MCMB Anode Research Articles

(Invited) Effects of LiPF6 Salt Concentration on the Cycling Performance of NMC532 Cell Containing Organic Carbonate Solvents

Pouch-type cells with NMC532 cathode, MCMB anode (A/C loading ratio of 1.1) and electrolytes containing various LiPF6 concentrations in EC/EMC (3:7 by volume) + 2wt% VC were prepared for investigating the effects of lithium salt concentration on the cycling performance of NMC532 cells. These cells were cycled at 0.5 C rate within 3.0 and 4.2 V until their residual capacity become lower than 70% of their initial capacities, respectively, as shown in Figure 1. After end of life, these cells were disassembled for post-mortem study. The cycled electrodes were used to assemble into coin-type cells with lithium metal for estimating their losses of lithium inventory (LLI), losses of cathode material (LAMC) and losses of anode material (LAMA) by comparing their specific capacities of first and second cycles of the coin-cells with those of the coin-cells prepared with fresh electrodes, respectively. XRD, SEM, HRTEM and XPS were also used to reveal the phase evolution, structure and morphology changes of the electrode materials after cycling. Results suggest that the fast capacity fade of the cell prepared with the electrolyte containing 1 M LiPF6 salt concentration can be attributed to the carbonate solvent oxidation via dehydrogenation on the cathode surface at voltages higher than 3.8 V as reported by Zhang et al.(1) The oxidation can not only accelerate the increase of impedances at anode side, the losses of lithium inventory and anode material by the SEI formation from the reactions between the oxidation products and lithium ions, but also cause the loss of cathode active material and resistance growth at the cathode side, though they are less significant. They can be caused by the phase evolution of spinel and rock-salt phases on the surface of cathode particles, which had been observed from the HRTEM and SAD studies of the cathode particle collected from the cycled cell prepared with 1 M LiPF6 in EC/EMC electrolyte after 600 cycles. It was also found that the amounts of spinel and rock-salt phases formed on the NMC particle surface, rates of capacity fading and resistance growth of the aged cells decreased with the increased LiPF6 salt concentration contained in the electrolytes of the cells. It can be due to the higher salt concentration can induce the less free solvent for being oxidized on the cathode particle surface at voltages higher than 3.8 V. Whereas the layered NMC phase only can be found on the surface of NMC particle collected from the cathode of the cycled cell prepared with 3 M LiPF6 electrolyte after 1100 cycles. This cell shows lower LLI, LAMC, LAMA and impedances growth after 1100 cycles than those of the cell with electrolyte of 1 M concentration after 600 cycles.Reference: Zhang, Y. Katayama, R. Tatara, L. Giordano, Y. Yu, D. Fraggedakis, J. G. Sun, F. Maglia, R. Jung, M. Z. Bazant and Yang Shao-Horn, Energy Environ. Sci., 2020, 13, 183-199.

Scalable preparation of practical 1Ah all-solid-state lithium-ion batteries cells and their abuse tests

All-solid-state lithium-ion batteries are considered as a promising electric energy storage platform for electric vehicles due to the replacement of flammable liquid organic electrolytes in current lithium-ion batteries by inflammable solid ones; thus promoting high safety. Despite plenty of research on various solid electrolytes and other components, reports on the scalable production of all-solid-state lithium-ion batteries using electrodes with meaningful areal capacities are rather scarce. Consequently, the safety of all-solid-state lithium-ion batteries has not been systematically investigated yet, especially on cells with higher than lab-scale capacities. The aim of this report is to build a bridge between academic research and more industrially meaningful information on the safety of all-solid-state lithium-ion batteries. Thus, three 1Ah all-solid-state lithium-ion batteries were fabricated, where hybrid solid electrolyte consisting of PEO-LiTFSI polymer matrix with Lithium Ionic Conductive Glass Ceramic (LICGC™, Ohara Inc.) particle as active filler was sandwiched between NMC622 cathode and advanced graphite MCMB anode, both of which have a practically valuable areal capacity of higher than 1.0 mAh/cm2. Initial formation cycling was performed to build conformal interface between solid electrolyte film and electrodes. Comparable specific capacity of cathode active materials (∼90.0 mAh/g @ C/10 & 60 °C) could be achieved in three pouch cells with high consistence. Typical abuse tests including overcharge, external short, and nail penetration were conducted, the three 1Ah all-solid-state lithium-ion batteries cells showed excellent safety performance: there was no thermal runaway, no explosion, only slight increase of temperature was observed. This work demonstrates the scalable fabrication of practical all-solid-state lithium-ion batteries with consistent electrochemical performance and thereafter confirms their intrinsic safety.

