Cation‐Assisted Lithium Ion Transport for High Performance PEO‑based Ternary Solid Polymer Electrolytes

AbstractN‐alkyl‐N‐alkyl pyrrolidinium‐based ionic liquids (ILs) are promising candidates as non‐flammable plasticizers for lowering the operation temperature of poly(ethylene oxide) (PEO)‐based solid polymer electrolytes (SPEs), but they present limitations in terms of lithium‐ion transport, such as a much lower lithium transference number. Thus, a pyrrolidinium cation was prepared with an oligo(ethylene oxide) substituent with seven repeating units. We show, by a combination of experimental characterizations and simulations, that the cation's solvating properties allow faster lithium‐ion transport than alkyl‐substituted analogues when incorporated in SPEs. This proceeds not only by accelerating the conduction modes of PEO, but also by enabling new conduction modes linked to the solvation of lithium by a single IL cation. This, combined with favorable interfacial properties versus lithium metal, leads to significantly improved performance on lithium‐metal polymer batteries

Lithium bis­(2-methyl­lactato)borate monohydrate

The title compound {systematic name: poly[[aqua­lithium]-μ-3,3,8,8-tetra­methyl-1,4,6,9-tetra­oxa-5λ4-borataspiro­[4.4]nonane-2,7-dione]}, [Li(C8H12BO6)(H2O)]n (LiBMLB), forms a 12-membered macrocycle, which lies across a crystallographic inversion center. The lithium cations are pseudo-tetra­hedrally coordinated by three methyl­lactate ligands and a water mol­ecule. The asymmetric units couple across crystallographic inversion centers, forming the 12-membered macrocycles. These macrocycles, in turn, cross-link through the Li+ cations, forming an infinite polymeric structure in two dimensions parallel to (101)

Revealing the Effect of High Ni Content in Li-Rich Cathode Materials: Mitigating Voltage Decay or Increasing Intrinsic Reactivity

Li-rich layered oxides are considered as one of the most promising cathode materials for secondary lithium batteries due to their high specific capacities, but the issue of continuous voltage decay during cycling hinders their market entry. Increasing the Ni content in Li-rich materials is assumed to be an effective way to address this issue and attracts recent research interests. However, a high Ni content may induce increased intrinsic reactivity of materials, resulting in severe side reactions with the electrolyte. Thus, a comprehensive study to differentiate the two effects of the Ni content on the cell performance with Li-rich cathode is carried out in this work. Herein, it is demonstrated that a properly dosed amount of Ni can effectively suppress the voltage decay in Li-rich cathodes, while over-loading of Ni, on the contrary, can cause structural instability, Ni dissolution, and nonuniform Li deposition during cycling as well as severe oxygen loss. This work offers a deep understanding on the impacts of Ni content in Li-rich materials, which can be a good guidance for the future design of such cathodes for high energy density lithium batteries

Coordinating Anions “to the Rescue” of the Lithium Ion Mobility in Ternary Solid Polymer Electrolytes Plasticized With Ionic Liquids

Lithium salts with low coordinating anions such as bis(trifluoromethanesulfonyl)imide (TFSI) have been the state-of-the-art for polyethylene oxide (PEO)-based “dry” polymer electrolytes for 3 dec- ades. Plasticizing PEO with TFSI-based ionic liquids (ILs) to form ternary solid polymer electrolytes (TSPEs) increases conductivity and Li+ diffusivity. However, the Li+ transport mechanism is unaffected compared to their “dry” counterparts and is essentially coupled to the dynamics of the polymer host matrix, which limits Li+ transport improvement. Thus, a paradigm shift is hereby suggested: the utilization of more coordinating anions such as trifluo- romethanesulfonyl-N-cyanoamide (TFSAM), able to compete with PEO for Li+ solvation, to accelerate the Li+ transport and reach a higher Li+ transfer- ence number. The Li–TFSAM interaction in binary and ternary TFSAM-based electrolytes is probed by experimental methods and discussed in the context of recent computational results. In PEO-based TSPEs, TFSAM drastically accelerates the Li+ transport (increases Li+ transference number by a factor 6 and the Li+ conductivity by 2–3) and computer simulations reveal that lithium dynamics are effectively re-coupled from polymer to anion dynamics. Last, this concept of coordinating anions in TSPEs is successfully applied in LFP||Li metal cells leading to enhanced capacity retention (86% after 300 cycles) and an improved rate performance at 2C

