Lithium Lanthanum Zirconate Research Articles

Synergistic effect of cation ordered structure and grain boundary engineering on long-term cycling of Li0.35La0.55TiO3-based solid batteries

In this study, Li0.35La0.55TiO3 (LLTO) was coupled with Al-doped lithium lanthanum zirconate (LLZO) to improve the grain boundary and total conductivity. The obtained ceramic pellets (LLTZO) demonstrated a recordable grain boundary and total conductivity of 3.41 × 10−4 and 3.03 × 10−4 S/cm, respectively. The obtained results establish that the heteroatoms can perturb the cation ordered structure and improve the 3D conductivity in grain bulk. In addition, the residual Al-doped LLZO on the grain boundary led to a decline in the boundary resistance. An LiFeCoPO4 |Li cell was adopted to demonstrate the enhanced conductivity of LLTO. The solid state battery rendered a specific capacity of over 101.2 mAhg−1 after 300 cycles at a relatively high rate of 0.5C. It is established from the experiments that manufacturing a solid battery using the all-coating technique provides a promising approach to achieve a practical application.

Investigation on Varying Aluminum Doping Concentrations and Sintering Temperatures on the Synthesis of Garnet Li<sub>7</sub>La<sub>3</sub>Zr<sub>2</sub>O<sub>12 </sub>solid Electrolyte via Modified Pechini Method

Solid electrolytes such as lithium lanthanum zirconate have shown a lot of promise in an all-solid-state Lithium-based battery since the discovery of its highly conductive cubic garnet structure. In this study, different concentrations of Al-doped Lithium Lanthanum Zirconate (Al-doped LLZ) having the formula of Li7-.3xAlxLa3Zr2O12 with x = 0.1,0 .2, 0.3, were synthesized via modified Pechini method and the effect of sintering temperatures, 1150 and 1200 °C, on the resulting properties were investigated. X-ray diffraction results have shown that cubic Al-doped LLZ can be obtained at a lower temperature using Pechini method. Significant effect to the conductivity on the different sintering temperatures was observed for the 0.1 Al-doped LLZ. With the different studied compositions synthesized via modified Pechini method, it was revealed that the 0.2 Al doped LLZ sintered either at 1150 or 1200 °C showed the highest conductivity of about 1.4x10-4 S/cm.

High-pressure field assisted sintering of half-cell for all-solid-state battery

High-pressure field assisted sintering (FAST/SPS) of half-cell for all-solid-state Li batteries was proposed and tested. The half-cell included the layer of lithium lanthanum zirconate (LLZO) electrolyte and the layer of mixed cathode. The mixed cathode consisted of lithium cobalt oxide (LCO) used as energy storage material and LLZO used as ionic conductor. A tool made of TZM molybdenum alloy was used to apply a high pressure of 440 MPa during FAST/SPS at a temperature of 675 °C ensuring stability of materials. An average relative density of sintered half-cell was around of 95%. The half-cell was assembled with a lithium anode and electrochemically tested. The results were compared with the performance of a half-cell sintered in an established graphite tool at the same temperature but under a lower pressure of 50 MPa and with a lower density (around of 78%). The battery with half-cell sintered at high pressure showed two-fold larger surface storage capacity. Further optimization of materials and processing is in progress.

(Invited) Molten Salt Synthesis of Lithium Conducting Garnets for More Scalable Solid-State Batteries