Reserve lithium-ion batteries: Deciphering in situ lithiation of lithium-ion free vanadium pentoxide cathode with graphitic anode

One of the major challenges in development of next-generation lithium-ion batteries is the discrepancy in the capacity between electrodes. Vanadium pentoxide is recognized as a potential candidate for cathode owing to attractively high theoretical capacity. Due to the lack of Li+ ions in its crystal lattice, V2O5 has always remained far away from practical realization. Various strategies viz., pre-lithiation, blended cathodes have been studied for Li+ ion free cathodes with no commercial interests. We report the development of reserve lithium-ion batteries (RLIBs) for Li+ ion free V2O5 cathode with graphitic anode, which delivered a high charge capacity of 264 mAh g−1, attained by the in situ lithiation process. Through the different operational modes of RLIB, V2O5 cathode's intrinsic voltage characteristics with MCMB anode were achieved during the full-cell cycling studies. The mechanistic elucidation of RLIBs has been conducted using impedance spectroscopy and boundary conditions of Fick's law of diffusion could be observed in the different modes. Pouch cell configuration exhibited stable cycling performance for 300 cycles at 0.5C rate. The development of the RLIBs offers the potential to unlock the usage of various Li+ ion free cathodes viz., vanadium oxides, sulfur, FeS2, MnO2, etc. for the realization of high capacity and energy-dense applications.

A Robust Cathode Structure for Eco-Friendly Li-Ion Battery: NMC Coated Li-Rich LMO Cathode

Remarkable efforts have been put forth for the development of environmentally benign, abundant, low-cost and high-performance cathode materials for Li-ion batteries. Spinel LiMn2O4 has been considered as the most promising cathode among the many candidates for next-generation energy storage systems due to afore-mentioned advantages[1]. However, there are some challenges associated to this cathode that inhibit its practical usage for future applications. During cycling, the structural change from cubic to tetragonal takes place, in the Mn3+ configuration due to Jahn-teller distortion followed by Mn2+ dissolution under the influence of acidic electrolyte which destabilises the cathode structure[2]. These changes lead to cathode’s structural transformation and particle cracking resulting in active material loss and capacity fading. The deposition of soluble Mn2+ on anode's SEI results in increased cell’s impedance[3]. Moreover, severe capacity fading at elevated temperatures is still an issue hindering its full-scale commercial development due surface manganese dissolution in the electrolyte at those temperatures[4]. Ever since the emergence of LiMn2O4, various strategies have been employed to exploit its potential. Among many techniques, surface-coating, material composites and doping have been widely used[5]. Most of these techniques focus either on the restriction of direct contact between the active material and electrolyte via coating or the structural enhancement to accommodate for the anisotropic volume changes caused due to disproportionation reaction. Although, these strategies have shown some positive impact on the cycle life of the LMO based Li-ion battery but, in most of the cases the protection from the acidic electrolyte and structural strengthening of LMO has not been addressed simultaneously. Therefore, In order to develop a practical LMO based Li-ion battery, the active material requires a robust protection from the acidic electrolyte contact via a continuous, uniform and Li-ion permeable coating with minimum mismatch while enhancing the structural stability simultaneously to mitigate the irreversible phase transitions.Herein, we report a novel heterostructure design; NMC layered Li-ion permeable phase grown on the surface of Lithium-rich LiMn2O4 octahedra. The layered surface phase protects the host spinel from being directly exposed to the acidic electrolyte during electrochemical cycling. In addition, it provides an efficient path for the ionic and electronic mobility resulting in improved kinetics due to its Li-ion permeability. On the other hand, the excess Li in LMO contributes to the structural enhancement during cycling to accommodate anisotropic volume changes, thus resulting in a robust cathode for high-voltage Li-ion batteries. In comparison to spinel LMO, the newly modified LMO displays an enhanced cyclic performance with superior charge-discharge rate capability. The uniquely developed LiMn2O4 phase surface coated with layered structure demonstrated discharge capacity of 120 mAh g-1 at 20 ℃ temperature while retaining >97% of its initial capacity after 300 cycles at 0.5C. Further, The cathode was tested at elevated temperatures of 60 °C, showing stabilised reversible specific capacity of 113 m Ah g-1 at 0.2 C-rate ensuring energy density of 452 W h kg-1. The full-cell utilising MCMB anode and newly modified LMO cathode showed the areal capacity of 1.22 m Ah cm-2, after 100 cycles with a capacity retention of 95.3% at 0.44 mA cm-2 while maintaining its trend till 300 cycles.

