Symmetric Lithium Research Articles

Enabling room temperature solid-state lithium batteries by blends of copolymers and ionic liquid electrolytes

High lithium-concentration phosphonium ionic liquids electrolytes have shown outstanding properties even overcoming ammonium derivatives in terms of viscosity and transport properties. Consequently, they have been also combined with fluorinated polymers, such as poly(vinylidene fluoride) (PVDF) or poly(ionic liquids), for solid-state batteries with satisfying performance at 50 °C. The aim of this work is to develop highly lithium conducting solid-state electrolyte (≥0.1 mS cm−1) at room temperature but maintaining solid-state properties. For this, polymer electrolytes based on ISOBAM alternating copolymer (isobutylene and maleic anhydride) and ionic liquid (P111i4FSI) were developed. The composition-dependent behavior of the solid electrolytes was studied in terms of electrochemical impedance spectroscopy (EIS), reaching σLi+ of 0.52 mS cm−1; differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR) under different ionic liquid electrolyte loadings and salt concentration. The polymer electrolytes presented a solid-like behavior in the range of 25 to 90 °C with a storage modulus of 2.3·104 Pa. Finally, the best free-standing membrane electrolytes were tested and compared electrochemically in lithium symmetrical cells and lithium iron phosphate full cells exhibiting an excellent cycling at room temperature.

Cross-Linked Composite Solid Polymer Electrolyte Doped with Li6.4La3Zr1.4Ta0.6O12 for High Voltage Lithium Metal Batteries.

Composite solid polymer electrolytes (CSPEs) are safer alternatives to liquid electrolytes and excellent candidates for high-voltage solid-state batteries. However, interfacial instabilities between the electrodes and CSPEs are one of the bottlenecks in pursuing these systems. In this study, a cross-linked CSPE was synthesized based on polypropylene carbonate, polyethylene glycol methyl ether acrylate, polyethylene glycol diacrylate with additives including lithium bis(trifluoromethane)sulfonimide salt, and tantalum-doped lithium lanthanum zirconium oxide (LLZTO). Mass fractions of 10, 20, and 40% LLZTO were added to the CSPE matrix. In a symmetric cell, lithium plating and stripping revealed that the interface between the lithium metal anode and CSPE with 10% of the LLZTO (CSPE-10LLZTO) shows the most stable interface. The CSPE-10LLZTO sample demonstrated high flexibility and showed no degradation over 800 h of cycling at varying current densities. The ionic conductivity for the CSPE-10LLZTO sample at 40 °C was 6.4 × 10-4 S/cm. An all-solid-state full cell was fabricated with LiNi0.5Mn0.3Co0.2O2 as the cathode, CSPE-10LLZTO as the electrolyte and separator, and Li metal as the anode, delivering approximately 140 mAh/g of capacity. Differential scanning calorimetry measurements on CSPE-xLLZTO showed high miscibility and the elimination of crystallinity. Raman spectroscopy revealed uniformity in the structure. These findings demonstrate the capability of the CSPEs to develop high-voltage solid-state lithium metal batteries.

One stone, three birds: Cu2+-substituted chloride electrolyte for high-performance all-solid-state lithium batteries

Emerging solid electrolytes, represented by Li2ZrCl6 (LZC), hold great potential due to their lower costs and superior electrochemical stability compared to sulfide SEs (e.g. Li5.4PS4.4Cl1.6). However, challenges such as relatively low ionic conductivity and instability with lithium hinder its widespread application. This work develops a cost-effective strategy by substituting Cu2+ for Zr4+ in LZC electrolyte. The evolution of electrolyte structure at varying substitution levels is comprehensively investigated by synchrotron X-ray diffraction and Raman spectroscopy. The optimized Cu2+-substituted LZC achieves a notable ionic conductivity of 0.75 mS cm−1 due to a reduced energy barrier for Li+ migration confirmed by first-principles calculations. Symmetric lithium cells with the Cu2+-substituted LZC exhibit enhanced inhibition to lithium dendrites than those with Li5.4PS4.4Cl1.6. X-ray photoelectron spectroscopy unveils the key role of Cu2+ reduction in the inhibition of the lithium dendrite, enabling the cell to stably cycle at 0.5 mA cm−2. Moreover, the Cu2+-substituted LZC exhibits improved electrochemical stability, marked by small anodic current exceeding 4 V, reduced polarization, and rapid lithium-ion diffusion kinetics. All-solid-state batteries fabricated with the Cu2+-substituted LZC and Li/LiNi0.8Mn0.1Co0.1O2 electrodes present a high reversible capacity of 139.2 mAh g−1 with retention rate of 96.9 % after 200 cycles at 0.5 C.

