Electrolytes For Solid-state Batteries Research Articles

Insights into polymer electrolyte stability and reaction pathways: A first-principle calculations study.

To identify suitable polymer candidates for electrolytes in solid-state batteries, this study investigates the electrochemical behavior and decomposition pathways of four monomers involving esters, ethers, and carbonates via first-principles calculations. In particular, we determine the oxidation and reduction potentials of these monomers near different ions (Li+, TFSI-, and [Li]+[TFSI]-) and the corresponding reorganization energies. The latter quantity is central to Marcus theory of electron transfer and, therefore, provides additional kinetic information. Our results reveal notable sensitivity of the monomers to reduction in a Li+-rich regime and to oxidation in a TFSI--rich regime. Additionally, the reactivity and decomposition pathways of the monomers were investigated for various electrochemical environments, focusing on the quantification of gaseous and ionic products during the initial stage of formation of interphasial layers. Based on the electrochemical windows and spontaneous Ab initio molecular dynamics calculations, we observe that monomers containing carbonate groups exhibit greater stability against decomposition caused by reduction, especially in different regimes, when compared to monomers with ester and ether groups.

Molecular Control Based on Electrostatically Driven Modification for Solid-State Lithium Metal Batteries.

With the rapid development of energy vehicles, the demand for high-safety and high-energy-density battery systems, such as solid-state lithium metal batteries, is becoming increasingly urgent. Polyethylene oxide (PEO), as a commonly used electrolyte in solid-state batteries, has the advantages of easy processing and good interface compatibility but also faces the issue of poor ionic conductivity. In this study, we have enhanced the mechanical properties and ion conductivity of PEO electrolytes significantly, stabilizing electrochemical cycling, utilizing positively charged MXene as a modifying material for PEO solid electrolytes and leveraging stronger electrostatic forces. With these enhanced properties, the modified solid electrolyte in Li/Li cells demonstrates excellent cycling stability of over 430 h at 0.1 mA cm-2. Furthermore, the Li/LiFePO4 cells show excellent cycling performance, and the capacity retention rate is 92.1%.

Research Progress on Improvement Strategies of Polymer Electrolytes in Solid-State Batteries

The solid electrolyte material can replace the liquid electrolyte in the lithium-ion batteries, which ensures higher safety due to the flammable and corroded of liquid electrolyte. The polymer electrolytes demonstrated feasibility due to its suitable ductility. However, lithium ions in the polymer electrolytes are more difficult to ionize, resulting in worse ionic conductivity. At the same time, the mechanical strength of polymer electrolytes is not as good as that of inorganic electrolytes, which is not enough to inhibit the penetration of lithium dendrite. To solve these problems, researchers adopt two strategies: adding fillers or reactants and constructing artificial interface layers, focusing on improving ionic conductivity and mechanical strength. Based on the latest research, the problems faced by polymer electrolytes and improvement measures are reviewed, which provide references for the future development of polymer electrolytes.

Molecular engineering of renewable cellulose biopolymers for solid-state battery electrolytes

Molecular engineering of renewable cellulose biopolymers for solid-state battery electrolytes

