• Energy Research

Nickel-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) is one of the most promising Li-ion battery cathode materials and has attracted the interest of the automotive industry. Nevertheless, storage conditions can affect its properties and performance. In this work, both NMC811 powder and electrodes were storage-aged for one year under room conditions. The aged powder was used to prepare electrodes, and the performance of these two aged samples was compared with reference fresh NMC811 electrodes in full Li-ion coin cells using graphite as a negative electrode. The cells were subjected to electrochemical as well as ante- and postmortem characterization. The performance of the electrodes from aged NM811 was beyond expectations: the cycling performance was high, and the power capability was the highest among the samples analyzed. Materials characterization revealed modifications in the crystal structure and the surface layer of the NMC811 during the storage and electrode processing steps. Differences between aged and fresh electrodes were explained by the formation of a resistive layer at the surface of the former. However, the ageing of NMC811 powder was significantly mitigated during the electrode processing step. These novel results are of interest to cell manufacturers for the widespread implementation of NMC811 as a state-of-the-art cathode material in Li-ion batteries.

The use of water‐soluble binders enables the transition to more sustainable batteries by the replacement of toxic N‐methyl‐2‐pyrrolidone (NMP) by water. Herein, two new fluorine‐free poly(ionic liquid)s are proposed as binders for LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes, based on poly(diallyldimethylammonium) (PDADMA) and two‐phosphate counter anions, which are recognized as effective corrosion inhibitors and electrolyte additives. Due to their high ionic conductivity (10−6 S cm−1 at 25 °C) and ability to prevent degradation of NMC811 particles, the PDADMA phosphate cells are able to achieve a 91% of capacity retention after 90 cycles at 0.5C, similar to the organic fluorinated polyvinylidene fluoride (PVDF) (96%) under the same conditions. However, aqueous sodium carboxymethyl cellulose (Na‐CMC) only provides 81% of capacity retention. Among the PDADMA‐based binders under study, PDADMA‐ diethyl phosphate (PDADMA‐DEP) delivers the highest discharge capacity (101.1 mAh g−1) at high C‐rate (5C). Degradation of Na‐CMC electrodes is observed in postmortem analysis and a notable increase in the charge transfer‐resistance. However, the NMC811 particles preserve their spherical shape when PDADMA‐phosphates are used as binders, also leading to lower polarization resistances and improved lithium diffusion. In conclusion, PDADMA‐phosphates manifest high performance as binders for sustainable NMC811 cathodes, while disposing of fluoropolymers and toxic solvents.

Summary New applications and emerging markets in electromobility and large-scale stationary energy storage require the development of new electrochemical systems with higher energy density than current batteries. Rechargeable metal–air batteries, mainly lithium–air and zinc–air systems, are considered one of the most promising candidates. In contrast to lithium, zinc is abundant, inexpensive and its electrodeposition in aqueous electrolytes is relatively easy. Unfortunately, achieving a rechargeable zinc–air battery is still hindered by various technical problems related to the reversibility and lifetime of the electrodes. The most widely used electrolyte in zinc–air batteries has been the classical aqueous alkaline. In this context and with the main objective of providing a complete overview, we studied a wide number of articles starting from the beginning of the development of secondary zinc–air batteries (1970–1980s) to more recent works, with the aim of compiling all available information. It is essential to revise older papers to find relevant information that may get otherwise forgotten and not taken into account to develop new solutions. This information could also be applied in other storage systems based on zinc as nickel–zinc, zinc hybrid or zinc-ion. Copyright © 2016 John Wiley & Sons, Ltd.

Herein, the post-mortem study on 16 Ah graphite//LiFePO4 pouch cells is reported. Aiming to understand their failure mechanism, taking place when cycling at low temperature, the analysis of the cell components taken from different portions of the stacks and from different positions in the electrodes, is performed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS). Also, the recovered electrodes are used to reassemble half-cells for further cycle tests. The combination of the several techniques detects an inhomogeneous ageing of the electrodes along the stack and from the center to the edge of the electrode, most probably due to differences in the pressure experienced by the electrodes. Interestingly, XPS reveals that more electrolyte decomposition took place at the edge of the electrodes and at the outer part of the cell stack independently of the ageing conditions. Finally, the use of high cycling currents buffers the low temperature detrimental effects, resulting in longer cycle life and less inhomogeneities.

Transitioning to more ambitious electrode formulations facilitates developing high-energy density cells, potentially fulfilling the demands of electric car manufacturers. In this context, the partial replacement of the prevailing anode active material in lithium-ion cells, graphite, with silicon-based materials enhances its capacity. Nevertheless, this requires adapting the rest of the components and harmonizing the electrode integration in the cell to enhance the performance of the resulting high-capacity anodes. Herein, starting from a replacement in the standard graphite anode recipe with 22% silicon suboxide at laboratory scale, the weight fraction of the electrochemically inactive materials was optimized to 2% carbon black/1% dispersant/3% binder combination before deriving an advantage from including single-wall carbon nanotubes in the formulation. In the second part, the recipe was upscaled to a semi-industrial electrode coating and cell assembly line. Then, 1 Ah lithium-ion pouch cells were filled and tested with different commercial electrolytes, aiming at studying the dependency of the Si-based electrodes on the additives included in the composition. Among all the electrolytes employed, the EL2 excelled in terms of capacity retention, obtaining a 48% increase in the number of cycles compared to the baseline electrolyte formulation above the threshold capacity retention value (80% state of health).

Silicon has become an integral negative electrode component for lithium-ion batteries in numerous applications including electric vehicles and renewable energy sources. However, its high capacity and low cycling stability represent a significant trade-off that limits its widespread implementation in high fractions in the negative electrode. Herein, we assembled high-capacity (1.8 Ah) cells using a nanoparticulate silicon–graphite (1:7.1) blend as the negative electrode material and a LiFePO4–LiNi0.5Mn0.3Co0.2O2 (1:1) blend as the positive electrode. Two types of cells were constructed: cylindrical 18650 and pouch cells. These cells were subjected both to calendar and cycling aging, the latter exploring different working voltage windows (2.5–3.6 V, 3.6–4.5 V, and 2.5–4.5 V). In addition, one cell was opened and characterised at its end of life by means of X-ray diffraction, scanning electron microscopy, and further electrochemical tests of the aged electrodes. Si degradation was identified as the primary cause of capacity fade of the cells. This work highlights the need to develop novel strategies to mitigate the issues associated with the excessive volumetric changes of Si.