Large-scale Lithium-ion Batteries Research Articles

Study of relationship between temperature and thermal energy, operating conditions as well as environmental factors in large-scale lithium-ion batteries

SUMMARY We have developed a thermal model for a large-scale lithium-ion cell and have simulated its thermal behaviors during charge, discharge, and charge–discharge cycles with different current rates by using the software of COMSOL Multiphysics 3.5a. In this work, thermal energy and its distribution were firstly calculated based on experimental data under different operating conditions. A new parameter, called thermal energy conversion efficiency, was proposed to describe relative value of thermal energy in the cell. The thermal energy conversion efficiency and the temperature were plotted in a figure to show their relativity. The temperature variation was also studied systemically when the cell underwent discharge–charge cycles. A low rate charge is validated to be a favorable factor in protecting the cell from overheating during charge–discharge cycles. A connection resistance is proved to be a main factor that accelerates the rise of temperature in the spot near a terminal column, which should be eliminated as much as possible to protect the cell from local overheating. Copyright © 2014 John Wiley & Sons, Ltd.

Multi-dimensional modeling of large-scale lithium-ion batteries

Multi-dimensional model of large-scale lithium-ion batteries is developed. The model is based on equivalent circuit model (ECM) which is capable of dynamic response simulation. Model parameters are functions of both state of charge and temperature, which are implemented by bilinear interpolation method. Local degradation effects such as capacity fade and resistance growth are incorporated into the multi-D model by empirical method. Local distributions of current, potential, temperature, state of charge (SOC), and state of health (SOH) are observed with the developed model. It is found that local degradation worsens under severe operating condition. Low thermal conductivity of a battery results in non-uniform SOH distribution. Simulation result shows good agreement with experiment data under various operation modes.

Thermal Security Analysis of Lithium-Ion Batteries Based on Electro-Thermal Modeling

The power lithium-ion battery with its high specific energy, high theoretical capacity and good cycle-life is a prime candidate as a power source for electric vehicles (EVs) and hybrid electric vehicles (HEVs). Sacurity is especially important for large-scale lithium-ion batteries, especially the thermal analysis is essential for their development and design. Mathematical model and thermal model for Li-ion battery were built to analyze the effects of discharge rate on the peak temperature and on the homogeneity of temperature field, and to compare the calculated and the simulated results.

Higher-capacity lithium ion battery chemistries for improved residential energy storage with micro-cogeneration

Combined heat and power on a residential scale, also known as micro-cogeneration, is currently gaining traction as an energy savings practice. The configuration of micro-cogeneration systems is highly variable, as local climate, energy supply, energy market and the feasibility of including renewable type components such as wind turbines or photovoltaic panels are all factors. Large-scale lithium ion batteries for electrical storage in this context can provide cost savings, operational flexibility, and reduced stress on the distribution grid as well as a degree of contingency for installations relying upon unsteady renewables. Concurrently, significant advances in component materials used to make lithium ion cells offer performance improvements in terms of power output, energy capacity, robustness and longevity, thereby enhancing their prospective utility in residential micro-cogeneration installations. The present study evaluates annual residential energy use for a typical Canadian home connected to the electrical grid, equipped with a micro-cogeneration system consisting of a Stirling engine for supplying heat and power, coupled with a nominal 2kW/6kWh lithium ion battery. Two novel battery cathode chemistries, one a new Li–NCA material, the other a high voltage Ni-doped lithium manganate, are compared in the residential micro-cogeneration context with a system equipped with the presently conventional LiMn2O4 spinel-type battery.

Free-standing and bendable carbon nanotubes/TiO2 nanofibres composite electrodes for flexible lithium ion batteries

Carbon nanotube (CNT) and TiO2 nanofibre composite films are prepared and used as anode materials for lithium ion batteries (LIBs) without the use of binders and conventional copper current collector. The preliminary experimental results from X-ray diffraction, scanning electron microscopy and transmission electron microscopy suggest that the TiO2 nanofibres were well-dispersed and interwoven by the CNTs, forming freestanding, bendable and light weighted composite. In comparison with TiO2 nanofibre based LIBs, the CNTs could significantly improve the battery performance due to their high conductivity property and 3D network morphology. In both 1–3V and 0.01–3V testing voltage ranges, the as-prepared composites show excellent reversible capacity and capacity retention. The superior lithium storage capacity of the CNT/TiO2 composite was mainly attributed to dual functions of the CNTs – the CNTs not only provide conductive networks to assist the electron transfer but also facilitate lithium ion diffusion between the electrolyte and the TiO2 active materials by preventing agglomeration of TiO2 nanofibres. This work demonstrates that the CNT–TiO2 composite film could be one type of potential electrode material for large-scale LIB applications.

