Li Conductivity Research Articles

Stabilized Cathode/Sulfide Electrolyte Interface through Conformally Interfacial Nanocoating for All-Solid-State Batteries

All-solid-state lithium batteries (ASSLBs) composed of sulfide-based solid-state electrolyte and LiNixMnyCo1–x–yO2 (NMC) cathode are expected to become the promising next generation of energy storage systems due to their great potential in highly improved safety and energy density. However, the poor interfacial stability between the NMC cathode and sulfide-based electrolyte remains an important challenge for the commercialization of ASSLBs. In this study, a thin layer of fast lithium-ion conductor Li1.3Al0.3Ti1.7(PO4)3 (LATP) with a thickness of 8 nm was coated at the interface between LiNi0.8Co0.1Mn0.1O2 (NCM811) and Li5.5PS4.5Cl1.5 via a facile wet chemical method to improve interfacial stability. It has been found that the nanoscale LATP coating layer can not only accelerate lithium ions across the NCM811/Li5.5PS4.5Cl1.5 interface but also effectively alleviate the interfacial problems. The initial discharge capacity of the as-prepared LATP@NCM811/Li5.5PS4.5Cl1.5/Li batteries at 0.1 C is 151.5 mAh/g, and the capacity retention rate is 81.6% after 100 cycles at room temperature. The results indicate that interfacial modification with the nanosized LATP coating is an effective strategy for providing more possibilities for commercial application of ASSLBs.

Influence of Cation Vacancies on Li Conductivity of La1/2Li1/2-2x Sr x TiO3 Perovskites (0 < x ≤ 0.25): The Role of Nominal and Effective Vacancies.

The Li1/2-2x Sr x La1/2TiO3 series (0 ≤ x ≤ 0.25) is investigated with X-ray diffraction, nuclear magnetic resonance, and impedance spectroscopy techniques. The substitution of two Li+ by one Sr2+ in Li1/2La1/2TiO3 perovskite generates cation vacancies that, when ordered in alternating planes along the c-axis, confer a two-dimensional character to Li mobility. In previous works, it was shown that Li+ ions partially occupy the center of the six faces of the cubic perovskite, resulting in the associated A-sites to participate like a vacancy in the definition of the percolation vacancy threshold. The results obtained in the Li1/2-2x Sr x La1/2TiO3 series are compared with those obtained in the Li3x La2/3-x TiO3 series, and other Sr-doped solid solutions (Li1/2-x Sr2x La1/2-x TiO3 and Li x Sr x La2/3-x TiO3), to highlight the importance of the effective vacancies with respect to the nominal ones in conductivity. The analysis of four series, belonging to the ternary SrTiO3-La2/3TiO3-Li2TiO3 phase diagram, permits a better understanding of the ionic conduction mechanism in perovskites. The results show that the vacancy percolation model is more adequate to explain Li conductivity than the conventional hopping probability model. In the analyzed series, Li conductivity is maximum when a small amount of Sr is incorporated into the pseudo-cubic La1/2Li1/2TiO3 end member, while it decreases as the amount of strontium increases.

Effects of applied voltages on Lithium-6 enrichment by electrodialysis with lithium ionic conductor

Enrichment of Lithium-6 (6Li) is one of the necessary conditions to produce tritium as a fuel of fusion reactors by the neutron capture reactions. In previous studies, we have established the Li extraction technique using a fast ionic conductor Li0.29La0.57TiO3 (LLT) —Lithium Separation Method by Ionic Conductor (LiSMIC). LiSMIC can also be applied to the enrichment of 6Li, because 6Li has a lighter mass than 7Li and has a different extraction speed. In the LiSMIC, applied voltage gives a electrical driving force which may enhance the difference in the motions of 6Li and 7Li. In this work, we explore effects of applied voltage on the 6Li enrichment from a 3 mol/L LiOH solution when a LLT plate with 16 cm2 electrode area and 0.5 mm thickness was employed. We examined the Li extraction speed and 6Li enrichment when square and sine wave voltage profiles of maximally 5 V with 1 Hz frequency were applied, then compared them with the case of 5 V DC voltage. We found that the 1 Hz square wave voltage achieved the highest 6Li enrichment, ∼1.08, until 40% of Li was extracted from the source solution of 400 ml. Instead, the Li extraction speed for square wave was lower than the DC voltage case owing to the reduction of the application. In the DC voltage case, a high separation factor ∼1.06 was obtained at early stage of the electrodialysis but it gradually decreased. The sine wave case was in between. These results indicate that carefully choosing the applied voltage will accelerate the 6Li enrichment process.

