Mechanochemical Partial Prelithiation of Si Reacted with Li 2 O for Negative Electrode Material

Taking into account power needs for portable devices, the energy storage through electrochemical reactions seems to be a crucial technology, especially due to the growing technological advances requirements. Electrochemical capacitors have attracted great attention as promising energy storage devices because of their high power density and cycle life noticeably longer than batteries [i],[ii]. Recently, extensive works have been focused on enhancing both the energy and power density accompanied by reasonable cost of device production as well as its environment-friendly character. One of the approaches is idea initiated in 2001 [iii], of improving capacitors performance by merging advantages of capacitors and lithium-ion batteries. This procedure was aimed to increase the energy of the capacitor while maintaining the level of supplied power. Starting from 2001 till now in the literature we can find examples of different methods involving various electrode materials [iv],[v],[vi],[vii],[viii],[ix],[x]. Asymmetric supercapacitors composed of battery-type electrode and a high surface area carbon electrode [xi] combine the advantages and reduces the drawback of redox and capacitive based systems. Therefore, the asymmetric design offers the advantages of supercapacitors (power rate, cycle life) and batteries (energy density) [xii]. This work is focused on high-energy electrochemical capacitors utilizing chemically reduced graphite oxide (CRGO) as a negative electrode material and activated carbon (AC) with the well-developed surface area as a positive electrode material. For comparison, electrochemical characteristic of capacitors utilizing graphite negative electrode was also performed. The pre-lithiation process, made by electrochemical intercalation of lithium ions into graphite, has been chosen as the main method of negative electrode material preparing. Performed electrochemical measurements, i.e., cyclic voltammetry and galvanostatic charging/discharging presented improved energy efficiency compared with results for symmetric cells (i.e. AC/AC capacitor). All measurements were performed in the organic electrolyte to provide a wide range of operating voltage. In the case of the hybrid system energy density has been improved and exceed 90 Wh kg-1 accompanied by good power profile. Additionally, good cycle performance was also achieved. Chemically reduced graphite oxide (CRGO) displays excellent performance at current densities up to 8 A g-1and, therefore, it can be considered as a very promising material for high energy Lithium-ion capacitors (LICs). Moreover, for more detailed analysis, measurements in three-electrode cells were also conducted. Fig. 1 shows an example of cyclic voltammetry curves for two systems composed of activated carbon cathode and graphite or CRGO anode. For graphite anode, Faradaic reactions can be observed in very narrow working range (134 mV) comparing to the positive electrode (1266 mV). CRGO characteristics merge two mechanisms of lithium storage, namely, Faradaic and capacitive one. In result, the quite good proportion of working potentials between positive and negative electrodes (772 mV vs. 628 mV, respectively) can be seen. The intercalation of lithium ions into graphite material occurs relatively slowly, hence the difference in power between the electrochemical capacitors and lithium-ion batteries. The electrode with the slowest sweep of potential will determine the power of the device. In this case chemically reduced graphite oxide seems to be promising material as an anode in lithium ion capacitors due to the merged lithium insertion movement, that’s why the energy storage can take place comparatively fast, as in the positive electrode. Financial support from the project DEC-2013/09/D/ST5/03886 is gratefully acknowledged. Fig. 1. Comparison of working potentials positive and negative electrodes in hybrid systems AC/G(Li) and AC/CRGO(Li), obtained from cyclic voltammetry measurements. [i] A. Burke, J. Power Sources 91 (2000) 37 [ii] P. Simon, Y. Gogotsi, Nat. Mater. 7 (2008) 845 [iii] G.C. Amatucci, F. Badway, A.D. Pasquier, T. Zheng, J. Electrochem. Soc. 148 (2001) A930 [iv] D. Cericola, R. Kötz, Electrochimica Acta 72 (2012) 1 [v] W.J. Cao, J. Shih, J.P. Zheng, T. Doung, J. Power Sources 257 (2014) 388 [vi] S.R. Sivakkumar, A.G. Pandolfo, J. Appl. Electrochem. 44 (2014) 105 [vii] X. Sun, X. Zhang, H. Zhang, N. Xu, K. Wang, Y. Ma, J. Power Sources 270 (2014) 318 [viii] S. Dsoke, B. Fuchs, E. Gucciardi, M. Wohlfahrt-Mehrens, J. Power Sources 282 (2015) 385 [ix] J. Zhang, Z. Shi, J. Wang, J. Shi, J. Electroana. Chem. 747 (2015) 20 [x] K. Naoi, P.Simon, Electrochem. Soc. Interface 17 (1) (2008) 34 [xi] J.W. Long, D. Belanger, T. Brousse, W. Sugimoto, M.B. Sassin, O. Crosnier, MRS Bull. 36 (2011) 513 [xii] Z.J. Fan, J. Yan, T. Wei, L.J. Zhi, G.Q. Ning, T.Y. Li, F. Wei, Adv. Funct. Mater. 21 (2011) 2366 Figure 1

