Organic Liquid Electrolytes Research Articles

(Digital Presentation) Nanoscaffold Porosity and Surface Chemistry Effects on Li-Ion Conductivity in Metal Hydride Nanocomposite Electrolytes

The development of energy storage technologies, such as rechargeable batteries, is crucial for the transition to a sustainable energy supply. Lithium-ion batteries are an effective means of energy storage, which is demonstrated by their wide application ranging from mobile phones to laptops and electric vehicles. Unfortunately, Li-ion batteries suffer from safety issues arising from their combustible organic electrolytes. All-solid-state batteries, in which the common liquid organic electrolyte is replaced by a solid-state electrolyte, could potentially lead to safer batteries with increased energy density.[1] Recently, metal hydrides (e.g. LiBH4 and LiCB11H12) have gained attention as promising solid electrolytes due to their electrochemical and thermal stability, low density and high ionic conductivity albeit at elevated temperatures. However, for successful incorporation of metal hydride electrolytes in all-solid-state batteries, sufficient ionic conductivity at room temperature is a prerequisite. Therefore, the development of strategies that enhance the room temperature conductivity in complex hydrides (10-8 S cm-1 for LiBH4) is of major importance.In this contribution, we combined two promising strategies to enhance ion mobility in metal hydrides, namely, partial ionic substitution[2] and nanoconfinement[3], which led to highly conductive metal hydride-based nanocomposites (Figure 1). Specifically, via partial ion substitution with LiNH2, followed by nanoconfinement in a mesoporous oxide scaffold, LiBH4-LiNH2/metal oxide nanocomposites with conductivities reaching 5x10-4 S cm-1 at 30 °C were obtained[4], compared to 2x10-8 S cm-1 for pure LiBH4.Interestingly, the conductivity of the LiBH4-LiNH2/metal oxide nanocomposites is strongly influenced by the chemical and physical nature of the mesoporous metal oxide. We systematically studied the influence of the scaffold properties on the conductivity of nanoconfined LiNH2-substituted LiBH4 using mesoporous silica scaffolds (SBA-15) with varying surface chemistry and pore structure. The conductivity varied over three orders of magnitude when tuning both the porosity and surface chemistry of the metal oxide scaffold.[5] Our study reveals that the LiBH4-LiNH2/metal oxide conductivity is affected by the chemical nature of the scaffold, similar to LiBH4/metal oxide nanocomposites. A conductivity improvement of a factor of two is achieved by changing the SiO2 (SBA-15) surface chemistry through alumination (Figure 2a). On the other hand, different from nanoconfined LiBH4, the conductivity of LiBH4-LiNH2/metal oxide nanocomposites is largely dictated by the pore structure of the scaffold, especially the pore volume (Figure 2b). Notably, the conductivity can be varied from 4x10-7 S cm-1 to 5x10-4 S cm-1 by increasing the scaffold pore volume from 0.51 to 1.00 cm3 g-1.Our work demonstrates that the origin of the conductivity enhancement in anion-substituted complex hydride-based nanocomposite electrolytes is different from other nanoconfined complex hydrides, e.g. LiBH4. In particular, for nanoconfined LiBH4-LiNH2, the conductivity improvement is attributed to stabilization of a highly conductive phase inside the scaffold pores, rather than the formation of a conductive interfacial layer at the hydride/oxide interface as observed for nanoconfined LiBH4. Thus, it is clear that the conductivity of metal hydride-based nanocomposite ion conductors is closely linked to the properties of scaffold material. The fundamental insights on the influence of scaffold properties on ion mobility in nanocomposite materials could be applicable to other cation- and anion substituted ion conductors as well. Thereby, this work provides useful insights for the design novel solid-state electrolytes with excellent ionic conductivity, crucial for the development of next generation batteries.

