bluuebunny/crossref_metadata_2025 huggingface dataset:
Reverse Monte Carlo Simulation of Lithium Transition Metal Oxide for Cathode Material of Lithium-Ion Battery
Authors: Kitamura Naoto , Ishida Naoya , Idemoto Yasushi
Published: February 2020

INTRODUCTION

In last few decades, lithium transition-metal oxides with layered structures, such as Li(Ni,Mn)O2 and Li(Mn,Ni,Co)O2, have drawn much attention as a cathode material for the lithium-ion battery. Electrochemical properties of these oxides are supposed to be affected by the local cation configurations in the crystals, and thus the local structures have been studied actively by various methods, like NMR, extended X-ray absorption fine structure (EXAFS) technique and pair distribution function (PDF) fitting.

In this study, we perform the Reverse Monte Carlo (RMC) modelling using the Bragg reflections and total scatterings simultaneously for an analysis on atomic configurations of crystalline lithium transition-metal oxides. Based on the result, we try to determine average (periodic) and local (non-periodic) atomic configurations at the same time.

EXPERIMENTAL

In this work, a lithium transition-metal oxide LiNi0.5Mn0.5O2 was synthesized. The sample was identified preliminarily by laboratorial X-ray diffraction measurement, and the metal composition was evaluated by the inductively-coupled plasma (ICP) technique. Neutron total scattering pattern of the sample was recorded with HIPPO installed at LANSCE, USA. From the pattern, the normalized reciprocal space data, F(Q), and the real space data, G(r), were obtained. By using these data and the neutron Bragg reflections, we performed the RMC modelling with RMCProfile. A rhombohedral simulation box of 2400 atoms, Li600Ni300Mn300O1200, was used in the modelling, and then the atomic configuration was simulated.

RESULTS AND DISCUSSION

From laboratorial X-ray diffractions, it was confirmed that the LiNi0.5Mn0.5O2 had the layered rock-salt structure (space group: R-3m). The ICP analysis demonstrated that the analytical molar ratio of Li and the transition-metal ions was in good agreement with the nominal composition.

For the sample, we measured neutron total scattering pattern and then performed the RMC simulation using the Bragg reflection, F(Q) and G(r). In the analysis, F(Q) was degraded by convolution in order to take the finite cell size into account, which is denoted as F
conv.(Q) in this work. Fig. 1 shows the RMC simulation result for the F
conv.(Q). as an example. This result demonstrates that the RMC simulation was successfully carried out by using the data set mentioned above. Fig. 2 shows partial radial distribution functions, g(r), of Li-O, Ni-O and Mn-O. It is found that average bond distances of Ni-O and Li-O are the same essentially, but that of Mn-O is shorter than the others. This tendency can be explained well by differences in the ionic radii of Li+, Ni2+ and Mn4+ with 6-fold coordination. From distribution of the bond angles, it is suggested that Ni and Mn forms a local ordering in the transition-metal layer.
Electrochemical Properties of Si-Alloy/Graphite/Carbon Nanotubes Blending Electrode for Li-Ion Batteries
Authors: Park Cheol-Ho , Kim Seon-Kyong , Choi Young-Pil , Kim Min-Hyun , Kim Young-Nam , Kim Yoon-Keun
Published: February 2020

Si-based alloy[1] is one of the most promising anode materials for substituting graphite due to its excellent characteristics such as high gravimetric capacity exceeding 1000mAh/g, high safety, good electrochemical stability and low production cost, etc. Currently, graphite anode material is widely used with water-based SBR binder in commercial Li-Ion Batteries and its electrode capacity is about 350mAh/g. In order to increase the energy density of anode electrode there have been many attempts of blending small (less than 10%) quantity of Si-based anode materials with graphite without changing water-based SBR binder system.

In this study, we made Si-alloy/Graphite/Single-walled Carbon nanotubes(SWCNTs) blending electrode and evaluate the electrochemical properties. In case of 8% of Si-alloy / 89% of Graphite / 0% SWCNT / 2% of SBR /1% of CMC electrode, the initial discharge capacity is 387mAh/g, initial the coulombic efficiency is 86.2% and the capacity retention after 50th cycle is 80.7%. In case of 8% of Si-alloy/89.7% of Graphite/ 0.3% SWCNT/ 2% of SBR /1% of CMC electrode, the initial discharge capacity is 393.5mAh/g, the initial coulombic efficiency is 88.4% and the discharge capacity retention after 50cycle is 99.2%.

This improvement in the electrochemical properties of the SWCNT added electrode was mainly attributed to the good electric contact between Si-alloy particles and graphite particles during cycles. In other words, the main cause of initial capacity lose in Si-alloy/Graphite blending electrode is to lose electric contact due to the volume change of Si-alloy. This result gives many hints to improve Si-based anode materials.

[1] M. Kim et al. Journal of Electroanalytical Chemistry 687 (2012) 84-88
Analysis of Crystal Structure, Electronic and Nuclear Densities, and Local Structure for LiNi0.8Co0.2O2 during Charge Process Using Synchrotron X-Ray and Neutron Sources
Authors: Ishida Naoya , Horie Ayano , Kitamura Naoto , Idemoto Yasushi
Published: February 2020

INTRODUCTION

Positive electrode material, Li(Ni,Co)O2 system, of Li-ion battery has been attractive because it has the advantage in low environmental load due to low Co content. There are many previous works about the Li(Ni,Co)O2 and the aluminum-substituted one because of high heat stability. However, detail structural changes during electrochemical processes are still ambiguous for site occupancy, local structures, and electronic structures even though these would play important roles on the battery characteristics. In this research, we used several quantum beam techniques to reveal the crystal structures, electronic and nuclear densities, and local structures of LiNi0.8Co0.2O2 during charge process.

