Research progress of cathode materials for lithium-sulfur batteries

锂硫电池作为一种非常有前途的高能化学电源,随着电动汽车和便携式电子设备的发展,因其高理论比容量（1675 mA·h/g）和高理论能量密度（2600 W·h/kg）引起了人们的广泛关注。然而,锂硫电池发展过程中的一些挑战不可避免,包括硫较低的离子和电子导电性,较差的循环性以及生成的多硫化物易溶于有机溶剂等缺点,制约了锂硫电池的发展。本文结合近年来锂硫电池正极材料的研究进展,简要阐述了锂硫电池正极材料的研究现状、问题及面临的挑战。锂硫电池由于其发展中面临技术瓶颈难以突破,导致现在还无法大规模的应用,因而对其性能的改进也就成了当今的研究热点。硫电极材料电导率低、循环性能差,可以通过碳包覆或者掺杂改善材料性能。然而由于成本和技术问题,大部分锂硫电池正极材料目前还主要处于研究试验阶段。因此,在提高材料性能的前提下,通过碳包覆或者掺杂改善工艺,探索一条适合工业化生产的道路是下一阶段研究的重点。     

Rational design and fabrication of frame-structured doped bismuth vanadate nanoarchitectures as a polysulfide shield to boost the performance of lithium-sulfur batteries

Lithium-sulfur (Li-S) battery has been evoked increasing attention due to its creditable energy density and the abundant sulfur in nature. Nevertheless, its commercialization is still hampered in virtue of the poor conductivity of sulfur and grievous polysulfide shuttling. To address these issues, in this work, we report a cost-efficient and facile tactic to fabricate frame-structured neodymium-doped bismuth vanadate (BiVO₄) nanoarchitectures, which are reasonably designed as a polysulfide shield to alleviate the shuttling effects. The synthesized nanoarchitectures exhibit typical tetragonal phase with a unique frame structure. The frame structure of BiVO₄ impedes polysulfide shuttling, and supplies electronic and ionic transmission routes. Furthermore, the rational doping of neodymium within the BiVO₄ nanoarchitectures can improve electric conductivity, as well as efficiently alleviate the loss of sulfur and improve activity for sulfur reduction. Benefitting from the structural feature and doping strategy, the Li-S battery performance with a neodymium-doped BiVO₄ nanoarchitecture is significantly improved. This strategy is easily adopted for fabricating other nanostructures, providing a feasible way to design cheap and efficient battery materials. This work is further available for synergistically uniting the virtues of the frame nanoarchitectures and doping protocol to develop advanced Li-S batteries.     

Novel construction of nanostructured carbon materials as sulfur hosts for advanced lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) are among the most promising next generation electrochemical energy storage systems due to their ultrahigh energy density, which has attracted enormous attentions. Nevertheless, the development and application of LSBs are still subject to some major technical obstacles such as the insulating nature of sulfur, the shuttle effect of intermediate polysulfides, and the drastic volume expansion. To overcome these challenges, various strategies have been employed to promote the performance of LSBs. This review focuses on summarizing the major development of novel nanostructured carbon hosts for advanced LSBs. The carbon nanotubes, graphene, and carbon spheres are introduced to improve our understanding of the morphology effects on LSBs. The heterogeneous atom-doping, unique hollow structures are summarized to investigate the chemical bonding effects during the charge/discharge process. The organic framework derived carbon structures are discussed to inspire us to find novel routes to enhance the performance of LSBs. Finally, the conclusions and prospects of nanostructured carbon in LSBs are proposed, while the challenges in the further development of LSBs are also discussed.     