Interface Lithiophobicity Regulation for Lithium Metal Solid-State Batteries

Solid-state lithium batteries (SSLBs) using garnet electrolytes potentially have a higher energy density and are safer than commercial liquid organic electrolyte Li-ion batteries. However, SSLBs still face challenges of lithium dendrite growth and high interface resistance. In this work, we addressed both challenges by doping strontium (Sr) into lithium anodes. Different from all previous reported metal/metal oxide coating on garnet or lithium alloy anodes that forms lithiophilic interlayer at Li | garnet, strontium/strontium oxide are enriched on the interface between Li and garnet forming a lithiophilic/lithiophobic bifunctional layer of Li-Sr/SrO-doped-Li2O. This interlayer simultaneously reduces the interfacial resistance and suppresses the growth of lithium dendrite, which is confirmed by comprehensive material characterizations, simulations and electrochemical evaluations using Ta-doped LLZTO (Li6.5La3Zr1.5Ta0.5O12) as a model solid-state electrolyte. The unique stability of the lithiophobic SrO doped Li2O layer against Li prevents reducing the garnet and suppresses lithium dendrite, which distinguishes it from all reported alloy electron-conductor interlayers. The optimized Li-Sr | LLZTO | Li-Sr symmetrical cells have a critical current density of 1.3 mA/cm2 and can be cycled for 1,000 cycles under 0.5 mA/cm2 at room temperature. The bifunctional lithiophilic/lithiophobic interlayer provides a new strategy for high-performance garnet solid-state lithium batteries. Figure 1

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

Ta-LLZO Garnet Processed By Spark Plasma Sintering for All Solid State Batteries

All Solid State Lithium based Batteries (ASSLB) using a stable inorganic solid state electrolyte are envisaged as the most promising answer to solve the safety issues of Li-ion batteries using inflammable organic liquid electrolyte. Garnet Li7La3Zr2O7 showing high ionic conductivity and high stability versus metallic lithium is currently the most appealing solid electrolyte to be used in oxide based ASSLB. However, its high reactivity with moisture and sensitivity to all energetic process lead to strong difficulties in obtaining stable fully dense pellets while mandatory to ensure its role as mechanical barrier to avoid the short-circuit caused by Li-dendrites [1-2]. In this work, Spark Plasma Sintering is used as both a characterization and a fast sintering techniques to determine the influence of side products and efficiency of applied processes to remove them in reaching dense pellets with high ionic conductivity.Commercial Ta-doped LLZO powder is fully characterized using conventional techniques to identify chemical and thermal stability. SPS experiments are conducted to determine the influence of the side products on the sintering. The efficiency of powder pretreatment designed to remove side products is determined based on data collected during SPS experiments. SPS parameters (applied pressure, temperature ramping, densification dwell ...) are then optimized allowing reaching in a reproducible way pellets with high density (>97 %) and high mechanical strength. Analysis using XPS, SEM and XRD of obtained pellets shows that decomposition occurs only at the surface while the core of the pellet is made of pure cubic phase Ta-doped LLZO. Impedance spectroscopy is used to evidence the influence of side products on the electrical properties and confirms high ionic conductivity (0.5 mS/cm) and very low electronic conductivity of optimized electrolyte. The sintering temperature and dwell time are then optimized by advanced sintering techniques (high pressure, Flash SPS) allowing to prevent the chemical instability usually observed between LLZO and active materials (LiCoO2 or Li[Ni1-x-yCoxMny]O2 (NCM)) and to obtain a cathodic half-cell (LLZO/positive electrode) in one step. References : [1] H. Yamada, T. Ito, R. Basappa, Electrochimica Acta 222 (2016) 648–656.[2] M. Kotobuki, M.Koishi, Journal of Alloys and Compounds 826 (2020) 15421.

(Invited) Operando Measurement of Heterogeneities in All-Solid-State Li Battery Electrodes

All-solid-state Li batteries are under intense research and development due to their potential to (a) replace flammable organic liquid electrolytes with solid materials, and (b) increase energy density by allowing Li metal anodes and resulting in a more compact battery.[1]Several types of Li+-conducting solid electrolytes are being studied, e.g. sulfides, oxides, phosphates, polymers, and various composites of these.[2] While polymers are very processable, they have low conductivities, generally <10-4 S/cm. Sulfides have high conductivities, >10-2 S/cm, but are unstable materials and require cells to be under high compression to get good cycling results.[3] Oxides and phosphates have good conductivity, but are hard and brittle, forming poor interfaces with electrode active materials. The ideal combination of solid electrolyte and active material remains elusive, but work continues.An additional challenge looms for the design of all-solid-state electrodes, as reaction distributions in battery electrodes are often heterogeneous, resulting in uneven utilization of active materials.[4] Uneven reaction distributions are generally the result of an imbalance between electronic and ionic transport in the cell, but can also be caused by other resistances such as those introduced by insulating layers surrounding active materials. In this talk I will report our experimental results measuring heterogeneous phenomena in all-solid-state batteries. We have employed electrochemical impedance spectroscopy (EIS) as well as energy dispersive X-ray diffraction (EDXRD). EDXRD is a high-energy synchrotron technique that allows the interiors of batteries to be profiled in a tomographic way during battery operation. We use this to directly observe heterogeneous lithiation gradients across the thickness of cathodes in all-solid-state batteries. We will focus on cells with sulfide electrolytes, such as Li6PS5Cl and Li6.6Ge0.6Sb0.4S5I. Heterogeneous structural stability of the electrolyte itself will also be discussed.[5] Acknowledgments We acknowledge financial support from the National Science Foundation under Award Number CBET-ES-1924534.

