Eco‐Friendly Aqueous Polymeric Binders for High‐Performance Graphite Anodes: Structure–Property Insights for Lithium‐Ion Batteries

Carbon-based anode materials used in lithium-ion batteries have a composite structure consisting of carbon powder bonded with a binder. With the advent of aqueous electrolytes and solid electrolytes, water resistance is also required for anode materials. In this study, carbon-based anode materials made of polyvinylidene fluoride (PVDF), a solvent-based binder with higher water resistance than aqueous binder, were immersed in water and subjected to static tensile and creep tests to investigate the mechanical properties and creep characteristics of the anode and binder materials in water. Based on the test results, a simple prediction of creep deformation of the anode material in water was proposed. The test results showed that both the anode and binder materials exhibited a transition creep region, in which the creep rate, that is the increase amount of tensile strain with respect to time, gradually decreases after reaching the holding stress, and a steady state creep region, in which the creep rate remains constant after the transition creep region. Due to the PVDF softening, the creep transition region became longer, and the creep strain was larger in water than in air. Using the creep properties of the PVDF, the proposed method successfully estimated the creep properties of the anode material.

Li-ion batteries have polymeric binder in their electrodes resulting in high internal resistance and hence long charge times and compromised product lifetime. We previously developed Li-ion batteries utilizing binder-free NMC cathodes containing carbon nanotube (CNT). In this work, we extend the ‘binder-free’concept to two types of battery anodes - graphite and lithium titanate (LTO) anodes. Our proprietary processing of CNT into viscous organic or water-based slurry without surfactant or dispersant eliminates the need for organic binder and carbon black additives in both cathode and anode electrodes. To formulate the binder-free anodes, our processed CNT slurry was mixed with a target quantity of either battery-grade graphite or LTO in IPA solvent using a conventional planetary mixer. The IPA-based binder-free anode mixes were coated onto either Cu foil (graphite) or Al foil (LTO) using a commercial slot-die coater, resulting in uniform coatings after drying which did not exhibit any signs of flaking off or delamination from the respective current collector foils. LiB pouch cells rated at 1.5 Ah and 3 Ah were subsequently assembled containing NMC cathode paired with both types of binder-free anodes. LiB cells with binder-free graphitic anode exhibit very low impedance of 5.2 x 10-2 mΩ/cm2, or >35 % reduction in impedance compared to conventional LiB cell with binder containing graphitic anode, while LiB cells with binder-free LTO anode showed >75 % reduction in impedance compared to LiB cell with binder containing LTO anode. Moreover, the LiB cells with binder-free anodes exhibit superior high-rate capability compared to their counterpart cells containing electrodes with polymeric binder. The LiB pouch cells were tested for fast discharge rate performance at 10C. LiB cells with binder-free graphitic anode display >2x higher specific capacity compared to the cell with binder, while cells with binder-free LTO show 8x higher capacity at 10C rate than conventional LiB cell with polymeric binder after high discharge rate testing. Figure 1

In the pursuit of high-performance anode materials for Li-ion batteries over the past few decades, bismuth molybdate (BMO) has emerged as a promising candidate. However, its interaction with traditional polyvinylidene fluoride (PVDF) binder is not favorable, leading to rapid degradation of cyclic capacity. Furthermore, PVDF is considered an environmentally toxic binder. Therefore, finding a suitable binder that enhances the cycle life of this material and is more environmentally friendly is essential. In this study, BMO material was successfully grown at a low annealing temperature (200 °C) in an air environment. Analyses including X-ray diffraction, transmission electron microscopy, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy were employed to obtain a comprehensive understanding of the material morphology and structure. BMO was identified as a polycrystalline Bi2MoO6 material consisting of approximately 6.94 nm grains and 300–500 nm long rods with diameters ranging from 10 to 25 nm. In addition, an amorphous phase was observed in the BMO material. The effect of the binder on the electrochemical properties of BMO was evaluated using two binders: PVDF and poly(acrylic acid) (PAA). The BMO electrode using the PAA binder (BMO_PAA) demonstrated significantly better performance as an anode for lithium-ion batteries (LIBs) than that using the PVDF binder (BMO_PVDF). The BMO_PAA anode attained a 60th-cycle specific capacity of 738 mAh g−1 at 0.1 A g−1, whereas this value for the BMO_PVDF electrode was 202 mAh g−1. Therefore, this report presents the synthesis of a superior anode material for LIB fabrication that is compatible with a PAA binder, an environmentally friendly, fluorine-free binder.

