Metal Negative Electrode Research Articles

Rational design of a topological polymeric solid electrolyte for high-performance all-solid-state alkali metal batteries

Poly(ethylene oxide)-based solid-state electrolytes are widely considered promising candidates for the next generation of lithium and sodium metal batteries. However, several challenges, including low oxidation resistance and low cation transference number, hinder poly(ethylene oxide)-based electrolytes for broad applications. To circumvent these issues, here, we propose the design, synthesis and application of a fluoropolymer, i.e., poly(2,2,2-trifluoroethyl methacrylate). This polymer, when introduced into a poly(ethylene oxide)-based solid electrolyte, improves the electrochemical window stability and transference number. Via multiple physicochemical and theoretical characterizations, we identify the presence of tailored supramolecular bonds and peculiar morphological structures as the main factors responsible for the improved electrochemical performances. The polymeric solid electrolyte is also investigated in full lithium and sodium metal lab-scale cells. Interestingly, when tested in a single-layer pouch cell configuration in combination with a Li metal negative electrode and a LiMn0.6Fe0.4PO4-based positive electrode, the polymeric solid-state electrolyte enables 200 cycles at 42 mA·g−1 and 70 °C with a stable discharge capacity of approximately 2.5 mAh when an external pressure of 0.28 MPa is applied.

Development of vanadium-based polyanion positive electrode active materials for high-voltage sodium-based batteries

Polyanion compounds offer a playground for designing prospective electrode active materials for sodium-ion storage due to their structural diversity and chemical variety. Here, by combining a NaVPO4F composition and KTiOPO4-type framework via a low-temperature (e.g., 190 °C) ion-exchange synthesis approach, we develop a high-capacity and high-voltage positive electrode active material. When tested in a coin cell configuration in combination with a Na metal negative electrode and a NaPF6-based non-aqueous electrolyte solution, this cathode active material enables a discharge capacity of 136 mAh g−1 at 14.3 mA g−1 with an average cell discharge voltage of about 4.0 V. Furthermore, a specific discharge capacity of 123 mAh g−1 at 5.7 A g−1 is also reported for the same cell configuration. Through ex situ and operando structural characterizations, we also demonstrate that the reversible Na-ion storage at the positive electrode occurs mostly via a solid-solution de/insertion mechanism.

Poly(ethylene oxide)-Based Electrolytes for Solid-State Potassium Metal Batteries

Most conventional batteries today employ organic liquid electrolytes (LEs) that are not only flammable, but also serve as a medium for irreversible side reactions at the electrode interfaces, especially when metal is used as electrode. In post-lithium systems, such as potassium batteries, this issue is even more pronounced due to a higher reactivity of the metal as compared to lithium, and typically results in electrochemical instability leading to a rapid capacity fade of the battery.[1] When switching from LEs to solid polymer electrolytes (SPEs) that typically show better electrochemical stability at low (< 0.5 V vs. K+/K) and high (> 4 V vs. K+/K) potentials due to polymers inherent inertness, enhanced cycle life of the battery is expected.[2] Moreover, well-known disadvantage of SPEs in Li-based batteries, i.e., poor ionic conductivity at ambient temperature, could be overcome in systems with larger cation size, e.g. K+ [3,4], potentially removing some of the bottlenecks previously encountered in the case of Li-transport.In this presentation, a series of poly(ethylene oxide) - potassium bis(trifluoromethane sulfonyl)imide (PEO-KTFSI) compositions with different salt concentration was investigated for their potential application as SPEs in potassium metal batteries. To identify the most promising candidate in terms of ion transport and mechanical integrity, the effect of KTFSI concentration on thermal, rheological and electrochemical properties was studied. Several electrolyte compositions were examined in solid-state potassium batteries with a potassium metal negative electrode, and a positive electrode from Prussian blue analogue family. Our results reveal the advantages of solid-state systems with respect to improved capacity retention and Coulombic efficiency as compared to the reference system with carbonate-based LE, as demonstrated in Figure 1, thus paving the way for a new generation of potassium batteries with significantly improved key performance parameters. Figure 1. Comparison of potassium half-cells employing different electrolyte systems: carbonate-based liquid electrolyte (LE) vs. PEO-based solid polymer electrolyte (SPE) (a) capacity retention and (b) corresponding Coulombic efficiencies.[1] H. Wang, D. Zhai, F. Kang, Energy Environ. Sci. 2020, 13, 4583–4608.[2] J. Mindemark, M. J. Lacey, T. Bowden, D. Brandell, Prog. Polym. Sci. 2018, 81, 114–143.[3] M. Perrier, S. Besner, C. Paquette, A. Vallée, S. Lascaud, J. Prud’homme, Electrochim. Acta 1995, 40, 2123–2129.[4] U. Oteo, M. Martinez-Ibañez, I. Aldalur, E. Sanchez-Diez, J. Carrasco, M. Armand, H. Zhang, ChemElectroChem 2019, 6, 1019–1022. Figure 1

