Critical aspects in the development of lithium-air batteries

Intensive research has been done on lithium-air batteries, especially in the last few years. Due to their very high theoretical specific energy, lithium-air batteries are one of the most promising candidates to power future electric vehicles. However, this new technology is in a very early stage of development, and several challenges must be overcome before there will be a commercially viable product. This review describes the most important critical aspects in the development of lithium-air batteries: the electrocatalysis of the oxygen electrode reactions, the degradation of the electrolyte and the oxygen electrode components, the structure of the oxygen electrode, and the passivation of the oxygen electrode during the discharge of the battery. Recent works in these areas are critically reviewed, and suitable research strategies to address these issues are discusse

The Effect of Water on Quinone Redox Mediators in Nonaqueous Li-O2 Batteries.

The parasitic reactions associated with reduced oxygen species and the difficulty in achieving the high theoretical capacity have been major issues plaguing development of practical nonaqueous Li-O2 batteries. We hereby address the above issues by exploring the synergistic effect of 2,5-di-tert-butyl-1,4-benzoquinone and H2O on the oxygen chemistry in a nonaqueous Li-O2 battery. Water stabilizes the quinone monoanion and dianion, shifting the reduction potentials of the quinone and monoanion to more positive values (vs Li/Li+). When water and the quinone are used together in a (largely) nonaqueous Li-O2 battery, the cell discharge operates via a two-electron oxygen reduction reaction to form Li2O2, with the battery discharge voltage, rate, and capacity all being considerably increased and fewer side reactions being detected. Li2O2 crystals can grow up to 30 μm, more than an order of magnitude larger than cases with the quinone alone or without any additives, suggesting that water is essential to promoting a solution dominated process with the quinone on discharging. The catalytic reduction of O2 by the quinone monoanion is predominantly responsible for the attractive features mentioned above. Water stabilizes the quinone monoanion via hydrogen-bond formation and by coordination of the Li+ ions, and it also helps increase the solvation, concentration, lifetime, and diffusion length of reduced oxygen species that dictate the discharge voltage, rate, and capacity of the battery. When a redox mediator is also used to aid the charging process, a high-power, high energy density, rechargeable Li-O2 battery is obtained.The authors thank EPSRC-EP/M009521/1 (T.L., G.K., C.P.G.), Innovate UK (T.L.), Darwin Schlumberger Fellowship (T.L.), EU Horizon 2020 GrapheneCore1-No.696656 (G.K., C.P.G.), EPSRC - EP/N024303/1, EP/L019469/1 (N.G.-A., J.T.F.), Royal Society - RG130523 (N.G.-A.), and the European Commission FP7-MC–CIG Funlab, 630162 (N.G.-A.) for research funding

2021 roadmap on lithium sulfur batteries

Abstract: Batteries that extend performance beyond the intrinsic limits of Li-ion batteries are among the most important developments required to continue the revolution promised by electrochemical devices. Of these next-generation batteries, lithium sulfur (Li–S) chemistry is among the most commercially mature, with cells offering a substantial increase in gravimetric energy density, reduced costs and improved safety prospects. However, there remain outstanding issues to advance the commercial prospects of the technology and benefit from the economies of scale felt by Li-ion cells, including improving both the rate performance and longevity of cells. To address these challenges, the Faraday Institution, the UK’s independent institute for electrochemical energy storage science and technology, launched the Lithium Sulfur Technology Accelerator (LiSTAR) programme in October 2019. This Roadmap, authored by researchers and partners of the LiSTAR programme, is intended to highlight the outstanding issues that must be addressed and provide an insight into the pathways towards solving them adopted by the LiSTAR consortium. In compiling this Roadmap we hope to aid the development of the wider Li–S research community, providing a guide for academia, industry, government and funding agencies in this important and rapidly developing research space

Critical aspects in the development of lithium–air batteries

Intensive research has been done on lithium–air batteries, especially in the last few years. Due to their very high theoretical specific energy, lithium–air batteries are one of the most promising candidates to power future electric vehicles. However, this new technology is in a very early stage of development, and several challenges must be overcome before there will be a commercially viable product. This review describes the most important critical aspects in the development of lithium–air batteries: the electrocatalysis of the oxygen electrode reactions, the degradation of the electrolyte and the oxygen electrode components, the structure of the oxygen electrode, and the passivation of the oxygen electrode during the discharge of the battery. Recent works in these areas are critically reviewed, and suitable research strategies to address these issues are discusse