In-depth safety-focused analysis of solvents used in electrolytes for large scale lithium ion batteries

To better rule out the complex fire risk related to large format lithium ion cells, a detailed and systematic evaluation, both at component and cell levels, could be an invaluable milestone. Therefore, combustion analysis was conducted for major single organic solvents and their mixtures used in lithium ion battery technology, both in oxygen rich and lean environments using a Tewarson calorimeter. Well controlled test conditions have enabled the determination of key parameters governing the fire induced hazards such as flash point, ease of ignition, heat release rate, effective heat of combustion, specific mass loss rate, as well as the assessment of fire induced toxicity. Moreover, a rule of thumb for the screening of new solvents including the safety perspective such as the Boie correlation and N-factor were introduced for predicting the heat of combustion and combustion kinetics, respectively, prior to conducting any experimental work. Fire induced toxicity of single solvents and their mixtures was also briefly examined by performing toxic gas measurements.

鉄置換Li<sub>2</sub>MnO<sub>3 </sub>系正極材料の合成と充放電特性に及ぼすチタン置換効果

Fe- or Fe and Ti-substituted Li2MnO3 positive electrode material (FM or FMT sample) with monoclinic Li2MnO3 type structure (C2/m) was synthesized using coprecipitation-hydrothermal-calcination. Both materials exhibited high specific capacity greater than 200 mAh/g against a Li metal negative electrode at moderate current density of 40 mA/g between 2.0 and 4.8 V using stepwise charging. The cycle performance for the FMT sample (Li1+x(Fe0.2Ti0.2Mn0.6)1−xO2, 0 < x< 1/3) using a graphite negative electrode was better than that for the FM sample (Li1+x(Fe0.2Mn0.8)1−xO2, 0<x<1/3), indicating that partial substitution of Ti4+ for Mn4+ ion is effective for improving cycle performance under the practical lithium-ion cell configuration. The results presented above demonstrate that an Fe-substituted Li2MnO3 based positive electrode material can become an attractive candidate as an inexpensive constituent material for a large-scale lithium-ion battery by selecting suitable additional elements such as Ti and electrochemical charge conditions for activation.

高電圧，高出力，高安全二次電池に向けた縮合リン酸塩の科学

Alkali metal pyrophosphate, A2MP2O7 (A = Li, Na, M = Fe Mn, Co), have been recently reported as novel polyanionic cathode materials for rechargeable alkali-ion batteries with competent electrochemical properties with high rate durability. A closer look revealed they offer the highest operating voltage by M3+/M2+ redox couple among ever reported related compounds. Of particular interest is its much safer nature than olivine LiFePO4 currently recognized as the only practical option providing definitely safe large-scale lithium-ion battery. Scientific origins of these promising features will be unveiled in this article.

Electrical Constriction Resistance in Current Collectors of Large-Scale Lithium-Ion Batteries

A new two-dimensional model is proposed to describe the electrical conduction in current collectors of prismatic lithium-ion batteries, and to investigate the effects of tab design on voltage drop. Polarization expression for a large-scale lithium-ion cell is determined experimentally and implemented in a numerical analysis to show that reaction current remains approximately uniform when depth-of-discharge is less than 85%. Based on this observation, a compact analytical model is developed to determine bulk and constriction/spreading resistances in current collectors. Moreover, the model predictions are successfully validated through comparisons with experimental data. It is demonstrated that constriction/spreading resistance in current collectors of the considered battery is fairly small; about 10% of the total cell resistance but it is larger than the contribution of bulk resistance which is about 3%. The model confirms that constriction/spreading increase with: decrease in the aspect ratio of the current collector, decrease in the tab width, and increase in the tab eccentricity.

Challenges toward higher temperature operation of LiFePO4

Large-scale lithium-ion batteries operating at higher temperature may provide additional advantageous aspects such as higher power and use of new materials which are inactive at ambient temperatures. As a first step for this direction, we applied LiFePO4 cathode to middle-temperature region of 60 °C–115 °C and investigated temperature-dependent charge–discharge properties. By selecting suitable electrolyte and battery components tolerant to the elevated temperature, stable operation was attained for no less than 50 cycles below 115 °C. High-rate performance was significantly improved as operating temperature increased up to 100 °C, but suffered from abrupt increase in polarization above 100 °C, where the corresponding impedance signal emerged, which might be assigned to some side reactions occurring at the surface of LiFePO4 particles. At 100 °C, the discharge capacity over 100 mAh g−1 was achieved at 200C rate, even with 10wt% of carbon in the electrode composite of LiFePO4. Shrinkage of miscibility gap was not confirmed for samples larger than 40 nm at < 115 °C.