Synergistic effect of titanium-oxide integrated with graphitic nitride hybrid for enhanced electrochemical performance in lithium-sulfur batteries

Lithium-sulfur (Li-S) secondary batteries have been limited by the poor cyclic stability, mainly caused by the dissolution polysulfide species into the electrolyte and subsequent irreversible shuttling effect. Recently, addition of the polysulfide adsorbents within sulfur cathode is effectively improving the electrochemical performance. Herein, TiO₂ integrated with g-C₃N₄ (TiO₂@g-C₃N₄: TOCN) hybrid was prepared by a facile heating treatment from the precursor of urea and TiO₂composites, which used as host material for elemental sulfur (TOCN@S) in Li-S batteries. The multifunctional TOCN not only reduced the electrochemical resistance but also provided strong adsorption sites to immobilize sulfur and polysulfide. As a result, the TOCN@S cathode with a sulfur content of 74.5 wt% and a sulfur loading of 3.1 mg cm⁻²exhibits a high initial capability of 804 mAh g⁻¹ at 0.5°C with capacity retention of 67.2% after 500 cycles. Additionally, the composite cathode also possesses excellent high-rate performance, retaining a remarkable specific capacity of 630 mAh g⁻¹ even at a rate of 2°C.     

Improve redox activity and cycling stability of the lithium-sulfur batteries via in situ formation of a sponge-like separator modification layer

The electronic nonconductivity of S and shuttle effect of soluble polysulfides are two fundamental issues that limit the application of lithium-sulfur (Li-S) batteries. Regarding these issues, herein, a sponge-like Ketjen black (KB)-triphenylphosphine sulfide (TPS) multifunctional modification layer was proposed to coat the separator of the advanced Li-S batteries. The layer was formed by an in situ spontaneous reaction between triphenylphosphine (TPP) of the conventional KB-TPP layer and Li₂S₆ solution. This functional layer can ensure a high e⁻ and Li⁺ conductivity while inhibiting the diffusion of soluble polysulfides. As a result, the redox activity, rate capability, and cycling stability of the batteries are significantly enhanced. Comparing with the discharge capacities at 2C for the PE separator, introducing the KB-TPS functional layer was beneficial for the capacity retentions of the cells, since the capacity increased from 16.1% to 66.6% at the same C-rate. A capacity degeneration rate of 0.045% per cycle was obtained for the cell with an S area density of 3.6 mg cm⁻². This work is a step forward in the exploration of advanced Li-S batteries, being a valuable reference for the study of related systems.     

Carbon-based materials for advanced lithium-sulfur batteries

随着能源和环境问题的日益突出以及电子电动设备的迅猛发展,传统锂离子电池已经越来越难以满足人们对于高能量密度电池的需求.锂硫电池因其能量密度高,成本低以及无污染等优点,被认为是极有潜力的下一代高能量密度储能体系.然而由于锂硫电池中正极材料电子,离子电导率低,充放电过程中电极体积变化大,聚硫化物等中间产物的溶解和伴随的"穿梭效应"以及锂负极的使用所带来的锂枝晶等一系列问题,导致锂硫电池的循环寿命差,阻碍其产业化的应用发展.锂硫电池体系中碳质材料的引入可以提高材料导电性,缓冲体积变化,抑制聚硫化物穿梭,是提高其电化学性能的有效手段.本文综述了近年来最新的锂硫电池中碳质材料的应用研究进展,包括硫/碳复合物,柔性自支撑电池和碳质锂硫电池负极,分析了其对锂硫电池性能提升的作用机理,并展望了锂硫电池将来可能的发展方向.     

Modeling the effect of key cathode design parameters on the electrochemical performance of a lithium‐sulfur battery