PI-LATP-PEO Electrolyte with High Safety Performance in Solid-State Lithium Metal Batteries

Although lithium metal is extensively used as an anode material for next-generation secondary batteries, the lithium metal reacts with the commonly used organic electrolytes, forming lithium dendrites, resulting in short-circuiting of batteries, which is a safety hazard. Solid-state electrolytes are a feasible solution to overcome these limitations. We prepared a PI–PEO–LATP composite solid electrolyte by compounding poly(ethylene oxide) (PEO) and Li1.4Al0.4Ti1.6(PO4)3 (LATP) with an electrospun polyimide (PI) nanofiber membrane using a solution-casting method. The best electrochemical and battery performance was obtained when the ratio of LATP to PEO was 15%. LATP reduces the crystallinity of PEO and increases its ionic conductivity. The 3,3′,4,4′-biphenyltetracarboxylic dianhydride-4,4′-oxydianiline PI nanofibrous membrane exhibited enhanced thermal stability and self-extinguishing performance. The lithium symmetric battery assembled with the PI–PEO–LATP composite solid electrolyte functioned stably for 1000 h at a current density of 0.5 mA·cm–2. The solid electrolyte showed good compatibility with a lithium metal anode and could inhibit the growth of lithium dendrites. When using the LiNi0.8Co0.1Mn0.1O2 positive electrode and lithium metal negative electrode, the assembled coin cell maintained a discharge capacity of 170.7 mAh·g–1 after 100 cycles at 0.2 C, with a capacity retention rate of 95% and Coulombic efficiency of approximately 100%.

Communication—Porous Current Collector with Randomly Distributed Pores for Li Metal Negative Electrode in All-Solid-State Batteries

The increase in mechanical stress at the interface of the Li metal and solid electrolyte induces dendritic Li growth in all-solid-state Li batteries. We demonstrated the increasing stress in Li metal was significantly reduced by porous current collectors (PCCs). Here, we demonstrate the PCC with 3- dimensional pores prepared by sintering a mixture of micrometer-sized Ni spherical particles and polymethyl methacrylate spheres as a template of pores. The low-cost sintering method realized not only reduction of the preparation cost of PCCs, but high internal short circuit resistance comparable to the expensive PCCs with regularly arranged through-holes using electroforming methods.

Solid Gel Electrolytes with Highly Concentrated Liquid Electrolyte in Polymer Networks and Their Physical and Electrochemical Properties and Application to Sodium Secondary Batteries

Gel polymer electrolytes consisting of sulfolane (SL)-NaN(SO2CF3)2 liquid electrolyte and a polyether-based host polymer were prepared, and their physicochemical and electrochemical properties were investigated. The prepared gel electrolytes generally exhibited high thermal stability regardless of the NaN(SO2CF3)2 concentrations. The glass transition temperature decreased with the NaN(SO2CF3)2 concentration owing to the strong interaction between SL and Na+. The ionic conductivities of all gel polymer electrolytes were higher than 10−4 S cm−1 at 303.15 K as a result of the plasticizer effect of SL. Although a relatively large interfacial resistance of the electrolyte/Na metal electrode was observed owing to the high reactivity of the SL-NaN(SO2CF3)2 electrolyte, the fabricated [Na metal negative electrode∣gel polymer electrolyte∣sulfur-modified polyacrylonitrile positive electrode] cell, i.e., the Na-S battery, achieved reversible charge-discharge operation at 333 K and demonstrated its potential to serve as an electric power storage system capable of low-temperature operation.