EXPERIMENTAL

To synthesize the LiNi0.8Co0.2O2, the precursor was prepared by co-precipitation method. The co-precipitated material was annealed at 800 °C in air for 15 h. The product was identified by powder XRD and ICP-OES. To study change of crystal and electronic structure of this cathode material during electrochemical process, cathode materials were prepared by four charge depths, and were investigated using the synchrotron X-ray diffraction (BL02B2, SPring-8) and neutron diffraction (BL20, J-PARC). The data was analyzed with the Rietveld technique using Rietan-FP and Z-Rietveld, and by the MEM using the Dysnomia and Z-MEM programs. To examine the local structures, X-ray absorption spectroscopy (BL14B2, SPring-8) and X-ray total scattering (BL04B2, SPring-8) were measured.

RESULTS AND DISCUSSION

The neutron diffraction patterns were measured for the cathode after 2nd discharge process as well as the pristine electrode. It was demonstrated that the crystal structure analysis by ex-situ measurement could be successfully performed even for the electrode with an amount of about 10 mg. The values of 3b-6c bond length decreased and λ2, which expresses the distorted degree of the Li-O6 and M-O6 octahedra, were increased with increasing charge depth. Synchrotron-based experiments using high energy X-ray total scattering and pair distribution function (PDF) analysis (Fig. 1) indicated that the oxygens arranged to crystallographic a-b plane were disturbed in the charge state of 4.3 V after 2nd cycle (Fig. 2).

ACKNOWLEDGMENTS

This research was supported by the RISING-project of the New Energy and Industrial Technology Development Organization (NEDO), Japan.
Lithium Powder Electrode As Anode in Lithium-Oxygen Batteries
Authors: Hwang Sunwoo , Cho Sung Man , Koo Bon Seok , Yoon Woo Young
Published: February 2020

The rechargeable non-aqueous lithium-air (O2) battery system is a promising to apply the large scale storage system such as electric vehicle. It can store much higher theoretical energy density than regular Li-ion batteries. Nevertheless this advantage, Li-O2 cell has the problems such as polarization of the oxygen reduction reaction (ORR), decomposition of the organic electrolyte and dendrite growth on the Li metal anode. Li dendrite can make dead Li which significantly drop the cycle retention. Also Li dendrite growth can occurs the unstable solid electrolyte interface (SEI) layer, it is promote the electrolyte decompose. In this study we use Li powder electrode (LPE) instead of the Li metal anode.

The Li powder was made by droplet emulsion technique (D.E.T) (the diameter of lithium powder is 10μm). A Li powder was revealed effective to reduce dendrite growing by the previous study of our group. To make the LPE, we loaded 20mg Li powder on the 15 Φ Sus-mesh and pressed 20kgcm-2. To compose the O2 cathode, Poly (vinylidene fluoride) (PVdF), Ketjen black (KB) carbon and MnO2 catalysts were mixed by 2: 4: 4 wt. %. The current collector of O2cathode was Ni foam and punched 14 Φ. The electrolyte was used by a 1M LiTFSI in TEGDME. The morphology of electrode was pictured by field emission scanning electron microscope (FE-SEM).

To estimate the galvanostatically electrochemical properties we analyze the impedance data, voltage profile and cycle data. The rate of current is 100mAg-1 and limited the time at 10 hours in charge and discharge respectively. In voltage profile we check there a stable cycle process until 40cycles. Li powder has much stable interface reaction than Li metal, it can possible to reduce the over potential at the charge/discharge and make good cycle ability. To analyze the morphology and chemical reaction after cycle was estimated by the FE-SEM, TEM, XPS and FT-IR.

Reference to a journal publication

[1] G. Girishkumar, B. McCloskey, A. C. Luntz, S. Swanson and W. Wilcke, J. Phys. Chem. Lett.1 2193-2203. (2010)

[2] S. A. Freunberger, Y. Chen, N. E. Drewett, L. J. Hardwick, F. Barde and P. G. Bruce, Angew. Chem. 50, 8609-8613. (2011)

[3] J. G. Zhang, D. Wang, W. Xu, J. Xiao and R. E. Williford, Journal of Power Sources 195, 4332-4337. (2010)

[4] S.K Kong, B.K. Kim and W.Y. Yoon, Journal of the Electrochemical Society 159, A1551-A1553. (2012)
The Influence of Platinum Doping on the Structure, Morphology and Electrochemical Properties of LiFePO4/C Cathode Material
Authors: Talebi-Esfandarani Majid , Savadogo Oumarou
Published: February 2020

In this work, a dual approach of metal doping and carbon coating was employed to improve the poor ion diffusion rate and low electrical conductivity of LiFePO4, respectively. LiFePO4 and LiFe0.96Pt0.04PO4 materials were synthesized using a sol-gel method followed by carbon coating with sucrose. The effect of platinum doping on the physical-chemical properties and the electrochemical performance of LiFePO4/C material were investigated by XRD, XPS, SEM, carbon analyzer, charge/discharge testing, cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical results showed that the specific discharge capacities of the material significantly increased by platinum doping. This improvement will be discussed considering the expansion of the lattice parameter, reducing the particles size with uniform distribution and pillar effect of platinum element for stabilizing the crystal structure.
Model-Based Analysis of a 12V Dual-Battery System for Design Optimization of Microhybrid Vehicles
Authors: Zhang Zhenli , Rick Anthony , Sisk Brian C
Published: February 2020

12V microhybrid (MHEV) technology has potential to deliver 5-10% fuel economy improvement over traditional gasoline vehicles without adding excessive cost to the consumer. Parallelizing the traditional lead acid battery with a high-power lithium ion battery has the potential to enable critical microhybrid function such as regenerative braking. Enabling a low-cost passive connection between the lead-acid and lithium-ion batteries requires compatibility between the two batteries, including design factors such as battery size, resistance, and open-circuit voltage (OCV).

