Electrolytes and interphases in Li-ion batteries and beyond.

Ionically conducting polymer membranes (polymer electrolytes) might enhance lithium-battery technology by replacing the liquid electrolyte currently in use and thereby enabling the fabrication of flexible, compact, laminated solid-state structures free from leaks and available in varied geometries1. Polymer electrolytes explored for these purposes are commonly complexes of a lithium salt (LiX) with a high-molecular-weight polymer such as polyethylene oxide (PEO). But PEO tends to crystallize below 60 °C, whereas fast ion transport is a characteristic of the amorphous phase. So the conductivity of PEO–LiX electrolytes reaches practically useful values (of about 10−4 S cm−1) only at temperatures of 60–80 °C. The most common approach for lowering the operational temperature has been to add liquid plasticizers, but this promotes deterioration of the electrolyte's mechanical properties and increases its reactivity towards the lithium metal anode. Here we show that nanometre-sized ceramic powders can perform as solid plasticizers for PEO, kinetically inhibiting crystallization on annealing from the amorphous state above 60 °C. We demonstrate conductivities of around 10−4 S cm−1 at 50 °C and 10−5 S cm−1 at 30 °C in a PEO–LiClO4 mixture containing powders of TiO2 and Al2O3 with particle sizes of 5.8–13 nm. Further optimization might lead to practical solid-state polymer electrolytes for lithium batteries.

Nanocomposite polymer electrolytes for lithium batteries

This critical review presents an overview of the various classes of Li(+) conductors for use as electrolytes in lithium polymer batteries and all-solid state microbatteries. Initially, we recall the main models for ion transport and the structure-transport relationships at the basis of the observed conductivity behaviours. Emphasis is then placed on the physico-chemical and functional parameters relevant for optimal electrolytes preparation, as well as on the techniques of choice for their evaluation. Finally, the state of the art of polymer and ceramic electrolytes is reported, and the most interesting strategies for the future developments are described (121 references).

Electrolytes for solid-state lithium rechargeable batteries: recent advances and perspectives

Department of Chemical Engineering, University of California, Berkeley, California 94720-1462, USAPast theories of electrode stability assume that the surface tension resists the ampliﬁcation of surface roughness at cathodes andshow that instability at lithium/liquid interfaces cannot be prevented by surface forces alone @Electrochim. Acta, 40, 599 ~1995!#.This work treats interfacial stability in lithium/polymer systems where the electrolyte is solid. Linear elasticity theory is employedto compute the additional effect of bulk mechanical forces on electrode stability. The lithium and polymer are treated as Hookeanelastic materials, characterized by their shear moduli and Poisson’s ratios. Two-dimensional displacement distributions that satisfyforce balances across a periodically deforming interface are derived; these allow computation of the stress and surface-tensionforces. The incorporation of elastic effects into a kinetic model demonstrates regimes of electrolyte mechanical properties whereampliﬁcation of surface roughness can be inhibited. For a polymer material with Poisson’s ratio similar to poly~ethylene oxide!,interfacial roughening is mechanically suppressed when the separator shear modulus is about twice that of lithium.© 2005 The Electrochemical Society. @DOI: 10.1149/1.1850854# All rights reserved.Manuscript submitted January 16, 2004; revised manuscript received July 29, 2004. Available electronically January 11, 2005.

https://iopscience.iop.org/article/10.1149/1.1850854/pdf

The impact of elastic deformation on deposition kinetics at lithium/polymer interfaces

Review of gel-type polymer electrolytes for lithium-ion batteries

Studies of some poly(vinylidene fluoride) electrolytes

Polyacrylonitrile (PAN)-based electrolytes have been prepared by encapsulating Li salt solutions. The conductivity of these electrolytes is governed by a combination of factors including the relative amounts of PAN, EC, PC and the Li salt, and temperature. A conductivity of about 4.5 x 10{sup -3}{Omega}{sup -1} cm{sup -1} at 30 {degrees}C was exhibited by EC-rich electrolytes containing both LiN(SO{sub 2}CF{sub 3}){sub 2} and LiPF{sub 6}. The cationic transference numbers, measured using a dc polarization method coupled with impedance spectroscopy, were found to be between 0.2 and 0.3 for electrolytes containing LiN(CF{sub 3}SO{sub 2}){sub 2} and LiPF{sub 6}. The tensile strength of the electrolytes was observed to increase from 60 to 140 lb/in.{sup 2} upon incorporation of the thermally activated cross-linking agent ethylene glycol dimethacrylate. Cyclic voltammetry on Pt electrodes has shown that these electrolytes have an inherent oxidation stability window extending up to about 5 V versus Li{sup +}/Li. On Al, Ni, and Cu electrodes, however, oxidation was observed at lower potentials because of metal corrosion reactions. Copper was reversibly oxidized at 3.5 V, irrespective of the Li salt present in the electrolyte. On the other hand, the nature of the Li salt influenced the corrosion potentials of Al andmore » Ni. Nickel was found to be stable up to 4.2 V in the presence of LiAsF{sub 6}, whereas it was oxidized at about 3.5 and 4 V when the electrolyte contained LiN(SO{sub 2}CF{sub 3}){sub 2} and LiSO{sub 3}CF{sub 3} showing oxidation at {le}4 V. The electrochemical stability of the electrolytes was further verified in Li/LiMn{sub 2}O{sub 4} cells. 10 refs., 15 figs., 9 tabs.« less

