High Lithium Ion Conductivity Research Articles

Amorphous Boron Nitride Nanosheet‐Based Solid State Electrolytes with High Ionic Conductivity

AbstractAmorphous boron nitride nanosheets, with natural electrical insulation, outstanding chemical stability and mechanical properties, are introduced as a matrix to be incorporated with lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) and polymer polyvinylidene fluoride‐hexafluoropropylene copolymer (PVDF‐HFP), for constructing a novel composite solid‐state electrolyte by a simple solution‐casting method. Amorphous boron nitride nanosheets are produced via a combination method of ball milling and pure water exfoliation. The obtained composite solid‐state electrolyte containing 40 % (mass fraction) PVDF‐HFP shows a high lithium ion conductivity (1.936×10−3 S cm−1) and lithium ion transference number (0.47), and a wide electrochemical stability window (5 V) at room temperature. The LiFePO4/Li based all solid‐state battery, consisting of the composite solid electrolyte (40 % PVDF‐HFP), delivers a capacity of 128.1 mAh g−1, a Coulombic efficiency of 99.79 % after 500 cycles and a capacity retention rate of 94.5 % at 1.0 C and 25 °C. The composite solid electrolyte (40 % PVDF‐HFP) can maintain flat and stable stripping/plating plateaus for over 800 hours in symmetrical cells. The amorphous boron nitride nanosheets with high lithium ion conductivity are employed to construct solid‐state electrolytes, which is important significant for the development of high energy density, high safety, and long cycle life all‐solid‐state lithium‐ion batteries.

Lithium-Ion Conductive Coatings for Nickel-Rich Cathodes for Lithium-Ion Batteries.

Nickel (Ni)-rich cathodes are among the most promising cathode materials of lithium batteries, ascribed to their high-power density, cost-effectiveness, and eco-friendliness, having extensive applications from portable electronics to electric vehicles and national grids. They can boost the wide implementation of renewable energies and thereby contribute to carbon neutrality and achieving sustainable prosperity in the modern society. Nevertheless, these cathodes suffer from significant technical challenges, leading to poor cycling performance and safety risks. The underlying mechanisms are residual lithium compounds, uncontrolled lithium/nickel cation mixing, severe interface reactions, irreversible phase transition, anisotropic internal stress, and microcracking. Notably, they have become more serious with increasing Ni content and have been impeding the widespread commercial applications of Ni-rich cathodes. Various strategies have been developed to tackle these issues, such as elemental doping, adding electrolyte additives, and surface coating. Surface coating has been a facile and effective route and has been investigated widely among them. Of numerous surface coating materials, have recently emerged as highly attractive options due to their high lithium-ion conductivity. In this review, a thorough and comprehensive review of lithium-ion conductive coatings (LCCs) are made, aimed at probing their underlying mechanisms for improved cell performance and stimulating new research efforts.

Structural and electrical properties of mol% (100 − x)Li2SO4:xP2O5 solid electrolyte system (0 ≤ x ≤ 20)

Abstract Extensive research has been focused on solid electrolytes exhibiting high lithium ion conductivity, with the goal of advancing their use in solid-state lithium-ion batteries. This study investigates the influence of a glass former, P2O5, on the structure and ionic conductivity of the solid electrolyte Li2SO4. Quenching of Li2SO4 in the presence of P2O5 resulted in a glass–crystal composite with significant amorphous content. The XRD analysis of the 20 mol% glass ceramics detects the presence of Li4P2O7 without altering the original crystal structure. Notably, a conductivity value of 1.11 × 10−4 S cm−1 at 563 K was observed for 20 mol%, which is around two orders higher than that of polycrystalline Li2SO4. The introduction of a small amount of glass former P2O5 appears to loosen the structure of Li2SO4 creating an easier path for Li+ ion migration in the combined SO4–PO4 network structure.