Estimating lithium-ion battery behavior from half-cell data

The electrochemical behavior of lithium-ion battery electrode materials is often studied in the so-called ‘lithium half-cell configuration’, in which the electrode is tested in an electrochemical cell with a lithium metal electrode acting as both counter and reference electrode. However, the performance of lithium-ion batteries is affected by the electrochemical behavior of the two electrodes composing the battery. Therefore, in order to understand the behavior of battery materials under conditions representative of commercial applications, it is necessary to perform electrochemical measurements in the so-called ‘full-cell configuration’, in which a cathode (e.g. lithium iron phosphate or LFP) and an anode (e.g. graphite) are combined in an appropriate capacity ratio. In this work, we provide further understanding of how the behavior of the electrodes in half-cell configuration affects the electrochemical response of the full cell. For that, we characterize two commercially relevant battery materials, LFP and graphite, in lithium half-cells, and also combined in a LFP vs graphite full-cell. Additionally, we employ the electrochemical response of the LFP and graphite electrodes in lithium-half cells to predict the electrochemical response of the LFP vs graphite full-cell, and the results of our calculations are in very good agreement with the experimental measurements

A review of gas evolution in lithium ion batteries

This is a review on recent studies into the gas evolution occurring within lithium ion batteries and the mechanisms through which the processes proceed. New cathode materials such as lithium nickel manganese cobalt oxides are being heavily researched for the development of higher specific capacity electrodes. These materials often suffer from rapid degradation which coincides with gas evolution. Further sources of gas evolution include electrolyte reduction at the anode during the initial cycles culminating in formation of a solid electrolyte interphase and surface layer compounds formed on the cathode during production and storage. There have been several techniques established for detection and quantification of gas evolution in ex situ and in situ studies, primarily gas chromatography mass spectrometry and differential/on-line electrochemical mass spectrometry

New insight on the behavior of the irreversible adsorption and underpotential deposition of thallium on platinum (111) and vicinal surfaces in acid electrolytes

We report, for the first time, the electrochemical behavior of thallium irreversibly adsorbed on Pt (111) and platinum stepped surfaces composed of (111) terraces and monoatomic steps. Similar to the case of thallium UPD, the voltammograms obtained after thallium irreversible adsorption present three characteristic features. After a careful analysis of the effect of the thallium concentration, the concentration and nature of the anion of the supporting electrolyte and the pH of the solution on these voltammetric features, we have been able to ascribe these processes to Tl/Tl+ oxidation and anion adsorption on the Tl-modified surface. In addition, the results obtained with stepped surfaces, indicate that some of the features are clearly associated to the presence of (111) surface domains, and thus they could be used for the quantification of these sites

Highly sensitive operando pressure measurements of Li-ion battery materials with a simply modified Swagelok cell

A new cell design has been developed using a standard Swagelok cell for Li-ion battery material characterisation, which has been modified by replacing one of the electrode cylindrical plungers with an adaptor to a pressure sensor. By simplifying the cell design (no valves or unnecessary connectors have been included), the cell headspace volume is kept at a minimum (ca. 1.9 ml for a one-inch-diameter cell) which produces a dramatic increase in sensitivity of the measurements with respect to conventional set-ups. Changes in pressure induced by Li-ion battery materials processes (gas evolution, structural changes in volume of the battery material due to Li-ion insertion/extraction) are monitored with unprecedented sensitivity. Here we illustrate the application of this novel cell design for the operando pressure measurements of LiFePO4 and graphite in Li half-cell configurations, and detailed procedures of cell calibration, protocols for cell preparation and assembly and technical drawings of the cell parts are provided to facilitate the adoption of this technique for testing new battery materials. We also demonstrate the high sensitivity of this new set-up to study the corrosion of cell materials in contact with LiPF6-containing electrolytes, which had not been explored before with operando pressure measurements

An unsuitable Li-O₂ battery electrolyte made suitable with the use of redox mediators

The unique properties of room temperature ionic liquids make them promising electrolytes for next-generation rechargeable batteries. Unfortunately, many promising ionic liquid electrolytes suffer degradation under the operation conditions of Li-O2 batteries. This work demonstrates that the addition of redox mediators can transform the reaction mechanism and suppress the degradation of the electrolytes in Li-O2 batteries. 1-ethyl-3-methylimidazolium bis(trifluoro-methylsulfonyl)imide (EMIMTFSI) is a room temperature ionic liquid that is widely being explored for battery applications, but its instability in the presence of reduced oxygen species (superoxide) limits application in Li-O2 batteries. The addition of redox mediators can suppress the degradation of EMIMTFSI in Li-O2 cells, leading to remarkable improvements in capacity and reversibility. In-situ Surface Enhanced Raman Spectroscopy and operando-pressure evaluation demonstrate that 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ) is capable of suppressing the attack of superoxide species against EMIMTFSI, thus promoting the desirable 2-electron pathway to Li2O2 discharge product. A detailed evaluation of the gas evolution was carried out using online mass spectrometry. In spite of an efficient 2-electron oxygen reduction with the use of DBBQ additive, this effect did not translate into a substantial improvement in the oxygen evolution during charging. However, when a charge mediator was used in combination with DBBQ, a significant improvement in oxygen evolution could be observed. This work provides the first direct experimental evidence that redox mediators can enable the incorporation of electrolytes prone to degradation by the attack of superoxide species in practical and reversible Li-O2 batteries