Poly(ethylene oxide)-Based Electrolytes for Solid-State Potassium Metal Batteries with a Prussian Blue Positive Electrode

Potassium-ion batteries are an emerging post-lithium technology that are considered ecologically and economically benign in terms of raw materials’ abundance and cost. Conventional cell configurations employ flammable liquid electrolytes that impose safety concerns, as well as considerable degrees of irreversible side reactions at the reactive electrode interfaces (especially against potassium metal), resulting in a rapid capacity fade. While being inherently safer, solid polymer electrolytes may present a solution to capacity losses owing to their broad electrochemical stability window. Herein, we present for the first time a stable solid-state potassium battery composed of a potassium metal negative electrode, a Prussian blue analogue K2Fe[Fe(CN)6] positive electrode, and a poly(ethylene oxide)-potassium bis(trifluoromethanesulfonyl)imide polymer electrolyte. At an elevated operating temperature of 55 °C, the solid-state battery achieved a superior capacity retention of 90% over 50 cycles in direct comparison to a conventional carbonate-based liquid electrolyte operated at ambient temperature with a capacity retention of only 66% over the same cycle number interval.

A Squaraine-Linked Zwitterionic Covalent Organic Framework Nanosheets Enhanced Poly(ethylene oxide) Composite Polymer Electrolyte for Quasi-Solid-State Li–S Batteries

A squaric acid-based zwitterionic covalent organic framework nanosheet (HUT4) was successfully prepared and incorporated as a filler into a poly(ethylene oxide) (PEO) matrix for excellent-performance solid-state polymer electrolytes (SPEs). Introduction of a HUT4 nanosheet will have a positive impact on the migration number of lithium ions and also improve the stability of the lithium metal negative electrode, which can increase the overall cycle capacity of quasi-solid-state lithium sulfur (Li–S) batteries. Among the obtained membranes with different proportions, the PEO–10%HUT4 electrolyte exhibits the highest lithium ion migration number, up to 0.62 at 60 °C. The Li–S battery composed of PEO–10%HUT4 electrolyte displays outstanding electrochemical performance, with a superior cycling stability of 1057 mAh g–1 at 0.2 C and an outstanding capacity retention, reaching 93.1% after 500 cycles.

High-Rate Lithium Metal Plating and Stripping on Solid Electrolytes Using a Porous Current Collector with a High Aperture Ratio

Dendritic Li metal growth and low Coulombic efficiency hinder the Li metal negative electrode’s applications. Solid electrolytes (SEs) have the potential to inhibit the growth of dendritic Li metal due to their high mechanical strength and number of transmissions; however, the extrusion of the Li metal into voids and cracks in the SEs due to the increased mechanical stress of the Li metal during the plating reaction makes it difficult to prevent internal short circuits. Here, this obstacle was uniquely solved using a porous current collector (PCC) with a high aperture ratio. Li metal plating in many pores of the PCC prevented the increase of mechanical stress of the Li metal. Moreover, the combination with the SE, which also has a high tolerance to the dendritic Li metal growth, showed a synergic effect. Additionally, the Au coating on the PCC’s surface extended the Li plating/stripping performance. As a result, a record-high value of critical current density (the maximum plating/stripping current density without internal short circuits) over 6 mA cm–2 was recognized by the galvanostatic Li metal plating/stripping tests. Notably, the excellent cycle performance with a high average Coulombic efficiency of 98.7% for 300 cycles was also achieved in the Li electrode-free system. Our works exhibit the potential for attaining Li metal all-solid-state cells.

