Prolonged Cycle Life Research Articles

Free-standing sulfur host based on titanium-dioxide-modified porous-carbon nanofibers for lithium-sulfur batteries

Abstract Lithium-sulfur (Li-S) batteries are regarded as a promising next-generation electrical-energy-storage technology due to their low cost and high theoretical energy density. Furthermore, flexible and wearable electronics urgently requires their power sources to be mechanically robust and flexible. However, the effective progress of high-performance, flexible Li-S batteries is still hindered by the poor conductivity of sulfur cathodes and the dissolution of lithium polysulfides as well as the weak mechanical properties of sulfur cathodes. Herein, a new type of flexible porous carbon nanofiber film modified with graphene and ultrafine polar TiO 2 nanoparticles is designed as a sulfur host, in which the artful structure enabled the highly efficient dispersion of sulfur for a high capacity and a strong confinement capability of lithium polysulfides, resulting in prolonged cycle life. Thus, the cathode shows an extremely high initial specific discharge capacity of 1501 mA h g −1 at 0.1 C and an excellent rate capability of 668 mA h g −1 at 5 C as well as prolonged cycling stability. The artful design provides a facile method to fabricate high-performance, flexible sulfur cathodes for Li-S batteries.

Numerical Analyses on Aluminum Foams Cooling Plate for Lithium-ion Batteries

Successful implementation of electric vehicle relies strongly on its energy storage systems. Li-ion battery is the best candidate for the energy storage systems due to its energy density, power density and low maintenance. Temperature will affect the power availability, driveability and cycle life of the battery. Hence, effective thermal management system is needed to prolong cycle life and ensure balance charging/discharging among the cell in the battery pack. In this study, a battery module comprised three pieces of Li-ion pouch cell is arranged side by side and attached to aluminum foam heat sink to extract heat generated. The performance of two different type of pores density aluminum foams with different porosity were investigated numerically. Experimental correlation of Nusselt Number, permeability and resistance loss coefficient from the literature was extracted and used in the steady state CFD simulation. Among the metal foams, 10 PPI aluminum foam with 0.918 porosity offered the highest thermal performance and lowest flow resistance. Hence, it was shown that aluminum foam can be used to replace heat sink in the battery pack.

A Li2s@SiO2 Modified Separator to Suppress Polysulfide Shuttle Effect and Li Dendrite Growth for Li-S Batteries

High-energy Li-S batteries hold the promise of prolonging the electric vehicles’ mileage, but have been largely impeded by the polysulfide shuttle effect. It is recently reported that the uniform Li2S passivation layer deposited on the Li anode formed by side reactions (Li+(Sx)2-→Li2S) can perform a role in inhibiting polysulfide corrosion, however the Li dendrite growth usually leads to the collapse of the passivation layer and aggravates the side reactions [1, 2]. In this work, we propose to separate the Li2S passivation layer from the Li dendrites, which is realized by fabricating a SiO2 nanosphere layer impregnated with Li2S. With such a pre-passivation strategy, the Li-S batteries exhibit a substantial prolonged cycle life (4 mg cm-2 sulfur loading, > 3.6 mAh cm-2, 84% capacity retention) for the reasons: (i) the impregnated Li2S within the SiO2 spheres chemically anchor the polysulfides and thus largely suppress the polysulfide crossover; (ii) the mechanically strong SiO2 layer is capable of effectively mitigating the Li dendrite growth. The achieved results suggest that our strategies of building up a passivation layer separated from the Li anode is facile and effective, and can be readily for use in battery production. Key words: Li-S battery; passivation layer; shuttle effect; Li dendrite.

4D printing of high performance shape memory polymer using stereolithography

High shape fixity, shape recovery, and prolonged shape memory cycle life are desirable aspects of 4D printed parts; however, the durability of 4D printed parts is rarely investigated. Here, we demonstrated a photopolymer printable by stereolithography apparatus (SLA) which uses a tBA-co-DEGDA network based on dual-component phase switching mechanism to build parts of complex geometries and exhibit shape memory behavior. The material can achieve a high curing rate and precise printing that are highly desired for SLA process. The mechanical strength of the printed parts is comparable statistically to industrial SMPs and shape memory tests showed excellent shape memory performance with higher durability of >20 shape memory cycles as compared to current 4D printed parts. This work is believed to enable the use of SLA technology to fabricate responsive components of high performance, which also significantly advances the 3D printing technology for more robust applications.

