Portable Power Tools Research Articles

Improving the Thermal Stability of Lithium-Ion Batteries Using a Separator Protective Film Made By Novel Materials

Lithium-ion batteries (LIBs) are widely used in the portable electronics, power tools, and electric vehicle power markets. As the demand for higher battery density and energy density increases, improving the safety of LIBs has become an important issue. The separator in a LIB maintains physical isolation between the cathode and anode and allows the movement of lithium ions through the electrolyte through the porous separator structure during cycling. Therefore, cycle life and energy density are important components for achieving high battery performance.Generally, most separators are porous polyolefin films made of polyethylene or polypropylene. Polyolefin separators have excellent mechanical strength and chemical stability, but they shrink significantly at high temperatures, and internal short circuits occur under conditions such as abnormal heating. In order to improve the thermal stability of the separator, many methods have been reported for coating the surface of the separator with inorganic powder, and most of them use dip coating or simple bar coating. The coating layer formed on the surface of the separator has a porous structure and is several microns thick. Coated separators reduce thermal shrinkage while ensuring ion transport, but there are concerns that increased film thickness may reduce the battery's energy density.In this study, the coating was carried out on porous membranes such as separators at 50 °C by spray pyrolysis using methylaluminoxane diluted with N-methylpyrrolidone. The solution penetrated the separator during spraying and deposited an ultrathin layer on the side walls of the internal pores. These layers were suggested to be fine polycrystalline Al2O3. In the obtained film, most of the pores were exposed on the surface, and there was almost no increase in film thickness. Furthermore, it has ionic conductivity equivalent to that of film and has improved thermal stability. This method was considered to be an effective technique for improving the functionality of separators used in LIB.

Research on fire hazard assessment of metro baggage based on improved hierarchical analysis

Underground station passenger flow is large, the number of parcels carried by passengers is large and varied, and the parcels carried have an impact on the fire hazard and evacuation of the station. In order to determine the weights of the passenger luggage risk and environmental factor index system in the fire risk evaluation of underground stations in a more realistic way, an optimized and improved hierarchical analysis method for determining the judgement matrix is proposed, which improves the traditional nine-scaled method and adopts the three-scaled method for the four major categories of luggage, namely, handbags, rucksacks, portable power tools and trolley cases. The advantage of this method is that there is no need for consistency judgement in determining packages with a wide range of types and uncertain contents, thus simplifying the calculation. Meanwhile, the reasonableness and reliability of the method is verified by combining it with an actual metro station fire risk assessment system.

Reflections on Lithium-Ion Cells. Genesis of the Problem and Theoretical Introduction

Aim: This article presents an identification and analysis of the hazards associated with the operation of lithium-ion technology, the range of applications, an overview of hazardous incidents domestically and also internationally, the brief history of lithium-ion batteries, as well as recommendations on the use and storage of batteries published not only by domestic but also foreign fire and occupational safety organizations. Introduction: The increased mobility of people doing their work with computers has created the need to produce portable devices that require concentrating as much energy as possible in a limited enclosure volume. These devices accompany the user in everyday life, during travel and also in a variety of work. In order to meet these criteria, it was necessary to solve these problems, first of all, the problem of power supply, which would allow to use the electricity stored by them in a long-lasting but also very efficient way. However, modern solutions bring a number of new risks that are not obvious at first glance and require detailed analysis. Project and methods: Based on a critical analysis of the literature, the authors presented the advantages and disadvantages of cells used in smartphones, laptops, portable power tools used in households across the globe and even electric cars. The development of lithium-ion battery technology and the expansion of their range of applications makes it necessary to develop solutions to enhance safety during their use, together with procedures to prevent possible explosions and fires, allowing effective life and health protection of users, as well as safeguarding all property and the environment. Methodology: Opierając się na krytycznej analizie literatury, autorzy przedstawili zalety i wady ogniw wykorzystywanych w smartfonach, laptopach, przenośnych elektronarzędziach, a nawet samochodach elektrycznych. Rozwój technologii produkcji akumulatorów litowo-jonowych oraz rozszerzenie zakresu ich zastosowania sprawia, że konieczne jest opracowanie rozwiązań zwiększających bezpieczeństwo podczas ich użytkowania oraz procedur zapobiegania ewentualnym wybuchom i pożarom, pozwalających na skuteczną ochronę życia oraz zdrowia użytkowników, a także zabezpieczenie wszelkiego mienia i środowiska. Conclusions: In order to prevent fires spreading, it is necessary to understand the mechanisms that lead to ignition and possible explosions of cells and batteries. From the point of view of preventing such failures and fires, it is important to recognize the response of burning batteries to various types of fire extinguishing agents and preventive measures. Continued research in this area can contribute to the evolution of more sophisticated and advanced safety technologies and the development of regulatory standards that in the future will guarantee the effective control of lithium-ion battery fires directly linked to their storage, use at high quantities, and the correct storage of waste (in the form of damaged and depleted batteries). Keywords: lithium-ion batteries, fire hazard, environmental protection, environmental pollution, toxic products of combustion