In this work, we study and compare the electrochemical performance of Li-ion battery (LIB) with and without a BiFe0.95Cu0.05O3 thin film coating. The BiFe0.95Cu0.05O3 thin film is deposited on both LiNi0.5Mn0.3Co0.2O2 (NMC532) cathode and graphite anode electrodes using radio frequency magnetron sputtering. By using galvanostatic charge–discharge measurements, we observe that, in contrast to LIB without BiFe0.95Cu0.05O3 coating, the charging curve of LIB with BiFe0.95Cu0.05O3 coating exhibits a counterintuitive negative slope of the negative electron compressibility (NEC) with a rate of NEC equal to −16.36 × 10−11 meV per electron per cm2. Importantly, we find that the NEC effect has the potential to enhance the energy density in LIB with BiFe0.95Cu0.05O3 coating. The energy density of the first discharge cycle is dramatically increased from 190 Wh/kg for pristine LIB to 255 Wh/kg for LIB coated with the BiFe0.95Cu0.05O3 film. We suggest the origin of this with the change in Mott gap and a concept to apply the NEC effect for enhancing energy density LIB batteries.

In the production of commercial Li-ion batteries, the active materials slurries are generally prepared using polyvinylidene fluoride (PVdF) as binder because of its good adhesion properties and electrochemical stability. Unfortunately, there are some disadvantages related to the use of PVdF: the most important is the use of toxic and environmentally unfriendly solvents, such as N-methyl-pyrrolidone (NMP), and the second is the high costs. In the light of these considerations, it seemed straightforward to investigate the suitability of some water-soluble, inexpensive, and eco-friendly materials to test as alternative binders (sodium alginate, chitosan tragacanth gum, gelatin). The rheological properties of these materials have been investigated in addition to the electrochemical characterization. Furthermore, graphite electrodes with PVdF, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binders have been considered for sake of comparison. We found that some of these water-soluble binders, besides good electrochemical performances, showed a high adhesion to the current collector and a good electrochemical stability under the experimental conditions employed, which makes them interesting for the next generation of Li-ion batteries.

Poly(vinylidene fluoride) (PVDF) has been a choice of the binder for both cathode and graphite anode in stateof-the-art Li-ion batteries [1, 2]. However, there is currently a demand to replace PVDF with non-fluorinated binder since at elevated temperatures the fluorinated polymers react with lithiated graphite (LixC6) and metal lithium to form more stable LiF and >C@CF– double bonds. In particular, the reaction of PVDF and metal lithium produces an enthalpy as high as 7180 J (g PVDF) [1]. It has been reported that in the presence of electrolytes, PVDF and lithiated graphite undergo a series of exothermic reactions, including (i) temperature-induced degradation of the solid electrolyte interface (SEI) at 120–140 C, (ii) reactions of lithiated graphite and electrolyte at 210–230 C, and (iii) dehydrofluorination of PVDF initiated by LixC6 at >260 C [1, 2]. Among these reactions, the last one is known to be very exothermic and is believed to be a potential source for the thermal runaway of Li-ion batteries under abuse conditions. Therefore, safety concerns with Li-ion batteries may arise from the use of PVDF in the graphite anode. To replace the rather reactive PVDF, we attempt to evaluate poly(acrylonitrile-methyl methacrylate) (AMMA) as a non-fluorinated binder for the graphite anode of Li-ion batteries. Differential scanning calorimetry (DSC) study has shown that the heat of reaction of the lithiated graphite and electrolyte can be reduced significantly by using AMMA instead of PVDF [3]. That is, total enthalpies for the reactions (as indicated by two exothermic peaks in DSC curves) of the fully lithiated graphite (MAG-10, Hitachi Chemical) and electrolyte (1.2 M LiPF6 3:7 EC/EMC) in the temperature range 280–340 C can be reduced to 1211 J (g AMMA) from 2699 J (g PVDF). In this paper, we will electrochemically evaluate AMMA as a binder of the graphite anode of Li-ion batteries. 2. Experimental details

