Promising Solid-state Electrolyte Research Articles

A novel flame-retardant nitrile-based gel polymer electrolyte for quasi-solid-state lithium metal batteries

In this work, a novel type of highly Li+-ions conductive, nonflammable adiponitrile (ADN)-based gel polymer electrolyte (denoted as AT11-GF) was prepared as a promising solid-state electrolyte for lithium (Li)-metal batteries by in-situ polymerization method. In order to overcome the parasitic reactions of ADN and triethyl phosphate (TEP) on Li-anode surface, fluoroethylene carbonate (FEC) was utilized as film-forming agent to generate LiF-enrich interface in this system of ADN-based electrolyte. The as-prepared electrolyte exhibited high ionic conductivity of 1.724 × 10−3 S/cm at ambient temperature, wide electrochemical window (∼5.75 V vs. Li+/Li), favorable Li+-ion transfer number (tLi+=0.70), and superior interfacial compatibility with Li anode (ultra-stable at a current density of 0.2 mA/cm2 for 1000 h). The LiFePO4|AT11-GF|Li battery presented an excellent rate capacity of 116.9 mAh/g at 2.0 C, and long-term cycling performance with a specific capacity of 134.6 mAh/g and a capacity retention of 94.5% after 1000 cycles at a current density of 1.0 C. Therefore, this as-prepared ADN-based electrolyte exhibited great promise for the application in solid-state Li-metal batteries.

Increase ionic conductivity of a Zn2+/F− synergy Na3Zr2Si2PO12 solid electrolyte for sodium metal batteries

Na3Zr2Si2PO12 (NZSP) solid-state electrolyte is considered one of the most promising solid-state electrolyte because of their excellent electrochemical and thermal stability. Even though, the low conductivity of NZSP solid-state electrolytes hinders practical application. Therefore, an anions/cations co-assisting strategy is proposed by introducing the Zn2+ and F−. The influence of adding different amounts of Zn2+ and F− on the Na+ conductivity of NZSP was investigated computationally and experimentally. The Zn2+/F− co-assisting (Na3.3Zr1.85Zn0.15Si2PO12) solid-state electrolyte exhibits the ionic conductivity of 0.722 mS cm−1 at 30 °C, and the activation energy of ∼0.237 eV. Its applicability in a solid-state battery is tested, and the assembled Na/Na3V2(PO4)3 (NVP) battery exhibits an outstanding electrochemical performance of 98.4% capacity retention after being cycled at 0.5 C. Moreover, DFT calculations also have been used to demonstrate the effect of doping on the crystal structure and space migration energy barrier. This research provides new ideas for improving the electrochemical properties of inorganic solid electrolytes.

Structural, electronic, and Li-ion mobility properties of garnet-type Li7La3Zr2O12 surface: An insight from first-principles calculations

Garnet-type Li7La3Zr2O12 (LLZO) is a promising solid-state electrolyte for Li-ion batteries, but Li-dendrite’s formation greatly limits the applications. In this paper, we systematically investigate the stability, electronic properties, and Li-ion mobility of the LLZO surface by the first-principles calculations. We consider the (110) and (001) slab structures with different terminations in the t- and c-LLZO. Our results indicate that both (110) and (001) surfaces prefer to form Li-rich termination due to their low surface energies for either t- or c-LLZO. Moreover, with the decrease of Li contents the stability of Li-rich surfaces is improved initially and degrades later. Unfortunately, the localized surface states at the Fermi level can induce the formation of metallic Li on the Li-rich surfaces. In comparison, Li/La-termination has a relatively low metallic Li formation tendency due to its rather low diffusion barrier. In fact, Li-ion can spontaneously migrate along path II (Li3 → Li2) on the Li/La–T(001) surface. In contrast, it is more difficult for Li-ion diffusion on the Li–T(001) surface, which has a minimum diffusion barrier of 0.50 eV. Interestingly, the minimum diffusion barrier decreases to 0.34 eV when removing four Li-ions from the Li–T(001) surface. Thus, our study suggests that by varying Li contents, the stability and Li-ion diffusion barrier of LLZO surfaces can be altered favorably. These advantages can inhibit the formation of metallic Li on the LLZO surfaces.