Organization of the safe work management system at agricultural enterprises

The occupational health and safety management system, as a target production management system, establishes a unified procedure for the activities of heads of organizations, structural divisions, and other officials in the field of occupational health and safety. It is designed to create working conditions in each structural subdivision, at each workplace, that meet the requirements of regulatory and legal acts and are the basis for a stable reduction of industrial injuries, accidents, and occupational diseases. Therefore, the problems of the creation and widespread implementation of a modern labor protection management system at enterprises are at the center of the constant attention of the State Labor Service of Ukraine. To improve its work, first of all, it is necessary to study the state of labor protection in units and workplaces, identify dangerous factors and possible risks and evaluate them. The main principle of the occupational health and safety management system is that all potential industrial injuries and accidents can and should be prevented promptly. In this paper, we explore the possibilities of applying the modeling of traumatic and emergencies and structural-functional analysis when using portable power tools in agricultural enterprises in the occupational health and safety management system. The execution of agricultural technological operations is characterized by the impact on the human body of various physical, chemical, biological, and psychophysiological factors, which can cause industrial injuries, occupational diseases, and deterioration of workers' health. The main task of labor protection is the creation of favorable conditions in the agricultural enterprise, which would guarantee the safety of the life of workers and in which the maximum labor productivity would be achieved with the least energy expenditure, and the human body would not be exposed to the harmful effects of production factors.

Applications and Advantages of Atomic Layer Deposition for Lithium-Ion Batteries Cathodes: Review

Nowadays, lithium-ion batteries (LIBs) are one of the most convenient, reliable, and promising power sources for portable electronics, power tools, hybrid and electric vehicles. The characteristics of the positive electrode (cathode active material, CAM) significantly contribute to the battery’s functional properties. Applying various functional coatings is one of the productive ways to improve the work characteristics of lithium-ion batteries. Nowadays, there are many methods for depositing thin films on a material’s surface; among them, one of the most promising is atomic layer deposition (ALD). ALD allows for the formation of thin and uniform coatings on surfaces with complex geometric forms, including porous structures. This review is devoted to applying the ALD method in obtaining thin functional coatings for cathode materials and includes an overview of more than 100 publications. The most thoroughly investigated surface modifications are lithium cobalt oxide (LCO), lithium manganese spinel (LMO), lithium nickel-cobalt-manganese oxides (NCM), lithium-nickel-manganese spinel (LNMO), and lithium-manganese rich (LMR) cathode materials. The most studied processes of deposition are aluminum oxide (Al2O3), titanium dioxide (TiO2) and zirconium dioxide (ZrO2) films. The primary purposes of such studies are to find the synthesis parameters of films, to find the optimal coating thickness (e.g., ~1–2 nm for Al2O3, ~1 nm for ZrO2, <1 nm for TiO2, etc.), and to reveal the effect of the coating on the electrochemical parameters of batteries. The review summarizes synthesis conditions, investigation results of deposited films on CAMs and positive electrodes and some functional effects observed due to films obtained by ALD on cathodes.

Investigation of Cellulose-Based Separators for Secondary Lithium Metal Batteries