A Post-Mortem Study of Stacked 16 Ah Graphite//LiFePO₄ Pouch Cells Cycled at 5 °C

Herein, the post-mortem study on 16 Ah graphite//LiFePO4 pouch cells is reported. Aiming to understand their failure mechanism, taking place when cycling at low temperature, the analysis of the cell components taken from different portions of the stacks and from different positions in the electrodes, is performed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS). Also, the recovered electrodes are used to reassemble half-cells for further cycle tests. The combination of the several techniques detects an inhomogeneous ageing of the electrodes along the stack and from the center to the edge of the electrode, most probably due to differences in the pressure experienced by the electrodes. Interestingly, XPS reveals that more electrolyte decomposition took place at the edge of the electrodes and at the outer part of the cell stack independently of the ageing conditions. Finally, the use of high cycling currents buffers the low temperature detrimental effects, resulting in longer cycle life and less inhomogeneities

Ionic Liquid Electrolytes for Li-Air Batteries : Lithium Metal Cycling

In this work, the electrochemical stability and lithium plating/stripping performance of N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI) are reported, by investigating the behavior of Li metal electrodes in symmetrical Li/electrolyte/Li cells. Electrochemical impedance spectroscopy measurements and galvanostatic cycling at different temperatures are performed to analyze the influence of temperature on the stabilization of the solid electrolyte interphase (SEI), showing that TFSI-based ionic liquids (ILs) rank among the best candidates for long-lasting Li–air cells

Solid‐State Batteries with Polymer Electrolytes

Expectations on solid-state lithium batteries are at their highest as they are seen as a “next-generation” technology, although solid polymer electrolytes have already enabled the commercialization of electrical vehicles for almost 10 years. These are powered by lithium metal batteries and use a polyethylene oxide (PEO)-based electrolyte. Thus, after a quick review of the current state of the art on lithium batteries including various polymers electrolytes, we present some fundamentals about the lithium metal anode. We then give an overview of the different approaches that have been proposed in the past 40 years for improving the performance of these types of electrolytes. The trends that have led to the current generation of solid polymer electrolytes are reported first: They consisted in decreasing the crystallinity of PEO and increasing its chain segmental mobility while preventing electrolyte creeping at high temperature, and the use of plasticizers, fillers, statistical copolymers, and branched polymers such as cross-linked and comb-shaped polymers was developed. However, PEO and “dry” solid polymer electrolytes incorporating dissolved lithium salts, in general, suffer from intrinsic limitations. Thus, we then present as perspectives, the most promising polymer electrolyte concepts for improving lithium metal polymer batteries. In particular, the use of polycarbonates as alternative polymer matrixes, the use of polymers in hybrid organic/inorganic electrolytes, the use of block copolymers and liquid crystals for decorrelating conductivity from mechanical properties, and finally, the development of single-ion conductors

Nouveaux électrolytes polymères pour batterie au lithium

GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Towards practical sulfolane based electrolytes: Choice of Li salt for graphite electrode operation

Sulfolane (tetramethylene sulfone, SL) is known for leading to Li-ion electrolytes with high anodic stability. However, the operation of graphite electrodes in alternative electrolytes is usually challenging, especially when ethylene carbonate (EC) is not used as co-solvent. Thus, we study here the influence of the lithium salt on the physico-chemical and electrochemical properties of EC-free SL-based electrolytes and on the performance of graphite electrodes based on carboxymethyl cellulose (CMC). SL mixed with dimethyl carbonate (DMC) leads to electrolytes as conductive as state-of-the-art alkyl carbonate-based electrolytes with wide electrochemical stability windows. The compatibility with graphite electrodes depends on the Li salt used and, even though cycling is possible with most salts, lithium difluoro-oxalato borate (LiDFOB) is especially interesting for graphite operation. LiDFOB electrolytes are conductive at room temperature (ca. 6 mS cm−1) with an anodic stability slightly below 5 V vs. Li/Li+ on particulate carbon black electrodes. In addition, it allows cycling graphite electrodes with steady capacity and high coulombic efficiency without any additive. The testing of graphite electrodes in half-cells is, however, problematic with SL:DMC mixtures and, by switching the Li metal counter electrode for LiFePO4, the graphite electrode achieves better practical performance in terms of rate capability