Oxygen-deficient Nb2O5-x decorated MCMB anode with much enhanced rate and cycle performances for Li-ion batteries

Nanosized oxygen-deficient orthorhombic niobium pentoxide (Nb2O5-x) that possess high electronic conductivity and stable cycle performance for Li storage are uniformly deposited on the surface of mesophase carbon microspheres (MCMB), which as a whole exhibits very encouraging electrochemical Li ion storage performance, including a high specific capacity of 107 mAh g−1 at 10C (1C = 372 mA g−1) and a high capacity retention of 85.4 % after 300 cycles at 3C in the optimized case. The Li+ diffusion coefficient of the composite anode as determined by the potentiostatic intermittent titration technique (PITT) is obviously improved as compared to that of pristine MCMB. Ex situ X-ray diffraction characterizations confirm the phase transformation from orthorhombic Nb2O5-x to amorphous LiyNb2O5-x accompanied by the formation of NbO through a conversion reaction in the first lithiation process. The ultrafast Li+ diffusion within the amorphous LiyNb2O5-x as well as the current-sharing effect of the secondary particles can explain the much enhanced Li ion storage property. The results of this work convincingly demonstrate that designing MCMB/Nb2O5-x composite can be a more practical way to improve the energy and powder densities of Li-ion batteries rather than seeking alternative anode materials with higher capacities.

Single‐crystal spinel Li1.08Mn1.92O4 octahedra cathode covered with Li-ion permeable robust NMC thin-layer protection for high voltage lithium‐ion batteries

An innovative cathode structure consisting of NMC, a Li-ion permeable coating on single crystal (SC) of Li-rich Li1.08Mn1.92O4 (NMC@SC LR-LMO) cathode is reported for first-time as a multifunctional cathode material for Li-ion batteries. The purpose of NMC coating is to protect the active material from acid corrosion while excess Li in LMO crystallite has been added intentionally to increase the structural stability and to mitigate the irreversible phase transitions. At 0.5 C-rate, this NMC@SC LR-LMO cathode vs. Li metal anode provides a stable reversible specific capacity of 115 m Ah g–1 with an energy density of 460 W h kg–1 for 500 cycles. At 60 °C, a stable reversible specific capacity of 113 m Ah g–1 at 0.2 C-rate ensuring energy density of 452 W h kg–1 after 100 cycles is obtained. Full-cell of NMC@SC LR-LMO cathode and MCMB anode exhibit the capacity of 1.23 m Ah cm–2, 95.3% capacity retention even after 100 cycles at 0.44 mA cm–2/ 29.3 m Ah g–1, and the trend is maintained till 500 cycles. Finally, a pouch cell of NMC@SC LR-LMO cathode and MCMB anode of ∼38 m Ah is tested with a reversible areal capacity of 1.27 m Ah cm–2/ 85 m Ah g–1 after 150 cycles.

In Situ Thermal Safety Aspect of the Electrospun Polyimide-Al2O3 Separator Reveals Less Exothermic Heat Energies Than Polypropylene at the Thermal Runaway Event of Lithium-Ion Batteries.

Polyimide-Al2O3 membranes are developed as a direct alternative to current polyolefin separators by the electrospinning technique and their chemical structures confirm the carbonyl group with the presence of asymmetric and symmetric stretching and bending vibrations at 1778, 1720, and 720 cm-1 and stretching vibration at 1373 cm-1 for the imide group. Porous nanofiber architecture morphology is realized with a nanofiber thickness of ∼200 nm and shows an ultrasmooth surface and >1 μm pore size in the architecture, built with the chemical constituents of carbon, nitrogen, aluminum, and oxygen elements. The galvanostatic cycling study of the Li/PI-Al2O3/LiFePO4 lithium cell delivers stable charge-discharge capacities of 144/143 mAh g-1 at 0.2 C and 110/100 mAh g-1 at 1 C for 1-100 cycles. The fabricated MCMB/PI-Al2O3/LiFePO4 lithium-ion full-cell reveals less charge transfer resistance of Rct ∼ 25 Ω and yields stable charge-discharge capacities of 125/119 mAh g-1. The thermogravimetric curve for the PI-Al2O3 separator discloses thermal stability up to 525 °C, and the differential scanning calorimetric curve shows a straight line until 300 °C and depicts high thermal stability than the PP separator. In situ multimode calorimetry analysis of the MCMB/PP/LiFePO4 full-cell showed a pronounced exothermic peak at 225 °C with a higher released heat energy of 211 J g-1 at the thermal runaway event, while the MCMB/PI-Al2O3/LiFePO4 full-cell revealed an almost 8-fold less exothermic released heat energy of 25 J g-1 than the Celgard polypropylene separator, which was because the MCMB anode and LiFePO4 cathode can be mechanically isolated without any additional separator's melting and burning reactions, as a fire-suppressant separator for lithium-ion batteries.

Improved Zero-Charge Storage Performance of LiCoO2/Mesocarbon Microbead Lithium-Ion Batteries by Li5FeO4 Cathode Additive.

