Organic Carbonate-based Electrolyte Research Articles

Synergistic Effect of Lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)Imide (LiDFTFSI) and Vinylene Carbonate (VC) on High Performance of NMC811║Graphite Cells

Lithium-ion batteries (LIBs) have gained increasing importance in energy storage systems, driven by the growing demands of grid storage, automotive, and portable consumer applications. To meet the need for high energy density batteries, one promising approach involves the utilization of high capacity layered transition metal oxide cathodes, such as nickel-rich LiNi0.8Mn0.1Co0.1O2 (NMC811), which can deliver a high reversible specific capacity of over 180 mAh·g-1 [1,2]. However, due to the structural and interfacial instability[3], nickel-rich NMC cathode still faces challenges in long-term galvanostatic cycling. For these reasons, design of novel electrolyte formulations, which enable formation of an effective cathode electrolyte interphase (CEI), is highly desirable. Recent studies have highlighted the cross-talk between the cathode and anode, indicating that the evolution of the solid electrolyte interphase (SEI) can impact the formation of the CEI[4]. Thus, establishing an effective SEI/CEI pair is essential for achieving long-term cycling of nickel-rich NMC cathode-based cells. Electrolyte optimization plays a crucial role in facilitating the formation of a desirable SEI/CEI pair, leading to an improved cell performance and longevity. Lithium (difluoromethanesulfonyl)(trifluoro-methanesulfonyl)imide (LiDFTFSI) has proven to be promising in solid-polymer-electrolyte batteries due to the good SEI/CEI formation ability and suppressed Al-dissolution[5]. Additionally, LiDFTFSI exhibits also good compatibility with Li-metal batteries[6], heralding promising applications in Li-ion batteries. However, there is lack of systematic research investigating the potential impact of LiDFTFSI on the cathode as well as on resulting CEI formation and dynamics.In this work, we demonstrated enhanced galvanostatic cycling performance of NMC811||graphite cells achieved by utilizing LiDFTFSI and lithium hexafluorophosphate (LiPF6) in a blended salt organic carbonate-based electrolyte formulation. Comprehensive electrochemical and post mortem analysis revealed that the LiDFTFSI alone can effectively mitigate the structural changes in the NMC811 electrode by facilitating the formation of modified CEI. However, the continued growth of an inhomogeneous CEI, caused by the cross-talk effect between electrodes, adversely affected long-term cycling stability. To address this, vinylene carbonate (VC) was introduced to the electrolyte. Synergistic effect with LiDFTFSI leads to the formation of effective and uniform SEI and CEI. As a result, 720 charge/discharge cycles were achieved in NMC811||graphite cells with LiDFTFSI and VC containing electrolytes at 1C while maintaining 80% state-of-health (SOH80%).

3D Printed Rechargeable Aqueous and Non-Aqueous Lithium-Ion Batteries: Evolution of Design and Performance

Here we describe the modeling and design evolution of vat polimerized (Vat-P) stereolithographic apparatus (SLA) 3D printed coin cell-type aqueous and non-aqueous rechargeable lithium-ion batteries, cases and current collectors. We detail the rationale for design evolution that improved performance, handling and assembly of the printed batteries. Some guidance into the modeling, 3D printing process, material choice, chemical and electrochemical stability, assembly, sealing, and performance of 3D printed Li-ion batteries is outlined. 3D printed Li-ion batteries demonstrated promising results in terms of gravimetric capacity, rate capability, and capacity per unit footprint area compared to conventional coin cells in both aqueous and non-aqueous systems. For aqueous cells, the cell level capacity is a factor of 2–3x higher than similar metal coin cells due to the lighter weight and better rate response. We also outline design requirements for a Vat-P printed battery that are compatible with organic carbonate-based electrolytes, where the cell provides 115 mAh g−1 specific capacity using an LiCoO2–graphite chemistry, which is only ∼20% less than the maximum reversible capacity of LCO. Despite the challenges faced in optimizing the design and materials for 3D printed Li-ion batteries, this study provides valuable information for future research and development.

