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Secondary zinc-air batteries (ZABs) offer a promising alternative for the future of sustainable energy storage. However, the current capability of secondary ZABs is far from satisfactory. The limitations for achieving high reversibility are mainly related to the bifunctional air electrodes as it severely hampers practical applications and commercialization of secondary ZABs. Many efforts have been devoted to the development of efficient and corrosion resistant bifunctional electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In ZABs, carbon is commonly used as conductive additive, however, it has been observed that carbon materials are not resistant to the high positive voltages applied in electrical recharge. In this work, the use of metallic nickel as alternative conductive additive in bifunctional air electrodes is explored and compared with carbon nanotubes (CNT). We demonstrate that the chemical resistance of CNT does not limit the electrode performance; but the density of the additive as well as its interaction with the active material is crucial for achieving long cycle life. The use of Ni as conductive agent in secondary ZABs boosted the cycle life by delivering more than 2,400 cycles, in contrast to the 88 cycles delivered by the analogous carbon-based battery. This work was supported by CDTI (ALMAGRID of the “CERVERA Centros Tecnológicos” program, CER-20191006), the Basque Country Government (CIC energiGUNE’20 of the ELKARTEK program, N° Exp. KK-2020/0078), the European Commission through the project ZABCAT “A New Zn-Air Battery Prototype to Overcome Cathode Degradation Through Catalyst Confinement” (grant agreement 966743) and the Ministerio de Ciencia e Innovación through the project AVANZA “Advanced Zn-Air Battery Prototype for the Energy Transition Horizon” (TED2021-131451B-C22). N. Ortiz-Vitoriano thanks Ramon y Cajal grant (RYC-2020-030104-I) funded by MCIN/AEI/10.13039/501100011033 and by FSE invest in your future.

In recent decades, rechargeable Mg batteries (RMBs) technologies have attracted much attention because the use of thin Mg foil anodes may enable development of high‐energy‐density batteries. One of the most critical challenges for RMBs is finding suitable electrolyte solutions that enable efficient and reversible Mg cells operation. Most RMB studies concentrate on the development of novel electrolyte systems, while only few studies have focused on the practical feasibility of using pure metallic Mg as the anode material. Pure Mg metal anodes have been demonstrated to be useful in studying the fundamentals of nonaqueous Mg electrochemistry. However, pure Mg metal may not be suitable for mass production of ultrathin foils (, Ultra‐thin Mg alloy: Rechargeable magnesium batteries are considered as the most promising alternative to lithium battery technologies Similar electrochemical performance of 100 μm thick pure Mg foils and 25 μm thin and ductile AZ31 Mg alloy foils as anodes in rechargeable Mg batteries is demonstrated. Comprising Chevrel‐phase (Mo6S8) cathodes, thin foils of AZ31 Mg alloy can serve as very suitable anodes in rechargeable Mg batteries.

The organic solvents that are widely used as electrolytes in lithium ion batteries present safety challenges due to their volatile and flammable nature. The replacement of liquid organic electrolytes by non-volatile and intrinsically safe ceramic solid electrolytes is an effective approach to address the safety issue. However, the high total resistance (bulk and grain boundary) of such compounds, especially at low temperatures, makes those solid electrolyte systems unpractical for many applications where high power and low temperature performance are required. The addition of small quantities of a polymer is an efficient and low cost approach to reduce the grain boundary resistance of inorganic solid electrolytes. Therefore, in this work, we study the ionic conductivity of different composites based on non-sintered lithium lanthanum titanium oxide (La0.5Li0.5TiO3) as inorganic ceramic material and organic polymers with different characteristics, added in low percentage (0.5Li0.5TiO3., We thank the Spanish Ministry for Science and Technology (MAT2007-64486-C07-05) and CDTI (ALMAGRID of the ‘CERVERA Centros Tecnológicos’ program, CER-20191006) for financial their support. JS, AV, SG, and FG also want to acknowledge Agencia Española de Investigación /Fondo Europeo de Desarrollo Regional (FEDER/UE) for funding the projects PID2019-106662RB-C41, C42, C43, and C44.

