LiCoO<Subscript>2</Subscript> electrode/electrolyte interface of Li-ion batteries investigated by electrochemical impedance spectroscopy

The storage behavior and the first delithiation of LiCoO₂ electrode in 1 mol/L LiPF₆-EC:DMC:DEC electrolyte were investigated by electrochemical impedance spectroscopy (EIS). It has found that, along with the increase of storage time, the thickness of SEI film increases, and some organic carbonate lithium compounds are formed due to spontaneous reactions occurring between the LiCoO₂ electrode and the electrolyte. When electrode potential is changed from 3.8 to 3.95 V, the reversible breakdown of the resistive SEI film occurs, which is attributed to the reversible dissolution of the SEI film component. With the increase of electrode potential, the thickness of SEI film increases rapidly above 4.2 V, due to overcharge reactions. The inductive loop observed in impedance spectra of the LiCoO₂ electrode in Li/LiCoO₂ cells is attributed to the formation of a Li_1−x CoO₂/LiCoO₂ concentration cell. Moreover, it has been demonstrated that the lithium-ion insertion-deinsertion in LiCoO₂ hosts can be well described by both Langmuir and Frumkin insertion isotherms, and the symmetry factor of charge transfer has been evaluated at 0.5. Supported by the Special Funds for Major State Basic Research Project of China (Grant No. 2002CB211804)     

Impedance Studies of Spinel LiMn2O4 Electrode/electrolyte Interfaces

The formation process of solid electrolyte interphase（SEI） film on spinel LiMn2O4 electrode surface was studied by electrochemical impedance spectroscopy（EIS） during the initial storage in 1 mol/L LiPF6-EC：DMC：DEC electrolyte and in the subsequent first charge-discharge cycle. It has been demonstrated that the SEI film thickness increased with the increase of storage time and spontaneous reactions occurring between spinel LiMn2O4 electrode and electrolyte can be prevented by the SEI film. In the first charge-discharge cycle succeeding the storage, the electrolyte oxidation coupled with Li-ion insertion is evidenced as the main origin to increase the resistance of SEI film. The results also confirm that the variations of the charge transfer resistance（Rot） with the electrode potential（E） can be well described using a classical equation.     

锂离子电池有机电解液材料研究进展

综述了锂离子电池有机电解液材料的研究现状。锂离子电池有机电解液主要由电解质锂盐、有机溶剂和添加剂三个部分组成,新型电解质锂盐的研究开发可分为三个方面：（1）LiTFSI及其类似物;（2）络合硼酸锂化合物;（3）络合磷酸锂化合物。有机溶剂的研究工作主要集中在新型有机溶剂的开发上。最重要的添加剂主要有三类：（1）主要用以改善碳负极SEI膜性能的添加剂;（2）过充电保护添加剂;（3）配体添加剂。     

Goethite nanorods as anode electrode materials for rechargeable Li-ion batteries

Although various transition metal oxides have been reported to act as low potential Li insertion hosts, the oxyhydroxides have remained unexplored to date. We show here that the hydroxide ions present in transition metal oxyhydroxides do not interfere with the lithium uptake and extraction, permitting very good reversibility of the reduction/oxidation reactions. Goethite (α-FeOOH) nanocrystals can uptake and extract large amount of Li via the conversion reaction mechanism, providing a reversible capacity of 500 mA h g⁻¹ at an average potential of 0.85 V vs. Li/Li⁺. The mechanism was examined using a combination of X-ray diffraction, electron microscopy, and the corresponding selected area electron diffractions (SAEDs). The α-FeOOH is reduced into nanoparticles of metallic Fe⁰ embedded in an amorphous matrix of Li₂O and LiOH in the first discharge; the subsequent cyclings are redox reactions between metallic Fe⁰ and Fe₂O₃ clusters.     