Elastomeric Electrolyte for High Capacity and Long-Cycle-Life Solid-State Lithium Metal Battery.

High room-temperature ionic conductivity and good compatibility with lithium metal and cathode materials are prerequisites for solid-state electrolytes used in lithium metal batteries. Here, the solid-state polymer electrolytes (SSPE) are prepared by combining the traditional two-roll milling technology with interface wetting. The as-prepared electrolytes consisting of elastomer matrix and high-mole-loading of LiTFSI salt show a high room temperature ionic conductivity of 4.6×10-4 S cm-1 , a good electrochemical oxidationstability up to 5.08V, and improved interface stability. These phenomena are rationalized with the formation of continuous ion conductive paths based on sophisticated structure characterization including synchrotron radiation Fourier-transform infrared microscopy, wide- and small-angle X-ray scattering. Moreover, at room temperature, the Li||SSPE||LFP coin cell shows a high capacity (161.5 mAh g-1 at 0.1 C), long-cycle-life (retaining 50% capacity and 99.8% Coulombic efficiency after 2000 cycles), and good C-rate compatibility up to 5 C. This study, therefore, provides a promising solid-state electrolyte that meets both the electrochemical and mechanical requirements of practical lithium metal batteries.

Co-doping strategy enhanced the ionic conductivity and excellent lithium stability of garnet-type Li7La3Zr2O12 electrolyte in all solid-state lithium batteries

Garnet-type Li7La3Zr2O12 (LLZO) is one of the most promising solid-state electrolytes (SSEs). However, the application of LLZO is limited by structural instability, low ionic conductivity, and poor lithium stability. To obtain a garnet-type solid electrolyte with a stable structure and high ionic conductivity, a series of TaCe co-doping cubic Li6·4La3Zr1.4-xTa0.6CexO12 (LLZTCO, x = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.20, 0.30) electrolytes were successfully synthesized through conventional solid-phase method. The Ta5+ doping can introduce more lithium vacancies and effectively maintain the stability of the cubic phase. The Ce4+ with a larger ionic radius is introduced into the lattice to widen the Li+ migration bottleneck size, which significantly increased the ionic conductivity to 1.05 × 10−3 S/cm. It also shows excellent stability to lithium metal by the optimization of Li+ transport channel. Li||LLZTCO||Li symmetric cells can cycle stably for more than 6 000 h at a current density of 0.1 mA/cm2 without any surface modifications. The commercialization potential of LLZTCO samples in all solid-state lithium batteries (ASSLBs) is confirmed by the prepared LiFePO4||LLZTCO||Li cells with a capacity retention rate of 98% after 100 cycles at 0.5C. This new co-doping method presents a practical solution for the realization of high-performance ASSLBs.

In-situ constructed SnO2 gradient buffer layer as a tight and robust interphase toward Li metal anodes in LATP solid state batteries

Li1.3Al0.3Ti1.7(PO4)3 (LATP), of much interest owing to its high ionic conductivity, superior air stability, and low cost, has been regarded as one of the most promising solid-state electrolytes for next-generation solid-state lithium batteries (SSLBs). Unfortunately, the commercialization of SSLBs is still impeded by severe interfacial issues, such as high interfacial impedance and poor chemical stability. Herein, we proposed a simple and convenient in-situ approach to constructing a tight and robust interface between the Li anode and LATP electrolyte via a SnO2 gradient buffer layer. It is firmly attached to the surface of LATP pellets due to the volume expansion of SnO2 when in-situ reacting with Li metal, and thus effectively alleviates the physical contact loosening during cycling, as confirmed by the mitigated impedance rising. Meanwhile, the as-formed SnO2/Sn/LixSn gradient buffer layer with low electronic conductivity successfully protects the LATP electrolyte surface from erosion by the Li metal anode. Additionally, the LixSn alloy formed at the Li surface can effectively regulate uniform lithium deposition and suppress Li dendrite growth. Therefore, this work paves a new way to simultaneously address the chemical instability and poor physical contact of LATP with Li metal in developing low-cost and highly stable SSLBs.

A novel phase of superionic conductor β'-Na3PS4 with a large band gap and a low migration barrier.