Gas Evolution from Sulfide-Based All-Solid-State Batteries

The demand for high-performance batteries for electrical vehicles (EV) and large-scale energy storage systems have accelerated the development of all-solid-state batteries. Switching from organic liquid electrolyte to solid electrolyte (SE) ensures, not only the high energy density (Wh/L), but also an intrinsic improvement to safety from the removal of flammable solvent in the liquid electrolyte. However, for the development of all-solid-state batteries, still many problems exist toward commercialisation. One challenge is their chemical/electrochemical stability. In case of Li6PS5Cl argyrodite, their electrochemical decomposition was proposed as following reaction. [1]Li6PS5Cl → Li4PS5Cl + 2Li+ + 2e → Li3PS4 + Sx + LiCl → P2Sx + Sx + LiCl + 3Li+ + 3e (1) However, this proposed reaction is bulk electrochemical decomposition of argyrodite. To understand the decomposition in actual cell, layered oxide cathode/argyrodite composite were analysed by in situ Raman microscopy, X-ray photoelectron spectroscopy and Time-of-flight secondary ion mass spectrometry. [2, 3] This research reports actual solid decomposition product formed by active material and solid electrolyte such as POx or (S2)2- compound. Not only for solid decomposition product, but also gaseous decomposition product can be generated from the interface between cathode materials and SE. Previously, much work has demonstrated that O2 and CO2 gases are released from the positive electrode material within the lithium-ion cell. [4] These exothermic surface reactions are important not only for cell swelling in the long-term usage, but also for cell combustion. However, the gas releasing behaviour of positive electrode mixture in all-solid-state batteries are still not well recognised. In this research, we focused on the gas releasing behaviour of all-solid-state batteries. LiNi0.6Mn0.2Co0.2O2 was selected for cathode materials in this research. For the solid electrolyte itself and LiNi0.6Mn0.2Co0.2O2/SE mixture were analysed by Differential Electrochemical Mass Spectroscopy (DEMS). Furthermore, to understand the importance of surface chemistry, air stored LiNi0.6Mn0.2Co0.2O2 and Al2O3 coated LiNi0.6Mn0.2Co0.2O2were prepared. Since air contamination (H2O and CO2) is detrimental for Ni-rich cathode and battery [5], we propose role of surface chemistry in all-solid-state batteries by comparing different LiNi0.6Mn0.2Co0.2O2 composites. As shown in Figure 1, CO2 and O2 gas evolution is observed within an all-solid-state cell as it is charged up to 5 V, with evolution beginning at ca. 4 V highlighting the requirement of stabilising interfaces even when a solid-state electrolyte is used.Figure 1. Comparison of O2 and CO2 gas evolution from (a) Li6PS5Cl and (b) LiNi0.6Mn0.2Co0.2O2/ Li6PS5Cl composite when charged to 5 V vs. Li/Li+.[1] L. Zhou, N. Minafara, W. G. Zeier, L. F. Nazar, Innovative Approaches to Li-Argyrodite Solid Electrolytes for All-Solid-State Lithium Batteries, Acc. Chem. Res., 54, (2021) 2717–2728[2] Y. Zhou, C. Doerrer, J. Kasemchainan, P. G. Bruce, M. Pasta, L. J. Hardwick, Observation of Interfacial Degradation of Li6PS5Cl against Lithium Metal and LiCoO2 via In Situ Electrochemical Raman Microscopy, Batter. & Supercaps, 3, (2020) 647 –652[3] F. Walther, R. Koerver, T. Fuchs, S. Ohno, J. Sann, M. Rohnke, W. G. Zeier, J. Janek, Visualization of the Interfacial Decomposition of Composite Cathodes in Argyrodite-Based All-Solid-State Batteries Using Time-of-Flight Secondary-Ion Mass Spectrometry, Chem. Mater, 31, (2019), 3745-3755[4]S. Sharifi-Asl, J. Lu, K. Amine, R. Shahbazian-Yassar, Oxygen Release Degradation in Li-Ion Battery Cathode Materials: Mechanisms and Mitigating Approaches, Adv. Energy Mater., 9, (2019) 1900551[5] H. Kim, A. Choi, S. W. Doo, J. Lim, Y. Kim, K. T. Lee, Role of Na+ in the cation disorder of [Li1-xNax] NiO2 as a cathode for lithium-ion batteries, J. Electrochem. Soc., 165, (2018), A201 Figure 1