In this work we have developed a dual-battery model that couples an electrochemical model of a lithium ion battery and an equivalent circuit model of a lead acid battery in order to perform design optimization of a passively-connected dual-battery MHEV system. We analyzed the dynamic responses of the two batteries upon high power charge and discharge pulses, with and without simulated vehicle accessory loads. The current split between the two batteries is explored in detail as a function of pulse characteristics, operating voltage, and accessory load. Finally, a simulated vehicle regulatory drive cycle, specifically the New European Driving Cycle (NEDC), is implemented for analysis of contributions of two batteries.
Evaluation of Electrode Structure and Simulation of Transport Phenomena in Lithium-Ion Battery
Authors: Inoue Gen , Ikishima Junya , Kawase Motoaki
Published: February 2020

Recently, the importance of various secondary batteries is increasing remarkably, because it is expected as the energy storage devices for renewable energy, such as solar and wind, as the basic technology for energy security and as the power storage for automotive. Especially, in order to increase the high-rate performance, Innovative design of electrode structure on the basis of kinetics and transport phenomena of ion and electron is needed. In our previous study, we focused on the binder and examined the effect of binder distribution and porous structure on the discharge performance by numerical analysis. In this study, actual porous electrode structure was obtained by FIB-SEM and the effective electrical and ionic conductivities were estimated, and these were compared with experimental results. Moreover, the effect of structure on the discharge performance and reaction rate distribution by 3D direct simulation. As a result, the correlation model of the relationship between porosity and relative conductivity of Li+ and electron could be obtained. And the remarkable difference between heterogeneous structure and uniform particle packed model could be confirmed. The validity of this simulation method could be confirmed by the comparison of tortuosity and relative conductivity between estimation and experimental results. From the electrochemical reaction simulation, in the case of reducing binder to 1/3 of actual condition, overall current could increase twice. So it was found that the optimization of structure of sub-material, which consists of binder and conductive material, is very important to increase high-rate discharge performance. In addition, we examined the effect of binder adhesion model and migration in the direction of through-plane.
Li Storage Behavior of C-Coated Si/SiOx Nanospheres As a High Capacity Anode Material for Lithium-Ion Battery
Authors: Park Eunjun , Park Minsik , Lee Jaewoo , Kim Young-Jun , Kim Hansu
Published: February 2020

Si has gained much attention as anode materials for lithium-ion battery due to its high theoretical capacity (3,580 mAhg-1) and low standard oxidation potential (0.4 V vs. Li/Li+). Despite these features, Si anode materials still have limits to commercial uses by poor cycle performance associated with their mechanical pulverization of Si due to severe volume change during alloying/dealloying with Li. To overcome this problem, various approaches have been suggested. In particular, the composites, which are composed of active Si and inactive buffer material, showed promising approaches for reducing the mechanical strain during cycles. On the other hand, nanostructuring of active materials would be helpful for further improvement of cycle performance. After heat treatment of Si/SiOx precursor at 1200 °C under inert atmosphere, we obtained Si nanocrystals embedded SiOx nanospheres with a size of 200 nm, in which about 10 nm sized Si nanocrystals are embedded in amorphous SiOx matrix. In order to improve electrical conductivity of Si/SiOx nanocomposites, carbon layer was coated on the surface of Si/SiOx nanocomposites.

The Si/SiOx nanospheres and C-coated Si/SiOx nanospheres were characterized by a field emission scanning electron microscope (FESEM), a high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD) patterns, solid state 29Si magnetic angle spinning nuclear magnetic resonance (MAS NMR) and X-ray photoelectron spectroscopy (XPS) analyses.

The C-coated Si/SiOx composites showed a reversible capacity of 950 mAh/g-1 at current density of 200 mAg-1 with stable cycle performance over 100 cycles and high rate capabilities. In this presentation, the electrochemical properties of the C-coated Si/SiOx nanocomposites will be discussed in more detail.
Degradation Studies on LiFePO4 cathode
Authors: Scipioni Roberto , Jørgensen Peter Stanley , Hjelm Johan , Norby Poul , Rasmussen Claus Nygaard , Jensen Søren Højgaard
Published: February 2020

Lithium-ion batteries are a promising technology for automotive application, but limited performance and lifetime is still a big issue. The aim of this work is to study and address degradation processes which affect LiFePO4 (LFP) cathodes - one of the most common cathodes in commercial Li-ion batteries.