Optimization of Lithium Metal Anode Performance: Investigating the Interfacial Dynamics and Reductive Mechanism of Asymmetric Sulfonylimide Salts

Asymmetric lithium salts, such as lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide (LiDFTFSI), have been demonstrated to surpass traditional symmetric lithium salts with improved Li+ conductivity and the capacity to generate a stable solid electrolyte interphase (SEI) while maintaining compatibility with an aluminum (Al0) current collector. However, the intrinsic reductive mechanism through which LiDFTFSI influences battery performance remains unclear and under debate. Herein, detailed SEI reactions of LiDFTFSI–based electrolytes were investigated by combining density functional theory and molecular dynamics, aiming to clarify the formation process and atomic structure of the SEI. Our results show that asymmetric DFTFSI− weakens the interaction between carbonate solvents and Li+, and substantially alters the solvation structure, exhibiting a well-balanced coordination capacity compared to bis(trifluoromethanesulfonyl)imide (TFSI−). Nanosecond hybrid molecular dynamics simulation further reveals that preferential decomposition of LiDFTFSI produces sufficient LiF and Li2O to facilitate a robust SEI. Moreover, abundant F− generated from LiDFTFSI decomposition accumulates on the Al surface and subsequently combines with Al3+ from the current collector to form AlF3, potentially inhibiting corrosion of the current collector. Overall, these findings elucidate how LiDFTFSI regulates the solvation sheath and SEI structure, advancing the development of high-performance electrolytes compatible with current collectors.

In situ polymerized polydioxolane interlayer enabled dendrite-free argyrodite-based solid-state batteries

Solid-state batteries (SSBs) involving argyrodite-type sulfide electrolytes are considered as promising candidates for the state-of-art lithium-ion batteries (LIBs) due to their superior safety, energy and power density. However, the incompatibility between the argyrodite-type sulfide and lithium anode has plagued the development of the sulfide-based SSBs. Herein, we introduced a poly-dioxolane-based (PDOL) interlayer at the lithium anode, which is ring-opening polymerized via poly(acrylamide-2-methyl-1-propane-sulfonate) (PAMPS) loaded on the separator. The in-situ polymerized PDOL interlayer could match with the solvent-sensitive lithium argyrodite while enabling a stable and tight lithium interface. The symmetric lithium cell with the PDOL interlayer exhibits over-1200-hour dendrite-free lithium deposition and stripping at 0.5 mA cm-2, and the critical current density reaches 2.7 mA cm-2. The as-cycled lithium interface is further investigated via the depth-profiling X-ray photoelectron spectroscopy, and solid electrolyte interphase (SEI) is determined to be composed of ether polymer as well as inorganic compounds like LiC, Li2O, LiF, and Li2S. The Li|LiCoO2 SSB with PDOL interlayer presents a high discharge capacity of 120.7 mAh g-1 at 0.1 C and a capacity retention rate of 95.4% after 200 cycles. The rational design of the PDOL interlayer at the lithium anode opens a new alternative for high-performance SSBs.

The Effect of Battery Configuration on Dendritic Growth: A Magnetic Resonance Microscopy Study on Symmetric Lithium Cells

The potential of metallic lithium to become the anode material for next-generation batteries is hampered by significant challenges, chief among which is dendrite growth during battery charging. These dendritic structures not only impair battery performance but also pose safety risks. Among the non-destructive analytical techniques in battery research, Magnetic Resonance Imaging (MRI) stands out as a promising tool. However, the direct imaging of lithium by 7Li MRI is limited by its low sensitivity and spatial resolution, making it a less effective way of imaging dendrite growth. Instead, a recently introduced indirect imaging approach which is based on 1H MRI of the electrolyte was used in this study. This method was used to sequentially 3D image and thus monitor the charging process of lithium metal symmetric cells in three different electrical circuits, namely those composed of a single cell, four cells in parallel, and four cells in series. The measured sequential images allowed for the measurement of dendrite growth in each cell using volumetric analysis. The growth results confirmed the theoretical prediction that the growth across cells is uneven in a parallel circuit, and even in a series circuit. The methods presented in this study can also be applied to analyze many other dendrite-related issues in batteries.