Methodology and Electrochemical Techniques for Development of All-Solid-State Batteries

Despite some progress performed, state-of-the-art lithium ion batteries still require improvements in energy and power to extend the range of electric vehicles and reduce charging time. In this domain, all-solid-state batteries are viable alternatives to conventional batteries employing organic electrolytes because of their benefits, i.e., high power density, high energy density, long-life operation and safety. These advantages stem from the great features of inorganic solid electrolytes, which are single ion conductor, so a high lithium ion transport number, and no-liquid nature. In particular, the sulfide-based solid electrolytes possess favorable mechanical properties, allowing all-solid-state batteries to be easily prepared via simple mixing and cold-pressing processes, facilitating the scale-up.Sulfide-based solid-electrolytes can potentially be employed in conjunction with a lithium metal negative electrode and 5V-class high voltage positive electrode material. Indeed, lithium metal is believed to be the most promising negative electrode due to its specific large capacity (3862 mAh.g-1), low volumetric density (0.534 g.cm-3 at 20°C) and the lowest electrochemical potential (-3.03V vs ENH). Nevertheless, like most metal, lithium metal is morphologically dynamic. Its surface morphology is modified, since during the electrochemical cycling, a part of lithium migrates to the other electrode to react and is then plating on its surface heterogeneously, leading to a volume change and sometimes dendrite growth with potential internal short circuit and life-threatening accidents. Ceramic solid electrolytes have been considered to be the ideal solution to prevent dendrite growth because of their high shear modulus and high lithium transference number. In the same time, the chemical nature and composition of ceramic solid electrolyte can affect its reactivity with lithium metal. In the same time, the electrochemical stability of solid electrolyte depending of its nature and composition is a key parameter to mix it with the different components of positive electrode as active materials and electronic conductors to ensure the better percolation and performances. The oxide–based ceramic solid electrolytes can be shaped by sintering at high temperature, leading to a grain and –grain boundary microstructure with some porosity, facilitating the lithium dendrite growth through grain boundaries. Due to the low density and plasticity of sulfide based inorganic solid electrolyte, the dendrite growth through the particle-particle contact can be reduced but still present.Hence different parameters can influence the performances and aging of all solid state ceramic battery. To explore them, various electrochemical technics and associated specific treatments can be developed to extract and identify each phenomena and ensure the better development of this technology. A specific sequential methodology will be presented with different examples from the materials, interfaces with lithium metal, pseudo-composites and temperature effects up to aging of total all-solid–state ceramic battery based on sulfide technology. The extracted different parameters and the relationship between them will be presented.

In Situ Imaging Comparison of Lithium Electrodeposits By Neutron and X-Ray (Synchrotron and Laboratory) Tomography