PVDF-HFP composite polymer electrolyte with excellent electrochemical properties for Li-ion batteries

Poly (vinylidene fluoride-co-hexafluoropropylene)-based composite polymer electrolyte (CPE) was prepared by phase inversion technique. In this work, we first applied a novel surface-modified sub-micro-sized alumina, PC-401, as ceramic filler. Various electrochemical methods were applied to investigate the electrochemical properties of the polymer electrolytes. We found that the CPE with 10 wt.% PC-401 has excellent electrochemical properties, including the ionic conductivity as high as 0.89 mS cm⁻¹ and the Li-ion transference number of 0.46. Polymer Li-ion batteries using LiFePO₄ as cathode active material exhibited excellent cycling and high-temperature performances. PC-401 shows a promising applicability in the preparation of polymer electrolyte with high electrochemical properties.     

柠檬酸溶胶凝胶法制备LiCoO_2电极材料及其表征

目前研究较多的锂离子电池正极材料主要有LiCoO2、LiNiO2和LiMn2O4犤1犦,虽然LiCoO2的成本相对较高,但LiCoO2具有最为优良的电化学性能,如高且平稳的充放电平台、高比容量以及良好的循环性能犤2犦,是目前应用最广泛的商品化电极材料。LiCoO2材料主要采用高温固相法犤3～5犦制备,该方法工艺简单,容易实现大规模生产,但缺点是需要较高的焙烧温度和较长的焙烧时间,且反应原料混合均匀程度有限,易导致非化学计量、非均相以及不规则的颗粒形貌等,因此材料的比容量、循环寿命等电化学性能以及反应的可控性还不甚理想。研究表明犤6犦电极材…     

温度对LiCoO2中锂离子嵌脱过程的影响

摘要 运用EIS研究了LiCoO2正极在1M LiPF6-EC:DEC:DMC和1M LiPF6-PC:DMC+5%VC电解液中0~30℃范围内阻抗谱特征、SEI膜阻抗、电子电阻和电荷传递电阻等随温度的变化。结果表明,LiCoO2正极的EIS谱特征与温度有关,随温度的升高其低频区域在1M LiPF6-EC:DEC:DMC和1M LiPF6-PC:DMC+5%VC电解液中分别于10和20℃出现反映锂离子固态扩散的斜线。LiCoO2正极在 1M LiPF6-EC:DEC:DMC和1M LiPF6-PC:DMC+5%VC电解液中,锂离子迁移通过SEI膜的离子跳跃能垒平均值分别为37.74和26.55KJ/mol;电子电导率的热激活化能平均值分别为39.08和53.81KJ/mol;嵌入反应活化能平均值分别为68.97和73.73KJ/mol。     

Nanotopography and electrochemical impedance spectroscopy of palladium deposited on different electrode materials

The objective of this work was to describe the characteristics of chemically and electrochemically deposited Pd surface layers on HOPG and polycrystalline gold electrode, using in situ ECSTM and EIS measurements, and SEM-EDX element analysis. Pd surface layers were deposited, in successive voltammetric cycles, and anodically dissolved in 0.01 M HCl+0.01 M (NH₄)₂PdCl₄ aqueous electrolyte. Both of the electrode materials used in the study were treated as standard testing electrodes: (i) HOPG for STM/ECSTM measurements, and (ii) polycrystalline Au as the well known working electrode in various electro-analytical applications. The elements surface analysis and nano-surface pictures were used to interpret the EIS diagrams and electrical equivalent circuits. Pd chemical and electrochemical deposition on the HOPG surface was compared with the same process on the polycrystalline gold electrode, on which palladium can be electrodeposited only by means of electrochemical cathodic deposition. Surface topographies of the electrodeposited palladium layers on HOPG and Au were completely different. The equivalent electrical circuits were fitted and the surface roughness of the investigated electrodes calculated. Relations between the surface topography, EIS and SEM-EDX, and interface model of the electrolyte solution electrodeposited Pd layer matrix electrode were proposed.     