Analysis of aging of commercial composite metal oxide – Li4Ti5O12 battery cells

Lithium-ion batteries (LIBs) are used in various fields due to their high energy density and high cycle characteristics. In general, graphite materials are used for the negative electrode materials for lithium-ion batteries (LIBs). However, since the amount of Li ion that can be stored in the graphite material of the negative electrode is approaching the theoretical value for LIBs, a significant increase in capacity cannot be expected.Calcium ion batteries (CIBs) use Ca ion as charge carriers. Therefore, they can be expected to have twice the capacity of LIBs. In LIBs, charge and discharge mechanism occurs by intercalation and deintercalation of Li ion into graphite layers. However, Ca ion are poor in reactivity, intercalation and deintercalation of Ca ion do not occur in the graphite negative electrode, and charge and discharge capacity cannot be obtained. For this reason, we used Marimo Nano Carbon (MNC) as a new negative electrode material. MNC is an aggregate of carbon nano filaments (CNF). CNF has a layered structure similar to graphite and also has amazing electronic properties and many other unique properties. This CNF has coin-stacked structure in which graphene layers are stacked, and the edge surface is exposed. Hence, we expected that MNC negative electrode would react with less reactive Ca ions and indicated larger charge / discharge capacity than that of the graphite negative electrode. In this study, we evaluated MNC negative electrode performance.For MNC synthesis, nano metal particles carried on oxidized diamond were used. Oxidized diamond has oxygen-containing functional groups arranged regularly. Thus, nano metal particles are a highly dispersed on it. Pd metal was used for carried metal. Pd metal could synthesized CNF having coin-stacked structures. Pd metal was carried on oxidized diamond by metal nano-colloidal method. C2H4 as a feedstock for CNF was used, and MNC was synthesized by the chemical vapor deposition (CVD) method.When MNC was used as the negative electrode material, the charge and discharge capacity was larger than that of the graphite negative electrode. In addition, the intercalation of Ca ions between the graphene layers was confirmed.

Hybrid metal‐ion capacitors, merging the merits of batteries and supercapacitors, are considered as a promising energy storage technology able to satisfy the rising energy requirements of modern powered devices. Regrettably, their development is currently hampered by the diffusion‐controlled storage mechanism taking place at the battery‐type, negative electrode material. Herein we highlight and review the promising role of carbon nanospheres ‐that combine a dense morphology with short solid‐state diffusion pathways‐ in minimizing the kinetic restrictions in the battery‐type electrode. Besides, carbon nanospheres presenting a highly developed pore structure and readily available micropores fully satisfy the requirements for the supercapacitor‐type electrode. The recent findings collected in this concept paper support the suitability of carbon nanospheres for the production of negative and positive electrode materials for these hybrid systems.