Lithium-ion batteries (LIBs) have been the predominant energy storage technology for a variety of applications such as portable electronic devices and wireless power tools. However, the rising demand for emerging technologies such as long-range electric vehicles and grid-level energy storage and delivery has drastically increased the necessity for low-cost LIBs with enhanced performance and safety.Improvements in the modern LIB technology can be achieved through improvements in different, individual components of the battery. Among the key components of the battery, the separator plays a vital role. To date, polypropylene (PP)/polyethylene (PE) membranes have been used as separators in LIBs due to their desired electrochemical stability. However, these separator materials suffer from low thermal stability, which results in their deformation or decomposition at elevated temperatures upon high charging rates1. A dangerous consequence of this material degradation is an electrical short, leading to an aggressive discharge of the battery and subsequent fire. Moreover, PP/PE separators possess relatively low electrolyte wettability and an expensive and eco-unfriendly fabrication process. Hence, alternative separator materials for future LIB technology are indispensable.Among alternative separator materials, cellulose is a promising candidate2. Cellulose is derived from biomass which is one of the most abundant and renewable resources on Earth. It also is non-toxic and has high mechanical and chemical stability. Additionally, with an initial decomposition temperature of 270°C, cellulose offers a major advantage in thermal stability compared to its polymeric competitors3. The thermal and electrochemical stability, electrolyte wettability, and performance of cellulose-based separators in LIBs have been studied3,4. However, those reports mostly consider the conventional LIB electrode materials– Li transition metal oxide and graphite; and focus on the separator/electrolyte compatibility. Therefore, to be considered for future generations of high-performance Li-based batteries, cellulose-based separators must be investigated in batteries with new electrode chemistries.This work presents new insights on the interaction of cellulose-based separator and metallic Li – the leading candidate for future anodes. Coin cells were prepared using various cathode materials, Li metal anode, and a commercial cellulose-based separator. The cycling performance of the cells was tested at different C rates. Results were compared with the cycling performance of the coin cells with similar electrodes but a commercial PP/PE separator. Comparable discharge profiles were observed in the two groups of cells, but the cellulose separator hampered the charging process. Additional electrochemical analysis suggested an undesired interaction between the cellulose-based separator and metallic Li. To further understand this interaction, various protective coatings on the separator were investigated, the results of which suggest a mechanical degradation in the cellulose separator during cycling and consequently a soft short. These results are expected to provide a new understanding regarding the stability of cellulose-based separators in Li metal-containing batteries, which can help with their implementation in the next generation of Li-based batteries with enhanced performance and safety.

The Effect of Binder on the Structure and Performance of Sulfur Cathodes in Lithium-Sulfur Batteries

Lithium-ion batteries (LIBs) are a reliable energy storage technology that have been used in various applications such as portable devices and power tools. However, the specific capacities of the electrode materials in the current LIB technology are approaching their theoretical limits which impedes their utilization in a variety of emerging applications such as long-range electric vehicles, next-generation mobile devices, and grid level energy storage and delivery. Therefore, alternative electrode materials with high specific capacity beyond the conventional LIB electrode materials are needed 1.Sulfur has been touted as a promising alternative cathode material in recent years. Sulfur offers superior theoretical capacity, and a high practical energy density when it is paired with a Li metal anode in so called Li-S batteries2. Non-toxicity, low cost and high natural abundance also make Sulfur environmentally and economically appealing. However, achieving the desired high energy density and long cycle life in Li-S batteries have been proven difficult because of the: (1) insulating nature of the two end products of charge and discharge; S8 and Li2S, (2) electrode degradation due to the volumetric change during cycling, and (3) dissolution of the Sulfur discharge products, Li-polysulfides (LiPSs), in the ether-based electrolyte, resulting in the “shuttling effect” that leads to capacity decay over extended cycling 3,4.In this work, new insights are presented on how the binder, its solvent, and dissolution process affect the electrode microstructure and performance. The Sulfur cathodes were prepared using commercially available Sulfur powder, carbon black and various binders and solvents. The cathode structures prepared using different binder and solvent combinations were characterized using scanning electron microscopy (SEM). The cycling performance of the Sulfur cathodes were tested in coin cells. The results showed considerable structural and performance variations between cathodes with similar binders but different solvents, or different treatment conditions with the same solvent. In particular, when binders were minimally dissolved in N-Methylpyrrolidone a porous shell-like structure was observed around the sulfur particles that evolved to a denser sponge-shape structure upon excessive dissolution. The porous shell structure resulted in enhanced performance and cycle life. Using spectroscopic data, it is possible that enhanced cycle life might be attributable to physical trapping of the LiPSs and providing a buffer for the volumetric change during discharge. Thus, a new perspective will be presented that the binder/solvent interaction can impact the performance of sulfur cathodes by manipulating both its structural and chemical behavior. These results are expected to provide a new understanding regarding the effect of binder and its processing on the performance of Li-S batteries and help to write a new narrative regarding electrode chemistry and preparation techniques for future applications.References M. Zhao et al., ACS Cent. Sci., 6, 1095–1104 (2020).A. Manthiram, Y. Fu, S.-H. Chung, C. Zu, and Y.-S. Su, Chem. Rev., 114, 11751–11787 (2014).A. Manthiram, Y. Fu, and Y.-S. Su, Acc. Chem. Res., 46, 1125–1134 (2013).W. Ren, W. Ma, S. Zhang, and B. Tang, Energy Storage Mater., 23, 707–732 (2019).