Characterization of some polyacrylonitrile-based electrolytes

Both the dispersion state of nanoparticles (NPs) within polymer nanocomposites (PNCs) and the dynamical state of the polymer altered by the presence of the NP/polymer interfaces have a strong impact on the macroscopic properties of PNCs. In particular, mechanical properties are strongly affected by percolation of hard phases, which may be NP networks, dynamically modified polymer regions, or combinations of both. In this article, the impact on dispersion and dynamics of surface modification of the NPs by short monomethoxysilanes with eight carbons in the alkyl part (C8) is studied. As a function of grafting density and particle content, polymer dynamics is followed by broadband dielectric spectroscopy and analyzed by an interfacial layer model, whereas the particle dispersion is investigated by small-angle X-ray scattering and analyzed by reverse Monte Carlo simulations. NP dispersions are found to be destabilized only at the highest grafting. The interfacial layer formalism allows the clear identification of the volume fraction of interfacial polymer, with its characteristic time. The strongest dynamical slow-down in the polymer is found for unmodified NPs, while grafting weakens this effect progressively. The combination of all three techniques enables a unique measurement of the true thickness of the interfacial layer, which is ca. 5 nm. Finally, the comparison between longer (C18) and shorter (C8) grafts provides unprecedented insight into the efficacy and tunability of surface modification. It is shown that C8-grafting allows for a more progressive tuning, which goes beyond a pure mass effect.

/pdf/influence-of-the-graft-length-on-nanocomposite-structure-and-3bzux4l7.pdf

Influence of the Graft Length on Nanocomposite Structure and Interfacial Dynamics

The interfacial region formed in a polymer matrix around nanoparticles (NPs) controls many macroscopic properties of polymer nanocomposites (PNCs). However, understanding the factors controlling the structure and properties of the interfacial region remains a challenge. We demonstrated that the initial trapping of polymer chains at surfaces of NPs in solution strongly affects the macroscopic properties of PNCs. The most surprising result is that the differences in properties of PNCs persist even after an extremely long thermal annealing time. We ascribe the observed changes to the formation of an interfacial layer that is trapped in a deep metastable state already in solution. Furthermore, the presented analysis suggests that the PNC equilibration time is defined by the chain desorption time that can be extremely long and, in some cases, even not accessible on a reasonable experimental time scale. These results highlight the importance of polymer solution concentrations on the formation of an interfacial layer and the macroscopic properties of PNCs. 

Tuning the Properties of Nanocomposites by Trapping Them in Deep Metastable States

Fundamental understanding of the macroscopic properties of polymer nanocomposites (PNCs) remains difficult due to the complex interplay of microscopic dynamics and structure, namely interfacial layer relaxations and three-dimensional nanoparticle (NP) arrangements. The effect of surface modification by alkyl methoxysilanes at different grafting densities has been studied in PNCs made of poly(2-vinylpyridine) and spherical 20 nm silica NPs. The segmental dynamics has been probed by broadband dielectric spectroscopy and the filler structure by small-angle X-ray scattering and reverse Monte Carlo simulations. By combining the particle configurations with the interfacial layer properties, it is shown how surface modification tunes the attractive polymer-particle interactions: bare NPs slow down the polymer interfacial layer dynamics over a thickness of ca. 5 nm, while grafting screens these interactions. Our analysis of interparticle spacings and segmental dynamics provides unprecedented insights into the effect of surface modification on the main characteristics of PNCs: particle interactions and polymer interfacial layers.

pdf/how-tuning-interfaces-impacts-the-dynamics-and-structure-of-jf0wuvma.pdf

How Tuning Interfaces Impacts the Dynamics and Structure of Polymer Nanocomposites Simultaneously.

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