(Digital Presentation) Electrochemical-Mechanical Coupling between Single-Ion Conducting Electrolytes and Metal Electrodes

Solid-state metal batteries provide increased gravimetric and volumetric energy density compared to conventional Li-ion batteries and their development is essential for meeting performance and cost targets for consumer applications. Conventional liquid electrolytes exhibit reactivity with pure Li and undergo significant dendrite formation, thus single-ion conducting solid electrolytes have been explored to prevent and mitigate dendrite formation as they possess high modulus, high room temperature ionic conductivity, and the potential to improve safety compared to organic liquid electrolytes. Unfortunately, ceramic single-ion conducting electrolytes such as LLZO have been demonstrated to form dendrites above critical current densities. Understanding the electrochemical-mechanical coupling between the electrolyte and electrode can help elucidate the mechanisms of dendrite formation and propagation in solid-state metal batteries as well as methods for prevention and mitigation. Mechanical stresses arise during battery operation due to external stack pressure, expansion and contraction of intercalation electrodes, and the deposition and stripping of metal electrodes. As we demonstrated in a previous work1, the thermodynamic state of the electrode is affected by its mechanical state, therefore, applied stresses alter the equilibrium potential of metal electrodes. Additionally, the mechanical state of the electrode can influence the metal electrode plating and stripping kinetics. Previous studies in the literature have examined the effect of mechanics on the current distribution; however, careful attention is required when coupling electrochemistry and mechanics as well as consideration as to the importance of the mechanical state of the electrolyte. This talk will focus on the effects of mechanical stresses on the current distribution at the metal electrode/single-ion conducting electrolyte interface and the implications on dendrite formation and mitigation.

The Influence of Polar Functional Groups in Hot-Melt Extruded Polymer Blend Electrolytes for Solid-State Lithium Batteries