Hairy graphite of high electrochemical performances prepared through in-situ decoration of carbon nanotubes

A hairy graphite is synthesized through a modified chemical vapor deposition (CVD) method, in which 2,3-dipicolinic acid and Ni(NO3)2 are employed as the carbon source and the catalyst precursor, respectively. Under Ar/H2 (95:5) reducing atmosphere at 900°C, Ni(NO3)2 is reduced to nickel nanoparticles and 2,3-dipicolinic acid is pyrolyzed into carbon fragments. With the catalysis of nickel nanoparticles, carbon nanotubes (CNTs) are in-situ grown on the graphite surface through realignment of the carbon fragments. The hairy pattern of geometry of the graphite@CNT composite not only improves the mechanics and conductivity of the electrode, but also has more room to accommodate the volume change of the graphite particle upon prolonged electrochemical cycles. A superb rate performance and prolonged cycle life are obtained. The simple and effective strategy for integration of graphite with in-situ grown CNTs is very useful for boosting its electrochemical properties.

Regenerative Polysulfide-Scavenging Layers Enabling Lithium-Sulfur Batteries with High Energy Density and Prolonged Cycling Life.

Lithium-sulfur batteries, notable for high theoretical energy density, environmental benignity, and low cost, hold great potential for next-generation energy storage. Polysulfides, the intermediates generated during cycling, may shuttle between electrodes, compromising the energy density and cycling life. We report herein a class of regenerative polysulfide-scavenging layers (RSL), which effectively immobilize and regenerate polysulfides, especially for electrodes with high sulfur loadings (e.g., 6 mg cm-2). The resulting cells exhibit high gravimetric energy density of 365 Wh kg-1, initial areal capacity of 7.94 mAh cm-2, low self-discharge rate of 2.45% after resting for 3 days, and dramatically prolonged cycling life. Such blocking effects have been thoroughly investigated and correlated with the work functions of the oxides as well as their bond energies with polysulfides. This work offers not only a class of RSL to mitigate shuttling effect but also a quantified design framework for advanced lithium-sulfur batteries.

The effects of oxygen plasma implantation on bipolar resistive-switching properties of copper nitride thin films

Copper nitride (CuxN) thin films were prepared by plasma ion immersion implantation (PIII) then post-processed with oxygen plasma implantation at a voltage of −1.5kV. The resistive-switching properties of the CuxN:O-based RRAM devices were studied with different oxygen implantation time from 0 to 20min. The memory cells processed with oxygen plasma implantation for 5min showed longest endurance performances, largest resistance window and highest yield. Linear fitting results of the electrical measurements indicated the formation of copper oxide (CuO) is benefit for prolonged cycle life of the CuxN based RRAM devices, while increasing Cu2O species will lead to severe performance degradation.

Ethylene vinyl acetate-based binder a promising material to produce high power and high energy electrodes with a prolonged cycle life

Ethylene vinyl acetate, a hydro dispersible polymer largely used in the plastic industry, was employed as a polymer binder for the fabrication of the positive electrode of lithium-ion batteries. LiNi0.5Mn1.5O4 was used as the active material. The electrode was prepared by painting a thin aluminum sheet with a suspension obtained by mixing the carbon, the active material, and the polymer in water. The electrode was first analyzed from a chemical-physical point of view. The electrode morphology was evaluated by scanning electron microscopy (SEM) and the surface chemistry mapped by energy dispersive X-ray spectroscopy (EDS). The thermal stability was tested by heating the electrode in air using a simultaneous TG-DTA. The anodic stability of the polymer was examined versus a lithium anode. Finally the electrode was used to prepare a two electrodes lithium cell and the cell was tested to evaluate the electrode capacity retention as a function of the applied current and cycle number. The electrochemical properties of the electrode have been found very promising for the realization of high energy, high power, long cycle life batteries being capable of cycling for hundreds of cycles with excellent performance and reduced loss of capacity.