Solid-state lithium-ion batteries (SSLIBs) can simultaneously improve both energy density and safety over current state-of-the-art lithium-ion batteries (LIBs). These critical advantages are expected to enable next generation battery-based energy storage for both commercial applications such as consumer devices and transportation and greater utilization of renewable energy technologies. The key component to SSLIBs is the solid-electrolyte, ideally allowing fast ion conduction, possessing electrochemical stability with metallic lithium to enable higher energy density, and exhibiting chemical stability under ambient conditions. Lithium conducting garnets, in particular doped lithium lanthanum zirconate (LLZO) possess all of these advantageous characteristics. While lithium garnets have demonstrated exceptional properties under laboratory conditions, only a few groups have demonstrated a robust, scalable process to integrate them into SSLIBs. Some of the main challenges to incorporating garnets such as LLZO are the relatively high processing temperatures required and brittle nature of devices based on these sintered polycrystalline ceramics. Processing schemes amenable to roll-to-roll type processing such as tape-casting have been demonstrated, but generally require very fine powders to produce thin electrolyte membranes and subsequently low cell resistance. However, lithium garnets are most commonly synthesized via solid-state reactions (SSR), generally requiring high temperatures (> 900 °C), long reaction times (often in excess of 8 h), and concomitant high energy cost. Further, the resultant particle sizes of LLZO synthesized via SSR are relatively large, and fine powders are only obtained after further processing via high energy milling. Molten salt synthesis (MSS) has recently been demonstrated as an alternative strategy to obtain phase-pure crystalline LLZO, with the added benefit of generally shorter reaction times (4 h or less), lower temperatures, and in some cases inherently submicron particle sizes, while maintaining expected high ionic conductivity. Design principles for formation of doped and co-doped LLZO are discussed, wherein salt and reagent composition have direct effects on the formation temperature, particle size, particle size distribution, and electrochemical performance of the as-synthesized material. By engineering inherently fine LLZO powders, a more direct route to practical processing methods such as tape-casting becomes accessible. As such, MSS may prove to be a crucial method to allow LLZO and SSLIBs based on it to transition to a scalable solution for safer, more efficient battery-based energy storage.

Controlling Ionic Transport through the PEO-LiTFSI/LLZTO Interface

A highly resistive Polyethylene oxide-LiTFSI(PEO-LiTFSI)/ Lithium Lanthanum Zirconium Oxide (LLZO) interface, with a resistivity of 95 kOhms.cm2 (30°C) is believed to limit the total conductivity of ceramic-polymer composite electrolyte (CPE). To achieve higher ionic conductivity, the interfacial impedance (Rinterface) must be reduced to <~100 Ohms.cm2 to enable cell impedances comparable to Li-ion technology. The goal of this study was to investigate the origin of this high Rinterface. It was hypothesized that LLZO surface impurities and abrupt changes in Li-ion concentration between the PEO-LiTFSI/LLZO electrolytes contribute to the high impedance. By removing surface impurities through heat-treatment, the Rinterface was reduced to 180 Ohms.cm2 at 30°C. Optimization of Li-salt concentration in PEO to 15:1, resulted in reduction of Rinterface from 1.6 kOhms.cm2 to 421 Ohms.cm2. By understanding the underpinning mechanisms that govern the ceramic-polymer interface impedance, we believe it is possible to develop high conductivity CPE that are easy to fabricate and integrate into solid-state batteries.

A Study on Cathode Interface of Li-La-Zr-O Solid-State Electrolyte Fabricated Via Rapid Sintering Process

