Characterizing capacity loss of lithium oxygen batteries by impedance spectroscopy

Polymer based carbon aerogels were prepared by synthesis of a resorcinol formaldehyde gel followed by pyrolysis at 1073K under Ar and activation of the resultant carbon under CO2 at different temperatures. The prepared carbon aerogels were used as active materials in the preparation of cathode electrodes for lithium oxygen cells and the electrochemical performance of the cells was evaluated by galvanostatic charge/discharge cycling and electrochemical impedance measurements. It was shown that the storage capacity and discharge voltage of a Li/O2 cell strongly depend on the porous structure of the carbon used in cathode. EIS results also showed that the shape and value of the resistance in the impedance spectrum of a Li/O2 cell are strongly affected by the porosity of carbon used in the cathode. Porosity changes due to the build up of discharge products hinder the oxygen and lithium ion transfer into the electrode, resulting in a gradual increase in the cell impedance with cycling. The discharge capacity and cycle life of the battery decrease significantly as its internal resistance increases with charge/discharge cycling.

Low pressure carbon dioxide solubility in pure electrolyte solvents for lithium-ion batteries as a function of temperature. Measurement and prediction

Experimental values for the carbon dioxide solubility in eight pure electrolyte solvents for lithium ion batteries – such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ?-butyrolactone (?BL), ethyl acetate (EA) and methyl propionate (MP) – are reported as a function of temperature from (283 to 353) K and atmospheric pressure. Based on experimental solubility data, the Henry’s law constant of the carbon dioxide in these solvents was then deduced and compared with reported values from the literature, as well as with those predicted by using COSMO-RS methodology within COSMOthermX software and those calculated by the Peng–Robinson equation of state implemented into Aspen plus. From this work, it appears that the CO2 solubility is higher in linear carbonates (such as DMC, EMC, DEC) than in cyclic ones (EC, PC, ?BL). Furthermore, the highest CO2 solubility was obtained in MP and EA solvents, which are comparable to the solubility values reported in classical ionicliquids. The precision and accuracy of the experimental values, considered as the per cent of the relative average absolute deviations of the Henry’s law constants from appropriate smoothing equations and from literature values, are close to (1% and 15%), respectively. From the variation of the Henry’s law constants with temperature, the partial molar thermodynamic functions of dissolution such as the standard Gibbs free energy, the enthalpy, and the entropy are calculated, as well as the mixing enthalpy of the solvent with CO2 in its hypothetical liquid state.

Low pressure carbon dioxide solubility in lithium-ion batteries based electrolytes as a function of temperature. Measurement and prediction

We present in this study the effect of nature and concentration of lithium salt, such as the lithium hexafluorophosphate, LiPF6; lithium tris(pentafluoroethane)-trifluorurophosphate LiFAP; lithium bis(trifluoromethylsulfonyl)imide, LiTFSI, on the CO2 solubility in four electrolytes for lithium ion batteries based on pure solvent that include ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), as well as, in the EC:DMC, EC:EMC and EC:DEC (50:50) wt.% binary mixtures as a function of temperature from (283 to 353) K and atmospheric pressure. Based on experimental solubility values, the Henry’s law constant of the carbon dioxide in these solutions with the presence or absence of lithium salt was then deduced and compared with reported values from the literature, as well as with those predicted by using COSMO-RS methodology within COSMOThermX software. From this study, it appears that the addition of 1 mol · dm-3 LiPF6 salt in alkylcarbonate solvents decreases their CO2 capture capacity. By using the same experimental conditions, an opposite CO2 solubility trend was generally observed in the case of the addition of LiFAP or LiTFSI salts in these solutions. Additionally, in all solutions investigated during this work, the CO2 solubility is greater in electrolytes containing the LiFAP salt, followed by those based on the LiTFSI case. The precision and accuracy of the experimental data reported therein, which are close to (1 and 15)%, respectively. From the variation of the Henry’s law constant with temperature, the partial molar thermodynamic functions of dissolution such as the standard Gibbs energy, the enthalpy, and the entropy, as well as the mixing enthalpy of the solvent with CO2 in its hypothetical liquid state were calculated. Finally, a quantitative analysis of the CO2 solubility evolution was carried out in the EC:DMC (50:50) wt.% binary mixture as the function of the LiPF6 or LiTFSI concentration in solution to elucidate how ionic species modify the CO2 solubility in alkylcarbonates-based Li-ion electrolytes by investigating the salting effects at T = 298.15 K and atmospheric pressure.

