High discharge capacity solid composite polymer electrolyte lithium battery

In this study, a series of nanocomposite polymer electrolytes (CPEs), PAN/LiClO₄/SAP, with high conductivity are prepared based on polyacrylonitrile (PAN), LiClO₄ and low content of the silica aerogel powder (SAP) prepared by the sol-gel method with ionic liquid (IL) as the template. The effect of addition of SAP on the properties of the CPEs is investigated by FTIR, AC impedance, linear sweep voltagrams and cyclic voltammetry measurements as well as the charge-discharge performance. It is found that the ionic conductivity of the CPE is significantly improved by addition of SAP. The maximum ambient ionic conductivity of CPEs is about 12.5 times higher than that without addition of SAP. The results of the voltammetry measurements of CPE-3, which contained 3 wt% of SAP, show that the anodic and cathodic peaks are well maintained after 100 cycles, showing excellent electrochemical stability and cyclability over the potential range between 0 V and 4 V vs. Li/Li⁺. Besides, the room temperature discharge capacity measured at 0.5C for the coin cell based on CPE-3 is 120 mAh g⁻¹ and the capacity is retained after 20 cycles discharge, indicating the potential for practical use. This is perhaps the first report of the room temperature charge-discharge performance on the solid composite polymer electrolyte to the best of our knowledge.     

Characterization of high-power lithium-ion batteries by electrochemical impedance spectroscopy. I. Experimental investigation

The influence of the operation conditions temperature and state of charge (SOC) on the performance of a commercial high-power lithium-ion cell is investigated by electrochemical impedance spectroscopy. Based on the results of several preliminary tests, measurements were run covering the complete range of automotive applications.The cell impedance is presented and analyzed. A strong nonlinear temperature correlation is shown for all frequency ranges. Although the ohmic resistance is nearly unaffected by variation in SOC, the mass transport impedance reduces from 100% to 60% SOC and increases significantly again for lower SOCs.     

Characterization of high-power lithium-ion batteries by electrochemical impedance spectroscopy. II: Modelling

A common way to model lithium-ion batteries is to apply equivalent circuit (EC) models. In this work two different EC models are build up and parameterized for a commercial 6.5 Ah high-power lithium-ion cell. Measured impedance spectroscopy data depending on temperature and state of charge (SOC) are used for parameter estimation.The first EC model consists of an ohmic resistor (R), an inductor (L) and three RC-elements (a parallel connection of a capacitor (C) and a resistor). The second EC model consists of one R, one L, two Zarc elements and a Warburg element. The estimated parameters were used to develop two empirical electrical cell models which are able to predict the voltage of the cells depending on current, temperature and SOC. Hereby the internal cell resistance Ri is based on the EC models and a Butler-Volmer adjustment. Both approaches were validated by current profiles, which cover typical automotive applications to prove the model performance at low temperatures and high dynamic operation. An accurate voltage prediction could be realized with both EC models. The second, more complex, model is able to predict cell voltage more precisely, but at the expense of up to four times higher computational effort.     

New insight into the discharge process of sulfur cathode by electrochemical impedance spectroscopy

In this paper, the electrochemical reactions of sulfur cathode during discharge–charge process were investigated by EIS technique combining with XRD, SEM and EDS methods. The discharge process of the sulfur cathode could be divided into two discharge regions. These are the first discharge region (2.5–2.05 V) where the reduction of elemental sulfur to form soluble polysulfides and further reduction of the soluble polysulfides occurs, and the second discharge region (2.05–1.5 V) where the soluble polysulfides are reduced to form a Li₂S solid film covered over the carbon matrix. It was found that the EIS can distinguish the individual contributions of charge transfer resistances, ion diffusion impedance and properties originating from Li₂S film in the frequency domain of 100 kHz to 100 mHz. During the upper voltage plateau, the impedance of interfacial charge transfer dominates the reduction reaction, while during the lower voltage plateau, the mass transport in the cathode is a control step. It was also proved that the solid Li₂S appeared at the beginning of the lower voltage plateau region and became denser during the following discharge process.     