Following the COP26 Summit in November 2021, more than hundred countries pledged to reach zero-emission by 2070 at the latest and the major car manufacturers committed to selling only electric vehicles by 2040. Currently, lithium-ion batteries (LIBs) are among the most widely used storage systems because of their high energy and power densities and long lifespan.1 The early LIBs are composed of intercalation electrodes, electronically isolated by an ion-conducting organic liquid electrolyte. However, the use of liquid electrolytes presents some disadvantages – especially in regard to consumer safety – related to short-circuits and potential leakages of the flammable liquid solvent. Moreover, in the case of lithium metal batteries, the combination of a liquid electrolyte and a high-capacity lithium metal anode leads to the uncontrolled deposition of lithium during the reduction, forming dendrites between the electrodes. A promising way to avoid this instability and improve battery safety is to replace the liquid electrolyte with an ion-conducting solid electrolyte.2 Among them, solid polymer electrolytes (SPEs) represent one of the most attractive alternatives due to their capacity to effectively conduct ions and higher mechanical resistance than their liquid counterparts.3 An important criterion for selecting polymers for use in SPEs is their ability to dissolve lithium salts through polar functional groups. Salt dissolution results in the replacement of ion-ion interactions in the lithium salt, with ion-dipole interactions in the polymer. The transport mechanisms of these ion-conducting materials differ from those of liquid electrolytes. Cation transport in polymer involves two steps which are considered to be dissociated or not, depending on the model chosen (Arrhenius or Vogel-Fulcher-Tammann, respectively). The application of one of these models provides interesting information on the ionic mobility dynamics in SPEs and, in particular, on the interplay between ionic jumps and polymer chain mobility. In the Arrhenius model, ionic jumps occur between coordinating sites, without taking into account the influence of segmental relaxation. Conversely, the VTF equation implies a strong relationship between these parameters. According to previous studies, higher segmental motions in the amorphous phase of polymers mainly provide ionic transport, which explains the limited ionic conductivity of SPEs at ambient temperature (less than 10-5 S/cm).Another major limitation of SPEs is primarily related to their dual role as electrolyte and binder in composite electrodes, which requires contradictory requirements to be met. Indeed, SPEs must have both sufficient flexibility to allow good interfacial contact between the electrode components and sufficient rigidity to limit short circuits.Polymer blending has emerged as an economic and effective technique to develop new SPEs which may simultaneously combine properties of each polymer and control the intrinsic properties of the resulting blend by adjusting the formulation.4 Moreover, polymer blends can be obtained by a solvent-free processing method, which reduce SPE toxicity and production time (no solvent evaporation). However, polymer blending makes both the salt dissociation processes and the ionic transport more difficult to understand as both polymers can dissolve lithium salts with their polar functional groups. Each polymer has different ionic transport properties depending on its architecture and thermal properties. Currently, no systematic survey comparing the ability of polymers with various functional groups to dissolve lithium salts in blends has thus far been conducted.In this presentation, we will discuss the salt dissociation ability of polar functional groups in various polymer blend SPEs. These groups are limited to those that are most commonly present in SPEs : ether, nitrile, carbonate, ester, alcohol and amide.5 The blends presented have been obtained by extrusion, which allows the effect of solvents on salt/polymer interactions to be neglected. In this work, coupled FTIR, EDX and 7Li NMR analyses allow the interactions between LiTFSI and the polymer blends to be determined with a good degree of certainty. Our original study combines experimental and theoretical approaches to determine effects of polymers’ lithium salt solvating ability on polymer blend electrolyte properties and represents an advancement in understanding and optimizing polymer selection for SPEs, used in lithium-ion batteries. References Xie, W., Liu, X., He, R., Li, Y., Gao, X., Li, X., Peng, Z., Feng, S., Feng, X. and Yang, S. Journal of Energy Storage 2020, 32, 101837.Chen, R., Qu, W., Guo, X., Li, L. and Wu, F. Materials Horizons 2016, 3, 487-516.Gray, F. M. Solid polymer electrolytes, VCH New Tork 1991.Caradant, L., Lepage, D., Nicolle, P., Prébé, A., Aymé-Perrot, D. and Dollé, M. ACS Applied Polymer Materials 2020, 4943-4951.Caradant, L., Verdier, N., Foran, G., Lepage, D., Prébé, A., Aymé-Perrot, D. and Dollé, M. ACS Applied Polymer Materials 2021. Figure 1

Fabrication and Performance of Li-S/Se Solid State Cathodes with Holey Graphene As a Conductive Scaffold and Binder

Electric aircraft demonstrate potential as the future of aviation, offering zero emissions, lower noise, and potentially lower operational costs than aircraft powered by internal combustion engines. Currently, state-of-the-art lithium (Li) ion batteries used to enable today’s electrical vehicles lack the specific energy (< 250 Wh/kg) required to make electric flight (ideally requiring >400 Wh/kg) an economically beneficial endeavor. Additionally, Li ion batteries introduce serious safety concerns due to the highly flammable organic liquid electrolytes contained within the cell. Li-sulfur/selenium (Li-S/Se) cell chemistries possess high theoretical energy densities (2600 and 1160 Wh/kg, respectively) and therefore are a promising option to power electric aircraft. Rings of S doped with Se as the active cathode material result in a cell electrochemistry that can provide a balanced energy and power output during their reaction with Li. To improve safety, the S/Se cathode can be implemented with a solid-state electrolyte (SSE) to ensure the batteries would not be flammable. However, there are tremendous challenges in optimizing the interface between SSEs and the active material in the cathode composite to achieve desirable performance. In this presentation, we report our findings on the cathode fabrication and performance for solid-state Li-S/Se battery cells. We demonstrate that holey graphene (hG), a structural derivative of graphene, can serve as a scaffold host and binder to facilitate the close contact between the active material and SSEs. In addition, hG has unique properties such as through plane holes and dry compressibility that can aid in the fabrication and electrochemical performance of these high energy density solid-state batteries.

