Investigation of Water-Soluble Binders for LiNi0.5Mn1.5O4-Based Full Cells

Two water-soluble binders of carboxymethyl cellulose (CMC) and sodium alginate (SA) have been studied in comparison with N-methylpyrrolidone-soluble poly(vinylidene difluoride–co-hexafluoropropylene) (PVdF-HFP) to understand their effect on the electrochemical performance of a high-voltage lithium nickel manganese oxide (LNMO) cathode. The electrochemical performance has been investigated in full cells using a Li₄Ti₅O₁₂ (LTO) anode. At room temperature, LNMO cathodes prepared with aqueous binders provided a similar electrochemical performance as those prepared with PVdF-HFP. However, at 55 °C, the full cells containing LNMO with the aqueous binders showed higher cycling stability. The results are supported by intermittent current interruption resistance measurements, wherein the electrodes with SA showed lower resistance. The surface layer formed on the electrodes after cycling has been characterized by X-ray photoelectron spectroscopy. The amount of transition metal dissolutions was comparable for all three cells. However, the amount of hydrogen fluoride (HF) content in the electrolyte cycled at 55 °C is lower in the cell with the SA binder. These results suggest that use of water-soluble binders could provide a practical and more sustainable alternative to PVdF-based binders for the fabrication of LNMO electrodes.     

Surfactant-Mediated and Morphology-Controlled Nanostructured LiFePO4/Carbon Composite as a Promising Cathode Material for Li-Ion Batteries

The synthesis of morphology-controlled carbon-coated nanostructured LiFePO₄ (LFP/Carbon) cathode materials by surfactant-assisted hydrothermal method using block copolymers is reported. The resulting nanocrystalline high surface area materials were coated with carbon and designated as LFP/C123 and LFP/C311. All the materials were systematically characterized by various analytical, spectroscopic and imaging techniques. The reverse structure of the surfactant Pluronic® 31R1 (PPO-PEO-PPO) in comparison to Pluronic® P123 (PEO-PPO-PEO) played a vital role in controlling the particle size and morphology which in turn ameliorate the electrochemical performance in terms of reversible specific capacity (163 mAh g⁻¹ and 140 mAh g⁻¹ at 0.1 C for LFP/C311 and LFP/C123, respectively). In addition, LFP/C311 demonstrated excellent electrochemical performance including lower charge transfer resistance (146.3 Ω) and excellent cycling stability (95 % capacity retention at 1 C after 100 cycles) and high rate capability (163.2 mAh g⁻¹ at 0.1 C; 147.1 mAh g⁻¹ at 1 C). The better performance of the former is attributed to LFP nanoparticles (<50 nm) with a specific spindle-shaped morphology. Further, we have also evaluated the electrode performance with the use of both PVDF and CMC binders employed for the electrode fabrication.     

A Porous Mooncake-Shaped Li4Ti5O12 Anode Material Modified by SmF3 and Its Electrochemical Performance in Lithium Ion Batteries

Reasonably designing and synthesizing advanced electrode materials is significant to enhance the electrochemical performance of lithium ion batteries (LIBs). Herein, a metal–organic framework (MOF, Mil-125) was used as a precursor and template to successfully synthesize the porous mooncake-shaped Li₄Ti₅O₁₂ (LTO) anode material assembled from nanoparticles. Even more critical, SmF₃ was used to modify the prepared porous mooncake-shaped LTO material. The SmF₃-modified LTO maintained a porous mooncake-shaped structure with a large specific surface area, and the SmF₃ nanoparticles were observed to be attach on the surface of the LTO material. It has been proven that the SmF₃ modification can further facilitate the transition from Ti⁴⁺ to Ti³⁺, reduce the polarization of electrode, decrease charge transfer impedance (R_ct) and solid electrolyte interface impedance (R_sei), and increase the lithium ion diffusion coefficient (D_Li), thereby enhancing the electrochemical performance of LTO. Therefore, the porous mooncake-shaped LTO modified using 2 wt % SmF₃ displays a large specific discharge capacity of 143.8 mAh g⁻¹ with an increment of 79.16 % compared to pure LTO at a high rate of 10 C (1 C=170 mAh g⁻¹), and shows a high retention rate of 96.4 % after 500 cycles at 5 C-rate.     