To exploit LIBs to their maximum applications, innovative electrode materials should be developed and existing materials should be improved. As negative electrode materials are needed in excess in comparison with positive electrode materials (in terms of specific capacity) in a lithium-ion battery, it is important to reduce their amounts so as to reduce the cell size and production cost[1]. Moreover, innovative negative electrode material classes delivering high capacity and offering fast Li diffusion kinetics should be developed. Parallel to this, research in alternative low cost energy storage systems became more intensive. Due to the high abundance and cost effectiveness of the electrode materials used, Na-ion batteries have become one of the best alternative energy storage systems to LIBs. Many of the attractive Li-insertion electrode materials are also tested for Na-insertion as a part of developing this system further. As different from the wide variety of positive electrode materials, there are only few choices for negative electrode materials for Na-ion batteries[2]. Na does not insert into graphite. Binary alloys of Na with Sn, Pb or other metals and conversion metal oxides are expected to have very high gravimetric capacity[3]. However, the enormous volume changes are supposed to bring out poor cycling behavior of these materials. SnO2 is a promising negative electrode material for Li-ion batteries due to its high theoretical specific capacity of 1491 mAh g-1 [4]. The first step in the Li insertion of SnO2 is a conversion reaction involving 4 Li, where metallic Sn particles are formed in a matrix of Li2O. In the second step, metallic Sn alloys with Li and produce Li4.4Sn. Hence in total 8.4 Li ions can be inserted per formula unit of SnO2 [4]. Nevertheless, this material suffers from extreme volume changes which can lead to a drop in the electric contact and further to severe capacity fading during cycling. This can be overcome by preparing nanocrystalline materials, composite materials with carbon derivatives etc. In the present work, SnO2 nanoparticles are synthesized via a hydrothermal process. The obtained SnO2 material has a particle size of ~50 nm. The material was investigated as negative electrode candidate for both Li- and Na-ion batteries in corresponding half cells. The respective electrochemical mechanism was investigated by in situ and quasi in situ X-ray absorption spectroscopy. It was observed that at the end of discharge, SnO2 was converted to metallic Sn nanoparticles in a Li-ion cell (see Figure 1). Meanwhile, no complete reduction of the SnO2 was observed in the Na-ion cell at the end of discharge. The details of the electrochemical mechanism of SnO2 as negative electrode material for Li-ion and Na-ion batteries will be discussed. Acknowledgement: Financial support from DFG within the Research Priority Program SPP 1473, “Materials with new design for improved Li ion batteries-WeNDeLIB” under grant no EH183/16-2 is gratefully acknowledged. This work has benefitted from beam time allocation by the core-level absorption and emission spectroscopies (CLAESS) beamline, ALBA, Barcelona.

Room-temperature sodium-ion batteries have shown great promise in large-scale energy storage applications for renewable energy and smart grid because of the abundant sodium resources and low cost. Although many interesting positive electrode materials with acceptable performance have been proposed, suitable negative electrode materials have not been identified and their development is quite challenging. Here we introduce a layered material, P2-Na0.66[Li0.22Ti0.78]O2, as the negative electrode, which exhibits only ~0.77% volume change during sodium insertion/extraction. The zero-strain characteristics ensure a potentially long cycle life. The electrode material also exhibits an average storage voltage of 0.75 V, a practical usable capacity of ca. 100 mAh g(-1), and an apparent Na(+) diffusion coefficient of 1 × 10(-10) cm(-2) s(-1) as well as the best cyclability for a negative electrode material in a half-cell reported to date. This contribution demonstrates that P2-Na0.66[Li0.22Ti0.78]O2 is a promising negative electrode material for the development of rechargeable long-life sodium-ion batteries.

Negative electrode materials for Li-ion batteries can be selected from several choices that have different potentials vs Li metal. In this paper, using , , and as examples, we show how the heat of reaction between these electrode materials and nonaqueous solvents or electrolytes depends on the negative electrode potential. The three fully lithiated negative electrode materials react with ethylene carbonate/diethyl carbonate solvent, producing , , and the delithiated phases [C, , or ]. The heat of reaction depends strongly on the negative electrode potential and is for , for , and for , respectively. Thermodynamic considerations show that the heat of reaction per mole of lithium vs electrode potential should vary as , in good agreement with experiment. These results suggest that energy of Li-ion cells can be traded for increased safety by switching to higher potential negative electrode materials.