2.5 μm‐Thick Ultrastrong Asymmetric Separator for Stable Lithium Metal Batteries

Lithium metal batteries (LMBs) are considered the ideal choice for high volumetric energy density lithium‐ion batteries, but uncontrolled lithium deposition poses a significant challenge to the stability of such devices. In this paper, we introduce a 2.5 μm‐thick asymmetric and ultrastrong separator, which can induce tissue‐like lithium deposits. The asymmetric separator, denoted by utPE@Cu2O, was prepared by selective synthesis of Cu2O nanoparticles on one of the outer surfaces of a nanofibrous (diameter ~10 nm) ultrastrong ultrahigh molecular weight polyethylene (UHMWPE) membrane. Microscopic analysis shows that the lithium deposits have tissue‐like morphology, resulting in the symmetric lithium cells assembled using utPE@Cu2O with symmetric Cu2O coating exhibiting stable performance for over 2000 h of cycling. This work demonstrates the feasibility of a facile approach ultrathin separators for the deployment of lithium metal batteries, providing a pathway towards enhanced battery performance and safety.

Constructing Enhanced Composite Solid-State Electrolytes with Sb/Nb Co-Doped LLZO and PVDF-HFP

Composite solid-state electrolytes are viewed as promising materials for solid-state lithium-ion batteries due to their combined advantages of inorganic solid-state electrolytes and solid-state polymer electrolytes. In this study, the solid electrolytes Li6.7−xLa3Zr1.7−xSb0.3NbxO12 (LLZSNO) with Sb and Nb co-doping were prepared by a high-temperature solid-phase method. Results indicate that Sb/Nb co-doping causes lattice deformation in LLZO and increases the lithium vacancy concentration and conductivity of LLZO. Then, with the co-doped LLZSNO as an inorganic filler, a composite solid electrolyte of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was prepared with a casting method. The obtained composite solid electrolyte exhibits a high ionic conductivity of 1.76 × 10−4 S/cm at room temperature, a wide electrochemical stable window of 5.2 V, and a lithium-ion transfer number of 0.32. The Li|LiFePO4 coin battery with the composite solid electrolyte shows a high specific capacity of 161.2 mAh/g and a Coulombic efficiency close to 100% at 1 C. In addition, the symmetrical lithium battery Li|Li with the composite electrolyte could cycle stably for about 1500 h without failure at room temperature.

Flexible Composite Electrolyte Membranes with Fast Ion Transport Channels for Solid-State Lithium Batteries.

Numerous endeavors have been dedicated to the development of composite polymer electrolyte (CPE) membranes for all-solid-state batteries (SSBs). However, insufficient ionic conductivity and mechanical properties still pose great challenges in practical applications. In this study, a flexible composite electrolyte membrane (FCPE) with fast ion transport channels was prepared using a phase conversion process combined with in situ polymerization. The polyvinylidene fluoride-hexafluoro propylene (PVDF-HFP) polymer matrix incorporated with lithium lanthanum zirconate (LLZTO) formed a 3D net-like structure, and the in situ polymerized polyvinyl ethylene carbonate (PVEC) enhanced the interface connection. This 3D network, with multiple rapid pathways for Li+ that effectively control Li+ flux, led to uniform lithium deposition. Moreover, the symmetrical lithium cells that used FCPE exhibited high stability after 1200 h of cycling at 0.1 mA cm-2. Specifically, all-solid-state lithium batteries coupled with LiFePO4 cathodes can stably cycle for over 100 cycles at room temperature with high Coulombic efficiencies. Furthermore, after 100 cycles, the infrared spectrum shows that the structure of FCPE remains stable. This work demonstrates a novel insight for designing a flexible composite electrolyte for highly safe SSBs.