Artificial Interphase Design Employing Inorganic–Organic Components for High-Energy Lithium-Metal Batteries

To increase the energy density of today's lithium batteries, it is necessary to develop an anode with higher energy density than graphite or carbon/silicon composites. Hence, research on metallic lithium has gained a steadily increasing momentum. However, the severe safety issues and poor Coulombic efficiency of this highly reactive metal hinder its practical application in lithium-metal batteries (LMBs). Herein, the development of an artificial interphase is reported to enhance the reversibility of the lithium stripping/plating process and suppress the parasitic reactions with the liquid organic carbonate-based electrolyte. This artificial interphase is spontaneously formed by an alloying reaction-based coating, forming a stable inorganic/organic hybrid interphase. The accordingly modified lithium-metal electrodes provide substantially improved cycle life to symmetric Li||Li cells and high-energy Li||LiNi0.8Co0.1Mn0.1O2 cells. For these LMBs, 7 μm thick lithium-metal electrodes have been employed while applying a current density of 1.0 mA cm-2, thus highlighting the great potential of this tailored interphase.

Ammonium and Tetraalkylammonium Salts as Additives for Li Metal Electrodes

Lithium metal batteries are considered a promising technology to implement high energy density rechargeable systems beyond lithium-ion batteries. However, the development of dendritic morphology is the basis of safety and performance issues and represents the main limiting factor for using lithium anodes in commercial rechargeable batteries. In this study, the electrochemical behaviour of Li metal has been investigated in organic carbonate-based electrolytes by electrochemical impedance spectroscopy measurements and deposition/stripping galvanostatic cycling. Low amounts of tetraalkylammonium hexafluorophosphate salts have been added to the electrolytes with the aim of regulating the lithium deposition/stripping process through the electrostatic shielding effect that improves the lithium deposition. The use of NH4PF6 also determined good lithium deposition/stripping performance due to the chemical modification of the native solid electrolyte interphase via direct reaction with lithium.

Phosphonate-Functionalized Ionic Liquid Gel Polymer Electrolyte with High Safety for Dendrite-Free Lithium Metal Batteries.

The conventional lithium-ion battery technology relies on the liquid carbonate-based electrolyte solution, which causes excessive side reactions, serious risk of electrolyte leakage, high flammability, and significant safety hazards. In this work, phosphonate-functionalized imidazolium ionic liquid (PFIL) is synthesized and used as a gel polymer electrolyte (GPE) to replace the organic carbonate-based electrolyte solution. The as-prepared ionic liquid-based gel polymer electrolyte (IL-GPE) shows low crystallinity, flame retardance, and excellent electrochemical performance. Thanks to the fast double channel transport of lithium ions in the IL-GPE electrolyte, a high ionic conductivity of 0.48 mS cm-1 and a lithium-ion transference number of 0.37 are exhibited. Symmetrical lithium cells with IL-GPE retain stable cycling even after 3000 h under 0.1 mA cm-2. IL-GPE exhibits good compatibility toward lithium metal, yielding excellent long-term electrochemical kinetic stability. IL-GPE induces the formation of a uniform and robust SEI layer, inhibiting the growth of lithium dendrites and improving the rate performance and cycle stability. Furthermore, Li/LiFePO4 cells exhibit a specific capacity of 63 mA h g-1 after 150 cycles at 5.0 C, with a capacity retention of 90.2%. It is foreseen that this GPE is a promising candidate to enhance the safety of high-performance lithium metal batteries.

Impact of in coin cell atmosphere on lithium metal battery performance

Research on lithium metal as a high-capacity anode for future lithium metal batteries (LMBs) is currently at an all-time high. To date, the different influences of a highly pure argon glovebox (GB) and an industry-relevant ambient dry room (DR) atmosphere have received little attention in the scientific community. In this paper, we report on the impact of in coin cell atmosphere (ICCA) on the performance of an LMB as well as its interphase characteristics and properties in combination with three organic carbonate-based electrolytes with and without two well-known interphase-forming additives, namely fluoroethylene carbonate (FEC) and vinylene carbonate (VC). The results obtained from this carefully executed systematic study show a substantial impact of the ICCA on solid electrolyte interphase (SEI) resistance (RSEI) and lithium stripping/plating homogeneity. In a transition metal cathode (NMC811) containing LMBs, a DR ICCA results in an up to 50% increase in lifetime due to the improved chemical composition of the cathode electrolyte interphase (CEI). Furthermore, different impacts on electrode characteristics and cell performance were observed depending on the utilized functional additive. Since this study focuses on a largely overlooked influential factor of LMB performance, it highlights the importance of comparability and transparency in published research and the importance of taking differences between research and industrial environments into consideration in the aim of establishing and commercializing LMB cell components.