Electrochemical performance of highly mesoporous nitrogen doped carbon cathode in lithium-oxygen batteries

Nitrogen doped carbon with a high surface area was used as cathode electrode in a solid-state lithium-oxygen battery. Various techniques including the Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) were employed to evaluate the nitrogen functionality on carbon. The electrochemical properties of nitrogen doped carbon as cathode electrode in lithium-oxygen battery were studied using galvanostatic charge-discharge characteristics and electrochemical impedance spectroscopy (EIS). The lithium-oxygen cell fabricated with nitrogen doped Ketjenblack-Calgon activated carbon cathode exhibits two times higher discharge cell capacity than that of a cathode composed of only Ketjenblack-Calgon activated carbon. This work shows that the nitrogen functionality on carbon is responsible for the electro-catalytic activity of cathode and an enhancement in cell capacity of lithium-oxygen battery.     

Experimental measurement and analysis methods of electrochemical impedance spectroscopy for lithium batteries

电化学阻抗谱是一种重要的电化学测试方法,在电化学领域尤其是锂离子电池领域具有广泛的应用,如电导率、表观化学扩散系数、SEI的生长演变、电荷转移及物质传递过程的动态测量。本文介绍了电化学阻抗谱的基本原理、测试方法、测试注意事项、常用电化学阻抗测量设备及测试流程,并结合实际案例,具体分析了电化学阻抗谱在锂离子电池中的应用。     

Estimation of the kinetic parameters of processes at the negative plate of lead-acid batteries by impedance studies

Impedance characteristics of the negative electrode of lead-acid battery were derived on the basis of fundamental interfacial processes occurring at the electrode. The solution of the governing equations was presented in terms of a simple equivalent circuit consisting of resistive and capacitive loops in which charge transfer and sulfate layer formation and also mass transfer (Warburg) elements are considered. The kinetic parameters were deduced by fitting the theoretically derived impedance to the experimental data. Impedance at various States of Charge (SoC) was also examined.     

Analysis of the effect of resistance increase on the capacity fade of lithium ion batteries

Lithium ion cells, when cycled, exhibit a two‐stage degradation behavior characterized by a first linear stage and a second nonlinear stage where degradation is rapid. The multitude of degradation phenomena occurring in lithium ion batteries complicates the understanding of this two‐stage degradation behavior. In this work, a simple and intuitive model is presented to analyze the coupled effect of resistance growth and the shape of the state of charge (SOC)‐open circuit voltage (OCV) relationship in representing the complete degradation behavior. The model simulations demonstrate that a single resistance that increases linearly on cycling can capture the transition from slow to fast degradation, primarily due to the shape of the SOC‐OCV curve. Further, the model simulations indicate that the shape of the degradation curve depends strongly on the magnitude of current at the end of discharge of the cycling protocol. To verify these observations, specific experiments are designed with minimal capacity loss but with shrinking operating voltage ranges that result in shrinking operating OCV range. The results of the experiments validate the observations of model simulations. Further, long‐term cycling experiment with a commercial lithium ion cell shows that the operating OCV range shrinks substantially with aging and is a major reason for the observed accelerated degradation. The analysis of the present work provides significant insights towards developing simple semiempirical models suitable for battery life management in microcontrollers.     

Compatibility of the Py24TFSI-LiTFSI ionic liquid solution with Li4Ti5O12 and LiFePO4 lithium ion battery electrodes

Ionic liquids are assuming a constantly growing importance as preferred media for the progress of various energy devices such as solar cells, supercapacitors and lithium batteries. However, their electrochemical properties are not yet fully recognized and in this paper we try to contribute to fill the gap by investigating the stability window of a sample IL-based solution, as well as its interfacial properties with two typical lithium ion battery electrodes, namely lithium titanate, Li₄Ti₅O₁₂ and lithium iron phosphate, LiFePO₄. The results of a detailed impedance spectroscopy analysis demonstrate that, although operating well within the stability domain of the selected IL-based electrolyte, both electrodes undergo passivation phenomena with the formation on their surface of a solid electrolyte interface, SEI, layer. The impedance spectra show that the resistance of the SEI is very low and stable, this suggesting that its occurrence is highly beneficial in terms of assuring reversible and safe electrode processes.     

Investigation of the thermal properties of a Li-ion pouch-cell by electrothermal impedance spectroscopy

Electrothermal impedance spectroscopy (ETIS), is introduced as a new measurement method and thermal parameters derived from a pouch-type lithium-ion cell are presented. ETIS is a valuable tool for (i) the determination of the thermal impedance and (ii) the validation of thermal models. The excitation signal applied to the cell during measurement does not cause a change in entropy, thus facilitating the parameter identification of a thermal model for heat conduction and thermal capacity.ETIS can be applied to measurements in time domain and in frequency domain. Both approaches are presented and a combination further improves measurement time and accuracy.     

