Polyvinylidene Fluoride Binder Research Articles

Instability of PVDF Binder in the LiFePO4versus Li4Ti5O12 Li‐Ion Battery Cell

AbstractThe conventional formulation of electrodes used in Li‐ion batteries consists of a mixture of three components: an active material, a conductive additive (carbon), and an organic binder. While the first encompasses a broad spectrum of chemistries, the carbon and the binder are often standard elements of the composite, with the latter being, in most of the cathode cases, the polyvinylidene fluoride (PVDF). The high (electro‐)chemical inertia spanning over a broad range of oxidative and reductive potentials gives grounds for this choice. Herein, we demonstrate, contrary to electrochemical expectations, that the PVDF is electrochemically unstable at relatively low potentials. We consider in this study the LiFePO4 (LFP) cathode cycled versus Li4Ti5O12 (LTO) anode as a representative low‐voltage battery cell system. The binder degradation process starts upon charge on the LFP electrode at 3.45 V vs. Li+/Li when the PVDF binder reacts with lithium and forms LiF. The latter does not precipitate on the LFP but migrates/diffuses towards the LTO counter‐electrode, following the Li‐ions’ trajectory. X‐Ray photoelectron spectroscopy complemented with the high lateral resolution of X‐ray photoemission electron microscopy disclosed the formation of a thin layer of LiF homogenously distributed across the LTO electrode, which partially dissolves (or decomposes) upon discharge. The degradation of the PVDF and the deposition and dissolution (and/or decomposition) of the LiF layer continue over subsequent charge and discharge cycles. The process is augmented when the cycling temperature is increased to 80 °C. The results shown in this work are crucial to interpret electrochemical data, such as specific charge decay or impedance rise, and have relevance for all PVDF‐based electrodes, especially when employed in high‐voltage battery cells where the more extreme cycling conditions exacerbate electrode components’ stability.

Synthesis and Electrochemical Research of the Properties of Mixed Nickel-Cobalt Oxides as Materials for Energy Storage Devices

Mixed nickel-cobalt oxide was prepared by hydrothermal synthesis. The morphology and structure of the produced oxide were studied using scanning electron microscopy and X-ray structural analysis: spinel NiCo2O4 forms spherical nanostructures. Electrodes were prepared from composite materials based on nickel-cobalt mixed oxides, polyvinylidene fluoride binder, and carbon black, applied to nickel foam by various methods. Electrochemical studies of electrodes in aqueous alkaline solutions have been carried out by the cyclic voltammetry. The obtained values of the specific capacity of the material in charge-discharge cycling reach 840 F g–1 at 5 mV s–1. The best value of the capacity retention of the produced materials is 87% for 100 cycles.

High-Voltage Performance Enhancement of Nickel-Rich Cathode through Improved Binding Ability of Designed Binder

As mobile electronics and electric vehicles become essential in our lives, the specific energy density of a lithium-ion battery is one of the criteria that determines the quality of a battery and customers’ use range. Cathode is the one that primarily determines the capacity and energy density of the battery, and consists of active material, binder and carbon black. Nickel-rich layered oxides such as LiNi0.8Co0.1Mn0.1O2 (NCM811) are promising high-capacity cathode active materials, and its reversible capacity increases more by charging to higher cut-off voltages than the conventional 4.2 V. We observed that NCM811 cathode fabricated with commercial polyvinylidene fluoride binder has an unstable interface to electrolyte under high cut-off charge voltages and undergoes drastic structural changes during cycling in particular at elevated temperature, leading to capacity fade and reduced lifespan of the battery. In order to acquire a high reversible capacity and enhanced cycling performance with NCM811 cathode by mitigating the problems, we have designed an unique and functional high-voltage binder and make the combination with NCM811. In the meeting, we are going to report improved thermal stability and cycling performance of the designed binder-assisted cathode. Acknowledgement This research was supported by the Ministry of SMEs and Startups (S2788978) of Korea, National Research Foundation grant funded by the Korean Ministry of Science and ICT (No. 2019R1A2C1084024) and Creative Human Resource Development Consortium for Fusion Technology of Functional Chemical/Bio Materials of BK Plus program by Ministry of Education of Korea.

