes because of its high room-temperature ionic conductivity and good compatibility with lithium metal. However, the current polymerization additives used in PDOL do not effectively contribute to the formation of a robust solid electrolyte interphase (SEI), leading to decreased cycle life. Herein, a film-forming Lewis acid, tris(hexafluoroisopropyl) borate (THB), is demonstrated not only to be a catalyst for the ring-opening polymerization of DOL, but also an additive for the formation of a stable fluorine- and boron-rich SEI to improve the interfacial stability and suppress the Li dendrite growth. Moreover, molecular dynamics simulations and experimental results demonstrate that the introduction of THB can promote the dissociation of lithium salt and release more Li+ while the boron site can effectively restrict the free movement of TFSI- anion, thus increasing Li+ transference numbers (0.76) and ensuring the long-term cycling stability of cells. By using THB-PDOL, a stable cycling of Li‖Li symmetric cell for 600 h at a capacity of 0.5 mA h cm-2 can be achieved. Furthermore, employing THB-PDOL in Li‖LiFePO4 full cell enables a capacity retention of 98.64% after 300 cycles at 1C and a capacity retention of 95.39% after 200 cycles at a high temperature (60 °C). At the same time, this electrolyte is also suitable for the Li‖NCM523 full cell, which also achieves excellent stability of more than 180 cycles. This film-forming Lewis acid additive provides ideas for designing low-cost, high-performance PDOL-based lithium metal batteries.

High-Voltage All-Solid-State Thin-Film Lithium Batteries Enabled by LiF Interlayer

All-solid-state thin-film lithium batteries (TFBs) with high voltage are crucial for powering microelectronics systems. However, the issues of interfacial instability and poor solid contact of cathode/electrolyte films have limited their application. In this work, the preferentially orientated LiCoO2 (LCO) nanocolumns and the LCO/LiPON/Li TFBs are fabricated by in situ heating sputtering. By introducing the LiF interlayer, the solid contact of the LCO/LiPON interface is improved, enabling the high-voltage TFBs. The elemental diffusion, morphology change, and interfacial deterioration are suppressed, as demonstrated by various in situ and ex situ tests. As a result, the LCO/LiF/LiPON/Li TFB exhibits a more stable and higher capacity compared to other TFBs. This work provides guidance to improve the solid contact of TFBs and increase the performance of all-solid-state lithium batteries.

In Situ Polymerization Derived from PAN-Based Porous Membrane Realizing Double-Stabilized Interface and High Ionic Conductivity for Lithium-Metal Batteries

Polymer polyacrylonitrile (PAN), with exceptional mechanical strength and ionic conductivity, is considered a potential electrolyte. However, the huge interfacial impedance of PAN-derived C≡N polar nitrile groups and Li anode limited its application. In this study, a double-stabilized interface was integrated by in situ polymerization of DOL between electrodes and a three-dimensional (3D) porous PAN polymer matrix containing SN plasticizer and LLZTO ceramic fillers to optimize the challenge of interfacial instability. The fabricated PDOL-PAN(SN/LLZTO)-PDOL composite solid electrolyte (CSE) exhibited the maximum ionic conductivities of 1.9 × 10-3 S cm-1 at room temperature and 2.5 × 10-3 S cm-1 at 60 °C, an electrochemical stability window (ESW) of 4.9 V, and a high Li+ transference number (tLi+) of 0.65. In addition, the side reactions of the PAN/Li metal were effectively prevented by inserting PDOL between the 3D porous membrane and Li electrode. Benefiting from the superior interface compatibility and ion conductivity, the Li symmetric battery showed more than 2000 h of cyclability. The solid Li/LiFePO4 full battery delivered excellent cycling performance, showing an original specific capacity of 136.2 mAh g-1 with a capacity retention of 90.1% after 350 cycles at 1C and 60 °C. Furthermore, the cycling of solid-state Li/NCM622 batteries also proved their application potential. This work presents an effective approach to solving interface problems of the PAN electrolyte for solid lithium-metal batteries (LMBs).