Aqueous superconcentrated electrolyte solutions have recently attracted attention for aqueous high-voltage Li-ion batteries due to their wider potential window than that of conventionally concentrated aqueous ones. According to literatures, 21 mol kg-1 LiN(SO2CF3)2 (LiTFSA)/H2O and 27.8 mol kg-1 Li(TFSA)0.7[N(SO2C2F5)2 (BETI)]0.3/H2O electrolytes show potential window wider than 2 V and 3.5 V, respectively (1, 2). As well as the Li electrolytes, superconcentrated aqueous Na and K electrolytes have been recently studied. Thanks to weak Lewis acidity of Na+ and K+ ions, aqueous Na and K solutions show higher ionic conductivity than Li counterparts in principle. Indeed, 17 mol kg-1 NaClO4/H2O solution exhibits a very high ionic conductivity of 108 mS cm-1; however, potential window wider than 2 V is still challenging in aqueous Na-ion batteries (3). In this study, we have developed superconcentrated mixed cation electrolytes demonstrating wide potential window and high ionic conductivity based on NaN(SO2F)2 (NaFSA), KFSA, and H2O system to realize 2 V-class aqueous Na/K multi-ion batteries. Ionic conductivities of the electrolytes were measured at 25 °C. NaTi2(PO4)3 carbon composite (NTP/C) (4) and Na3V2(PO4)3 (NVP) (5) were used as negative electrode materials, and K2Mn[Fe(CN)6] (6) was as a positive electrode material. Al and Ti foils were used as a current collector for the negative and positive electrodes, respectively. Figure 1a shows water content of saturated aqueous K x Na1-x FSA solutions. The concentration of the saturated NaFSA and KFSA solutions as endmembers is 20 mol kg-1 and 31 mol kg-1, respectively. Higher concentration is realized at eutectic or close to eutectic composition of NaFSA - KFSA: 35 mol kg-1 for Na0.55K0.45FSA/H2O and 33 mol kg-1 for Na0.45K0.55FSA/H2O. Both Na/K mixed electrolytes show ionic conductivity of 20–25 mS cm-1 which is much higher than 3 mS cm-1 of 27.8 mol kg-1 Li(TFSA)0.7(BETI)0.3 (2). Figure 1b shows the LSV curves of Al and Ti foil for a cathodic and anodic scan, respectively, in the superconcentrated Na, K, and mixed electrolytes. 20 mol kg-1 NaFSA/H2O and 31 mol kg-1 KFSA/H2O as endmembers show potential window of 3.2 V and 3.4 V, respectively. As expected, the Na/K mixed electrolytes demonstrate a wider potential window of 3.5 V. NTP//K2Mn[Fe(CN)6] and NVP//K2Mn[Fe(CN)6] cells were fabricated using 33 mol kg-1 K0.55Na0.45FSA/H2O electrolyte. The NTP//K2Mn[Fe(CN)6] cell shows reversible charge/discharge curves with mainly two discharge voltage plateaus located at 1.7 V and 1.3 V and delivers reversible capacity of ca. 130 mAh g (positive electrode)-1 and 70 mAh g (negative electrode)-1 with excellent capacity retention over 30 cycles as shown in Fig. 1c. On the other hand, the NVP//K2Mn[Fe(CN)6] cell demonstrate 2 V-class operation as shown in Fig. 1d. Electrochemical performance and charge/discharge mechanism of the electrode materials in terms of insertion/extraction of Na/K multi-ions will be discussed in the presentation. References L. Suo, O. Borodin, T. Gao, M. Olguin, J. Ho, X. Fan, C. Luo, C. Wang and K. Xu, Science, 350, 938 (2015).Y. Yamada, K. Usui, K. Sodeyama, S. Ko, Y. Tateyama and A. Yamada, Nat. Energy, 1, 16129 (2016).K. Nakamoto, R. Sakamoto, Y. Sawada, M. Ito and S. Okada, Small Methods, 1800220 (2018).S. I. Park, I. Gocheva, S. Okada and J. Yamaki, J. Electrochem. Soc., 158, A1067 (2011).K. Saravanan, C. W. Mason, A. Rudola, K. H. Wong and P. Balaya, Adv. Energy Mater., 3, 444 (2013).T. Hosaka, K. Kubota, H. Kojima and S. Komaba, Chem. Commun., 54, 8387 (2018). Figure 1