Silicon has been one of the most investigated electrodes to replace graphite, with having over ten times the theoretical capacity of graphite at 4200 mAh/g vs 372 mAh/g, respectively. While silicon promises to be a cheap, abundant, alternative, it’s use imparts a host of challenges before wide-spread commercialization can be adopted. Silicon expands several times it’s original size upon lithium insertion, which not only compromises structural integrity of the electrode itself, but cracks the adjacent solid-electrolyte interface layer, causing SEI stability to fluctuate. The methods adopted to overcome this volume expansion have been numerous, from decreasing silicon particle size to nanoscale, to creating nanowires, to nanotubes, that expand inward yet protect the outward facing SEI layer. The binder component in the original slurry is an important ingredient that aids in adhesion to the current collector as well as particle to particle adhesion. A common aspect of slurry composition is that binders are typically on the order of 10-20% by mass of all slurry components. Various binders have been explored for use with silicon, including the common polyvinylidene fluoride (PVDF) and polyvinylpyrrolidone (PVP). Recent literature has also highlighted that binders such as carboxymethyl cellulose (CMC) and polydimethylsiloxane (PDMS) can significantly improve performance over traditional binders when used with silicon electrodes. Another common method for enhancing silicon performance is by using a metal additive such as tin or copper, in small 1-2% by mass amounts. In the case of copper additive, a desired Cu3Si phase has been noted to improve performance and is obtained once the casted film is heat treated at 700°C. When heat treating a film to such high temperatures, traditionally, the nature of the binder is assumed to be burned off, or converted to some miniscule amounts of carbon, as all polymers carbonize around 400°C. Our investigation of increasing capacity of silicon electrodes at low temperatures has shown that the nature of the binder in fact does play a role in cell performance, even after the binder has carbonized through the heat treatment step. We have compared the traditional PVDF and PVP binders in full cells with lithium metal and an ether-based electrolyte, with the PVDF binder actually demonstrating significantly improved capacity over PVP at both room temperature and -20°C through long cycle life testing. The resultant cells using PVDF binder maintain over 1000 mAh/g capacity after 100 cycles at room temperature and 250 cycles at -20°C.

In this study, biofuel properties of poplar wood materials rich in organic materials were investigated for microbial fuel cells. Therefore, in this study, investigates the chemical, biochemical properties with electrochemical performance of single chamber microbial fuel cell manufactured using poplar biomass materials, natural soil, graphite anode electrode and graphite cathode electrode. With the increase in the weight of the poplar tree in the microbial fuel cells, the power density increased. SEM, EDS, FTIR analyses showed that bacillus and coccus type bacteria in the natural structure of the soil act as the catalyst in the anode electrode. Poplar wood, electrodes and bacteria have served in harmony. According to experimental results, the maximum power reaches to 16.88 mW and microbial fuel cell successfully displays a maximum power density of 8555 mW/m 2 . All these results indicate that poplar wood may be appropriate biofuel sources for electrical energy generation as an effective environmentally microbial fuel cell technology.

Graphene modified copper current collector for enhanced electrochemical performance of Li-ion battery