Na3PS4 crystals with high ionic conductivity are promising solid-state electrolytes. Here, a novel phase of Na3PS4 (β'-NPS) crystallizing in a cubic lattice with a space group of P4̄3m was systematically investigated using first-principles calculations. First of all, β'-NPS is determined to be thermodynamically, dynamically and mechanically stable. The phase transition from tetragonal Na3PS4(α-NPS) to a cubic β'-NPS system occurs at approximately 480 K, suggesting high feasibility of experimental access. Moreover, the β'-NPS is an insulator with a large band gap of 4.05 eV and a low migration energy barrier of 0.10 eV for an interstitial Na ion. Significantly, a novel Na ion diffusion mechanism, that is, interstitial diffusion, is proposed, in contrast to traditional vacancy diffusion or kick-off diffusion as observed in most solid electrolytes. This work proposes β'-NPS as a promising superionic conductor for sodium ion batteries and provides theoretical guidance towards designing future ideal solid-state electrolytes.

Effects of Li content on stability, electronic and Li-ion diffusion properties of Li<sub>3<i>x</i></sub>La<sub>(2/3)–<i>x</i></sub>†<sub>(1/3)–2<i>x</i></sub>TiO<sub>3</sub> surface

Li<sub>3<i>x</i></sub>La<sub>(2/3)–<i>x</i></sub>†<sub>(1/3)–2<i>x</i></sub>TiO<sub>3</sub>(LLTO) is a promising solid-state electrolyte for Li-ion batteries. We study the effect of Li content on the stability, electronic and Li-ion diffusion properties of LLTO surface based on first-principles and molecular dynamics simulations. We consider both Li-poor and Li-rich LLTO surfaces. The results show that La/O/Li-terminated LLTO (001) is the most stable crystal surface. Further, LLTO (001) surface gives better stability when Li content is 0.17, 0.29, and 0.38 for Li-poor phase, while 0.33, 0.40, and 0.45 for Li-rich phase . Electronic structure calculations infer that in both Li-poor and Li-rich LLTO(001) surfaces there occurs the transition from conductor to semiconductor with the increase of Li content. Besides, we find that Li-ion always keeps a two-dimensional diffusion path for different Li content. As Li content increases from 0.17 to 0.38 for Li-poor LLTO (001) surface, Li-ion diffusion coefficient increases gradually and Li-ion diffusion barrier decreases from 0.58 eV to 0.42 eV. Differently, when Li content increases from 0.33 to 0.45 for Li-rich LLTO(001) surface, it does not follow a monotonic trend for diffusion coefficient nor for diffusion barrier of Li-ion. In this case, Li-ion diffusion coefficient is the largest and Li-ion diffusion barrier is the lowest (0.30 eV) when Li content is 0.40. Thus, our study suggests that by varying Li content, the stability, band gap, and Li-ion diffusion performance of LLTO (001) can be changed favorably. These advantages can inhibit the formation of lithium dendrites on the LLTO (001) surface.

Machine Learning Interatomic Potential to Investigate Fundamentals of Electrolytes for Li-ion Solid-State Batteries

Machine learning and deep learning are used to construct interatomic potential with superior performance by satisfying the accuracy of density functional theory (DFT) calculations while requiring computational resources comparable to those required for classical molecular dynamics simulations. In this study, the machine learning interatomic potential (MLIP) is successfully constructed using moment tensor potential (MTP) for predicting the ionic conductivity of Li-ion solid-state electrolytes with Li-Ge-P-X′ and Li-X″-P-S structures, where X′ = O, S, or Se and X″ = Ge, Si, or Sn. <i>Ab initio</i> molecular dynamics (AIMD) simulations are performed to construct the initial training database for MTP; the constructed MLIP exhibits excellent accuracy with an R<sup>2</sup> value of 0.98 for predicting the potential energy value. The excellent performance of MLIP is further validated by calculating the lattice constant and bulk modulus. Finally, the ionic conductivity is obtained by performing MTP-based molecular dynamics (MD); the predicted value exhibits good agreement with previous AIMD results. Further, MTP-MD evidently runs three orders of magnitude faster than AIMD. The obtained results clearly demonstrate that MLIP can be used to rapidly determine promising solid-state electrolytes with accuracy comparable to that of DFT while greatly reducing the computational cost.

