Lithium Bis(fluorosulfonyl)imide Research Articles

Ionic Liquid Additive Mitigating Lithium Loss and Aluminum Corrosion for High-Voltage Anode-Free Lithium Metal Batteries.

Concentrated electrolytes based on lithium bis(fluorosulfonyl)imide (LiFSI) have been proposed as an effective Li-compatible electrolyte for anode-free lithium metal batteries (AFLMBs). However, these electrolytes suffer from severe aluminum corrosion at an elevated potential. To address this issue, we propose a binary ionic liquid (IL) electrolyte additive comprising the 1-methyl-1-butyl pyrrolidinium cation (Pyr14+), difluoro(oxalate)borate anion (DFOB-), and difluorophosphate (PO2F2-) anion to mitigate the Li inventory loss and Al corrosion in 4 M LiFSI/DME electrolyte simultaneously. On the anode side, the IL additive facilitates the formation of a robust Li3N- and LiF-rich solid electrolyte interphase, promoting highly reversible Li plating/stripping and uniform Li deposition. Additionally, the ILs alter the Li+ solvation structure, leading to enhanced tLi+ and rapid Li+ desolvation kinetics. Concurrently, on the cathode side, the ILs aid in the generation of dense LiF- and AlF-rich passivation films against Al corrosion. By using the IL-added electrolyte, the Cu||LiMn0.7Fe0.3PO4 cell operates stably at 4.5 V, and the Cu||NCM613 cell with a high loading of 4.0 mA h cm-2 sustains 142 cycles until 80% capacity retention. This research contributes to a deeper understanding of the IL additive mechanism at the electrode-electrolyte interfaces and offers a straightforward approach to designing practical high-voltage AFLMB electrolytes.

Unveiling degradation mechanisms of anode-free Li-metal batteries

Anode-free Li-metal batteries (AFLMBs), in which Li+ ions from the cathode are deposited on a Cu substrate and the deposited Li-metal serves as the anode, exhibit higher energy density compared to Li-metal batteries (LMBs). However, achieving stable cycle performance, even at moderate operating conditions, is difficult and has so far hindered their practical uses. In AFLMBs, the homogeneity of solid electrolyte interphase (SEI), initially created by electrolyte reduction on Cu substrate, is not maintained during Li-metal deposition, leading to uncontrolled electrolyte decomposition. The SEI is therefore not conserved, and uneven Li deposition morphology is induced on the Cu substrate and the eventual instability of SEI leads to the overall degradation of AFLMBs. Here, we report on the failure mechanisms of AFLMBs through a comparative study with LMBs using 3 M lithium bis(fluorosulfonyl)imide (LiFSI) dissolved in N,N-dimethylsulfamoyl fluoride. Our investigation reveals that the SEI inhomogeneity in AFLMBs makes Li+ transport through SEI sluggish and non-uniform, triggering local compositional changes of the initially formed SEI on the Cu substrate and unwanted consumption of FSI– anion from the electrolyte. This work provides clear understanding to the interfacial engineering and important roles of Li-metal on the Cu substrate in AFLMBs, promising the creation of stable SEI, reversible electrochemical reaction of Li-metal, and interfacial stability of the cathode in LMBs.

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.

Solvation Regulation via Hydrogen Bonding to Mitigate Al Current Collector Corrosion for High‐Voltage Li‐Ion Batteries