Enabling High-Stability of Aqueous-Processed Nickel-Rich Positive Electrodes in Lithium Metal Batteries.

Lithium batteries occupy the large-scale electric mobility market raising concerns about the environmental impact of cell production, especially regarding the use of poly(vinylidene difluoride) (teratogenic) and N-methyl-2-pyrrolidone (NMP, harmful). To avoid their use, an aqueous electrode processing route is utilized in which a water-soluble hybrid acrylic-fluoropolymer together with sodium carboxymethyl cellulose is used as binder, and a thin phosphate coating layer is in situ formed on the surface of the nickel-rich cathode during electrode processing. The resulting electrodes achieve a comparable performance to that of NMP-based electrodes in conventional organic carbonate-based electrolyte (LP30). Subsequently, an ionic liquid electrolyte (ILE) is employed to replace the organic electrolyte, building stable electrode/electrolyte interphases on the surface of the nickel-rich positive electrode (cathode) and metallic lithium negative electrode (anode). In such ILE, the aqueously processed electrodes achieve high cycling stability with a capacity retention of 91% after 1000 cycles (20 °C). In addition, a high capacity of more than 2.5 mAh cm-2 is achieved for high loading electrodes (≈15mg cm-2 ) by using a modified ILE with 5% vinylene carbonate additive. A path to achieve environmentally friendly electrode manufacturing while maintaining their outstanding performance and structural integrity is demonstrated.

PEGDA with Metal-Organic Frameworks As Composite Electrolyte for All-Solid-State Lithium Batteries

The widely use of volatile and flammable traditional organic carbonate-based electrolytes in high-performance lithium-ion batteries (LIBs) is prone to cause safety hazards. Solid-state polymer electrolytes (SPE) have been developed to address the safety issues due to their numerous advantages, such as solvent-free, low flammability, wide electrochemical stability window, and good thermal and mechanical stability. However, the polymer tends to recrystallize at room temperature leading to insufficient ionic conductivity. Organic-matter-based fillers (e.g., metal-organic frameworks, covalent−organic frameworks, and lithiophilic polymers) have been found to increase the ionic conductivity of SPEs effectively by decreasing the crystallinity of polymer, synchronously to improve the mechanical property, thermal stability, and interfacial compatibility. Porous zeolitic imidazolate framework-8 (ZIF-8) has been used as fillers in this study. The ZIF-8 are integrated with the PEGDA matrix in this study, showing enhanced electrochemical and mechanical properties. Such performance enhancement is due to the composite solid-state electrolyte inherited the advantages of both polymer and fillers. The fillers not only inhibited the recrystallization of the polymer but also prevent the dendrite growth of the Li. The polymeric PEGDA enhanced the contact interface between the electrolyte and electrodes. Therefore, PEGDA-based SPEs with ZIF-8 is of great promise for all-solid-state lithium metal batteries.

Poly (vinyl ethylene carbonate)-based dual-salt gel polymer electrolyte enabling high voltage lithium metal batteries

Rechargeable lithium metal batteries (LMBs) have been regarded as one of the most promising next-generation energy-storage systems due to their high theoretical energy density. However, the practical application of LMBs is greatly impeded by poor high-voltage tolerance and safety concerns originated from flammable organic carbonate-based liquid electrolytes. Herein, a novel dual-salt gel polymer electrolyte (DS-GPE) is prepared via in situ polymerization of vinyl ethylene carbonate (VEC) and pentaerythritol tetra acrylate (PETEA) monomers in a poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) porous structure. The newly developed DS-GPE shows high ionic conductivity (6.9 mS cm−1) at room temperature, adequate Li+ transference number (tLi+= 0.512), outstanding oxidative resistance (5.3 V vs. Li/Li+) and favorable interfacial compatibility. Stable interfacial layers are rich in B-, F-, components on both the Li metal anode and high-voltage LiCoO2 cathode, realizing excellent cycling stability in Li||Li symmetrical cells, and a capacity retention of 83.42% over 100 cycles with average Coulombic efficiency of 99.86% in Li||LiCoO2 cell.

