A review of the features and analyses of the solid electrolyte interphase in Li-ion batteries

The solid electrolyte interphase (SEI) is a protecting layer formed on the negative electrode of Li-ion batteries as a result of electrolyte decomposition, mainly during the first cycle. Battery performance, irreversible charge “loss”, rate capability, cyclability, exfoliation of graphite and safety are highly dependent on the quality of the SEI. Therefore, understanding the actual nature and composition of SEI is of prime interest. If the chemistry of the SEI formation and the manner in which each component affects battery performance are understood, SEI could be tuned to improve battery performance. In this paper key points related to the nature, formation, and features of the SEI formed on carbon negative electrodes are discussed. SEI has been analyzed by various analytical techniques amongst which FTIR and XPS are most widely used. FTIR and XPS data of SEI and its components as published by many research groups are compiled in tables for getting a global picture of what is known about the SEI. This article shall serve as a handy reference as well as a starting point for research related to SEI.     

Performance evaluation of printed LiCoO2 cathodes with PVDF-HFP gel electrolyte for lithium ion microbatteries

In order to improve the discharge capacity in lithium ion microbatteries, a thick-film cathode was fabricated by a screen printing using LiCoO₂ pastes. The printed cathode showed a different discharge curves when the cell was tested using various (liquid, gel and solid-state) electrolytes. When a cell test was performed with organic liquid electrolyte, the maximum discharge capacity was 200 μAh cm⁻², which corresponded to approximately 133 mAh g⁻¹ when the loading weight of LiCoO₂ was calculated. An all-solid-state microbattery could be assembled using sputtered LiPON electrolyte, an evaporated Li anode, and printed LiCoO₂ cathode films without delamination or electrical problems. However, the highest discharge capacity showed a very small value (7 μAh cm⁻²). This problem could be improved using a poly(vinylidene fluoride-hexafluoro propylene) (PVDF-HFP) gel electrolyte, which enhanced the contact area and adhesion force between cathode and electrolyte. The discharge value of this cell was measured as approximately 164 μAh cm⁻² (≈110 mAh g⁻¹). As the PVDF-HFP electrolyte had a relatively soft contact property with higher ionic conductance, the cell performance was improved. In addition, the cell can be fabricated in a leakage-free process, which can resolve many safety problems. According to these results, there is a significant possibility that a film prepared using the aforementioned paste with screen printing and PVDF-HFP gel electrolyte is feasible for a microbattery.     

湿法制备聚偏氟乙烯-六氟丙烯聚合物隔膜的研究

采用湿法以PVDF-HFP(聚偏氟乙烯-六氟丙烯)为本体聚合物制备了聚合物锂离子电池用隔膜.正交实验结果分析表明,工艺条件中静置时间和水浴温度为主要影响因素,并研究了这两个因素对隔膜形貌和电化学性能的影响.采用交流阻抗技术和PC(碳酸丙烯酯)浸入实验分别测定了隔膜的电导率和吸液率.采用最佳的工艺条件:搅拌温度/静置时间/空气湿度/水浴温度为55℃/10min/45%/40℃制备的聚合物隔膜装配电池,首次充放电效率为87%,放电比容量335mAh/g,充电比容量291mAh/g,表现出良好的电化学性能.     

复合凝胶聚合物电解质的制备及电化学性能

以偏氟乙烯和六氟丙烯共聚物为基体,通过与聚甲基丙烯酸甲酯共混,加入导电盐LiPFs、增塑剂聚乙烯吡咯烷酮,制备了高电导率的复合凝胶聚合物电解质（CGPE）。用红外光谱测试了聚合物电解质膜的结构,用交流阻抗法测试了CGPE的导电性能,用线性扫描伏安法研究了它的电化学稳定性。测试了以CGPE为电解质制备的锂离子电池的充放电性能。结果表明,当聚甲基丙烯酸甲酯（PMMA）质量分数为20％时,CGPE电导率大于10^-3s／cm,在4．65V电化学窗口以下稳定。以磷酸亚铁锂为正极时,在0．1C和0．2C倍率下放电时,聚合物电解质电池的首次放电容量分别为138mAh／g和98．3mAh／g。     

Enhanced performance of a quasi-solid-state dye-sensitized solar cell with aluminum nitride in its gel polymer electrolyte

The effects of incorporation of aluminum nitride (AlN) in the gel polymer electrolyte (GPE) of a quasi-solid-state dye-sensitized solar cell (DSSC) were studied in terms of performance of the cell. The electrolyte, consisting of lithium iodide (LiI), iodine (I₂), and 4-tert-butylpyridine (TBP) in 3-methoxypropionitrile (MPN), was solidified with poly(vinyidene fluoride-co-hexafluoro propylene) (PVDF-HFP). The 0.05, 0.1, 0.3, and 0.5 wt% of AlN were added to the electrolyte for this study. XRD analysis showed a reduction of crystallinity in the polymer PVDF-HFP for all the additions of AlN. The DSSC fabricated with a GPE containing 0.1 wt% AlN showed a short-circuit current density (J_SC) and power-conversion efficiency (η) of 12.92±0.54 mA/cm² and 5.27±0.23%, respectively, at 100 mW/cm² illumination, in contrast to the corresponding values of 11.52±0.21 mA/cm² and 4.75±0.08% for a cell without AlN. The increases both in J_SC and in η of the promoted DSSC are attributed to the higher apparent diffusion coefficient of I⁻ in its electrolyte (3.52×10⁻⁶ cm²/s), compared to that in the electrolyte without AlN of a DSSC (2.97×10⁻⁶ cm²/s). At-rest stability of the quasi-solid-state DSSC with 0.1 wt% of AlN was found to decrease hardly by 5% and 7% at room temperature and at 40 °C, respectively, after 1000 h duration. The DSSC with a liquid electrolyte showed a decrease of about 40% at room temperature, while it virtually lost its performance in about 150 h at 40 °C. Explanations are further substantiated by means of electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and by porosity measurements.     