Electrochemical quartz crystal microbalance analysis of the cathodic process in a lithium-ion battery

The surface processes at carbon and platinum electrodes have been studied using the electrochemical quartz crystal microbalance technique in organic electrolyte solutions for lithium ion batteries. The changes in resonance frequency were analyzed as a function of the electrode potential, indicating that the process depended not only on the electrode material but also on the cathode potential. In the solution containing LiBF₄ as the electrolyte, the main product at the platinum surface was Li₂CO₃ and LiF, whereas formation of lithium alkylcarbonates was the primary process at the platinum and carbon electrodes in LiPF₆ solution.     

锂硫电池硫正极粘结剂的比较研究

本文将三类粘结剂体系(PVDF、LA133和CMC+SBR)用于构筑锂硫电池硫正极,表征了不同粘结剂材料的官能团结构、结晶性能、热力学性质、电解液吸收性与粘结强度,考察了粘结剂种类对电极电化学性能的影响。结果表明,由1∶1质量比的CMC+SBR制作的硫电极吸液率低,剥离强度低,循环稳定性较差;无定形LA133支持高的粘结强度,维稳电极结构的能力强;PVDF因半结晶状态制约粘结效果,制作的电极吸液量高,但电荷转移阻抗小。基于PVDF制作的硫正极具有相对最优的电化学性能,其0.2C下循环100周后保留的可逆容量达722mAh·g~(-1),容量保持率达82.9%。     

Cathode material for sodium-ion batteries based on manganese hexacyanoferrate: the role of the binder component

Sodium manganese hexacyanoferrate (NaMnHCF) was synthesized by a hydrothermal method and investigated as a cathode material for sodium-ion batteries. The morphology and the structure of NaMnHCF were investigated by X-ray diffraction, scanning electron microscopy, and EDX analysis. New composition of NaMnHCF cathode material for sodium-ion batteries with eco-friendly water-based binder consisting of conducting polymer poly-3,4-ethylenedioxythiopene/polystyrene sulfonate (PEDOT:PSS) dispersion and carboxymethyl cellulose (СМС) was proposed. The electrochemical properties of NaMnHCF cathode material with conductive polymer binder were investigated by cyclic voltammetry and galvanostatic charge-discharge, and the results were compared with the performance of a conventional PVDF-bound material. It was shown that the initial discharge capacity of electrodes with conductive binder is 130 mAh g⁻¹, whereas the initial discharge capacity of PVDF-bound electrodes was 109 mAh g⁻¹ (both at current density 120 mA g⁻¹, values normalized by NaMnHCF mass). The material with conductive binder also has better rate capability; however, it is losing in cycling capability to the electrode composition with conventional PVDF binder.

     

Conformal Surface Coatings to Enable High Volume Expansion Li‐Ion Anode Materials

An alumina surface coating is demonstrated to improve electrochemical performance of MoO₃ nanoparticles as high capacity/high‐volume expansion anodes for Li‐ion batteries. Thin, conformal surface coatings were grown using atomic layer deposition (ALD) that relies on self‐limiting surface reactions. ALD coatings were tested on both individual nanoparticles and prefabricated electrodes containing conductive additive and binder. The coated and non‐coated materials were characterized using transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, electrochemical impedance spectroscopy, and galvanostatic charge/discharge cycling. Importantly, increased stability and capacity retention was only observed when the fully fabricated electrode was coated. The alumina layer both improves the adhesion of the entire electrode, during volume expansion/contraction and protects the nanoparticle surfaces. Coating the entire electrode also allows for an important carbothermal reduction process that occurs during electrode pre‐heat treatment. ALD is thus demonstrated as a novel and necessary method that may be employed to coat the tortuous network of a battery electrode.     

Li4Ti5O12 Nanoparticles Prepared with Gel-hydrothermal Process as a High Performance Anode Material for Li-ion Batteries

Li₄Ti₅O₁₂ (LTO) nanoparticles were prepared by gel‐hydrothermal process and subsequent calcination treatment. Calcination treatment led to structural water removal, decomposition of organics and primary formation of LTO. The formation temperature of spinel LTO nanoparticles was lower than that of bulk materials counterpart prepared by solid‐state reaction or by sol‐gel processing. Based on the thermal gravimetric analysis (TG) and differential thermal gravimetric (DTG), samples calcined at different temperatures (350, 500 and 700°C) were characterized by X‐ray diffraction (XRD), field emitting scanning electron microscopy (FESEM), transmission electron microscopy (TEM), cyclic voltammogram and charge‐discharge cycling tests. A phase transition during the calcination process was observed from the XRD patterns. And the sample calcined at 500°C had a distribution of diameters around 20 nm and exhibited large capacity and good high rate capability. The well reversible cyclic voltammetric results of both electrodes indicated enhanced electrochemical kinetics for lithium insertion. It was found that the Li₄Ti₅O₁₂ anode material prepared through gel‐hydrothermal process, when being cycled at 8 C, could preserve 76.6% of the capacity at 0.3 C. Meanwhile, the discharge capacity can reach up to 160.3 mAh·g^?1 even after 100 cycles at 1 C, close to the theoretical capacity of 175 mAh·g^?1. The gel‐hydrothermal method seemed to be a promising method to synthesize LTO nanoparticles with good application in lithium ion batteries and electrochemical cells.     