Synergistic Effect of Hexagonal Boron Nitride-Coated Separators and Multi-Walled Carbon Nanotube Anodes for Thermally Stable Lithium-Ion Batteries

In this work, we report the development of separators coated with hexagonal boron nitride (hBN) to improve the thermal stability of Li-ion batteries (LIBs). Aiming to achieve a synergistic effect of separators and anodes on thermal stability and electrochemical performance, multiwalled carbon nanotubes (MWCNTs) were prepared via plasma-enhanced chemical vapor deposition (PECVD) method and used as potential anode materials for LIBs. The grown MWCNTs were well characterized by using various techniques which confirmed the formation of MWCNTs. The prepared MWCNTs showed a crystalline structure and smooth surface with a diameter of ~9–12 nm and a length of ~10 μm, respectively. Raman spectra showed the characteristic peaks of MWCNTs and BN, and the sharpness of the peaks showed the highly crystalline nature of the grown MWCNTs. The electrochemical studies were performed on the fabricated coin cell with a MWCNT anode using a pristine and BN-coated separators. The results show that the cell with the BN-coated separator in a conventional organic carbonate-based electrolyte and MWCNTs as the anode resulted in a discharge capacity (at 65 °C) of ~567 mAhg−1 at a current density of 100 mAg−1 for the first cycle, and delivered a capacity of ~471 mAhg−1 for 200 cycles. The columbic efficiency was found to be higher (~84%), which showed excellent reversible charge–discharge behavior as compared with the pristine separator (69%) after 200 cycles. The improved thermal performance of the LIBs with the BN-coated separator and MWCNT anode might be due to the greater homogeneous thermal distribution resulting from the BN coating, and the additional electron pathway provided by the MWCNTs. Thus, the fabricated cell showed promising results in achieving the stable operation of the LIBs even at higher temperatures, which will open a pathway to solve the practical concerns over the use of LIBs at higher temperatures without compromising the performance.

Compatibility of Various Electrolytes with Cation Disordered Rocksalt Cathodes in Lithium Ion Batteries

Cation disordered rock salt cathode materials have gathered increased research interest over the last couple of years due to their high specific capacity and wide array of element combinations. It is still unclear whether the capacity fading observed for this type of material is solely due to the occurrence of anionic redox reactions and consequent material degradation or also due to the side reactions between the cathode material and the carbonate-based electrolyte. In order to address it, this study compares the differences in electrochemical performance of a rock salt Li1.25Fe0.5Nb0.25O2 cathode and cathode electrolyte interphase (CEI) formation in both lithium metal and lithium ion cells by using a conventional carbonate-based electrolyte and an ionic liquid-based electrolyte. Thereby, the ionic liquid electrolyte promotes capacity retention, whereas the organic carbonate-based electrolyte leads to increased capacity fading and ineffective CEI formation. Severe side reactions between the carbonate-based electrolyte and the cathode material are characterized by poor Coulombic efficiency and result in continuous inner resistance growth, ongoing gas evolution, and the coverage of the cathode surface with electrolyte degradation products like LiF and Li2CO3. This study shows the mismatch of carbonate-based electrolytes with the Li1.25Fe0.5Nb0.25O2 cathode and offers a strategy that can be also applied for the improvement of performance of other disordered rock salt cathode materials.