Highly stabilized sulfur cathode with natural fenugreek gum as binder

• Natural polymer FG is proposed as a new cathode binder for Li/S cells. • FG provides the cathode with better structure integrity than PVDF. • FG can suppress the shuttle effect in Li/S cells. • The cells with FG present excellent cycling stability and rate capability. To address instability of sulfur cathode in lithium-sulfur batteries, we propose a novel binder, a water-soluble natural polymer fenugreek gum (FG). Physical characterizations demonstrate that FG exhibits outstanding mechanical strength, adhesion and ductility compared with traditional binder polyvinylidene fluoride (PVDF). Especially, FG possesses strong adsorption capability to trap the polysulfieds, as verified by immersion tests and density functional theory calculations. With these features, FG as binder provides the sulfur cathode with remarkable cycling stability, which presents a capacity retention of 91.6% with a Coulombic efficiency of 98.7% after 250 cycles at 0.5 C, compared to the 62.9% and 95.4% of the sulfur cathode using PVDF as binder. Impressively, FG outperforms other natural polymers that have been reported as the binders of sulfur cathodes.

Insight into Prolonged Cycling Life of 4 V All‐Solid‐State Polymer Batteries by a High‐Voltage Stable Binder

AbstractPolyethylene oxide (PEO) based solid polymer electrolytes (SPEs) are incompatible with the 4 V class cathodes such as LiCoO2 due to the limited electrochemical oxidation window of PEO. Herein, a number of binders including commonly used binders PEO, polyvinylidene fluoride (PVDF), and carboxyl‐rich polymer (CRP) binders such as sodium alginate (Na‐alginate) and sodium carboxymethyl cellulose, are studied for application in the 4 V class all‐solid‐state polymer batteries (ASSPBs). The results show ASSPBs with CRP binders exhibit superior cycling performance up to 1000 cycles (60% capacity retention, almost 10 times higher than those with PEO and PVDF binders). Synchrotron‐based X‐ray absorption spectroscopy (XAS), morphology studies and density functional theory studies indicate that, with their carboxyl groups, CRPs can strongly bind the electrode materials together, and work as coating materials to protect the cathode/SPE interface. Cyclic voltammetry studies indicate that CRP binders are more stable at high voltage compared to PEO and PVDF. The stability under high voltage and the coating property of CRP binders contribute to stable cathode/SPE interfaces as disclosed by the X‐ray photoelectron spectroscopy and Co L‐edge XAS results, enabling long cycling life, high performance 4 V class ASSPBs.

Amylopectin from Glutinous Rice as a Sustainable Binder for High‐Performance Silicon Anodes

Silicon (Si) has been investigated as a promising anode material because of its high theoretical capacity (4200 mAh g‐1). However, silicon anode suffers from huge volume changes during repeated charge–discharge cycles. In this work, inspired by a remarkable success of the glutinous rice mortar in the Great Wall with ca. 2000‐year history, amylopectin (AP), the key ingredient responsible for the strong bonding force, is extracted from glutinous rice and utilized as a flexible, aqueous, and resilient binder to address the most challenging drastic volume‐expansion and pulverization issues of silicon anode. Additionally, the removal of toxic N‐methyl‐2‐pyrrolidone (NMP) organic solvent makes the electrode fabrication process environmentally friendly and healthy. The as‐prepared Si‐AP electrode with 60 wt% of Si can uphold a high discharge capacity of 1517.9 mAh g−1 at a rate of 0.1 C after 100 cycles. The cycling stability of the Si‐AP has been remarkably improved in comparison with both traditional polyvinylidene fluoride (PVDF) and aqueous carboxymethylcellulose (CMC) binders. Moreover, when the content of silicon in the Si‐AP electrode increases to 70 wt%, a high discharge capacity of 1463.1 mAh g−1 can still be obtained after 50 cycles at 0.1° C. These preliminary results suggest that the sustainably available and environmentally benign amylopectin binders could be a promising choice for the construction of highly stable silicon anodes.