High-performance pyrrolidinium-based poly(ionic liquid) binders for Li-ion and Li-air batteries

The role of binders is crucial to achieve high performance and long cycle lifes in next-generation electrodes for lithium batteries. Currently used binders in electrode configurations, such as poly(vinylidene difluoride) (PVDF) are inactive polymers that do not transport lithium ions themselves, causing restrictions for high-power applications. Thus, developing innovative binders with an affinity towards lithium mobility is important for both lithium-ion and lithium-air batteries. In this work, we present for the first time the use of PDADMA poly(ionic liquid)s with fluorinated anions (FSI, TFSI, BETI, and CFSO) as cathode binders in Li-ion and Li-air batteries. The high-voltage NMC 532 cathodes with fluorinated PDADMA binders showed improved cells performances as: capacity values, rate performance, and cycling stability in accelerating aging conditions dedicated for more environmental-friendly mobility applications. Especially, PDADMA-CFSO binder in cathodes shows a cell capacity increase of 26% at 5C (12 min charge), when compared to PVDF one. Moreover, the fluorinated PDADMA binders in cathode improve the discharge capacities in Li–O₂ cells, both with liquid and solid gel polymer electrolytes. Impressively, the Coulombic efficiency improves by 146% and the cycling capacity by 70% in solid-state Li–O₂ cells using PDADMA-CFSO binder in the cathode, instead of common lithiated Nafion. All in all, the proposed fluorinated PDADMA Poly(ionic liquid)s can be a highly competitive alternative to conventional binders used nowadays in Li-ion and Li-air batteries.     

高性能锂离子电池正极黏合剂研究进展

正极黏合剂是维持锂离子电池正极结构稳定性的关键材料,对于锂离子电池的能量密度及安全性具有重要作用.本文综述了锂离子电池正极黏合剂材料的研究及应用进展,重点介绍了锂离子电池正极黏合剂对于正极材料及锂离子电池电化学性能的影响,详细总结了以聚偏氟乙烯(PVDF)、聚酰亚胺(PI)、功能性聚合物黏合剂为代表的油溶性黏合剂和以聚丙烯酸(PAA)、羧甲基纤维素(CMC)为代表的水溶性黏合剂的特点:PVDF具备良好的化学稳定性,黏合效果较好,但耐高温性能差且在电解液中易溶胀;PI的耐高温性能优异,机械性能较好,但成本相对较高;功能性聚合物黏合剂具备良好的导电性,可有效抑制Li-S锂电池中多硫化物的穿梭效应,但制备工艺复杂;PAA的柔性较好,抗高压能力较强,但是力学性能较差;CMC具有良好的分散性,机械强度较大,因脆性较大需与丁苯橡胶(SBR)配合使用.结合已有的研究报道,探讨了高性能锂离子电池先进正极黏合剂材料的未来发展方向及前景.     

High loading LiFePO<Subscript>4</Subscript> on activated carbon fiber cloth as a high capacity cathode for Li-ion battery

The LiFePO₄/carbon fiber (LFP/CF) cathodes were prepared by using activated carbon fiber cloth as current collector in place of conventional Al foil. The electrochemical properties of LFP/CF electrodes were analyzed by the cyclic voltammetry and galvanostatic charge/discharge tests. The results indicate that the activated carbon fiber cloth with high specific surface area and high porosity makes the LFP/CF electrode that possesses higher mass loading of 18–21 mg cm^–2 and stronger redox reaction ability compared with Al foil-based electrode. The LFP/CF electrode shows excellent rate performance and cycle stability. At 0.1C, the discharge capacity is up to 190.1 mAh g^–1 that exceeds the theoretical capacity due to the combination effect of battery and capacitor. Furthermore, the LFP/CF electrode shows an initial capacity of 150.4 mAh g^–1 at 1C with a capacity retention of 74.7% after 425 cycles, which is higher than 62.4% for LFP/Al foil electrode, and an initial discharge capacity of 130 mAh g^–1 at 5C with a capacity retention of 61.5% after 370 cycles. But this composite electrode is not suitable for charging/discharging at higher rate as 10C due to too much mass loading.     