Advanced Composite Solid Electrolyte Architecture Constructed with Amino‐Modified Cellulose and Carbon Nitride via Biosynthetic Avenue

AbstractPolyethylene oxide (PEO) solid electrolytes are regarded as a promising candidate for all‐solid‐state lithium batteries owing to their high safety and interfacial compatibility. However, PEO electrolyte is plagued by relatively weak structural strength and unsatisfactory Li+ conductivity. Herein, a mechanically strong and Li+ conductively favorable cellulosic scaffold of PEO is fabricated through amino (‐NH2) modification and g‐C3N4 (CN) incorporation of bacterial cellulose (BC) under a microbial circumstance. The biologically ‐NH2 modified BC (B‐NBC) is entangled with CN nanosheets (CN@B‐NBC) through an in situ secretion of nanocellulose followed by hydrogen bond‐induced self‐assembly. The ‐NH2 groups from B‐NBC weaken the complexation of Li+ with its counterpart, thus facilitating the release of more free Li+. CN with strong C‐N covalence and extra lone electrons of N further strengthens the BC skeleton and meanwhile offers sufficient anchors for Li+ migration. After infiltrating by LiTFSI/PEO (LP), the LP/CN@B‐NBC composite solid electrolyte (CSE) exhibits high lithium transference number and ionic conductivity. Upon coupling with LiFePO4 cathode, the full battery exhibits a remarkably high specific capacity, superior rate capability, and decent cycling stability. This work pioneers the attempts of chemical decoration and ingredient incorporation of BC architecture in CSE with the aid of a bottom‐up biosynthetic avenue.

Synthesis, Crystal structure, electronic structure, and Raman spectra of Li4Sr2SiP4

AbstractRecently, ternary lithium phosphides have been studied intensively owing to their high lithium ion conductivities. During investigations aiming for derivatives with less lithium content the new compound Li4Sr2SiP4 was obtained. It crystallizes in the monoclinic space group P21/m (N°11) with lattice parameters of a=7.2919(8) Å, b=8.3679(6) Å, c=6.9965(8) Å, and β=90.061(9)°. The crystal structure contains isolated [SiP4]8− tetrahedra that are charge balanced by two Sr2+ and four Li+ counter ions. The structure can be derived as a superstructure of the layered CaAl2Si2 structure type comprising a hexagonal closest packing of P atoms and tetrahedral voids filled with Si and Li atoms, whereas octahedral voids are filled with Sr and Li atoms. DFT calculations confirm the structure with ordered atom positions as a global minimum and predict an indirect band gap of 2.23 eV. In addition, the experimental Raman spectrum is in good agreement with the calculated one.

Garnet-type lithium sensors for the monitoring and control of Pb-Li alloys in tritium breeding modules

During the EU-DEMO conceptualization, eutectic Pb-Li was considered as the prime candidate liquid breeding material. Nonetheless, the conversion of lithium into tritium through the breeding reaction will result in a decrease in the lithium concentration within the alloy. Then, the monitoring of the lithium concentration in Pb-Li alloys is critical for the optimal Tritium Breeding Blanket (TBB) performance, as lithium affects dissolution of structural materials, tritium inventory and extraction rates. Garnet-like ceramics possess desirable properties for their use in lithium sensors, like high lithium-ion conductivity, good chemical stability, low thermal expansion coefficient, and great mechanical strength. For these reasons, electrochemical sensors based on garnet-type ceramics offer advantages for measuring lithium in molten Pb-Li alloys, such as high selectivity and fast response. This work presents the development of lithium sensors based on the garnet-type ceramic Li6BaLa2Ta2O12. The material was characterized by XRD and SEM, exhibiting good crystallinity and a homogeneous microstructure. The sensors were evaluated in a potentiometric configuration in molten Pb-Li alloys with lithium concentrations ranging from 3 to 35 at% Li. Potentiometric measurements were used to obtain correlations that allow the determination of the lithium activity in the lead–lithium alloys studied.

Zwitterion grafted polyimide separator for improving lithium-ion transport and its application in LiCoO2 batteries