For recent lithium-ion batteries (LIBs), there have been lots of researches about convert liquid-phase electrolyte to solid-state electrolyte (i. e. all-solid-state battery) to improve safety and stability. Solid-state electrolyte materials have to satisfy some criteria including high ionic conductivity at room-temperature, chemical stability against reducing environment, and mechanical strength. Many solid-materials for electrolyte have been researched, including perovskite, garnet, and sulfide-type of materials. Among them, garnet-type based lithium lanthanum zirconium oxide (LLZO, Li7La3Zr2O12) has been received attention due to its high ionic conductivity (~10-4 S/cm at room temperature) and wide electrochemical stability window (~6 V versus Li/Li+). The main issue of LLZO is the high interfacial resistance with anode and cathode materials such as Li metal and LiCoO2. Many researchers have tried to understand the cause of this interfacial resistance for LLZO. K. Park et al. researched about the cathode/electrolyte (LLZO) interface and revealed co-diffusion and second-phase formation of LLZO at high-temperature [1]. M. Zarabian et al. reported that spin-coated LLZO on the LiCoO2 pellet fabricated at low-temperature (~400oC) and co-diffusion of La and Co at the interface by using X-ray photoelectron spectroscopy (XPS) [2]. They commonly suggested that elevated temperature make chemical interaction and this make high interfacial resistance. In this study, we adopted novel sintering method, flash light annealing (FLA) process, to fabricate LLZO solid-electrolyte. This method is also called rapid, cool sintering because of its unique characteristics compared to conventional sintering methods [3]. FLA uses instantaneous high current to generate intensive pulsed light (IPL), and irradiate IPL toward the specimen to sinter the materials. Unlike the conventional sintering methods, this novel method has lots of advantages including availability of treatment at STP and fast sintering time (~ a few ms). Rapid sintering process gives no time for the diffusion at the interface, thus the interfacial resistance between cathode and LLZO solid-electrolyte must be reduced. We fabricated LLZO solid-electrolyte on the commercial LiCoO2 pellet by using solution-based spin-coating method and sintered the film by using FLA method. XPS and energy-dispersive X-ray spectroscopy (EDX) analysis were conducted to observe interface and diffusion of La and Co elements. Also, X-ray diffraction (XRD) method was used to investigate sintering ability of FLA through crystallinity development. The interfacial resistance between LiCoO2 and LLZO solid-electrolyte was analyzed by electrochemical impedance spectroscopy (EIS) through cross-plane set-up.

Poly(propylene carbonate) Interpenetrating Cross-Linked Poly(ethylene glycol) Based Polymer Electrolyte for Solid-State Lithium Batteries

Solid polymer electrolyte based on semi-interpenetrating polymer network (s-IPN) was synthesized from the mixture of poly(propylene carbonate) (PPC), poly(ethylene glycol) methylether acrylate (PEGMEA), poly(ethylene glycol) diacrylate (PEGDA), and lithium bis(trifluoromethane)sulfonimide (LiTFSI) salt via one-pot thermal curing method. The crosslinker PEGDA content and salt concentration were optimized. The ionic conductivity, lithium-ion transference number and electrochemical stability window of the s-IPN electrolyte were correlated with its thermal and physical properties. Differential scanning calorimetry measurements have shown a low degree of crystallinity in this s-IPN electrolyte. The electrolyte with higher salt concentration has lower ionic conductivity, consistent with higher glass transition temperature of poly(ethylene glycol) chain. The ionic conductivity was further enhanced by dispersion of lithium-ion conductive ceramic powder, lithium lanthanum zirconate (LLZO) into the s-IPN matrix. The optimized s-IPN has potential as a baseline material for future solid-state electrolyte designs.

Structural (in)stability and spontaneous cracking of Li-La-zirconate cubic garnet upon exposure to ambient atmosphere

Among the Li-ion conducting inorganic materials, lithium lanthanum zirconate (LLZO) is believed to possess good chemical stability against Li metal and hence considered to be a promising solid electrolyte for Li-ion batteries. However, systematic sets of studies conducted here at regular intervals during storage of Al-doped LLZO (cubic garnet) sintered pellets in ambient atmosphere have raised serious concerns over their structural/mechanical stability/integrity upon exposure to air. Spontaneous cracking/disintegration/pulverization of LLZO pellets takes place after about three weeks of exposure, primarily due to formation of La2Zr2O7 in the LLZO bulk; as found to be thermodynamically feasible at room temperature upon reaction with CO2/moisture. Steep increase in La2Zr2O7 content coincides with the spontaneous cracking/disintegration. Estimation suggests that internal stresses associated with the formation of La2Zr2O7 from LLZO can be high enough to cause spontaneous fracture. This mandates the development/fabrication/usage of solid-state cells using LLZO under stringent controls against exposure to atmospheric species.

Crystal Orientation-Dependent Reactivity of Oxide Surfaces in Contact with Lithium Metal.