Novel Design Concepts of Efficient Mg‐Ion Electrolytes toward High‐Performance Magnesium–Selenium and Magnesium–Sulfur Batteries

Developing high‐voltage Mg‐compatible electrolytes (>3.0 V vs Mg) still remains to be the biggest R&D challenge in the area of nonaqueous rechargeable Mg batteries. Here, the key design concepts toward exploring new boron‐based Mg salts in a specific way of highlighting the implications of anions are proposed for the first time. The well‐defined boron‐centered anion‐based magnesium electrolyte (BCM electrolyte) is successfully presented by facile one‐step mixing of tris(2H‐hexafluoroisopropyl) borate and MgF2 in 1,2‐dimethoxyethane, in which the structures of anions have been thoroughly investigated via mass spectrometry accompanied by NMR and Raman spectra. The first all‐round practical BCM electrolyte fulfills all requirements of easy synthesis, high ionic conductivity, wide potential window (3.5 V vs Mg), compatibility with electrophilic sulfur, and simultaneously noncorrosivity to coin cell assemblies. When utilizing the BCM electrolyte, the fast‐kinetics selenium/carbon (Se/C) cathode achieves the best rate capability and the sulfur/carbon (S/C) cathode exhibits an impressive prolonged cycle life than previously published reports. The BCM electrolyte offers the most promising avenue to eliminate the major roadblocks on the way to high‐voltage Mg batteries and the design concepts can shed light on future exploration directions toward high‐voltage Mg‐compatible electrolytes.

Improved Interfacial Properties of MCMB Electrode by 1-(Trimethylsilyl)imidazole as New Electrolyte Additive To Suppress LiPF6Decomposition

Trace water content in the electrolyte causes the degradation of LiPF6, and the decomposed products further react with water to produce HF, which alters the surface of anode and cathode. As a result, the reaction of HF and the deposition of decomposed products on electrode surface cause significant capacity fading of cells. Avoiding these phenomena is crucial for lithium ion batteries. Considering the Lewis-base feature of the N-Si bond, 1-(trimethylsilyl)imidazole (1-TMSI) is proposed as a novel water scavenging electrolyte additive to suppress LiPF6 decomposition. The scavenging ability of 1-TMSI and beneficiary interfacial chemistry between the MCMB electrode and electrolyte are studied through a combination of experiments and density functional theory (DFT) calculations. NMR analysis indicated that LiPF6 decomposition by water was effectively suppressed in the presence of 0.2 vol % 1-TMSI. XPS surface analysis of MCMB electrode showed that the presence of 1-TMSI reduced deposition of ionic insulating products caused by LiPF6 decomposition. The results showed that the cells with 1-TMSI additive have better performance than the cell without 1-TMSI by facilitating the formation of solid-electrolyte interphase (SEI) layer with better ionic conductivity. It is hoped that the work can contribute to the understanding of SEI and the development of electrolyte additives for prolonged cycle life with improved performance.

Development of Non-Fluorinated Cathodes Based on Li3V1.95Ni0.05(PO4)3/C with Prolonged Cycle Life: A Comparison among Na-Alginate, Na-Carboxymethyl Cellulose and Poly(acrylic acid) Binders

