Experimental and optimization of material synthesis process parameters for improving capacity of lithium‐ion battery

New methods for synthesis of active materials have been developed to improve capacity and cycle life performance of lithium‐ion batteries. Past studies have focused on routes of development of materials and new processes, which might not be economical for large‐scale production. In this regard, this study examines a widely employed carbothermal reduction technology for the synthesis of lithium‐iron phosphate (LiFePO₄/C) and investigates effects of process conditions during this synthesis on final battery performance. An experimental combined genetic programming approach is used to model the effects of crucial process conditions (sintering time, the carbon content, and the sintering temperature) on the discharge capacity of the assembled battery. Experiments are conducted to collect the discharge capacity data based on varying LiFePO₄/C synthesis conditions, and genetic programming is employed to develop a suitable functional relationship between them. The results show that the battery discharge capacity is controlled significantly by adjusting sintering temperature and carbon content, while the effect of sintering time is found to be insignificant. Further, the interaction effect of the sintering time and carbon content is much more obvious than that of the sintering time and the sintering temperature. The findings from the study pave the way for the optimum design of the synthesis process of LiFePO₄/C for a higher battery performance.     

彩色纳米碳酸钙的研制

以纳米碳酸钙中试装置为平台,通过控温碳化、加热湿法染色、加热湿法改性和分散处理,制得了具有良好一次粒子形态的彩色纳米碳酸钙产品。激光粒度仪测试表明,彩色纳米碳酸钙产品的D₅₀约为350 nm,具有粒度分布均匀、分布范围窄等特点。产品在空气中长期放置不氧化、不褪色,说明具有良好的化学稳定性。亲水性实验表明,彩色纳米碳酸钙产品在水中长时间放置、反复搅拌,仍然不沉降、不掉色,说明染色和活化都是牢固的。以酸性媒染蓝黑B染料和硬酯酸为例,分析了纳米碳酸钙的湿法染色和湿法活化机理,并且探讨了硬酯酸分子、染色剂分子和碳酸钙颗粒之间的化学交联作用。     

Electrochemical performance and modeling of lithium‐sulfur batteries with varying carbon to sulfur ratios

Lithium‐sulfur batteries have attracted much research interest because of their high theoretical energy density and low‐cost raw materials. While the electrodes are composed of readily available materials, the processes that occur within the cell are complex, and the electrochemical performance of these batteries is very sensitive to a number of cell processing parameters. Herein, a simple electrochemical model will be used to predict, with quantitative agreement, the electrochemical properties of lithium‐sulfur cathodes with varying carbon to sulfur ratios. The discharge capacity and the polarization were very similar for the lowest sulfur loadings, while above 23.2 wt% sulfur the gravimetric capacity dropped significantly, and there was an increase in the cell polarization. In addition, a transition in the electrode morphology, from well dispersed to aggregated sulfur at the surface, will be reflected in the change in a critical model parameter demonstrating the sensitivity and functionality of even this simple model in predicting complex behavior in the lithium‐sulfur cells.     

Introducing the energy efficiency map of lithium‐ion batteries

The charge, discharge, and total energy efficiencies of lithium‐ion batteries (LIBs) are formulated based on the irreversible heat generated in LIBs, and the basics of the energy efficiency map of these batteries are established. This map consists of several constant energy efficiency curves in a graph, where the x‐axis is the battery capacity and the y‐axis is the battery charge/discharge rate (C‐rate). In order to introduce the energy efficiency map, the efficiency maps of typical LIB families with graphite/LiCoO₂, graphite/LiFePO₄, and graphite/LiMn₂O₄ anode/cathode are generated and illustrated in this paper. The methods of usage and applications of the developed efficiency map are also described. To show the application of the efficiency map, the effects of fast charging, nominal capacity, and chemistry of typical LIB families on their energy efficiency are studied using the generated maps. It is shown how energy saving can be achieved via energy efficiency maps. Overall, the energy efficiency map is introduced as a useful tool for engineers and researchers to choose LIBs with higher energy efficiency for any targeted applications. The developed map can be also used by energy systems designers to obtain accurate efficiency of LIBs when they incorporate these batteries into their energy systems.     

Design and analysis of an aging‐aware energy management system for islanded grids using mixed‐integer quadratic programming

The rapid increase of renewable energy sources made coordinated control of the distributed and intermittent generation units a more demanded task. Matching demand and supply is particularly challenging in islanded microgrids. In this study, we have demonstrated a mixed‐integer quadratic programming (MIQP) method to achieve efficient use of sources within an islanded microgrid. A unique objective function involving fuel consumption of diesel generator, degradation in a lithium‐ion battery energy storage system, carbon emissions, load shifting, and curtailment of the renewable sources is constructed, and an optimal operating point is pursued using the MIQP approach. A systematic and extensive methodology for building the objective function is given in a sequential and explicit manner with an emphasis on a novel model‐based battery aging formulation. Performance of the designed system and a sensitivity analysis of resulting battery dispatch, diesel generator usage, and storage aging against a range of optimization parameters are presented by considering real‐world specifications of the Semakau Island, an island in the vicinity of Singapore.     