Trilithium salt of tetrahydroxyanthraquinone: A high-voltage and stable organic cathode material for rechargeable lithium metal and lithium-ion batteries

Organic cathode materials (OCMs) have drawn considerable attention for lithium batteries but suffer from unfavorable dissolution problem and thus inferior cycling performance. Salification is a simple approach to restrain the dissolution but most reported lithium-salt-type OCMs are still unable to achieve good cycling stability due to poorly conjugated and/or asymmetric structure. Herein, we report a novel air-stable, largely conjugated, and symmetric organic lithium salt synthesized from 1,4,5,8-tetrahydroxyanthraquinone (THAQ), namely Li3THAQ. It possesses a layered crystalline structure with large interlayer spacings, which is relatively stable in the reversible conversion between Li4THAQ and Li2THAQ. Benefiting from this, Li3THAQ exhibits exceptional electrochemical performance within 2.0–3.6 V, including high reversible capacity (192 mAh g−1), high discharge potential (2.93 V vs. Li+/Li), high rate capability (75 % capacity retention at 5000 mAh g−1 vs. 50 mAh g−1), and high cycling stability (95 % capacity retention after 500 cycles). Additionally, it can be also matched with natural graphite anode to construct a Li-ion full-cell, which was rarely reported for OCMs. In brief, Li3THAQ shows great advantages in structure stability, electrochemical performance, and practicability compared to its counterparts, and the in-depth mechanism understanding provides important insights into the development of lithium-salt-type OCMs.

Ethylene Carbonate Free Electrolytes with High Oxidative Stability for High Voltage Lnmo Spinel Cathode in Li-Ion Cells

The increasing implementation of lithium-ion batteries (LIBs) for the fast growing electric vehicle market calls for further improvements in energy density and drives research and innovation to investigate beyond state-of-the-art cell chemistries [1]. Currently, the capacity of the commonly employed transition metal oxide cathodes (NMC series) is approaching their theoretical limit. Thus, to further promote the energy density of LIBs, the most promising strategies are the adoption of a high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) cathode in combination with a high energy density anode. While commercial grades of LNMO are now available, the main challenge toward their implementation is the identification of suitable electrolyte systems with high oxidative stability enabling safe operation of LNMO cathodes at voltages beyond 4.7 V vs Li/Li+, which are also compatible with advanced anode materials operating at low potential. Indeed, electrolytes represent a crucial component in LIBs, and hence a great deal of research has been focusing on the next generation electrolyte systems. These should present a wide electrochemical stability window, high ion conductivity over a wide range of temperature, good thermal stability, and the ability to form stable interphases.[2] In this work we present results on a range of novel electrolytes, based on previous publications [3-5] including super concentrated systems with unconventional solvents to improve the anodic stability, beyond LiPF6 salts to mitigate transition metal dissolution at the cathode, and phosphorous and boron-based additives to improve the stability of the solid/electrolyte interphase (SEI) at the anode. The electrolytes are comprehensively characterised in terms of ionic conductivity over a range of temperatures (see Fig. 1a), viscosity, and thermal stability. Electrochemical impedance spectra (EIS) has been carried out in symmetrical lithium // lithium cells to investigate the interphase stability evolution upon time. Linear sweep voltammetry has been conducted to investigate the anodic stability (see Fig. 1b). The systems have been then investigated in combination with high voltage LNMO cathode, graphite anodes as well as a novel silicon/graphite composite anode. The results will highlight the results achieved so far toward the identification of suitable electrolytes for high energy density Li-ion cells, while discussing the remaining challenges and strategies to mitigate them.[1] Energies 2017, 10(9), 1314, G. Berckmans, M. Messagie, J. Smekens, N. Omar, L. Vanhaverbeke, J. V. Mierlo.[2] Chem. Soc. Rev., 2021, 50, 10486, X. Fan, C. Wang.[3] J. Am. Chem. Soc., 136 (2014) p. 5039, Y. Yamada, K. Furukawa, K. Sodeyama, K. Kikuchi, M. Yaegashi, Y. Takeyama & A. Yamada.[4] Nature Communications, 7 (2016) 12032, J. Wang, Y. Yamada, K. Sodeyama, C. H. Chiang, Y. Tateyama & A. Yamada[5] J. Mater. Sci: Mat. Elec. , 30 (2019) p. 5098, H. Zhou, B. Liu, D. Xia, C. Yin & J. Li Figure 1