Effects of Coating on the Electrochemical Performance of a Nickel-Rich Cathode Active Material

Due to their safety and high power density, one of the most promising types of all-solid-state lithium batteries is the one made with the argyrodite solid electrolyte (ASE). Although substantial efforts have been made toward the commercialization of this battery, it is still challenged by some technical issues. One of these issues is to prevent the side reactions at the interface of the ASE and the cathode active material (CAM). A solution to address this issue is to coat the CAM particles with a material that is compatible with both ASE and CAM. Prior studies show that the lithium niobate, LiNbO3, (LNO) is a promising material for coating CAM particles to reduce the interfacial side reactions. However, no systematic study is available in the literature to show the effect of coating LNO on CAM performance. This paper aims to quantify the effect of LNO coating on the electrochemical performance of a nickel-rich CAM. The electrochemical performance parameters that are studied are the capacity, cycling performance, and rate performance of the coated-CAM; and the effectiveness of the coating to prevent the side reactions at the ASE and CAM interface is out of the scope of this study. To eliminate the effect of side reactions at the ASE and CAM interface, we conduct all tests in the organic liquid electrolyte (OLE) cells to solely present the effect of coating on the CAM performance. For this purpose, 0.5 wt.% and 1 wt.% LNO are used to coat the LiNi0.6Mn0.2Co0.2O2 (NMC-60) CAM through two synthesizing methods. Consequently, the effects of the synthesizing method and the coating weight percentage on the NMC-60 performance are presented.

A flexible [(DMPI+)(AlCl4−)]/PVDF-HFP polymer gel electrolyte and its electrochemical performance for dual-graphite batteries

Recently, dual-graphite batteries (DGBs) receive growing attention for their advantages of high working voltage, environmental friendliness and inexpensive. However, the conventional liquid organic electrolytes used in DGBs still possess issues of safety and electrolyte leakage that might limit their further development. Herein, a non-flammable [(DMPI+)(AlCl4−)] ionic liquid (DAIL) is embedded into a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) matrix to prepare a [(DMPI+)(AlCl4−)] polymer gel electrolyte (DAPGE) for solving these conventional issues. The DAPGE, as both the electrolyte and separator, is characterized and electrochemically tested in DGB, which shows favourable ionic conductivity of 2.28 × 10−3 S cm−1. The DGB using a DAPGE shows a specific capacity of 80 mAh g−1 at a current density of 100 mA g−1. Moreover, the DGB pouch cell with DAPGE can work well under bending, critical temperature and even exposure to air. Besides, DAPGE decreases the utilization (around 40%) of liquid IL electrolyte as compared to that of conventional glass fibre separators does. Consequently, the application of DAPGE in DGBs shows promise for achieving higher energy density and better robustness.

Reactivity at the Electrode-Electrolyte Interfaces in Li-Ion and Gel Electrolyte Lithium Batteries for LiNi0.6Mn0.2Co0.2O2 with Different Particle Sizes.

The layered oxide LiNi0.6Mn0.2Co0.2O2 is a very attractive positive electrode material, as shown by the good reversible capacity, chemical stability, and cyclability upon long-range cycling in Li-ion batteries and, hopefully, in the near future, in all-solid-state batteries. Three samples with variable primary particle sizes of 240 nm, 810 nm, and 2.1 μm on average and very similar structures close to the ideal 2D layered structure (less than 2% Ni2+ ions in Li+ sites) were obtained by coprecipitation followed by a solid-state reaction at high temperatures. The electrochemical performances of the materials were evaluated in a conventional organic liquid electrolyte in Li-ion batteries and in a gel electrolyte in all-solid-state batteries. The positive electrode/electrolyte interface was analyzed by X-ray photoelectron spectroscopy to determine its composition and the extent of degradation of the lithium salt and the carbonate solvents after cycling, taking into account the changes in particle size of the positive electrode material and the nature of the electrolyte.

Double‐Network Ionogel Electrolyte with Superior Mechanical Performance and High Safety for Flexible Lithium‐Ion Batteries

AbstractThe development of high‐performance solid‐state electrolytes to replace conventional liquid organic electrolytes has received intensive attention because of the improvements in the safety, flexibility, reliability, and cycling stability of lithium‐ion batteries (LIBs). In this work, we present a double‐network ionogel electrolyte (DNIE) through the preparation of interpenetrating polymer networks (IPNs). This DNIE exhibits good mechanical properties, excellent flexibility, nonflammability, high ionic conductivity (4.13×10−4 S cm−1 at room temperature), electrochemical stability (&gt;4.8 V), and the ability to suppress Li dendrite formation. The Li/LiFePO4 cell assembled with the DNIE exhibits superior cycling performance while also delivering a steady high discharge capacity of 133.7 mAh g−1 and a Coulombic efficiency of 99.8 % after 220 cycles at a charge/discharge rate of 0.2 C. Importantly, the DNIE(200 %)‐20 % electrolytes can be prepared on the surface of graphite anodes through in situ gelling, which can improve the stability of the active layer and the adhesion between the active layer and current collector in mechanical bending at different angles. After assembling into soft‐packed batteries in the configuration of LiCoO2|DNIE(200 %)‐20 %|graphite via the in situ gelling of DNIE(200 %)‐20 % on the surface of the graphite electrode, the flexible batteries showed excellent cycling stability (capacity retention &gt;98 %) even when folded more than 100 times.