In order to evaluate how the LFP cathode is affected by C-rate a LFP working electrode, Lithium metal foil counter electrode and Lithium metal reference electrode was tested in a 3-electrode setup with a standard 1M LiPF6 in 1:1 EC/DMC electrolyte and glass fiber separator. The working electrode/counter electrode was subjected to several charge/discharge cycles between 3.0 V and 4.0 V at different discharge rates. Figure 1 shows the voltage profile of the LFP electrode (solid line) and full battery (dotted line) during charge/discharge process. It is seen that the higher the C-rate, the higher is the polarization furnished by the counter electrode which reduces the capacity.

In Figure 2, the discharge capacity [mAh/g] is plotted vs the number of charge/discharge cycles. Series of 10 cycles at a given C-rate was applied to the battery. Each series was followed by a C/10 cycle (green points). A linear fit has been applied to the first series (omitting first two cycles where instability of the system is observed), in order to calculate the degradation rates.

High C-rates are seen to affect the discharge capacity, but the capacity is almost completely recovered (green points) and only a limited degradation occurs.

Impedance spectroscopy has been also applied to investigate the LFP cathode degradation. Figure 3 shows the imaginary part of the impedance measured at 50% State-of-Charge after each series of cycles. The relative increase in the impedance arc around 1 KHz (assumed to be associated with charge transfer resistance at the LFP particle surfaces) is seen to gradually decrease with increasing number of series. This indicates that more cycles per series is needed to establish a convincing relation between C-rate and degradation.

The degradation studies will be coupled with FIB/SEM analysis in order to observe changes in the pore structure or micro cracks that would affect electronic percolation. Figure 4 displays an example of a fresh LFP cathode after FIB cutting. White particles are LFP grains while the black area contains carbon particles and pores, which are difficult to distinguish from each other. Substitution of the epoxy resin with a silicon resin increases the contrast between pores and carbon particles [1] and this will be used in the forthcoming FIB/SEM analysis.

References

[1] M. Ender et al, Journal of The Electrochemical Society, 159 (7) A972-A980 (2012)
Electrochemical Performance of Overlithiated Li1+XNi0.8Co0.2O2: Structural and Oxidation State Studies
Authors: Rusdi Roshidah , Kamarulzaman Norlida , Elong Kelimah , Rusdi Hashlina , Abd Rahman Azilah
Published: February 2020

Pure layered compound of overlithiated Li1+xNi0.8Co0.2O2 (x=1,1.05,1.1) samples were successfully prepared by a combustion method. Structural studies of the XRD results showed that when lithium was doped into the LiNi0.8Co0.2O2 cathode materials, the structural parameters of the materials changed slightly when more lithium is doped, that is the cell parameter decreased. Scanning electron microscopy (SEM) revealed that the morphology of the particle c0.2hanged a little from rounded polyhedral-like particle to sharp edged polyhedral crystals when more lithium is doped. Energy dispersive X-ray spectroscopy (EDX) showed that the stoichiometries of Ni and Co agrees with calculated synthesized values. X-ray photoelectron spectroscopy (XPS) studies showed that the binding energy of Li 1s is decreased for the doped Li1.05Ni0.8Co0.2O2 compound followed by Li1.1Ni0.8Co0.2O2 and LiNi0.8Co0.2O2. This implies that the Li+ ions can be more easily extracted from Li1.05Ni0.8Co0.2O2 materials than the other stoichiometries. The XPS results are supported by the electrochemical performance of the samples. Li1.05Ni0.8Co0.2O2 showed the best results with a specific capacity of 113.29 mAh/g compared to Li1.1Ni0.8Co0.2O2 with a specific capacity of 112.32 mAh/g and LiNi0.8Co0.2O2 with a specific capacity of 94.71 mAh/g. Li1.05Ni0.8Co0.2O2 also showed the best capacity retention of 7.8 % over 10 cycles.

Reference

[1] R.Santhanam, B.Rambabu, "Improved High Rate Cycling of Li-rich Li1.1Ni1/3Co1/3Mn1/3O2

Cathode for Lithium Batteries" Int.J,Electrochem.Sci.,4 (2009) pp. 1770-1778
Hybrid Polyvinyl Alcohol/Silicon Nanofiber Anodes with High Concentrated Graphene Nanoribbons for Rechargeable Lithium-ion Batteries
Authors: Kim Yong Seok , Li Zhong , Patel Bharat , Chakrapani Srinivasan , Lee Sangho , Joo Yong Lak
Published: February 2020

Despite the highest theoretical capacity of 3579 mAh/g in lithium–ion batteries,[1,2] silicon (Si) anodes have been still suffered from severe capacity fading, because of two kinds of drawbacks such as (i) dramatic volume expansion called pulverization leading to electrical disconnection as well as (ii) formation of solid–electrolyte interface on their surfaces.