Eutectic Mixtures As Highly Concentrated and Molten Electrolytes with Nearly Single-Ion Conducting Behavior

Today's state-of-the-art liquid electrolytes in lithium ion batteries (LIBs) have a high ionic conductivity and good performance regarding their cycle life. (1) However, they pose a safety risk due to their high vapor pressures and low thermal stability. (1) Furthermore, due to the limited electrochemical stability of the solvent, liquid electrolytes are not suitable for the application in high-voltage LIBs. (2) Molten salts, also called ionic liquids (IL), or highly concentrated electrolytes (HCE) have high lithium ion concentrations, where nearly every solvent molecule is coordinated. Due to this, there are strong ion interactions and the formation of ion clusters that lead to an increased lithium ion transference number of >0.5. (3) Therefore, they can represent an alternative in the field of liquid electrolytes. Additionally, HCE exhibit a higher thermal and electrochemical stability compared to dilute electrolytes and can improve the cycle performance in lithium metal batteries. (4, 5)McOwen et al. reported the coordination of lithium ions and crystalline structures in HCE of the binary mixtures of ethylene carbonate (EC) and lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) with molar ratio up to 1:1. (6) Based on the concept of melting point depression as known from thermodynamics, room-temperature molten, highly concentrated electrolytes of a carbonate-based solvent with lithium sulfonyl imides were investigated. Instead of EC, the solvent pinacol carbonate (PIC) without acidic α-hydrogen atoms, but four bulky methyl groups was synthesized and used for eutectic mixtures, as the melting point of PIC is with 187 °C far above room-temperature. The physicochemical properties of these electrolytes are studied with respect to the different influence of lithium bis(fluorosulfonyl)imide and LiTFSI despite their same basic molecule structure. The focus will be on the electrochemical analysis by the means of the ionic conductivity, transference number and the electrochemical stability.In comparison to dilute liquid electrolytes the molten electrolytes show extremely high transference numbers, especially for the PIC-LiTFSI mixtures nearly a single-ion conducting behavior (0.9) is observed. This behavior can be explained by the formation of a 2D polymeric network within the HCE electrolyte as determined by crystallographic measurements in the solid state. Combined with the high electrochemical stability, a stable long-term cycling and dendrite suppression in symmetric lithium cells could be shown. Cycling in full cells with high-voltage cathode materials such as LiNi0.6Mn0.2Co0.2O2 (NMC622) or LiMn4O2 (LMO) against lithium metal anodes is applicable. References K. Xu, Chemical Reviews, 104(10), 4303–4417 (2004).J. Li, C. Ma, M. Chi, C. Liang and N. J. Dudney, Advanced Energy Materials, 5(4) (2015).K. M. Diederichsen, E. J. McShane and B. D. McCloskey, ACS ENERGY LETTERS, 2(11), 2563–2575 (2017).G. Jiang, F. Li, H. Wang, M. Wu, S. Qi, X. Liu, S. Yang and J. Ma, Small Struct., 2(5), 2000122 (2021).V. Nilsson, A. Kotronia, M. Lacey, K. Edstrom and P. Johansson, ACS Applied Energy Materials, 3(1), 200–207 (2020).D. W. McOwen, D. M. Seo, O. Borodin, J. Vatamanu, P. D. Boyle and W. A. Henderson, Energy & Environmental science, 7(1), 416–426 (2014).