To improve the lithium-ion transport ability and cycle life of lithium-ion batteries, a high-performance polyimide-based lithium-ion battery separator (PI-SO3) was prepared by chemically grafting zwitterion onto the surface of heat-resistant polyimide nanofiber matrix with the assistance of amino-rich polyethyleneimine (PEI). The PI-SO3 not only maintains good dimensional stability (over 200 °C) and flame retardancy, but also ensures the safety of the battery under extreme conditions. Electrochemical experimental results show that PI-SO3 has high ion conductivity (1.99 mS·cm−1), Li+ transference number (0.632), and excellent oxidation potential (5.28 V), which are all higher than those of pure PI separator (1.14 mS·cm−1, 0.444, and 4.56 V, respectively). Meanwhile, LiCoO2/PI-SO3/Li batteries exhibit excellent high-rate performance (139.5 mAh·g−1 at 5C current) and long-term cycle stability (138.9 mAh·g−1 after 100 cycles at 1C current, and 127.9 mAh·g−1 after 100 cycles at 2C current). In addition, the symmetrical battery, Li/PI-SO3/Li, shows stable more than 360 cycles. Compared with batteries using commercial separators, such as Celgard 2325 and pure polyimide matrix, the assembled coin cells with PI-SO3 separators have higher lithium-ion conductivity, Li+ transference number, and diffusion coefficient after grafting zwitterion, showing better rate ability and capacity retention. In this paper, the modification strategy of thermal-resistant separator by grafting zwitterions provides an efficient way to prepare next generation high-performance lithium-ion batteries with good safety.

In Situ/Operando Techniques for Unraveling Mechanisms of Ionic Transport in Solid-State Lithium Indium Halide Electrolyte

Over the past years, lithium-ion solid-state batteries have demonstrated significant advancements regarding such properties as safety, long-term endurance, and energy density. Solid-state electrolytes based on lithium halides offer new opportunities due to their unique features such as a broad electrochemical stability window, high lithium-ion conductivity, and elasticity at close to melting point temperatures that could enhance lithium-ion transport at interfaces. A comparative study of lithium indium halide (Li3InCl6) electrolytes synthesized through a mechano-thermal method with varying optimization parameters revealed a significant effect of temperature and pressure on lithium-ion transport. An analysis of Electrochemical Impedance Spectroscopy (EIS) data within the temperature range of 25–100 °C revealed that the optimized Li3InCl6 electrolyte reveals high ionic conductivity, reaching 1.0 mS cm−1 at room temperature. Herein, we present the utilization of in situ/operando X-ray Photoelectron Spectroscopy (XPS) and in situ X-ray powder diffraction (XRD) to investigate the temperature-dependent behavior of the Li3InCl6 electrolyte. Confirmed by these methods, significant changes in the Li3InCl6 ionic conductivity at 70 °C were observed due to phase transformation. The observed behavior provides critical information for practical applications of the Li3InCl6 solid-state electrolyte in a broad temperature range, contributing to the enhancement of lithium-ion solid-state batteries through their improved morphology, chemical interactions, and structural integrity.

Improvement of Ionic Conductivity in Li7La3Zr2O12 (LLZO) Solid Electrolyte By Doping with Aluminum/Tungsten

Recently, there has been increasing interest in solid electrolytes, which are the most important materials in all-solid-state lithium-ion batteries. Among all solid electrolytes, garnet-type Li7La3Zr2O12 (LLZO) has been proven to be one of the most promising electrolytes due to its high Li+ conductivity, wide potential window, and electrochemical stability towards metallic lithium anode. In particular, cubic garnet-type LLZO solid electrolytes have received a lot of attention for the development of high-performance all-solid-state batteries with safety, energy density, and long cycle life. In this study, we synthesized LLZO solid electrolyte powders with garnet structure and determined the optimal composition and sintering temperature by adding Al/W to form a stable cubic phase.In this study, Al or W-doped LLZO were prepared by a post-doping method. In this process, LLZO powder was first prepared, and then mixed with Al2O3 or WO3 powders to produce doped LLZO ceramic electrolytes, respectively. During this process, the doped ions entered the LLZO lattice, increasing the lithium ion transport channels and promoting lithium ion conductivity. The sintering time, crucible, and sintering temperature were adjusted to investigate the optimal process conditions of the post-doping method. As a result, the doped solid electrolyte exhibited high lithium ion conductivity and low activation energy. Using the high lithium ion conductivity and broad electrochemical stability window of the Al or W doped LLZO SSE, the (NCM622)/(Al or W doped-LLZO) cell delivered a steady cycle for 100 cycles at 0.1C. The Al or W doped-LLZO prepared in this study showed advantages of high conductivity, simple preparation process, high reproducibility, and low cost, which provides technical support and reference for further application of garnet-type SSEs in solid-state batteries with high energy density.