A 1D model is developed for the Li‐S cell to predict the effect of critical cathode design parameters—carbon‐to‐sulfur (C/S) and electrolyte‐to‐sulfur (E/S) ratios in the cathode—on the electrochemical performance. Cell voltage at 60% depth of discharge corresponding to the lower voltage plateau is used as a metric for calculating the cell performance. The cathode kinetics in the lower voltage plateau is defined with a single electrochemical reaction; thus, the model has a single apparent kinetic model parameter, the cathode exchange current density (i_0,pe). The model predicts that cell voltage increases considerably with increasing carbon content until a C/S ratio of 1 is attained, whereas the enhancement in the cell voltage at higher ratios is less obvious. The model can capture the effect of the C/S ratio on the cathode kinetics by expressing the electrochemically active area in the cathode in carbon volume fraction; the C/S ratio in the cathode does not affect i_0,pe in the model. On the other hand, the electrolyte amount has a significant impact on the kinetic model parameter such that increasing electrolyte amount improves the cell voltage as a result of increasing i_0,pe. Therefore, in the model, i_0,pe needs to be defined as a function of the electrolyte volume fraction, which is known to have a crucial effect on reaction kinetics.     

新型固态聚合物电解质在锂硫电池中的性能研究

本工作采用（氟磺酰）（三氟甲基磺酰）亚胺锂{Li[(FSO2)(CF3SO2)N],LiFTFSI}和聚氧乙烯（PEO）分别作为导电锂盐和聚合物主链,通过简单的溶液浇铸法制备了新型固态聚合物电解质（SPEs）,并采取示差扫描量热（DSC）、热重（TGA）、线性扫描伏安（LSV）、交流阻抗（EIS）和恒电位直流（DC）极化等方法研究了LiFTFSI/PEO （EO/Li+摩尔比为16）电解质的理化性质和电化学性质。结果表明,LiFTFSI/PEO电解质具有较高的室温离子电导率（σ ≈10−5 S/cm）,较高的氧化电位（4.63 V vs. Li/Li+）,并且耐热温度高达256 ℃。锂硫电池测试结果表明,该类SPEs展现出相对高的首周放电比容量（881 mA•h/g）,有效地抑制了多硫离子的“穿梭效应”,表现出良好的电池循环性能。     

Multi-functional TiO2 nanosheets/carbon nanotubes modified separator enhanced cycling performance for lithium-sulfur batteries

TiO₂ nanosheets (TiO₂NSs) have been investigated for lithium-sulfur (Li-S) batteries as strategically designed TiO₂ nanosheet/carbon nanotube (TiO₂NS/CNT) composite modified polypropylene (PP) separator to inhibit the shuttling of the intermediate polysulfides. The modified separator was fabricated by the vacuum filtration method using the exfoliation TiO₂NSs and untreated carbon nanotube (CNT) composites. The multi-functional TiO₂NS/CNT coating not only reduced the electrochemical resistance but also localized the migrating polysulfides by the cooperative effect of physical adsorption and chemical binding. Specifically, the composition ratio of TiO₂NSs/CNTs and the interface character have been studied. It was found that the optimum ratio and perfect electrolyte wettability of the TiO₂NS/CNT layers were all the critical reasons to achieve good battery performance. The high initial discharge capacity of 1247 mA h g⁻¹ at 0.2 C rate, which was 75% of the theoretical capacity of sulfur, 98% average coulombic efficiency, and 627 mA h g⁻¹ discharge capacity retention after 100 cycles were obtained with the TiO₂NS/CNT coating separator.     

The role of long-period stacking ordered phase on the discharge and electrochemical behaviors of magnesium anode Mg-Zn-Y for the primary Mg-air battery

This work investigated and discussed the role of long-period stacking ordered (LPSO) phase on discharge performance and electrochemical behaviors of Mg-Zn-Y anode for Mg-air battery in detail. The volume fraction of LPSO phase increases with the increasing Y and Zn content. Compared with Mg-2Zn anode, Mg-Zn-Y anode with low content of LPSO phase has better discharge properties due to high open-circuit potential and low corrosion rate. However, anodes contained a high volume of LPSO phase exhibit poor corrosion resistance and discharge properties. The ZW12 alloy shows the best discharge capacity and anodic efficiency as high as 1612.9 mAh·g⁻¹ and 74.49% at the 40 mA·cm⁻². It also outputs a high peak specific energy 1859.15 mWh·g⁻¹ at 10 mA cm⁻², which is 37.56% higher than Mg-2Zn anode and 249.44% higher than ZW39 anode. The LPSO phase totally changes the decomposition process of Mg matrix, displaying the lamellar peeling surface in LPSO-affect zone. This lamellar peeling mode can help to take away the discharge products from the anodic surface, improving the anode performance.     