Discharging lithium-ion batteries to zero-charge state is one of the most reliable ways to avoid the thermal runaway during their transportation and storage. However, the zero-charge state causes the degradation or even complete failure of lithium-ion batteries. Specialized solutions are required to endow lithium-ion batteries with improved zero-charge storage performance, namely, the ability to tolerate zero-charge state for a long time without unacceptable capacity loss. Here, we report that a Li5FeO4 cathode additive can improve the zero-charge storage performance of LiCoO2/mesocarbon microbead (MCMB) batteries. The irreversible charge capacity of the Li5FeO4 additive results in the downregulation of anode and cathode potentials when the battery is at zero-charge state. More importantly, the Li5FeO4 additive offers a small discharge plateau below 2.9 V versus Li/Li+, which can hold the anode potential at zero-charge battery state (APZBS) in a potential range of 2.4∼2.5 V versus Li/Li+ during storage for 10 days. Such a precise control on APZBS not only suppresses the decomposition of the solid electrolyte interface film on the MCMB anode and inhibits the dissolution of the copper current collector occurring at high potentials but also avoids the excessive decrease of the cathode potential at the zero-charge battery state and consequently protects the LiCoO2 cathode from overlithiation occurring at low potentials. As a result, the Li5FeO4 additive with a charge capacity percentage of 23% in the cathode increases the capacity recovery ratio of the LiCoO2/MCMB battery from 37.6 to 95.5% after being stored at the zero-charge state for 10 days.

Electrochemical behaviors in the anode of LiCoO2/mesocarbon microbead battery and their impacts on the capacity degradation

Though LiCoO2/mesocarbon microbead (MCMB) battery has wide application, its capacity loss mechanisms at different cycling stages are still not clear. Here, we report the electrochemical behaviors in MCMB anode at different stages and their impacts on the capacity degradation. The exfoliation of anode material from current collector tends to occur in single-side pasted region, which is one of the reasons for the quick capacity fading at early stage. After long-term cycles, MCMB anode has larger capacity loss than LiCoO2 cathode. The carbonates with poor Li+ conductivity are formed in the solid electrolyte interface (SEI) film at later stage. MCMB structure has no obvious variations. Lithium deposits appear on single-side pasted region firstly and then double-side pasted region. They are distributed more widely and become thicker with the cycling. The deposits contain metallic lithium while the battery at fully charged state and reduce the battery capacity significantly. Suppose each behavior exists in the whole MCMB anode, lithium deposit will have the most impact on the capacity loss; for the MCMB anode in full battery, SEI film has the largest effect. This work will help to improve the battery’s manufacturing techniques pointedly and obtain the lithium-ion batteries with high capacity and long life.

Ca2+-Based Dual-Carbon Batteries in Ternary Ionic Liquid Electrolytes

Herein, we propose Ca2+-based dual carbon batteries (DCBs) that undergo a simultaneous occurrence of reversible accommodations of Ca2+ in a graphite anode (mesocarbon microbeads) and of bis(trifluoromethanesulfonyl)imide (TFSI-) in a graphite cathode (KS6L). For this purpose, we precisely tune electrolytes composed of Ca2+ complexed with a single tetraglyme molecule ([Ca:G4]) in N-butyl-N-methylpyrrolidinium TFSI (Pyr14TFSI) ionic liquid (IL). This ternary electrolyte is required for the enhancement of anodic stability that is needed to accomplish maximal TFSI- intercalation into KS6L at a high potential. A solution of 0.5 M [Ca:G4] in IL ([Ca:G4]/IL) is found to be optimal for DCBs. First, the electrochemical properties and the structural evolution of each graphite in a half-cell configuration are described to demonstrate excellent electrochemical performance. Second, the negligible intercalation of Pyr14+ into MCMB anode is ascertained in 0.5 M [Ca:G4]/IL. Finally, DCBs are constructed by coupling two electrodes to show high capacity (54.0 mAhg-1 at 200 mAg-1) and reasonable cyclability (capacity fading of 0.022 mAhg-1cycle-1 at 200 mAg-1 during 300 charge/discharge cycles). This work is the first to examine DCBs based on Ca2+ intercalation and helps pave the way for the development of a new type of next-generation batteries.

Deciphering the Interface of a High‐Voltage (5 V‐Class) Li‐Ion Battery Containing Additive‐Assisted Sulfolane‐Based Electrolyte

AbstractNext generation high energy density lithium‐ion batteries have aroused great interests worldwide. Herein, in a high‐voltage (5 V‐class) LiNi0.5Mn1.5O4/MCMB (graphitic mesocarbon microbeads) battery system using 1 m lithium difluoro(oxalate)borate/sulfolane, tris(trimethylsilyl) phosphite (TMSP) additive is added to significantly improve room/high temperature cycling performances. The unchanged X‐ray diffraction patterns suggest the bulk crystal structure of cycled MCMB anode and LiNi0.5Mn1.5O4 cathode are well preserved. Moreover, soft X‐ray absorption spectroscopy (XAS) taken from bulk sensitive fluorescence‐yield (FY) mode reveals the unchanged bulk electronic structure of cycled LiNi0.5Mn1.5O4 cathode. Therefore, it is concluded that only interface instability contributes to capacity fading of full‐cells. However, electrode/electrolyte interface and corresponding interfacial reaction processes are always “enigmatic.” First, X‐ray photoelectron spectroscopy (XPS) and in situ differential electrochemical mass spectrometry (DEMS) are used to more accurately decipher the TMSP additive action mechanism in MCMB/electrolyte interfacial reaction processes, by identifying the interfacial solid and gas byproducts, respectively. Then, the crucial role of TMSP additive in modifying cathode/electrolyte interface is revealed by XPS and soft XAS taken from surface sensitive total electron yield (TEY) mode. This paper provides valuable perspectives for formulating novel electrolytes, and for more accurately depicting additive action mechanism in “enigmatic” electrode/electrolyte interfacial reaction processes.