STATE AND PROBLEMS OF PRODUCTION AND HOUSEHOLD ELECTROTRAUMATISM IN UKRAINE

Technogenic development of society has caused widespread use in the system «man – production environment» and the system «man – household environment» of household electrical equipment, industrial electrical installations. Failure to comply with the regulated rules of electrical safety of electric current leads to electrical injuries. Designs of electrical installations, equipment, electrical protective measures are constantly being improved. But the level of electrical injuries in Ukraine and abroad tends to increase. This leads to social and economic losses as a result of economic costs in accidents, employee deaths, loss of working time and so on. The most objective indicator of injury is fatal. Thus, the level of fatal injuries at work per 1,000 workers in the developed world compared to the same rate in Ukraine in the UK is 10 times less, in Japan 7 times less, in the US 3 times less. This situation requires analysis and development of appropriate measures to reduce the level of electrical injuries. The analysis of statistical data revealed that the highest level of electrical injuries is observed in the following areas: - in agriculture; - service sector; - in public utilities; - in everyday life. At the same time, the tendency of its growth in the non-productive sphere and the household sector is expressed. So, at present in the general list of accidents from action of an electric current household electric injuries make the largest part – more than 46%. This is due to the insufficient level of education of the population on electrical safety, operation of electrical equipment in high-risk areas or in particularly dangerous by the degree of electric shock. At the same time, the level of domestic electrical injuries is higher in rural than in urban areas. It was also found that the greatest danger is posed by mobile and portable electrical installations, power tools and internal wiring. In addition, the housing of such electrical installations is often grounded through one of the cores of the power cable, which is unacceptable. The reasons for the high level of electrical injuries also include non-compliance with regulated organizational measures to ensure occupational safety and the so-called «human» factor. To improve the situation, it is necessary to intensify and increase the level of training of the population and employees on electrical safety, development and application of more modern switching electrical protection.

Early intervention mechanism for preventing electrocution in construction engineering.

The aim of this study is to establish an effective early intervention mechanism for construction engineering to prevent electrocution while improving labor safety and reducing the casualty risk. This study used narrative text analysis and the Haddon Matrix for data collection, and analyzed the causes from the 113 electrocution deaths among in the construction industry, the exhaustive chi-square automatic interaction detector algorithm was employed the segmentation of the correlations. Based on the theory of inventive problem solving, through IDEF0 (ICAM DEFinition) for function modeling was designed the early intervention mechanism. This study revealed the operating features related to electric shock hazards. Early intervention was introduced to reduce the relevant risks and establish safety mechanisms. The first contribution of this study is the determination of hazard correlations between operating features and conductive media, and entry point for the prevention of electrocutions. The second contribution is the suggestion of the establishment of inspection stations for electric tools, thereby ensuring that the portable power tools are safe. The final contribution is the joint application of TRIZ (Teoriya Resheniya Izobreatatelskikh Zadatch) and IDEF0, which establishing the pre-entry testing, strengthening safety mechanisms.

Thermo‐Chemo‐Mechanical Modeling of Cathode Particles in Lithium‐Ion Batteries

AbstractLithium‐ion batteries are widely used in portable consumer electronics, power tools and electric vehicles. As the demand for Li‐ion batteries increases, a deeper understanding of the physical phenomena present in their operation becomes necessary. So far, there remain some obstacles to the wider use of Li‐ion batteries, e.g., capacity loss, self‐discharge and thermal runaway. These effects are mostly related to thermal phenomena in the battery. This underlines the importance of a deeper understanding of thermal effects in batteries. In this work, a four‐field formulation of the coupled problem of diffusion with stress generation and heat transfer in cathode particles of Li‐ion batteries is presented.

Silicon anodes will give lithiumion batteries a boost

There was a time when budding inventors were advised to build a better mousetrap. Nowadays, they'd do rather well to build a better lithiumion battery. These are what power our phones, laptops, portable power tools, an increasing number of cars, even homes. Some places are turning to giant lithium-ion batteries to store energy from solar panels so that it can be used after dark. While lithium-ion cells have gotten incrementally better over the years, they seem set for a big boost in 2019 through the increased use of an element not unfamiliar to the electronics industry: silicon.