Polymer electrolytes shielded by 2D Li0.46Mn0.77PS3 Li+-conductors for all-solid-state lithium-metal batteries

The development of solid polymer electrolytes (SPEs) is impeded by the severe Li-dendrites growth at the unstable SPE-Li interface. Herein, we demonstrate that the interfacial stability of poly(ethylene oxide) (PEO) electrolytes against Li metal is significantly improved by a shielding strategy, where the nanosheets of a 2D Li+ conductor Li0.46Mn0.77PS3 (LiMPS) serve as nanosized shields to armor PEO against the spears - lithium dendrites. Besides physical inhibition, LiMPS also homogenizes Li+ flux owing to its 2D nature, superior Li+ conductivity (2.1 × 10−4 S cm−1 at 30 ℃) and strong adsorption of Li+. This strategy also enables PEO-LiMPS electrolytes to exhibit superior ionic conductivity of 2.6 × 10−4 S cm−1 at 45 ℃, a nearly tenfold increase compared to bare PEO electrolytes. Furthermore, the electrochemical stability window (ESW) of PEO-LiMPS electrolytes is expanded to 4.8 V (3.8 V for pristine PEO). As a result, symmetric Li/PEO-LiMPS/Li cells deliver short circuit-free cycling over 600 h, and LiNi0.8Co0.1Mn0.1O2/PEO-LiMPS/Li batteries also present a high-capacity retention over 80% after 200 cycles at 0.2 C. In addition, LFP/PEO-LiMPS/Li pouch cell retains 93% of the initial capacity after cycling at 0.2 C for 230 cycles. This 2D Li+-conductive shielding strategy provides a unique protective mechanism for SPEs in solid-state Li metal batteries (SSLMBs).

Accelerating Li-ion diffusion in β-eucryptite by tuning Li–Li correlation

Solid-state Li-ion batteries are emerging as promising next-generation energy storage devices, but new solid-state Li-ion conductors or electrolytes, a critical component of such devices, are highly demanded to meet the conductivity and stability requirements. In this study, one of the cost-effective and stable silicate-based solid Li-ion conductors, β-eucryptite LiAlSiO4, was studied via ab initio molecular dynamics simulations. The Si/Al ratio from 0 to 7 corresponding to x in Li1+xAl1+xSi1-xO4 from 1 (Li-rich) to −0.75 (Li-poor) was adjusted to investigate its impact on Li-ion diffusion. The results show that the Li-ion diffusion barrier can be greatly decreased from 0.61 eV in β-eucryptite LiAlSiO4 (x = 0) to 0.20 eV in Li0.5Al0.5Si1.5O4 (x = −0.5; Si/Al = 3) and 0.24 eV in Li1.25Al1.25Si0.75O4 (x = 0.25; Si/Al = 0.6). The predicted Li-ion conductivity is 6.976 mS/cm in Li0.5Al0.5Si1.5O4 and 3.773 mS/cm in Li1.25Al1.25Si0.75O4 at 25 °C, both allowing room-temperature operation of solid-state batteries. The modulation of Li–Li correlation at these two distinctive Si/Al ratios results in significantly lower diffusion barrier and higher Li-ion conductivity than those of the parent composition. Our work facilitates the design of low-cost silicate-based Li-ion conductors with high Li conductivity.

Enhancement of ionic conductivity and fracture toughness by infiltrating porous Li0.33La0.56TiO3 pellets

Although solid-state lithium electrolytes have the potential to reduce the safety issues associated with organic liquid electrolytes, disadvantages such as low total conductivity, large interface impedance, and delamination of the interface due to cyclic stress still need to be addressed. The solid-state lithium-ion conductor Li0.33La0.56TiO3 (LLTO) was prepared via a hydrothermal route by using CTAB as templates in this paper. Perovskite LLTO with micro-porous channels was obtained and the total conductivity is comparable to the non-porous LLTO. Porous LLTO pellets are infiltrated with the non-porous LLTO precursor solution, and the total conductivities of the infiltrated porous LLTO are all higher than those without infiltration. After infiltration, the porous LLTO calcined at 600 °C achieves the highest total conductivity, 7.88 × 10−5 S/cm. The fracture toughness of the infiltrated LLTO is higher than that of the non-porous LLTO. The results demonstrate a new way to prepare solid-state lithium-ion conductors with high ionic conductivity and great tolerance to cyclic stress.