After conquering the scene of portable electronics (i.e. mobile phones and laptop computers) since their introduction to the marketplace in 1991, lithium ion batteries (LIBs) are set to further enable wide-scale deployment of electric vehicles (EVs) and hybrid electric vehicles (HEVs). However, a series of challenges still remain with respect to a number of important factors, such as the operational safety of LIBs, raw material supply, cost, recycling and environmental aspects. In order to fulfill future demands for large-scale applications, significant improvements and deeper understanding are required in these areas. As of today, graphite is the anode (negative electrode) material primarily used in commercial LIBs, mainly due to its charge-discharge capacity retention capability and an attractively low, flat operational voltage as well as a manageable voltage hysteresis upon (de)intercalation which altogether maximizes both the energy density and energy efficiency of the cell in which it is employed. However, recent projections regarding the future cost and availability of graphite have prompted researchers to explore alternatives in the context of cheap and sustainable materials for electrochemical energy storage. Silica (SiO2) is currently being explored as a possible alternative candidate material in this context. SiO2 was long disregarded as a potential electrode material due to its apparent electrochemical inactivity. However, studies in recent years have sparked renewed interest in SiO2 after it was demonstrated that modified nano-SiO2 may indeed be electrochemically active. SiO2 is a conversion-type anode material which irreverisbly produces various silicates (e.g. Li4SiO4 and Li2Si2O5) as well as elemental Si during electrochemical lithiation. Although the precise reaction mechanism is still a topic for debate, it is believed that the by-products formed in-situ during electrochemical cycling can mechanically buffer the stress and strain associated with continued (de)lithiation of Si and thereby extending the cycle life of the electrode material. The present study systematically investigates the electrochemical properties of amorphous SiO2 as a negative electrode material for Li-ion batteries. The SiO2 materials in question include spherical nano-particulate SiO2 recovered as an industrial by-product or naturally nano-sized 3D-architectured SiO2 extracted from a renewable resource of biological origin – the main motivation here clearly being the study of dirt-cheap, highly abundant materials and the possible prospect of their implementation in electrochemical storage devices. By virtue of its electronically insulating properties, SiO2 needs to be carefully engineered in order to activate the material. Important factors in this regard include control of particle morphology, surface area and porosity as well as enhancement of electronic conductivity. Consequently, various carbon sources (i.e. glucose, sucrose, starch) have been utilized in varying amounts in order to achieve a conductive carbon coating on the SiO2 particles via high-temperature pyrolysis (i.e. carbonization), ultimately yielding SiO2/C composites with improved electrochemical properties in relation to bare SiO2. Here, these variations in carbon precursor, carbon content and coating thickness etc. are directly related to the electrochemical activity of the different SiO2 materials. These aspects are additionally highlighted by means of a series of advanced characterization techniques. The influence of particle size and morphology is further made possible by the direct comparison of spherical SiO2 nanoparticles to the intricate 3D-architecture of the SiO2 derived from harvested biomass. Preliminary results indicate it appears possible to electrochemically activate (i.e. displace Si followed by its electrochemical lithiation at low voltages vs. Li+/Li) the latter via careful considerations in terms of electrode design and electrochemical testing procedures which results in gravimetric capacities of >1000 mAh g-1 at an average (de)lithiation voltage in the range of 0.2-0.4 V vs. Li+/Li. By comparison, the spherical nanoparticles exhibit significantly lower electrochemical activity, i.e. a reversible gravimetric capacity of 300-400 mAhg-1 with highly sloping voltage profiles in an electrochemical cycling windowof ~0-2 V vs. Li+/Li.