Evaluating the Use of Critical Current Density Tests of Symmetric Lithium Transference Cells with Solid Electrolytes

AbstractAlkali metal filament penetration into solid electrolytes causes short circuit induced cell failure, commonly evaluated using the bidirectional critical current density (CCD) test with stepwise increases in current density in alternating directions across symmetric lithium cells. However, the CCD is neither intrinsic to the cell nor to the material but rather depends on various extrinsic factors, such as current profile, transferred charge, pressure, resting intervals, and interface chemistry. The purpose of this study is to disambiguate the interpretation of CCD analyses in the literature and propose alternative approaches to analyze the stability and kinetics of the alkali metal/solid electrolyte interface. Two types of failure modes of electrochemical cells with solid electrolytes are defined: 1) failure of the solid electrolyte by crack formation coupled with or followed by dendrite growth, and 2) failure of the alkali metal electrode by the formation of pores at the interface with the solid electrolyte followed by filament initiation that eventually leads to short‐circuiting. Therefore, the study recommends that CCD tests specify the failure mode. It is demonstrated that unidirectional polarization enablesunambiguous differentiation between failure modes. The proposals for bi‐ and unidirectional testing presented here are expected to provide more reliable and consistent CCD values across the community.

Exceptional interfacial conduction and LiF interphase for ultralong life PEO-based all-solid-state batteries

Composite electrolytes, with large ionic conductivity and stable seamless interfaces, are recognized as potential ones for solid-state batteries (SSBs). Herein, a flexible all-solid-state composite electrolyte composed of TiO2 (Bronze) nanotubes and poly(ethylene oxide) was synthesized. The composite electrolyte was found to be able to offer an exceptional interfacial conduction and a reasonable electrode compatibility in the SSBs. The interfacial phase between TiO2(B) and polymer formed a new lithium-ion transport pathway, which enhanced the interfacial conduction. Moreover, DFT and MD simulation showed that TiO2(B) can promote the dissociation of lithium salts and produce more free lithium ions, thereby enhancing the ionic conductivity. Furthermore, the incorporations of TiO2(B) can achieve a rich LiF interphase layer, realizing a rapid lithium-ion transport and uniform Li deposition, as was revealed by the results of TOF-SIMS, Cryo-TEM, and COMSOL Multiphysics. Consequently, the symmetric lithium cell obtained an excellent electrochemical performance of more than 2350 h and a high critical current density of 1.6 mA cm−2. The as-prepared LiFePO4/Li SSBs exhibited an impressive ultralong cycle lifespan of over 3100 cycles at 1 C. This work is regarded as opening a new avenue for designing reasonably the ultralong life of PEO-based SSBs.

Electrochemical Characterization of Thiophosphate- Ionic Liquid Hybrid Lithium Electrolytes Against Li Metal