Non-fluorinated Li3V1.95Ni0.05(PO4)3/C-based electrodes were prepared by using sodium carboxymethyl cellulose, sodium alginate and poly(acrylic acid) as alternative binders of the standard poly(vinylidene difluoride). The effect of the binders was investigated on several aspects, starting from the rheological properties of the dispersions, to the physical-chemical properties of the layers (adhesion test, electrode porosity, surface conductivity). The prepared Li3V1.95Ni0.05(PO4)3/C-based electrodes were characterized as cathodes at different C-rates ranging from 1 C to 200 C in two different potential windows, between 3.0–4.3 and 3.0–4.8 V vs. Li/Li+. The cycle life of the LVNP/C-based electrodes was characterized for each potential window at C-rate as high as 100 C and for 10000 cycles. Electrochemical impedance spectroscopy, scanning electrode microscopy, X-ray diffraction and energy dispersive X-ray measurements were used to study the aged electrodes. Among the electrodes, the one prepared with Na-alginate binder displays the best electrochemical performance, with a specific capacity of 100 and 85 mAh g−1 delivered at 100 C when charged up to 4.3 and 4.8 V vs. Li/Li+, respectively. Moreover, in the same potential windows, it displays an excellent cycling stability over 10000 cycles at 100 C, with a capacity retention of 80% and 65%.

Preparation of Nanoporous Si by Dealloying in Metallic Melt and Its Application for Negative Electrode of Lithium Ion Battery

Three dimensional nanoporous Si with controlled pore and ligament size was prepared by immersing Mg-Si alloy precursor in Bi metal bath. The miscible nature of Bi-Mg and immiscible one of Bi-Si caused selective dissolution of Mg from Mg-Si precursor in Bi melt, leaving interconnected ligaments enriched by Si element. The lithium ion battery negative electrode made from the developed nanoporous Si exhibited larger capacity and longer cycle life compared with nanoparticle Si based electrode. By controlling amount of Li insertion, volume expansion of Si can be limited below pore volume. In such an operation condition, volume expansion is accommodated within pores thus electrode degradation was suppressed resulting in the prolonged cycle life of the electrode.

Reduction of capacity decay in vanadium flow batteries by an electrolyte-reflow method

Abstract Electrolyte imbalance is a major issue with Vanadium flow batteries (VFBs) as it has a significant impact on electrolyte utilization and cycle life over extended charge-discharge cycling. This work seeks to reduce capacity decay and prolong cycle life of VFBs by adopting a novel electrolyte-reflow method. Different current density and various start-up time of the method are investigated in the charge-discharge tests. The results show that the capacity decay rate is reduced markedly and the cycle life is prolonged substantially by this method. In addition, the coulomb efficiency, voltage efficiency and energy efficiency remain stable during the whole cycle life test, which indicates this method has little impact on the long lifetime performance of the VFBs. The method is low-cost, simple, effective, and can be applied in industrial VFB productions.

A sulfur host based on titanium monoxide@carbon hollow spheres for advanced lithium-sulfur batteries.

Lithium–sulfur batteries show advantages for next-generation electrical energy storage due to their high energy density and cost effectiveness. Enhancing the conductivity of the sulfur cathode and moderating the dissolution of lithium polysulfides are two key factors for the success of lithium–sulfur batteries. Here we report a sulfur host that overcomes both obstacles at once. With inherent metallic conductivity and strong adsorption capability for lithium-polysulfides, titanium monoxide@carbon hollow nanospheres can not only generate sufficient electrical contact to the insulating sulfur for high capacity, but also effectively confine lithium-polysulfides for prolonged cycle life. Additionally, the designed composite cathode further maximizes the lithium-polysulfide restriction capability by using the polar shells to prevent their outward diffusion, which avoids the need for chemically bonding all lithium-polysulfides on the surfaces of polar particles.

Preparation, structure study and electrochemistry of layered H2V3O8 materials: High capacity lithium-ion battery cathode

The present study explores H2V3O8 as high capacity cathode material for lithium-ion batteries (LIB's). Despite having high discharge capacity, H2V3O8 material suffers from poor electrochemical stability for prolonged cycle life. Ultra-long H2V3O8 nanobelts with ordered crystallographic patterns are synthesized via a hydrothermal process to mitigate this problem. The growth of the crystal is facile along [001] direction, and the most common surface is (001) as suggested by Wulff construction study. Electrochemical performance of H2V3O8 cathode is tested against Li/Li+ at various current rates. At 50 mA g−1current rate, it delivers a discharge capacity of 308 mAh g−1, whereas, at 3000 mA g−1, an initial discharge capacity of 144 mAh g−1 is observed and stabilized at 100 mAh g−1 till 500 cycles. Further, the density functional theory (DFT) based simulations study of both the pristine and lithiated phase of H2V3O8 cathode materials is undertaken. DFT study reveals the presence of hydrogen as hydroxyl unit in the framework of the host. In correlation, the magnetic property of vanadium atoms is examined in detail with through partial density of states (PDOS) calculation during three stage lithiation processes and evaluating various potential steps involved in lithium insertion.