Improved electrochemical performance of high voltage spinel LiNi0.5Mn1.5O4 achieved by a dual electronic and ionic surface modification strategy

Spinel LiNi0.5Mn1.5O4 (LNMO) is considered as a promising cathode for lithium-ion batteries for its high operating voltage, energy density and low cost. However, it suffers from serious capacity fading due to the unstable surface structure. In this work, LNMO modified with ionic conductor Li1.4Al0.4Ti1.6(PO4)3 (LATP) and helical carbon nanotube (HCNT) was prepared. The effects of LATP and HCNT coating on the structure, morphology and electrochemical performance of LNMO were explored. It is found that the phase structure and morphology were little altered while the concentration of Mn3+ increased with LATP coating. The sample modified with both LATP and HCNT shows the best electrochemical performance. It kept the capacity of 109.2 mAh g−1 after 500 cycles at 2C with the capacity retention rate of 92.3%, much higher than those of pristine LNMO and the HCNT or LATP-only coated cathodes. The enhanced performance could be ascribed to the improved electronic and/or ionic conductivity of the interface between the cathode and electrolyte and the protective effect against the side reaction from the electrolyte.

Suppressing structural degradation of single crystal nickel-rich cathodes in PEO-based all-solid-state batteries: Mechanistic insight and performance

All-solid-state batteries (ASSBs) with poly(ethylene oxide) (PEO)-based electrolytes are believed to be pragmatic and economical. However, the oxidation of PEO-based electrolytes on high-voltage cathode hinders its application in high-energy-density ASSBs. Single crystal LiNixCoyMnzO2 (x + y + z = 1) (SCNCM) cathode is one of the most promising cathode due to its ability to relieve the formation of cracks to remain structural integrity. However, the poor compatibility between SCNCM cathode and PEO remains a challenge. Besides, the mechanism of single crystal Ni-rich cathode structure degradation induced by PEO is still unclear. In this work, the interaction mechanism between PEO-based electrolyte and SCNCM is firstly revealed: 1) the strong oxidizability of SCNCM at high voltage accelerates the oxidization of PEO, leading to the self-oxygen loss and the consequent formation of rock-salt phase of SCNCM; 2) free H+ formed in the oxidation/dehydration reaction of PEO reacts with TFSI− to form HTFSI, resulting in the dissolution of transition metal ions on the surface of SCNCM83 particles. Based on this, a Li+ conductor Li1.4Al0.4Ti1.6(PO4)3 (LATP) surface coating layer on single crystal LiNi0.83Co0.12Mn0.05O2 (SCNCM83) is introduced to stabilize the cathode/electrolyte interface and ensure lithium-ion transport simultaneously. The LATP coated SCNCM83 (LATP@SCNCM83) shows excellent cycling performance with retention of 90.5% after 100 cycles, while SCNCM83 shows inferior cycling performance with retention of 63.4% after 100 cycles. In brief, this work reveals the interaction mechanism at the cathode/electrolyte interface and provides an effective interfacial stabilization strategy by LATP coating to enable high-voltage operation with PEO-based electrolytes.

A high ionic conductive PDOL/LAGP composite solid electrolyte film for Interfacial Stable solid-state lithium batteries

High ionic conductivity for solid electrolyte and stable electrode/electrolyte interface have always been the main requirements for solid-state lithium batteries. Herein, a high ionic conductive composite solid electrolyte (CSE) film was prepared by combining 1.3-dioxolanes (DOL) capable of in-situ polymerization with high ionic conductive Li1.5Al0.5Ge1.5(PO4)3 (LAGP)ceramic fillers. The CSE film also shows high interface compatibility and stability with lithium metal. The optimized poly-DOL (PDOL)-30% LAGP CSE exhibits a desirable dense and uniform structure, which endows the CSE with a high ion conductivity of 4.63 × 10−4 S cm−1, a high ion migration number up to 0.73 and a wide electrochemical stability window of 5.1 V. The assembled high-voltage NCM622/PDOL-30%LAGP CSE/Li solid-state cell exhibits good rate and cycle performances with a capacity of 125 mAh/g at 2 C and a capacity retention of 76% at 0.5C after 400 cycles with an average Coulomb efficiency of 99.7%. The PDOL-30%LAGP CSE also possesses a high inhibition ability of lithium dendrites owing to the dense and uniform structure and the stable electrolyte/lithium electrode interface including Li–Ge, LiF and CF3 components. The Li/CSE/Li cell maintains a relatively stable voltage up to 650 h at a current density of 0.1 mA/cm2. This high ionic conductive composite solid electrolyte film shows a good application prospect in high-voltage solid-state lithium batteries.