Physical properties of a new Deep Eutectic Solvent based on lithium bis[(trifluoromethyl)sulfonyl]imide and N-methylacetamide as superionic suitable electrolyte for lithium ion batteries and electric double layer capacitors

Herein we present a study on the physical/chemical properties of a new Deep Eutectic Solvent (DES) based on N-methylacetamide (MAc) and lithium bis[(trifluoromethyl)sulfonyl]imide (LiTFSI). Due to its interesting properties, such as wide liquid-phase range from -60°C to 280°C, low vapor pressure, and high ionic conductivity up to 28.4mScm at 150°C and at x=1/4, this solution can be practically used as electrolyte for electrochemical storage systems such as electric double-layer capacitors (EDLCs) and/or lithium ion batteries (LiBs). Firstly, relationships between its transport properties (conductivity and viscosity) as a function of composition and temperature were discussed through Arrhenius' Law and Vogel-Tamman-Fulcher (VTF) equations, as well as by using the Walden classification. From this investigation, it appears that this complex electrolyte possesses a number of excellent transport properties, like a superionic character for example. Based on which, we then evaluated its electrochemical performances as electrolyte for EDLCs and LiBs applications by using activated carbon (AC) and lithium iron phosphate (LiFePO) electrodes, respectively. These results demonstrate that this electrolyte has a good compatibility with both electrodes (AC and LiFePO) in each testing cell driven also by excellent electrochemical properties in specific capacitance, rate and cycling performances, indicating that the LiTFSI/MAc DES can be a promising electrolyte for EDLCs and LiBs applications especially for those requiring high safety and stability. © 2013 Elsevier Ltd.

Synthesis of Co3O4 nano-octahedra enclosed by {111} facets and their excellent lithium storage properties as anode material of lithium ion batteries

Abstract
Nano-sized(nO-Co3O4, 387nm)andmicron-sized(mO-Co3O4, 6.65 mm) Co3O4 octahedraenclosedby
{111}facetshavebeenbothsynthesizedthroughawetchemicalmethodfollowedbythermal
treatment,andservedasanodematerialoflithium ionbatteries(LIBs).Electrochemicalresults
demonstratethatthenO-Co3O4 showsexcellentlongcyclabilityandratecapability.ThenO-Co3O4
candeliverastablechargecapacityashighas955.5mAhg1 upto200cycleswithoutnoticeable
capacityfadingatacharge/dischargecurrentdensityof0.1Ag1 (ca. 0.11C).Theexcellent
electrochemicalperformanceisascribedtothenano-sizeandthe{111}facetsthatenclosethe
octahedra. WhilethemO-Co3O4 could onlymaintain288.5mAhg1 after 200cycles,illustratingvery
poorcyclingperformance,whichisascribedtothelargeparticlesizethatmaycausehugevolume
changeduringrepeatedcharging/discharging process.TheresultsrevealthattheCo3O4 nano-
octahedrawouldbeapromisinganodematerialforthenext-generationofLIBs.

Deep eutectic solvents based on N-methylacetamide and a lithium salt as suitable electrolytes for lithium-ion batteries

In this work, we present a study on the physical and electrochemical properties of three new Deep Eutectic Solvents (DESs) based on N-methylacetamide (MAc) and a lithium salt (LiX, with X = bis[(trifluoromethyl)sulfonyl]imide, TFSI; hexafluorophosphate, PF; or nitrate, NO). Based on DSC measurements, it appears that these systems are liquid at room temperature for a lithium salt mole fraction ranging from 0.10 to 0.35. The temperature dependences of the ionic conductivity and the viscosity of these DESs are correctly described by using the Vogel-Tammann-Fulcher (VTF) type fitting equation, due to the strong interactions between Li, X and MAc in solution. Furthermore, these electrolytes possess quite large electrochemical stability windows up to 4.7-5 V on Pt, and demonstrate also a passivating behavior toward the aluminum collector at room temperature. Based on these interesting electrochemical properties, these selected DESs can be classified as potential and promising electrolytes for lithium-ion batteries (LIBs). For this purpose, a test cell was then constructed and tested at 25 °C, 60 °C and 80 °C by using each selected DES as an electrolyte and LiFePO (LFP) material as a cathode. The results show a good compatibility between each DES and LFP electrode material. A capacity of up to 160 mA h g with a good efficiency (99%) is observed in the DES based on the LiNO salt at 60 °C despite the presence of residual water in the electrolyte. Finally preliminary tests using a LFP/DES/LTO (lithium titanate) full cell at room temperature clearly show that LiTFSI-based DES can be successfully introduced into LIBs. Considering the beneficial properties, especially, the cost of these electrolytes, such introduction could represent an important contribution for the realization of safer and environmentally friendly LIBs. © 2013 the Owner Societies.