Infrared and Raman spectroscopy of nanostructured LT-LiCoO2 cathodes for Li-ion rechargeable batteries

Nano-engineered electrodes, such as porous LiCoO₂, exhibit improved electrochemical performance compared to the non-porous LiCoO₂ analogue. Structural studies of the pore walls composing the nanostructured LiCoO₂ materials have focused on long-range (diffraction) methods. However, the powder diffraction patterns of the low-temperature (LT) and high-temperature (HT) phases of non-porous LiCoO₂ are very similar and distinguishing the two phases can be challenging. In this work, infrared and Raman spectroscopy are used to unambiguously assign the LiCoO₂ crystalline domains present in two porous compounds (nanowire LiCoO₂ and mesoporous LiCoO₂) as LT-LiCoO₂. Moreover, the appearance of new bands in the infrared spectrum of LiCoO₂ nanowires might signal the presence of disordered LiCoO₂ domains that are XRD silent.     

Electrochemical impedance spectroscopy analysis of chalcopyrite CuFeS2 electrodes

A chalcopyrite CuFeS₂ electrode obtained from the “El Teniente” mine has been studied by Electrochemical Impedance Spectroscopy (EIS) in an alkaline solution for different oxidation potentials. The experimental results can be interpreted from a Randles equivalent circuit, V_dc<0.4 V vs. saturated calomel electrode (SCE), and a surface layer model for V_dc>0.4 V vs. SCE. From these results, the variation with the d.c. applied potentials of charge transfer electrical resistance of the redox reaction, the double layer capacitance and other characteristic parameters are considered.     

Porous nanostructured V2O5 film electrode with excellent Li-ion intercalation properties

Porous nanostructured V₂O₅ films were prepared by electrodeposition from V₂O₅ sol with the addition of block copolymer Pluoronic P123, and they can be readily applied as Li-ion battery cathode without adding any polymer binder or conductive additives. SEM images showed an ideal morphology for Li⁺ intercalation favored charge transfer kinetics, which is a combination of homogeneously distributed nano-pores and V₂O₅ nanoparticles. Electrochemical measurements revealed that, the porous nanostructured V₂O₅ films have a high discharge capacity of 160 mAh/g at 9 A/g, and maintain 240 mAh/g after 40 cycles at 300 mA/g. The excellent Li⁺ intercalation property could be ascribed to the high surface area, sufficient contact between electrode materials and electrolyte, short Li⁺ diffusion path, as well as the good accommodation for volume change which are benefited from homogeneously distributed nano-pores and V₂O₅ nanoparticles.     

Effect of nanoscale CeO<Subscript>2</Subscript> on PVDF-HFP-based nanocomposite porous polymer electrolytes for Li-ion batteries

New poly (vinylidenefluoride-co-hexafluoro propylene) (PVDF-HFP)/CeO₂-based microcomposite porous polymer membranes (MCPPM) and nanocomposite porous polymer membranes (NCPPM) were prepared by phase inversion technique using N-methyl 2-pyrrolidone (NMP) as a solvent and deionized water as a nonsolvent. Phase inversion occurred on the MCPPM/NCPPM when it is treated by deionized water (nonsolvent). Microcomposite porous polymer electrolytes (MCPPE) and nanocomposite porous polymer electrolytes (NCPPE) were obtained from their composite porous polymer membranes when immersed in 1.0 M LiClO₄ in a mixture of ethylene carbonate/dimethyl carbonate (EC/DMC) (v/v = 1:1) electrolyte solution. The structure and porous morphology of both composite porous polymer membranes was examined by scanning electron microscope (SEM) analysis. Thermal behavior of both MCPPM/NCPPM was investigated from DSC analysis. Optimized filler (8 wt% CeO₂) added to the NCPPM increases the porosity (72%) than MCPPM (59%). The results showed that the NCPPE has high electrolyte solution uptake (150%) and maximum ionic conductivity value of 2.47 × 10⁻³ S cm⁻¹ at room temperature. The NCPPE (8 wt% CeO₂) between the lithium metal electrodes were found to have low interfacial resistance (760 Ω cm²) and wide electrochemical stability up to 4.7 V (vs Li/Li⁺) investigated by impedance spectra and linear sweep voltammetry (LSV), respectively. A prototype battery, which consists of NCPPE between the graphite anode and LiCoO₂ cathode, proves good cycling performance at a discharge rate of C/2 for Li-ion polymer batteries.     