High Throughput Studies of Li-La-Zr-O Garnet Solid Electrolytes

Development of next-generation Li-ion batteries has increasingly focused on all-solid batteries employing either ceramic, polymer, or glass electrolytes in order to address shortcomings in currently commercialized liquid electrolyte Li-ion batteries including safety, limited lifetime, and lower energy densities resulting from instability with respect to Li metal anodes.[1] Lithium lanthanum zirconium oxide (LLZO) is a leading candidate for solid Li-batteries due to its high Li-ion conductivity, stability in air and against Li metal, and compatibility with high-voltage cathodes.[2],[3] Despite significant progress being made, our understanding of LLZO is limited by the relatively small number of compositions which have been studied; especially considering the leading contender is a pseudo-quaternary oxide (Ga-doped LLZO) and many studies are now utilizing multiple dopants.[4] Herein, we have applied a high-throughput methodology for synthesizing, characterizing, and testing sets of 64 LLZO electrolytes at the mg-scale. We employ a citrate sol-gel synthesis method whereby reagent solutions are dispensed across a well-plate to give a composition gradient. After drying the samples and burning off the citrates, the resulting powders are pressed into pellets using a custom-made 64-pellet die and the pellets are sintered at the desired temperature. The high-throughput characterization techniques utilized include powder X-ray diffraction, electrochemical impedance spectrometry and electrochemical cycling in order to test electrolyte stability; with each method performed on up to 64 samples simultaneously.Using our methodology, we have studied over 700 samples to produce a full phase stability diagram for the Li-La-Zr-O pseudoternary system. We find that within the Li-La-Zr-O system, there is significant solubility of Li into the La2Zr2O7 pyrochlore structure commonly found as an impurity in LLZO synthesis due to lithium loss. We also find that LLZO appears as both tetragonal and cubic forms throughout the system, with the cubic LLZO appearing in an extremely restricted region that is difficult to access as pure phase due to lithium loss, while excess lithium leads to the tetragonal LLZO. Li conductivity measurements show that both cubic and tetragonal undoped LLZO have similar bulk conductivities, but there is only a limited region near the formal Li7La3Zr2O12 composition where grain boundary conductivity is high. Our methodology is also applied to a comprehensive doping study where over 40 different dopants are evaluated and promising dopants are tested in co-doped compositions. [1] D. Aurbach et al., Electrochimica Acta 2004, 50, 247-254. [2] Q. Liu, et al., J. Power Sources 2018, 389, 120-134. [3] T. Thompson, et al., ACS Energy Letters 2017, 2, 462-468. [4] F. Zheng, et al., J. Power Sources 2018, 389, 198-213.

Li-Ion Conductive Li1.3Al0.3Ti1.7(PO4)3 (LATP) Solid Electrolyte Prepared by Cold Sintering Process with Various Sintering Additives.

The density, microstructure, and ionic conductivity of solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 (LATP) ceramics prepared by cold sintering using liquid and solid sintering additives are studied. The effects of both liquid (water and water solutions of acetic acid and lithium hydroxide) and solid (lithium acetate) additives on densification are investigated. The properties of cold-sintered LATP are compared to those of conventionally sintered LATP. The materials cold-sintered at temperatures 140–280 °C and pressures 510–600 MPa show relative density in the range of 90–98% of LATP’s theoretical value, comparable or higher than the density of conventionally sintered ceramics. With the relative density of 94%, a total ionic conductivity of 1.26 × 10−5 S/cm (room temperature) is achieved by cold sintering at the temperature of 200 °C and uniaxial pressure of 510 MPa using water as additive. The lower ionic conductivities of the cold-sintered ceramics compared to those prepared by conventional sintering are attributed to the formation of amorphous secondary phases in the intergranular regions depending on the type of additives used and on the processing conditions selected.