(Invited) Saft Gen 6 Electrochemistry for GEO/LEO Application

Satellite battery industry is facing a serious material obsolete issue. The MCMB anode and NCA cathode active materials were no longer available. Saft developed a Generation 6 space cell –VL51ES which addressed material obsolescence in the space industry and provided high specific energy to meet the demands of today’s space missions. The selected electrodes electrochemistry provides excellent storage and cycle life. VL51ES is an iteration of proven technology and a legacy of failure-free batteries with up to 18 years in space. Manufactured in both France and the US, the redundant manufacturing capability ensures effective product delivery to customers across the globe. Saft incorporated advanced technology and enhanced manufacturing processes. Compared with the previous generations of space cells, the Gen 6 space cell is more industrialized, efficient and cost effective. Change from tabbed design to tabless design significantly reduces cell impedance, it makes VL51ES capable for higher rate discharge and cold temperature charge than previous Saft space cells. It represents a 20% height reduction along with a 10% improvement in energy. This cell has excellent GEO mission life, 45 accelerated GEO seasons were demonstrated with only 6% total energy loss. VL51ES passed voltage reversal tests without safety event, it enables a by-pass less battery design to reduce cost and complexity at battery level and maintain the same reliability. The qualification of VL51ES covers a full range of space requirements including safety, electrical, mechanical, abuse, life test and reliability. A data package has been compiled for customers with records of all test results. The qualification data is incorporated into Saft’s Li ion model (SLIM) which help customers to predict battery life performance at different scenarios and help customer with proper battery sizing.

Scalable Pore Size Tuning Process for Seeking Better Cathode of Lithium Ion Capacitor and Development of High-Performance Full Cell Device through It

With the development of the industry, the need for better energy storage devices that can be used in various devices continues to grow, but the pace at which practical alternatives are developed is very slow. Many prior studies have succeeded in increasing the energy density of lithium-ion batteries to a significant level, but they have not been able to lead to actual production due to battery instability, life problems, production and price issues. Many battery manufacturers currently faced the limit capacity of the cathode and are aiming to improve the energy density by developing an anode with a capacity of 430 mAh / g by mixing graphite with a high capacity active materials. However, in such a method, it is difficult to satisfy the high power density due to the difference in charge/discharge speed between the graphite and the high capacity active material. So, in reality, current access and pricing policies are not able to create a significant gap in the lithium-ion battery platform. For this reason, the study of lithium-ion capacitors satisfying both energy density and power density has received much attention due to its high versatility. Lithium-ion capacitors can use conventional lithium-ion anodes and use carbon materials instead of heavy metal alloys as cathodes. Initial lithium-ion capacitor research was concentrated on an anode capable of high capacity such as a lithium-ion battery. In fact, the main factor that determines the capacity per mass/volume of lithium-ion capacitors is the capacity of the cathode. As the cathode of the lithium-ion capacitor, a porous carbon material which has been used as the electrode material of the electric double layer capacitor has been widely used. However, the electrode of the EDLC stores OH- ions, while the cathode of the lithium-ion capacitor should adsorb and store much larger ions such as PF6- ions. Thus, the electrode material originally used in the EDLC may be unsuitable for storing larger ions due to the small pore size. Here we have found improvements that can improve the capacity of lithium-ion capacitors. We intend to develop a cathode material for lithium-ion capacitors that can store larger ions such as PF6- ions in this work. We have developed seven cathode materials that composed of concentrate pores with a certain size using graphene and a template that is vaporized below 100 degrees of Celsius. The size of the pores ranges from less than 5 nm to 150 nm. Although the effects of the number of Angstrom pores have been addressed in the meantime, the impact of macro size pores has not been addressed in the lithium-ion capacitor research. We evaluated the capacity and characteristics of the developed cathode using PF6-, TFSI-, BF4-, ClO4-, and so on. In the experimental results, we confirmed that macro-sized pores have a profound effect on the adsorption and storage of ions and their obvious tendency. To put it briefly, the TFSI- and PF6- ions are significantly different in size, and thus the cathode with the highest capacity is different from each other, which is revealed by the tendency. Additionally, the full cell lithium-ion capacitor with developed cathodes and a commercial MCMB anode recorded the highest energy density of up to 145 Wh/kg and an energy density over 70 Wh/kg at a power density of 7200 W/kg. We have demonstrated the effect of macro-sized pores on the cathode of a lithium-ion capacitor and succeeded in developing a cathode material for an excellent lithium ion capacitor.