Low pressure methane solubility in lithium-ion batteries based solvents and electrolytes as a function of temperature. Measurement and prediction

The methane solubility in five pure electrolyte solvents and one binary solvent mixture for lithium ion batteries – such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and the (50:50 wt%) mixture of EC:DMC was studied experimentally at pressures close to atmospheric and as a function of temperature between (280 and 343) K by using an isochoric saturation technique. The effect of the selected anions of a lithium salt LiX (X = hexafluorophosphate,

On the Performances of Ionic Liquid-Based Electrolytes for Li-NMC Batteries

Herein, the N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)amide and the N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)amide room temperature ionic liquids, combined with the lithium bis(trifluoromethanesulfonyl)amide salt, are investigated as electrolytes for Li/LiNi1/3Mn1/3Co1/3O2 (Li/NMC) batteries. To conduct this study, volumetric properties, ionic conductivity and viscosity of the pure ionic liquids and selected electrolytes were firstly determined as a function of temperature and composition in solution. These data were then compared with those measured in the case of the standard alkyl carbonate-based electrolyte: e.g. the EC/PC/3DMC + 1 mol·L−1 LiPF6. The compatibility of the selected electrolytes with the lithium electrode was then investigated by following the evolution of Li/electrolyte interfaces through impedance measurements. Interestingly, the impedances of the investigated Li/electrolyte interfaces were found to be more than three times lower than that measured using the standard electrolyte. Finally, electrochemical performances of the ionic liquid-based electrolytes were investigated using galvanostatic charge and discharge and cyclic voltammetry of each Li/NMC cell. Using these electrolytes, each tested Li cell reaches up to 145 mA·h·g−1 at C/10 and 110 mA·h·g−1 at C with a coulombic efficiency close to 100 %.

A new self-learning TLBO algorithm for RBF neural modelling of batteries in electric vehicles

One of the main purposes of building a battery model is for monitoring and control during battery charging/discharging as well as for estimating key factors of batteries such as the state of charge for electric vehicles. However, the model based on the electrochemical reactions within the batteries is highly complex and difficult to compute using conventional approaches. Radial basis function (RBF) neural networks have been widely used to model complex systems for estimation and control purpose, while the optimization of both the linear and non-linear parameters in the RBF model remains a key issue. A recently proposed meta-heuristic algorithm named Teaching-Learning-Based Optimization (TLBO) is free of presetting algorithm parameters and performs well in non-linear optimization. In this paper, a novel self-learning TLBO based RBF model is proposed for modelling electric vehicle batteries using RBF neural networks. The modelling approach has been applied to two battery testing data sets and compared with some other RBF based battery models, the training and validation results confirm the efficacy of the proposed method.

An integrated approach for real-time model-based state-of-charge estimation of lithium-ion batteries

Lithium-ion batteries have been widely adopted in electric vehicles (EVs), and accurate state of charge (SOC) estimation is of paramount importance for the EV battery management system. Though a number of methods have been proposed, the SOC estimation for Lithium-ion batteries, such as LiFePo4 battery, however, faces two key challenges: the flat open circuit voltage (OCV) vs SOC relationship for some SOC ranges and the hysteresis effect. To address these problems, an integrated approach for real-time model-based SOC estimation of Lithium-ion batteries is proposed in this paper. Firstly, an auto-regression model is adopted to reproduce the battery terminal behaviour, combined with a non-linear complementary model to capture the hysteresis effect. The model parameters, including linear parameters and non-linear parameters, are optimized off-line using a hybrid optimization method that combines a meta-heuristic method (i.e., the teaching learning based optimization method) and the least square method. Secondly, using the trained model, two real-time model-based SOC estimation methods are presented, one based on the real-time battery OCV regression model achieved through weighted recursive least square method, and the other based on the state estimation using the extended Kalman filter method (EKF). To tackle the problem caused by the flat OCV-vs-SOC segments when the OCV-based SOC estimation method is adopted, a method combining the coulombic counting and the OCV-based method is proposed. Finally, modelling results and SOC estimation results are presented and analysed using the data collected from LiFePo4 battery cell. The results confirmed the effectiveness of the proposed approach, in particular the joint-EKF method.