Recent Advances in Solar Rechargeable Seawater Batteries Based on Semiconductor Photoelectrodes.

With the ever-increasing demand for energy in the world, the tendency to use renewable energies has been growing rapidly. Sunlight, as an inexhaustible energy source, and the oceans, as one of the most valuable treasures on Earth, are available for free. Simultaneous exploitation of these two sources of energy and matter (sunlight and oceans) in one configuration can provide a sustainable solution for future energy supply. Among the various types of such energy storage and conversion systems, solar rechargeable seawater batteries (SRSBs) can meet this need by storing the chemical energy of seawater by receiving solar energy. SRSBs consist of two compartments: a closed compartment including a sodium metal anode in an organic liquid electrolyte, and an open compartment containing a semiconductor photoelectrode immersed in seawater, which are separated from each other by a ceramic solid electrolyte membrane. In this complex system, the photoelectrode is irradiated by sunlight, whereby electrons are excited and reach the Na metal anode after passing though the external circuit. The ceramic solid electrolyte harvests only sodium ions from seawater and transfers them to the anodic part, where the transferred ions are reduced to sodium metal atoms. At the same time, an oxygen evolution reaction takes place at the cathodic part. In this way, the battery is charged. The use of a photoelectrode in the charging process significantly increases the voltage efficiency of SRSBs to more than 90%, whereas a cell with only the seawater compartment (without a photoelectrode) will not deliver satisfactory performance. Therefore, to achieve very high efficiencies, designing an accurate system with the best components is absolutely necessary. This review focuses on the working principle of SRSBs, at the same time explaining the effect of key components on the performance and stability of SRSBs. The role of the semiconductor photoelectrode in improving the voltage efficiency of SRSBs is also described in detail, and finally strategies proposed to overcome obstacles to the commercialization of SRSBs are introduced.

Recent advances of newly designed in-situ polymerized electrolyte for high energy density/safe solid Li metal batteries

It is revealed that the application of commercial liquid organic electrolytes encountered increasing safety hazards to achieve higher energy density. The replace of solid electrolytes could eliminate most safety issues induced by liquid electrolytes. However, both solo polymer electrolyte and inorganic electrolyte have difficulty to simultaneously acquire high ionic conductivity and good interfacial compatibility. At this circumstance, in-situ polymerization is developed to construct a compatible interface with high ionic conductivity and improved safety performances. In this review, recent advances of newly designed electrolyte are summarized and discussed. It is realized that the polymerization conversion of monomer and construction of 3D inorganic structure are the factors deserve consideration for high security and energy density. Finally, the challenges and future perspectives are outlined to foresee the development of in-situ polymerized electrolytes.

Dual-function redox mediator enhanced lithium-oxygen battery based on polymer electrolyte

The polymer electrolyte based lithium-oxygen battery has showed higher safety than that of organic liquid electrolyte. However, the energy efficiency and cycling stability are still the challenges for the practical application of lithium-oxygen battery. Herein, the 1,4 para benzoquinone has been demonstrated as dual-function redox mediator for promoting both oxygen reduction and oxygen evolution reactions of lithium-oxygen battery with polymer electrolyte, which have been confirmed by the Cyclic Voltammetry and discharge/charge test of battery under O2 gas, as well as the theoretical calculations. Furthermore, the composite cathode that in-situ constructed by polymerizing electrolyte precursors with redox mediator can be beneficial for the electrochemical reactions. Combing composite cathode and lithium ions source, the polymer electrolyte based lithium-oxygen batteries can operate for long lifetime with low charge potentials and good rate performances. Thus, this work has highlighted the promising implementation of lithium-oxygen battery based on polymer electrolyte, in which the dual-function redox mediator are employed for both discharge and recharge processes.