Solvent-Free Mechano-Fusion Assisted Carbon Coatings for High Capacity Cathode - a Practically Feasible Approach

Spinel LiMn2O4 (LMO) has emerged attractive as well as a potential alternative candidate to toxic LiCoO2 for high energy applications because of its relative abundance, low cost and environmentally benign. Although LMO has several advantages, it suffers from immense polarization, severe capacity decay and Mn dissolution resulting in Jahn-teller distortion with 6.5 % increased unit cell volume. Various strategies have already been proposed to alleviate these detrimental issues such as heteroatom doping, surface blocking coatings, and functional electrolyte additives. However, the surface coating is one of the promising techniques to improve the kinetics and long-term cycling performance over others. Herein, a simple and cost effective Mechano-thermal fusion was proposed because of its practical feasibility. The strong centrifugal force followed by a high shear and compression force fuse the guest molecule (super P) over the host (LMO), which ensures the uniform innate coating as like core-shell structure. Further, the fused carbon coating not only helps to reduce the polarization by improved conductivity but also acts as a barrier layer to control the Mn dissolution. The core-shell material delivered a specific capacity of 125 mAh g-1 at the initial and decreased to 103 mAh g-1 after 1000 cycles with 82 % of capacity retention at 0.75 C. Similarly, the above material exhibits excellent rate capability behaviour. The improved kinetics of the core-shell material has further been confirmed by heterogenous rate calculation and found to be 3.9 to 4.1. Further, the core-shell material exhibits stable cycling performance while couple to MCMB anode (full-cell) with above 70 % retention for the studied 1000 cycles.

Study of Capacity Retention of Mcmb Anode Using Various Nanostructured Conductive Additives

The global lithium-ion battery industry is growing at an impressive rate and is expected to grow even further in the near future. The main reasons for this are the high energy density and excellent cycling performance that these batteries exhibit. Researchers are experimenting with a handful of ideas that could make batteries vastly better than they are today, which could lead to more affordable electric cars and cheaper ways to store the intermittent energy1. The use of lithium-ion batteries (LIBs) in the automotive sector has been receiving quite significant attention. However, limitation of low electronic conductivity of electrodes has prohibited rapid commercialization of LIBs for automotive applications (such as EVs, HEVs, PHEVs, etc.) where high power density is required2. In addition, the lower electronic conductivity of active materials makes it difficult to achieve their theoretical capacities at implementation. A number of methods, such as surface coating with conductive material3, lattice doping4, addition of metallic particles (copper and nickel)5 were adopted to improve the conductivity of active materials with reasonable success. In this work, we examine the capacity retention characteristics of mesocarbon microbeads (MCMB) by the use of various nanostructure conductive additives such as carbon black (CB), multiwalled carbon nanotubes (MWCNTs) and graphene in a CR2016 type coin. Figure 1(a) shows the plot of electrical conductivity of MCMB anode with various proportion of CB and CNT. For the purpose of meaningful comparison, the weight percent of conducting agent in MCMB with CB, MCMB with CB and CNT, and MCMB with CNT composite anode remains the same. When some content of CB is replaced by CNT, electrical conductivity improves because of formation of hybrid conductive that meets both the long-range and short-range conduction requirement. In Figure 1(b) the experimental cycling behaviour for discharge capacity of MCMB-4 wt.% CB and MCMB-(3 wt.% CB+1 wt.% CNT) anode at 1C and 4C rate for first 50 cycles are compared and the effect of composite anodes with hybrid conductive network at 1C rate show 348 mAhg-1 capacity for initial cycle whereas electrodes with CB as additive exhibit about 337 mAhg-1. The MCMB-(CB+CNT) anode exhibits almost 99% capacity retention while MCMB-CB display the capacity retention of 92.6% after 50 cycles at 1C rate. Similarly, at 4C rate the initial capacity and capacity retention for mix conductive additives are superior as shown in Figure 1(b). The improvement of capacity retention performance is mainly because of improved electrical conductivity on addition of CNT due to their higher conductivity and high aspect ratio in comparison to CB. The cycling performance of MCMB anode with graphene as conductive additive will also be presented. Electrochemical impedance spectroscopy (EIS) will be employed to analyze the aging effects and rate of capacity degradation of cells by quantifying the growth of internal resistances with cycling. The morphological and structural changes of electrodes due to cycling will be examined by characterization at fresh and cycled stages. Reference [1] H. Y. Tran, G. Greco, C. Täubert, M. W. Mehrens, W. Haselrieder, A. Kwade, “Influence of electrode preparation on the electrochemical performance of LiNi0.8Co0.15Al0.05O2 composite electrodes for lithium-ion batteries” J. Power Sources 210 (2012) 276. [2] S. E. Cheon, C. W. Kwon, D. B. Kim, S. J. Hong, H. T. Kim, S. W. Kim, “Effect of binary conductive agents in LiCoO2 cathode on performances of lithium ion polymer battery” Electrochim. Acta 46 (2000) 599. [3] H. Momose, H. Honbo, S. Takeuchi, K. Nishimura, T. Horiba, Y. Muranaka, Y. Kozono, H. Miyadera, “X-ray photoelectron spectroscopy analyses of lithium intercalation and alloying reactions on graphite electrodes” J. Power Sources 68 (1997) 208. [4] Y. P. Wu, E. Rahm, R. Holze, “Effects of heteroatoms on electrochemical performance of electrode materials for lithium ion batteries” Electrochim. Acta 47 (2002) 3491. [5] F. Joho, B. Rykart, R. Imhof, P. Novak, M. E. Spahr, A. Monnier, “Key factors for the cycling stability of graphite intercalation electrodes for lithium-ion batteries”. J. Power Sources 81 (1999) 243. Figure 1