Quasi-solid polymer electrolytes with fast interfacial transport for lithium metal batteries

The quasi-solid electrolyte based on Poly(vinylidene fluoride-co-hexafluoropropylene) has drawn great interest owing to good wettability and compatibility with lithium metal anode. However, the low ionic conductivity and lithium-ion transfer number limit the practical application of Poly(vinylidene fluoride-co-hexafluoropropylene). Herein, quasi-solid electrolyte is prepared by adding NASICON-type lithium-ion conductor Li1.3Al0.3Ti1.7(PO4)3 to Poly(vinylidene fluoride-co-hexafluoropropylene). The Li1.3Al0.3Ti1.7(PO4)3 not only reduces the crystallinity of the polymer, but also participates in the conduction process of Li+. Through the synergistic effect of Li1.3Al0.3Ti1.7(PO4)3 and Poly(vinylidene fluoride-co-hexafluoropropylene), the quasi-solid polymer electrolyte has a high ionic conductivity (3.64 × 10−3 S cm−1) at room temperature and large lithium-ion transfer number (0.64). The symmetric cell exhibits a small overpotential (18 mV) as well as a stable cycle (3000 h) at 0.2 mA cm−2 with areal capacity of 0.2 mAh cm−2. The full cell with LiFePO4 cathode keeps a discharge capacity of 143.4 mAh g−1 after 600 cycles with capacity retention of 94.7%, and also performs good electrochemical performance with high voltage cathode (LiNi0.85Mn0.1Co0.05O2). Furthermore, the pouch cell assembled by quasi-solid polymer electrolyte have good flexibility, which can be used normally after folding and shearing. Our work supplies a feasible solution for the design of quasi-solid lithium metal batteries.

Artificial Intelligence-Aided Mapping of the Structure-Composition-Conductivity Relationships of Glass-Ceramic Lithium Thiophosphate Electrolytes.

Lithium thiophosphates (LPSs) with the composition (Li2S)x(P2S5)1–x are among the most promising prospective electrolyte materials for solid-state batteries (SSBs), owing to their superionic conductivity at room temperature (>10–3 S cm–1), soft mechanical properties, and low grain boundary resistance. Several glass–ceramic (gc) LPSs with different compositions and good Li conductivity have been previously reported, but the relationship among composition, atomic structure, stability, and Li conductivity remains unclear due to the challenges in characterizing noncrystalline phases in experiments or simulations. Here, we mapped the LPS phase diagram by combining first-principles and artificial intelligence (AI) methods, integrating density functional theory, artificial neural network potentials, genetic-algorithm sampling, and ab initio molecular dynamics simulations. By means of an unsupervised structure-similarity analysis, the glassy/ceramic phases were correlated with the local structural motifs in the known LPS crystal structures, showing that the energetically most favorable Li environment varies with the composition. Based on the discovered trends in the LPS phase diagram, we propose a candidate solid-state electrolyte composition, (Li2S)x(P2S5)1–x (x ∼ 0.725), that exhibits high ionic conductivity (>10–2 S cm–1) in our simulations, thereby demonstrating a general design strategy for amorphous or glassy/ceramic solid electrolytes with enhanced conductivity and stability.

Optimized Ni-rich LiNi0.83Co0.06Mn0.06Al0.05O2 cathode material with a Li1.3Al0.3Ti1.7(PO4)3 fast ion conductor coating for Lithium-ion batteries

The high nickel cathode LiNi0.83Co0.06Mn0.06Al0.05O2 (combination of NCM and NCA) coated with the Li+ conductor Li1.3Al0.3Ti1.7(PO4)3 in various mass fractions was prepared via using the typical sol-gel process. The LiNi0.83Co0.06Mn0.06Al0.05O2 after the Li1.3Al0.3Ti1.7(PO4)3 covering demonstrated the similar crystal structure and particle morphology in comparison with the bare cathode. The electrochemical test results indicated the superior rate capabilities and cycling performances were acquired for the coated cathodes due to the presence of the Li1.3Al0.3Ti1.7(PO4)3 film on the surface of LiNi0.83Co0.06Mn0.06Al0.05O2. The 2 wt% Li1.3Al0.3Ti1.7(PO4)3 covered LiNi0.83Co0.06Mn0.06Al0.05O2 exhibited the greatest electrochemical performance with a large cycle retention rate of 90.9% over 300 cycles at 45 °C, rate capacity of 139.8 mAh g−1 at 5 C current density, and a high capability of 126.5 mAh g−1 at − 30 °C, superior than those (80.9%, 99.8 mAh g−1, 71.3mAh g−1 accordingly) of the bare cathode. In addition, the safety and environmental reliability tests of pouch batteries suggested the Li1.3Al0.3Ti1.7(PO4)3 film on the surface of cathode acted as a protective layer to promote the stability for application.