The Importance of Pore Size and Surface Polarity for Polysulfide Adsorption in Lithium Sulfur Batteries

Polysulfide shuttling is a crucial factor in lithium sulfur batteries responsible for capacity fading and degradation. Liquid phase adsorption in combination with nuclear magnetic resonance and X‐ray photoelectron spectroscopy are used to elucidate and quantify polysulfide retention in typical porous cathode materials used in lithium sulfur batteries without cell assembly to achieve a more fundamental understanding of liquid phase adsorption phenomena as a responsible mechanism for polysulfide retention. The individual impact of each pore size increment is quantified on the polysulfide adsorption (PSA). Ultramicropores show eight times higher PSA (1.48 mmol cm−3) than mesopores. Strong heteroatom‐doped ultramicropores show even stronger interactions with polysulfides leading to 25 times higher adsorption compared to hydrophobic mesopores. These findings allow to precisely tailor pore structure and heteroatom distribution of cathode materials for next generation lithium sulfur batteries with prolonged cycle life and reduced capacity fading.

A Scaled‐Up Lithium (Ion)‐Sulfur Battery: Newly Faced Problems and Solutions

Lithium‐sulfur (Li‐S) batteries are extensively explored due to their substantially higher theoretical energy density compared to any commercially available rechargeable batteries. Highly innovative efforts are invested to demonstrate promising Li‐S cells at laboratory scales. In order to promote this battery technology further, it is important to develop and test sulfur cathodes with practically high loading per unit area. The work described herein is devoted to long‐term testing of Li‐S and Si‐Li‐S cells comprising electrodes with high loading of the active mass, in pouch cells. This study investigates composite cathodes in which sulfur is embedded in matrices of multiwall carbon nanotubes and composite anodes based on prelithiated Si/SiOx nano‐spheres. These full‐cells exhibit stable cycling performance for more than 400 cycles, substantially more than equivalent cells utilizing metallic lithium anodes, which suffer from dendritic Li growth. The use of pouch cells, high cathodes' loading, and relatively high charge exchange per unit area during each cycle, emphasize the limitation of Li metal anodes in rechargeable batteries and promote development of Si‐Li‐S batteries for prolonged cycle life.

Li-Ion Batteries and Beyond (Li-S, Li-oxygen, Na-ion and Mg): What Are the Realistic Horizons?