Tetrabromobisphenol a Bis(dibromopropyl ether) As a Flame Retardant Additive for Lithium-Ion Batteries

Increasing demands for portable electronic appliances have expanded the spectrum of lithium-ion batteries applications to a wider extent. In spite of the widespread use and deserved promise of lithium-ion batteries, battery safety is still a substantial issue of concern. [1]. Besides other aspects, the flammability of carbonates, frequently used as electrolyte components in most batteries, is one of the major challenges in battery safety. There are different approaches to overcome this problem. One approach is to replace the liquid electrolytes with, for example ionic liquids, gel polymer electrolytes or even solid electrolytes. Another approach is to add flame retardants (FRs) to suppress the flammability of the electrolytes. [2]. Among the wide range and variety of flame-retardants available, there is one class that has rarely been studied as an electrolyte additive in Li-ion batteries, that is, the brominated compounds. [3]. The organobromine compounds are known as the most effective as flame retardant additives for polymers. The reasons are explained as the C-Br bond is stable enough for environmental exposure and yet unstable enough that heat can easily break the bond, releasing the bromine under fire conditions to inhibit combustion free radical reactions. Also industrially speaking, producing organobromine compounds as flame retardants turns out to be a very efficient chemistry, making it possible to produce large amounts of organobromine compounds, cost effectively. This again is because of the unique aspects of bromine and carbon chemistry that make these compounds easy to perbrominate, and so one small organic molecule can deliver a high payload of effective bromine to the fire. [4] In this work, tetrabromobisphenol A bis(dibromopropyl ether) (TBBA-BDBPE) was analyzed as a potential brominated flame retardant candidate for lithium ion battery field. Electrolyte compositions with different concentrations of (TBBA-BDBPE) were prepared by mixing with reference electrolyte which is 1 M LiPF6in [EC:EMC (3:7) + 2%VC]. Self extinguishing time measurements were done to compare the flammability of different electrolyte systems.(Table1). Constant current cycling experiments were performed by full cells of MCMB as anode and NMC as cathode. (Figure 1) The electrolyte system with FR was tested on MCMB anode and NMC cathode as half cells with CV method. It was observed that on the cathode side there is no additional reaction occurring but on the anode side the FR decomposes at 1.3 V which only occurs in the first cycle and doesn’t go further. In order to prevent the decomposition of FR in the electrolyte system, different additives such as ES and LiBOB which reduce at potentials higher than 1.3 V were added to the system. 0.5 % LiBOB was enough to suppress the decomposition of FR on the anode side, also the addition of LiBOB to the system resulted an increase in initial cycle efficiency.It was concluded that the tetrabromobisphenol A bis(dibromopropyl ether) (TBBA-BDBPE) might be an effective candidate for Li-ion battery systems in terms of flame retardancy and cost. The addition of both (TBBA-BDBPE) and LiBOB to the reference electrolyte system, resulted to an enhanced intrinsic safety and stable cyclization performance.