Herein, we prepared an organic/inorganic hybrid anode of polyvinyl alcohol (PVA)/Si nanoparticles (NPs)/graphene nanoribbons (GNRs) nanofibers via electrospinning process. Since PVA polymer could be dissolved in water, our hybrid nanofibers have been made via water‒based electrospinning, which means that toxic solvents like N–Methyl–2–pyrrolidone (NMP) do not need to be used for preparing the electrodes. Furthermore, the PVA polymer as a good dispersant can effectively help to disperse high‒concentrated GNRs (20 mg/ml) under water, which are unzipped from multiwall carbon nanotubes for better dispersion ability. The battery cells using the hybrid PVA/Si/GNRs nanofibers exhibited an initial high discharge capacity of over 5000 mAh/g at 0.1C because of the contribution of well–dispersed GNRs and Si NPs, while only Si NPs have the first discharge capacity of ca. 2500 mAh/g. At even 1C (3.6 A/g), they showed a high reversible capacity of around 1800 mAh/g owing to highly–conductive GNRs within the hybrid nanofibers. Moreover, the nanofibers retained very stable cycle retention of over 90% during 200 cycles. Such excellent cycle retention should be attributed by cross–linked and stabilized PVA nanofibers covering Si NPs, available to not only prohibit the volume expansion but also alleviate the formation of SEI layers. In terms of electrochemical properties, the hybrid nanofibers represented much less charge transport resistance from electrochemical impedance spectroscopy and higher peak current density from cyclic voltammetry than only Si NPs, because the GNRs as electrical conductors in the electrodes must be well–distributed between Si NPs. As a result, we demonstrated an outstanding battery performance through a novel hybrid PVA/Si/GNRs nanofibers directly fabricated via water–based spinning.

References

[1] H. Wu, Y. Cui, Nano Today
2012,
7
, 414.

[2] Wu H.; Chan G.; Choi J. W.; Ryu I.; Yao Y.; McDowell M. T.; Lee S. W.; Jackson A.; Yang Y.; Hu L.; Cui Y. Nature Nanotech.
2012, 7, 310.
The Electrochemical Performances of Metal Ions and F- Co-Substituted Li4Ti5O12
Authors: Kim Jae Hyun , Park Jung Soo , Baek Seong-Ho
Published: February 2020

The graphite is usually selected as anode material of commercial lithium-ion batteries, because of its large theoretical capacity (372 mAh g-1) and reversible charged-discharge for Li+, but the potential safety problem is dendritic lithium growth on the anode surface during the charging and discharging. Li4Ti5O12 has almost no formation of SEI layer and dendritic lithium growth on the electrode surface during charging/discharging because its high flat operating voltage of about 1.5 V. To overcome the demerit of insulating property of Li4Ti5O12, doping the structure with small amounts of various transition metal ions have been tried.

The investigation of electrochemical performances of Al3+ and F- co-substituted compounds was previously done. But, the electrochemical performance of co-substituted specimen was worse than the Al3+ substituted one.

The electrochemical perfomances of the eight kinds of F- and metal ions (Fe, Mg, Ag, Zn, Sr, Sn Mo, and Co ions) co-doped Li4Ti5O12 specimens were studied. Among them, the cycle retention was best in F- and Co ion co-doped sample. The capacity of F- and Mg ion co-substituted one was largest. The capacity of all the co-substituted samples was larger than pure Li4Ti5O12. The good cycle performance was explained by the relative bonding strength between metal ion and oxygen ion.
Improved Lithium Sulfur Battery Performance through Attaching Nanosilica on the Backside of Nickel Foam
Authors: Cho Sung Ho , Yoon Woo Young
Published: February 2020

Lithium Sulfur (Li-S) battery has a theoretically high specific capacity of 1675 mAh g-1, which one of the most promising energy source for electric vehicles (EVs), hybrid electric vehicles (HEVs) and energy storage system (ESS). However, Li-S batteries have crucial problem resulting from the polysulfides dissolution which is called ‘Shuttle Effect’. This shuttle effect causes overpotential and lowers its Coulomb efficiency. Also, a loss of active material by dissolution makes capacity fading. So the prevention of the polysulfides dissolution is the main issue of sulfur batteries. To solve the polysulfides dissolution we use nanosilica material on the current collector of cathode. It is reported that nanosilica has a characteristics of absorbing polysulfides. Zhang. et. al reported that they could control the shuttle mechanism by using nanosilica on the separator. However, the polysulfides accumulated on the separator hinder Li ion transport, leading to low capacity values compared to pristine Li-S batteries. In our research, nickel foam based sulfur cathode with silica coated on backside is investigated. Silica on the backside absorbs polysulfides, eventually suppressing the shuttle effect and reducing the quantity of the polysulfides on the separator. As a result, the coulomb efficiency and the capacity of the Li-S battery has increased comparing the uncoated Li-S battery. The examination was conducted by comparing between the pristine and the silica coated sample. Cells were tested at the current densities of 0.1 C rate with limited voltage of 1.8 to 2.8V. The morphology of the samples was observed on a field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). The structure of the samples was characterized by X-ray diffraction (XRD) spectroscopy. The result was analyzed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV).

[1] S.S.Zhang, D.T.Tran, Electrochim. Acta, 114, 296 (2013).
Novel Design of Silicon Electrode Based on Stainless Steel Metal Fibril As Current Collector for Lithium-Ion Batteries
Authors: Song Seonghyun , Kim Chang-Hyeon , Choi Jaecheol , Yeon Subin , Ryou Myung-Hyun , Lee Yong Min
Published: February 2020

Silicon (Si) has been one of the promising anode materials targeting for the next high capacity lithium-ion batteries (LIBs). Lithium ions are reversibly stored in Si based on an alloy mechanism, and thus Si can possess much higher level of theoretical capacity (4,200mAh/g), over 10 times, compared to that of commercial graphite (372mAh/g) [1]. Unfortunately, however, inherent low electric conductivity and poor cell performance has hindered commercialization of Si for a decade.