Wet Chemical Processing of Protective Alumina and Silica Coatings for High Ni NMC Cathodes

Secondary Li-ion batteries outperform all other battery chemistries currently on the market with respect to energy density per weight and volume. As logical consequence Li-ion batteries dominate areas such as portable electronics, power tools and electric mobility. For the lattermost in particular, there is a difficult compromise between energy density and safety when using Li-ion chemistries, and safer high-performance chemistries are keenly sought. For electric vehicle (EV) applications, power and range requirements mean that the most common positive electrode is based on the LiNixMnyCozO2(NMC) system. Within this system increasing the Ni content results in higher capacity values, but to the detriment of the capacity retention and the safety rating. One way to mitigate cycle life and safety issues is to apply a thin protective coating onto the active material surface. Coatings of alumina applied by atomic layer deposition (ALD) have been shown to improve the cycle life of high Ni NMC cathodes [1-3], but ALD is not a technique which will scale easily and cheaply to the production volumes needed for battery manufacturing. Here we present a comparative study exploring the possibility of ultra-thin alumina and silica coatings on NMC 811 using wet chemical methods. NMC 811 was synthesised by a citric acid-aided gelling method with subsequent annealing. Alumina coatings were processed by a solution drying method employing NMC 811 particles dispersed in an aqueous Al(NO3)3 solution. The solution was sonicated and evaporated under vigorous stirring. Subsequently, the powder was heat-treated to form the desired alumina coating. The temperature and dwelling time were controlled so as to mitigate extensive Al diffusion into the layered structure and the formation of a LiAlO2 surface layer. [4] The silica coatings were processed by a solution drying process employing either a tetraethyl orthosilicate solution, or an aqueous solution with the addition of functionalised silanes. The powder/solution mixture was treated and dried in the same manner as for the alumina coating. After the solution was dried, the powders were heat treated to form an ultra-thin silica coating. The electrochemical performance and cycling stability of the coated NMC 811 materials are compared to the as-synthesised material, and morphology and chemical composition of the coatings and interface were analysed by electron microscopy and electron energy loss spectroscopy. Finally, the thermal stability of the charged (delithiated) material was determined by differential scanning calometry. Mohanty, D., et al., Modification of Ni-Rich FCG NMC and NCA Cathodes by Atomic Layer Deposition: Preventing Surface Phase Transitions for High-Voltage Lithium-Ion Batteries. Sci Rep, 2016. 6: p. 26532. Laskar, M.R., et al., Atomic Layer Deposition of Al2O3-Ga2O3 Alloy Coatings for Li[Ni0.5Mn0.3Co0.2]O2 Cathode to Improve Rate Performance in Li-Ion Battery. ACS Appl Mater Interfaces, 2016. 8(16): p. 10572-80. Wise, A.M., et al., Effect of Al2O3 Coating on Stabilizing LiNi0.4Mn0.4Co0.2O2 Cathodes. Chemistry of Materials, 2015. 27(17): p. 6146-6154. Han, B., et al., From Coating to Dopant: How the Transition Metal Composition Affects Alumina Coatings on Ni-Rich Cathodes. ACS Appl Mater Interfaces, 2017. 9(47): p. 41291-41302.

Grain boundaries impede ion conduction in solid-state Li-ion batteries

Rechargeable lithium-ion batteries power many of today’s electric vehicles and nearly all portable electronic gadgets and power tools. These devices boast extreme reliability, but they depend on a flammable liquid organic electrolyte solution to shuttle ions between the electrodes, and those liquids pose a tiny but potentially serious fire hazard. So researchers have been searching for nonflammable solid electrolytes as replacements. Although some are nearing commercialization, scientists still do not know some basics, for example, how grain boundaries—interfaces between crystallites of the electrolyte—affect lithium-ion conduction, which controls battery current. So James A. Dawson and M. Saiful Islam of the University of Bath and coworkers carried out molecular dynamics simulations to study how readily lithium ions can hop across grain boundaries in polycrystalline Li3OCl, a promising solid electrolyte candidate. The team stresses that grain boundaries may enhance or impede ion conduction: The effect ca...

Triisopropoxyboroxine (TiPBx) As an Electrolyte Additive for 18650-Type Li-Ion Batteries