Molybdenum carbide nanocrystals modified carbon nanofibers as electrocatalyst for enhancing polysulfides redox reactions in lithium-sulfur batteries

The high performance of lithium sulfur (Li S) batteries is the focus of research in recent years. However, the low sulfur loading, shuttling effect in electrolyte, and poor cycling stability limit their applications. Herein, molybdenum carbide nanocrystals embedded carbon nanofibers (Mo₂C@CFs: MCCFs) hybrid membrane was prepared in situ on CFs membrane based on carbonthermal reduction of ammonium molybdate. The fibrous MCCFs network is used as the current collector with Li₂S₆ catholyte solution for Li S batteries, which inhibits the shuttle effect and accelerates kinetics redox reaction. In addition, Mo₂C, as electrocatalyst, promotes nucleation of Li₂S of the MCCFs substance, which can reduce polarization and increase the specific capacity. As a result, the free-standing MCCFs@Li₂S₆ electrode (sulfur loading: 4.74 mg) shows a capacity of 977 mAh g⁻¹ and maintains at 828 mAh g⁻¹ at 0.2 C over 250 cycles, and indicates excellent reversibility and cycling stability. Even with sulfur loading as high as 7.11 mg, the MCCF@Li₂S₆ electrode exhibits an extremely high capacity of 5.75 mAh. Meanwhile, the Mo₂C modified CFs can be effectively retarding the self-discharge behavior by trapping the polysulfides. Furthermore, the stability improvement of lithium anode state by effectively suppressing the shuttle effect of polysulfide, played an important role in enhancing the electrochemical performance.     

Mechanical behavior of a battery separator in electrolyte solutions

The structural integrity of the separator is crucial to the abuse tolerance of a battery. To estimate its stress level in a battery, the mechanical property of the separator in situ in the battery environment must be known. This work investigated the tensile behavior of a single layer polypropylene (PP) separator in electrolyte solutions for Li-ion batteries using a dynamic mechanical analyzer (DMA). The measurements were carried out in both dry (ambient) and wet conditions for both the machine direction (MD) and the transverse direction (TD). In the wet condition, samples were submerged either in a DMC solvent or in a electrolyte solution of 1.1 M LiPF6 in EC/DMC (1/1 by volume). The DMA experiments were performed under uniaxial tension, creep, and frequency sweep modes. The results in all three modes demonstrated that the mechanical properties of the separator were significantly lower in wet conditions. For instance, in the MD, relative to the dry condition, the ratio of the Young's modulus was about 0.49 and 0.52 for DMC and 1.1 M LiPF6 in EC/DMC, respectively. The results indicate that the mechanical properties measured in dry condition using samples that had been preconditioned in solutions are not sufficient to represent the in situ material behavior.     

Influence of TiO2/TiC composite materials with different crystal structures on the electrochemical properties as sulfur-loaded matrix for lithium-sulfur batteries