Fabrication of ultrafine Gd2O3 nanoparticles/carbon aerogel composite as immobilization host for cathode for lithium‐sulfur batteries

Carbon aerogel (CA), possessing abundant pore structures and excellent electrical conductivity, have been utilized as conductive sulfur hosts for lithium‐sulfur (Li‐S) batteries. However, a serious shuttle effect resulted from polysulfide ions has not been effectively suppressed yet due to the weak absorption nature of CA, resulting in rapid decay of capacity as the cycle number increases. Herein, ultrafine (~3 nm) gadolinium oxide (Gd₂O₃) nanoparticles (with upper redox potential of ~ 1.58 V versus Li⁺/Li) are uniformly in‐situ integrated with CA through directly sol‐gel polymerization and high‐temperature carbonization. The Gd₂O₃ modified CA composites (named as Gdx‐CA, where x means molar ratio of Gd₂O₃ nanoparticles to carbon) are incorporated with S. Then, the products (S/Gdx‐CA) are acted as sulfur host materials for Li‐S batteries. The results demonstrate that adding ultrafine Gd₂O₃ nanoparticles can dramatically improve the electrochemical properties of the composite cathodes. The S/Gd2‐CA electrode (loading with 58.9 wt% of S) possesses the best electrochemical properties, including a high initial capacity of 1210 mAh g^?1 and a relatively high capacity of 555 mAh g^?1 after 50 cycles at 0.1 C. It is noteworthy that the performance of long‐term cycle (350 cycles) for the S/Gd2‐CA (317 mAh g^?1 after 100 cycles and 233 mAh g^?1 after 350 cycles at 1 C) is improved significantly than that of S/CA (150 mAh g^?1 after 150 cycles at 1 C). Overall, the enhancement of electrochemical performances can be due to the strong polar nature of the ultrafine Gd₂O₃ nanoparticles, which provide strong adsorption sites to immobilize S and polysulfide. Furthermore, the Gd₂O₃ nanoparticles present a catalytic effect. Our research suggests that adding Gd₂O₃ nanoparticles into S/CA composite cathode is an effective and novelty method for improving the electrochemical performances of Li‐S batteries.     

Preparation and properties of lithium sulfonated polyoxadiazoles electrolyte

以硫酸肼（HS）、对苯二甲酸（TPA）、4，4'-联苯醚二甲酸（DPE）为单体，发烟硫酸做溶剂和脱水剂一步合成了一系列不同TPA和DPE单体配比的磺化聚芳噁二唑（SPOD），再通过氢氧化锂中和得到聚芳噁二唑磺酸锂（Li-SPOD）聚合物电解质，采用浇铸成膜法制得Li-SPOD电解质膜，研究改变TPA和DPE两种单体配比对Li-SPOD结构及性能的影响。结果表明，几种不同单体配比均能实现在聚合过程中一步得到SPOD，磺酸基团接枝在DPE结构的苯环上，并且可以达到理论接枝量；同时Li-SPOD电解质膜的聚集态结构差异很小；热性能的表现均非常优异，初始热分解温度都在450 ℃以上；力学性能随DPE单体含量的增加稍有下降但依然保持在较高的水平；电导率约为10^-5S/cm级别，随DPE含量增加而逐渐降低；Li-SPOD固态电解质电化学稳定性较好，对锂稳定电化学窗口均在4.0 V以上。     

Sustainable synthesis of cyclic carbonates from bio‐based polyether polyol: the structure characterization,rheological behaviour and thermal properties

The cycloaddition of CO₂ to epoxides represents a green efficient method to form bis(cyclic carbonate)s. The main purpose of the work reported in this paper was to examine the effect of the gas flow rate (20, 40, 60 and 100 mL min^–1) during carbonation on the conversion yield, chemical structure, rheological behaviour and thermal properties of the prepared compounds. A series of new bis(cyclic carbonate)s was obtained from bio‐based polyether polyol. The syntheses were performed in the absence of toxic solvents and the process did not require the use of elevated pressure. The progressive structural changes and the presence of characteristic chemical groups were monitored by attenuated total reflection Fourier transform infrared spectroscopy. The characterization of the structure by ¹H NMR and ¹³C NMR also confirmed the formation of cyclic carbonate moieties. The non‐Newtonian behaviour and the optimal mathematical model (Herschel–Bulkley) were verified by rheological measurements. The materials obtained could be used as a chemical intermediate to synthesize advanced materials based upon polyurethanes without using isocyanates. © 2019 Society of Chemical Industry     

Physics‐based model of lithium‐ion batteries running on a circuit simulator

The authors developed a physics‐based equivalent circuit model of a lithium‐ion battery (LIB) whose parameters are continually updated, reflecting the theoretical calculation results of the Butler‐Volmer equation, diffusion equations of the lithium‐ion and lithium, and Nernst equations of the liquid and solid phases. The developed model was applied to the charge/discharge simulations of an LIB, and the experimental and simulated results of constant current discharges and pulsed‐charge/discharge were found to be in excellent agreement. In particular, using the developed model, analyzing transient responses of the LIB derived from the transition of the electric double layer charging to the electrode reaction is possible. These results demonstrate that the electrochemical performance of an LIB can be calculated on a circuit simulator using the developed model.