Cycling Performance of Lithium-Ion Batteries with Non-Uniform Size Particles in the Carbon Anode

Lithium-ion batteries (LIBs) are being considered as portable power sources for modern electric and hybrid vehicles due to their high gravimetric and volumetric energy density. However, the discharge capacity of LIBs decreases with continuous cycling due to various associated side reactions. The intensity of degradation caused by side reactions might be reduced through control of design and operational parameters i.e. charge & discharge rate, operational voltage, electrode thickness and particle size. Mathematical modeling is an important tool to analyze the effect of these variables on the performance of LIBs, while measuring their influence through experiments is difficult and expensive. In a recent study1, a mathematical model was developed to quantify the solid-electrolyte interface (SEI) film thickness and gas volume in a carbon electrode for different discharge rates up to a 1000 cycles; however, it was assumed that the carbon electrode is composed of identical particles. In this work, the model developed in ref. [1] is being extended to analyze the effect of cycling lithium-ion cells with carbon negative electrodes having different particle configurations and to observe the impact of electrode morphology over cell performance. For this purpose, the carbon electrode will be split into three equal sub-parts such that within each layer particles of the same size exist. The radius of particles is either 0.7Rp, Rp or 1.3 Rp (so that the interlayer sizing is non-uniform), where Rp is radius of the reference case considered in ref. [1]. All possible combinations of the final electrode morphologies to be considered are shown in Fig. 1. One representation of fresh and cycled negative electrode is shown in Fig. 2, with smallest particle section sandwiched between medium and largest particle layers at the current collector and separator ends, respectively. As is given in Eq. (1), cycling of the cell results in the decomposition of the electrolyte at the negative electrode leading to SEI film formation and generation of ethylene gas as a by-product of the side reaction. The SEI film increases the resistance for lithium diffusion in the carbon active material and the gas generated occupies the space previously occupied by the pores of the electrode (as shown in Fig. 2) slowing the movement of Li-ions in the electrolyte, both leading to reduction in cell capacity. The governing equations of the pseudo-2D model2-3 along with SEI formation and gas evolution1 will be solved using COMSOL Multiphysics 4.3a for all morphologies of MCMB anode shown in Fig. 1 with LiMn2O4 cathode. The cell will be cycled till either of 80% loss (end of life) of rated capacity or 1000 cycles is reached. A comparative analysis of discharge capacity, cycling performance, thickness of SEI film and gas generation will be demonstrated. It is expected that this study will pave the way for design of carbon electrodes for achieving higher discharge capacity. From preliminary data results obtained so far, B-A-C or C-A-B based negative electrodes have shown much better performance than the remaining four combinations. In the latter cases, the battery loses 80% of the rated capacity before the completion of 1000 cycles, whereas a high discharge capacity, low film thickness and lesser gas is generated after the same number of cycles in the former cases.

Effect of pre-lithiation degrees of mesocarbon microbeads anode on the electrochemical performance of lithium-ion capacitors

Lithium ion capacitors are assembled with pre-lithiated mesocarbon microbeads (LMCMB) anode and activated carbon (AC) cathode. The effect of pre-lithiation degrees on the crystal structure of MCMB electrode and the electrochemical capacitance behavior of LIC are investigated by X-ray diffraction (XRD) and the charge-discharge test of three-electrode cell. The structure of graphite still maintained when the pre-lithiation capacity is less than 200 mAh g−1, phase transition takes place with the increase of pre-lithiation capacity from 250 mAh g−1 to 350 mAh g−1. Pre-lithiation degrees of MCMB anode greatly affect the charge-discharge process and behavior, which impact on the electrochemical performance of LIC. The LIC with pre-lithiation capacity of 300 mAh g−1 has the optimal electrochemical performance. The energy density of LIC300 is up to 92.3 Wh kg−1, the power density as high as 5.5kWkg−1 and the capacity retention is 97.0% after 1000 cycles. The excellent electrochemical performance benefits from the appropriate pre-lithiation capacity of negative electrode. The appropriate pre-lithiation ensures the working voltage of negative electrode in low and relative stable charge-discharge platform corresponding to the mutual phase transition from the second stage graphite intercalation compound (LiC12) to the first stage graphite intercalation compound (LiC6). The stable charge-discharge platform of negative electrode is conductive to the sufficient utilization of AC positive electrode.

Effect of Low Cell Voltages on the Performance of MCMB Anode and LiNi0.8Co0.2O2 Cathode

Lithium-ion cells employing graphitic anodes (graphite or MCMB) and lithiated metal oxide cathodes, Li(Ni,Co,Al)O2 are generally intolerant to low cell voltages, which is often attributed to the side reactions on the anode. Even though dissolution of the copper substrate at the anode is not thermodynamically favored at the anode potentials positive to lithium, mild copper dissolution was often reported to occur at positive potentials. Furthermore, the cell performance appears to degrade upon exposure to low voltages, even without any visible copper dissolution. One of the engineering batteries for the NASA Mars Science Laboratory (MSL) mission sustained a high impedance short due to a failure in the harness insulation, which resulted in the deep-discharge of multiple cells to low voltages, and an overall performance loss in these cells. Results from the laboratory test cells confirm the trend in the performance degradation as a function of low voltage exposure and point to, surprisingly, a degradation of the cathode, more than the anode. Electrochemical measurements, both ac impedance (EIS) and DC polarization show an unexpected trend that the cathode kinetics are affected by the deep-discharges to low voltages.

Effect of Low Cell Voltages on the Performance of MCMB Anode and LiNi0.8Co0.2O2 Cathode

not Available.