Theoretical insight into lithium triborates as solid-state electrolytes

Owing to the inherent properties combining high ionic conductivity and electrochemical stability, the lithium triborates (LBOs) have emerged as a promising solid-state electrolyte for next-generation batteries. Specific fundamental details of the ionic conduction mechanism and related physicochemical properties remain to be understood. In this study, using the first-principles density functional theory calculations, we present a systematic computational investigation on LBOs in the respect of electronic structures, mechanical and thermodynamic properties, Li-ion transport, and interfacial (with Li metal) behaviors. Our results show that LBO is a thermodynamically and mechanically stable insulator with an indirect wide bandgap of 6.4 eV. Notably, LBOs could behave as a fast Li-ion conductor with a low migration energy barrier (15 meV) and are characterized by a zig–zag Li+-diffusion path along the c direction. We found that the interface between Li metal and LBO is both physically and chemically stable with no new phase formed while exhibiting a metallic character due to the charge transfer from a Li metal. Our study highlights the intriguing promise of LBOs as solid-state electrolytes for high-energy cells.

Preparation and performances of gallium-doped LLZO electrolyte with high ionic conductivity by rapid ultra-high-temperature sintering

Garnet-type Li7La3Zr2O12 (LLZO) is a promising solid-state electrolyte (SSE) for next generation lithium batteries due to its high Li+ conductivity and stability against lithium metal, especially the Li7−3xGaxLa3Zr2O12 (Ga-LLZO) is most valuable because of its high ionic conductivity (> 1 ×10−3 S cm−1). However, it is difficult to prepare high-quality Ga-LLZO by the traditional air ambient sintering. Herein, we develop a simple and efficient rapid ultra-high-temperature sintering (RUHTS) method to prepare high-conductivity Ga-LLZO ceramic SSE. It has been found that the as-prepared Ga-LLZO ceramic SSE with the composition of Li6.25Ga0.25La3Zr2O12 exhibits high relative density of 99%, good ionic conductivity of 1.48 × 10−3 S cm−1 and large critical current density of 0.5 mA cm−2 after sintering at 1200 °C for 2 min. In addition, the Ga-LLZO SSE shows good electrochemical stability and interfacial compatibility against Li metal. The assembled Li-Li symmetric cell represents a small interfacial impedance of 37 Ω cm2. In the same time, the Li/Ga-LLZO/LE+LMNCO full battery has a total impedance of 205 Ω cm2, and can deliver a first discharge capacity of 235.1 mAh g−1 at 0.5 C, and the capacity retention rate is 88.3% after 100 cycles. This indicates that the as-prepared Ga-LLZO has good application prospect in the Li-metal solid-state batteries (LMSSBs). Moreover, this method does not require the use of mother powder during preparation process, which will effectively reduce the waste of raw materials, save manufacture costs and be beneficial to quantity production of Ga-LLZO ceramic electrolyte.

On the interfacial properties of the garnet-type electrolyte ceramic pellets of cubic Li6.4La3Zr1.4Ta0.6O12: A comprehensive improvement of the sintering additive of Li-ion conducting LiCl

The garnet-type Li fast ion conductor of cubic Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is one of the most promising solid-state electrolytes for safety-critical lithium-ion batteries, and the involved interfacial problems of LLZTO ceramic pellet must be alleviated prior to practical application. In this paper, the low-melting-point Li-ion conductor of LiCl is chosen as a sintering additive of LLZTO crystallites to address its positive effect on the structural properties of 1140°C-sintered LLZTO - x wt% LiCl (x = 0, 2, 4, 6 and/or 8). Through the physically filling into inter-particle gaps and chemically anchoring onto LLZTO particles' surface, an optimal mass fraction of LiCl (4 wt%) makes the resulting ceramic pellet to acquire a room-temperature ionic conductivity of 3.66 × 10−4 S cm−1, and the corresponding Li–C/LLZTO - 4 wt% LiCl/Li–C or Li–C/LLZTO - 4 wt% LiCl/LiCoO2 cell is endowed with a high critical current density (2.00 mA cm−2) or a good cycling stability at 20 mA g−1 within 2.5–4.2 V (e.g., discharge capacity - 124.4/91.1 mAh g−1, the 1st/100th cycle). Aside from these, a plausible mechanism of the agglutinant's actions suggests an effective approach to the further development of LLZTO-based all-solid-state lithium-ion batteries in future.