AbstractThe exceptional thermal stability and conductivity of lithium bis(fluorosulfonyl)imide (LiFSI) have made it a preferred salt for lithium‐ion batteries (LIBs). However, the corrosion of aluminum (Al) current collectors by LiFSI at low potentials (3.8 V vs Li/Li+) poses a persistent challenge, hindering the application of LiFSI in 4 V‐class LIBs. Herein, 2,2,2‐trifluoroethyl methanesulfonate (TFMS) is proposed as a versatile co‐solvent to address the issue of Al current collector corrosion. It is demonstrated that incorporating TFMS into a conventional LiFSI‐based carbonate electrolyte can precisely tailor the Li+ solvation structure by hydrogen bonding interactions with dimethyl carbonate (DMC) solvent. This weakens the coordination between DMC and Li+ while increasing the participation of FSI− anions in the primary solvation shell, effectively suppressing the Al current collector caused by free FSI− anions attacking. Furthermore, TFMS and FSI− synergically induce the formation of an inorganic‐rich and compact cathode electrolyte interphase, significantly avoiding undesired side reactions. As a result, the TFMS‐electrolyte enables 1.2 Ah‐graphite||NCM811 (LiNi0.8Co0.1Mn0.1O2) pouch‐cells to achieve 89.9% capacity retention with high average Coulombic efficiency of >99.9% for 200 cycles at a cut‐off voltage of 4.4 V, opening up opportunities for the development of advanced high‐voltage LIBs.

On the moisture tolerance of LiFSI based lithium-ion batteries: A systematic study on NMC622/graphite full cells

Lithium-ion battery (LIB) technology is state-of-the-art energy storage technology for portable electronics and electric vehicles (EVs). In this incumbent LIB technology, lithium hexafluorophosphate (LiPF6) is the most widely used electrolyte salt to date. However, the challenges related to its chemical/thermal stability, sensitivity to moisture and the consequent formation of strong acids such as hydrogen fluoride (HF) need to be resolved with alternative salts. Due to its better chemical/thermal stability, resistance to moisture and HF formation, and better ionic conductivity, lithium bis(fluorosulfonyl)imide (LiFSI) has been considered as a promising alternative electrolyte salt to LiPF6. In this study, the effect of addition of 1000 ppm water on LiFSI based electrolytes was systematically investigated by testing NMC622/lithium and artificial graphite/lithium half and NMC622/graphite full cells in four LiFSI based electrolytes; plain LiFSI, LiFSI + 1000 ppm H2O, LiFSI + 10 wt% FEC, and LiFSI + 1000 ppm H2O + 10 wt% FEC. Post mortem characterization of selected electrodes was also conducted with SEM imaging and XPS to study the surface chemistry and morphology of cycled electrodes. Overall, this study shows that 1000 ppm water can slightly improve the electrochemical performance of NMC622/lithium half cells; however, the same amount of moisture severly degrades the graphite half and NMC622/graphite full cells.

Understanding Li6.24La3Zr2Al0.24O11.98 effect on poly(ionic liquid)-based electrolytes for high voltage solid-state lithium batteries working at room temperature

Hybrid electrolytes composed of poly(ionic liquid), ionic liquids (ILs), and fillers are very promising candidates for solid-state lithium metal batteries (SSLMBs). However, a significant knowledge gap in the field of hybrid electrolytes lies in the understanding of filler effect on properties and performance. Herein, we have investigated hybrid electrolytes based on poly(diallyldimethylammonium) bis(fluorosulfonyl)imide (PDDA-FSI), N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (PYR13FSI), lithium bis(fluorosulfonyl)imide (LiFSI) and different loadings (from 0 to 19.2 vol%) of Li6.24La3Zr2Al0.24O11.98 (Al-LLZO) particles. All the electrolytes present a homogeneous morphology and excellent thermal stability. Moreover, our results demonstrate that Al-LLZO particles do not contribute to the ionic conductivity of the hybrid electrolytes. A 2.6 vol% of Al-LLZO led to the excellent performance in full cells at room temperature. Surprisingly, the battery performance was not correlated with the transport properties. Instead, this study found out a mechanical-performance relationship, which follows a master equation: t = A (−12.48 (1-e(1.53x10-4σy))) / P that enables to correlate the effect Al-LLZO particles on the cell performance, and predicts, for the first time, the lifetime of the battery through the mechanical properties.