Electrochemical Properties of Sn/C Nanoparticles Fabricated by Pulse Wire Evaporation for Lithium Secondary Batteries.

In this work, bare Sn and carbon-coated Sn nanoparticles were prepared by a pulsed wire evaporation process. The effect of binder and pressing ratio on electrochemical properties of Sn/C composite electrodes was investigated to enhance the structural stability of Sn anode. The electrode containing the polyamide-imide (PAI) binder with high tensile strength (52 MPa) exhibited higher coulombic efficiency and better cycle performance compared to the electrode with the conventional polyvinylidene fluoride (PVdF) binder. The 5%-pressed Sn/C electrode with the proper porosity in the electrode demonstrated the best cycle performance corresponding to 45% of capacity retention ratio until 100 cycles.

Effects of water‐based binders on electrochemical performance of manganese dioxide cathode in mild aqueous zinc batteries

AbstractIn the majority of rechargeable batteries including lithium‐ion batteries, polyvinylidene fluoride (PVdF) binders are the most commonly used binder for both anode and cathode. However, using PVdF binder requires the organic solvent of N‐methyl‐2‐pyrrolidone which is expensive, volatile, combustible, toxic, and has poor recyclability. Therefore, switching to aqueous electrode processing routes with non‐toxic binders would provide a great leap forward towards the realization of ideally fully sustainable and environmentally friendly electrochemical energy storage devices. Various water‐soluble binders (aqueous binders) were characterized and compared to the performance of conventional PVdF. Our study demonstrates that the electrochemical performance of Zn/MnO2 aqueous batteries is significantly improved by using sodium carboxymethyl cellulose (CMC) binder. In addition, CMC binders offer desirable adhesion, good wettability, homogeneous material distribution, and strong chemical stability at certain pH levels (3.5–5) without any decomposition for long‐cycle life.

Fast Heat Transport Inside Lithium-Sulfur Batteries Promotes Their Safety and Electrochemical Performance.

SummaryLithium-sulfur batteries are paid much attention owing to their high specific capacity and energy density. However, their practical applications are impeded by poor electrochemical performance due to the dissolved polysulfides. The concentration of soluble polysulfides has a linear relationship with the internal heat generation. The issue of heat transport inside lithium-sulfur batteries is often overlooked. Here, we designed a functional separator that not only had a high thermal conductivity of 0.65 W m−1 K−1 but also alleviated the diffusion of dissolved active materials to the lithium anode, improving the electrochemical performance and safety issue. Lithium-sulfur batteries with the functional separator have a specific capacity of 1,126.4 mAh g−1 at 0.2 C, and the specific capacity can be remained up to 893.5 mAh g−1 after 100 cycles. Pouch Cells with high sulfur loading also showed a good electrochemical performance under a lean electrolyte condition of electrolyte/sulfur (E/S) = 3 μL mg−1.

Enhanced electrochemical properties of Co3O4 anode with PEDOT:PSS/CMC binder for lithium-ion batteries

A superior electrochemical performance of Co3O4 anode with water-soluble binder consisting of a combination of intrinsically conducting polymer poly-3,4-ethylenedioxythiophene:polystyrene sulfonate (PEDOT:PSS) dispersion and carboxymethyl cellulose (CMC) is presented. This type of electrode material shows ultrahigh capacity value of 1200 mA·h·g−1. It also demonstrates an excellent stability during continuous cycling at 0.2 C (capacity loss is near 4–5%) and has no significant capacity fading at high current densities. Cyclic voltammetry measurements show that Co3O4-electrode containing conducting polymer has smaller changes in shape of the curves than in the case of anode material where polyvinylidene fluoride (PVDF) binder was used.