Inverted Glasses As Ductile Lithium Ion Conductors for Solid State Batteries

Inorganic electrolytes for solid state batteries with Li metallic anodes must combine properties such as high ionic conductivity, chemical stability, and resistance to failure due to propagation of Li dendrites. Abundance of experimental evidence suggests that cracking of the solid electrolytes due to pressure exerted by lithium plating into the material defects is the primary source of failure [1]. This is due to inherent brittleness of the ceramic ionic conductors, i.e. their inability to reduce stress by means other than fracture. Unlike ceramics, plastic deformation in glass can be achieved via shear and (or) by densification. Both mechanisms can be operational in glasses with reduced content of glass formers relative to the content of glass modifiers – i.e. inverted glasses. Using the example of lithium phosphorous oxynitride, Lipon, we demonstrate how these two mechanisms are capable of accommodating applied stress while avoiding creation of new surfaces by cracking. We investigate the resistance to fracture in Lipon-like glasses and the underlying connection to their composition via instrumented nano-indentation, Raman spectroscopy, and numerical simulations. We observe enhancement of isochoric shear with increase of Li content, similarly to the reports of increased plasticity in sodium aluminoborate glases with high alkali content [2]. Nano-indentation demonstrates that Lipon is extremely resistant to fracture, compared to other inorganic solid electrolytes [3].[1] Porz, T. Swamy, B.W. Sheldon, D. Rettenwander, T. Fromling, H.L. Thaman, S. Berendts, R. Uecker, W.C. Carter, Y.-M. Chiang, Mechanism of lithium metal penetration through inorganic solid electrolytes. Adv. Energy Mater. 7, 1701003 (2017)[2] Sellappan, T. Rouxel, F. Celarie, E. Becker, P. Houizot, R. Conradt, Composition dependence of indentation deformation and indentation cracking in glass. Acta Mater. 61, 5949–5965 (2013)[3] Kalnaus, A. Westover, M. Kornbluth, E.J. Herbert, N.J. Dudney, Resistance to fracture in the glassy solid electrolyte Lipon. J. Mater. Research, 36, 787-795 (2021)

Mixed Metal Amide-Hydride Solid Solutions for Energy Storage Applications

Metal amide-hydride materials have been extensively studied for usage in energy applications, especially as solid electrolytes for all-solid-state batteries and as hydrogen storage. In specific cases, the formation of mixed metal amide hydride solid solutions promotes fast hydrogen sorption kinetics and tune the thermodynamics, allowing hydrogen absorption/desorption below 150 °C in hydrogen storage systems. In addition, these intermediates, such as Li2(BH4)(NH2) or Li4(BH4)(NH2)3 are potentially ionic conductors that can be used as solid electrolytes for solid-state batteries’ applications. In this work, a series of M-N-H solid solution structures based on mixed MNH2-MH materials of Group 1 elements (M = K, Rb, Cs and their combinations), such as KNH2-KH, KNH2-RbH, RbNH2-KH, RbNH2-CsH, RbNH2-CsNH2, etc., are reported. The results obtained by experimental determination (e.g., ex-situ XRD / in-situ synchrotron powder X-ray diffraction, IR, 1H 2D solid-state MAS NMR, QENS) and theoretical calculations (e.g., molecular dynamics calculations) confirm the formation of mixed metal amide hydride solid solutions associated with an exchange between both anionic (NH2 - and H-) and cationic species (K, Rb and Cs). These structurally disordered solid solutions exhibit high ionic conductivity compared to the pure materials, e.g., mixed RbNH2-CsNH2 shows an ionic conductivity in the range of 4×10-5 S×cm-1 at 373 K compared to that of pure RbNH2 and CsNH2 (< 10-7 S×cm-1 at the same condition). Although this solid solution exhibits only moderate ionic conductivity, it offers the possibility of tuning the functional and physical properties of mixed metal amide-hydrides by structural modification.

Diagnostic of Solid-State Lithium Metal Batteries with the Sand Equation: A Symmetric Cell Electrochemical Characterization Method upon Plating