All-solid-state lithium secondary batteries with high capacity using black phosphorus negative electrode

Black phosphorus was prepared from red phosphorus by using mixer mill and planetary ball-mill apparatuses. The composites with black phosphorus and acetylene black (AB) were also prepared by using the mixer mill apparatus. The mechanical milling of black phosphorus and AB brought about a decrease in size of secondary particles of the composites. The all-solid-state lithium cells with the composite and the Li₂S-P₂S₅ glass-ceramic electrolyte exhibited the first discharge capacity of 1962 mAh g⁻¹ and the coulombic efficiency of 89% at the current density of 0.064 mA cm⁻² (24 mA g⁻¹). The all-solid-state cells worked at 3.8 mA cm⁻² (1.47 A g⁻¹) at 25 °C and showed the excellent cycle performance with a high capacity of over 500 mAh g⁻¹ for 150 cycles. Black phosphorus is one of the most attractive negative electrodes with both high capacity and high-rate performance in all-solid-state lithium rechargeable batteries with sulfide electrolytes.     

Sorting methods of lithium ion batteries consistency

锂离子电池因其高能量密度和长循环寿命而得到广泛应用.然而当多个电池通过串联或者并联成组时,电池组往往存在容量衰减过快,寿命较短的问题,这是由于电池单体之间的非一致性而造成的.如何利用简单,可靠的分选方法,筛选出性能尽可能一致的电池用来成组,对锂离子电池在大规模储能中的推广应用具有重要的科学与实践意义.该文综述了目前国内外锂离子电池一致性的分选方法,包括各方法的机理特点,并且简单介绍了作者课题组在这方面的研究进展.采用阻抗谱方法或许是建立准确,快速的评价体系和提高配对电池的一致性的有效分选方法.     

Study of current distribution and oxygen diffusion in the fuel cell cathode catalyst layer through electrochemical impedance spectroscopy

In this study, an analysis of the current distribution and oxygen diffusion in the Polymer Electrolyte Fuel Cell (PEFC) Cathode Catalyst Layer (CCL) has been carried out using Electrochemical Impedance Spectroscopy (EIS) measurements. Cathode EIS measurements obtained through a three-electrode configuration in the measurement system are compared with simulated EIS data from a previously validated numerical model, which subsequently allows the diagnostics of spatio-temporal electrochemical performance of the PEFC cathode. The results show that low frequency EIS measurements commonly related to mass transport limitations are attributed to the low oxygen equilibrium concentration in the CCL–Gas Diffusion Layer (GDL) interface and the low diffusivity of oxygen through the CCL. Once the electrochemical and diffusion mechanisms of the CCL are calculated from the EIS measurements, a further analysis of the current density and oxygen concentration distributions through the CCL thickness is carried out. The results show that high ionic resistance within the CCL electrolyte skews the current distribution towards the membrane interface. Therefore the same average current density has to be provided by few catalyst sites near the membrane. The increase in ionic resistance results in a poor catalyst utilization through the CCL thickness. The results also show that non-steady oxygen diffusion in the CCL allows equilibrium to be established between the equilibrium oxygen concentration supplied at the GDL boundary and the surface concentration of the oxygen within the CCL. Overall, the study newly demonstrates that the developed technique can be applied to estimate the factors that influence the nature of polarization curves and to reveal the effect of kinetic, ohmic and mass transport mechanisms on current distribution through the thickness of the CCL from experimental EIS measurements.     

Electrochemical characteristics of aluminum sulfide for use in lithium secondary batteries

In our effect to develop a lithium secondary battery with high energy density, aluminum sulfide (Al₂S₃) was studied for use as an active material. The measured initial discharge capacity of Al₂S₃ was ca. 1170 mAh g⁻¹ at 100 mA g⁻¹. This corresponds to 62% of the theoretical capacity for the sulfide. Al₂S₃ exhibited poor capacity retention in the potential range between 0.01 V and 2.0 V, mainly due to the structural irreversibility of the charge process or Li extraction. XRD and Al and S K-XANES analyses indicated that the surface of Al₂S₃ reacts reversibly during charge and discharge processes, while the core of Al₂S₃ showed structural irreversibility because LiAl and Li₂S were formed from Al₂S₃ at the initial discharge and remained as they were afterward.     