High-value utilization of graphite electrodes in spent lithium-ion batteries: From 3D waste graphite to 2D graphene oxide

The graphite electrodes of spent lithium-ion batteries (LIBs) have a good crystalline composition and layered structure, and the recovery potential is promising. However, the internal and external surfaces of the waste graphite are often polluted with various organic and inorganic impurities, which seriously restrict its high-value utilization. Herein, the microstructure and surface analysis of waste graphite at variable scales were carried out systematically to reveal the types and occurrence status of impurities and their influence on the preparation of graphene oxide (GO) using a modified Hummers method. The results show that the graphite surface contaminants are polyvinylidene fluoride binder, LiPF6 electrolyte and LiF residue from the solid electrolyte interface, while residual lithium (Li2CO3) and CuO were found to have invaded the crystal structure of graphite. Fortunately, the modified Hummers method can effectively remove these complicated associated impurities and prevent their re-contamination on the GO surface. More importantly, the modified Hummers method can not only destroy the longitudinal molecular bonds between graphite layers, but also splice them horizontally to form 2D GO, which is verified by high-resolution transmission electron microscope (HR-TEM) images. This paper provides theoretical support and practical guidance for the high-value utilization of waste graphite in spent LIBs.

Enhanced electrochemical performance by GeOx-Coated MXene nanosheet anode in lithium-ion batteries

Here, we demonstrate a facile method to synthesize an amorphous GeOx-coated MXene nanosheet structure as the anode in lithium-ion batteries. By using the GeO32− as the precursor, NaBH4 as the reduction agent, we performed a one-pot in situ synthesis to prepare a composite of GeOx nanoparticles coated on MXene nanosheet. The size of the GeOx nanoparticles is approximately 50 nm, which offers abundant contact surface between active materials with the electrolyte, as well as fast pathways for Li-ion interaction. Moreover, the unique two-dimensional MXene nanosheet serves as the excellent conductive additives to improve the electrochemical stability and electrical conductivity of composite when used in LIBs. The results indicate that the GeOx/MXene nanosheet structure significantly improves the stability during the lithiation/delithiation processes, with the enhanced capacity through an improved kinetic process. Another attractive element of this novel anode is the flexibility to tune the electrochemical properties by using different combination of binder and solvent when the slurry is prepared for the electrode fabrication. The electrode prepared with polyvinylidene fluoride binder and N-methyl pyrrolidinone solvent exhibits an excellent sustainable capacity of 381 mAh g−1 at 15 A g−1. By contrast, the electrode with lithium polyacrylate and de-ionized water delivers a reversible capacity of 950 mAh g−1 at 0.5 A g−1 after 100 cycles. These interesting results are ascribed to the inner characteristic structure of the two types of electrodes, which have been verified by electrochemical kinetics and scanning electron microscopic images. It also reveals that the different dispersion state is responsible to the difference of electrochemical properties, which highlights the importance of the electrode design for high-performance lithium-ion batteries.

Mechanochemical synthesis of SnS anodes for sodium ion batteries

Orthorombic tin (II) sulfide are synthesized by a simple and cost effective mechanochemical method in a high energy ball mill over different time scales. After the detailed characterization by X-ray photoelectron spectroscopy (XPS), X-ray diffraction, Fourier Transform Infrared (FTIR) spectroscopy, thermogravimetricanalysis (TGA), scanning electron microscopy (SEM) and EDX mapping, 2 hours milling time is found to be the optimum as anode in sodium-ion batteries. Later, electrochemical performances are investigated with regards to the binder type; sodium carboxy methyl cellulose (CMC), sodium alginic acid (Na-alginate) and polyvinylidene fluoride (PVdF), in which the best performances are obtained with Na-alginate. Comprehensive electrochemical impedance spectroscopy (EIS) measurements are pursued in order to examine the effect of binders. EIS tests of SnS anodes after C-rate test reveal much bigger resistivity with PVdF binder than that of CMC and Na-alginate. Postmortem surface morphology analysis by means of SEMdemonstrates the self-healing properties of Na-alginate binder with no visible crack formation after cycles. As a whole, more than 300 mAh/g capacity is obtained over 60 cycle at C/5 current density without the help of carbon addition during the synthesis of the SnS composite.

