Biobased Acrylic Latexes/Sodium Carboxymethyl Cellulose Aqueous Binders for Lithium-Ion NMC 811 Cathodes

The increasing demands for sustainable energy storage technologies have prompted extensive research in the development of eco-friendly materials for lithium-ion batteries (LIBs). This research article presents the design of biobased latexes, which are fluorine-free and rely on renewable resources, based on isobornyl methacrylate (IBOMA) and 2-octyl acrylate (2OA) to be used as binders in batteries. Three different compositions of latexes were investigated, varying the ratio of IBOMA and 2OA: (1) Poly2OA homopolymer, (2) Poly(2OA0,6-co-IBOMA0,4) random copolymer, and (3) PolyIBOMA homopolymer. The combination of the two monomers provided a balance between rigidity from the hard monomer (IBOMA) and flexibility from the soft one (2OA). The study evaluated the performance of the biobased latexes using sodium carboxymethyl cellulose (CMC) as a thickener and cobinder by fabricating LiNi0.8Mn0.1Co0.1O2 (NMC 811) cathodes. Also, to compare with the state of the art, organic processed PVDF electrodes were prepared. Among aqueous slurries, rheological analysis showed that the CMC + Poly(2OA0,6-co-IBOMA0,4) binder system resulted in the most stable and well-dispersed slurries. Also, the electrodes prepared with this latex demonstrated enhanced adhesion (210 ± 9 N m-1) and reduced cracks compared to other aqueous compositions. Electrochemical characterization revealed that the aqueous processed cathodes using the CMC + Poly(2OA0,6-co-IBOMA0,4) biobased latex displayed higher specific capacities than the control with no latex at high C-rates (100.3 ± 2.1 vs 64.5 ± 0.8 mAh g-1 at 5C) and increased capacity retention after 90 cycles at 0.5C (84% vs 81% for CMC with no latex). Overall, the findings of this study suggest that biobased latexes, specifically the CMC + Poly(2OA0,6-co-IBOMA0,4) composition, are promising as environmentally friendly binders for NMC 811 cathodes, contributing to the broader goal of achieving sustainable energy storage systems.

Carrageenans as Sustainable Water-Processable Binders for High-Voltage NMC811 Cathodes

Poly(vinylidene fluoride) (PVDF) is the most common binder for cathode electrodes in lithium-ion batteries. However, PVDF is a fluorinated compound and requires toxic N-methyl-2-pyrrolidone (NMP) as a solvent during the slurry preparation, making the electrode fabrication process environmentally unfriendly. In this study, we propose the use of carrageenan biopolymers as a sustainable source of water-processable binders for high-voltage NMC811 cathodes. Three types of carrageenan (Carr) biopolymers were investigated, with one, two, or three sulfonate groups (SO3-), namely, kappa, iota, and lambda carrageenans, respectively. In addition to the nature of carrageenans, this article also reports the optimization of the cathode formulations, which were prepared by using between 5 wt % of the binder to a lower amount of 2 wt %. Processing of the aqueous slurries and the nature of the binder, in terms of the morphology and electrochemical performance of the electrodes, were also investigated. The Carr binder with 3SO3- groups (3SO3-Carr) exhibited the highest discharge capacities, delivering 133.1 mAh g-1 at 3C and 105.0 mAh g-1 at 5C, which was similar to the organic-based PVDF electrode (136.1 and 108.7 mAh g-1, respectively). Furthermore, 3SO3-Carr reached an outstanding capacity retention of 91% after 90 cycles at 0.5C, which was attributed to a homogeneous NMC811 and a conductive carbon particle dispersion, superior adhesion strength to the current collector (17.3 ± 0.7 N m-1 vs 0.3 ± 0.1 N m-1 for PVDF), and reduced charge-transfer resistance. Postmortem analysis unveiled good preservation of the NMC811 particles, while the 1SO3-Carr and 2SO3-Carr electrodes showed damaged morphologies.