Effects of different carbon sources on the electrochemical properties of Li4Ti5O12/C composites

Li4Ti5O12/C composites have been synthesized via a solid state reaction with TiO2-anatase, Li2CO3 and different carbon sources, such as conductive graphite KS-6 and sucrose, as the starting materials. It was found that the carbon layer from sucrose was homogeneously coated on the Li4Ti5O12 surface and the KS-6 was embedded among the Li4Ti5O12 particles as a conductive bridge without affecting the spinel structure of Li4Ti5O12. Moreover, it was demonstrated that the sucrose and KS-6 played different roles in improving the electrochemical properties of Li4Ti5O12/C composite. Compared with samples prepared by solely KS-6 or sucrose as the carbon source, the Li4Ti5O12/C composite (LTO-1) with KS-6 and sucrose as carbon sources together revealed the optimal electrochemical performance. It showed a high initial specific capacity of 152.5 mAh g−1 at 0.2 C and an excellent cycling performance with 96.8% capacity retention after 1000 cycles at 25 °C at 1 C. Furthermore, the (LTO-1)/LiMn2O4 full battery demonstrated a good cycling performance at 55 °C and could pass the 5 C–20 V overcharge test, external short-circuit and nail-puncture test. Therefore, it is believed that the Li4Ti5O12/C might be a promising anode material for large-scale lithium ion batteries of electric vehicle (EV), hybrid electric vehicle (HEV) and energy storage devices for solar or wind energy.

Lithium bis(fluorosulfonyl)imide–PYR 14TFSI ionic liquid electrolyte compatible with graphite

Lithium bis(fluorosulfonyl)imide (LiFSI) in 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR 14TFSI) was successfully tested as an electrolyte for graphite composite anodes at elevated temperature of 55 °C. The graphite anode showed a good cyclability during the galvanostatic testing at C/10 rate and 55 °C with the capacity close to theoretical. The formation of SEI in different electrolytes was the subject of study using impedance spectroscopy on symmetrical cells containing two lithium electrodes. The 0.7 m LiFSI in PYR 14TFSI exhibits a good ionic conductivity (5.9 mS cm −1 at 55 °C) along with high electrochemical stability and high thermal stability. These properties allow their potential application in large-scale lithium ion batteries with improved safety.

Effect of Aluminum Substitution on the Structure, Electrochemical Performance and Thermal Stability of Li1+x(Ni0.40Mn0.40Co0.20−zAlz)1−xO2

“Li1.04(Ni0.40Mn0.40Co0.20−zAlz)0.96O2” (z = 0; 0.05 and 0.10) samples were synthesized using a coprecipitation method followed by calcinations at 500°C for 5 h and then at 950°C for 2 h. Structural and physico-chemical characterizations have shown that these materials were obtained pure with a small overlithiation ratio (Li/M = 1.01–1.03) and thus a significant exchange between the divalent nickel ions from the slabs and the lithium ions from the interslab spaces (between 4% for the non substituted material and 8% for the aluminum substituted ones). Aluminum substitution induces a decrease of the reversible capacity, but also a major improvement of the thermal stability in the deintercalated state (corresponding to the charge state of the battery). These results have thus shown that the composition Li1.01(Ni0.39Mn0.40Co0.15Al0.06)0.99O2 is very attractive for large scale lithium-ion batteries to be developed for EV and HEV applications.

Olivine LiFePO4: development and future

In view of the limited oil storage and the global warming threats, it has been a worldwide topic to build a low carbon society supported by sustainable energy. As an effective energy storage device for the sustainable energy, the lithium-ion battery has been attracting wide attention. Olivine LiFePO4 has been considered as the most promising cathode candidate for the next-generation large-scale lithium-ion battery used for hybrid electric vehicles (HEVs) or electric vehicles (EVs), because of its inherent merits including low toxicity, potential for low cost, long cycle ability and high safety. From 1997 to present, continuous efforts have been made to understand and improve the performance of LiFePO4. Now, it seems that olivine LiFePO4 is ready for its big time. In the present paper, we review the development of LiFePO4 in the past years, and discuss some remaining problems for LiFePO4 in the future based on our current study.

Residential electrical power storage scenario simulations with a large-scale lithium ion battery

The advent of time-of-use (TOU) household electricity prices provides an opportunity for large lithium ion batteries to become a component of residential electrical power equipment for either storage or cogeneration. This project investigates household power use and cogeneration scenarios combined with lithium ion battery technology via simulation. The simulation treats transient battery charge and discharge based on electrochemical fundamentals. The analysis of both storage and cogeneration systems containing a batteries serves to demonstrate economic advantages of these types of power storage, as well as to identify size, materials, and performance criteria suitable for designing a lithium ion battery unit meeting real application demands.