Lithium-sulfur battery is a type of high-performance chemical power supply system, and the structure of composite substrate material will influence on the electrochemical properties of sulfur cathode active materials. In this paper, a TiO₂/TiC composite substrate material with the different crystal structure by means of changing sintering temperature is synthesized and its physical properties and electrochemical performances have been researched. Through X-ray diffraction analysis, it can be found that the crystal structures of TiC and TiO₂ in the TiO₂/TiC composite substrate material sinter at different temperature both have been changed obviously due to the strong interaction between the oxygen atom and titanium and carbon atoms. By comparison, when sintering at 600°C, the composite matrix material has higher crystallinity and they accordingly have some confusion after sintering at 500°C. Raman spectrum information displays that TiO₂/TiC composite substrate materials with high crystallinity allow the loaded sulfur to enter the pores and it is easier to form a stable physical adsorption. However, TiO₂/TiC composite substrate material with some confusion is easier to form chemical adsorption with sulfur. Electrochemical test results illustrate that the specific discharge capacities of TiO₂/TiC composite substrate material with the higher crystallinity loaded 55% sulfur can be achieved to 1247.91 and 834.62 mAh g⁻¹ at 0.1 and 0.5C, respectively. Then, after 300 times charge and discharge cycles at 0.2C, the discharge capacity retention rate of TiO₂/TiC composite substrate material with some confusion loaded 45% sulfur can reach 54.40%. To sum up, we can conclude that the TiO₂/TiC composite materials with different crystal structures will have a serious impact on the electrochemical performances of sulfur cathode for lithium-sulfur batteries.     

Towards impedance-based temperature estimation for Li-ion battery packs

In order to meet the required power and energy demand of battery-powered applications, battery packs are constructed from a multitude of battery cells. For safety and control purposes, an accurate estimate of the temperature of each battery cell is of vital importance. Using electrochemical impedance spectroscopy (EIS), the battery temperature can be inferred from the impedance. However, performing EIS measurements simultaneously at the same frequency on each cell in a battery pack introduces crosstalk interference in surrounding cells, which may cause EIS measurements in battery packs to be inaccurate. Also, currents flowing through the pack interfere with impedance measurements on the cell level. In this paper, we propose, analyse, and validate a method for estimating the battery temperature in a battery pack in the presence of these disturbances. First, we extend an existing and effective estimation framework for impedance-based temperature estimation towards estimating the temperature of each cell in a pack in the presence of crosstalk and (dis)charge currents. Second, the proposed method is analysed and validated on a two-cell battery pack, which is the first step towards development of this method for a full-size battery pack. Monte Carlo simulations are used to find suitable measurement settings that yield small estimation errors and it is demonstrated experimentally that, over a range of temperatures, the method yields an accuracy of ±1°C in terms of bias, in the presence of both disturbances.     

Modeling,optimization and control of a FC/battery hybrid locomotive based on ADVISOR

This paper presents a hybrid locomotive system which combines proton exchange membrane fuel cell (PEMFC) as primary energy source for its advantages of high efficiency and low emissions, and Pb acid battery as secondary energy storage (ESS) to supplement the output of FC during acceleration or whenever else needed and to absorb regenerative energy during braking. Advanced Vehicle Simulator (ADVISOR), a vehicle simulating software, is secondly developed in this paper for the locomotive modeling and simulation. An analysis of simulation is conducted to verify the effectiveness of the proposed model. Then the power of FC, battery and motor are optimized by adopting bisection algorithm under certain constraints. It is confirmed that the dynamic performance and economy performance are improved after optimization. An advanced energy management system is extremely necessary to contribute the demand power of locomotive between energy sources in a suitable way, therefore a fuzzy logic based control strategy is proposed for the hybrid locomotive. With advantages of easy understanding, flexibility and capability to deal with imprecise data, fuzzy logic methodology is suitable for the control of hybrid locomotive. The simulation results demonstrate the superiority of fuzzy logic energy management system in terms of dynamic and economy performance.     