Technology of electrochemical impedance spectroscopy for an energy-sustainable society

Electrochemical impedance spectroscopy has been widely used to understand the chemistry and physics of battery systems. This review covers electrochemical impedance spectroscopy used for the interpretation of impedance data of lithium-ion batteries (LIBs) from advanced equivalent circuit models to the mathematical model, which is developed by John Newman. In addition, as a method to realize an energy-sustainable society using diagnostics based on the combination of LIBs and electrochemical impedance spectroscopy, on-board diagnostics of battery packs are achieved based on an input signal generated by a power controller in a battery management system instead of the conventionally used frequency response analyzer. The diagnostic system is applicable to energy management systems which are installed in homes, buildings, and communities, accumulating the impedance data on state of health of LIBs. Finally, a future possibility regarding the diagnostics of battery packs coupled with the machine learning of impedance data is introduced.     

Original electrochemical mechanisms of CaSnO3 and CaSnSiO5 as anode materials for Li-ion batteries

Calcium stannate (CaSnO₃) and malayaite (CaSnSiO₅) were synthesized by means of a high temperature solid-state reaction. Their crystal structures and morphologies were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy; their electrochemical properties were analyzed by galvanostatic tests. The amorphization of the initial electrode materials was followed by XRD. The first discharge of the oxides CaSnO₃ and CaSnSiO₅ shows a plateau at low potential, which is due to the progressive formation of Li–Ca–Sn and/or Li–Sn alloys as shown by ¹¹⁹Sn Mössbauer spectroscopy. The results reveal similar electrochemical mechanisms for CaSnO₃ and CaSnSiO₅ but they completely differ from those related to SnO₂.     

Hierarchically structured MoO2/dopamine-derived carbon spheres as intercalation electrodes for lithium-ion batteries

A hydrogen peroxide initiated sol-gel process involving molybdenum transformation in the presence of dopamine (Dopa) hydrochloride excess produced the metastable precipitate composed of polydopamine (PDopa) spheres coated with Dopa preintercalated molybdenum oxide, (Dopa)_xMoO_y@PDopa. The hydrothermal treatment (HT) of the (Dopa)_xMoO_y@PDopa precursor resulted in the simultaneous carbonization of Dopa and molybdenum reduction generating MoO₂ nanoplatelets distributed and confined on the surface of the Dopa-derived carbon matrix (HT-MoO₂/C). The consecutive annealing (An) of the HT-MoO₂/C sample at 600 °C under Ar atmosphere led to the formation of MoO₂ with increased Mo oxidation state and improved structural stability (AnHT-MoO₂/C). Annealing had also further facilitated interaction between the molybdenum-derived and Dopa-derived components resulting in the modification of the carbon matrix confirmed by Raman spectroscopy. Morphology of both materials is best described as Dopa-derived carbon spheres decorated with MoO₂ nanoplatelets. These integrated metal oxide and carbon structures were tested as electrodes for lithium-ion batteries in the potential window that corresponds to the intercalation mechanism of charge storage. The AnHT-MoO₂/C electrode showed enhanced electrochemical activity, with an initial specific discharge capacity of 260 mAh/g and capacity retention of 67% after 50 cycles, compared to the HT-MoO₂/C electrode which exhibited an initial specific discharge capacity of 235 mAh g^?1 and capacity retention of 47% after 50 cycles. The rate capability experiments revealed that the capacity of 93 mAh/g and 120 mAh/g was delivered by the HT-MoO₂/C and AnHT-MoO₂/C electrodes, respectively, when the current density was increased to 100 mA/g. The improved specific capacity, electrochemical stability, and rate capability achieved after annealing were attributed to higher crystallinity of MoO₂, increased oxidation state of Mo, and formation of the tighter MoO₂/carbon contact accompanied by the annealing assisted interaction between MoO₂ and Dopa-derived carbon.     