A novel phosphonium ionic liquid electrolyte enabling high-voltage and high-energy positive electrode materials in lithium-metal batteries

The synthesis of a new ionic liquid (IL), consisting of the symmetric tetra-butyl-phosphonium (P4444+) cation and the (nonafluorobutanesulfonyl)(trifluoromethanesulfonyl)imide (IM14–) anion, via a facile and environmentally-friendly aqueous route is reported. The novel P4444IM14 IL demonstrates excellent thermal and electrochemical stability (beyond 6 V vs. Li+/Li0 (against Ni-foil)) in combination with good near-room temperature conductivity and ionic liquid characteristics, such as non-measurable volatility and exceptional flame-retardant properties. Employed as electrolyte component in Li-metal cells together with the high-voltage, Li1.2Ni0.2Mn0.6O2 positive electrode material, enables an initial discharge capacity of 264 mA h g-1 at 12.5 mA g−1 and improved initial Coulombic efficiency. Additionally, the discharge capacity retention is promising (92.3% after 50 cycles and 84.4% after 100 cycles) when compared with using a conventional organic carbonate-based electrolyte (55.5% after 50 cycles). Further development of this ionic liquid electrolyte may facilitate the practical application of Li-metal anodes in high-voltage/high-energy lithium batteries.

Highly conductive polymer electrolytes based on PAN-PEI nanofiber membranes with in situ gelated liquid electrolytes for lithium-ion batteries

The development of solid state electrolytes is considered as an effective approach to build safer lithium-ion batteries by replacing the conventional liquid electrolytes. However, the solid state electrolytes face continuous challenges to improve their ionic conductivities and mechanical properties. Herein, we report the synthesis of novel polymer electrolytes based on cross-linked polyacrylonitrile-polyethylenimine (PAN-PEI) nanofiber membranes infiltrated with in-situ gelated electrolytes using tripropylene glycol diacrylate as crosslinking agent in the organic carbonate-based liquid electrolytes. The PAN-PEI nanofiber membranes with different mass ratios of PAN/PEI prepared by electrospinning method are constructed with entangled nanofibers of an average diameter of ~600 nm. The optimized PAN-PEI based electrolyte has a high ionic conductivity up to 3.39 mS cm−1 at room-temperature and decent tensile strength of 9.36 MPa. Linear sweep voltammetry shows that the polymer electrolyte also has a wide electrochemical window of 5.4 V (vs. Li/Li+). This polymer electrolyte exhibits excellent cycling stability even in the high energy density of LiNi0.8Co0.1Mn0.1O2/Graphite, delivering an initial discharge capacity of 175 mAh g−1 at 0.5 C with a capacity retention of 91.4% after 200 cycles.

Waste to life: Low-cost, self-standing, 2D carbon fiber green Li-ion battery anode made from end-of-life cotton textile

In this study, self-standing and flexible Li-ion battery negative electrodes made of interconnected two-dimensional carbonized cotton fibers are developed by using a controlled pyrolysis method, and their electrochemical performance in laboratory-scale lithium-based cells is investigated at ambient temperature. By applying this binder- and current collector-free cotton-based carbon fiber electrode, both the Li+-ion intercalation and capacity decay mechanisms are explored using conventional organic carbonate-based liquid electrolyte. The cotton-based carbon fiber electrode shows excellent cycling performance and delivers a high discharge capacity in the voltage range of 0.02 - 1.2 V. The post cycling analysis of carbon fiber using HR-TEM shows the major SEI layer components formed at the surface of the active fibers during the charge/discharge process. The same electrode is used to assemble a lab-scale Li-ion full cell with high mass loading LiFePO4-based composite electrode, which demonstrates excellent cycling stability, high Coulombic efficiency and remarkable rate capability at ambient temperature.

Detection of protons using the rotating ring disk electrode method during electrochemical oxidation of battery electrolytes

Knowledge of the degradation mechanisms inside lithium-ion batteries (LIBs) is critical in designing robust next-generation materials. While significant efforts have led to advances in characterization techniques and in our general understanding of the numerous decomposition reactions, the complex, multicomponent nature of batteries has hindered our progress towards developing a complete picture of these processes. In this work, we present a method for the detection of protons—one of the commonly proposed products of battery electrolyte decomposition at high potentials—using the rotating ring disk electrode (RRDE) method. Using the H2 oxidation reaction (HOR) as a model reaction, we first determine that protons generated at the disk electrode can be detected in organic carbonate-based electrolyte at the ring electrode with a ring collection efficiency close to the theoretical value. We then show that protons are indeed generated during the electrochemical decomposition of the battery electrolyte on Pt(111) at high potentials. Furthermore, quantitative detection of protons provided a valuable insight into the mechanism of oxidation for the electrolyte used. Overall, our work demonstrates the value of RRDE as a complementary method for studying potential-dependent electrolyte stability.