Solvation structures in weakly solvating solvents lead to hybrid vehicular/structural ion transport

Despite the reported benefits of weakly solvating electrolytes (WSEs), investigations on the solvation structures and ion transport mechanisms present in WSEs are limited. This is particularly the case for electrolytes containing the weakly solvating 1,2-diethoxyethane (DEE), which has shown great promise recently. It is for this purpose, we employ molecular dynamics simulations and quantum mechanical calculations to investigate the solvation structure and Li+ transport for lithium bis(fluorosulfonyl)imide (LiFSI) in DEE. From the results reported herein, it was found that at lower concentrations, solvent separated ion pairs are particularly stable, primarily due to the presence of FSI– in the second solvation shell of Li+. As the salt concentration increases, cation–anion complexes appear and form large aggregates. The presence of these large aggregates promotes a hybrid/structural diffusion mechanism at high concentrations, where Li+ ions readily exchange ligands with FSI– anions but remains coordinated with DEE molecules. Hence, the results reported herein investigate how the solvation structure influences transport properties in weakly solvating solvents and provides insights that can be used to optimize electrolytes for energy storage applications.

Functional ternary salt construction enabling an in-situ Li3N/LiF-enriched interface for ultra-stable all-solid-state lithium metal batteries

Poly(ethylene oxide)-based polymer all-solid-state lithium metal batteries (ASSLBs) have received widespread attention due to their low cost, good process ability, and high energy density. Nevertheless, the growth of Li dendrites within polymer solid-state electrolytes damages the reversibility of Li anodes and still impedes their widespread application. One efficient strategy is to construct a superior solid electrolyte interface. Herein, a stable interface enriched with Li3N and LiF is in-situ formed between Li anode and a ternary salt electrolyte. This ternary salt electrolyte is innovatively designed by introducing lithium bis(trifluoromethane sulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and LiNO3 to poly(ethylene oxide) matrix. Surface characterization indicates that LiNO3 and LiFSI contribute to forming a Li3N-LiF-enriched interface and meanwhile LiTFSI ensures excellent conductivity. Theoretically, among various Li compound components, Li3N has high ionic conductivity, which is beneficial for reducing overpotential, while LiF has high interfacial energy which can enhance nucleation energy and suppress the formation of Li dendrites. The experimental results show that ASSLBs coupled with LiFePO4 cathode display extremely excellent cycle stability approximately 2200 cycles at 2 C, with a final and corresponding discharge specific capacity of 96.7 mA h g−1. Additionally, a schematic illustration of the working mechanism for the Li3N-LiF interface is proposed.

(Invited) Fluorinated Linear Carbonate Electrolyte for Lithium-Ion Batteries with Fast-Charging, High Voltage, and Wide Operating Temperatures

Lithium-ion batteries (LIBs) are key solutions to clean energy. Their high energy densities have led to the dominance of LIBs in mobile devices and electric vehicles. However, traditional electrolyte limits their operation at high voltage and extreme environmental temperatures. Here, we designed a new multifunctional electrolyte, in which lithium bis(fluorosulfonyl)imide (LiFSI) is used as salt and fluorinated diethyl carbonate (DFDEC) is used as the major solvent. With this optimized electrolyte, the graphite||LiNi0.8Mn0.1Co0.1O2 (NMC811) full cells are capable of fast-charging and can deliver long-term cycling with a cutoff voltage as high as 4.5V. Specifically, the battery shows the capacity retention of 84.3% after 500 cycles with an average coulombic efficiency (CE) as high as 99.93%. Synchrotron-based characterization suggests the formation of anion derived, LiF-rich interphases on the surfaces of both graphite anode and NMC811 cathode. Thanks to the fast ion transport and stable interphase, the cell in the optimized electrolyte demonstrates stable cycling behavior within a wide operating temperature. At high temperature (60 ºC), the full cell delivers 88.8% of its initial capacity after 130 cycles at a high current density of 1C. At low temperature (-20 ºC), the optimized electrolyte enables a capacity retention of 90.9% after 100 cycles when charging and discharging at 0.2C.Acknowledgment: The work done at Brookhaven National Laboratory was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office of the U.S. DOE through Applied Battery Research for Transportation (ABRT) program under contract no. DE-SC0012704. The electrodes used in this study were produced at the U.S. Department of Energy’s (DOE) CAMP (Cell Analysis, Modeling and Prototyping) Facility, Argonne National Laboratory. The CAMP Facility is fully supported by the DOE Vehicle Technologies Office (VTO). This research used beamline 7-ID-2 (SST-2) of the National Synchrotron Light Source II, U.S. DOE Office of Science User Facilities, operated for the DOE Office of Science by Brookhaven National Laboratory under contract number DE-SC0012704. SEM measurements for this manuscript were performed at Center for Functional Nanomaterials, a U.S. DOE office of Science User Facility, at Brookhaven National Laboratory under the contract number DE-SC0012704.