Fabrication of solid thin film electrolyte and LiCoO2 by aerosol flame pyrolysis deposition

Aerosol flame pyrolysis deposition method was applied to deposit the oxide glass electrolyte film and LiCoO₂ cathode for thin film type Li-ion secondary battery. The thicknesses of as-deposited porous LiCoO₂ and Li₂O–B₂O₃–P₂O₅ electrolyte film were about 6 μm and 15 μm, respectively. The deposited LiCoO₂ was sintered for 2 min at 700 °C to make partially densified cathode layer, and the deposited Li₂O–P₂O₅–B₂O₃ glass film completely densified by the sintering at 700 °C for 1 h. After solid state sintering process the thicknesses were reduced to approximately 4 μm and 6 μm, respectively. The cathode and electrolyte layers were deposited by continuous deposition process and integrated into a layer by co-sintering. It was demonstrated that Aerosol flame deposition is one of the good candidates for the fabrication of thin film battery.     

XPS valence characterization of lithium salts as a tool to study electrode/electrolyte interfaces of Li-ion batteries

X-ray photoelectron valence spectra of lithium salts LiBF4, LiPF6, LiTFSI, and LiBETI have been recorded and analyzed by means of density functional theory (DFT) calculations, with good agreement between experimental and calculated spectra. The results of this study are used to characterize electrode/electrolyte interfaces of graphite negative electrodes in Li-ion batteries using organic carbonate electrolytes containing LiTFSI or LiBETI salts. By a combined X-ray photoelectron spectroscopy (XPS) core peaks/valence analysis, we identify the main constituents of the interface. Differences in the surface layers' composition can be evidenced, depending on whether LiTFSI or LiBETI is used as the lithium salt.     

In-situ FTIR investigations on the reduction of vinylene electrolyte additives suitable for use in lithium-ion batteries

Lithium-ion batteries operate beyond the thermodynamic stability of the aprotic organic electrolyte used and electrolyte decomposition occurs at both electrodes. The electrolyte must therefore be composed in a way that its decomposition products form a film on the electrodes which stops the decomposition reactions but is still permeable to the Li(+) cations which are the charge carriers. At the graphite anode, this film is commonly referred to as a solid electrolyte interphase (SEI). Aprotic organic compounds containing vinylene groups can form an effective SEI on a graphitic anode. As examples, vinyl acetate (VA) and acrylonitrile (AN) have been investigated by in-situ Fourier transform infrared (FTIR) spectroscopy in a specially developed IR cell. The measurements focus on electrolyte decomposition and the mechanism of SEI formation in the presence of VA and AN. We conclude that cathodic reduction of the vinylene groups (i.e., via reduction of the double bond) in the electrolyte additives is the initiating and thus a most important step of the SEI-formation process, even in an electrolyte which contains only a few percent (i.e. electrolyte additive amounts) of the compound. The possibility of electropolymerization of the vinylene monomers in the battery electrolytes used is critically discussed on the basis of the IR data obtained.     

锂空气电池空气电极LiCoO2电催化性能研究

自设计建立锂空气电池实验装置,研究以掺入LiCoO2作为电催化剂的空气正极的电化学性能及其放电前后催化剂结构的变化.循环伏安、XRD及充放电测试等表明,LiCoO2能够很大程度地改善空气电极的放电性能.尤其是在放电前,将掺有LiCoO2的空气正极充电至4.1 V,此时LiCoO2的Co元素呈现较高的价态（Co3＋/Co4＋）,催化作用因此更加显著.