Solid Electrolyte Coated NCM523 for Composite Cathode in All-Solid-State Batteries

All-solid-state battery using sulfide solid electrolyte has advantages such as high lithium ionic conductivity and wide electrochemical stability window. Although it is attracting great attention in that it is capable of high power and high energy density, there are problems to be improved.Organic liquid electrolytes in conventional lithium ion batteries have excellent wettability and can form uniform lithium ion transfer channels in electrodes. However, in the case of all-solid-state battery, the formation of a solid-solid interface is limited due to the solid characteristics. In addition, the degradation of the interfacial contact between the active material and solid electrolyte in the composite electrode due to the volume change of the active material with (de)-intercalation of lithium ion during cycling causes loss of the lithium ionic pathway and deterioration of cell performance. This study focuses on improving battery performance by coating the surface of active material with solid electrolyte to maintain an even lithium ion transfer path in the composite electrode. The solid electrolyte coating of the active material has a decisive effect on the electrochemical behavior of the cell because it affects the formation of smooth lithium ionic pathway and suppression of voids in the composite electrode. Therefore, the focus of this study is to confirm the formation of uniform solid electrolyte coating layer according to the size of the solid electrolyte.Therefore, the particle size of the solid electrolyte was diversified using a liquid-phase process and a dispersant, and the solid electrolyte coating was performed using a dispersion process. It was confirmed that an even solid electrolyte coating layer was formed as the particles size of the solid electrolyte decreased, and the electrochemical performance was improved due to the solid electrolyte coating layer. In addition, it was confirmed that the lithium ionic pathway was maintained even after long cycling with the solid electrolyte coating layer, and also the side reactions occurred less according to the homogeneous electrochemical reaction.

Firefighting Gel Polymer Electrolyte for Non-Flammable Li-Ion Batteries Based on Extremely Low Amount of a Cross-Linkable Polymer

Safety issues of lithium-ion batteries(LIBs) have caught a priority of concerns as the electric vehicle(EV) market expands dramatically and requires higher energy densities. To be free from a variety of unpredictable situations and environments triggering such a safety issue, materials that provide a mechanism to control the factors causing fire and explosion are required to be involved in LIB cells.In this work, we present a gel polymer electrolyte(GPE) characterized by nonflammability and fire-extinguishing capability by radical scavenging(Rs). This GPE was realized within battery cells by in situ crosslinking a small amount of a cross-linkable fluoro-functionalized cyanoethyl polyvinyl alcohol(F7) in conventional carbonate electrolytes having LiPF6. The cyanoethyl functional groups(-CN) is responsible for gelation by cross-linking while the fluorine-containing moiety terminated radical chain reactions triggering thermal runaway by Rs. The strong interaction between the polymer and solvent molecules restricted solvent volatility. The tiny solid content at 2 wt. % in GPE guaranteed a liquid-level ionic conductivity at 9 mS/cm, disallowing battery performances to be sacrificed. Formation of the LiF-dominant solid-electrolyte-interphase(SEI) layer on anodes was encouraged by the fluoro-moiety of F7.In previous research of our group, PVA-CN was used as cross-linkable polymer for enhancement of mechanical property with additional metal-chelating functional group. Hydroxy group of PVA-CN is useful to modify the functional group by DCC coupling mechanism. Herein, as same as previous modification, the Heptafluorobutyric acid(HFB) was used for non-flammability and battery performance. F7 was expected to not only increase thermal stability but also scavenge the radicals. In addition, LiF-rich SEI layers would be made by fluorine groups.First, GPE increase its thermal stability by strong interaction between cross-linked polymer matrix and organic solvents. The binding energy of ethylene carbonate (EC) and hydrogen of cyanoethyl side chain was 0.4 eV which is stronger compared with general hydrogen bond(0.2 eV). Therefore, the flammable gas generation was suppressed by strong interaction between solvents and polymer matrix.In addition, the flash point demonstrated the strong interaction in GPE. The flash point of GPE which contained different polymer contents was decreased as the ratio of polymer content was increased. The composition of the atmosphere in the devices changed into more flammable because of the higher ratio of EMC gas in the atmosphere within enough time to equilibrate. In other words, EC forms a greater number of strong interactions with the polymer matrix while the polymer contents increased. The SET test of 2 wt.% PVA-CN-based GPE(G2)(3.36 s/g) and 5 wt.% PVA-CN-based GPE(G5)(0 s/g) proved that higher contents of PVA-CN in GPE ensure the non-flammability.Second, to overcome the poor electrochemical ability of G5, Rs functionalized F7 was used instead of PVA-CN. Unlike G2, only with 2 wt. % of F7 guaranteed the 0 s/g of SET. Non-flammability of 2 wt.% F7-based GPE(FG2) is due to the fluorine moiety scavenge the O• or H•. In the nail penetration test, only the FG2 was not exploded and maintained charged voltage while the nail penetrates the whole pouch cell vertically because of its elasticity.The Rs capability was demonstrated by cyclic voltammetry(CV) with 2,2’-azobisisobutyronitrile(AIBN) and alpha-tocopherol(α-TOH). After α-TOH react with AIBN radicals at the 70 ℃, the oxidation current decreased because of consumption of α-TOH. The Rs capability was calculated by ratio of current retention of α-TOH oxidation current with a same amount of among scavenger additives. The Rs capability of F7 was 214%.Lastly, our findings suggest sufficient non-flammability without battery performances degradation. The capacity retention of FG2 was higher than LE at the 300th Cycles. This is because the fluorine moiety contributed to make LiF-rich SEI layers. The rigid SEI layers and GPE suppressed volume expansion of graphite. Also, the capacity fade was not observed in FG2 with higher current density. The reason for great rate capability is higher lithium-ion conductivity which is a multiplication of ionic conductivity and lithium-ion transference number(tLi+). FG2has 4.82 of lithium-ion conductivity, while 3.63 in LE. Therefore, the mass transfer resistance was not large on the electrode surface due to the higher lithium-ion mobility in FG2.In this work, the non-flammability and battery performance were successfully demonstrated by thermal stability and Rs capability without any battery performances degradation. The thermal stability was enhanced by strong intermolecular forces between polymer chain and polar organic solvents. The radical chain reaction was terminated by fluorine moiety of GPEs matrix. The capacity retention of FG2 was outstanding compared with LE. Therefore, due to the FG2, the battery will be able to ensure non-flammability without degradation of performance. Figure 1