Thermal runaway of three lithium ion cells (“A” - NCA/Graphite, “B” - LFP/Graphite, “C” - NCA/LTO) at 0%, 50%, and 100% state of charge (SOC) is studied by Accelerating Rate Calorimetry (ARC). Thermal behaviour of harvested positive and negative electrodes at three SOC (0%, 50%, and 100%) is analyzed using Differential Scanning Calorimetry (DSC). Thermal stability of recovered separators is also investigated by DSC. Harvested electrodes and separators are studied alone and in contact with a liquid electrolyte. The thermal behaviour of each component and its contribution is quantified and thoroughly discussed. A crucial negative impact of the state of charge and presence of highly flammable liquid electrolyte on the thermal instability of the investigated cells and “electrode - electrolyte” systems is clearly revealed. Among studied cells, LiFePO4/Graphite one is the safest due to intrinsic thermal stability of lithium iron phosphate LiFePO4 based cathode and despite the fact of using a microporous polyolefin separator with limited thermal stability.

Redox polymers with high energy storage capacity are searched in order to diminish the weight to the actual batteries. Poly(anthraquinonyl sulfide) PAQS is a popular redox polymer which has shown a high performance cathode for lithium, sodium and magnesium batteries. Although PAQS cathodes show high cycling stability it has a relatively low theoretical specific capacity of 225 mAh/g. In this paper we show the synthesis and characterization of new poly(anthraquinonyl sulfides) PAQxS in an attempt to improve the specific capacity of PAQS. Thus, a series of PAQxS polymers with different polysulfide segment lengths (x between 2 and 9 sulfur atoms) have been synthesized in high yields by reacting in situ formed sodium polysulfides with 1,5-dicholoroanthraquinone. The poly(anthraquinonyl sulfides) powders were characterized by ATR-FTIR, solid state 13C NMR for the organic part and Raman spectroscopy for the chalcogenide part. This characterization confirmed the chemical structure of the PAQxS based on an anthra...

Rechargeable magnesium batteries (RMBs) are highly attractive due to their high volumetric capacity, relatively low cost, and enhanced safety. Significant progress in the development of RMBs was the introduction of nonaqueous electrolyte solutions that enable reversible electrodeposition of Mg metal. These solutions contain a unique mixture of organo−aluminum and chloro−aluminum species. While these solutions are shown to be stable during cathodic polarization, the presence of chlorine anions in the solution can promote the corrosion process during the anodic polarization. Among all the cell components, the cathode current collector is most prone to corrosive processes. In this study, we characterize the corrosion behavior of different metallic current collectors in standard APC (All-Phenyl Complex) electrolyte solutions by following their electrochemical response and surface morphology changes during anodic polarization. In addition, we investigate the influence of carbon coating on the corrosive behavior of Ni metal. The study shows the efficacy of carbon coating on the current collector. We demonstrate that Ni@C current collector possesses higher corrosion pit initiation potential (2.25 V vs Mg/Mg2+) with respect to the uncoated metallic foils. Improving the anodic stability of the current collectors is a crucial step in the development of a practical rechargeable Mg battery.

Summary Electricity will increasingly be produced from sources that are geographically decentralized and/or intermittent in their nature. In consequents, there is an urgent need to increase the storage of energy to guarantee the continuity of energy supply. Rechargeable zinc-air battery is a promising technology due to the high theoretical energy density and the abundant and environmentally benign materials that are used. In the state of the art, the information about secondary zinc anode for rechargeable zinc-air batteries is scarce. The main development of the technology has been lately concentrated on the bifunctional air electrodes while the used zinc anode is mainly based on a planar zinc electrode providing low specific energy densities for the full system. This overview compiles the available information in the literature regarding the development and manufacturing of zinc anodes for electrical rechargeable batteries applications, where secondary porous zinc electrodes are generally desired. In this context, the zinc-based anode electrode composition (namely, active material, binder, conductive material, current collector, and additives), pretreatments, and processing techniques are described and their impact on the zinc anode performance analyzed.

