Suitable Cathode NMP Replacement for Efficient Sustainable Printed Li-Ion Batteries

Abstract

N -methyl-2-pyrrolidone (NMP) is the most common solvent for manufacturing cathode electrodes in the battery industry; however, it is becoming restricted in several countries due to its negative environmental impact. Taking into account that ∼99% of the solvent used during electrode fabrication is recovered, dimethylformamide (DMF) is a considerable candidate to replace NMP. The lower boiling point and higher ignition temperature of DMF lead to a significant reduction in the energy consumption needed for drying the electrodes and improve the safety of the production process. Additionally, the lower surface tension and viscosity of DMF enable improved current collector wetting and higher concentrations of the solid material in the cathode slurry. To verify the suitability of DMF as a replacement for NMP, we utilized screen printing, a fabrication method that provides roll-to-roll compatibility while allowing controlled deposition and creation of sophisticated patterns. The battery systems utilized NMC (LiNi x Mn y Co z O 2 ) chemistry in two configurations: NMC523 and NMC88. The first, well-established NCM523, was used as a reference, while NMC88 was used to demonstrate the potential of the proposed method with high-capacity materials. The cathodes were used to create coin and pouch cell batteries that were cycled 1000 times. The achieved results indicate that DMF can successfully replace NMP in the NMC cathode fabrication process without compromising battery performance. Specifically, both the NMP blade-coated and DMF screen-printed batteries retained 87 and 90% of their capacity after 1000 (1C/1C) cycles for NMC523 and NMC88, respectively. The modeling results of the drying process indicate that utilizing a low-boiling-point solvent (DMF) instead of NMP can reduce the drying energy consumption fourfold, resulting in a more environmentally friendly battery production process.

Green Synthesis for Battery Materials: A Case Study of Making Lithium Sulfide via Metathetic Precipitation

“…To obtain the dry product, the residual NMP coexisting with the as-precipitated Li 2 S after centrifugation/filtration needs to be removed. As NMP is difficult to evaporate off due to its high boiling point (202 °C) and high viscosity (1.66 mPa·S), the product was rinsed twice by a low-boiling-point (83 °C) and low-viscosity (0.43 mPa·S) solvent dimethyl ether (DME) and then heated at 200 °C for 6 h . Afterward, the sample was reheated in a quartz tube, and meanwhile, the exhaust gas was monitored by mass spectrometry (MS).…”

“…To obtain the dry product, the residual NMP coexisting with the as-precipitated Li 2 S after centrifugation/filtration needs to be removed. As NMP is difficult to evaporate off due to its high boiling point (202 °C) and high viscosity (1.66 mPa•S), 26 the product was rinsed twice by a low-boiling-point (83 °C) and low-viscosity (0.43 mPa•S) solvent dimethyl ether (DME) and then heated at 200 °C for 6 h. 27 Afterward, the sample was reheated in a quartz tube, and meanwhile, the exhaust gas was monitored by mass spectrometry (MS). As shown in Figure 2c, the signals of NMP and DME after heating the sample tube both showed zero increase (for NMP) and tiny increase (for DME, from 7.39 × 10 −11 to 1.25 × 10 −10 mbar, Δ 1 = 5.11 × 10 −11 mbar), confirming the effectiveness of solvent removal.…”

A 5V-class Cobalt-free Battery Cathode with High Loading Enabled by Dry Coating

“…Conventionally, N-Methyl-2-pyrrolidone (NMP) is widely used as the mixing solvent due to its excellent chemical and thermal stability as well as its ability to dissolve polyvinylidene fluoride (PVDF) binder, which offers high mechanical and electrochemical stability in cathode operation. [27][28] However, NMP's notorious toxicity and requirement of expensive solvent recycling equipment make the slurry-based fabrication process costly (> $5M for NMP solvent recovery equipment), more energy demanding, and less sustainable. 29 Unlike the abovementioned slurry-based methods, fabrication using binder fibrillation is a dry process, where polytetrafluoroethylene (PTFE) is the widely used binder, with the first use in dry electrodes for LIBs reported in 1979.…”

Gravure Printing of Graphite-Based Anodes for Lithium-Ion Printed Batteries

“…Among the printing techniques, widely used industrial gravure printing appears very appealing for the cost-effective production of functional films, especially in the field of energy, thanks to its ability to combine high speed (up to 400 m/min) and high printing quality (resolution below 0.2 µm) [ 8 , 9 , 10 ]. The gravure is a roll-to-roll large-area printing technique able to produce films of every shape with a very limited waste of energy and materials [ 11 ]. In particular, the material wastage limitation is attributed to the large-scale production process (in-line) while most of the used deposition technologies are small-area and/or batch processes resulting in waste.…”

“…The proposed anodes involved a water-based binder, and water was used as the main solvent in the ink formulation, in response to the most recent green requests on highly sustainable and safe manufacturing and improving the energy efficiency [ 5 , 11 ].…”