In order to solve these drawbacks, nano-sized and nano-structured silicon has been introduced. In this work, we developed novel design silicon electrode based on stainless steel metal fibril. In order to achieve this goal, we introduced 3-D current collectors based on stainless steel metal fibril (SF) to increase free volume within Si anodes [2] Subsequently, Si coated by radio frequency (RF) magnetron sputtering method. Coating thickness and loading amount of Si active material on SF was controlled around 1μm and 0.2mg/cm2, respectively. Electrochemical performance of as-prepared SF based Si anode was evaluated using charge-discharge machine (PNE, Koran). Surface changes of as-prepared Si anodes were monitored by Scanning Electron Microscope (TOPCOM, japan)-Energy Dispersive X-ray Spectroscopy (AMETEK, USA).

References

[1] D.J. Lee et al, Electrochemistry Communications, 34 (2013) 98-101

[2] D.J. Lee et al, Journal of Materials Chemistry A, 10 (2014) 1039

Acknowledgements

This work was supported by the IT R&D program of MKE/KEIT. [10041142, Electrolyte Additive for 200Wh/kg High LIB of High Cycle Life]
Alginate Nanofibers as a Binder in Lithium-Ion Cells
Authors: Dufficy Martin K , Khan Saad A , Fedkiw Peter S
Published: February 2020

It is well known that the volume expansion upon Li-alloying, followed by pulverization, deleterious side reaction, and electronic isolation limits the commercial use of high-capacity anode materials such as silicon and tin. Despite these challenges, researchers aspire to discover means to integrate high-capacity materials into electrodes. The electrode binder, one of the least investigated components in a lithium-ion battery, is posited as a potential remedy to many of the issues that lead to cell failure. Manipulating the composition and morphology of the binder impacts the longevity of the cell as well as the capacity retention. Here we show that alginate nanofibers as an anode binder can be used to enhance the performance of Si anodes for lithium-ion batteries.

Alginate is an anionic polysaccharide derived from brown algae [1]. Although it has many industrial uses such as a textile processing and a thickening agent in foods, alginate has recently been reported [1] as an eco-friendly alternative to the conventional PVDF binder. Sodium alginate has been shown to protect the active material by forming an inert passivating layer with common organic carbonate electrolyte solvents while providing ample Li conductivity [1]. Recently, our group has shown that alginate nanofibers can be formed via electrospinning alginate-PEO blends [2]. PEO, albeit electrochemically stable, can be leached away to form porous alginate nanofibers (Figure 1). Electrospinning provides a desirable fiber extrusion technique because it allows for a continuous and facile method to produce multi-component nanofibers. The small size scale of these fibers can further enhance the electronic and ionic transport through the cell.

Here we report physical and electrochemical characteristics of alginate fibers as the binding component in both graphite and silicon anodes. X-ray diffractograms and energy-dispersive x-ray spectroscopy are used to determine the phase and location of the electrochemically active materials, respectively. Cyclic voltammetry test are employed to observe reversibility of the cell. Lithium diffusion rates into the anode materials are also determined. Charge and discharge curves demonstrate alginate fibers may be used in lieu of PVDF as a binding material in Li-ion cells.

Figure 1: SEM image showing alginate fibers. The fibers were not sputter-coated and slight charging effects are evident.

[1] I. Kovalenko et al., Science
334, 75 (2011)

[2] C. A. Bonino et al., Carbohydrate Polymers
85, 111(2011)
Synthesis and Electrochemical Performance of Low Surface Area Alloy Anodes for Lithium-Ion Battery
Authors: Zhao Xiuyun , Dunlap Richard A , Obrovac Mark N
Published: February 2020

Introduction

Alloy negative-electrode materials could significantly increase the energy density of commercial Li-ion batteries [1]. From a practical point of view, alloys prepared by ball milling are inexpensive lithium hosts and easily scalable. However, such alloys typically have small particle sizes and high surface area, increasing their reactivity with electrolyte. Here, we describe a composite alloy material which has been post treated to significantly reduce surface area. The resulting composites have significantly reduced surface area and improved cycling performance over ball milled alloys of similar composition.

Experimental

Alloys were prepared ball milling stoichiometric amounts of Si and Fe. Post-treated alloys were ground and sieved to a 53 μm particle size. Electrodes comprising active material, carbon black and polyimide binder were cycled in 2325 coin-type cells with two Celgard 2300 separators, a lithium foil counter/reference electrode and 1M LiPF6 in EC/DEC/FEC 60/30/10 by volume electrolyte at 30 °C. Cells were cycled at a C/4 rate and trickled discharged to C/20 in a voltage range of 0.005 V-0.9 V. X-ray diffraction (XRD) measurements were collected using a Rigaku Ultima IV diffractometer with a Cu Kαsource. A Phenom G2-pro Scanning Electron Microscope (SEM, Nanoscience, Arizona) was used to study the particle size and morphology of the samples. Surface area was determined by single-point Brunauer, Emmett, and Teller (BET) method using a Micromeritics Flowsorb II 2300 surface area analyzer.

Results

Figure 1 shows the XRD pattern of ball-milled Si/Fe alloy, which consists of XRD peaks from Si, Fe and FeSi2 phases. Figure 2 shows the SEM images of the Si/Fe and post-treated alloy particles. For Si/Fe, many fine particles with a diameter less than 3 μm can be observed along with a few large particles. The particle size range for the post-treated particles is between 10 and 40 μm. BET surface area measurement shows that the post treated particles have a significantly reduced surface area compared to the Si/Fe ball milled alloy (2.6 m2/g for Si/Fe, 0.9 m2/g for post-treated particles), which is consistent with the SEM results.