Lithium Metal Anodes (LMAs) have generated significant interest for use in solid-state batteries (SSBs) due to their high theoretical specific capacity. Nonetheless, issues such as dendrite growth (1) and cell failure caused by lithium loss with solid polymer electrolytes (SPEs) (2) of decent ionic conductivities have hindered widespread commercialization. In this work, we report the electrochemical characterization of symmetric Li- SPE– Li cells using thermoplastic vulcanizate (TPV) electrolytes comprised of: PCL:HNBR LiTFSI. Full plating of the lithium metal (LiM) electrode was achieved at 100 μA.cm-2 during constant polarization in pressurized pouch cells. Complete polarization was confirmed through ex-situ analysis by scanning electron microscopy (SEM) with SEM images showing that no dendrites were formed at this current density. Furthermore, cell polarization performed at higher current densities allowed lithium diffusion in the TPV electrolyte to be calculated using the Sand Equation (3, 4). Lithium diffusion was found to be 1.7 x 10-8 cm2.s-1 at 60 °C, which was consistent with other published values (5). The calculated threshold current density (j*) of the corresponding symmetric Li cell was approximately 200 μA.cm-2, confirming the cell failures due to dendrite growth and short circuiting that were observed in the system above this current density. This j* provides valuable information regarding the design of a full cell as the operation current density would be driven by the Li-SPE interface limitation. To this end, 100 cycles were performed in Li-Li symmetric cells with the TPV electrolyte without failure at currents below j* with 0.1 mAh.cm-2 of charge being transferred per cycle, while a charge of 0.5 mAh.cm-2 resulted in rapid cell failure. These findings emphasize the need for current densities and charge references in symmetric Li-Li cells and cells employing solid electrolytes. C. Monroe, J. Newman, The Impact of Elastic Deformation on Deposition Kinetics at Lithium/Polymer Interfaces. Journal of The Electrochemical Society 152, A396 (2005).L. Caradant et al., Effect of Li+ Affinity on Ionic Conductivities in Melt-Blended Nitrile Rubber/Polyether. ACS Applied Polymer Materials 2, 4943-4951 (2020).L. Stolz, G. Homann, M. Winter, J. Kasnatscheew, The Sand equation and its enormous practical relevance for solid-state lithium metal batteries. Materials Today 44, 9-14 (2021).D. Devaux et al., Effect of Electrode and Electrolyte Thicknesses on All-Solid-State Battery Performance Analyzed With the Sand Equation. Frontiers in Energy Research 7, (2020).T. Meyer, T. Gutel, H. Manzanarez, M. Bardet, E. De Vito, Lithium Self-Diffusion in a Polymer Electrolyte for Solid-State Batteries: ToF-SIMS/ssNMR Correlative Characterization and Modeling Based on Lithium Isotopic Labeling. ACS Applied Materials & Interfaces 15, 44268-44279 (2023).

Fabrication of 60μm-Thick Free-Standing Bilayer Solid Electrolytes for Solid-State Batteries Using Solution Processing and Lamination

Development of solid-state batteries with a high voltage cathode and lithium metal anode could enable high energy density while avoiding safety issues of flammable liquid electrolytes. However, the solid electrolyte (SE) should meet multiple requirements, including 1) electrochemical stability at both the cathode and anode side interfaces, 2) small thickness (tens of μm) to maximize energy density of the cell, and 3) fabrication with a scalable manufacturing method. Using bilayer SEs with different electrochemical stability windows could enable stability at both cathode|SE and anode|SE interfaces. In this work, we developed a manufacturing process to fabricate thin (60 μm) free-standing bilayer SE films from slurry casting and lamination, which can be used for large scale manufacturing of SSBs.Halide SE (Li3InCl6) and sulfide SE (Li6PS5Cl) were slurry casted on different substrates, and then were dried in vacuum before being laminated onto each other to make a free-standing bilayer film. The parallel slurry casting approach eliminates cross-compatibility requirements of the solvents used for slurry preparation. The resulting bilayer films after densification were pin-hole free without intermixing between the two phases. The ionic conductivity of the bilayer SE film was ~70% of the bilayer SE pellet (1 mm thickness in total) made with a conventional powder pressing method. However, because the thickness of bilayer SE film (60 μm) was much smaller than the bilayer SE pellet (1 mm), the bilayer SE film had ~10x lower area-specific resistance (ASR) compared to the bilayer SE pellet. Because of the lower total cell resistance, the cell made with the bilayer SE film had a better rate capability compared to the reference cell in pellet geometry.The strategy developed in this work could be integrated into current manufacturing infrastructure of battery fabrication as it is based on slurry casting, which is already a well-established fabrication method for lithium-ion batteries. Moreover, it could be used to fabricate multi-layered solid-state architectures in general, which are challenging to manufacture due to solvent compatibility issues during slurry casting. The study will assist the progress of solid-state battery manufacturing by providing a scalable manufacture method to prepare thin free-standing bilayer SEs.