Reclaiming Neglected Compounds as Promising Solid State Electrolytes by Predicting Electrochemical Stability Window with Dynamically Determined Decomposition Pathway

AbstractThe accurate prediction of the electrochemical stability windows (ESWs) enables the rational design of solid state electrolytes (SSEs). Currently, the ESW prediction is based on direct and indirect decomposition analysis methods (DDAM and IDAM). However, DDAM/IDAM can only involve thermodynamically/kinetically favorable decomposition pathway, both resulting in the large deviation between the predicted ESW and the experimental one. Specifically, certain excellent candidate SSEs may be continuously neglected in the high‐throughput screening due to underpredicted ESWs. Herein, a high‐accuracy ESW prediction method is proposed enabling dynamical determination of the appropriate decomposition pathway by analyzing the electronic conductivities of all direct and indirect decomposition products. Following this, a high‐throughput computation is performed on the ESWs of 328 possible fast Li‐ion conductors with low ionic migration energy barriers from the previous research, obtaining good agreement with the available experimental results (Li10GeP2S12 and Li7La3Zr2O12). Furthermore, six previously neglected fluorides exhibiting ESWs over 4 V, oxidation potentials exceeding 6 V, excellent phase stability, and interfacial compatibility with seven typical cathodes are reclaimed as promising SSEs. This work demonstrates a strategy to accelerate the SSE development by improving the accuracy of the ESW prediction and enlarging the database of promising SSEs.

(Digital Presentation) H2o and CO2 Surface Contamination of the Lithium Garnet Li7La3Zr2O12 Solid Electrolyte

Garnet-type Li7La3Zr2O12 is a promising solid-state electrolyte for lithium (Li)-ion batteries, and it readily reacts with H2O and CO2 when exposed to ambient air. Such reactions form a contamination layer on Li7La3Zr2O12, which is detrimental to the battery operation. Here, using first-principles calculations, we investigate the adsorption and reactions of H2O and CO2 on a Li7La3Zr2O12 surface. We show that H2O reacts through the exchange of protons and Li+ and produces metal hydroxide species. At high H2O coverage, half of the H2O molecules dissociate, while the other half remain intact. CO2 reacts with the Li7La3Zr2O12 surface directly to produce carbonate species. We clarify that the individual reactions of H2O and CO2 with Li7La3Zr2O12 are thermodynamically more favorable than the co-adsorption of H2O and CO2. Finally, we demonstrate that low temperature and high partial pressure promote the reactions of H2O and CO2 with Li7La3Zr2O12. Our study provides guidance on processing conditions for the garnet Li7La3Zr2O12 solid electrolyte to minimize its surface contamination.

Designing High Entropy Amorphous Oxides for Li-Battery Electrolytes

Amorphous Li-oxides such as LiPON and amorphous Li garnet are considered as promising solid-state electrolytes for use in hybrid or all-solid-state oxide- and sulfide-based batteries as separators or protective layers.1-3 These materials possess several appealing characteristics, such as their intrinsic grain-boundary-free nature and relatively low manufacturing temperature (ranging from room temperature to 600 °C), which facilitates co-synthesis with Co-substituted or even Co-free cathodes that are unstable at standard electrolyte sintering temperatures. Alternatively, they can be applied as protective coatings toward Li anodes and other Li-free anode concepts, bridging the electrochemical stability voltage gap with liquid electrolytes or catholytes and preventing uneven interfacial reactions. The amorphous Li-oxides can be classified based on their structural entropy, i.e., the number and types of local bonding units (LBUs). As of today, ‘low entropy’ amorphous LiPON with only one type of LBU achieves the highest cycle number and battery lifetime.4 ‘High entropy’ amorphous Li-ion conductors, such as Li perovskites or Li garnets, exhibit an unusually high number of LBUs. local ordering and the Li-ion dynamics remain poorly understood, in part owing to the difficulty in characterizing their disordered states. This study employed a novel synthesis protocol to stabilize amorphous Al-doped Li garnets, representing so far the highest number of LBUs (≥ 4) in an amorphous Li-ion conductor.5 We resolved their phase evolution and local structures by a combination of spectroscopy, microscopy, and calorimetry techniques. A much wider (<680 °C) but processing-friendly temperature range was identified to stabilize various amorphous phases with edge- and face-sharing Zr, La, and Li LBUs that do not conform to the formation rules for Zachariasen’s glasses. These amorphous Li-ion conductors reveal an unusual setting in which Li and Zr act as network formers and La acts as a network modifier, with the highest Li-dynamics observed for smaller Li–O and Zr–O coordination among the amorphous phases. Our insight provides fundamental guidelines for the phase, local structure, and Li-transport modulation for amorphous Li garnets and pave the way for their integration in next-generation solid-state or hybrid battery designs with enhanced safety and lifetime. Acknowledgments Y.Z. acknowledges financial support provided by the MIT Energy Initiative fellowship offered by ExxonMobil. This research was supported by Samsung Electronics. This research was performed in part at the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Coordinated Infrastructure Network (NNCI), which was supported by the National Science Foundation under NSF award no. 1541959. CNS is a part of Harvard University. This research used resources of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, and was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357, and the Canadian Light Source and its funding partners.