In situ generated polymer electrolyte coating-based Janus interfaces for long-life LAGP-based NMC811/Li metal batteries

NASCION-type Li+ conductor Li1.5Al0.5Ge1.5P3O12 (LAGP) has been well considered as a promising solid-state electrolyte for solid-state lithium mental batteries (SSLMBs) by virtue of several strengths (e.g., high ionic conductivities, good stability under ambient conditions, and wide electrochemical stability windows). However, there are rare reports concerning the utilization of LAGP-based solid electrolytes in the high-voltage LiNi0.8Mn0.1Co0.1O2 (NMC811)/Li metal cell. This can be ascribed to the fact that the mechanochemically stable interface toward Li metal anodes and compatible interface close to NMC811 cathodes cannot be simultaneously achieved. To address this, herein, a LAGP-type solid electrolyte with in situ generated polymer electrolyte coating-based Janus interfaces is developed. The as-developed solid electrolyte is prepared by coating LAGP with in situ crosslinked polymethyl methacrylate and poly(cyclic carbonate urethane methacrylate)-based polymer electrolytes toward lithium anode and NMC811 cathode, respectively. It is demonstrated that the as-developed solid electrolyte can achieve both compatible electrode–electrolyte interphases. As a result, this solid electrolyte endows 4.3 V and 4.5 V-class NMC811/Li batteries with superior cycling stability. Our work provides a good paradigm to address the interfacial issues confronting solid state electrolyte chemistries.

Synthesis of Superionic Conductive Li1+x+yAlxSiyTi2-xP3-yO12 Solid Electrolytes.

Commercial lithium-ion batteries using liquid electrolytes are still a safety hazard due to their poor chemical stability and other severe problems, such as electrolyte leakage and low thermal stability. To mitigate these critical issues, solid electrolytes are introduced. However, solid electrolytes have low ionic conductivity and inferior power density. This study reports the optimization of the synthesis of sodium superionic conductor-type Li1.5Al0.3Si0.2Ti1.7P2.8O12 (LASTP) solid electrolyte. The as-prepared powder was calcined at 650 °C, 700 °C, 750 °C, and 800 °C to optimize the synthesis conditions and yield high-quality LASTP powders. Later, LASTP was sintered at 950 °C, 1000 °C, 1050 °C, and 1100 °C to study the dependence of the relative density and ionic conductivity on the sintering temperature. Morphological changes were analyzed using field-emission scanning electron microscopy (FE-SEM), and structural changes were characterized using X-ray diffraction (XRD). Further, the ionic conductivity was measured using electrochemical impedance spectroscopy (EIS). Sintering at 1050 °C resulted in a high relative density and the highest ionic conductivity (9.455 × 10−4 S cm−1). These findings corroborate with the activation energies that are calculated using the Arrhenius plot. Therefore, the as-synthesized superionic LASTP solid electrolytes can be used to design high-performance and safe all-solid-state batteries.

Effect of Nb5+ doping on the microstructure and conductivity of Li1.125Ta0.875Zr0.125SiO5 electrolyte

The microstructure and electrochemical properties of Li1.125Ta0.875-xNbxZr0.125SiO5 (x = 0, 0.0625, 0.1875, 0.25, 0.5) ceramics prepared via the solid-phase reaction method were studied. The results reveal that the conductivity of the ceramic specimens at 25 °C increases and then decreases as the Nb increases from 0 to 0.5 mol. 0.1875 mol of Nb doping facilitates the fusion and connection between grains, reduces the number of grain boundaries, leads to densification of the ceramics, decreases the total resistance, and thus increases the conductivity. Moreover, the small structural distortion caused of the discrepancy in ionic radii of Ta5+ and Nb5+ creates more space to accommodate Li ions and promotes the diffusion of Li+, reducing the energy potential barrier for ion transport. The best performing Li1.125Ta0.6875Nb0.1875Zr0.125SiO5 has a conductivity of 3.521 × 10-5 S/cm at 25 °C, with an order of magnitude greater than that of the original sample Li1.125Ta0.875Zr0.125SiO5, reaching 2.288 × 10-4 S/cm at 150 °C and has a minimum activation energy: 0.225 eV. The prepared Li1.125Ta0.6875Nb0.1875Zr0.125SiO5 ceramic is a new type of fast Li-ion conductor with potential for application in all-solid-state batteries.