Organic Ionic Plastic Crystal/Polymer Composite Electrolyte Prepared By Solution Casting Method for Solid-State Lithium Batteries

Solid-state electrolytes have been considered as a promising candidate to address the safety issues for next-generation lithium batteries. Organic ionic plastic crystals (OIPCs) are attracting increasing interests as solid electrolyte materials due to their unique advantages, such as plasticity, nonflammability, good thermal and electrochemical stability. In this study, an OIPC-based composite electrolyte consisting of the OIPC 1-ethyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr12TFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and the polymer polyvinylidene fluoride (PVDF) has been developed by a facile solution casting strategy. A free-standing and flexible OIPC/polymer composite membrane was fabricated by the solution casting method, which not only provides flexibility and better electrode/electrolyte contact, but also is more compatible with current battery processing methods. The composite membrane used in Li/Li symmetric cell was cycled stably over 900 h at a current density of 0.1 mA cm−2 at 50 °C, demonstrating that the OIPC/polymer composite electrolyte enabled the reversible and stable lithium plating and stripping behaviors. Further tests of the OIPC/polymer composite as solid electrolyte in LiFePO4/Li cell presented a high specific capacity of 149 mAh g−1 at 0.1 C and a long cycle life of over 440 cycles with capacity retention of 89% at 0.5 C at 50 °C, which showed improved rate capability and cycling stability in comparison with the composites with similar compositions but obtained by powder pressing method. This study demonstrated the potential of the OIPC/polymer composite solid electrolyte prepared by solution casting method and will promote the development of high-performance OIPC-based composite electrolytes for solid-state batteries.

Across Interfacial Li+ Conduction Accelerated by a Single-Ion Conducting Polymer in Ceramic-Rich Composite Electrolytes for Solid-State Batteries.

Composite electrolytes have been accepted as the most promising species for solid-state batteries, exhibiting the synergistic advantages of solid polymer electrolytes (SPEs) and solid ceramic electrolytes (SCEs). Unfortunately, the interrupted Li+ conduction across the SPE and SCE interface hinders the ionic conductivity improvement of composite electrolytes. In our study on a ceramic-rich composite electrolyte (CRCE) membrane composed of borate polyanion-based lithiated poly(vinyl formal) (LiPVFM) and Li1.3Al0.3Ti1.7(PO4)3 (LATP) particles, it is found that the strong interaction between the polyanions in LiPVFM and LATP particles results in a uniform distribution of ceramic particles at a high proportion of 50 wt % and good robustness of the electrolyte membrane with a Young's modulus of 9.20 GPa. More importantly, ab initio molecular dynamics simulation and experimental results demonstrate that Li+ conduction across the SPE and SCE interface is induced by the polyanion-based polymer due to its high lithium-ion transference number and similar Li+ diffusion coefficient with the SCE. Therefore, the unblocked Li+ conduction among ceramic particles dominates in the CRCE membrane with a high ionic conductivity of 6.60 × 10-4 S cm-1 at 25 °C, a lithium-ion transference number of 0.84, and a wide electrochemical stable window of 5.0 V (vs Li/Li+). Consequently, the high nickel ternary cathode LiNi0.8Mn0.1Co0.1O2-based batteries with CRCE deliver a high-rate capability of 135.08 mAh g-1 at 1.0 C and a prolonged cycle life of 100 cycles at 0.2 C between 3.0 and 4.3 V. The polyanion-induced Li+ conduction across the interface sheds new light on solving composite electrolyte problems for solid-state batteries.

A locally solvent-tethered polymer electrolyte for long-life lithium metal batteries

Solid polymer electrolytes exhibit enhanced Li+ conductivity when plasticized with highly dielectric solvents such as N,N-dimethylformamide (DMF). However, the application of DMF-containing electrolytes in solid-state batteries is hindered by poor cycle life caused by continuous DMF degradation at the anode surface and the resulting unstable solid-electrolyte interphase. Here we report a composite polymer electrolyte with a rationally designed Hofmann-DMF coordination complex to address this issue. DMF is engineered on Hofmann frameworks as tethered ligands to construct a locally DMF-rich interface which promotes Li+ conduction through a ligand-assisted transport mechanism. A high ionic conductivity of 6.5 × 10−4 S cm−1 is achieved at room temperature. We demonstrate that the composite electrolyte effectively reduces the free shuttling and subsequent decomposition of DMF. The locally solvent-tethered electrolyte cycles stably for over 6000 h at 0.1 mA cm−2 in Li | |Li symmetric cell. When paired with sulfurized polyacrylonitrile cathodes, the full cell exhibits a prolonged cycle life of 1000 cycles at 1 C. This work will facilitate the development of practical polymer-based electrolytes with high ionic conductivity and long cycle life.