Flexible ion-conducting membranes with 3D continuous nanohybrid networks for high-performance solid-state metallic lithium batteries

Polyethylene oxide (PEO)-based electrolytes are considered as one of the most promising solid-state electrolytes for next-generation lithium batteries with high safety and energy density; however, the drawbacks such as insufficient ion conductance, mechanical strength and electrochemical stability hinder their applications in metallic lithium batteries. To enhance their overall properties, flexible and thin composite polymer electrolyte (CPE) membranes with 3D continuous aramid nanofiber (ANF)–Li1.4Al0.4Ti1.6(PO4)3 (LATP) nanoparticle hybrid frameworks are facilely prepared by filling PEO–LiTFSI in the 3D nanohybrid scaffolds via a solution infusion way. The construction of the 3D continuous nanohybrid networks can effectively inhibit the PEO crystallization, facilitate the lithium salt dissociation and meanwhile increase the fast-ion transport in the continuous LATP electrolyte phase, and thus greatly improving the ionic conductivity (∼3 times that of the pristine one). With the integration of the 3D continuity and flexibility of the 3D ANF networks and the thermostability of the LATP phase, the CPE membranes also show a wider electrochemical window (∼5.0 V vs. 4.3 V), higher tensile strength (∼4–10 times that of the pristine one) and thermostability, and better lithium dendrite resistance capability. Furthermore, the CPE-based LiFePO4/Li cells exhibit superior cycling stability (133 mAh/g after 100 cycles at 0.3 C) and rate performance (100 mAh/g at 1 C) than the pristine electrolyte-based cell (79 and 29 mAh/g, respectively). This work offers an important CPE design criteria to achieve comprehensively-upgraded solid-state electrolytes for safe and high-energy metal battery applications.

High-performance Ta-doped Li7La3Zr2O12 garnet oxides with AlN additive

Garnet-type oxide is one of the most promising solid-state electrolytes (SSEs) for solid-state lithium-metal batteries (SSLMBs). However, the Li dendrite formation in garnet oxides obstructs the further development of the SSLMBs seriously. Here, we report a high-performance garnet oxide by using AlN as a sintering additive and Li as an anode interface layer. AlN with high thermal conductivity can promote the sintering activity of the garnet oxides, resulting in larger particle size and higher relative density. Moreover, Li3N with high ionic conductivity formed at grain boundaries and interface can also improve Li-ion transport kinetics. As a result, the garnet oxide electrolytes with AlN show enhanced thermal conductivity, improved ionic conductivity, reduced electronic conductivity, and increased critical current density (CCD), compared with the counterpart using Al2O3 sintering aid. In addition, Li symmetric cells and Li∣LiFePO4 (Li∣LFP) half cells using the garnet electrolyte with the AlN additive exhibit good electrochemical performances. This work provides a simple and effective strategy for high-performance SSEs.

Engineered interfaces between perovskite La2/3xLi3xTiO3 electrolyte and Li metal for solid-state batteries.