Understanding ionic transport across interfaces between dissimilar materials and the intrinsic chemical stability of such interfaces is a fundamental challenge spanning many disciplines and is of particular importance for designing conductive and stable solid electrolytes for solid-state Li-ion batteries. In this work, we establish a surface science-based approach for assessing the intrinsic stability of oxide materials in contact with Li metal. Through a combination of experimental and computational insights, using Nb-doped SrTiO3 (Nb/STO) single crystals as a model system, we were able to understand the impact of crystallographic orientation and surface morphology on the extent of the chemical reactions that take place between surface Nb, Ti, and Sr upon reaction with Li. By expanding our approach to investigate the intrinsic stability of the technologically relevant, polycrystalline Nb-doped lithium lanthanum zirconium oxide (Li6.5La3Zr1.5Nb0.5O12) system, we found that this material reacts with Li metal through the reduction of Nb, similar to that observed for Nb/STO. These results clearly demonstrate the feasibility of our approach to assess the intrinsic (in)stability of oxide materials for solid-state batteries and point to new strategies for understanding the performance of such systems.

Poly(propylene carbonate) Interpenetrating Cross-Linked Poly(ethylene glycol) Based Polymer Electrolyte for Solid-State Lithium Batteries

Lithium-ion conducting solid polymer electrolytes (SPEs) are promising materials to replace flammable liquid electrolytes to solve the safety and performance issues in conventional rechargeable lithium batteries [1]. Poly(ethylene oxide) (PEO) has been studied extensively as baseline materials for SPEs. It is well known that pure PEO crystallizes at room temperature, hampering lithium ion migration and resulting in low ionic conductivity. This drawback hinders PEO based SPEs applied in real battery configuration that usually requires ionic conductivity greater than 10-4 S cm-1 at 25 ℃. In general, suppression of polymer crystallinity is favorable for SPEs to enhance the ionic conductivity [2]. Here, we synthesized a semi-interpenetrating polymer network (s-IPN) from the mixture of poly(propylene carbonate) (PPC), poly(ethylene glycol) methylether acrylate (PEGMEA), poly(ethylene glycol) diacrylate (PEGDA), and lithium bis(trifluoromethane) sulfonimidate (LiTFSI) salt using one-pot thermal curing method. The amorphous PPC performs as film forming agent, whereas the crosslinked network with PEG pendants provides lithium conducting channel. The s-IPN architecture inhibits the phase segregation of two different polymers. Curing temperature, crosslinker PEGDA content and salt concentration were optimized carefully to attain a flexible film with ionic conductivity reaching 5×10-6 S cm-1 at ambient temperature. The ionic conductivity and working potential window were correlated with the thermal and physical properties of the s-IPN electrolytes. Differential scanning calorimetry measurements have shown a decrease in the crystallinity of the s-IPN electrolytes. The electrolyte with higher salt concentration has lower ionic conductivity, consistent with higher glass transition temperature of PEG chain. The ionic conductivity was further enhanced by incorporating lithium ion conductive ceramic powder, lithium lanthanum zirconate (LLZO) as a filler into the s-IPN matrix, even though LLZO aggregation occurred during film forming. The optimized s-IPN has potential as a baseline material for future solid-state electrolyte designs. Acknowledgements We gratefully acknowledge the financial support from the NASA MIRO Program #NNX15AP44A and the National Science Foundation under Award #162-6449.

Improving the Performance of PEO-Based Electrolytes to Enable Metallic Li As an Anode