The role of chemo-mechanical modelling in the development of battery technology—a perspective

In the race to reduce global CO2 emissions and achieve net-zero, chemomechanics must play a critical role in the technological development of current and next-generation batteries to improve their energy storage capabilities and their lifetime. Many degradation processes arise through mechanics via the development of diffusion-induced stress and volumetric strains within the various constituent materials in a battery. From particle cracking in lithium-ion batteries to lithium dendrite-based fracture of solid electrolytes in solid-state batteries, it is clear that significant barriers exist in the development of these energy storage systems, where chemomechanics plays a central part. To accelerate technological and scientific advances in this area, multi-scale and highly coupled multiphysics modelling must be carried out that includes mechanics-based phenomena. In this perspective article, we provide an introduction to chemomechanical modelling, the various physical problems that it addresses, and the issues that need to be resolved in order to expand its use within the field of battery technology.

Lithium Superionic Conductive Nanofiber-Reinforcing High-Performance Polymer Electrolytes for Solid-State Batteries.

Although composite solid-state electrolytes (CSEs) are considered promising ionic conductors for high-energy lithium metal batteries, their unsatisfactory ionic conductivity, low mechanical strength, poor thermal stability, and narrow voltage window limit their practical applications. We have prepared a new lithium superionic conductor (Li-HA-F) with an ultralong nanofiber structure and ultrahigh room-temperature ionic conductivity (12.6 mS cm-1). When it is directly coupled with a typical poly(ethylene oxide)-based solid electrolyte, the Li-HA-F nanofibers endow the resulting CSE with high ionic conductivity (4.0 × 10-4 S cm-1 at 30 °C), large Li+ transference number (0.66), and wide voltage window (5.2 V). Detailed experiments and theoretical calculations reveal that Li-HA-F supplies continuous dual-conductive pathways and results in stable LiF-rich interfaces, leading to its excellent performance. Moreover, the Li-HA-F nanofiber-reinforced CSE exhibits good heat/flame resistance and flexibility, with a high breaking strength (9.66 MPa). As a result, the Li/Li half cells fabricated with the Li-HA-F CSE exhibit good stability over 2000 h with a high critical current density of 1.4 mA cm-2. Furthermore, the LiFePO4/Li-HA-F CSE/Li and LiNi0.8Co0.1Mn0.1O2/Li-HA-F CSE/Li solid-state batteries deliver high reversible capacities over a wide temperature range with a good cycling performance.

Unlocking the concentration polarization for Solid-State lithium metal batteries

Ceramic-polymer composite electrolytes for solid-state batteries are promising candidates due to the combination of safe reliability and mechanical flexibility. However, the sluggish lithium-ion transport and the inadequate electrochemical stability with high-voltage cathode materials limit the practical applications. Herein, we report a garnet-polymer solid electrolyte with high ionic conductivity and Li-ion transference number, favorable elasticity and good interface stability. A galvanostatic charge-relaxation process is designed to identify the inhibition effect of high Li-ionic transference number on concentration polarization and reveal its proportion to total polarization. By additionally adding lithium difluoro(oxalato)borate as stabilizer, the electrochemical window of the garnet-polymer composite electrolyte can extend to 5.3 V. The high cation conductivity and excellent antioxidant ability of composite electrolyte contribute to long cycling performance of LiNi0.8Mn0.1Co0.1O2 cathode at threshold voltage of 4.4 V. Furthermore, the pouch cell with high mass loading cathode and limited lithium anode was demonstrated successfully. Our findings provide an effective strategy on fabricating solid-state lithium-metal batteries towards practical applications.