Theoretical study on discharge behavior of LiFePO4 battery

使用多孔电极理论对LiFePO4（LFP）锂离子电池的放电行为进行了详细探讨,发现随着放电过程进行,电极内部的电化学反应从隔膜侧向集流体侧移动,并且移动过去之后LFP基本完成放电过程,放电截止时电化学反应截止在电极的某个位置,并不是所有的LFP颗粒都完成了放电。随后对放电速率、电极电导率和电解液扩散系数对放电过程的影响进行了研究。随着放电倍率增加,电化学反应推进的距离不断减少,并且峰值不断增大,峰值区域变窄。提高电极电导率可以保证电化学反应从隔膜侧开始进行,但是继续提高电极电导率并不能进一步将电化学反应的峰值向电极深处推进。较高的扩散系数可以保证所有的活性材料都能发生电化学反应。以上结论可对高性能LFP锂离子电池的设计和制备提供了有效的指导作用。     

Carbon-based cathode host derived from crosslinked porous polyimides for lithium-sulfur batteries and their electrochemical properties

Carbon-based porous materials as Li–S batteries cathode hosts have received widespread attention because of the superiority of fine physical confinement, vast accommodation voids and excellent conductive networks, towards realizing the adsorption-diffusion-conversion of lithium polysulfides (LiPSs). However, carbon-based materials are usually non-polar, which can only act as physical barriers to limit polysulfides shuttle behavior during short-term cycling of Li–S batteries, lacking strong chemical entrapment towards the polar polysulfides. Herein, we successfully synthesize two novel carbon-based hierarchical porous materials (CR-PPIs@800) derived from crosslinked porous polyimides (CR-PPIs) via traditional polymerization and crosslinking reaction as well as high-temperature treatment. Because the pre-designed porous architectures, CR-PPIs@800 not only give hierarchical porous structure for accommodating LiPSs, but also afford strong chemisorption interaction from high heteroatom N species for adsorbing LiPSs and buffering shuttle behaviors. The carbon networks of CR-PPIs@800 possess valid ion storage and transportation network for accelerating charge/ion migration of LiPSs. Profiting from above advantages, S/CR-PPIs@800 composites cathodes realize the fast conversion of LiPSs, and show promoted electrochemical properties.     

Equivalent circuit model parameters of a high-power Li-ion battery: Thermal and state of charge effects

Equivalent circuit model (EMC) of a high-power Li-ion battery that accounts for both temperature and state of charge (SOC) effects known to influence battery performance is presented. Electrochemical impedance measurements of a commercial high power Li-ion battery obtained in the temperature range 20 to 50 °C at various SOC values was used to develop a simple EMC which was used in combination with a non-linear least squares fitting procedure that used thirteen parameters for the analysis of the Li-ion cell. The experimental results show that the solution and charge transfer resistances decreased with increase in cell operating temperature and decreasing SOC. On the other hand, the Warburg admittance increased with increasing temperature and decreasing SOC. The developed model correlations that are capable of being used in process control algorithms are presented for the observed impedance behavior with respect to temperature and SOC effects. The predicted model parameters for the impedance elements R_s, R_ct and Y₀₁₃ show low variance of 5% when compared to the experimental data and therefore indicates a good statistical agreement of correlation model to the actual experimental values.     

Modeling and validation of temperature changes in a pouch lithium-ion battery at various discharge rates

This paper deals with the thermal modeling of temperature rise in a pouch lithium-ion battery with LiFePO₄ (also known as LFP) cathode material. The developed model represents the main thermal phenomena in the cell in terms of temperature change. The proposed model is validated with the collected experimental data from a module composed of 11 cells. In the conducted experiments, the different charge and discharge rates of 1/2C, 1C, 2C and 2.5C are applied. It is seen that, the increased discharge rates result in increased temperature on the surface of the battery. When the discharge rate is doubled, from 1C to 2C, cell temperatures have risen by 3.5 times. A simplified model for determining the heat generation is developed and validated with the test results.     

专利视域下全球锂硫电池技术竞争态势分析

锂硫电池是一种以硫作正极,锂作负极的锂电池,具有原材料储量丰富、成本低和环保等特点,已经成为燃料电池领域的新兴技术的研究热点和发展方向.以全球锂硫电池技术专利作为研究对象,利用专利数据挖掘和主题聚类的方法,分析了全球该技术的专利申请总体发展态势、地域分布、专利技术构成与功效、申请人技术构成与主题聚类,以及主要机构的技术...