Facile Processing of Unsubstituted π-Conjugated Aromatic Polymers through Water-solubilization Using Aromatic Micelles

π-Conjugated aromatic polymers (πCAPs) are central components of functional materials yet suffer from insolubility without multiple covalent substituents on their backbones. We herein disclose a new strategy for the facile processing of unsubstituted heterocyclic πCAPs (i.e., poly(para-phenylene-2,6-benzobisoxazole) and poly(benzimidazobenzo-phenanthroline)), independent of the polymer length, via non-covalent encircling with aromatic micelles, composed of bent aromatic amphiphiles, in water. The UV-visible studies reveal that the efficiencies of the present encircling method are ~10 to 50-fold higher than those using conventional amphiphiles under the same conditions. The AFM and SEM analyses of the resultant aqueous polymer composites show that otherwise insoluble πCAPs form fine bundles (e.g., ~1 nm in thickness) in the tubular aromatic micelles, through efficient π-stacking interactions. In the same way, pristine poly(para-phenylene) can be dissolved in water, displaying enhanced fluorescence (10-fold), relative to the polymer solid. Two types of unsubstituted πCAPs are likewise co-encircled in water, indicated by UV-visible analysis. Importantly, aqueous processing of the encircled πCAPs into free-standing single- or multicomponent films with submicrometer thickness is demonstrated through a simple filtration-annealing protocol.

Enabling Aqueous Processing of Ni-Rich Layered Oxide Cathode Materials by Addition of Lithium Sulfate

Aqueous processing of Ni-rich layered oxide cathode materials is a promising approach to simultaneously decrease electrode manufacturing costs, while bringing environmental benefits by substituting the state-of-the-art (often toxic and costly) organic processing solvents. However, an aqueous environment remains challenging due to the high reactivity of Ni-rich layered oxides towards moisture, leading to lithium leaching and Al current collector corrosion because of the resulting high pH value of the aqueous electrode paste. Herein, a facile method was developed to enable aqueous processing of LiNi_0.8 Co_0.1 Mn_0.1 O₂ (NCM811) by the addition of lithium sulfate (Li₂ SO₄ ) during electrode paste dispersion. The aqueously processed electrodes retained 80 % of their initial capacity after 400 cycles in NCM811||graphite full cells, while electrodes processed without the addition of Li₂ SO₄ reached 80 % of their capacity after only 200 cycles. Furthermore, with regard to electrochemical performance, aqueously processed electrodes using carbon-coated Al current collector outperformed reference electrodes based on state-of-the-art production processes involving N-methyl-2-pyrrolidone as processing solvent and fluorinated binders. The positive impact on cycle life by the addition of Li₂ SO₄ stemmed from a formed sulfate coating as well as different surface species, protecting the NCM811 surface against degradation. Results reported herein open a new avenue for the processing of Ni-rich NCM electrodes using more sustainable aqueous routes.

Important Impact of the Slurry Mixing Speed on Water-Processed Li4Ti5O12 Lithium-Ion Anodes in the Presence of H3PO4 as the Processing Additive

The aqueous processing of lithium transition metal oxides into battery electrodes is attracting a lot of attention as it would allow for avoiding the use of harmful N-methyl-2-pyrrolidone (NMP) from the cell fabrication process and, thus, render it more sustainable. The addition of slurry additives, for instance phosphoric acid (PA), has been proven to be highly effective for overcoming the corresponding challenges such as aluminum current collector corrosion and stabilization of the active material particle. Herein, a comprehensive investigation of the effect of the ball-milling speed on the effectiveness of PA as a slurry additive is reported using Li₄Ti₅O₁₂ (LTO) as an exemplary lithium transition metal oxide. Interestingly, at elevated ball-milling speeds, rod-shaped lithium phosphate particles are formed, which remain absent at lower ball-milling speeds. A detailed surface characterization by means of SEM, EDX, HRTEM, STEM-EDX, XPS, and EIS revealed that in the latter case, a thin protective phosphate layer is formed on the LTO particles, leading to an improved electrochemical performance. As a result, the corresponding lithium-ion cells comprising LTO anodes and LiNi_0.5Mn_0.3Co_0.2O₂ (NMC₅₃₂) cathodes reveal greater long-term cycling stability and higher capacity retention after more than 800 cycles. This superior performance originates from the less resistive electrode-electrolyte interphase evolving upon cycling, owing to the interface-stabilizing effect of the lithium phosphate coating formed during electrode preparation. The results highlight the importance of commonly neglected─frequently not even reported─electrode preparation parameters.

