Matthew J. Lacey

Why PEO as a binder or polymer coating increases capacity in the Li-S system.

PEO, used either as a binder or a polymer coating, and PEGDME, used as an electrolyte additive, are shown to increase the reversible capacity of Li-S cells. The effect, in all three cases, is the same: an improved solvent system for the electrochemistry of sulfur species and suppression of cathode passivation on discharge. This constitutes a novel interpretation of the mechanistic behaviour of polyethers in the Li-S system, and sheds new light upon several previous studies.

The Li–S battery: an investigation of redox shuttle and self-discharge behaviour with LiNO3-containing electrolytes

The polysulfide redox shuttle and self-discharge behaviour of lithium–sulfur (Li–S) cells containing the electrolyte additive LiNO3 has been thoroughly explored by a range of electrochemical and surface analysis techniques on simple Li–S (i.e., not specifically optimised to resist self-discharge) and symmetrical Li–Li cells. Despite the relatively effective passivation of the negative electrode by LiNO3, fully charged cells self-discharged a quarter of their capacity within 3 days, although in the short-term cells can be recharged without any noticeable capacity loss. The processes governing the rate and reversibility of self-discharge in these cells have been investigated and explained in terms of the reactions of polysulfides occurring at both electrodes during idle conditions.

A Robust, Water‐Based, Functional Binder Framework for High‐Energy Lithium–Sulfur Batteries

We report here a water-based functional binder framework for the lithium-sulfur battery systems, based on the general combination of a polyether and an amide-containing polymer. These binders are applied to positive electrodes optimised towards high-energy electrochemical performance based only on commercially available materials. Electrodes with up to 4 mAh cm-2 capacity and 97-98 % coulombic efficiency are achievable in electrodes with a 65 % total sulfur content and a poly(ethylene oxide):poly(vinylpyrrolidone) (PEO:PVP) binder system. Exchange of either binder component for a different polymer with similar functionality preserves the high capacity and coulombic efficiency. The improvement in coulombic efficiency from the inclusion of the coordinating amide group was also observed in electrodes where pyrrolidone moieties were covalently grafted to the carbon black, indicating the role of this functionality in facilitating polysulfide adsorption to the electrode surface. The mechanical properties of the electrodes appear not to significantly influence sulfur utilisation or coulombic efficiency in the short term but rather determine retention of these properties over extended cycling. These results demonstrate the robustness of this very straightforward approach, as well as the considerable scope for designing binder materials with targeted properties.

State-of-charge indication in Li-ion batteries by simulated impedance spectroscopy

We here explore the possibilities of correlating experimental cell impedance with finite element methodology modelling for state-of-charge (SoC) indication in LiFePO

ε-Caprolactone-based Solid Polymer Electrolytes for Lithium-Ion Batteries: Synthesis, Electrochemical Characterization and Mechanical Stabilization by Block Copolymerization

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Functional, water-soluble binders for improved capacity and stability of lithium–sulfur batteries

4-based half-cells. The impedance response has been modelled sequentially during battery cycling using Newman theory, and is compared with experimental data. It is found that the charge-transfer resistance is dependent of SoC during battery charging, which can be modelled in good agreement with experimental results. Moreover, it is seen that cell design parameters—e.g. calendering-dependent electrode porosity—influence the EIS response and can thus be estimated using the presented methodology.Graphical Abstract

Porosity Blocking in Highly Porous Carbon Black by PVdF Binder and Its Implications for the Li-S System

The complexation of single walled carbon nanotubes (SWNTs) with neutral, anionic and cationic porphyrins has been investigated under identical complex forming conditions. The determination of the porphyrin loading reveals large differences depending on the nature of the porphyrin used. Combinations of different porphyrins to form mixed hetero-porphyrin complexes shows that the mixture of a cationic and anionic porphyrin results in loading which is an order of magnitude larger than in all other complexes. This complex also exhibits high adsorption and emission intensities and can be regarded as an extended co-operative binary ionic (CBI) solid. The complexes were further studied using Raman spectroscopy, elemental analysis, AFM and cyclic voltammetry.

In situ growth of polymer electrolytes on lithium ion electrode surfaces

In this work, three types of polymers based on e-caprolactone have been synthesized: poly(e-caprolactone), polystyrene-poly(e-caprolactone), and polystyrene-poly(e-caprolactone-r-trimethylene carbonate) (SCT), where the polystyrene block was introduced to improve the electrochemical and mechanical performance of the material. Solid polymer electrolytes (SPEs) were produced by blending the polymers with 10–40 wt% lithium bis(trifluoromethane)sulfonimide (LiTFSI). Battery devices were thereafter constructed to evaluate the cycling performance. The best performing battery half-cell utilized an SPE consisting of SCT and 17 wt% LiTFSI as both binder and electrolyte; a Li|SPE|LiFePO4 cell that cycled at 40 °C gave a discharge capacity of about 140 mA h g−1 at C/5 for 100 cycles, which was superior to the other investigated electrolytes. Dynamic mechanical analysis (DMA) showed that the storage modulus E’ was about 5 MPa for this electrolyte.