Li-ion batteries are currently used in portable electronic and power tools, electric vehicles, and grid energy applications due to their high energy density. They have already been commercialized. However the development of higher power and capacity as well as longer life batteries becomes more pressing. One method to attain a longer life cells is to adopt electrolyte additives such as vinylene carbonate (VC) exhibiting the significant increase in lifetime [1]. Boron-based compounds have possibilities to develop advanced liquid electrolytes [2]. Xu and Angell discovered lithium bis(oxalate)borate (LiBOB), which furnished superior anodic stability up to 4.5V vs Li/Li+ [3]. The LiBOB also provided the other interactive properties for Li-ion batteries such as high stability at high temperature [4]. In this report the effects of tri-isopropoxy-boroxine (TiPBx) as an electrolyte additive were evaluated with composition analysis. Thus 18650-type battery cells equipped with electrolytes (1.0 mol/L LiPF6 in ethylmethyl carbonate (EMC) and ethylene carbonate (EC)) with or without TiPBx were prepared and the charge-discharge tests were conducted. In fact the cell with TiPBx showed the long-life time as compared with no TiPBx where the decrease in discharged capacity was constricted. Therefore the electrolyte solutions were extracted from cycled cells and their solution compositions were detected by nuclear magnetic resonance (NMR) techniques so as to examine the impact of charge-discharge cycles and the presence of TiPBx. The electrolyte compositions analyses with 1H- and 13C-NMR indicated that composition transformations were observed after 1000 cycles without TiPBx. In particular the ester exchange reaction of EMC took place to form diethyl and dimethyl carbonates respectively. 2D HMQC NMR indicated that the ester exchange reaction of EC was also detected to afford linear polycarbonates. On the other hand, the electrolyte composition after 1000 cycles with TiPBx has almost been kept as compared with the initial composition since the ester exchange reactions were suppressed. These indicated that TiPBx prevented the ester exchange reactions giving rise to constricting the decrease in discharge capacity. We will discuss relations of the reaction mechanism of the electrolyte with the degradation of the battery performance. [1] D. Aurbach, K. Gamolsky, B. Markovsky, Y. Gofer, M. Schmidt and U. Heider, Electrochimica Acta., 47, 1423 (2002).[2] H.Horino, H. Tamada, A. Kishimoto, J.Kaneko, Y. Iriyama, Y. Tanaka and T. Fujinami, J. Electrochem., Soc., 157 (6) A677 (2010).[3] K.Xu and C.A.Angell, Electrochem. Solid-State Lett., 4, E1 (2001).[4] K. Amine, J.Liu, S.Kang, I.Belharouak, Y, Hyung, D. Vissers and G.Henriksen, J. Power Sources., 129, 14 (2004).

Electrodeposition of Carbon from High Temperature Carbonate Melts

The storage and release of electrical energy is vital to the functioning of many necessities of modern life including portable electronic devices, power tools, and automobiles. In the face of our ever-increasing need for better energy storage devices, it is desirable that we continue to investigate superior materials for use in battery and supercapacitor devices. It has long been known that carbons may be produced through the electrolytic reduction of molten carbonates, with the mechanism of this reduction being thought to proceed by way of Eqn 1 [1], i.e.; CO3 2- + 4e- ---> C+3O2- …(1) For this research carbons were prepared by varying the electrodeposition parameters around a standard set of conditions (Li2CO3-Na2CO3-K2CO3 electrolyte, 0.25 A/cm2 current density, graphite substrate, 600°C). The research of this group indicates at this point that there exist reproducible patterns in the properties of our carbons based on most of these variables, with the primary result of the research linking decreased current densities, decreased temperatures, and every electrolyte except Li2CO3-Na2CO3, but not substrate to any major degree, to increased capacitive performance. 1. Le Van, K., et al., Electrochemical formation of carbon nano-powders with various porosities in molten alkali carbonates. Electrochimica Acta, 2009. 54(19): p. 4566-4573.

Exploring Key Descriptors of Solid Electrolyte Interphase Formation in Lithium Ion Batteries through Atomistic Simulations

Lithium ion batteries (LIBs) have allowed for a technological revolution in portable electronics, power tools, and electric vehicles. Future improvements, however, require an advancement of existing battery technology to provide for faster charging and larger capacities, while maintaining safety and longevity. This fundamentally represents a knowledge and materials challenge that needs to develop a deeper understanding of electrode and electrolyte materials as well as their interfaces. Electrolyte and electrode materials used in LIBs have been studied separately to a great extent, however the structural and dynamical properties of the electrode/electrolyte interface still remain largely unexplored despite its critical role in governing battery performance. In particular, a key issue restraining the utilization of high-energy density anode materials, such as silicon (Si), is their inability to form a stable interphase during charging which results in continuous capacity fade or even cell failure. The design of better storage devices may be improved through a greater fundamental understanding of the formation of the solid electrolyte interphase (SEI) at the anode/electrolyte interface through atomistic computer simulations. We have utilized molecular dynamics (MD) simulations to correlate the bulk composition of the electrolyte to the interfacial structure and its effect on the transport behavior of key intermediates in the reductive decomposition of this electrolyte at a graphitic carbon electrode. Our study clearly demonstrates that the interfacial structure is sensitive to the molecular geometry and polarity of each solvent molecule as well as the surface structure and charge distribution of the negative electrode. Such quantitative analysis of the molecular arrangements at the electrode/electrolyte interface improves the understanding and description of electrolyte decomposition and SEI formation. Using MD and metadynamics techniques, we have systematically studied how factors such as the bulk composition of mixed carbonate electrolytes, precipitation of lithium fluoride (LiF, a result of the unstable PF6- anion species) onto the anode, and some commonly utilized additives (shown to improve the quality of the SEI layer) influence the transport and accumulation of decomposition products/intermediates. In this talk, we will present some of our recent findings including what we believe to be key descriptors in to predicting the decomposition products arising from the electrochemical reduction of the electrolyte. This improved understanding provides design principles for future investigation into forming a stable SEI on high-energy anodes such as Si.