Increasing industrial and human populations potentially lead to various types of water contamination and increasing water demand. Membrane technology is a popular technology that is highly efficient in separation processes and is cost-effective for water purification. One membrane technology that is widely applied in industry is microfiltration membranes. Microfiltration membranes can operate at pressures in the range of 0.02 to 0.5 MPa, thus enabling the separation of high molecular weight compounds at low pressure. Polyvinylidene fluoride (PVDF) is a commonly used microfiltration membrane material known for its excellent thermal stability, chemical resistance, and ease of membrane formation. However, PVDF has a hydrophobic structure that has low water flux. The hydrophilicity of the PVDF membrane surface modification is an effective strategy to enhance water flux. This experiment aims to increase the hydrophilicity of the membrane using polyvinyl alcohol (PVA). In this study, surface modification of the PVDF membrane is performed using polyvinyl alcohol (PVA), a hydrophilic substance that enhances the membrane's ability to attract water. The addition of 0.1% PVA yielded the average flux value, achieving 65.7 Lm⁻²·h⁻¹. PVA increases the hydrophilic properties of the PVDF membrane and could be a modification agent for water treatment or purification. Keywords: Flux, Membran Surface Modification, PVDF, PVA Abstrak Populasi manusia dan industri yang meningkat dapat mengakibatkan berbagai jenis pencemaran air dan meningkatkan kebutuhan air. Teknologi membran menjadi teknologi populer dengan tingkat pemisahan efisiensi tinggi serta harga yang relative murah untuk pemurnian air. Salah satu teknologi membran yang diterapkan secara luas di industri adalah membran mikrofiltrasi. Membran mikrofiltrasi dapat beroperasi pada tekanan dengan rentang 0,02 sampai 0,5 MPa, sehingga memungkinkan pemisahan senyawa dengan berat molekul besar bertekanan rendah. Material membran mikrofiltrasi polyvinylidene fluoride (PVDF) merupakan material dengan stabilitas termal, ketahanan terhadap bahan kimia yang baik, serta mudahnya kemampuan pembentukan membran. Namun PVDF merupakan polimer yang memiliki struktur hidrofobik yang membuat membran rentan terhadap fluks rendah. Inovasi peningkatan hidrofilik permukaan membran pada material PVDF merupakan salah satu cara efektif meningkatkan fluks pada membran. Penelitian ini bertujuan untuk meningkatkan hidrofilisitas permukaan membrane PVDF yang berpengaruh terhadap nilai fluks. Modifikasi permukaan membran pada penelitian ini menggunakan Polyvinyl Alcohol (PVA) karena PVA bersifat hidrofilik yang dapat meningkatkan kemampuan membran menarik air. Penambahan 0,1% kadar PVA nilai fluks mencapai 65,7 Lm-2h-1. PVA meningkatkan sifat hidrofilik membrane PVDF dapat menjadi salah satu agen modifikasi untu pengolahan atau pemurnian air. Kata kunci: Fluks, Modifikasi Permukaan Membran, PVDF, PVA.

A novel microporous layer (MPL) coated gas diffusion layer (GDL) is developed to improve water management of polymer electrolyte fuel cells (PEFCs) by incorporating hydrophobic and hydrophilic pores within the same layer. This MPL expels excess water at the interface between the catalyst layer and MPL through hydrophilic pores while maintaining efficient oxygen transport through hydrophobic pores, reducing oxygen transport resistance under high humidity conditions. The water permeability and relative oxygen permeance tests demonstrate the presence of separate hydrophobic and hydrophilic pores in the appropriate composite MPL. The effects of combinations of hydrophilic and hydrophobic binders used in the composite MPLs on the oxygen transport resistance are evaluated. The hydrophobic polytetrafluoroethylene (PTFE) binder and the hydrophilic polyvinyl alcohol (PVA) binder cannot enhance performance due to mismatched sintering temperatures. Although the hydrophobic polyvinylidene fluoride (PVDF) and PVA binders have the same sintering temperature, the performance was degraded due to the strong hydrophilicity of PVA. Another combination of composite MPL incorporates hydrophobic PVDF and Nafion binders. Hydrophilic TiO2 particles are introduced in the Nafion binder to reinforce the hydrophilicity. The appropriate composite MPL significantly reduced the total oxygen transport resistance compared to those obtained with the hydrophobic MPL.