Formation of Passivate Interphases by Na3BS3-Glass Solid Electrolytes in All-Solid-State Sodium-Metal Batteries

Interphase formation at the interface between a solid electrolyte and negative electrode is one of the main factors limiting the practical use of all-solid-state sodium batteries. Sulfide-type solid electrolytes with group 15 elements (P and Sb) exhibit high ductility and ionic conductivity, comparable to those of organic liquid electrolytes. However, the electronically conductive interphase formed at the interface between Na3PS4 and sodium metal increases the cell resistance and deteriorates its electrochemical properties. Contrarily, Na3BS3, containing boron as an electrochemically inert element, forms an electronically insulating thin passivate interphase, facilitating reversible sodium plating and stripping. Sodium-metal symmetric cells with Na3BS3 exhibit steady operation over 1000 cycles. Thus, reduction-stable solid electrolytes can be developed by substitution with an electrochemically inert element versus sodium.

Preparation of hybrid perovskite-type Li0.33La0.56TiO3 by adding ionic liquids

Perovskite-type Li0.33La0.56TiO3 (LLTO) shows greater advantages than organic liquid electrolytes to be used in all-solid-state lithium-ion batteries with high energy densities. Ionic liquid [BMIM][BF4] was used to improve the properties of Li0.33La0.56TiO3 by attrition milling in this study. The microstructure, crystallinity and lithium-ion conductivity of the samples were measured by scanning electron microscopy (SEM), X-ray diffraction (XRD), and impedance spectroscopy (IS). The total ionic conductivities of the samples LLTO + x wt% [BMIM][BF4] increase upon adding [BMIM][BF4] and the maximum conductivity reaches 4.71 × 10−4 S/cm when x = 12.5 wt%. The enhancement of the total conductivity is ascribed to the bridging role of the ionic liquid among grains, as evidenced by the low activation energy of 0.17–0.25 eV and the SEM observation. The Li+ transference numbers of the hybrid samples are all lower than that of the pure LLTO, indicating the existence of electronic conductions. The hybrid material with a mixed conductivity and good stability in the atmosphere can find uses in all-solid-state lithium-ion batteries to improve the interface contact between electrolytes and electrodes.

Activated microporous carbon spheres for electric double-layer capacitor

Supercapacitors (SC) are essential energy storage devices for renewable energies. In this study, activated microporous carbon spheres (AMCS) and nitrogen-doped AMCS (N-AMCS) were synthesized using a modified extended Stöber method followed by CO2 activation. A high specific area (>3400 m2 g−1) was obtained for AMCS and N-AMCS, and the diameters of the sphere could be tuned from 400 nm to 1.0 µm. The SC study revealed that the AMCS and N-AMCS achieved specific capacitances of 232.75 and 263.59 F g−1, respectively, in 6 M potassium hydroxide (KOH). The SC pouch cells were filled with aqueous, organic, and ionic liquid electrolytes. In 1 M MeEt3NBF4 in acetonitrile, the energy densities of AMCS and N-AMCS were 27.96 and 31.20 Wh kg−1, respectively, at the current density of 0.5 A g−1, whereas the energy densities of AMCS and N-AMCS were 69.19 and 117.69 Wh kg−1, respectively, in EMIMBF4. In addition, in the aqueous electrolytes, AMCS and N-AMCS had capacitance retentions of 94% and 97%, respectively, after 10,000 cycles, while the capacitance retentions of 82% and 97% were achieved with AMCS and N-AMCS, respectively, after 50,000 cycles.

Impact of Low Temperatures on the Lithiation and Delithiation Properties of Si-Based Electrodes in Ionic Liquid Electrolytes.

Lithium-ion batteries are used in various extreme environments, such as cold regions and outer space; thus, improvements in energy density, safety, and cycle life in these environments are urgently required. We investigated changes in the charge and discharge properties of Si-based electrodes in ionic liquid electrolytes with decreasing temperature and the cycle life at low temperature. The reversible capacity at low temperature was determined by the properties of the surface film on the electrodes and/or the ionic conductivity of the electrolytes. The electrode coated with a surface film formed at a low temperature exhibited insufficient capacity. In contrast, a Si-only electrode precoated with the surface film at room temperature exhibited a cycle life at low temperatures in ionic liquid electrolytes longer than that in conventional organic liquid electrolytes. Doping phosphorus into Si led to improved cycling performance, and its impact was more noticeable at lower temperatures.