Figure 3 shows the cycling performance of Si/Fe and the post-treated particles. The post-treated particles have a reversible capacity of 600 mAh/g after the first cycle and good capacity retention. By contrast, the capacity of the ball milled Si/Fe alloy electrode fades gradually during cycling.

Acknowledgements

The authors acknowledge funding from NSERC and 3M Canada, Co. Xiuyun Zhao acknowledges the support from the DREAMS program.

References

[1]. M.N. Obrovac, Leif Christensen, Dinh Ba Le and J.R. Dahn, J. Electrochem. Soc. 154, A849 (2007).
Effect of Conductive Materials and Binder Distribution on Mass Transport by Multi-Scale Simulation Method
Authors: Inoue Gen , Ikishima Junya , Kawase Motoaki
Published: February 2020

Recently, from the viewpoint of the effective utilization of energy and the positive application of renewable energy, the high performance and large-scale secondary batteries are expected as the energy storage devices, the basic technology for energy security and the power storage of automotive. Especially, in order to increase the high-rate performance of lithium ion secondary batteries, the kinetics and transport phenomena of ion and electron have to be understood in detail more and more. This knowledge is very important for the innovative design of electrode structure. In the case with large-scale cell, the electrode layer has to be evaluated in the micro-scale and macro-scale because of ion and electron transfer mechanisms consist of various paths and phenomena, such as interface contact, tortuosity, volume ratio and heterogeneous structure. However, it is very difficult to understand these complex conditions by only direct experimental measurements and observations because actual electrode is heterogeneous structure. In our previous study, we focused on the carbon black (CB) conductive materials. Various CB structures were simulated and characterized by numerical analysis. And the effect of primary aggregation structure on the effective electron conductivity was evaluated. In this study, actual porous electrode structure was obtained by FIB-SEM. By using this structure, the effect of CB primary and secondary aggregation and the contact interface between active materials and CB on the conductivity were evaluated by simulation. Moreover, the effect of CB surface properties on discharge performance was evaluated by experiment. LiCoO2 positive electrode layer was used. The weight ratios of active material, conductive material (Acetylene black) and binder (PVdF) were 92.6, 4.6 and 2.8 wt%. The numerical 3D reconstruction image of this electrode was obtained by FIB-SEM (slice pitch: 500 nm, 160 images) and image processing. CB primary aggregate was simulated by setting particle diameter distribution and particle numbers, and these structures were compared by experimental results, such as TEM image and primary aggregate size distribution. This CB was distributed in 3D reconstruction image by using adhesion to active material model and CB agglomeration model. Effective CB conductivity was simulated by random-walk method and simple conductivity obtained by direct measurement. As a result, it was found that the effective electrical conductivity and effective active material utilization were strongly affected by CB structure and CB agglomeration. And tortuosity of electron path in actual electrode is much larger than that of packed bed model. Furthermore, in the case of high dispersed CB by controlling surface property, the effective electrical conductivity and discharge performance were increased. In addition, we examined the effect of fiber structure conductive material on micro and macro electron transfer.
In-Situ Electrochemical Studies of Li-Ion Start-Stop Vehicle Batteries through a Novel Cell Design
Authors: Wang John , Sherman Elena , Soukiasian Souren , Graetz Jason , Tataria Harshad , Verbrugge Mark W
Published: February 2020

Lithium ion batteries are now used extensively for vehicle traction applications. Because of their high specific power and long usage life, lithium ion batteries are very appealing for power assist vehicular applications. Implementation of Li-ion batteries for start-stop systems is one of the pragmatic approaches being considered for reducing vehicle fuel consumption. During start-stop operation, the engine automatically shuts down when the vehicle comes to stop and then quickly restarts when propulsion is desired by the operator. Such start-stop operations of the vehicle can effectively reduce the amount of engine idling time, leading to fuel savings.

One of the main challenges for start-stop applications is meeting the cold-cranking power requirements at -30oC. Due to the kinetic limitations, pulse power performance of Li-ion batteries drop dramatically at low temperatures. Given the requirement for starting the engine at low temperature, it is typical that the cold cranking power capability determines the module size needed for start-stop systems; and therefore directly impacts the system weight and cost. It is essential to understand the source of the kinetic limitations (e.g. electrolyte resistance, electrode-electrolyte interfacial resistance, or diffusion resistance) and design a system that can dramatically improve the cold cranking power.

In this talk, we demonstrate the implementation of a new cell design to investigate the pulse power performance of LiMn2O4 (LMO) / Li4Ti5O12 (LTO) batteries for start-stop applications. Figure 1 shows the schematic of the cell design; it is composed of four electrodes, with two LTO and two LMO electrodes adjacent to each other. The current collectors are porous, allowing the ions to pass through them. This type of design enables the in-situ investigation of LTO/LTO, LTO/LMO, LMO/LMO cells in a single cell while the neighboring electrodes are used for voltage monitoring. In this report, our focus is to investigate the kinetics of each individual electrode under low temperatures. Using EIS and linear voltage polarization studies, we provide insight on the source of resistance limiting the pulse power capability of the cell at low temperatures (-30oC). We found that electrolyte transport limitations control the cell performance at low temperatures, which directly impacts the cold cranking power.
3M Lithium Ion Battery Material and Solution for EV and Energy Storage Application
Authors: Lu Zhonghua
Published: February 2020

3M Company is committed to providing high quality products and services to our customers to enable our customers to develop high quality products. In this presentation, we first share the potential application of 3M product Novec 1230 in the lithium-ion battery pack to improve its safety. Then we will discuss more on the 3M cathode status and new developments. We also cover 3M Si-alloy anode and 3M advanced high-voltage electrolyte.