Recently, water-soluble and aqueous polymers (water-based polymers) have attracted much attention as binders for lithium ion batteries (LIBs) because of the need for low-cost materials and environmentally compatible electrode fabrication processes. For example, N-methyl-2-pyrrolidone (NMP), which is listed as a carcinogenic chemical with reproductive toxicity is often used as a solvent to prepare a slurry (cathode material particle/conducting carbon additive/conventional polyvinylidene difluoride (PVdF) binder/ NMP solvent) employed in the fabrication process of electrode films on current collectors; this slurry should be recycled without releasing it to the atmospheric environment. Therefore, switching from a nonaqueous-based fabrication process to an aqueous-based process has been widely investigated. The hurdles in developing water-soluble and aqueous polymer binders for use in cathodes in LIBs are still high; improvements are necessary to increase the resistance to electrochemical oxidation and dissolution of metal oxide surfaces in water. In order to overcome these problems, a variety of polymer materials have been applied in the fabrication of cathodes with water-based slurries. In recent years, Li-rich solid-solution layered cathode materials comprising layered LiMO2 (M: transition metals) and Li2MnO3 have attracted much interest because some materials exhibit capacities as high as 250 mAh g-1 in the voltage range of 2.0 and 4.8 V. These materials are charged to above 4.5 V (vs. Li/Li+) to fully activate the Li2MnO3 component, and after activation, the cathodes are charged to 4.5 V to reach discharge capacities over 250 mAh g-1. To use these promising high-voltage and high-capacity cathodes in the next-generation Li-ion batteries prepared in environmentally compatible electrode fabrication processes with a water-based binder, water-based binders having high resistances to electrochemical oxidation during charging process should be developed. In this study, an aqueous hybrid polymer (TRD202A, JSR), which was composed of acrylic polymer and fluoropolymer, was selected as a binder for the Li-rich solid-solution layered cathode material Li[Ni0.18Li0.20Co0.03Mn0.58]O2. A cathode prepared with Li[Ni0.18Li0.20Co0.03Mn0.58]O2 particles, TRD202A binder, CMC and conductive carbon additive was tested and analyzed for charge/discharge capacity, cycle stability, rate performance, mechanical resistance, resistance of electrochemical oxidation, and changes of the surface composition and structure after water-treatment used for preparing water-based slurry. The water-based TRD202A cathode binder is a water-based emulsion and is designed with a unique hybrid polymer developed from acrylic polymer and fluoropolymer to satisfy both the requirements of high adhesion and chemical and electrochemical resistances. Wu and co-workers have already reported an application of the TRD202 binder in a Li-rich solid-solution cathode. They mentioned that the TRD202A binder can be used for high-voltage cathodes in the voltage range of 2.0-4.6 V [1], and its thermal stability is equivalent to that of PVdF. However, they have not examined the water-based binders for charge/discharge capacities, long cycle stability, rate performance, mechanical resistance, resistance of electrochemical oxidation, or changes of the surface composition and structure after water-treatment used for preparing the water-based slurry. We have examined in depth the above points with the Li-rich solid-solution cathode (3/5)Li2MnO3·(1/5)Li[Ni0.5Mn0.5]O2 ·(1/5)Li[Ni1/3Co1/3Mn1/3]O2. [1] Wu Q, Ha S, Prakash J, Dees DW, Lu W (2013) Electrochim. Acta 114:1-6

Functional additives assisted ester-carbonate electrolyte enables wide temperature operation of a high-voltage (5 V-Class) Li-ion battery

Sulfide-based solid electrolyte such as Li6PS5Cl (LPSCl) is unstable in contact with Li metal electrode due to decomposing to by-product resulting in poor performance. Therefore, the introduction of an interlayer to suppress reactivity is essential. In this study, instead of an interlayer, an oxide/polymer composite electrolyte was applied to suppress side reactions, while a sulfide-based electrolyte was used at the cathode to improve interfacial control between the cathode and the electrolyte. All-solid-state lithium batteries (ASLBs) were prepared by applying sulfide-based solid electrolyte (argyrodite, Li6PS5Cl) including NCM424, polyvinylidene fluoride (PVDF), and Super-P in a composite cathode layer, and a composite solid electrolyte (CSE) layer by mixing an oxide-based solid electrolyte (garnet, Al-doped Li7La3Zr2O12 (LLZO)), polymer (PEO, polyethylene oxide) and lithium metal as the anode. In this study, NCM424 powder was coated with LiNbO3 to prevent chemical reaction with the sulfide electrolyte. As the PVDF binder was applied to the cathode of the ASLB, the discharge capacity of the cell was approximately 163 mAh g−1 at 70 °C, 0.1 C, and 4.2 V cut-off and its capacity retention was 83% after 50 cycles. The effects of the PVDF were evaluated using both pouch-type cells. The capacity and cycle retention are greatly dependent on the PVDF content of the cathode materials and the drying temperature during the fabrication of the cathode. When the cathode with PVDF binder was dried at 130 °C, initial cycling was required for activation of the pouch cell, and it was possible to overcome this by adding a plasticizer.