Hybrid Electrolyte Based on PEO and Ionic Liquid with In Situ Produced and Dispersed Silica for Sustainable Solid-State Battery

This work introduces the synthesis of hybrid polymer electrolytes based on polyethylene oxide (PEO) and electrolyte solution bis(trifluoromethane)sulfonimide lithium salt/ionic liquid 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide (LiTFSI/EMIMTFSI) with in situ produced and dispersed silica particles by the sol–gel method. Conventional preparation of solid polymer electrolytes was followed by desolvation of lithium salt in a polymer matrix of PEO, which, in some cases, additionally contains plasticizers. This one-pot synthesis is an alternative route for fabricating a solid polymer electrolyte for solid-state batteries. The presence of TFSI- reduces the crystallinity of the PEO matrix (plasticizing effect), increases the dissociation and solubility of LiTFSI in the PEO matrix because of a highly delocalized charge distribution, and reveals excellent thermal, chemical, and electrochemical stability. Tetraethylorthosilicate (TEOS) was chosen due to the slow reaction rate, with the addition of (3-glycidyoxypropyl)trimethoxysilane (GLYMO), which contributes to the formation of a silica network. FTIR studies confirmed the interactions between the silica, the polymer salt, and EMIMTFSI. Impedance spectroscopy measurements were performed in a wide range of temperatures from 25 to 70 °C. The electrochemical performance was explored by assembling electrolytes in LiCoO2 (LCO), NMC(811), and LiFePO4 (LFP) coin half-cells. The HPEf15 shows a discharge capacity of 143 mA/g for NMC(811) at 0.1 C, 134 mA/g for LCO, and 139 mA/g for LFP half-cells at 0.1 C and 55 °C. The LFP half-cell with a discharge capacity of 135 mA/g at 0.1 C (safety potential range of 2.8 to 3.8) obtained a cyclability of 97.5% at 55 °C after 100 cycles. Such a type of electrolyte with high safety and good electrochemical performance provides a potential approach for developing a safer lithium-ion battery.

Characterization of Li+ Transport through the Organic-Inorganic Interface by using Electrochemical Impedance Spectroscopy

Understanding Li+ transport at polymer||inorganic interfaces is crucial for developing composite electrolytes in solid-state batteries. In our investigation, we employed impedance spectroscopy and established a multilayer methodology for assessing Li+ transport at this interface. The inorganic phase chosen was Li6.25Al0.25La3Zr2O12 (Al−LLZO), and the organic phase comprised a Poly(ethylene oxide) (PEO) network with dangling chains. Li+ incorporation in the polymer, as a free either salt or associated with anion grafting onto the PEO network, was explored. Additionally, the PEO network was either pressure-adhered to the inorganic surface (ex-situ configuration) or synthesized onto the Al−LLZO surfaces (in situ configuration) to investigate processing effects on Li+ transport. Using a Transmission Line Model for impedance data analysis, our study identified two key elements governing Li+ transport at the interface: Ri, representing resistance along the ionic pathway, and Rt and Ct, describing distributed resistance and capacitance within the interface. We observed that Ri is influenced by the polymerization process in the presence of Al−LLZO ceramic, while Rt remains constant regardless of the synthesis method. This suggests varying Li+ concentrations at the interphase in the in situ configuration, while interface/interphase heterogeneity remains consistent across configurations. The estimated activation energy indicates more energetically favorable direct Li+ transport in the in−situ configuration.

Direct wetting of Li7La3Zr2O12 electrolyte with molten Li anode and its application in solid-state lithium batteries

Garnet Li6.5La3Zr1.5Ta0.5O12 (LLZTO) is a promising solid electrolyte for solid-state batteries (SSBs) owing to its high ionic conductivity and high chemical/electrochemical stability. However, the solid-to-solid interface between LLZTO electrolyte and Li anode restricts its application. In this work, an in-situ integration of LLZTO electrolyte with Li anode is proposed to solve this problem. Superior to reported works, the LLZTO obtained by our self-consolidation method can be directly wetted by molten Li without any surface treatment. The self-consolidated LLZTO exhibits a dense microstructure consisting of grains and interstitial phases among them, both of which are accessible to molten Li. Removal of surface contaminants on molten Li rather than that on LLZTO is a prerequisite for direct wetting. Benefiting from direct wetting, an intimate interfacial contact between the LLZTO and Li anode is achieved and the interfacial resistance is significantly reduced. The Li symmetric cell exerts a stable Li plating/stripping cycle for 1000 h at 0.20 mA cm−2 and the solid-state battery paired with LiCoO2 cathode exhibits a capacity retention of 90.0 % at 0.2 C after 200 cycles at room temperature. This work highlights the surface chemistry of electrolyte and electrode, which is crucial for designing their integration and application.