Most of the post-Lithium-ion (Li-ion) devices, such as Li–sulfur, Li–O2, or all-solid-state Li batteries, have in common an negative electrode made of metallic Li.1 The main failure mode of Li based batteries is the inhomogeneity of the Li electrodeposits onto the Li metal negative electrode during charge steps, leading to dendrite growth and low Coulombic efficiency.2 Tomography and radiography imaging techniques are now vastly employed for battery materials analysis thanks to the possibility to perform noninvasive in situ and operando experiments.3 X-ray tomography is a powerful tool for studying dendrites as it provides useful information about their locations, dynamics, and microstructures. However, the use of neutron tomography is scarcely reported for Li electrodeposit analysis due to the difficulty to reach sufficient image resolution to capture the deposit microstructure, that is, typically below 10 to 20 µm. Furthermore, the different interactions of X-rays and neutrons with Li, which has significantly different opacity in the two cases, make the two techniques highly complementary.4 Notably, the capacity of neutrons to discern different Li isotopes is pivotal to get insight into the composition of Li deposits, by distinguishing between Li originating from an electrode (6Li in this study) and Li originating from the Li salt electrolyte (mainly in 7Li here). Indeed, the theoretical linear neutron attenuation coefficient of 6Li is about 15 and 2,000 times larger than that of natural Li and 7Li, respectively.In this study, we report as a proof of concept, an in situ neutron tomography imaging of Li electrodeposits in a cycled Li symmetric cell (see Figure 1).5 The electrochemical cell comprises a natural Li electrode, a 6Li electrode, and a deuterated liquid electrolyte. The neutron tomography is compared with X-ray tomography images of the same electrochemical cell acquired both at an X-ray synchrotron beamline and at a laboratory X-ray tomograph. Neutron tomography is shown to be compatible with in situ analysis and capable of capturing the overall morphology of the Li deposits in good accordance with X-ray tomography analyses. References M. S. Whittingham, Lithium batteries and cathode materials. Chem. Rev. 104 (2004) 4271.Z. Li et al., A review of Li deposition in Li-ion and Li metal secondary batteries. J. Power Sources 254 (2014) 168.K. Harry et al., Detection of subsurface structures underneath dendrites formed on cycled Li metal electrodes, Nat. Mater. 13 (2014) 69.M. Strobl et al., Advances in neutron radiography and tomography. J. Phys. D: Appl. Phys. 42 (2009) 243001.L. Magnier et al., Tomography imaging of Li electrodeposits using Neutron, synchrotron X-ray, and laboratory X-ray sources: A comparison. Front. Energy Res., 9 (2021) 657712. Figure 1

Comparison between Dissolved and Coated LiBr As Redox Mediator for Li-Air Batteries

Lithium-air battery (LAB) is one of promising next-generation batteries because of its theoretical energy density as high as 3500 Wh kg-1. However, the battery still has some difficulties to be challenged, among which large overpotential during charging is the most important one for the air electrode (AE). Application of redox mediator (RM) is a common strategy to lower the overpotential. Although RM is usually dissolved into electrolyte solution to make it react uniformly on the surface of the AE, the oxidized product of RM, RM+, diffuses to the Li electrode to be reduced into RM, which is a kind of short-circuit reaction, shuttle effect [1]. Therefore, we fixed LiBr as the RM on the surface of the AE by coating it as a mixture with carbon powder (Ketjen black, KB) and a binder (PVDF) not only to suppress the shuttle effect but also to concentrate the RM on the surface of the AE where it works [2].Three types of LAB cells were used in this study. The first one is “ no RM ” cell as a reference consisting of an air electrode coated on a carbon paper with a slurry of KB and PVDF, an electrolyte solution of 0.2 M lithium bis(trifuluoromethanesulfonyl)imide/diethyleneglycol dimehtyl ether, 0.2 M LiTFSI/G2, and a Li metal negative electrode. The other two contain LiBr as a RM in different ways. The second one is “ RM in EL (electrolyte)” cell which contains 50 mM of LiBr in addition to 0.2 M LiTFSI/G2. The third one is “ RM on AE” cell which contains LiBr in the slurry of KB-PVDF coated on the carbon paper with the same amount as that in the electrolyte solution of the RM in EL cell. Discharge/charge cycle tests were carried out at a current density of 200 mA (g-KB)−1 with a constant capacity of 500 mAh (g-KB)−1 in the range of 2.0 – 4.5 V at 30oC.Figure 1 shows the cycle performance of three types of LAB cells, which presents a better cyclability of the RM on AE cell than the others while that for the RM in EL cell is almost the same as the no RM cell. Figure 2 shows the charge and discharge voltage evolution during cycles as the voltages at midpoint, 250 mAh (g-KB)−1, for each discharge/charge cycle. The RM on AE cell shows the highest discharge voltages, the lowest charge voltages and the longest cycle life between the voltage range of 4.5 to 2.0 V among the three cells. However, the RM in EL cell shows slightly suppressed charge voltage merely early stage of the cycle test, and lower discharge voltages than the others probably due to the shuttle effect of RM, i.e. Br3 -. Therefore, coating of LiBr on AE, RM on AE , is proved to be a better strategy than dissolving LiBr into the electrolyte solution.At the presentation, we will discuss the detail of LiBr reactions as RM and compare the effect of LiBr between RM in EL and RM on AE cells with some analytical data.This study was supported by JST Projest ALCA-SPRING (JPMJAL1301) and NIMS Joint Research Hub Program, Japan.[1] X. G. Wang et al., ChemElectroChem, 4, 2145 (2017).[2] Y. Hayashi et al., J. Electrochem. Soc., 167, 020542 (2020). Figure 1