An effective three-dimensional ordered mesoporous ZnCo2O4 as electrocatalyst for Li-O2 batteries

Three-dimensional ordered mesoporous (3DOM) ZnCo₂O₄ materials have been synthesized via a hard template and used as bifunctional electrocatalysts for rechargeable Li-O₂ batteries. The as-prepared ZnCo₂O₄ nanoparticles possess a high specific surface area of 127.2 m² g^-1 and a spinel crystalline structure. The Li-O₂ battery utilizing 3DOM ZnCo₂O₄ shows a higher specific capacity of 6024 mAh g^-1 than that with pure Ketjen black (KB). Moreover, the ZnCo₂O₄-based electrode enables much enhanced cyclability with a smaller discharge-recharge voltage gap than that of the carbon-only cathode. Such excellent catalytic performance of ZnCo₂O₄ could be associated with its larger surface area and 3D ordered mesoporous structure

A design strategy of large grain lithium-rich layered oxides for lithium-ion batteries cathode

Li-rich materials are considered the most promising for Li-ion battery cathodes, as high capacity can be achieved. However, poor cycling stability is a critical drawback that leads to poor capacity retention. Here a strategy is used to synthesize a large-grain lithium-rich layered oxides to overcome this difficulty without sacrificing rate capability. This material is designed with micron scale grain with a width of about 300 nm and length of 1-3 μm. This unique structure has a better ability to overcome stress-induced structural collapse caused by Li-ion insertion/extraction and reduce the dissolution of Mn ions, which enable a reversible and stable capacity. As a result, this cathode material delivered a highest discharge capacity of around 308 mAh g^-1 at a current density of 30 mA g^-1 with retention of 88.3% (according to the highest discharge capacity) after 100 cycles, 190 mAh g^-1 at a current density of 300 mA g^-1 and almost no capacity fading after 100 cycles. Therefore, Lithium-rich material of large-grain structure is a promising cathode candidate in Lithium-ion batteries with high capacity and high cycle stability for application. This strategy of large grain may furthermore open the door to synthesize the other complex architectures for various applications.

One-dimensional porous La0.5Sr0.5CoO2.91 nanotubes as a highly efficient electrocatalyst for rechargeable lithium-oxygen batteries

The electrochemical performance of one-dimensional porous La_0.5Sr_0.5CoO_2.91 nanotubes as a cathode catalyst for rechargeable nonaqueous lithium-oxygen (Li-O₂) batteries is reported here for the first time. In this study, one-dimensional porous La_0.5Sr_0.5CoO_2.91 nanotubes were prepared by a simple and efficient electrospinning technique. These materials displayed an initial discharge capacity of 7205 mAh g^-1 with a plateau at around 2.66 V at a current density of 100 mA g^-1. It was found that the La_0.5Sr_0.5CoO_2.91 nanotubes promoted both oxygen reduction and oxygen evolution reactions in alkaline media and a nonaqueous electrolyte, thereby improving the energy and coulombic efficiency of the Li-O₂ batteries. The cyclability was maintained for 85 cycles without any sharp decay under a limited discharge depth of 1000 mAh g^-1, suggesting that such a bifunctional electrocatalyst is a promising candidate for the oxygen electrode in Li-O₂ batteries.

In situ preparation of 3D graphene aerogels@hierarchical Fe3O4 nanoclusters as high rate and long cycle anode materials for lithium ion batteries

We describe a novel strategy for in situ fabrication of hierarchical Fe₃O₄ nanoclusters-GAs. Fe₃O₄ NCs-GAs deliver excellent rate capability (the reversible capacities obtained were 1442, 392 and 118 mA h g^-1 at 0.1C, 12C and 35C rates), and a high reversible capacity of 577 mA h g^-1 over 300 cycles at the current density of 5.2 A g^-1 (6C).

Three-dimensional graphene-Co3O4 cathodes for rechargeable Li-O2 batteries

A three-dimensional (3D) graphene-Co₃O₄ electrode was prepared by a two-step method in which graphene was initially deposited on a Ni foam with Co₃O₄ then grown on the resulting graphene structure. Cross-linked Co₃O₄ nanosheets with an open pore structure were fully and vertically distributed throughout the graphene skeleton. The free-standing and binder-free monolithic electrode was used directly as a cathode in a Li-O₂ battery. This composite structure exhibited enhanced performance with a specific capacity of 2453 mA h g^-1 at 0.1 mA cm^-2 and 62 stable cycles with 583 mA h g^-1 (1000 mA h g_carbon^-1). The excellent electrochemical performance is associated with the unique architecture and superior catalytic activity of the 3D electrode.