We propose a novel intercalated metal–organic framework (iMOF) electrode material, 2,6-naphthalene dicarboxylate dilithium (2,6-Naph(COOLi)2) as a next-generation negative electrode material for advanced lithium-ion batteries or asymmetric capacitors.This iMOF material exhibits an operating potential of 0.8 V (vs. Li/Li+) between those of graphitic carbon, operating at 0.1 V, and Li4Ti5O12, operating at 1.55 V. Given the risks of an internal short circuit because of lithium metal deposition in the case of graphitic carbon electrodes and cell-voltage reduction in the case of high-operating-potential Li4Ti5O12 electrodes, this iMOF material possibly represents an advantageous battery design. In addition, because Al can be used as a current collector for this iMOF negative electrode material, whose operating potential is more positive than the potential of the Li–Al alloy reaction (0.4 V), it can potentially be used as a negative electrode material in high-voltage bipolar batteries using only Al current collector. The proposed electrode material has an organic-inorganic layered structure of p-stacked naphthalene and tetrahedral LiO4 units (Figure 1(a)), and shows a reversible two-electron-transfer Li intercalation (220 mAh g-1) at a flat potential of 0.8 V vs. Li/Li+ with a small polarization (Figure 1(b)). 1, 2 Detailed crystal structure analysis during Li intercalation of this material shows the layered framework to be maintained and its volume change is only 0.33%. This value is much lower than that of the conventional Li-intercalated electrode materials such as graphite (ca. 10%) and Li transition metal oxides (~ 10%). Furthermore, the proposed material exhibits improved regularity of p-stacked packing via self-organization induced by heat treatment under inert atmosphere; this improved packing led to an improvement of reversible capacity as well as to a reduction of internal resistance.3 We examined the device performance of novel asymmetric capacitors comprising the iMOF negative and activated carbon positive electrodes. In this presentation, the possibility of the iMOF as the negative electrodes for asymmetric capacitors will be discussed.

Dual‐graphite batteries (DGBs), being an all‐graphite‐electrode variation of dual‐ion batteries (DIBs), have attracted great attention in recent years as a possible low‐cost technology for stationary energy storage due to the utilization of inexpensive graphite as a positive electrode (cathode) material. However, DGBs suffer from a low specific energy limited by the capacity of both electrode materials. In this work, a composite of black phosphorus with carbon (BP‐C) is introduced as negative electrode (anode) material for DIB full‐cells for the first time. The electrochemical behavior of the graphite || BP‐C DIB cells is then discussed in the context of DGBs and DIBs using alloying anodes. Mechanistic studies confirm the staging behavior for anion storage in the graphite positive electrode and the formation of lithiated phosphorus alloys in the negative electrode. BP‐C containing full‐cells demonstrate promising electrochemical performance with specific energies of up to 319 Wh kg–1 (related to masses of both electrode active materials) or 155 Wh kg–1 (related to masses of electrode active materials and active salt), and high Coulombic efficiency. This work provides highly relevant insights for the development of advanced high‐energy and safe DIBs incorporating BP‐C and other high‐capacity alloying materials in their anodes.

Two-dimensional (2D) materials have opened new avenues for the fabrication of ultrathin, transparent, and flexible functional devices. However, the conventional inorganic graphene analogues are either semiconductors or insulators with low electronic conductivity, hindering their use as supercapacitor electrode materials, which require high conductivity and large surface area. Recently, 2D charge density wave (CDW) materials, such as 2D chalcogenides, have attracted extensive attention as high performance functional nanomaterials in sensors, energy conversion, and spintronic devices. Herein, TaS2 is investigated as a potential CDW material for supercapacitors. The quantum capacitance (CQ) of the different TaS2 polymorphs (1T, 2H, and 3R) was estimated using density functional theory calculations for different numbers of TaS2 layers and alkali-metal ion (Li, Na and K) intercalants. The results demonstrate the potential of 2H- and 3R-polymorphs as efficient negative electrode materials for supercapacitor devices. The intercalation of K and Na ions in 1T-TaS2 led to an increase in the CQ with the intercalation of Li ions resulting in a decrease in the CQ. In contrast, Li ions were found to be the best intercalant for the 2H-TaS2 phase (highest CQ), while K ion intercalation was the best for the 3R-TaS2 phase. Moreover, increasing the number of layers of the1T-TaS2 resulted in the highest CQ. In contrast, CQ increases upon decreasing the number of layers of 2H-TaS2. Both 1T-MoS2 and 2H-TaS2 can be combined to construct a highly performing supercapacitor device as the positive and negative electrodes, respectively.