Quantification of Efficiency in Lithium Metal Negative Electrodes via Operando X-ray Diffraction

Quantification of Efficiency in Lithium Metal Negative Electrodes via Operando X-ray Diffraction

Lithium anode in carbonate-based electrolyte: High-performance by self-protected solid-electrolyte-interphase

Lithium metal is considered as the ultimate negative electrode for future high-energy batteries because of its lowest electrode potential and very high theoretical capacity. However, its practical application is severely plagued by the hazardous lithium dendritic growth upon charge and low coulombic efficiency resulting from the inhomogeneous mass and charge transfers across the Li/electrolyte interface. Herein we report an economical and effective approach to step out of this dilemma, using self-protected Solid electrolyte interphase (SEI) in carbonate-based electrolyte with Vinylethylene carbonate (VEC) additive. VEC as a sacrificing material can prevent the Li salts and solvent decomposition, and further free radical reaction of VEC decomposition products in-situ form self-protected highly uniform and mechanical strength SEI layer on Li metal surface. The versatile effects of this unique SEI layer are demonstrated by the uniform lithium plating/stripping and very high Coulombic efficiency (up to 96% after 150 cycles at 1 mA cm−2 with 1 mAh cm−2). Lithium metal batteries, employing the self-protected Li metal negative electrode coupled with LiFePO4, exhibit excellent performance in both cycling stability and rate capability. Even the anode free cell Cu|NMC811, an impressive high initial coulombic efficiency of 92.5% and promising improvement of cycling performance are achieved.

Characteristics of Perovskite Solar Cells (PSCs) with Various Metal Electrode Deposited Using Thermal Evaporators.

Organic material-based solar cell devices such as perovskite solar cells (PSCs) have attracted attention as renewable energy resources with low production cost, lightweight, wearable device applications, and large-area processability. To enhance device performance, many research groups have attempted to develop new materials and structures. Metal electrode materials play an important role in solar energy conversion in PSCs, owing to the ohmic contact and contact resistance between metal negative electrodes and photoactive layers. Until recently, conventional metal sources such as Ag, Au, or Cu have been used as electrodes. In this study, PSCs were employed in various metal negative electrodes using a thermal evaporator. The authors investigated the effect of metal negative electrodes on PSCs.

Nano-channel-based physical and chemical synergic regulation for dendrite-free lithium plating

Uncontrollable dendrite growth resulting from the non-uniform lithium ion (Li+) flux and volume expansion in lithium metal (Li) negative electrode leads to rapid performance degradation and serious safety problems of lithium metal batteries. Although N-containing functional groups in carbon materials are reported to be effective to homogenize the Li+ flux, the effective interaction distance between lithium ions and N-containing groups should be relatively small (down to nanometer scale) according to the Debye length law. Thus, it is necessary to carefully design the microstructure of N-containing carbon materials to make the most of their roles in regulating the Li+ flux. In this work, porous carbon nitride microspheres (PCNMs) with abundant nanopores have been synthesized and utilized to fabricate a uniform lithiophilic coating layer having hybrid pores of both the nano- and micrometer scales on the Cu/Li foil. Physically, the three-dimensional (3D) porous framework is favorable for absorbing volume changes and guiding Li growth. Chemically, this coating layer can render a suitable interaction distance to effectively homogenize the Li+ flux and contribute to establishing a robust and stable solid electrolyte interphase (SEI) layer with Li-F, Li-N, and Li-O-rich contents based on the Debye length law. Such a physical-chemical synergic regulation strategy using PCNMs can lead to dendrite-free Li plating, resulting in a low nucleation overpotential and stable Li plating/stripping cycling performance in both the Li‖Cu and the Li‖Li symmetric cells. Meanwhile, a full cell using the PCNM coated Li foil negative electrode and a LiFePO4 positive electrode has delivered a high capacity retention of ∼ 80% after more than 200 cycles at 1 C and achieved a remarkable rate capability. The pouch cell fabricated by pairing the PCNM coated Li foil negative electrode with a NCM 811 positive electrode has retained ∼ 73% of the initial capacity after 150 cycles at 0.2 C.