Perovskite La2/3xLi3xTiO3 (LLTO) materials are promising solid-state electrolytes for lithium metal batteries (LMBs) due to their intrinsic fire-resistance, high bulk ionic conductivity, and wide electrochemical window. However, their commercialization is hampered by high interfacial resistance, dendrite formation, and instability against Li metal. To address these challenges, we first prepared highly dense LLTO pellets with enhanced microstructure and high bulk ionic conductivity of S cm−1 at room temperature. Then, the LLTO pellets were coated with three polymer-based interfacial layers, including pure (polyethylene oxide) (PEO), dry polymer electrolyte of PEO-LITFSI (lithium bis (trifluoromethanesulfonyl) imide) (PL), and gel PEO-LiTFSI-SN (succinonitrile) (PLS). It is found that each layer has impacted the interface differently; the soft PLS gel layer significantly reduced the total resistance of LLTO to a low value of 84.88 Ω cm−2. Interestingly, PLS layer has shown excellent ionic conductivity but performs inferior in symmetric Li cells. On the other hand, the PL layer significantly reduces lithium nucleation overpotential and shows a stable voltage profile after 20 cycles without any sign of Li dendrite formation. This work demonstrates that LLTO electrolytes with denser microstructure could reduce the interfacial resistance and when combined with polymeric interfaces show improved chemical stability against Li metal.

Phase evolution, structure, and electrochemical performance of Al-, Ga- and Ta- substituted Li7La3Zr2O12 ceramic electrolytes by a modified wet chemical route

Garnet-type Li7La3Zr2O12 (LLZO) is one of the most promising solid-state electrolytes (SSEs) for advanced solid-state lithium batteries (SSLBs). In this work, Li6.25Al0.25La3Zr2O12, Li6.4Ga0.2La3Zr2O12, and Li6.4La3Zr1.4Ta0.6O12 ceramics are prepared by a modified wet chemical route. The composition of the black mixtures derived from the precursors is ascertained. The phase evolution and structural properties from the ceramic mother powders to the final ceramic electrolytes are discussed in detail. The characteristic of cubic LLZO with the space group I-43d arises in the Li6.4Ga0.2La3Zr2O12 ceramic electrolyte pellet after the secondary higher-temperature (1200 °C) sintering. The Rietveld refinement reveals the roles of Al3+ substitution at the Li+ sites and Ta5+ substitution at the Zr4+ sites to adjust crystal structure. In addition, the electrochemical performance of the ceramic pellets is also investigated. Remarkably, the Li6.4La3Zr1.4Ta0.6O12 ceramic electrolyte has the most outstanding electrochemical performance, showing the high ionic conductivity of 6.88 × 10−4 S cm−1 (25 °C), the low activation energy of 0.42 eV and an extremely low electronic conductivity of 1.77 × 10−8 S cm−1 (25 °C). Overall, it is supposed that this work may help to achieve high-quality modified LLZO ceramic electrolytes, especially using the wet chemical strategy.

In situ construction of Li3N-enriched interface enabling ultra-stable solid-state LiNi0.8Co0.1Mn0.1O2/lithium metal batteries

Solid polymer electrolytes (SPEs) are considered as the most promising solid-state electrolytes for next-generation lithium (Li) batteries with high safety and electrochemical performance. Whereas the interfacial side reactions between SPEs and Li metal anode hinder the development of SPEs in solid-state lithium metal batteries (SLMBs). Herein, we propose a g-C3N4 nanosheets (GCNs) reinforced poly(vinylidene fluoride) (PVDF-GCN) composite polymer electrolyte with high ionic conductivity of 6.9 × 10−4 S cm−1 and low activation energy (0.192 eV). The GCNs react with Li metal to in situ produce a Li3N-enriched SEI during cycling, which significantly suppresses the continuous side reactions and ensures rapid charge-transfer between PVDF-GCN SPEs and Li metal anode. In addition, the GCNs present a strong adsorption ability to the residual N, N-dimethylformamide molecule, which greatly enhances the electrochemical stability of PVDF-GCN SPEs. As a result, the Li symmetrical cell stably cycled over 2200 h. Moreover, the SLMBs using LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode achieve excellent cycling stability for more than 1700 cycles at 1 C and a high discharge capacity of 108 mAh g−1 at 5 C. This work provides novel insights into the construction of a stable SPEs/Li interface for long lifespan SLMBs.