Aqueous zinc–air batteries (ZABs) are a low-cost, safe, and sustainable technology for stationary energy storage. ZABs with pH-buffered near-neutral electrolytes have the potential for longer lifetime compared to traditional alkaline ZABs due to the slower absorption of carbonates at nonalkaline pH values. However, existing near-neutral electrolytes often contain halide salts, which are corrosive and threaten the precipitation of ZnO as the dominant discharge product. This paper presents a method for designing halide-free aqueous ZAB electrolytes using thermodynamic descriptors to computationally screen components. The dynamic performance of a ZAB with one possible halide-free aqueous electrolyte based on organic salts is simulated using an advanced method of continuum modeling, and the results are validated by experiments. X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy measurements of Zn electrodes show that ZnO is the dominant discharge product, and operando pH measurements confirm the stability of the electrolyte pH during cell cycling. Long-term full cell cycling tests are performed, and rotating ring disk electrode measurements elucidate the mechanism of oxygen reduction reaction and oxygen evolution reaction. The analysis shows that aqueous electrolytes containing organic salts could be a promising field of research for zinc-based batteries, due to their Zn2+ chelating and pH buffering properties. The remaining challenges including the electrochemical stability of the electrolyte components are discussed., publishedVersion

Lithium-sulfur batteries are among the most promising next-generation battery systems due to the high capacity of sulfur as cathodic material. Beyond its interesting intrinsic properties, sulfur possesses a very low conductivity and complex electrochemistry, which involves the high solubility of the lithium sulfides in the electrolyte. These two characteristics are at the core of a series of limitations of its performance as active cathode material, which leads to batteries with low cyclability. Recently, inverse vulcanized sulfur was shown to retain capacity far better than elemental sulfur, leading to batteries with excellent cyclability. Nevertheless, the diene co-monomers used so far in the inverse vulcanization process are man-made molecules. Herein, a tentative work on exploring inverse vulcanization using two naturally available monomers, diallyl sulfide and myrcene, is presented. The inverse vulcanization of sulfur was successfully completed, and the resulting polymers were characterized by FTIR, NMR spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Afterwards these polymers were tested as cathodic materials in lithium-sulfur cells. The sulfur-natural dienes materials exhibited high capacity at different C rates and high lifetime over 200 cycles with very high capacity retention at a moderate C rate of C/5. Altogether, these materials made from inexpensive and abundant chemicals are an excellent option as sustainable materials for electrochemical energy storage.

An efficient, durable and low cost air cathode with low polarization between the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential for a high performance and durable secondary zinc-air battery. Different valence states and morphologies of MnxOy catalysts were synthetized via thermal treatment of EMD (generating Mn2O3 and Mn3O4) and acid digestion of synthetized Mn2O3 (producing a-MnO2) in order to develop an efficient Bifunctional Air Electrode (BAE). Change in the ratio H+ to Mn2O3 during the acid digestion affects the sample microporosity, the crystallographic plane distribution, as well as the physical and chemical adsorbed water which was related to defects, i.e. cation vacancies (Mn4+) and Mn3+. These characteristics were discussed and linked to the electrocatalytic activity. The best ORR performing catalyst was that with the higher surface water content (associated to material BET surface area) and a (310) surface as the 2nd more contributing plane (after 211). On the other hand, the catalyst with the higher structural water and with (110) and (200) crystallographic planes being the most intensity contributors (after 211) was the most OER active material. In this work, it was able to find a relationship between catalyst structure and air-efficiency through a volcano-like relationship between air-efficiency and surface water content. Air-efficiency (also take as round-efficiency discharge/charge in battery context) can be taken as a good descriptor of potentially good materials for Zn-Air secondary batteries technology. In this term, we were able to prepare a Bifunctional Air Electrode based on the selected a-MnO2 sample which demonstrated a roundefficiency of 53%, a DV around 1 V and a neglected loss of the charge potential (about 2.1 V) over the entire lifecycle test (more 200 cycles over 30 hours) with a capacity retention superior to 95%. European Commission H2020: Proyecto ZAS “Zinc Air Secondary innovative nanotech based batteries for efficient energy storage” (Grant Agreement 646186)