Degradation Mechanism of Lithium-Oxygen Batteries with High Areal Capacity and Lean Electrolyte

Because the nonaqueous Li–O2 batteries are still in their infancy due to numerous problems, there is no report, which actually attained the energy density of 500 Wh/kg in a complete cell level as a rechargeable battery. Except a few works[ref.1-3], almost all studies reported so far included too much excess weight of electrolytes, which results in much lower energy densities than those of LIBs. When the electrolyte amount is decreased to fulfill the energy density of 500 Wh/kg, the cell cannot be cycled. Therefore, it is especially important to quantify the decomposition reactions in Li–O2 batteries under more practical conditions of less electrolyte amount and high areal capacity[ref.4].In previous studies, less attention have been payed about the amounts of Li metal electrode and liquid electrolyte, when they determined cycle life of Li–O2 cells, even though these amounts are the important factors to determine not only energy density but also cycle life. Almost all studies so far have been carried out using a thick Li foil (100–500 μm thick). Because the equivalent weight of Li and graphite are 3860 and 372 mAh/g, respectively, the capacity ratio of negative to positive electrodes (N/P ratio) should be at least less than 3860/372 ≒ 10 to keep the advantage over graphite electrodes. When the areal capacity of the Li metal anode is set to 4 mAh/cm2, the thickness of the Li metal is calculated to be about 20 μm. On the other hand, the electrolyte amount has a more significant influence on the energy density than the Li metal thickness owing to the larger mass density of the electrolyte (1.16 g/cm3) than that of Li metal (0.53 g/cm3). The ratio of the electrolyte volume to the total pore volume of cell components is an important parameter, however, the ratio of electrolyte weight to cell capacity (E/C, gA/h) is empirically used to represent the electrolyte amount in LIBs.10 The E/C ratio in our experiments is 10 gA/h, which is much smaller than those of previous studies (E/C ≥ 50 gA/h).In the present study, we have examined reaction products in a porous carbon positive electrode by using a two-compartment cell design, where anode and cathode compartments were separated by a solid-state Li+ conductor to eliminate possible interference from the reactions at Li metal negative electrode. Because the monitoring the gas consumed/produced during the operation is nearly the only way to determine the CE of the O2 electrode, we used on-line gas analysis as well as pressure change measurements for understanding parasitic reactions coming from electrolyte decomposition. As a result, we clarified that the ratio of electrolyte weight to cell capacity is a good parameter to correlate with cycle life. Only 5 cycles were obtained at an areal capacity of 4 mAh/cm2. When the areal capacity was decreased to half, the cycle life was extended to 18 cycles. However, the total electric charge consumed for parasitic reactions was 35 and 59% at the first and the third cycle, respectively. This surprisingly large amount of parasitic reactions was suppressed by half using redox mediators while keeping a similar cycle life. Based on by-product distribution, we will propose possible mechanisms of TEGDME decomposition.

