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 LiNi0.8 Co0.1 Mn0.1 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.

Opportunities and Challenges of Li2 C4 O4 as Pre-Lithiation Additive for the Positive Electrode in NMC622||Silicon/Graphite Lithium Ion Cells.

Silicon (Si)-based negative electrodes have attracted much attention to increase the energy density of lithium ion batteries (LIBs) but suffer from severe volume changes, leading to continuous re-formation of the solid electrolyte interphase and consumption of active lithium. The pre-lithiation approach with the help of positive electrode additives has emerged as a highly appealing strategy to decrease the loss of active lithium in Si-based LIB full-cells and enable their practical implementation. Here, the use of lithium squarate (Li2 C4 O4 ) as low-cost and air-stable pre-lithiation additive for a LiNi0.6 Mn0.2 Co0.2 O2 (NMC622)-based positive electrode is investigated. The effect of additive oxidation on the electrode morphology and cell electrochemical properties is systematically evaluated. An increase in cycle life of NMC622||Si/graphite full-cells is reported, which grows linearly with the initial amount of Li2 C4 O4 , due to the extra Li+ ions provided by the additive in the first charge. Post mortem investigations of the cathode electrolyte interphase also reveal significant compositional changes and an increased occurrence of carbonates and oxidized carbon species. This study not only demonstrates the advantages of this pre-lithiation approach but also features potential limitations for its practical application arising from the emerging porosity and gas development during decomposition of the pre-lithiation additive.

Practical Implementation of Magnetite-Based Conversion-Type Negative Electrodes via Electrochemical Prelithiation.

We report the performance of a conversion-type magnetite-decorated partially reduced graphene oxide (Fe3O4@PrGO) negative electrode material in full-cell configuration with LiNi0.8Co0.15Al0.05O2 (NCA) positive electrodes. To enable practical implementation of the conversion-type negative electrodes in full cells, the beneficial impact of electrochemical prelithiation on mitigating active lithium losses and improving cycle life is shown here for the first time in the literature. The initial Coulombic efficiency (ICE) of the full cells is improved from 70.8 to 91.2% by prelithiation of the negative electrode to 35% of its specific delithiation capacity. The prelithiation is shown to improve the surface passivation of the Fe3O4@PrGO electrodes, leading to less electrolyte reduction on their surface which is prominent from the significantly lowered accumulated Coulombic inefficiency values, lower polarization growth, and doubled capacity retention by the 100th cycle. The reduced surface reactions of the negative electrode by prelithiation also aids in reducing the extent of aging of the NCA positive electrode. Overall, the prelithiation leads to a longer cycle life, where a retained capacity of 60.4% was achieved for the prelithiated cells by the end of long-term cycling, which is 3 times higher than the capacity retention of the non-prelithiated cells. Results reported herein indicate for the first time that the electrochemical prelithiation of the Fe3O4@PrGO electrode is a promising approach for making conversion negative electrode materials more applicable in lithium-ion batteries.

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 LiNi0.83 Co0.12 Mn0.05 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.

Synergistic Effects of Surface Coating and Bulk Doping in Ni-Rich Lithium Nickel Cobalt Manganese Oxide Cathode Materials for High-Energy Lithium-Ion Batteries.

Invited for this month's cover is a combined work of the Helmholtz Institute Münster together with the MEET Battery Research Center and the Universities of Münster and Mainz. The cover shows multiple treatment choices for the modification of cathode active materials for lithium-ion batteries. Similar to a car wash program, the treatment will typically result in an improvement of the status quo. However, the best treatment procedure will only become clear if all modification pathways are explored. The Research Article itself is available at 10.1002/cssc.202102220.

Synergistic Effects of Surface Coating and Bulk Doping in Ni-Rich Lithium Nickel Cobalt Manganese Oxide Cathode Materials for High-Energy Lithium Ion Batteries.