The positive electrodes based on nano- and micrometric carbon coated LiFePO 4 (LFP) powders are prepared via aqueous slurry processing using “normal” and “intensive” mixing procedures. The XRD, XPS, and electrochemical characterization reveal that the “intensive” mixing process improves the discharge C-rate capability of the n-LFP cathode however provokes formation of an undesirable thin surface layer enriched by Fe 3+ species. The waterborne graphite anodes and LiFePO 4 cathodes for the energy and power cells are being developed, upscaled and manufactured on a pilot plant. Energy LiFePO 4 /C pouch cells demonstrate outstanding durability maintaining 80% of initial discharge capacity (IDC) after 7450 and 2400 full cycles under 1D and 4D discharge currents, respectively. Moreover, further cycling of the energy cell working under 1C/4D protocol reveals its extra-long secondary life (70% of IDC on 9200 th cycle). Power LiFePO 4 /C pouch cell shows long lasting cycle life retaining 80% of IDC after 3350 cycles under harsh cycling conditions (3C/8D). The reported results are being achieved despite confirmed water release from lithium iron phosphate cathodes to the electrolyte. Finally, viability of aqueous processing of the electrodes without sacrificing electrochemical performance of LiFePO 4 /C batteries is clearly proven.

Lithium-Sulfur (Li-S) battery technology is one of the promising candidates for next generation energy storage systems. Many studies have focused on the cathode materials to improve the cell performance. In this work we present a series of poly (S-DVB) copolymers synthesised by inverse vulcanization of sulfur with divinylbenzene (DVB). The poly (S-DVB) cathode shows excellent cycling performances at C/2 and C/4 current rates, respectively. It was demonstrated poly (S-DVB) copolymer containing 20% DVB did not influence the electrochemical performance of the sulfur material, compared to elemental sulfur as high specific capacities over ∼700 mAh g −1 at 500 cycles were achieved at C/4 current rate, comparable to conventional carbon-based S cathodes. However, the use of copolymer network is assumed to act firstly as sulfur reservoir and secondly as mechanical stabilizer, enhancing significantly the cycling lifetime. The Li-poly (S-DVB) cell demonstrated an extremely low degradation rate of 0.04% per cycle achieving over 1600 cycles at C/2 current rate.

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.

Electrically rechargeable zinc-air batteries have attracted significant research interest due to their low price, high security and energy density. However, they present low power density which should be improved to increase its commercial possibilities. In that sense, different strategies were followed in the state of the art including the development of new kind of high power based technology: secondary zinc-air/silver hybrid (ZASH) battery. This technology integrates the low cost and high energy density of zinc-air and the high power density of silver-zinc technologies. However, the approaches described in the state of the art are focused on material development at half-cell level without really knowing the practical technology characteristics on basis of all cell components. Exploring somewhat beyond the beaten path of material development could lead to an approach for future progress in the technology oriented to practical applications in the market. In the present work different silver loadings are analyzed and the practical characteristics of ZASH battery are defined. Here reported secondary zinc-air/silver battery presents an outstanding stability higher than 1,000 h with competitive specific energy (52.22 Wh kg−1Cell) and energy density (253.64 Wh L−1Cell).

This paper presents a combined theoretical and experimental investigation of aqueous near-neutral electrolytes based on chloride salts for rechargeable zinc-air batteries (ZABs). The resilience of near-neutral chloride electrolytes in air could extend ZAB lifetime, but theory-based simulations predict that such electrolytes are vulnerable to other challenges including pH instability and the unwanted precipitation of mixed zinc hydroxide chloride products. In this work, we combine theory-based simulations with experimental methods such as full cell cycling, operando pH measurements, ex-situ XRD, SEM, and EDS characterization to investigate the performance of ZABs with aqueous chloride electrolytes. The experimental characterization of near-neutral ZAB cells observes the predicted pH instability and confirms the composition of the final discharge products. Steps to promote greater pH stability and control the precipitation of discharge products are proposed., 13 pages, 12 figures

