Thermal activated (thermal) battery technology: Part II. Molten salt electrolytes

This article gives an overview of the important properties and design characteristics of electrolyte used in thermally activated (thermal) batteries. The basic physical properties of the main compositions are reviewed. The properties of electrolytes such as melting point, ionic conductivity, surface tension, density, thermal characteristics, and moisture sensitivity were analyzed in relation with the functioning of the batteries. Solubility data of alkali metals, sulphides, and oxides were compiled and analyzed. The important parameters of separator pellets are discussed in terms of both electrical and mechanical properties as they pertain to thermal-battery design and functioning. A number of lower-melting electrolytes are presented along with key physical properties for possible use in applications requiring lower operating temperatures such as borehole power supplies.     

Dimethyl methylphosphonate (DMMP) as an efficient flame retardant additive for the lithium-ion battery electrolytes

Dimethyl methylphosphonate (DMMP) was used as a flame retardant additive to 1 M LiPF₆/EC + DEC system. The flammability, electrochemical stability and cycling performance of electrolyte containing DMMP were studied. The addition of DMMP to electrolytes provides a significant suppression in the flammability of the electrolyte concluded from the measurements of self-extinguish time and limited oxygen index. The totally nonflammable electrolytes can be achieved with only 10 wt.% DMMP addition—the highly efficient retardant additive. The addition of DMMP causes little damage on the cell electrochemical performance. DMMP is a promising flame retardant additive to improve the safety of lithium-ion batteries.     

Nanofiltration of NaCl solutions using a SPPO membrane (BQ01) Part 1. Membrane characterization and separation mechanisms

Results from an experimental investigation of BQ01 nanofiltration (NF) are reported in this paper aiming at delineating the role of process parameters on BQ01 performances. The data highlight the specific behavior of BQ01 membranes in response to solute type and to variations in solution concentration. Variations in permeability and separation factors due to the presence of electrolytes are recorded. It is demonstrated that the concentration polarization cannot explain the observed variations. To elucidate the mechanisms related to this particular membrane, another approach based on conformational properties of polymer coating (sulfonated polyphenylene oxide, SPPO) is proposed and discussed in relation with characterization results. The hypothesis about mechanisms that are developed in this part will be confronted to a series of NF experiments under the same operating conditions but under electric field (ENF) in part 2 of this study.     

Time-dependent modelling and asymptotic analysis of electrochemical cells

A (time-dependent) model for an electrochemical cell, comprising a dilute binary electrolytic solution between two flat electrodes, is formulated. The method of matched asymptotic expansions (taking the ratio of the Debye length to the cell width as the small asymptotic parameter) is used to derive simplified models of the cell in two distinguished limits and to systematically derive the Butler–Volmer boundary conditions. The first limit corresponds to a diffusion-limited reaction and the second to a capacitance-limited reaction. Additionally, for sufficiently small current flow/large diffusion, a simplified (lumped-parameter) model is derived which describes the long-time behaviour of the cell as the electrolyte is depleted. The limitations of the dilute model are identified, namely that for sufficiently large half-electrode potentials it predicts unfeasibly large concentrations of the ion species in the immediate vicinity of the electrodes. This motivates the formulation of a second model, for a concentrated electrolyte. Matched asymptotic analyses of this new model are conducted, in distinguished limits corresponding to a diffusion-limited reaction and a capacitance-limited reaction. These lead to simplified models in both of which a system of PDEs, in the outer region (the bulk of the electrolyte), matches to systems of ODEs, in inner regions about the electrodes. Example (steady-state) numerical solutions of the inner equations are presented.     

偏析法提纯高锂钾盐电解质体系的探索与实践

随着近年来国内高品位铝土矿资源的逐渐减少,低品位铝矿石的综合利用技术已广泛应用到工业化氧化铝生产中。但其杂质含量较高,致使国内部分地区的铝土矿生产的氧化铝含有较高的锂、钾等成分,长期使用会导致工业电解质中的锂盐和钾盐的大量富集,电解槽出现效率低、电耗高、难控制、稳定性差等现象。目前,高锂、高钾电解质体系先后在甘肃、青海、山西等省区的电解铝厂出现,此电解质体系已经影响到该地区电解铝企业的正常生产。该文主要阐述偏析法提纯高锂高钾盐电解质体系过程中进行的探索和实践,经试验成功后在电解系列逐步推广。     

Si3N4结合SiC抗电解质侵蚀性能的研究状况

本文对国内外进行的氮化硅结合碳化硅耐火材料抗电解质侵蚀性能的研究做了较为全面的叙述,在已有研究的基础上对材料侵蚀机理和过程进行了总结,并对今后的研究方向提出了建议。     