Performance characteristics of guanine incorporated PVDF-HFP/PEO polymer blend electrolytes with binary iodide salts for dye-sensitized solar cells

In this work, we have investigated the influence of guanine as an organic dopant in dye-sensitized solar cell (DSSC) based on poly(vinylidinefluoride-co-hexafluoropropylene) (PVDF-HFP)/polyethylene oxide (PEO) polymer blend electrolyte along with binary iodide salts (potassium iodide (KI) and tetrabutylammonium iodide (TBAI)) and iodine (I₂). The PVDF-HFP/KI + TBAI/I₂, PVDF-HFP/PEO/KI + TBAI/I₂ and guanine incorporated PVDF-HFP/PEO/KI + TBAI/I₂ electrolytes were prepared by solution casting technique using DMF as solvent. The PVDF-HFP/KI + TBAI/I₂ electrolyte showed an ionic conductivity value of 9.99 × 10⁻⁵ Scm⁻¹, whereas, it was found to be increased to 4.53 × 10⁻⁵ Scm⁻¹ when PEO was blended with PVDF-HFP/KI + TBAI/I₂ electrolyte. However, a maximum ionic conductivity value of 3.67 × 10⁻⁴ Scm⁻¹ was obtained for guanine incorporated PVDF-HFP/PEO/KI + TBAI/I₂ blend electrolyte. The photovoltaic properties of all these polymer electrolytes in DSSCs were characterized. As a consequence, the power conversion efficiency of the guanine incorporated PVDF-HFP/PEO/KI + TBAI/I₂ electrolyte based DSSC was significantly improved to 4.98% compared with PVDF-HFP/PEO/KI + TBAI/I₂ electrolyte based DSSC (2.46%). These results revealed that the guanine can be an effective organic dopant to enhance the performance of DSSCs.     

聚偏氟乙烯-六氟丙烯多孔隔膜的制备工艺

采用倒相法制备PVDF-HFP(聚偏氟乙烯-六氟丙烯)多孔薄膜。主要研究了聚合物溶胶的制备工艺条件、薄膜的制作工艺、不同溶剂和非溶剂对薄膜孔结构及性能的影响。研究表明:以丙酮为溶剂、蒸馏水为非溶剂的溶胶在60 ℃下搅拌2 h,采用干法制膜,薄膜厚度控制在50 μm左右,这样制得的薄膜能满足聚合物锂离子蓄电池对隔膜材料性能的要求。以这种隔膜制作的聚合物锂离子蓄电池表现出良好的充放电性能。     

PVDF-HFP/TiO2多孔杂化电解质膜的研究

将溶胶-凝胶法与相转化法结合,以偏氟乙烯-六氟丙烯共聚物(PVDF-HFP)、钛酸四丁酯为主要原料,制备了PVDF-HFP/TiO2多孔杂化膜,经电解液活化后得到PVDF-HFP/TiO2多孔杂化电解质膜。采用扫描电子显微镜法(SEM)、透射电子显微镜法(TEM)、交流阻抗法等手段对多孔杂化电解质膜的结构和性能进行了测试分析。研究结果表明,与PVDF-HFP多孔电解质膜相比,PVDF-HFP/TiO2多孔杂化电解质膜在微孔结构、离子电导率等方面都有明显的改善;同时,随着TiO2含量的增加,也增大了多孔杂化膜的孔隙率和电导率。     

Nanocrystalline cellulose reinforced PVDF-HFP membranes for membrane distillation application

Polyvinylidenefluoride-co-hexafluoropropylene (PVDF-HFP) membranes containing different amounts of nanocrystalline cellulose (NCC) were fabricated by electrospining technique for application in membrane distillation (MD). The effect of incorporating NCC on the mechanical strength, morphology, pore size distribution, and liquid entry pressure (water) of the fibrous was investigated. Incorporation of NCC in PVDF-HFP matrix improved the tensile strength and Young's modulus and narrowed down the pore size distribution of the fabricated membranes. Liquid entry pressure, which is an important parameter to ensure high salt rejection of the membranes in MD, was improved from ~ 19 psi to ~ 27 psi with the addition of 2 wt.% NCC. Fabricated membranes were tested in direct contact membrane distillation (DCMD). MD operation data revealed water flux of 10.2–11.5 Lh^− 1 m^− 2 with salt rejection of 99% for these NCC-incorporated membranes.     

倒相法制备PVDF-HFP基复合微孔聚合物电解质

为改善纳米粒子在聚合物电解质中的分散效果,采用倒相制膜法,以纳米SiO₂为填料,以OP-10为分散剂,制备复合微孔聚偏氟乙烯-六氟丙烯基电解质PVDF-HFP-SiO₂(OP-10)．用SEM、XRD、交流阻抗法等测试手段对电解质的微观形貌、内部结构和电化学相关性能等进行表征,结果表明:SiO₂的加入降低了聚合物电解质膜的结晶度,增强了电解质的拉伸强度,提高了PVDF-HFP-SiO₂(OP-10)聚合物电解质的电导率,在20 ℃时,可达到490×10-3 S·cm-1,电化学稳定窗口为53 V,电解质的离子迁移数为083．分散剂OP-10的加入改善了纳米SiO₂与基质的界面相容性,改善了SiO₂在基质中的分散度．