Development of secondary zinc-air batteries goes through a proper specification of the electrolyte formulation adapted to extend the cycle life of the battery. However, defining an optimal formulation is not a trivial work due to the specific requirements for each electrode. At half-cell level it has been determined that ZnO-saturated 4 M KOH with 2 M KF and 2 M K2CO3 (4s-2) is the most suitable formulation to increase the cycle life of secondary zinc electrode whereas additive-free 8 M KOH (8-0) formulation is more beneficial for the bifunctional air electrode (BAE). Through this systematic cycle life assessment, it has been found that the most suitable electrolyte formulation for the full cell system is a compendium for both electrodes requirements. It has determined an optimal electrolyte formulation for the full system consisting of ZnO-saturated 7 M KOH with 1.4 M KF and 1.4 M K2CO3 (7s-1.4). This electrolyte composition increases at least 2.5 times the reversibility of the secondary zinc-air battery in comparison to that employing the traditional formulation for primary zinc-air batteries (additive free 8 M KOH). In addition, the development of a proper cell design or separator is also necessary to further enhance the secondary zinc-air cycle life. Basque Country Government (ELKARTEK 2016 program); Basque Country University (UPV/EHU) under the program ZABALDUZ2012; European Commission H2020 (project ZAS) (grant/award number: 646186).

An innovative route to obtain Ni/NiO core-shell foam-based anodes for lithium-ion batteries is presented. Commercial Ni foams are conformally coated with NiO by ionic liquid-based electrodeposition. The electrochemical behavior of the resulting Ni/NiO electrodes in half coin cells with lithium counter electrode is investigated. The results are qualitatively correlated to the microstructural properties, including effects of the thermal annealing at 500 °C, of the NiO shell. The formation a NiO sub-layer by the thermal oxidation of the Ni foam seems to play a crucial role in the enhanced performance of the annealed Ni/NiO anodes, which exhibit a reversible discharge capacity around 0.8 mAh/cm 2 . Furthermore, the Ni/NiO core-shell foam-based anodes are evaluated in full coin Li-ion cells with high voltage LiMn 0.8 Fe 0.2 PO 4 cathode. Promising cyclability is reached in NiO-LMFP coin cells under cycling at 0.4C.

Electrically rechargeable zinc-air batteries have gained great attention in recent years due to their capacity to provide high energy density. The electrolyte has played a key role in the advancement of this technology and recently, aqueous chloride-based electrolytes have been demonstrated as a possible alternative to the traditional alkaline system. This study investigates, for the first time, the selection of an optimal bifunctional air electrode (BAE) formulation in two aqueous chloride-based electrolytes (pH4 and pH8) for zinc-air batteries. The effect of different MnxOy-based catalysts and carbon materials with different electrode formulations are electrochemically analyzed in the two electrolytic systems. The BAE formulation containing 20 wt% γ-MnO2, 70 wt% carbon nanotubes (CNT) and 10 wt% PTFE demonstrated the lowest overpotential, among all studied formulations, in both electrolytes. The cycling tests carried out using the selected electrode formulation, at both pH4 and pH8, reveal stable discharge-charge cycling over 400 h with an overpotential lower than 1.1 V. Moreover, the absence of manganese dissolution for the pH8 electrolyte is confirmed by ICP analysis, which overcomes the issue concerning the dissolution of manganese in more acidic media. Contrary to what is stated in conventional alkaline zinc-air batteries, where α-MnO2 is the most promising catalyst, this study highlights the potential of γ-MnO2-based BAEs when using aqueous chloride-based electrolyte.