Electrochemical deionization (ECDI) systems represent an enticing avenue in desalination technology, offering notable desalination capacity while maintaining energy efficiency, thus presenting themselves as potential replacements for existing desalination methods. Traditionally, ECDI systems rely on electric double-layer (EDL) materials to eliminate salts via electrode-induced ion adsorption under external electric fields. However, the practical utility of this conventional approach is hindered by the limitations of the EDL mechanism, constraining desalination capability. Consequently, there has been a notable shift towards exploring pseudocapacitive-type or battery-type faradaic materials, which offer promising alternatives. This novel approach entails the capture of ions within the solution through electrode charge transfer, effectively reducing energy consumption and bolstering desalination performance. Furthermore, the unique characteristic of the "memory effect" in faradaic materials, as proposed by Hu et al., has revolutionized resource recovery and water purification, eliminating the need for membranes and further elevating the appeal of such materials within the field [1]. Among these faradaic materials, polypyrrole (PPy) is recognized for its affordability, stability, and straightforward synthesis, rendering it an excellent choice for anion insertion applications. Prior research indicates that PPy demonstrates distinct behaviors depending on dopant variations. Large-size dopants confer cation exchange capabilities to PPy, whereas small-size dopants imbue it with anion exchange characteristics. Despite these qualities, conducting polymers have predominantly served as either anion or cation-removal electrode materials in ECDI systems [2].As a result, the study aims to design a low-voltage, membrane-free, ECDI system with high salt-removal capacity and excellent cycling stability through the utilization of an identical conducting polymer (i.e., PPy) doped with anions of different sizes for the positive (4-methylbenzenesulfonic acid, p-TS) and negative (ClO4 −) electrodes. Essentially, PPy is tailored to possess either cation or anion-exchange abilities to serve as both positive and negative electrode materials in the ECDI system. According to the results of XPS and CV measurements, the schematic diagram of the salt removal/release mechanisms on the two PPy electrodes is shown in Figure 1 [3]. The positive electrode (PPy-p-TS) exhibits the cation-capturing ability due to the trapping of bulky p-TS dopants with high electronegativity from the sulfonic acid groups during the electro-polymerization. Therefore, the reduction of PPy polarons (i.e., the + symbols) results in the presence of negative charges within the PPy-p-TS matrix, electrostatically attractive to cations. On the other hand, the negative (PPy-ClO4) electrode exhibits the anion-removing ability due to the positive charges generated on the oxidized PPy, which are charge-compensated by the small anion dopants (i.e., ClO4 − during the electro-polymerization step, which is replaced with Cl− during the desalination step). Moreover, to apply the unique "memory effect" in the ECDI system, the salt-removal/salt-concentration test was conducted in a full cell and the conductivity profile is shown in Figure 2. The PPy-p-TS//PPy-ClO4 system can transfer the total amount of 342 mg g−1 of NaCl in only 5 cycles with only 0.1902 kWh/kg-NaCl. With the characteristics of dual function and membrane-free, this full-polymer ECDI system has become an attractive and competitive technology in the water purification field.Furthermore, the similar redox couples between positive and negative electrode materials result in closely aligned redox potentials for ion capturing/releasing, leading to significantly reduced cell voltages during both deionization and concentration processes. Through optimization of mass loading ratios, the positive and negative electrodes in this ECDI system operate within their respective desirable potential windows, demonstrating substantial desalination capabilities of up to 83.4 mg g−1 in a 60-minute single-pass operation. Additionally, the adjustments in the charging/discharging time ratio and mass loading of active materials yield a low energy consumption (EC) of 0.2225 kWh/kg-NaCl. Therefore, in comparison with the other ECDI systems in Figure 3, this full-polymer ECDI system lies in the ideal performance area with great SAC and SAR performance. Moreover, this system shows ultra-low EC compared to other systems and industrial RO plants. Meanwhile, this system demonstrates its great stability with a SAC retention of 88 % after 250 cycles (66.7 h). Ultimately, according to the proposed design guidelines, we successfully demonstrate a superior desalination performance, high stability, and dual-function ECDI system without membrane as a potential future desalination system.