Investigation of Lithium Polyacrylate Binders for Aqueous Processing of Ni-Rich Lithium Layered Oxide Cathodes for Lithium-Ion Batteries

Ni-rich layered oxide cathodes are promising candidates to satisfy the increasing energy demand of lithium-ion batteries for automotive applications. Aqueous processing of such materials, although desirable to reduce costs and improve sustainability, remains challenging due to the Li⁺ /H⁺ exchange upon contact with water, resulting in a pH increase and corrosion of the aluminum current collector. Herein, an example was given for tuning the properties of aqueous LiNi_0.83 Co_0.12 Mn_0.05 O₂ electrode pastes using a lithium polyacrylate-based binder to find the "sweet spot" for processing parameters and electrochemical performance. Polyacrylic acid was partially neutralized to balance high initial capacity, good cycling stability, and the prevention of aluminum corrosion. Optimized LiOH/polyacrylic acid ratios in water were identified, showing comparable cycling performance to electrodes processed with polyvinylidene difluoride requiring toxic N-methyl-2-pyrrolidone as solvent. This work gives an exemplary study for tuning aqueous electrode pastes properties aiming towards a more environmentally friendly processing of Ni-rich cathodes.

Precursors and Pathways Leading to Enhanced Secondary Organic Aerosol Formation during Severe Haze Episodes

Molecular analyses help to investigate the key precursors and chemical processes of secondary organic aerosol (SOA) formation. We obtained the sources and molecular compositions of organic aerosol in PM_2.5 in winter in Beijing by online and offline mass spectrometer measurements. Photochemical and aqueous processing were both involved in producing SOA during the haze events. Aromatics, isoprene, long-chain alkanes or alkenes, and carbonyls such as glyoxal and methylglyoxal were all important precursors. The enhanced SOA formation during the severe haze event was predominantly contributed by aqueous processing that was promoted by elevated amounts of aerosol water for which multifunctional organic nitrates contributed the most followed by organic compounds having four oxygen atoms in their formulae. The latter included dicarboxylic acids and various oxidation products from isoprene and aromatics as well as products or oligomers from methylglyoxal aqueous uptake. Nitrated phenols, organosulfates, and methanesulfonic acid were also important SOA products but their contributions to the elevated SOA mass during the severe haze event were minor. Our results highlight the importance of reducing nitrogen oxides and nitrate for future SOA control. Additionally, the formation of highly oxygenated long-chain molecules with a low degree of unsaturation in polluted urban environments requires further research.

Characterization and Laser Structuring of Aqueous Processed Li(Ni0.6Mn0.2Co0.2)O2 Thick-Film Cathodes for Lithium-Ion Batteries

Lithium-ion batteries have led the revolution in portable electronic devices and electrical vehicles due to their high gravimetric energy density. In particular, layered cathode material Li(Ni_0.6Mn_0.2Co_0.2)O₂ (NMC 622) can deliver high specific capacities of about 180 mAh/g. However, traditional cathode manufacturing involves high processing costs and environmental issues due to the use of organic binder polyvinylidenfluoride (PVDF) and highly toxic solvent N-methyl-pyrrolidone (NMP). In order to overcome these drawbacks, aqueous processing of thick-film NMC 622 cathodes was studied using carboxymethyl cellulose and fluorine acrylic hybrid latex as binders. Acetic acid was added during the mixing process to obtain slurries with pH values varying from 7.4 to 12.1. The electrode films could be produced with high homogeneity using slurries with pH values smaller than 10. Cyclic voltammetry measurements showed that the addition of acetic acid did not affect the redox reaction of active material during charging and discharging. Rate capability tests revealed that the specific capacities with higher slurry pH values were increased at C-rates above C/5. Cells with laser structured thick-film electrodes showed an increase in capacity by 40 mAh/g in comparison to cells with unstructured electrodes.

Tragacanth Gum as Green Binder for Sustainable Water-Processable Electrochemical Capacitor

Enabling green fabrication processes for energy storage devices is becoming a key aspect in order to achieve a sustainable fabrication cycle. Here, the focus was on the exploitation of the tragacanth gum, an exudated gum like arabic and karaya gums, as green binder for the preparation of carbon-based materials for electrochemical capacitors. The electrochemical performance of tragacanth (TRGC)-based electrodes was thoroughly investigated and compared with another water-soluble binder largely used in this field, sodium-carboxymethyl cellulose (CMC). Apart from the higher sustainability both in production and processing, TRGC exhibited a lower impact on the obstruction of pores in the final active material film with respect to CMC, allowing for more available surface area. This directly impacted the electrochemical performance, resulting in a higher specific capacitance and better rate capability. Moreover, the TRGC-based supercapacitor showed a superior thermal stability compared with CMC, with a capacity retention of about 80 % after 10000 cycles at 70 °C.