(Invited) Design Criteria of Ether Electrolytes and Stable Interphase Toward Reversible Intercalation Chemistry of Graphite Anode in Li-Ion Batteries

To date, it is extensively believed that ether electrolytes are incompatible with graphite anode in Li-ion batteries due to detrimental solvent co-intercalation and exfoliation. Here, we provide design criteria of ether electrolytes for reversible graphite anode without the high salt concentration. In short, for ether electrolytes, the reductive stability of anions (or their solvated complex) and the solid-electrolyte interphase (SEI) govern the reversibility of graphite anode. Exfoliation and co-intercalation are not the root cause of as-documented cell failures using graphite anodes. While reductive-instable lithium bis(fluorosulfonyl)imide (LiFSI) is the optimal salt paired with DOL, reductive-stable LiBF4 finds applications with DME. Individual 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) based electrolytes can enable ~99.9% Coulombic efficiency with excellent capacity retention and fast-charge capability using natural graphite. In DOL electrolytes, weakened Li-solvent interaction and preferential reduction of FSI anion coordinated with Li-ion contribute to homogeneous SEI enriched with inorganic species, for example, LiF. Therefore, electrolyte reduction and Li-DOL co-intercalation are inhibited. In DME electrolytes, we show that LiBF4 has limited reduction, majorly on the edge site. We discover that a self-terminating, heterogeneous interphase based on grainy LiF proves to be desirable for operating Li-solvent co-intercalation. Taking advantage of the anisotropic characteristics of natural graphite, we conducted a holistic investigation into the nature, function, and formation of the heterogeneous SEI. In these studies, we clarify a long-lasting confusing issue in LIBs community-that is, the compatibility between ether electrolytes and graphite anode. Our findings not only shed light on the enigmatic interphase formed by ether electrolytes but also offer critical insights into future electrolyte design for graphite anodes operated under extreme conditions.

Lightweight Electrolyte Design for Li/Sulfurized Polyacrylonitrile (SPAN) Batteries.

Sulfurized polyacrylonitrile (SPAN) recently emergesas a promising cathode for high-energy lithium (Li) metal batteries owing to its high capacity, extended cycle life, and liberty from costly transition metals. As the high capacities of both Li metal and SPAN lead to relatively small electrode weights, the weight and specific energy density of Li/SPAN batteries are particularly sensitive to electrolyte weight, highlighting the importance of minimizing electrolyte density. Besides, the large volume changes of Li metal anode and SPAN cathode require inorganic-rich interphases that can guarantee intactness and protectivity throughout long cycles. This work addresses these crucial aspects with an electrolyte design where lightweight dibutyl ether (DBE) is used as adiluent for concentrated lithium bis(fluorosulfonyl)imide(LiFSI)-triethyl phosphate (TEP) solution. The designed electrolyte (d = 1.04g mL-1) is 40%-50% lighter than conventional localized high-concentration electrolytes (LHCEs), leading to 12%-20% extra energy density at the cell level. Besides, the use of DBE introduces substantial solvent-diluent affinity, resulting in a unique solvation structure with strengthened capability to form favorable anion-derived inorganic-rich interphases, minimize electrolyte consumption, and improve cell cyclability. The electrolyte also exhibits low volatility and offers good protection to both Li metal anode and SPAN cathode under thermal abuse.