Molybdenum Substitution for Improving the Charge Compensation and Activity of Li2MnO3

Lithium‐rich layer‐structured oxides xLi₂MnO₃? (1?x)LiMO₂ (0<x<1, M=Mn, Ni, Co, etc.) are interesting and potential cathode materials for high energy‐density lithium ion batteries. However, the characteristic charge compensation contributed by O^2? in Li₂MnO₃ leads to the evolution of oxygen during the initial Li⁺ ion extraction at high voltage and voltage fading in subsequent cycling, resulting in a safety hazard and poor cycling performance of the battery. Molybdenum substitution was performed in this work to provide another electron donor and to enhance the electrochemical activity of Li₂MnO₃‐based cathode materials. X‐ray diffraction and adsorption studies indicated that Mo⁵⁺ substitution expands the unit cell in the crystal lattice and weakens the Li?O and Mn?O bonds, as well as enhancing the activity of Li₂MnO₃ by lowering its delithiation potential and suppressing the release of oxygen. In addition, the chemical environment of O^2? ions in molybdenum‐substituted Li₂MnO₃ is more reversible than in the unsubstituted sample during cycling. Therefore molybdenum substitution is expected to improve the performances of the Li₂MnO₃‐based lithium‐rich cathode materials.     

Protic ionic liquids as electrolytes for lithium-ion batteries

In this work we report for the first time about the use of protic ionic liquids (PILs) as electrolyte for lithium-ion batteries. The electrolyte 1 M LiTFSI in Et₃NHTFSI displays a conductivity comparable to that of aprotic ionic liquids, and electrochemical stability window large enough to allow the realization of LIBs containing LFP as cathode and LTO as anode. The use of this PIL as electrolyte in LIBs allows the realization of devices able to deliver good capacity and promising cycling stability.     

Electochemical characteristics of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>/Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> battery with conducting polymeric binder

Lithium-ion battery based on LiMn₂O₄/Li₄Ti₅O₁₂ materials was assembled for the first time. The cathode and anode of this battery are prepared with the aqueous combined binder poly-3,4-ethylenedioxythiophene: polystyrene sulfonate/carboxymethylcellulose (without polyvinylidene fluoride). The capacity of the LiMn₂O₄/Li₄Ti₅O₁₂ battery was found to be 75 mA h g^–1 at 0.1 C and 55 mA h g^–1 at 1 C. A 95% capacity was retained after 100 charge-discharge cycles. The batteries demonstrated a high Coulombic efficiency close to 100%. Scanning electron microscopy demonstrated that using the conducting binder poly-3,4-ethylenedioxythiophene: polystyrene sulfonate/carboxymethylcellulose provides formation of dense compact layers of electrode materials with good adhesion to the substrate. The electrode structure remains maintained after 100 charge-discharge cycles.     

Enhanced electrochemical performance of LiFePO4 cathode with the addition of fluoroethylene carbonate in electrolyte

The effect of the fluoroethylene carbonate (FEC) addition in electrolyte on LiFePO₄ cathode performance was investigated in low-temperature electrolyte LiPF₆/EC/PC/EMC (0.14/0.18/0.68). Cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge tests were conducted in this work. In the presence of FEC, the polarization of LiFePO₄ electrode decreased both at room and low temperatures. Meanwhile, the exchange current density increased. The rate capability of LiFePO₄ electrode was greatly enhanced as well. The morphology of the solid electrolyte interphase (SEI) on LiFePO₄ surface was modified with the addition of FEC as confirmed by scanning electron microscopy measurement. A compact film with small impedance was formed on LiFePO₄ surface compared to the case of FEC-free. The compositions of the film were analyzed by X-ray photoelectron spectroscopic measurement. The contents of Li _x PO _y F _z , LiF, and the carbonate species generated from solvents decomposition were reduced. The modified SEI promoted the migration of lithium ion through the electrode/electrolyte interphase and enhanced the electrochemical performance of the cathode.     

Formation of lithium fluoride/metal nanocomposites for energy storage through solid state reduction of metal fluorides

In order to utilize high energy metal fluoride electrode materials as direct replacement electrode materials for lithium ion batteries in the future, a methodology to prelithiate the cathode or anode must be developed. Herein, we introduce the use of a solid state Li₃N route to achieve the lithiation and mechanoreduction of metal fluoride based nanocomposites. The resulting prelithiation was found to be effective with the formation of xLiF:Me structures of very fine nanodimensions analogous to what is found by electrochemical lithiation. Physical and electrochemical properties of these nanocomposites for the bismuth and iron lithium fluoride systems are reported.     