This presentation is aimed at reviewing the true horizons of Li ion battery technology and batteries considered as ‘beyond Li ion systems’. We will discuss first the frontier of Li ion battery technology. Ni rich Li[NiCoMn]O2 and Li&Mn rich Li1+x[NiCoMn]O2cathodes promise high specific capacity with serious questions about stability. Both types of cathode materials can be stabilized and demonstrate prolonged cycle life. We will describe stabilization means for these systems. The implementation of such cathodes can increase the energy density of advanced Li ion batteries by 20-30%. Regarding the anode side, I am not sure that we can replace carbonaceous materials (as main components) by other alternatives such as conversion reactions or alloying (e.g. LixSi, SnxSi) if high volumetric energy density and very prolonged cycling are important (as is the case for EV applications). Turning to electrolyte solutions, using fluorinated solvents can help to extend anodic stability and enhence passivation of the anodes. In recent years, we discovered the importance of binders in determining the performance of the composite electrodes we used. We will show that the choice of separators can also play an important role in detemining peformance. The inevitable energy density limitation of Li ion batteries for propulsion by full EVs, promotes intensive work on Li-sulfur and Li-oxygen batteries, which theoretical energy density may approach that of propulsion by ICE. However, it is not clear that there are non-aqueous sovents available, that are stable in the presence of superoxide or peroxide moieties formed by ORR, in solution phase and in the presence of Li ions. Work on these systems promotes renaissance of Li metal anodes. It is important to mention intensive earlier work (15 years ago) that demonstrated the inevitable limitations of Li metal anodes upon cycling at current densities required for practical, high rate batteries. In any event, energy density calculations show that the volumetric energy density of practical Li-S and Li-oxygen systems designed for prolonged cycle life, may not rival that of Li ion batteries. Recent work on both systems demonstrate success in developing sulfur and oxygen cathodes for prolonged cycling. However, replacing Li anodes in these systems by more stable and reversible alternatives without paying too high penalty re: energy density, remains a key challenge. Sodium ion batteries is an emerging field in recent years. While sodium is much more abundant than lithium on earth crust, the most expansive components are the same transition metals used in Li ion batteries. Despite advantages found for several sodium intercalation cathodes in terms of rate capabilities (higher than that of their Li counter-parts), there is no chance that Na ion systems can rival Li ion batteries in term of energy density. Hence, it is hard to see sodium ion batteries being relevant for electro-mobility. Thus, Na ion batteries can be addressed for load leveling application. Consequently, the greatest challenge in this field is development of Na ion batteries with very prolonged cycle life and relatively low hysteresis between charge and discharge. Another topic that attracts many researchers in the batteries field in recent years is rechargeable magnesium batteries. We can point out on impressive progress in development of non-complex electrolyte solutions, possessing wide electrochemical windows and fully reversible Mg anodes behavior in them. We will discuss this progress showing some examples. A great challenge remains the positive side. It is interesting that the first generation of rechargeable Mg batteries which comprises Mg metal anodes, complex electrolyte solutions and MgxMo6S8 Chevrel phase cathodes exhibits surprisingly high volumetric energy density with a main advantage which is prolonged cycle life. Our opinion is based on recent work that is summarized in the references below.

One-Pot Hydrothermal Synthesis of LiMn2O4 Cathode Material with Excellent High-Rate and Cycling Properties

The spinel LiMn2O4 was prepared by a one-step hydrothermal method using acetone as the reductant under different hydrothermal temperatures. X-ray diffraction and scanning electron microscopy analysis indicated that optimal LiMn2O4 particles (LMO-120) were synthesized at the temperature of 120°C and the particles were well distributed and about 410 nm in size. Electrochemical performance showed that the as-prepared LiMn2O4 particles exhibited a higher initial discharge capacity than commercial LiMn2O4 (131.5 mAh g−1 versus 115.6 mAh g−1 at 0.2 C). An excellent discharge capacity retention rate of 94.07% was observed after 60 charge–discharge cycles. On the other hand, when cycled at the high rate of 1 C, the optimal LiMn2O4 in this work showed a high discharge capacity of 107.5 mAh g−1 in contrast to only 92.3 mAh g−1 of the commercial LiMn2O4. These results indicate that LMO-120 showed excellent electrochemical performance, especially the prolonged cycling life and high-rate performance, which suggested that this spinel LiMn2O4 has promise for practical application as a high-rate cathode material for lithium ion batteries.

Cobalt carbonate hydroxide/carbon composite for lithium-oxygen battery cathode electrocatalyst

Cobalt carbonate hydroxide (CCH) composited with XC-72R carbon was synthesized via a simple hydrothermal process. Transmission electron microscopes(TEM) shows that CCH with nanowire morphology is well dispersed in carbon medium. The CCH/C-based oxygen cathode exhibited low polarization with specific capacity of 3500mAhg−1 at a current density of 0.05mAcm−2 and prolonged cycling life. The cell with CCH/C catalyst can run for 55 cycles before the terminal potential of discharge declines to 2.0V with a limited specific capacity of 500mAhg−1. The improved performance was mainly attributed to the excellent OER activity of CCH/C that Li2O2 can be decomposed in lower potential, which might help avoid generation of undesirable byproducts.