Investigation of discharge reaction mechanism of lithium|liquid electrolyte|sulfur battery

The influence of current density on the discharge reaction of Li–S batteries is investigated by discharge tests (first discharge curve), differential scanning calorimetry (DSC), X-ray diffraction (XRD) (discharge products), and scanning electron microscopy (the surface morphology of sulfur electrodes). The first discharge capacity and the plateau potential both decrease with increasing current density. When the current density is increased from 100 to 1600 mA g⁻¹ S, the discharge capacity decreases from 1178 to 217 mAh g⁻¹ S.     

Electrochemical impedance spectroscopy of BaCeO3 modified by Ti and Y

Barium cerate exhibits high protonic conductivity, especially when modified by trivalent dopant such as Y, Yb, Nd, Sm or Dy. Unfortunately, the poor chemical stability in the presence of CO₂ is the main disadvantage of this material. One of the possible approach to get the stable protonic conductor is the preparation of solid solutions. For example, doping of BaCeO₃ with Zr leads to the improvement of the chemical stability, but the electrical properties are simultaneously corrupted.In the present work the influence of Ti, per analogy to Zr, and Y dopants on electrical properties of BaCeO₃ was investigated using the electrochemical impedance spectroscopy (EIS) technique. BaCe_1−xTi_xO_3−δ (0 ≤ x ≤ 0.3) and Ba(Ce_0.95Ti_0.05)_0.95Y_0.05O_3−δ solid electrolytes were prepared by solid-state reaction method. It was found that the changes of electrical properties due to the introduction of Ti into the BaCeO₃ lattice is caused predominantly by the modification of the grain boundary properties. The Ti doping leads to the substantial decrease of grain boundary electrical conductivity, comparing to undoped material. The introduction of yttrium dopant to the BaCe_0.95Ti_0.05O₃ lattice has the opposite effect. The total electrical conductivity increases, due to significant modification of grain boundary electrical properties.     

Simple and fast synthesis of LiFePO4-C composite for lithium rechargeable batteries by ball-milling and microwave heating

A very simple and rapid method for synthesizing LiFePO₄-C composite has been developed by vibrant type ball-milling for 30 min and microwave heating for 2–4 min. X-ray diffraction and Mössbauer spectroscopy verify that well-crystallized LiFePO₄ without Fe³⁺ impurities is obtained. From laser particle size analysis and transmission electron microscopy, it is confirmed that a LiFePO₄-C composite with fine and uniform particle size (mean particle size ≤0.640 μm, D75 in volume distribution ≤0.592 μm) and with extremely uniform carbon distribution is prepared by vibrant type ball-milling and microwave heating. The LiFePO₄-C delivers a high initial discharge capacity of 161 mAh g⁻¹ at C/10 and shows very stable cycling behaviour.     

Electrochemical modeling of lithium polymer batteries

An electrochemical model for lithium polymer cells was developed and a parameter set for the model was measured using a series of laboratory experiments. Examples are supplied to demonstrate the capabilities of the electrochemical model to obtain the concentration, current, and potential distributions in lithium polymer cells under complex cycling protocols. The modeling results are used to identify processes that limit cell performance and for optimizing cell design. Extension of the electrochemical model to examine two-dimensional studies is also described.     

Electrochemical properties of new organic radical materials for lithium secondary batteries

The use of ionic liquid (IL)-supported organic radicals as cathode-active materials in lithium secondary batteries is reported in this article. Two different types of IL-supported organic radicals based on the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) radical and imidazolium hexafluorophosphate IL were synthesized. The first type is a mono-radical with one unit of TEMPO and the second is a symmetrical di-radical with 2 U of TEMPO; both are viscous liquids at 25 °C. The radicals exhibit electrochemical activity at ∼3.5 V versus Li/Li⁺ as revealed in the cyclic voltammetry tests. The organic radical batteries (ORBs) with these materials as the cathode, a lithium metal anode and 1 M LiPF₆ in EC/DMC electrolyte exhibited good performance at room temperature during the charge–discharge and cycling tests. The batteries exhibited specific capacities of 59 and 80 mAh g⁻¹ at 1 C-rate with the mono- and di-radicals as the cathodes, respectively, resulting in 100% utilization of the materials. The performance degradation with increasing C-rate is very minimal for the ORBs, thus demonstrating good rate capability.