Optimization of tin intermetallics and composite electrodes for lithium-ion batteries obtained by sonochemical synthesis

The optimization of active electrode materials for advanced lithium batteries obtained by sonochemically promoted reactions is discussed. Composites containing amorphous CoSn intermetallic compound and exfoliated graphite are prepared by a combination of graphite mechanical exfoliation followed by the reduction of Co²⁺ and Sn²⁺ solutions in tetraethyleneglycol with NaBH₄ with simultaneous high-intensity ultrasonication. X-ray diffraction and electron microscopy reveal relevant similarities with the negative electrode of the commercial Nexelion? battery. The resulting nanocomposite is tested as an electrode material using a lithium polyacrylate binder. The electrochemical cycling in lithium test cells shows capacities around 400 mAh/g after 400 cycles, and the ac impedance spectra reveal low resistance values. In the first discharge, nanocrystalline Li _x Sn is formed. After cycling, the metallic nanoparticles (ca. 7–20 nm) remain to be X-ray amorphous and embedded in the binder.     

Steady-state polarization measurements of lithium insertion electrodes for high-power lithium-ion batteries

Steady-state polarization measurements of lithium titanium oxide (LTO; Li[Li_1/3Ti_5/3]O₄) were carried out using the 0-V lithium-ion cells consisting of two identical LTO-electrodes with a parallel-plate symmetrical electrode configuration. The sinusoidal voltage with the peak amplitude of 1.0 V was imposed at 0.1 Hz upon the 0-V cells and the current response was measured as a function of time. The steady-state polarization, obtained by plotting the current versus applied voltage, was linear in current up to approximately 60 mA cm^?2 or 4 A g^?1 based on the LTO weight and suggested the resistance polarization only for the lithium insertion electrode of the LTO. The method was also applied to lithium aluminum manganese oxide (LAMO; Li[Li_0.1Al_0.1Mn_1.8]O₄) and the resistance polarization of the LAMO-electrode was determined for currents up to approximately 25 mA cm^?2 or 2 A g^?1 based on the LAMO weight. The validity of the results was examined for the polarization measurements of the 2.5-V lithium-ion battery consisting of LTO and LAMO, and the significance of the polarization measurements of lithium insertion electrodes for high-power applications was discussed.     

Electrochemical insertion of lithium into the ramsdellite-type oxide Li2Ti3O7: influence of the Li2Ti3O7 particle size

The effect of a milling process on the electrochemical performance of Li₂Ti₃O₇ electrodes has been investigated by the galvanostatic intermittent titration technique (GITT) and AC impedance spectroscopy. The insertion ratio is slightly increased by the milling treatment and a value of x _Li=1.25 per mol Li₂Ti₃O₇ has been determined. The average potential during insertion is close to 1.5 V/Li. The analysis of impedance data obtained at equilibrium during insertion and deinsertion shows two relaxation processes and a diffusion phenomenon at low frequency according to the Frumkin-Melik-Gayakazian model. Cycling experiments of batteries using this material were performed with unmilled and milled particles. Composite electrodes containing different amounts of electroactive material added to a binder and a conductive additive have also been prepared in order to check the effect of grinding on the cyclability of the compound. Interesting electrochemical performances have been determined with such electrodes: lithium uptake up to 1.25 Li per Li₂Ti₃O₇, low irreversible capacity loss between the first and the following cycles, good stability upon cycling even after 50 cycles. However, the milled process has not improved significantly the electrochemical performance of the Li₂Ti₃O₇ electrodes. Electronic Publication     

Electrochemical performance of Li4Ti5O12/carbon nanofibers composite prepared by an in situ route for Li-ion batteries

A Li₄Ti₅O₁₂/carbon nanofibers (LTO/CNFs) composite has been synthesized by solid-state reaction with the in situ growth of CNFs using the chemical vapor deposition method in N₂/C₂H₂. The nanocomposite is characterized by X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy, Raman spectrum, and nitrogen adsorption/desorption isotherms, and is investigated as an anode material for lithium-ion (Li-ion) batteries. The underlying mechanism for the improvement is analyzed by cyclic voltammetry and electrochemical impedance spectroscopy. The in situ synthesized composite shows better electrochemical performance than the bare LTO. The in situ formation of CNFs not only supply an efficient electronic conductive network but also reduce the particle size of LTO and increase in specific surface area, leading to increased electrical conductivity and rapider Li-ion diffusion in electrode/electrolyte interface and bulk electrode.