(Invited) To Understand Local Structure Evolution and Ion Dynamics of the Electrode/Electrolyte Materials Combined with Different Spectroscopic Techniques

Li-ion battery has become the most important energy systems for portable electronics, power tools and automobile applications such as hybrid and plug-in electric vehicles. However, it is still necessary to enhance their electrochemical performance such as energy density and cycle life, for promoting their competition capability as vehicle power system. Obviously, electrode materials, especially positive electrode materials either working voltage or reversible capacity determine the energy density of the Li-ion batteries at mostly[1,2]. In the presentation, some recent work about in-situ or ex-situ characterization of local structural evolution and Li-ion dynamics of new electrode/electrolyte materials combined with different techniques, such as synchtron X-ray diffraction, X-ray absorption spectroscopy (XAS), neutron diffraction, High-resolution transmision microscopy and solid state NMR techniques. The investigated electrode/electrolyte systems include Ti-doped LiMn2O4, FeF3, Na3V2(PO4)2F3 , Zn2+-doped P2- Na0.66Ni0.33Mn0.67O2and Garnet-type electrolytes. Acknowledgement: Financial support from National Natural Science Foundation of China ( Grant No. 21233004, 21473148, 21428303) are gratefully acknowledged References M. Armand, J.-M. Tarascon; Nature, 2008, 451，682 Z. L. Gong, Y. Yang；Energy & Environmental Science； 2011，4，3223 S. H. Wang, et al ; J. Power Sources, 2014, 245, 570-578 W. Zhang, et al, J Phys. Chem.C, 2013, 117(22), 11498-11505 Z. G. Liu et al , Chem. Mater.; 2014, 26(8), 2513-2521 X. H. Wu, et al, to be submitted D. W. Wang, et al Chem. Mater.; 2015, 27, 6650−6659

SnO2 nanocrystals into Three Dimensional Graphene Architectures for Lithium Ion Batteries

Li ion batteries (LIBs) are important for energy storage in portable electronic devices, power tools, and electrical vehicles, all of which require high energy density. In order to meet the increasing demand for high energy density batteries, it is essential to develop high-capacity electrode materials. Recently, metal- and metal oxide-based anode materials have been reported to exhibit higher Li storage capacities than commercial graphite anode. However, the reversible charging and discharging process is accompanied by large volume variation, which can result in the pulverization of high capacity anodes and loss of electrical contact, causing rapid capacity decay upon extended cycling. The most promising approach is the integration of metal oxides with carbonaceous materials. Inspired by this approach, we demonstrate a facile strategy for fabricating a 3D reduced graphene oxide (RGO)-SnO2 architecture that encompasses the merits of both SnO2 nanostructures and carbonaceous materials with the aim of improving energy storage in LIBs, especially in terms of cycling performances. The hierarchical SnO2-RGO aerogel shows excellent electrochemical performance, with a high reversible capacity, a high rate capacity and good cycleability. This performance is attributed to the uniform dispersion of SnO2 nanoparticles and the 3D macroporous continuity, which provide a large accessible area, easy ion accessibility, short ion diffusion length, and rapid charge and mass transport. More details will be discussed at the meeting.

Impact of Electrode Nature on Lithium-Ion Battery Performances with Ionic Liquids or Carbonate Electrolytes