In the battery pack for EV and HEV where a large number of lithium-ion batteries are used in the battery pack via serial or parallel connection, a safety issue is raised. The internal short inside the single battery via external force or from internal metal particle impurity cannot be avoided 100% completely. Once it happens, the whole battery pack may go into thermal runaway and produce fire. Several famous examples of this are published in consumer products every year.

3M is a major manufacturer of fluorinated chemicals. Novec 1230 was commercialized for fire protection. In this disclosing, we will report the benefits of the Novec 1230 to safety of the lithium-ion battery pack.

A set of 2.0Ah 18650 type lithium-ion batteries based on the LiCoO2/graphite chemistry were used to make 3P2S battery pack. The AC impedance at 1KHz for the single 18650 cell was about 40mOhm. Nail penetration was used to internally short a single 18650 causing thermal runaway in the 3P2S battery pack. We compared the response of the battery pack and its cell skin temperatures for one pack immersed in Novec 1230 to the another without Novec 1230. Fig 1 is the top view of the test device including the solvent container, 3P2S lithium ion battery pack and the position of the thermal couples. The Cell T0 was shorted at the location “X”. Without Novec 1230, after the cell T0 thermally runs away, the Cell T1 and T2 thermal runs away in about a 2.5mins interval, one by one. Flames were observed. The cell skin temperature reached more than 600oC. With immersing into about 300cc of Novec 1230, after cell T0 thermally runs away, all other cells never reach a temperature higher than 60oC It is very clear that Novec 1230 dramatically reduced the chance of the thermal runaway of the battery pack.
Facile Synthesis of a Carbon Encapsulated Metal Oxide Nanocomposite and Its Application As Conversion Anode Material for Lithium Ion Batteries
Authors: Ren Shuhua , Zhao Xiangyu , Chen Ruiyong , Fichtner Maximilian
Published: February 2020

Metal oxide has been reported to be an active conversion anode material in lithium-ion-batteries (LIBs) owing to its high specific capacity. The large volume change and the poor electronic conductivity during the Li+ insertion/extraction process limited its application, leading to capacity fade and poor cycling performance. Great efforts have been devoted on the combination of nanosized metal oxide with versatile carbon materials of special forms, such as carbon nanotubes, graphene, or fibers, in order to improve the cycling behavior. Most strategies to fabricate such functional composite structure involve multi-step processes or the use of certain templates, surfactants, or special solvents, removal of which in the post treatment complicates their practical applications. Thus, it is desirable to develop a facile straightforward synthetic strategy to generate such functional composite materials.

In our work, a simple pyrolysis-oxidation process has been developed to produce metal oxide/C-fiber composite in a solvent-free and template-free way. Metal oxide nanoparticles anchored onto in-situ formed carbon nanofibers were synthesized and have been investigated as promising conversion anode materials for Li-ion batteries. In the fabrication process, metallocene was used as precursor and acts as both metal and carbon source. As an example, Fe3O4 encapsulated into helical carbon nanofiber structure was fabricated by pyrolysis of ferrocene and subsequent oxidation of the pyrolysed product. The as-obtained Fe3O4/C composite shows a high and reversible capacity, good cycling and rate capability. The synthetic strategy has been further applied to a binary metal oxide CoFe2O4/C system through pyrolysis of the mixture of ferrocene and cobaltocene and further oxidation. The final composite shows a high and stable capacity. More than 700 mAhg-1 based on the total mass of the as-prepared composite was obtained in the composite after long-term cycling of 250 cycles. The synergistic effects by combining metal oxide nanoparticles and carbon and also their intimate contact developed in the synthetic process are suggested to be the major contribution to the observed superior electrochemical properties. This work opens a facile and broadly applicable way for fabrication and utilization of metal oxide/mixed metal oxide-C composites as anode materials for Li-ion batteries.
Low Voltage Anodes for Lithium-Ion Batteries
Authors: Clark Steve James , Armstrong Anthony Robert , Bruce Peter G
Published: February 2020

Graphite has proved a highly successful anode for lithium ion batteries; however it is not without its limitations. There is intensive research to perfect silicon based anodes but important challenges still remain in the quest for high cycling efficiency and high cycle numbers. As a result, there remains much need for investigation of alternative anodes for lithium-ion batteries. Recently we investigated anodes based on LiVO2
1,2. Intercalation into this compound, which is isostructural with LiCoO2, occurs in a two phase process with the formation of hexagonal close packed Li2VO2.1 We have now extended these studies to related compounds, and solid solutions, and have identified anodes with a capacity of over 215 mAh/g at C rate, Fig. 1. The density of these materials is 3.34 g/cm3 resulting in a volumetric capacity of 718 mAh/cm3 at 1C. Volumetric capacity is important for applications such as electric vehicles. Detailed results of these investigations will be presented at the meeting.

References:

1) A.R. Armstrong, C. Lyness, P.M. Panchmatia, M.S. Islam, P.G. Bruce, Nat. Mater. 10 (2011) 223-228.

2) F.d.r. Pourpoint, X. Hua, D.S. Middlemiss, P Adamson, D Wang, P.G Bruce, C.P. Grey, Chem. Mater. 2012, 24, 2880−2893.