Ni-rich layered oxide cathodes are promising candidates to satisfy the increasing energy demand of lithium-ion batteries for automotive applications. Thermal and cycling stability issues originating from increasing Ni contents are addressed by mitigation strategies such as elemental bulk substitution ("doping") and surface coating. Although both approaches separately benefit the cycling stability, there are only few reports investigating the combination of two of such approaches. Herein, the combination of Zr as common dopant in commercial materials with effective Li2 WO4 and WO3 coatings was investigated with special focus on the impact of different material processing conditions on structural parameters and electrochemical performance in nickel-cobalt-manganese (NCM) || graphite cells. Results indicated that the Zr4+ dopant diffusing to the surface during annealing improved the electrochemical performance compared to samples without additional coatings. This work emphasizes the importance to not only investigate the effect of individual dopants or coatings but also the influences between both.

Porous Graphene-like Carbon from Fast Catalytic Decomposition of Biomass for Energy Storage Applications.

A novel carbon material made of porous graphene-like nanosheets was synthesized from biomass resources by a simple catalytic graphitization process using nickel as a catalyst for applications in electrodes for energy storage devices. A recycled fiberboard precursor was impregnated with saturated nickel nitrate followed by high-temperature pyrolysis. The highly exothermic combustion of in situ formed nitrocellulose produces the expansion of the cellulose fibers and the reorganization of the carbon structure into a three-dimensional (3D) porous assembly of thin carbon nanosheets. After acid washing, nickel particles are fully removed, leaving nanosized holes in the wrinkled graphene-like sheets. These nanoholes confer the resulting carbon material with ≈75% capacitance retention, when applied as a supercapacitor electrode in aqueous media at a specific current of 100 A·g-1 compared to the capacitance reached at 20 mA·g-1, and ≈35% capacity retention, when applied as a negative electrode for lithium-ion battery cells at a specific current of 3720 mA·g-1 compared to the specific capacity at 37.2 mA·g-1. These findings suggest a novel way for synthesizing 3D nanocarbon networks from a cellulosic precursor requiring low temperatures and being amenable to large-scale production while using a sustainable starting precursor such as recycled fiberwood.

Iron-Catalyzed Graphitic Carbon Materials from Biomass Resources as Anodes for Lithium-Ion Batteries.

Graphitized carbon materials from biomass resources were successfully synthesized with an iron catalyst, and their electrochemical performance as anode materials for lithium-ion batteries (LIBs) was investigated. Peak pyrolysis temperatures between 850 and 2000 °C were covered to study the effect of crystallinity and microstructural parameters on the anodic behavior, with a focus on the first-cycle Coulombic efficiency, reversible specific capacity, and rate performance. In terms of capacity, results at the highest temperatures are comparable to those of commercially used synthetic graphite derived from a petroleum coke precursor at higher temperatures, and up to twice as much as that of uncatalyzed biomass-derived carbons. The opportunity to graphitize low-cost biomass resources at moderate temperatures through this one-step environmentally friendly process, and the positive effects on the specific capacity, make it interesting to develop more sustainable graphite-based anodes for LIBs.

Performance of biomorphic Silicon Carbide as particulate filter in diesel boilers.

Biomorphic Silicon Carbide (bioSiC) is a novel porous ceramic material with excellent mechanical and thermal properties. Previous studies have demonstrated that it may be a good candidate for its use as particle filter media of exhaust gases at medium or high temperature. In order to determine the filtration efficiency of biomorphic Silicon Carbide, and its adequacy as substrate for diesel particulate filters, different bioSiC-samples have been tested in the flue gases of a diesel boiler. For this purpose, an experimental facility to extract a fraction of the boiler exhaust flow and filter it under controlled conditions has been designed and built. Several filter samples with different microstructures, obtained from different precursors, have been tested in this bench. The experimental campaign was focused on the measurement of the number and size of particles before and after placing the samples. Results show that the initial efficiency of filters made from natural precursors is severely determined by the cutting direction and associated microstructure. In biomorphic Silicon Carbide derived from radially cut wood, the initial efficiency of the filter is higher than 95%. Nevertheless, when the cut of the wood is axial, the efficiency depends on the pore size and the permeability, reaching in some cases values in the range 70-90%. In this case, the presence of macropores in some of the samples reduces their efficiency as particle traps. In continuous operation, the accumulation of particles within the porous media leads to the formation of a soot cake, which improves the efficiency except in the case when extra-large pores exist. For all the samples, after a few operation cycles, capture efficiency was higher than 95%. These experimental results show the potential for developing filters for diesel boilers based on biomorphic Silicon Carbide.