Investigation of in-situ lithium dendrite growth in the garnet type electrolyte Li7-xLa3Zr2-xTaxO12 (LLZTO) under an applied DC voltage

A translucent Al-containing garnet type electrolyte (Al-LLZTO) with high lithium-ion conductivity was made by pressure filtration followed by sintering to study in-situ lithium dendrite growth. A transparent tube furnace was built for in-situ dendrite growth studies above room temperature. In-situ lithium dendrite growth in a garnet-type electrolyte under an applied DC voltage was investigated at three different temperatures (room temperature, 100 °C, and 200 °C (above the melting point of lithium)). Critical current density (CCD) was estimated based on a previous model developed for sodium dendrites (which are actually filaments) in Na-β”-alumina. The CCD defined here is different than most of the reported work in lithium and lithium-ion batteries. When the temperature is higher than room temperature but lower than the melting point of lithium, lithium dendrites grow rapidly. However, when the temperature is above the melting point of lithium, no lithium dendrites were observed under similar testing conditions. This is because the CCD for liquid lithium dendrites to form is much higher than that for solid lithium dendrites to form. Approximate estimates of the CCD below and above the melting point of lithium are also given. This investigation provides significant insights into dendrite (filament) growth above room temperature, and possible prevention of lithium dendrites in working solid-state lithium-ion batteries, and the efficiency improvement of solid-state batteries.

Effect of glass crystallization parameters on conductivity of Li1.5+xAl0.5Ge1.5SixP3–xO12 glass-ceramics

Glass-ceramic samples of the Li1.5+ x Al0.5Ge1.5Si x P3- x O12 system ( x = 0-0.1) were obtained by directional crystallization of glasses. The glass transition, onset and peak temperatures of crystallization were determined using differential scanning calorimetry. The phase composition of glass-ceramics was determined by X-ray phase analysis. Electrical conductivity is studied using electrochemical impedance. Based on the data obtained, the homogeneity region of solid solutions was established and the optimal conditions for producing SiO2-doped glass-ceramics were identified. The composition with x = 0.02, crystallized at 750°C with a heating rate of 3 deg/min for 2 h, had the highest lithium-ion conductivity at room temperature (4.55×10-4 S/cm).