A new ionic liquid-based electrolyte with both high conductivity and electrochemical stability

Ionic liquids with non-flammability and wide electrochemical window are the promising candidates for the next-generation high-energy lithium metal batteries (LMBs). However, their high viscosity and low ionic conductivity lead to a limited cycling performance, hindering their commercial application. Herein, a new ionic liquid-based electrolyte (ILE) composed of lithium bis(fluorosulfonyl)imide (LiFSI), N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (Pyr13FSI), ethyl methyl carbonate (EMC) and fluorinated ethylene carbonate (FEC) is designed to address this barrier. The new ILE exhibits high conductivity, which is twice that of pure ILE. In addition, FEC that is weakly coordinated to Li+ increases the combination between Li+ and FSI− indirectly, inducing a deeper co-decomposition of FSI− and FEC, thereby leading to a construction of LiF-rich solid electrolyte interphase (SEI). Consequently, Li/Cu battery maintains a higher lithium stripping/plating Coulombic efficiency (CE) of 96.3 % at 250 cycles and Li/LiFePO4 battery reaches a 93.2 % capacity retention at 150 cycles with an average CE of 99.8 %. The designed ILE with both high conductivity and electrochemical stability opens up a new insight for the rational design of electrolytes applied in next-generation LMBs.

Boosting Li-ion transport for graphite electrodes with lithium bis(fluorosulfonyl)imide salt and methyl acetate additive for fast-charging Li-ion batteries

Lithium-ion battery (LIB) is now widely used in the world. However, its unsatisfactory fast-charging performance is limiting its applications. The fast-charging capability of LIB is highly affected by the surface composition of graphite electrode, which can be modified through electrolyte design. Herein we demonstrate that the combination of lithium bis(fluorosulfonyl) imide (LiFSI) salt with methyl acetate (MA) additive in carbonate electrolyte enables fast-charging Li-ion battery. Results from X-ray photoelectron spectroscopy and transmission electron microscopy indicate that the LiFSI-based electrolyte with MA forms a stable and less-resistive solid electrolyte interphase on graphite anode compared to electrolyte with LiPF6, facilitating the transport of Li-ion and achieving a superior fast-charging performance with a capacity of 230 mAh g−1 at 2 C. An electrolyte swapping experiment also indicates that the LiFSI salt forms a more stable SEI on graphite than LiPF6. This work provides a conducive electrolyte design for fast charging Li-ion battery with graphite anode.

Toward Ultralow Temperature Lithium Metal Batteries: Advancing the Feasibility of 1,3‐Dioxolane Based Localized High‐Concentration Electrolytes via Lithium Nitrate

AbstractLithium metal batteries (LMBs) suffer severe capacity deterioration due to sluggish ionic transport kinetics at extremely low temperatures, which limits their practical operation. Selecting solvents with low desolvation energy, and promoting interfacial Li+ transport in solid electrolyte interphase (SEI) are regarded as effective methods to improve electrochemical performances. Herein, 1,3‐dioxolane (DOL) with weak solvating power is adopted for designing a DOL‐based localized high concentration electrolyte (DLHCE) with LiNO3 as a multifunctional additive. The strong coordination between NO3− and DOL molecules not only inhibits the polymerization of DOL at high lithium bis(fluorosulfonyl)imide (LiFSI) concentration, but also reduces the solvent‐diluent miscibility and extends the salt‐solvent solubility. As a result, an anion‐dominated solvation structure is obtained that derives an inorganic‐rich SEI composed of LiF and Li3N, guiding the uniform deposition of Li at low temperature. Remarkably, the Li||LiFePO4 cells retain 53.6% of room temperature capacity at −40 °C, and also present potential application of Li||NCM811 cells under cryogenic environments.