From symmetry breaking in the bulk to phase transitions at the surface: a quantum-mechanical exploration of Li6PS5Cl argyrodite superionic conductor.

Lithium superionic conductor electrolytes may enable the safe use of metallic lithium anodes in all-solid-state batteries. The key to a successful application is a high Li conductivity in the electrolyte material, to be achieved through the maintenance of intimate contact with the electrodes and the knowledge of the chemical nature of that contact. In this manuscript, we tackle this issue by a theoretical ab initio approach. Focusing on the Li6PS5Cl, a thiophosphate with high ionic conductivity, we carry on thorough modeling of the surfaces together with the prediction of the thermal and elastic behaviour. Our investigation leads to some new findings: the bulk structure, as reported in the literature, appears to be metastable, with spontaneous symmetry breaking. Moreover, the relevant stoichiometric surfaces identified for stable and metastable crystal structures are not up-down symmetry related and they expose from one side Li2S and LiCl. Surface reconstructions can be interpreted as local phase transitions. We also predict entirely ab initio the morphology of crystallites, charge, and electrostatic potential at surfaces, together with the effect of temperature on structural properties and the elastic behaviour of this material. Such findings may constitute the relevant groundwork for a better understanding of ionic transport in Li-ion conductors at the electrolyte/anode and electrolyte/cathode interfaces.

Tuning Site Energy by XO6 Units in LiX2(PO4)3 Enables High Li Ion Conductivity and Improved Stability.

Solid-state electrolytes (SSEs) with high ion conductivity are necessary for all-solid-sate lithium ion batteries. Here, a less studied NASICON-type LiZr2(PO4)3 (LZP) is screened out from seven LXP compounds (LiX2(PO4)3, X = Si, Ge, Sn, Ti, Zr, Hf, and Mo), which combines the electrochemical stability with high Li conductivity. The bond valence site energy (BVSE), climbing image nudged elastic band (Cl-NEB) method, and electrochemical phase diagram prove LZP has a lower Li migration barrier and the largest electrochemical stability window. The underlying reason for high Li conductivity is analyzed from the structural features to the electronic structures. Furthermore, the XO6 unit mixed frameworks Li1.667Ca0.333Zr1.667(PO4)3 (LCZP) and Li1.667Mg0.333Zr1.667(PO4)3 (LMZP) exhibit high Li ion conductivity associated with a very low Li migration barrier (∼0.20 eV). This work opens a new avenue of broad compositional spaces in LXP for SSEs.

First principles calculation of Li2+2xZn1-xSiO4 (x = 0.125–0.5) as solid electrolyte for lithium-ion battery

Li2ZnSiO4 has the structural characteristics of superionic conductor for Li, but the actual measured Li conductivity is not high. Based on first-principles calculations, the Li diffusion properties of varied configurations are studied, in which Li replaces Zn with different concentrations. Particularly, topological analysis is used to obtain the possible Li interstitial sites of Li2ZnSiO4. These interstitial sites can accommodate more lithium ions and increase the concentration of lithium ions. The Li ion conductivity of the Li-doped Li2+2xZn1-xSiO4 with increased lattice Li and interstitial Li is improved dramatically. When x = 0.375, the Li ion conductivity reaches 2.006 mS/cm and the Ehull is 23 meV/atom. The mean square deviation (MSD) and probability density indicate that Li2+2xZn1-xSiO4 (x = 0.125–0.5) is a three-dimensional Li conductor. In addition, the calculation of energy band structures shows the bandgap width of 5.7 eV and 5.8 eV for Li2ZnSiO4 and Li2.5Zn0.75Si4, respectively, indicating that these materials are poor conductors of electron. These characteristics (fast Li diffusion, good phase stability, and poor electronic conductivity) make Li-doped Li2ZnSiO4 one promising solid electrolyte for solid-state Li-ion batteries.