Peering into Batteries: Electrochemical Insight Through In Situ and Operando Methods over Multiple Length Scales

The NiMH battery is an intercalation battery with a positive NiOH electrode and a negative metal hydride electrode. The electrolyte used is a highly alkaline aqueous solution, typically 6:1 KOH:LiOH. As a consequence of this and the reaction potentials of the electrodes, splitting of water into its constituting elements is a part of normal battery operation. When charging at high SOC, as well as when overcharging, oxygen is formed as a side-reaction. It then diffuses through the separator and recombines at the negative electrode. This recombination cycle causes the temperature in the battery to rise, something that is commonly used to terminate battery charging, either through ΔT or -ΔV criteria. In addition to oxygen production at high state of charge, overdischarging of the battery can produce hydrogen at the positive electrode, with a pressure increase at end of discharge indicating a harmful overdischarge of the battery [1]. Hydrogen is also present in the battery gas composition as a consequence of the negative hydrogen intercalation electrode material which is in equilibrium with gaseous hydrogen, an equilibrium which shifts with electrode hydrogen content [2]. Figure Left: A schematic showing the main gas reactions in the metal NiMH battery. Right: An example cycle of a NiMH battery, showing cell voltage (blue), cell gas pressure (green) and cell surface temperature (teal).The internal gas reactions of the NiMH battery have a great impact on battery function, both in regard to energy efficiency and battery aging. While measurements of battery internal total gas pressure occur in some battery systems, measurements of individual constituents would be impractical in the field, as such measurements require laboratory equipment. Therefore, a gas model that can estimate the internal pressure distribution under dynamic conditions would be a valuable tool to study the effects of different application drive cycles, as well as a possibility to further enhance BMS function for battery stability and longevity.There have been many attempts at modeling the gaseous side reactions in the NiMH battery. Some of these models are part of comprehensive battery models, which combines a voltage response model with added side reactions [3,4]. Other models look only at specific gas related processes [5]. However, a limitation with these models is that they are not able to model the battery during dynamic current conditions. The main reason for this is the presence of a strong open circuit voltage hysteresis, something that these models do not capture well.This study presents a model of the gas reactions and heat generation in the NiMH battery. The model is not coupled to a voltage model, instead it simulates internal temperature and pressure when supplied with experimental current, voltage and surface temperature data. This removes the complication of the open circuit voltage hysteresis effect and lets us model dynamic battery behavior. The model is in zero dimensions and based on physical principles. There are several parameters that are optimized by fitting to experimental data. The model is then validated by simulating pressure for a second set of data, based on the fitted values of the parameters. The simplicity of the model not only allows for it to be used in battery monitoring hardware, it can also be coupled to voltage and multidimensional models to build a more comprehensive predictive model.References Notten, P. H. L.; Latroche, M. Nickel-Metal Hydride: Metal Hydrides. In Encyclopedia of Electrochemical Power Sources; Garche, J., Dyer, C., Moseley, P., Ogumi, Z., Rand, D., Scrosati, B., Eds.; Elsevier B.V., 2009; Vol. 50, pp 502–521.Tserolas, V.; Katagiri, M.; Onodera, H.; Ogawa, H. Thermodynamical Modeling of P-C Isotherms for Metal Hydride Materials. Trans. Mater. Res. Soc. Japan 2010, 35 (2), 221–226. https://doi.org/10.14723/tmrsj.35.221.Albertus, P.; Christensen, J.; Newman, J. Modeling Side Reactions and Nonisothermal Effects in Nickel Metal-Hydride Batteries. J. Electrochem. Soc. 2008, 155 (1), A48. https://doi.org/10.1149/1.2801381.Ledovskikh, A.; Verbitskiy, E.; Ayeb, A.; Notten, P. H. L. Modelling of Rechargeable NiMH Batteries. J. Alloys Compd. 2003, 356–357, 742–745. https://doi.org/10.1016/S0925-8388(03)00082-3.Notten, P. H. L.; Ouwerkerk, M.; Ledovskikh, A.; Senoh, H.; Iwakura, C. Hydride-Forming Electrode Materials Seen from a Kinetic Perspective. J. Alloys Compd. 2003, 356–357, 759–763. https://doi.org/10.1016/S0925-8388(03)00085-9. Figure 1