Replacing carbon-based anodes with metallic Li can drastically improve the performance of Li-ion batteries. However, stabilizing the Li metal/liquid electrolyte interface has been difficult and it is critical to replace them with solid state electrolytes. Solid polymer electrolytes (eg. PEO-LiTFSI) are of particular interest as they are easy to fabricate and have superior ductility, leading to suitable mechanical properties. This work addresses two challenges in developing viable PEO-based electrolytes – 1) factors affecting the SPE/Li interface are not well understood and 2) these electrolytes inherently have low room temperature conductivity. The first part of this work focuses on minimizing the interfacial impedance between PEO-LiTFSI (SPE) and lithium anode by controlling the external variables in a Li/PEO-LiTFSI symmetric cell. The stability and kinetics of the interface were correlated with temperature, stack pressure and electrode type using electrochemical impedance spectroscopy (EIS) and dc cycling in order minimize interfacial impedance and maximize the limiting current (j lim). Second, a critical stack pressure was established for 60oC and 80oC as 400 kPa and 200 kPa respectively by relating the stack pressure with interfacial impedance, below which interfacial impedance was shown to be at least 50 times higher. The effects of increasing temperature on the kinetics and mechanics of the interface manifest as variations in the EIS and cycling profiles. Lastly, the PEO-LiTFSI/Li interfacial impedance was reduced by 67%, from 4000 Ohms.cm2 to 1675 Ohm.cm2 at 30oC by using vapor deposited Li over Li foil electrode, increasing the limiting current from 0.5 mA/cm2 to 1mA/cm2. The second part of this work was dedicated towards increasing the room temperature conductivity of PEO-LiTFSI electrolytes by adding a filler material. LLZO (Lithium Lanthanum Zirconium Oxide) was chosen because of its high room temperature conductivity and good cycling capabilities. Low values of interfacial impedance calculated from EIS on a trilamilar PEO-LiTFSI and LLZO cell with blocking electrodes proved the viability of the composite electrolyte. A solvent casting method was developed for the fabrication of flexible composite electrolytes of 100-500 microns thickness. The flexibility of the composite electrolytes was comparable to that of nascent PEO-LiTFSI electrolyte membranes, while their ionic conductivity was an order of magnitude higher. EIS was also used to determine the temperature dependence of the composite electrolyte’s conductivity. Lastly, the variation in bulk impedance with increasing LLZO volume percent in the PEO-LiTFSI was studied to optimize conductivity, while maintaining its flexibility. Overall, this study provides effective guidelines for improving the performance of PEO-based electrolytes towards enabling viable all-solid state batteries.

Synthesis of Li-Ion Conducting Garnet Li7La3Zr2O12 Powders in Molten Salt Media: Implications for Future Li-Ion Batteries

Recently, solid-state electrolytes have been a highly active area of research for future Li-ion batteries due to the potential for drastically improved energy density and safety. Among these materials, garnet structured lithium lanthanum zirconate (Li7La3Zr2O12, LLZO) shows particular promise owing to the high ionic conductivity of its cubic polymorph, inertness, and electrochemical stability against metallic lithium. Herein we report the facile preparation of phase-pure cubic LLZO via molten salt synthesis at temperatures substantially lower than conventional solid-state reactions. Fine powders of cubic LLZO were obtained with primary particle sizes in the submicron range. Depending on the consolidation conditions, dense ceramics with Li+ conductivity values above 0.371 mS cm-1 could be obtained. It is also observed that the effect of hydration has a profoundly deleterious effect on sintering and densification, and that this effect can be mitigated by the simple addition of LiOH before sintering to reverse hydration and aid densification. Qualitative discussions on the mechanisms of LLZO formation in the molten salt medium are discussed, in addition to implications for future scalable processing of LLZO electrolytes.

Synthesis of Fine Cubic Li7La3Zr2O12 Powders in Molten LiCl–KCl Eutectic and Facile Densification by Reversal of Li+/H+ Exchange

Recently, solid-state electrolytes have been a highly active area of research for future Li-ion batteries due to the potential for drastically improved energy density and safety. Among these materials, garnet structured lithium lanthanum zirconate (Li7La3Zr2O12, LLZO) shows particular promise owing to the high ionic conductivity of its cubic polymorph, inertness, and electrochemical stability against metallic lithium. Herein we report the facile preparation of phase-pure, cubic LLZO via molten salt synthesis in a eutectic mixture of LiCl–KCl at 900 °C. Fine powders of Al- and Ga-doped LLZO were obtained with primary particle sizes ranging from 0.3 to 3 μm. Depending on the consolidation conditions, pellets with up to 86% relative density could be obtained, with Li+ conductivity values ranging from 0.230 to 0.371 mS cm–1. It is also observed that while the effect of hydration has a profoundly deleterious effect on sintering and densification, this effect can be mitigated by the simple addition of LiOH befo...