Electrochemical Behavior of Li2FeSiO4 with Ionic Liquids at Elevated Temperature

Ionic liquids, 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide and 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide with 0.7 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or 0.5 M , were successfully tested as electrolytes for cathodes operating at elevated temperatures of . The electrolytes based on ionic liquids show good ionic conductivity (from to ) together with good electrochemical stability up to 5 V vs . The electrochemical stability of electrolytes based on ionic liquids against an aluminum current collector was comparable to a diethyl carbonate:ethylene carbonate (DEC:EC) 1 M electrolyte and even better when the electrolytes were tested with blank electrodes (only aluminum current collector, carbon black, and binder). In the first cycle the electrochemical testing of showed a slightly lower reversibility in ionic liquids when compared to a DEC:EC 1 M electrolyte; at higher cycles the reversibility and the obtained capacity were comparable to the one obtained in a DEC:EC 1 M electrolyte. All electrochemical results show that LiTFSI can be used as a salt in ionic liquid-based electrolytes. These properties allow their potential application in large-scale lithium-ion batteries with improved safety.

Condition monitoring of Lithium-Ion Batteries for electric and hybrid electric vehicles

Since the early 1990s Lithium-Ion Batteries have stated a key technology in rechargeable batteries due to their high volumetric and gravimetric energy densities and were first introduced in personal devices like camcorders, cellular phones and mobile computers ("3-C applications"). Ongoing evolutionary advances release at present a new spate of research activities to extend the operational area of small-sized batteries with the final aim to achieve reliable energy storage in automotive environments (e.g. hybrid vehicles). High absolute energy amounts of large-scale Lithium-Ion Batteries raise safety and lifetime issues and set demands for methods to monitor the health conditions of batteries for automotive applications. By observing significant system variables, imminent failures of single cells or battery packs are in many cases predictable and suitable counteractions can be initiated. The paper gives a brief introduction to the state-of-the-art of advanced batteries for electric and hybrid electric vehicles. Special focus is put on the monitoring of safety-relevant system parameters like cell-voltage, system temperature and headspace-pressure, their significance on the battery's state-of-health (SOH) and possible cell-failures. Different in-situ, ex-situ and onboard measurement techniques are addressed.

Structure of Li2FeSiO4

A large-scale lithium-ion battery is the key technology toward a greener society. A lithium iron silicate system is rapidly attracting much attention as the new important developmental platform of cathode material with abundant elements and possible multielectron reactions. The hitherto unsolved crystal structure of the typical composition Li2FeSiO4 has now been determined using high-resolution synchrotron X-ray diffraction and electron diffraction experiments. The structure has a 2 times larger superlattice compared to the previous beta-Li3PO4-based model, and its origin is the periodic modulation of coordination tetrahedra.

Optimizing Chemical Composition and Preparation Conditions for Fe -Substituted Li2MnO3 Positive Electrode Material

Optimized Fe-substituted [, , ], a positive electrode material, exhibited high initial charge and discharge capacity (200–320 and , respectively) during charge-discharge tests between 2.5 and 4.5 or at . All samples were obtained from a mixed-alkaline hydrothermal reaction using the coprecipitate, , , and . The hydrothermally obtained samples showed an initial discharge capacity when the Fe content, , was less than 0.6. Both the initial charge and discharge capacities were governed by their Li contents. The electrochemical characteristics were improved by postheating treatment with . The initial discharge capacity for the samples with reached and capacity fading with cycles was less than in the hydrothermally obtained sample. The initial discharge capacity, energy density, and cycle efficiency were improved by maximizing their respective specific surface areas through minimization of their primary particle size. The electrochemical performance of Fe-substituted means that it is an attractive candidate as an inexpensive 3-V-class positive electrode material that is suitable for large-scale lithium-ion batteries. We note, however, that the capacity fade observed on extended cycling must be suppressed if this material is to become commercially viable (or practical).

Effect of the Addition of Conductive Material to Positive Temperature Coefficient Cathodes of Lithium-Ion Batteries

A conceptual positive temperature coefficient (PTC) cathode has been proposed to improve the safety of large-scale lithium-ion batteries. The PTC cathode contains the PTC compound as the conductive material, which increases its resistivity at temperatures above its melting point. In this paper, to improve the performance of cells using PTC cathodes, acetylene black (AB), which supports conductivity in the cathode as a secondary conductive material, was added. Cells using PTC cathodes containing a small amount of AB (PTC-AB cell) had better discharge characteristics and a longer cycle life than a cell using a PTC cathode without AB (PTC cell). For a basic evaluation of battery safety, an external short-circuit test and a discharge test were performed at a temperature higher than the melting point of the PTC compound. The short-circuit current of the PTC-AB cells was lower than 1 A at 140°C, which was almost the same as the current of the PTC cell. Moreover, under a discharge rate of 3C, the voltage of PTC-AB cells dropped sharply at 135°C due to a drastic increase in PTC cathode resistivity. These results indicate that the addition of AB to PTC cathodes improves cell performance while maintaining battery safety.