State-of-the-art (SOA) Li-ion batteries (e.g., with graphite anode and LiCoO2 cathode) for consumer electronic devices (e.g., cell phones, laptops) are designed to operate at a certain voltage range, e.g., 3-4.2V [1]. When an electronic device, like a cell phone, indicates “low battery”, the battery is near its low operating voltage threshold, and soon the device may automatically shut down to prevent the battery from further use (discharge). If a SOA Li-ion battery is allowed to further discharge to a very low cell voltage, e.g., near 0V, the battery will deteriorate quickly, manifested with a reduced battery capacity (electric charge, Ah), i.e., reduced battery use time. This is because, at or near 0V, the anode potential can exceed the substrate (commonly Cu) dissolution potential, which results in corrosion of the Cu substrate (pittings, holes) leading to compromised battery performance [2]. A battery capable of 0V (or near 0V) storage is desirable as it overcomes irreversible battery performance losses from self-discharge (to a very low voltage). For this reason, SOA Li-ion batteries are maintained above a certain threshold, e.g. > 20-30% capacity. For large format Li-ion batteries/packs, the energy left inside batteries at storage can cause serious concerns regarding: (i) safe battery transport, (ii) high maintenance cost (monitoring and periodically charging the batteries) and (iii) safe battery storage. Li-ion battery safety is a real issue exemplified by the recent Boeing 787 battery [3].Prior art to remedy Li-ion battery at or near 0V storage includes the use of an anode substrate with a higher dissolution potential, e.g., Ti substrate [4]. However Ti current collectors possess shortcomings including high cost of the Ti current collector and poor electrode coating adhesion on Ti substrate. Moreover, fundamentally, for a graphite-based anode, a solid-electrolyte-interface (SEI) film formed on graphite anode (due to organic electrolyte reduction) can break down at or near 0V and adversely impact battery performance and life. Here we present a novel approach to develop a high performance Li-ion battery, capable of deep discharge and/or storage near 0V. Our anode active material selection criterions include: (i) amenable to substrates with high dissolution potentials, (ii) sufficient (electrical) potential to avoid SEI film formation and (iii) high specific capacity for battery high energy density. Our cathode active material selection criterions include high specific capacity and high voltage to achieve high battery specific energy. Other criterions common to the anode and the cathode include high rate capability and robust cycle life. Figure 1 shows cell capacity retention as a function of cycle number for ADA near 0V capable Li-ion cells. The cells were stored at ~ 0V for 2 days for every 5 cycles. The control cell was cycled without low voltage storage. After accumulative storage for 30 days at 50mV and 100mV, respectively, the ADA near 0V capable cells demonstrated little or no capacity fade, comparable to the control cell. We attribute the excellent cell deep discharge/storage resilience to our near 0V tolerant electrode material selections. For comparison purposes, we applied the identical test conditions to graphite based Li-ion cells as shown in Figure 2. The graphite based Li-ion cells experienced rapid capacity deterioration (i.e., capacity drop to zero) after a short period of ~ 0V storage. This is likely due to Cu current collector dissolution and dissolution/reformation of SEI films on graphite anode.Our study showed that this battery technology is a very promising high performance and safe power source capable of long-term ~ 0V deep discharge/storage. This battery technology is being developed for applications in the transportation, consumer electronics, military and space markets. References "Lithium Ion technical handbook". Gold Peak Industries Ltd. November 2003. Rui Guo, Languang Lu, Minggao Ouyang, and Xuning Feng, Scientific Report, 2016; 6: 30248. National Transportation Safety Board Report, Case No. DCA131A037, March 7, 2013. Hisashi Tsukamoto, Clay Kishiyama, Mikito Nagata, Hiroshi Nakahara, Tiehua Piao, US6596439. Figure 1