Lithium Dendrite Propagation in Ta-Doped Li7La3Zr2O12 (LLZTO): Comparison of Reactively Sintered Pyrochlore-to-Garnet vs LLZTO by Solid-State Reaction and Conventional Sintering.

Ta-doped Li7La3Zr2O12 (LLZTO) garnet is a promising Li-ion-conducting ceramic electrolyte for solid-state batteries. However, it is still challenging to use LLZTO in Li metal batteries operating at high current densities because of the tendency for Li metal to nucleate and propagate along the grain boundaries. In this study, we carry out a detailed investigation to elucidate the effect of microstructure and grain size on the electrochemical properties and short circuit behavior in LLZTO. Pellets were prepared using reactive sintering from pyrochlore precursors (a method called pyrochlore-to-garnet, P2G) and compared with LLZTO synthesized using solid-state reaction (SSR) followed by conventional pressureless sintering. Both preparation methods were controlled to keep the phase and elemental composition, ionic and electronic conductivity, relative density, and area-specific resistance of the pellets constant. Reflection electron energy loss spectroscopy and X-ray photoelectron spectroscopy confirm that both types of LLZTO have similar band gaps and chemical states. Microstructure analysis shows that the P2G method results in LLZTO with an average grain size of around 3 μm, which is much smaller than the grain sizes (as large as 20 μm) seen in SSR LLZTO. Galvanostatic Li stripping/plating and linear sweep voltammetry measurements show that P2G LLZTO can withstand higher critical current densities (up to 0.4 mA/cm2 in bidirectional cycling and >1 mA/cm2 for unidirectional) than those seen in SSR LLZTO. Post-mortem examination reveals much less Li deposition along the grain boundaries of P2G LLZTO, particularly in the bulk of the pellet, compared to SSR LLZTO after cycling. The improved cycling behavior in P2G LLZTO despite the higher grain boundary area could be from more homogeneous current density at the interfaces and different grain boundary properties arising from the liquid-phase, reactive sintering method. These results suggest that the effect of grain size on Li dendrite propagation in LLZO may be highly dependent on the synthesis and sintering method employed.

Nanoscale Ion Transport Enhances Conductivity in Solid Polymer-Ceramic Lithium Electrolytes.

The predictive design of flexible and solvent-free polymer electrolytes for solid-state batteries requires an understanding of the fundamental principles governing the ion transport. In this work, we establish a correlation among the composite structures, polymer segmental dynamics, and lithium ion (Li+) transport in a ceramic-polymer composite. Elucidating this structure-property relationship will allow tailoring of the Li+ conductivity by optimizing the macroscopic electrochemical stability of the electrolyte. The ion dissociation from the slow polymer segmental dynamics was found to be enhanced by controlling the morphology and functionality of the polymer/ceramic interface. The chemical structure of the Li+ salt in the composite electrolyte was correlated with the size of the ionic cluster domains, the conductivity mechanism, and the electrochemical stability of the electrolyte. Polyethylene oxide (PEO) filled with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium bis(fluorosulfonyl) imide (LiFSI) salts was used as a matrix. A garnet electrolyte, aluminum substituted lithium lanthanum zirconium oxide (Al-LLZO) with a planar geometry, was used for the ceramic nanoparticle moieties. The dynamics of the strongly bound and highly mobile Li+ were investigated using dielectric relaxation spectroscopy. The incorporation of the Al-LLZO platelets increased the number density of more mobile Li+. The structure of the nanoscale ion-agglomeration was investigated by small-angle X-ray scattering, while molecular dynamics (MD) simulation studies were conducted to obtain the fundamental mechanism of the decorrelation of the Li+ in the LiTFSI and LiFSI salts from the long PEO chain.

Vat photopolymerization of tantalum-doped Li7La3Zr2O12 electrolytes: a new Frontier in solid-state battery design

Vat photopolymerization based 3D printing to fabricate Ta-doped LLZO electrolytes for solid state batteries, aiming to address limitations in traditional manufacturing methods.