Enhancing Cycling Stability of Lithium Metal Batteries by a Bifunctional Fluorinated Ether

AbstractThe lifespan of lithium (Li) metal batteries (LMBs) can be greatly improved by the formation of inorganic‐rich electrode‐electrolyte interphases (EEIs) (including solid‐electrolyte interphase on anode and cathode‐electrolyte interphase on cathode). In this work, a localized high‐concentration electrolyte containing lithium bis(fluorosulfonyl)imide (LiFSI) salt, 1,2‐dimethoxyethane (DME) solvent and 1,2‐bis(1,1,2,2‐tetrafluoroethoxy)ethane (BTFEE) diluent is optimized. BTFEE is a fluorinated ether with weakly‐solvating ability for LiFSI so it also acts as a co‐solvent in this electrolyte. It can facilitate anion decomposition at electrode surfaces and promote the formation of more inorganic‐rich EEI layers. With an optimized molar ratio of LiFSI:DME:BTFEE = 1:1.15:3, LMBs with a high loading (4 mAh cm−2) lithium nickel manganese cobalt oxide (LiNi0.8 Mn0.1 Co0.1) cathode can retain 80% capacity in 470 cycles when cycled in a voltage range of 2.8–4.4 V. The fundamental understanding on the functionality of BTFEE revealed in this work provides new perspectives on the design of practical high‐energy density battery systems.

Operando Raman Gradient Analysis for Temperature-Dependent Electrolyte Characterization.

Transport and thermodynamic properties are integral parameters to understand, model, and optimize state-of-the-art and next-generation battery electrolytes. The accurate measurement of these properties is experimentally challenging as well as time- and resource-intensive, and consequently, reports are scarce. Their dependence on temperature is explored even less and is commonly limited to a few temperature points. Recently, we introduced an operando Raman gradient analysis (ORGA) tool to extract transport and thermodynamic properties. Here, we expand the capabilities of ORGA by incorporating a temperature-sensitive external reference into the design. With this enhancement, we are able to visualize the local concentration of any Raman-active species in the electrolyte and detect lithium filament nucleation. We demonstrate and validate this new functionality of ORGA via an examination of lithium bis(fluorosulfonyl)imide (LiFSI) in tetraethylene glycol dimethyl ether (G4) as a function of temperature. All transport properties and activation energies are reported, and the effect of temperature is discussed.

“Dragging” effect induced formation of AGGs-rich solvation structures in lithium metal batteries

The chemically homogeneous and mechanically robust solid electrolyte interphase (SEI) is a prerequisite for the realization of high-efficiency and long-life lithium metal batteries (LMBs). The performance of SEI is considerably influenced by the solvation structure of Li+ which can be precisely regulated by the interaction between electrolytes. In this study, new mechanism of the “dragging” effect on Li+ by diluents located outside the first solvation shell of Li+ was described by investigating diluent-Li+ interaction and diluent-anion interaction in a locally concentrated ionic liquid electrolyte (LCILE) based on lithium bis(fluorosulfonyl)imide (LiFSI), N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (Pyr13FSI) and 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (TFETFE). A drag force on Li+ arising from the relatively powerful Li+-TFETFE interaction effectively contributes to the combination of Li+ with anion, creating a solvation structure rich in aggregate ion pairs (AGGs), which assists in the construction of high-quality SEI. With the exceptional lithium dendrite inhibition ability and Li+ transport characteristics of SEI, the lithium stripping/plating Coulombic efficiency is up to 99.2 % over 750 cycles at 1.0 mA cm−2 and Li/LFP cells achieves a remarkable capacity retention of 82.4 % for 100 cycles. This study presents a new viewpoint for diluents to modulate the solvation structure and provides a new strategy for the development of electrolytes suitable for next-generation high-performance LMBs.