Hydrometallurgical Regeneration of LiMn2O4 Cathode Scrap Material and Its Electrochemical Properties

AbstractThe main researches focus on the recovery of metal elements in lithium manganate and not consider regenerating the cathode scrap materials. In this study, first, the polyvinylidene fluoride (PVDF) binder is removed by a combination of solvent dissolution and heat treatment. PVDF is easily separated by dissolving in an N‐methyl‐2‐pyrrolidone solution at a heating temperature of 60 °C, stirring time of 50 min, and solid solution ratio of 80 g⋅L−1. The dissolution rate of the scrap material achieves 86.70 % under optimal conditions. Further, using inductively coupled plasma spectroscopy to define the Li and Mn metal contents, and the LiMn2O4 cathode material is regenerated by a hydrometallurgical method. At the optimum calcination conditions of 500 °C for 12 h, electrochemical performance show that there are obvious charge and discharge platforms in the charge/discharge curves, and high first‐cycle discharge capacity is 123.7 mAh g−1 (3.0–4.3 V and 0.1 C), after 50 cycles, it decrease to 83.2 mAh g−1.

Analysis of mechanical failure at the interface between graphite particles and polyvinylidene fluoride binder in lithium-ion batteries

The capacity fade corresponding to the mechanical failure of active materials is one of hurdles to overcome in the widespread of echo-friendly vehicles. However, the mechanisms of the mechanical failure at the electrode are not fully understood. In this study, the initiation and propagation of debonding at the interface between an active particle and a binder are investigated using a coupled electrochemical-mechanical and cohesive-zone finite-element model. The effects of particle sizes and lithiation kinetics on the progressive growth of interfacial debonding are studied, and critical states of charges are determined. The normal and shear tractions at the interface are systematically analyzed to understand their role in debonding behavior. The simulation results show that the interfacial debonding is less likely to happen as the particle size and C-rate increase, which is opposite to the inner-particle fracture behavior. The numerical study indicates that there is a trade-off between the inter-particle failure and inner-particle fracture. This study suggests that the binder effect needs to be included in the theoretical model for better understanding of the mechanical failure at the electrode. The debonding failure maps provided from the study can assist in engineering design of active materials and safe operation of batteries.

The Effect of Crystalline Microstructure of PVDF Binder on Mechanical and Electrochemical Performance of Lithium-Ion Batteries Cathode

Abstract In this paper, the effect of the crystalline microstructures of polyvinylidene fluoride (PVDF), as cathode binder, on mechanical and electrochemical properties of the cathode, and on the cell performance is investigated. The crystalline phases of the PVDF films prepared at different temperatures are determined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) and also mechanical strength of PVDF films evaluated by a tensile test. The cathodes were prepared at altered temperatures to achieve different PVDF phases. The effect of various crystalline phases on the cathode performance was studied. The obtained cathodes were analyzed by scanning electron microscope (SEM), contact angle measurement, and adhesion test. The electrochemical performance of the cathodes was evaluated by charge-discharge cycling test and AC impedance spectroscopy. Mechanical tests results showed that the cathode which is prepared at 60 °C has the best adhesion and mechanical stability. In addition, the charge-discharge cycling studies showed that this cathode has the highest capacity efficiency. AC impedance spectroscopy illustrated that this electrode has the lowest charge transfer resistance and SEI resistance.

Understanding the Conductive Carbon Additive on Electrode/Electrolyte Interface Formation in Lithium-Ion Batteries via in situ Scanning Electrochemical Microscopy.