Direct evidence of oxygen evolution from Li1+ x (Ni1/3Mn1/3Co1/3)1? x O2 at high potentials

Li_1+x (Ni_1/3Mn_1/3Co_1/3)_1−x O₂ (NMC) oxides are among the most promising positive electrode materials for future lithium–ion batteries. A voltage “plateau” was observed on the first galvanostatic charging curve of NMC in the extended voltage region positive to 4.5 V vs. Li/Li⁺ for compounds with x > 0 (overlithiated compounds). Differences were observed in the cycling stability of the overlithiated and stoichiometric (x = 0) NMC oxides in this potential region. A differential plot of the charge vs. potential profile in the first cycle revealed that, for the overlithiated compounds, a large irreversible oxidative peak arises positive to 4.5 V vs. Li/Li⁺, while in the same potential region only a small peak due to the electrolyte oxidation is detected for the stoichiometric material. Differential Electrochemical Mass Spectrometry (DEMS) was used to investigate the high voltage region for both compounds and experimental evidence for oxygen evolution was provided for the overlithiated compounds at potentials positive to 4.5 V vs. Li/Li⁺. No oxygen evolution was detected for the stoichiometric compound.     

Ionic liquids for CO2 electrochemical reduction

Electrochemical reduction of CO₂ is a novel research field towards a CO₂-neutral global economy and combating fast accelerating and disastrous climate changes while finding new solutions to store renewable energy in value-added chemicals and fuels. Ionic liquids (ILs), as medium and catalysts (or supporting part of catalysts) have been given wide attention in the electrochemical CO₂ reduction reaction (CO₂RR) due to their unique advantages in lowering overpotential and improving the product selectivity, as well as their designable and tunable properties. In this review, we have summarized the recent progress of CO₂ electro-reduction in IL-based electrolytes to produce higher-value chemicals. We then have highlighted the unique enhancing effect of ILs on CO₂RR as templates, precursors, and surface functional moieties of electrocatalytic materials. Finally, computational chemistry tools utilized to understand how the ILs facilitate the CO₂RR or to propose the reaction mechanisms, generated intermediates and products have been discussed.     

A panoramic view of Li7P3S11 solid electrolytes synthesis,structural aspects and practical challenges for all-solid-state lithium batteries

The development of an inorganic electrochemical stable solid-state electrolyte is essentially responsible for future state-of-the-art all-solid-state lithium batteries (ASSLBs). Because of their advantages in safety, working temperature, high energy density, and packaging, ASSLBs can develop an ideal energy storage system for modern electric vehicles (EVs). A solid electrolyte (SE) model must have an economical synthesis approach, exhibit electrochemical and chemical stability, high ionic conductivity, and low interfacial resistance. Owing to its highest conductivity of 17 mS·cm^-1, and deformability, the sulfide-based Li₇P₃S₁₁ solid electrolyte is a promising contender for the high-performance bulk type of ASSLBs. Herein, we present a current glimpse of the progress of synthetic procedures, structural aspects, and ionic conductivity improvement strategies. Structural elucidation and mechanistic approaches have been extensively discussed by using various characterization techniques. The chemical stability of Li₇P₃S₁₁ could be enhanced via oxide doping, and hard and soft acid/base (HSAB) concepts are also discussed. The issues to be undertaken for designing the ideal solid electrolytes, interfacial challenges, and high energy density have been discoursed. This review aims to provide a bird's eye view of the recent development of Li₇P₃S₁₁-based solid-state electrolyte applications and explore the strategies for designing new solid electrolytes with a target-oriented approach to enhance the efficiency of high energy density all-solid-state lithium batteries.     

Room temperature molten salts as lithium battery electrolyte

In the present study, are reported investigations obtained with the room temperature molten salt (RTMS) ethyl-methyl-imidazolium bis-(trifluoromethanesulfonyl)-imide (EMI-TFSI) in order to use it as solvent in lithium battery. The thermal stability, viscosity, conductivity and electrochemical properties are presented. A solution of 1m lithium bis-(trifluoromethanesulfonyl)-imide (LiTFSI) in EMI-TFSI has been used to test the electrolyte in a battery with LiCoO₂ and Li₄Ti₅O₁₂ as respectively cathode and anode materials. Cycling and power measurements have been obtained. The results have been compared with those obtained with a molten salt formulated with a different anion, BF₄⁻ and with a conventional liquid organic solvent EC/DMC containing LiTFSI. The 1m LiTFSI/EMI-TFSI electrolyte provides the best cycling performance: a capacity up to 106 mAh g⁻¹ is still delivered after 200 cycles, with 1C rate at 25 °C.