(Almost) solid-state batteries that utilize thiophosphate solid electrolytes (SE) are an exciting technology emerging as a potential alternative to lithium-ion batteries. When used alongside a lithium metal anode they can offer the high energy densities [1] required to meet the increasing demand for energy storage. However, they suffer from numerous issues which predominately occur at the cathode- or anode-SE interface. Issues include dendrite propagation through gaps, pores and grain boundaries of the solid electrolyte which can eventually puncture electrolyte crystallites and lead to cell failure. [2] Thiophosphate electrolytes are also unstable both chemically and electrochemically. As a result of the SEs having a low electrochemical stability window reduction or oxidation can occur at the anode or cathode interface, forming a resistive solid electrolyte interphase (SEI). [3] Finally, the ionic contact between Li metal anode and electrolyte is poor and thus high interfacial impedances can arise. These impedances can be dynamic which increase during stripping of the lithium and decrease during plating. [4] To solve some of the interfacial issues there is the option to add a small of amount of liquid electrolyte at the lithium metal-electrolyte interface. The liquid electrolyte can fill in the gaps and pores at the interface thus improving the ionic contact whilst allowing a more stable interface. Whilst the ionic contact can be improved the inherent instability of thiophosphate electrolytes against the liquid electrolyte means that a new interphase known as the solid-liquid electrolyte interphase (SLEI) can form. The presence of this interphase can therefore lower the energy density and round-trip efficiencies of cells which utilize hybrid electrolytes meaning that minimizing the SLEI resistance and maximizing total ionic conductivities is important in hybrid cells. [5]In this work a hybrid of the thiophosphate argyrodite Li6PS5Cl and the ionic liquid x-LiTFSI-1-butyl 1-methylpiperidinium TFSI (BMPipTFSI) with LiTFSI concentrations of 0.25 M and 0.5 M was studied. The choice of SE and liquid electrolyte boils down to the high ionic conductivity of the SE and the electrochemical and thermal stability of the ionic liquid. Temperature-dependent ionic conductivity measurements showed that hybrid systems exhibit lower in room temperature ionic conductivities and higher total activation energies. This hints at the presence of a SLEI forming between the LE and SE. To study how the SLEI resistances changes over time, ion blocking potential impedance spectroscopy measurements were performed. These measurements were performed at 10 °C to allow for the resistance contributions to be better resolved and showed a SLEI resistance of around 45-50 Ω cm2 for both hybrids. Over the period of 130 hours this resistance changed minimally (around 5 Ω cm2 on average) indicating good stability of the SLEI. To further test the suitability of this hybrid alongside lithium metal anodes impedance measurements in symmetrical lithium cells (Li0|LE|LPCL|LE|Li0) were undertaken. In this case galvanostatic impedance spectroscopy (GEIS) with an applied current density of ±0.4 mA cm-2 was used to probe the changes in resistance contributions in the system over the period of stripping (positive current) and plating (negative current). For cells with just SE a large change in the resistance owing to the electrochemical reaction (ECR) (Li0 ↔ Li+ + e-) occurred during stripping and plating indicating the dynamic nature of the ionic contact at the interface. For the hybrid electrolyte cells, this ECR resistance is decreased and becomes more stable however a larger interphase resistance is present. This resistance is a combination of the resistances of both the SLEI (the interphase between the LE and SE) and the SEI (the interphase between LE and Li anode) and it changes over stripping and plating showing that the S(L)EIs which are present are dynamic. Finally, post-mortem SEM/EDX of the surface of samples show a change in morphology and the presence of decomposition products from both the liquid and solid electrolytes. These studies show that the LPCL-BMPipTFSI hybrid is stable and improve ionic contact at the lithium metal anode interface. Further testing in half Li-S cells will determine the suitability of the use of the ionic liquid at the cathode side of the cell.

Fluorinated Nonflammable In Situ Gel Polymer Electrolyte for High-Voltage Lithium Metal Batteries.

Rechargeable lithium metal batteries (LMBs) offer excellent opportunities for applications requiring high-energy-density battery systems. So far, it has received a lot of interest in pairing higher-energy-density high-voltage nickel-rich cathodes. Here, fluorinated solvents were used instead of the usual carbonate solvents to prepare gel polymer electrolytes (FGPE) by in situ polymerization of polymers introducing the fluorine-containing groups. Theoretically and experimentally, FGPE has proven to be ultra-compatible with the lithium metal anode and LiNi0.8Co0.1Mn0.1O2 cathode. A stable plating/stripping process of over 2000 h can be achieved for symmetrical lithium cells using FGPE. The Li||FGPE||NCM811 cell has a longer cycle life at a high voltage (4.5 V). In addition, the zero self-extinguishing time indicates that the FGPE has sufficient safety. In summary, the design of this electrolyte provides ideas to improve the safety and energy density of LMBs.

Mechanical properties of three‐dimensional trilayered Li–garnet electrolyte for high‐rate cycling in solid‐state batteries

AbstractUtilizing tape casting–laminating–sintering technique, we developed a three‐dimensional (3D) porous–dense–porous trilayered Li–garnet framework that enables symmetric cycling lithium metal under high current densities for long time (∼3–10 mA/cm2 for over ∼500 h). To address the reasons that such 3D Li–garnet framework can withhold high current density and long‐term cycling, both experiments (nanoindentation and bending) and simulations (finite element analysis [FEA]) regarding mechanical properties on such 3D framework were employed. The results indicate that (1) the dense layer has high and uniform elastic modulus and hardness so can efficiently prevent lithium penetration and dendrites growth; (2) the porous layer, including the grains and the necking regions, has high nanomechanical properties to withhold the lithium penetration stress; (3) the spherical pores in the porous layer can withhold higher lithium penetration forces/stress compared with rectangular/regular pores based on FEA. The flexural strength of the whole structure was also characterized using the three‐point bending method to demonstrate the high strength (∼30.8–42.1 MPa) of the 3D framework. A rule‐of‐mixtures model was developed, which can be used to estimate the flexural strength of the trilayered framework based on the microstructures. Correlations between the mechanical properties and the high‐rate cycling are further discussed.