Lithium-ion batteries have rapidly become the most common power source for portable electronic devices, power tools and electric vehicles due to their high energy density and good cycling stability. However, before implementation of the Li-ion batteries in EVs and HEVs, many features still must be resolved, like low cost, long calendar life, safety and high power capability (1). Replacement of the organic carbonates with more thermally and electrochemically stable ionic liquids (ILs) could increase the security (2). A lot of work was already reported in the literature about the ILs as electrolytes, especially in comparison of cycling with organic electrolyte, but still with different electrodes combination. By following the nature of the electrodes couples, the power capacity could be tuned (1). Nevertheless, a few systematic comparison of these different systems are available (3-4). In this work, we report the performance of three full cell configurations: graphite (Cgr)// LiFePO4 (LFP), Li4Ti5O12 (LTO)// LiFePO4 (LFP) and Li4Ti5O12 (LTO)// LiNi1/3Mn1/3Co1/3O2 (NMC), with five different ionic liquids and one organic carbonate electrolytes. Their cycling results, at 333 K, with a pyrrolidinium [PYR14][NTf2], series of imidazolium ionic liquids ([C1CnIm][NTf2] and [C1C1CnIm][NTf2]/ n= 4 and 6) associated with LiNTf2 (1mol.L-1) then an organic electrolyte (LiPF6 (1mol.L-1) DEC: EC), are depicted in Figure 1 (a-c). Some trends have been found. For Cgr//LFP system cycling is observed only in the presence of organic additive, vinylene carbonate (VC) (Fig. 1a). Carbonates, except for LTO//NMC cell, show lower capacity then ILs based electrolytes (Fig. 1). The highest capacity is observed for LTO//NMC system with ([C1C4Im][NTf2], [PYR14][NTf2] and carbonate electrolyte, ~180 mAh.g-1, ~140 mAh.g-1 and ~180 mAh.g-1, respectively (Fig. 1c). The introduction of a donating group (-CH3) on position two of the imidazolium ring (C2-H → C2-CH3) in [C1C1CnIm][NTf2] highly improve the performance of Cgr//LFP cells (Fig. 1) (5). Besides LTO//NMC, the charge/discharge performance is improved by extending the alkyl chain length of the imidazolium ring. Finally, in LTO//LFP and LTO//NMC, higher performances were obtained with ([C1C4Im][NTf2] compare to [PYR14][NTf2]. From these results, we highlight the tremendous impact of each element of the system (electrode, electrolyte, and separator (6)) onto the charge discharge capacity, especially with ionic liquids based ones.

In-Situ Raman Spectroscopy and Electrochemical Studies on High Energy Density xLi2MnO3-(1-x)LiNi0.66Co0.17Mn0.17O2 Composite Cathode Materials

Development of high energy density cathode materials is the key to fabricate high power Li-ion batteries (LIBs) capable of meeting high power demands in new applications such as regenerative braking in hybrid electric vehicles, power backup, and portable power tools. Li2MnO3-based composite cathode materials are attracting much attention due to their excellent electrochemical performances [1-5]. In the present work, novel layered-layered composite cathode materials with small amount of cobalt and different amounts of Li2MnO3 e.g. xLi2MnO3-(1-x) LiNi0.66Co0.17Mn0.17O2 where x = 0.3, 0.5, and 0.7 were successfully synthesized by employing sol-gel technique and characterized using advanced techniques to investigate both the structural and electrochemical properties. Powder X-ray diffraction patterns confirmed the formation of layered-layered composite materials revealed by the presence of reflections corresponding to rhombohedral (R3m) and monoclinic (C2/m) space group symmetries. Structural analysis by Raman spectroscopy showed three distinct phonon modes. Peaks centered at 482 cm-1 and 596 cm-1 correspond to Eg and A1g modes of the rhombohedral phase and the one at 420 cm-1 represent the presence of monoclinic Li2MnO3 component. Microstructural evaluation by scanning electron microscopy and energy dispersive X-ray spectroscopy divulged the highly dense polyhedral-shaped agglomerates with respective elements. X-ray photoelectron spectroscopy analysis revealed 2+, 3+, and 4+ as the predominant oxidations of Ni, Co, and Mn respectively. Electrochemical measurements were performed using CR2032 type coin cells assembled with Li-metal foil as reference/counter electrode and spray-coated composite materials as cathode. Extended rate capability tests were also carried out at different C-rates, C/40, C/20, C/10, C/5, and 1C and compared performances of the three compositions. The results indicate that the composite cathode with x = 0.5 exhibited better electrochemical performances in terms of high discharge capacity (~250 mAh/g) , rate capability and cycleability in comparison with those with x = 0.3 and 0.7. According to the electrochemical studies, the first cycle charge profile was quite different from the subsequent cycles and irreversible capacity losses are much higher in the first cycle. The voltage in the cell increases monotonically until 4.45 V and reaches a plateau region between 4.45 and 4.6 V. To understand the local structural changes occurring in the materials and investigate the mechanisms associated with the first cycle charge-discharge profile, in situ Raman spectroscopy studies were conducted using specially designed/fabricated coin cells. Electrochemical properties of the composite cathode materials probed by charge-discharge profiles, cyclic voltammetry, cycleabilty, rate capabilty, electrochemical impedance spectroscopy and in situ Raman spectroscopic studies will be presented. Acknowledgements The financial support from NASA-URC grant #NNX10AQ17A is gratefully acknowledged. A part of the work was carried out at Jet Propulsion Laboratory under NASA’s Space Power Systems Program.