A novel solid-liquid route for synthesizing cubic garnet Al-substituted Li7La3Zr2O12

A solid-liquid composite method (SLM) of Al-substituted cubic lithium lanthanum zirconium garnet (c-LLZO) was developed. Cubic LLZO powders whose composition was Li6.23Al0.26La3Zr1.88O11.76 were prepared from the stoichiometric mixtures of lithium acetate, lanthanum oxide, zirconia and alumina, followed by an annealing of the dried precursor at 750°C for 12h in an air atmosphere. The resultant powders were characterized by XRD, SEM and ICP-OES. The conventional solid-state reaction methods using carbonates and hydroxides as lithium sources are also simply introduced as a comparison. In addition, the phase formation of c-LLZO powders synthesized by the ZrO2 powders with different specific surfaces as raw material was also investigated. The results show that the cubic garnet phase LLZO powders was obtained when the value of the specific surface area (SSA) of the material ZrO2 powder was about 110m2g−1. Sintering these cubic phase powders at 1150°C for 6h in air after uniaxial pressing obtained a dense ceramic pellet with a relative density of 91.2% and ionic conductivity of 2.54×10−4Scm−1 at 23°C.

Investigation of Thermal Compatibility of Various Cathode Materials with Li6.25Al0.25La3Zr2O12 Solid Electrolyte for All-Solid-State Rechargeable Lithium Batteries

Aluminum-doped lithium lanthanum zirconate (Li6.25Al0.25La3Zr2O12, Al-LLZ) has a relatively high Li+-ion conductivity of ~10-4 S cm-1 at room temperature and a wide electrochemical window enabling to use both lithium-metal anode and high potential cathodes, so that it has been focused as a promising solid electrolyte for all-solid-state rechargeable lithium batteries with high energy density. Several kinds of fabrication methods, which usually include heat treatment processes, have been utilized to fabricate cathode on Al-LLZ. However, the effect of heat treatments on the formation of impurities at the interface between Al-LLZ and cathode has not been fully understood yet. In this study, we investigated the thermal compatibility of conventional cathode materials (LiCoO2, LiMn2O4 and LiFePO4) with Al-LLZ by X-ray diffraction (XRD) and charge-discharge tests. The XRD analysis showed that LiCoO2/Al-LLZ mixture is stable up to 800°C, but impurities are formed in LiMn2O4/Al-LLZ mixture and LiFePO4/Al-LLZ mixture at 600 °C and 400 °C, respectively. This result indicates that the limit of heat treatment temperature for the formation of electrode/Al-LLZ interface strongly depends on the kind of electrode materials.

Composite Polymer Electrolytes with Li7La3Zr2O12 Garnet-Type Nanowires as Ceramic Fillers: Mechanism of Conductivity Enhancement and Role of Doping and Morphology.

Composite polymer solid electrolytes (CPEs) containing ceramic fillers embedded inside a polymer-salt matrix show great improvements in Li+ ionic conductivity compared to the polymer electrolyte alone. Lithium lanthanum zirconate (Li7La3Zr2O12, LLZO) with a garnet-type crystal structure is a promising solid Li+ conductor. We show that by incorporating only 5 wt % of the ceramic filler comprising undoped, cubic-phase LLZO nanowires prepared by electrospinning, the room temperature ionic conductivity of a polyacrylonitrile-LiClO4-based composite is increased 3 orders of magnitude to 1.31 × 10-4 S/cm. Al-doped and Ta-doped LLZO nanowires are also synthesized and utilized as fillers, but the conductivity enhancement is similar as for the undoped LLZO nanowires. Solid-state nuclear magnetic resonance (NMR) studies show that LLZO NWs partially modify the PAN polymer matrix and create preferential pathways for Li+ conduction through the modified polymer regions. CPEs with LLZO nanoparticles and Al2O3 nanowire fillers are also studied to elucidate the role of filler type (active vs passive), LLZO composition (undoped vs doped), and morphology (nanowire vs nanoparticle) on the CPE conductivity. It is demonstrated that both intrinsic Li+ conductivity and nanowire morphology are needed for optimal performance when using 5 wt % of the ceramic filler in the CPE.