Understanding the Role of Imide-Based Salts and Borate-Based Additives for Safe and High-Performance Glyoxal-Based Electrolytes in Ni-Rich NMC811 Cathodes for Li-Ion Batteries.

Herein, the design of novel and safe electrolyte formulations for high-voltage Ni-rich cathodes is reported. The solvent mixture comprising 1,1,2,2-tetraethoxyethane and propylene carbonate not only displays good transport properties, but also greatly enhances the overall safety of the cell thanks to its low flammability. The influence of the conducting salts, that is, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI), and of the additives lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFOB) is examined. Molecular dynamics simulations are carried out to gain insights into the local structure of the different electrolytes and the lithium-ion coordination. Furthermore, special emphasis is placed on the film-forming abilities of the salts to suppress the anodic dissolution of the aluminum current collector and to create a stable cathode electrolyte interphase (CEI). In this regard, the borate-based additives significantly alleviate the intrinsic challenges associated with the use of LiTFSI and LiFSI salts. It is worth remarking that a superior cathode performance is achieved by using the LiFSI/LiDFOB electrolyte, displaying a high specific capacity of 164mAhg-1 at 6C and ca. 95% capacity retention after 100 cycles at 1C. This is attributed to the rich chemistry of the generated CEI layer, as confirmed by ex situ X-ray photoelectron spectroscopy.

An Investigation of Li-Ion Cell Degradation Caused by Simulated Autoclave Cycles

Li[Ni0.6Mn0.4Co0.0]O2/graphite (NMC640, balanced for 4.1 V cut-off) and Li[Ni0.83Mn0.06Co0.11]O2/graphite (Ni83, balanced for 4.06 V cut-off) pouch cells were tested using lab-simulated autoclave conditions. After every cycle, the cells at either 3.4, 3.7, or 3.9 V were placed in a 120°C oven for 40 min to undergo an “autoclave” run, then continued for another cycle. Electrolyte blends using lithium bis(fluorosulfonyl)imide (LiFSI) salt were used to improve the cycle-life of autoclaved cells. The lab autoclave protocol was also performed on LiFePO4/graphite (LFP) and NMC commercial cylindrical cells, which were advertised for use in or found in autoclaved medical devices. LFP cells performed poorly in the simulated autoclave tests, while commercial high-temperature-tolerant NMC cylindrical cells and the pouch cells performed similarly. In continuous testing at 85°C, the pouch cells had better capacity retention than both cylindrical cell types. However, the pouch cells suffered from electrolyte permeation through the polymer seals. The pouch cell chemistries incorporated in cylindrical cell format would probably give superior performance to the commercial cells in the autoclave tests. Cell lifetimes were improved when cells were placed into the 120°C oven at a lower voltage suggesting that hospitals should charge Li-ion cells after the autoclaving process instead of standard practice of before.

Osteoporosis Failure of Aluminum Current Collector Induced Crosstalk Degradation at the Imide-Type Lithium Salt Comprised Practical-Level Lithium-Ion Batteries

The atypical failure mechanism caused by the inclusion of lithium bis(fluorosulfonyl)imide (LiFSI) salt in lithium-ion batteries (LIB) is elucidated. When subjected to elevated temperature cycling, the LiFSI salt triggers the degradation of the aluminum current collector, leading to the dissolution of Al ions into the electrolyte. These dissolved Al ions then migrate toward the negative electrode surface where they spontaneously reduce and form Al deposits due to the low electrode potential. This Al deposition further catalyzes the cathodic decomposition of the electrolyte, impacting the interphasial resistance of the negative electrode and consuming both Li ions and electrolyte components. Upon extended cycling with LiFSI-containing electrolytes, a notable decline in the reversible capacity of LIB becomes evident due to cross-talk failure resulting from Al current collector corrosion. Consequently, to enhance the cycling performance of LIBs using LiFSI-based electrolytes, it is necessary to simultaneously prevent Al corrosion and subsequent deposition on the surface of the negative electrode.