The revived interest and research on the development of novel energy storage systems with exceptional inherent safety, environmentally benign and low cost for integration in large scale electricity grid and electric vehicles is now driven by the global energy policies. Within various technical challenges yet to be resolved and despite extensive studies, the low cycle life of the zinc anode is still hindering the implementation of rechargeable zinc batteries at industrial scale. This review presents an extensive overview of electrolytes for rechargeable zinc batteries in relation to the anode issues which are closely affected by the electrolyte nature. Widely studied aqueous electrolytes, from alkaline to acidic pH, as well as non-aqueous systems including polymeric and room temperature ionic liquids are reported. References from early rechargeable Zn-air research to recent results on novel Zn hybrid systems have been analyzed. The ambition is to identify the challenges of the electrolyte system and to compile the proposed improvements and solutions. Ultimately, all the technologies based on zinc, including the more recently proposed novel zinc hybrid batteries combining the strong points of lithium-ion, redox-flow and metal-air systems, can benefit from this compilation in order to improve secondary zinc based batteries performance. Basque Country University (ZABALDUZ2012 program), and the Basque Country Government (Project: CIC energiGUNÉ16 of the ELKARTEK program) and the European Commission through the project ZAS: “Zinc Air Secondary innovative nanotech based batteries for efficient energy storage” (Grant Agreement 646186)

In this work carbon coated lithium iron phosphate (C-LiFePO 4 )/polypyrrole (PPy) composite preparation has been carried out using electrochemical techniques. This composite has been deposited on a stainless steel mesh in order to use it as a cathode in a lithium-ion battery. When an oxidation potential is applied to the working electrode, the pyrrole monomer is polymerized and the C-LiFePO 4 particles are incorporated into the polymer matrix and bound to the polymer and mesh. An experimental procedure was performed in order to understand how the composite formation is carried out and what the oxidation state of the composite material is during the charge–discharge process. As the electrochemical method of synthesis has a big influence in the electrochemical properties of the polymer, the use of consecutive potential steps has been studied in order to improve the charge-storage capacity of the composite material. The influence on the final composite properties of the oxidation-deposition time and potential and the effect of the number of cycles has been analyzed. An improvement of about 20% has been achieved using short oxidation times (3 s) at 0.9 V vs. Ag/AgCl. The reasons for this improvement are discussed and analyzed using different experimental techniques.

A series of novel hybrid proton conducting membranes based on sulfonated naphthalimides and phosphotungstic acid (PTA) were prepared from N-Methyl Pyrrolidone (NMP) solutions. These hybrid organic-inorganic materials, composed of two proton-conducting components, have high ionic conductivities (9.3 × 10−2 S cm−1 at 60 °C, 15% PTA), and show good performance in H2|O2 polymer electrolyte membrane fuel cells (PEMFC), previously reported by us. Moreover, they have low methanol permeability compared to Nafion®112. In this paper we describe, for the first time, the behaviour of these hybrid membranes as electrolyte in a direct methanol fuel cell (DMFC). The maximum power densities achieved with PTA doped sulfonated naphthalimide membrane, operating with oxygen and air, were 34.0 and 12.2 mW cm−2, respectively; about the double and triple higher than those showed by the non-doped membrane at 60 °C.

New poly(methyl methacrylate) bearing aromatic amine end groups has been prepared by atom-transfer radical polymerisation (ATRP) of methyl methacrylate (MMA) using functionalized initiators. Two different methods have been employed. In the first case, nitrophenyl functional initiators were used to obtain nitrophenyl end-functional polymers. Subsequent reduction of the nitro groups yielded the aminophenyl functionality. In the second method, aminophenyl macromonomers were directly prepared using aminophenyl functional initiators. The functionalization of the polymers was quantitative and the molecular weight was well controlled by adjusting the monomer to nitroinitiator molar ratio using NiBr 2 (PPh 3 ) 2 or the CuBr/3BiPyr as a catalyst at 85 °C. These new polymers have application as macromonomers in the synthesis of polyamide and polyimide graft copolymers.

A series of new sequenced sulfonated naphthalenic polyimides were synthesized containing a flexible aromatic–aliphatic diamine. The obtained membranes present the advantage of being soluble in N -methyl pyrrolidone (NMP) which is a less toxic solvent than the previously used m -cresol. In this work, we report on the solvent and acidification method effects on the properties of the membranes such as density, water uptake, proton conductivity as well as on the performance of these membranes in fuel cell operation. The membranes prepared from NMP solution and acidified with ion-exchange resins give the best results. They have good mechanical properties as well as high ionic conductivity (14.4 × 10 −2 S cm −1 at 80 °C) and good performances as proton exchange membrane (PEM) in fuel cell at 70 °C.