Toward adequate control of internal interfaces utilizing nitrile-based electrolytes.

Methods to control internal interfaces in lithium ion batteries often require sophisticated procedures to deposit coating layers or introduce interphases, which are typically difficult to apply. This particularly holds for protection from parasitic reactions at the current collector, which reflects an internal interface for the electrode composite material and the electrolyte. In this work, electrolyte formulations based on aliphatic cyclic nitriles, cyclopentane-1-carbonitrile and cyclohexane-1-carbonitrile, are introduced that allow for successful suppression of aluminum dissolution and control of internal interfaces under application-relevant conditions. Such nitrile-based electrolytes show higher intrinsic oxidative and thermal stabilities as well as similar capacity retentions in lithium nickel-manganese-cobalt oxide LiNi3/5Mn1/5Co1/5O2 (NMC622)||graphite based full cells compared to the state-of-the-art organic carbonate-based electrolytes, even when bis(trifluoro-methane)sulfonimide lithium salt is utilized. Moreover, the importance of relative permittivity, degree of ion dissociation, and viscosity of the applied electrolyte formulations for the protection of current collector interfaces is emphasized.

Graphene-Wrapped Silicon Nanoparticles for All-Solid-State Lithium-Ion Batteries

Current lithium-ion batteries consist of a graphite anode and a metal oxide cathode. Due to their relatively high energy density and rechargeability, they have enabled various applications over the past few decades. However, significant improvements to battery cost, performance, and safety for applications such as vehicle electrification require a shift to next-generation materials, such as silicon as an anode which offers higher capacity, as well as solid-state electrolytes (SSEs) which are non-flammable. Both of these technologies currently suffer challenges which have prevented their widespread adoption. Silicon suffers low conductivity, and large volume change on each cycle, subsequently causing loss in electrical contact and the formation of an unstable solid electrolyte interface (SEI) each cycle. This project aims to solve these challenges by wrapping silicon nanoparticles and a sacrificial spacing material with crumpled graphene sheets using a scalable, spray drying method, and coupling it with a solid electrolyte. The graphene shell provides electrical contact with the silicon and space for its expansion during lithiation. The solid electrolyte provides a safer alternative to liquid electrolytes, and further reduces the SEI formation which, with a liquid electrolyte, can leak into such crumpled structures. In this work we will present our initial results concerning how the spacing material affects the structure and how the overall structure can be modified by spray drying parameters to determine optimal conditions for capacity and cycle-life using, first, at typical, organic carbonate-based electrolyte. We will explore different spacing material candidates such as chitosan which, upon heat treatment of the sample, would not only provide space for the expansion of silicon, but the residual nitrogen-doped carbon would also act as a conductive filler inside the crumpled structure. Furthermore, we will investigate various binder systems and their impact on cycle-stability including polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), sodium alginate (SA), and cross-linked SA. Based on preliminary, both PAA and SA are shown to have improved performance compared to PVDF as well as higher cycle life, however, SA forms smoother, thinner electrode films. Cross-linked SA is also shown to increase the cycling life and decrease the capacity loss per cycle. We then explore powder mixing and solution infiltration methods to introduce high conductivity SSEs and their performance when coupled to the graphene-wrapped silicon anode structures.

Direct Operando Observation of Double Layer Charging and Early Solid Electrolyte Interphase Formation in Li-Ion Battery Electrolytes.