High‐Performance, Flame‐Retardant, Binder‐Free Li‐Hectorite‐Polybenzimidazole Fiber Separator for Li‐Ion Batteries

AbstractLi‐Hectorite (Li‐Hec) clays have inherent 2D diffusion slits offering high lithium (Li+) ion conductivity. Such Li‐Hec clays spontaneously delaminate into flexible nanosheets, allowing them to be coated on high‐temperature stable polybenzimidazole (PBI) nanofibers laid randomly onto each other in the form of non‐woven membranes. Here such Li‐Hec coated PBI nonwovens are shown to be excellent Li‐ion battery separators. An effective strategy based on electrospinning PBI followed by a filtration‐through coating of delaminated Li‐Hec nanosheets of appropriate diameter is applied to prepare the separators without the use of any binder. The composite separator shows excellent properties, such as superior wettability (solvent uptake 413%), thermostability (>500 °C), superior flame resistance, and interfacial compatibility. Additionally, the presented separator shows excellent ion conductivity, Li‐ion transference number, cycling stability, and a rate performance that outperforms the common commercial separators. In summary, this work allows for a better balance between safety, high performance, and separator functionality.

Dual-type gel polymer electrolyte for high-voltage lithium metal batteries with excellent cycle life

The most attractive approach for maximizing the energy density of rechargeable lithium batteries is to combine a lithium metal anode with a high-voltage cathode. However, the dendritic formation of lithium at the anode and the highly oxidizing conditions that cause electrolyte decomposition at the cathode have hindered the practical development of lithium metal batteries (LMBs). In this study, we report a dual-type gel polymer electrolyte (GPE) composed of an anolyte and a catholyte that can address the drawbacks of both the anode and cathode sides. The anolyte is a poly(ethylene oxide)-based composite solid polymer electrolyte that is chemically stable with lithium metal and has a high mechanical strength for suppressing lithium dendrite growth. A cross-linked gel polymer electrolyte with high lithium-ion conductivity and oxidative stability was used as the catholyte. The Li/LiCoO2 cell assembled with a dual-type GPE exhibited a high discharge capacity of 181.1 mAh g−1 (areal capacity: 3.15 mAh cm−2) in the voltage range of 3.0–4.5 V and excellent cycle life, with a capacity retention of 74 % after 700 cycles at 25 °C and 0.5 C rate. Our study proposes a promising electrolyte system for LMBs with high energy density and good cycle life.

Atom substitution of the solid-state electrolyte Li10GeP2S12 for stabilized all-solid-state lithium metal batteries

Solid-state electrolyte Li10GeP2S12 (LGPS) has a high lithium ion conductivity of 12 mS cm−1 at room temperature, but its inferior chemical stability against lithium metal anode impedes its practical application. Among all solutions, Ge atom substitution of the solid-state electrolyte LGPS stands out as the most promising solution to this interface problem. A systematic screening framework for Ge atom substitution including ionic conductivity, thermodynamic stability, electronic and mechanical properties is utilized to solve it. For fast screening, an enhanced model DopNetFC using chemical formulas for the dataset is adopted to predict ionic conductivity. Finally, Li10SrP2S12 (LSrPS) is screened out, which has high lithium ion conductivity (12.58 mS cm−1). In addition, an enhanced migration of lithium ion across the LSrPS/Li interface is found. Meanwhile, compared to the LGPS/Li interface, LSrPS/Li interface exhibits a larger Schottky barrier (0.134 eV), smaller electron transfer region (3.103 Å), and enhanced ability to block additional electrons, all of which contribute to the stabilized interface. The applied theoretical atom substitution screening framework with the aid of machine learning can be extended to rapid determination of modified specific material schemes.