The role of conductive carbon additive on the electrode/electrolyte interface formation mechanism was examined in the low-potential (3.0–0 V) and high-potential (3.0–4.7 V) regions. Here the most commonly used conductive carbon Super P was used to prepared electrode with polyvinylidene fluoride binder without any active material. The dynamic process of interface formation was observed with in situ Scanning Electrochemical Microscopy. The electronically insulating electrode/electrolyte passivation layer with areal heterogeneity was formed after cycles in both potential regions. The low-potential interface layer is mainly composed of inorganic compounds covering the conductive carbon surface; While the electrode after high-potential sweep tends to lose its original carbon structure and has more organic species formed on its surface.

Incineration of EV Lithium-ion batteries as a pretreatment for recycling – Determination of the potential formation of hazardous by-products and effects on metal compounds

In several industrial Lithium-ion batteries recycling processes, a thermal treatment with oxidative atmosphere is used to separate the battery components and to remove the organic components. This method is often combined with hydrometallurgical processes with the aim to increase the metal recovery rate or to improve the efficiency of the existing processes. Despite such efforts, the effects of a thermal treatment in an oxidative atmosphere on the microstructure and composition on cathode and anode materials has not been explored.In this manuscript, spent batteries which cathode active material has the composition Li(NixMnyCoz)Oz, i.e. NMC-LiBs, were subjected to thermal treatment at 400˚, 500˚, 600˚, and 700 °C for 30, 60, and 90 min. The microstructure and the composition were studied using XRD and ICP-OES. Thermodynamic calculations were performed to forecast the trend of the carbothermic reduction of active materials. It was observed the formation of gas and organic oil by-products from the decomposition of the polypropylene separator and the polyvinylidene fluoride binder. The identification of the composition of these by-products has great importance since they have a corrosive and toxic behavior. It was observed the fluorine behavior during the thermal treatment and its presence in the oil by-products.

Melt-processed electrode for lithium ion battery

With the advent of electric vehicles and the growing need for energy storage systems, the development of Li-ion batteries that are capable of increased GWh production is anticipated in the coming years. Thus, it is essential to develop new Li-ion battery manufacturing processes that are both environmentally sustainable and cost effective. In this regard, an original roll-to-roll industrial process was developed to manufacture composite Li-ion battery electrodes. This process consists of replacing the classical technique of dissolving polyvinylidene fluoride (PVdF) binder in an expensive and toxic solvent (typically N-methyl pyrrolidone) with a solvent-free process.In this study, the authors present a unique hot melt extrusion process which consists of mixing a polymer processing aid (PPA) and an elastomeric binder (hydrogenated nitrile butadiene rubber (HNBR)) to decrease the viscosity of the mixture and gain precise control on porosity in the resultant composite electrodes. The versatility of this process would make it easily adaptable to various active materials. In this work, the authors present each step of this unique process converting raw materials to porous composite electrodes. The competitive electrochemical performances of the composite electrodes are assessed using half-cell configurations, whereas power performances are measured using LiFePO4–Li4Ti5O12 full cells.

Mechanical robustness of composite electrode for lithium ion battery: Insight into entanglement & crystallinity of polymeric binder

To investigate the correlation between the molecular weight of the polymeric binder in Li-ion battery electrodes and their adhesion properties, polyvinylidene fluoride (PVdF) with three different molecular weights of 500,000, 630,000, and 1,000,000 are selected for LiCoO2 electrode fabrication. Using a surface and interfacial cutting analysis system, it is observed that, as the molecular weight of the PVdF increases, the adhesion strength not only in the electrode composite, but also at the electrode/current collector interface increases. This enhancement can be attributed to the increased polymeric chain entanglement and higher crystallinity of PVdF with higher molecular weight, which is confirmed using a microfluidic viscometer and differential scanning calorimeter, respectively. In summary, regardless of slightly higher electrode resistance, the LiCoO2 electrode with a PVdF binder of high molecular weight shows better electrochemical performance during cycling test even at 60 °C due to its stable mechanical integrity.