Solution-Processed Li2O-Al2O3/TiO2 Nanolaminate Stacks Containing Mobile Lithium Ions and with Increased Breakdown Voltages

An aqueous solution approach has been utilized to prepare nanolaminates of TiO₂ and ionically conductive Li₂O-Al₂O₃ (LiAlO). This new approach utilizes low curing temperatures, resulting in fully oxidized films as demonstrated by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The layered structures have been characterized by scanning electron microscopy, X-ray diffraction, and X-ray reflectivity. Incorporation of sufficiently thick (13 and 27 nm) ion blocking TiO₂ layers into nanolaminate structures with LiAlO layers resulted in an increase in breakdown voltage by more than a factor of two, relative to LiAlO. Nanolaminate structures also preserve the large double layer capacitance of the ionically conductive layer. Increased breakdown strength coupled with large capacitances results in a doubling of ultimate charge storage capacity, illustrating how nanolaminates can be used to improve properties relevant for energy/charge storage applications.

Green Processing of Carbon Nanomaterials

Carbon nanomaterials (CNMs) from fullerenes, carbon nanotubes, and graphene are promising carbon allotropes for various applications such as energy-conversion devices and biosensors. Because pristine CNMs show substantial van der Waals interactions and a hydrophobic nature, precipitation is observed immediately in most organic solvents and water. This inevitable aggregation leads to poor processability and diminishes the intrinsic properties of the CNMs. Highly toxic and hazardous chemicals are used for chemical and physical modification of CNMs, even though efficient dispersed solutions are obtained. The development of an environmentally friendly dispersion method for both safe and practical processing is a great challenge. Recent green processing approaches for the manipulation of CNMs using chemical and physical modification are highlighted. A summary of the current research progress on: i) energy-efficient and less-toxic chemical modification of CNMs using covalent-bonding functionality and ii) non-covalent-bonding methodologies through physical modification using green solvents and dispersants, and chemical-free mechanical stimuli is provided. Based on these experimental studies, recent advances and challenges for the potential application of green-processable energy-conversion and biological devices are provided. Finally, a conclusion section is provided summarizing the insights from the present studies as well as some future perspectives.

Direct observation of aqueous secondary organic aerosol from biomass-burning emissions

The mechanisms leading to the formation of secondary organic aerosol (SOA) are an important subject of ongoing research for both air quality and climate. Recent laboratory experiments suggest that reactions taking place in the atmospheric liquid phase represent a potentially significant source of SOA mass. Here, we report direct ambient observations of SOA mass formation from processing of biomass-burning emissions in the aqueous phase. Aqueous SOA (aqSOA) formation is observed both in fog water and in wet aerosol. The aqSOA from biomass burning contributes to the "brown" carbon (BrC) budget and exhibits light absorption wavelength dependence close to the upper bound of the values observed in laboratory experiments for fresh and processed biomass-burning emissions. We estimate that the aqSOA from residential wood combustion can account for up to 0.1-0.5 Tg of organic aerosol (OA) per y in Europe, equivalent to 4-20% of the total OA emissions. Our findings highlight the importance of aqSOA from anthropogenic emissions on air quality and climate.

High Temperature Stable Separator for Lithium Batteries Based on SiO₂ and Hydroxypropyl Guar Gum

A novel membrane based on silicon dioxide (SiO₂) and hydroxypropyl guar gum (HPG) as binder is presented and tested as a separator for lithium-ion batteries. The separator is made with renewable and low cost materials and an environmentally friendly manufacturing processing using only water as solvent. The separator offers superior wettability and high electrolyte uptake due to the optimized porosity and the good affinity of SiO₂ and guar gum microstructure towards organic liquid electrolytes. Additionally, the separator shows high thermal stability and no dimensional-shrinkage at high temperatures due to the use of the ceramic filler and the thermally stable natural polymer. The electrochemical tests show the good electrochemical stability of the separator in a wide range of potential, as well as its outstanding cycle performance.