The solid electrolyte interphase (SEI) is the most critical yet least understood component to guarantee stable and safe operation of a Li-ion cell. Herein, the early stages of SEI formation in a typical LiPF6 and organic carbonate-based Li-ion electrolyte are explored by operando surface-enhanced Raman spectroscopy, on-line electrochemical mass spectrometry, and electrochemical quartz crystal microbalance. The electric double layer is directly observed to charge as Li+ solvated by ethylene carbonate (EC) progressively accumulates at the negatively charged electrode surface. Further negative polarization triggers SEI formation, as evidenced by H2 evolution and electrode mass deposition. Electrolyte impurities, HF and H2O, are reduced early and contribute in a multistep (electro)chemical process to an inorganic SEI layer rich in LiF and Li2CO3. This study is a model example of how a combination of highly surface-sensitive operando characterization techniques offers a step forward to understand interfacial phenomena in Li-ion batteries.

Ultra-Stable Performance of Ni-Rich Layered Oxide Cathodes for Lithium-Ion Batteries Using Ionic Liquid Electrolyte

High energy density lithium-ion batteries (LIBs) have continually been of great research interest amplified by the exponentially growing demand for electric vehicles.[1] Among the investigated systems, nickel-rich transition metal oxides appear very promising owing to their high specific capacity,[2] and low cobalt content, according to necessity of reducing the cobalt proportion in LIB cathodes due to its severe shortage and strong environmental and ecological concerns.[3] However, the increased nickel content also introduces previously overcome challenges of poor capacity retention and thermal stability due to the vulnerability of the nickel rich oxide towards interfacial side reactions.[4] Herein, a low volatility and non-flammable ionic liquid-based (IL) electrolyte[5] consisting of 0.8Pyr14FSI-0.2LiTFSI is employed to overcome those challenges faced by a Ni-rich LiNi0.8Co0.1Mn0.1O2 positive electrode. The cathode exhibits remarkable electrochemical performance in half-cell configuration, delivering a specific capacity of approximately 200 mAh g-1 and practically no capacity fading after 100 cycles at 0.1C at room temperature. After 600 cycles at 0.5C the cathode has an outstanding capacity retention of 97%, which is substantially higher than with the conventional organic carbonate-based electrolyte used for reference, attributed to a much more stable electrode-electrolyte interfacial layer. Even at elevated temperature (40 °C) the LiNi0.8Co0.1Mn0.1O2 in combination with the IL electrolyte offers a specific capacity of more than 200 mAh g-1 as well as a capacity retention around 99% after 100 cycles at 0.5C. To the best of our knowledge these results exceed the state-of-the-art performance reported for any Ni-rich positive electrode. Reference [1] W. Liu, P. Oh, X. Liu, M. J. Lee, W. Cho, S. Chae, Y. Kim, J. Cho, Angewandte Chemie 2015, 54, 4440.[2] S. H. A. Heist, and S. H. Lee, J . Electrochem . Soc 2019, 166 (6) A873-A879.[3] C.Vaalma, D. Buchholz, M. Weil, S. Passerini, Nature Review Materials 2018, 3, 18013.[4] U.-H. Kim, L.-Y. Kuo, P. Kaghazchi, C. S. Yoon, Y.-K. Sun, ACS Energy Letters 2019, 4, 576.[5] G. A. Elia, U. Ulissi, S. Jeong, S. Passerini, J. Hassoun, Energy & Environmental Science 2016, 9, 3210.

Acyclic Acetals in Propylene Carbonate-Based Electrolytes for Advanced and Safer Graphite-Based Lithium Ion Batteries

In this work, we investigate the electrochemical and safety performance of the glyoxalic acyclic acetals, namely 1,1,2,2-tetramethoxyethane (TME) and 1,1,2,2 tetraethoxyethane (TEE) as substituted solvents for linear organic carbonates in propylene carbonate (PC)-based electrolytes in LiNi0.6Mn0.2Co0.2O2∣∣graphite cells. By means of conductivity measurements and under consideration of PC-intercalation suppression, an optimized electrolyte was formulated with excellent thermal properties and electrochemical performance. The optimized electrolyte shows excellent cycling performance at the level of established organic carbonate-based electrolyte consisted ethylene carbonate, ethyl methyl carbonate and with lithium hexafluorophosphate as conducting salt with an extended operating cycling temperature window, good C-rate behavior and promising safety properties, clearly demonstrating the application potential of this new solvent class for lithium ion battery electrolytes.