Highly conductive ceramic-in-polymer composite electrolyte enabling superior electrochemical performance for all-solid-state lithium batteries

In the present work, poly (vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] and various amounts of NASICON-type LiZr1.5Sn0.5(PO4)3 (LZSP) as the active filler were used to fabricate composite solid electrolytes (CSEs) by solution-casting method and their structural and electrochemical behaviour were studied. The X-ray diffraction (XRD) data showed the compatibility of the rhombohedral LZSP with P(VDF-HFP). A uniform distribution of ceramic particles in the polymer was observed from scanning electron microscopy (SEM) images and energy X-ray dispersive maps. The addition of 15% wt. ceramic filler to the polymer matrix enhanced the room temperature ionic conductivity (σ ∼ 2.87 × 10−5 S/cm), lithium-ion transference number (tLi+ ∼ 0.55), and electrochemical stability window (∼4.87 V). The reversibility and endurance of lithium-ion conduction across the composite electrolyte at various current densities were confirmed through galvanostatic charge-discharge measurements on a symmetric lithium cell for more than 500 h. A full cell fabricated using a commercial grade LiMn2O4 cathode and the optimized CSE electrolyte showed excellent rate performance at room temperature. The cell delivered a discharge capacity of 105 mAh/g with a nominal voltage of 4.0 V and retained 93% of its initial capacity after 100 cycles at a current density of 0.1 mA/cm2.

A Highly Salt-Soluble Ketone-Based All-Solid-State Polymer Electrolyte with Superior Performances for Lithium-Ion Batteries

Solid polymer electrolytes (SPEs) have great potential to be used in high-safety lithium-ion batteries (LIBs). However, it is still a significant challenge for SPEs to develop high ionic conductivity, high mechanical strength, and good interior interfacial compatibility. In this work, a ketone-based all-solid-state electrolyte (PAD) resulting from allyl acetoacetate (AAA), diacetone acrylamide (DAAM), and poly(ethylene glycol) diacrylate (PEGDA) was prepared by UV-inducing photopolymerization. The abundant ketone groups endow the prepared PAD all-solid-state electrolyte with strong dissociation of lithium salts and weak coordination interactions between ketone groups and Li+. Depending on the unique properties of the ketone groups in the electrolyte system, the prepared polymer electrolytes show a high lithium-ion transference number of 0.87 and a wide electrochemical window of 4.95 V. Furthermore, the PAD electrolyte also exhibits superior viscoelasticity, which is beneficial for good contact with electrodes. As a result, the assembled LFP/PAD/Li cells with PAD electrolytes show good cycle performance and rate performance. Concretely, the all-solid-state symmetric lithium cells with the PAD electrolyte can achieve stable lithium plating and stripping at 0.05 mA cm-2 for over 1000 h at 60 °C. This work highlights the advantages of ketone-based electrolyte as a polymer electrolyte and provides a design method for advanced polymer electrolytes applied in high-performance solid lithium batteries.

Synergistic interactions between the charge‐transport and mechanical properties of the ionic‐liquid‐based solid polymer electrolytes for solid‐state lithium batteries

AbstractThe performance sensitivity of the solid‐state lithium cells to the synergistic interactions of the charge‐transport and mechanical properties of the electrolyte is well acknowledged in the literature, but the quantitative insights therein are very limited. Here, the charge‐transport and mechanical properties of a polymerized ionic‐liquid‐based solid electrolyte are reported. The transference number and diffusion coefficient of lithium in the concentrated solid electrolyte are measured as a function of concentration and stack pressure. The elastoplastic behavior of the electrolyte is quantified under compression, within a home‐made setup, to substantiate the impact of stack pressure on the stability of the Li/electrolyte interface in the symmetric lithium cells. The results spotlight the interaction between the concentration and thickness of the solid electrolyte and the stack pressure in determining the polarization and stability of the solid‐state lithium batteries during extended cycling.