Impedance of Cubic Li7La3Zr2O12 Film Deposited on Strontium Ruthenate Substrate by Chemical Vapor Deposition

A garnet-type lithium lanthanum zirconium oxide (Li7La3Zr2O12) film was deposited on a strontium ruthenate (SrRuO3) substrate by chemical vapor deposition using metal organic precursors and its ionic conductivity was investigated by impedance spectroscopy in the temperature range of 298–368 K. A single-phase cubic Li7La3Zr2O12 film with a dense granular morphology was formed on the SrRuO3 electrode substrate at a deposition temperature of 1223 K and total pressure of 400 Pa. The complex plane plots of the Li7La3Zr2O12 film comprised part of a semicircle, associated with the transport of Li ions through the film at high frequencies, and a significant spike, attributed to the Warburg impedance at low frequencies. The ionic conductivity was 1.4 × 10-5 S·cm-1 at room temperature and increased with an increase in temperature, with an activation energy of 0.36 eV.

Preparation of Nano- and Microstructured Garnet Li7La3Zr2O12 Solid Electrolytes for Li-Ion Batteries via Cellulose Templating

Lithium lanthanum zirconate (LLZO) is a promising Li+ ion conductor for applications as a ceramic solid electrolyte in all-solid-state lithium batteries. However, the tetragonal and cubic phases of LLZO differ in lithium ionic conductivity by several orders of magnitude with extrinsic dopants or nanostructuring often required to stabilize the high conductivity cubic phase at room temperature. Here, we show that nanostructured LLZO can be prepared by templating onto various cellulosic fibers, including laboratory Kimwipes, Whatman filter paper, and nanocellulose fibrils, followed by calcination at 700–800 °C. The effect of templating material, calcination temperature, calcination time, and heating ramp rate on the LLZO crystal structure and morphology were thoroughly investigated. Templating was determined to be an effective method for controlling the LLZO size and morphology, and low calcination times and ramp rates were found to favor the formation of small ligaments. Furthermore, it was verified that cu...

Failure Mechanism from Direct Contact Between Lithium Metal and Solid Electrolytes

The demand for lithium secondary batteries having more safety and energy density is high. In this aspect, lithium ion batteries including typical liquid electrolytes have fundamental limitations. Liquid electrolytes can cause a fire or explosion of battery and decomposition of them at high potential obstructs applying high potential cathode. Applying solid electrolyte can solve these limitations so many solid electrolytes have been interested in and researched. Major types of solid electrolytes are sulfides and oxides and their pros and cons are obvious. It is commonly known that sulfides have advantages of high ionic conductivity and softness for easy contact, while oxides have high electrochemical stability. One of the tactics that fulfill high energy density is using lithium metal directly as anode and the researches that using lithium metal on solid electrolyte are progressed. Major oxide solid electrolytes not including transition metal had been considered stable with lithium metal. However, increased resistances of lithium symmetric cell with time and all solid-state cell after charge and discharge were observed and interphase reactions with lithium metal were calculated from some solid electrolytes. However, the relationship between them and the failure mechanism of the solid electrolytes with lithium metal are not fully understood yet. In this research, we discuss the phenomena from the interphase between lithium metal and solid electrolytes; lithium aluminum germanium phosphate (LAGP) and lithium lanthanum zirconium oxide (LLZO). We also suggest the mechanism of increased resistance with direct contact of lithium metal and the solid electrolyte.

Processing of Aluminum-Doped Lithium Lanthanum Zirconate Garnet-Type Solid Electrolyte Materials

Lithium lanthanum zirconate (LLZO) with the garnet crystal structure has high lithium ion conductivity and good electrochemical stability, so it is an attractive material for use as the solid electrolyte in lithium ion batteries. One of the challenges in the application of LLZO is processing the material to obtain the desired composition, crystal structure and morphology. In this paper, results on processing of LLZO materials for use in single-phase and composite solid electrolyte materials are presented.