MoS2/WS2 quantum dots co-doped two-dimensional carbon nanosheets with high lithium ion conductivity

MoS2/WS2 quantum dots co-doped two-dimensional carbon nanosheets with high lithium ion conductivity

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

Lithium lanthanum zirconium oxide (LLZO) is a leading candidate for solid Li-batteries due to its high lithium-ion conductivity, stability in air and against Li metal, and compatibility with high-voltage cathodes.1,2 Despite significant research being done, our understanding of LLZO is limited by the relatively small number of compositions which have been studied; both in the larger Li-La-Zr-O system and in the doped cubic LLZO system, which can accommodate an extremely wide range of dopants.3To study this large number of compositions, 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 and calcining the gels, the resulting powders are pelleted and then sintered at the desired temperature. High-throughput characterization techniques utilized include powder X-ray diffraction, impedance spectroscopy, DC polarization, and electrochemical stability window testing.Using our methodology, we have recently studied over 700 samples to produce a full phase stability diagram for the Li-La-Zr-O pseudoternary system.4 We found there is significant solubility of Li in the La2Zr2O7 pyrochlore structure, and that both cubic and tetragonal undoped LLZO appearing throughout the system have similarly poor bulk conductivities. This previous study again emphasizes the key role dopants play in LLZO. Herein, our methodology is applied to a comprehensive doping study where 60 different dopants are evaluated under identical synthesis conditions to allow for a thorough understanding of dopant effects on structure, ionic conductivity, electronic conductivity, and electrochemical stability window. Our samples achieve high conductivities over 1 mS/cm and relative densities above 90% with our combinatorial synthesis. Dopant content is optimized for each promising dopant to compare best-case results and correlate performance with structural properties like lattice parameters and density. Since comparing dopants in the literature is often difficult due to varying synthesis methods, this systematic work is essential in rational design of these electrolytes.1.Q. Liu, et al., J. Power Sources 2018, 389, 120-134.2.T. Thompson, et al., ACS Energy Letters 2017, 2, 462-468.3.F. Zheng, et al., J. Power Sources 2018, 389, 198-213.4.E. Anderson et al., DOI:10.1016/j.ssi.2022.116087.

High Performance Anode-Free Lithium Pouch Cells Employing Lithiophilic Gel Polymer Electrolyte with Ion Conductive Network

Anode-free lithium metal batteries have recently emerged as a next generation battery due to increased energy density by adopting bare current collector as an anode without excess lithium source. However, lithium tends to grow in uncontrolled dendritic form when depositied on a heterogeneous current collector, which eventually leads to low coloumbic efficiency and poor life span of the battery. Recent studies have attempted to apply artificial solid electrolyte interphase (SEI) on the current collector to solve theses problems. PEO-based polymeric artificial SEI is commonly used due to high lithium ion conductivity and flexiblility, but its weak physical properties limit its practical application. Herein, we report a chemically cross-linked poly (ethylene glycol) diacrylate (PEGDA)-based gel polymer electrolyte containing AgNO3 as Li nucleation seed for uniform Li deposition. It guides uniform Li-ion flux at the electrode/electrolyte interface and provides mechanical strength to suppress lithium dendrite growth. The gel polymer electrolyte was applied to anode free pouch cell and its cycling performance was investigated in the voltage range of 3.6 - 4.3 V at 0.5 C rate. Our results demonstrate that the proper combination of electrolyte and current collector can increase the conversion of polymerization and achieve stable interfacial properties with electrodes, resulting in improvement of the cycle life of anode free lithium pouch cell.

Combined Electrochemical, XPS, and STXM Study of Lithium Nitride as a Protective Coating for Lithium Metal and Lithium-Sulfur Batteries.

Li3N is an excellent protective coating material for lithium electrodes with very high lithium-ion conductivity and low electronic conductivity, but the formation of stable and homogeneous coatings is technically very difficult. Here, we show that protective Li3N coatings can be simply formed by the direct reaction of electrodeposited lithium electrodes with N2 gas, whereas using battery-grade lithium foil is problematic due to the presence of a native passivation layer that hampers that reaction. The protective Li3N coating is effective at preventing lithium dendrite formation, as found from unidirectional plating and plating-stripping measurements in Li-Li cells. The Li3N coating also efficiently suppresses the parasitic reactions of polysulfides and other electrolyte species with the lithium electrode, as demonstrated by scanning transmission X-ray microscopy, X-ray photoelectron spectroscopy, and optical microscopy. The protection of the lithium electrode against corrosion by polysulfides and other electrolyte species, as well as the promotion of smooth deposits without dendrites, makes the Li3N coating highly promising for applications in lithium metal batteries, such as lithium-sulfur batteries. The present findings show that the formation of Li3N can be achieved with lithium electrodes covered by a secondary electrolyte interface layer, which proves that the in situ formation of Li3N coatings inside the batteries is attainable.