Improved Ionic Conductivity and Battery Function in a Lithium Iodide Solid Electrolyte Via Particle Size Modification

Solid electrolytes (SEs) are a promising, safe alternative to liquid electrolytes in high energy density batteries, but challenges, including low ionic conductivity and dendrite formation, remain. In a recent work, it was determined that dendrite formation within representative SEs, Li7La3Zr2O12 and Li3PS4, is due to their non-negligible electronic conductivity.[1] Notably, LiI has negligible electronic conductivity and thus the formation of lithium dendrites may be lessened, making LiI a good candidate for SE development. Our previous work on LiI SE, utilized 1:2 lithium iodide:3-hydroxypropionitrile (LiI(HPN)2) as a conductive additive, creating an 80/20 LiI/LiI(HPN)2 composite as a self-forming, rechargeable battery.[3] Additional work has demonstrated interfacial modification can effectively lower the cell impedance and improve coulombic efficiency (CE).[2, 4]In this work, a LiI SE was improved by reducing particle size via several processing methods; grinding (G), sonicating (C-S), and grinding with sonicating (G-S), and compared to a control (C) sample of LiI which underwent no processing. Partial hydration of LiI results in increased conductivity via increased defect density, and thus this parameter was controlled to ca. 34 mol% LiI monohydrate between samples. With further processing, particle size was reduced from 5 ± 1 µm to 2.0 ± 0.2 µm for the C and G-S samples. Utilized in 80/20 LiI/LiI(HPN)2 composites, reducing particle size resulted in an order of magnitude increase in ionic conductivity, from 7.7 x 10-8 to 6.1 x 10-7 S cm-1, at room temperature. Improved conductivity is attributed to an increased number of grain boundaries and defects, enabling ion transport and better mixing with the electrolyte additive, LiI(HPN)2. 3D confocal Raman spectroscopy in conjunction with non-negative matrix factorization (NMF) analysis determined the degree of HPN aggregation was lessened in the sample with smallest particle size. This LiI SE was utilized in a self-forming Li/I2 battery, where reduced particle size (improved conductivity) led to significantly reduced overpotential, allowing the coulombic efficiency to reach 100% in the first cycle. The G-S cells also exhibited improved electrochemical function when cycling at higher rates compared with the other electrolyte types. This work demonstrates the effect of particle size on solid electrolyte in a self-forming, self-healing, all solid state battery with a lithium metal negative electrode.

A high-energy density hybrid capacitor derived from a graphite-oxide lithium primary battery

Graphite-oxide (GO) is a covalent-type graphite intercalation compound, which has been reported to be a precursor of graphene oxide. A lithium battery with a GO positive electrode and a lithium metal negative electrode following the first charge/discharge cycle is reported that acts as a hybrid capacitor (HC) and has a high volumetric energy density. In this HC, the discharged (electrochemically-reduced) GO positive electrode behaves as a capacitor-like electrode.

High performance flexible quasi-solid-state zinc-ion hybrid supercapacitors enable by electrode potential adjustment

Rechargeable zinc-ion batteries have received increasing attention because of their cost effectiveness, eco-friendliness, and high capacity. However, they suffer from poor rate capacities and low lifespans because of the uncontrolled formation of zinc dendrite on the zinc metal anode. Although replacing the zinc metal negative electrode could fundamentally solve the dendritic problem, it may lead to the lack of anodic Zn2+ source to sustain the charge carriers during charge-discharge. Here, by adopting a pre-zincation electrode treatment, we demonstrate a novel zinc-ion hybrid supercapacitor (ZIS) by using GNS/CNT@MnO2 electrode and activated carbon electrode as the positive and negative electrode, respectively. The ZIS exhibits a high specific energy of 41.5 Wh kg−1 and excellent cycle stability. It retains over 81% of its initial capacitance and near 100% coulombic efficiency after 10000 cycles at 2 A g−1. We also create a Flexible Quasi-Solid-State Zinc-ion Hybrid Supercapacitor (FQSSZIS) by using a ZnSO4/MnSO4-xanthan gel electrolyte and cheap graphite paper current collectors. The obtained device exhibits excellent flexibility, good cycling stability, and a high energy density of 3.13 mWh cm−3 with a power density of 7 mW cm−3. The pre-zincation approach exhibits great potential for exploring zinc-ion energy storage devices without zinc metal electrodes.