Garnet-type Solid-state Electrolytes Research Articles

Accelerating the Development of LLZO in Solid-State Batteries Toward Commercialization: A Comprehensive Review.

Solid-state batteries (SSBs) are under development as high-priority technologies for safe and energy-dense next-generation electrochemical energy storage systems operating over a wide temperature range. Solid-state electrolytes (SSEs) exhibit high thermal stability and, in some cases, the ability to prevent dendrite growth through a physical barrier, and compatibility with the "holy grail" metallic lithium. These unique advantages of SSEs have spurred significant research interests during the last decade. Garnet-type SSEs, that is, Li7La3Zr2O12 (LLZO), are intensively investigated due to their high Li-ion conductivity and exceptional chemical and electrochemical stability against lithium metal anodes. However, poor interfacial contact with cathode materials, undesirable lithium plating along grain boundaries, and moisture-induced chemical degradation greatly hinder the practical implementation of LLZO-based SSEs for SSBs. In this review, the recent advances in synthesis methods, modification strategies, corresponding mechanisms, and applications of garnet-based SSEs in SSBs are critically summarized. Furthermore, a comprehensive evaluation of the challenges and development trends of LLZO-based electrolytes in practical applications is presented to accelerate their development for high-performance SSBs.

Investigation of Li accumulations in LLZO based solid state batteries via operando neutron imaging and ex-situ correlative structural and chemical analysis

In this study, we present a comprehensive analysis of lithium dendrite formation in half-cells with lithium garnet-type solid-state electrolyte Li7La3Zr2O12 (LLZO) utilizing operando neutron imaging and subsequent ex-situ correlative structural and chemical analysis. The operando experiment involves cycling a solid-state symmetric half-cell (Li|LLZO|Li) until short-circuit failure, all while being irradiated with neutrons, providing invaluable insights into the dynamic processes within the symmetric half-cell. Post-mortem investigations were carried out, comprising two techniques: 1) secondary electron imaging for structural analysis and 2) secondary ion mass spectrometry (SIMS) for chemical mapping. This multifaceted approach creates complementary datasets, bridging the gap between neutron radiography, known for its quantitative transmission capabilities, and high-resolution, high-sensitivity structural and chemical imaging via scanning electron microscopy (SEM) and SIMS.Central to our investigation is the design and development of an operando neutron imaging approach, enabling the study of lithium penetration during the electrochemical cycling. Furthermore, structural, and chemical analyses through correlative SEM/SIMS unveil various morphologies of lithium accumulations. Specifically, regions with dense LLZO reveal intergranular lithium accumulations, while low-density areas within the LLZO pellet, such as pores and cracks, exhibit distinct types of lithium accumulations (e.g. whiskers).Notably, neutron analysis reveals an accumulation of lithium in selected regions, with a maximum increase of up to 3.6 vol.-%. These regions primarily correspond to the roughened LLZO/Li interface, as observed through neutron imaging, although the SEM/SIMS analysis unequivocally confirms the presence of lithium dendrites (with sizes at or below the resolution limit of neutron imaging) also within the bulk of LLZO.This work offers a comprehensive examination of the intricate dynamics of lithium dendrite formation and behaviour in LLZO-based solid-state half-cells, emphasizing the potential of operando techniques to advance our understanding of critical issues (e.g. degradation, dendrite formation, …) in battery research.

Near-strain-free anode architecture enabled by interfacial diffusion creep for initial-anode-free quasi-solid-state batteries

Anode-free (or lithium-metal-free) batteries with garnet-type solid-state electrolytes are considered a promising path in the development of safe and high-energy-density batteries. However, their practical implementation has been hindered by the internal strain that arises from the repeated plating and stripping of lithium metal at the interlayer between the solid electrolyte and negative electrode. Herein, we utilize the titanium nitrate nanotube architecture and a silver-carbon interlayer to mitigate the anisotropic stress caused by the recurring formation of lithium deposition layers during the cycling process. The mixed ionic-electronic conducting nature of the titanium nitrate nanotubes effectively accommodates the entry of reduced Li into its free volume space via interfacial diffusion creep, achieving near-strain-free operation with nearly tenfold volume suppressing capability compared to a conventional Cu anode counterpart during the lithiation process. Notably, the fabricated Li6.4La3Zr1.7Ta0.3O12 (LLZTO)-based initial-anode-free quasi-solid-state battery full cell, coupled with an ionic liquid catholyte infused high voltage LiNi0.33Co0.33Mn0.33O2-based cathode with an areal capacity of 3.2 mA cm−2, exhibits remarkable room temperature (25 °C) cyclability of over 600 cycles at 1 mA cm−2 with an average coulombic efficiency of 99.8%.

A Stable Matrix Assisting Highly Compatible and Maintainable Lithium-Garnet Interface for Solid-State Batteries.

Solid-state Li metal batteries (SSLMBs) are attractive due to their capability to simultaneously offer high energy density and high-level safety when combining Li metal anodes, solid-state electrolytes (SSEs), and high-voltage cathodes together. However, SSLMBs may well incur short circuits caused by Li dendrites penetrations, which mainly originate from the instability and poor contact between Li metal and SSEs. Herein, by taking full advantage of the reaction products of Li and Li1.3Al0.3Ti1.7(PO4)3 (LATP), a lithium-LATP composite anode (Li-LATP) is obtained, in which a stable matrix is formed to enhance the contact between Li and the garnet-type SSEs, alleviating the volume change and preserving an intact interface during the charge/discharge process. Consequently, the Li-LATP/garnet/Li-LATP symmetric cell displays a fairly low interfacial resistance of 6Ωcm2 and stable cycling performance for over 2500h with a low overpotential. Furthermore, the LiCoO2/garnet/Li-LATP full cell also shows a high discharge capacity of 159mAhg-1 and great cycling performance.

Grain boundary complexion modification for interface stability in garnet based solid-state Li batteries

The garnet type solid-state electrolyte (SSE) encounters challenges related to poor interfacial contact with Li metal and dendrite penetration problem. This study addresses these issues by manipulating the surface property of garnet-based LLZTO (Li6.5La3Zr1.6Ta0.4O12) SSE. The manipulation is achieved by varying thickness of Al2O3 atomic layer deposition (ALD), followed by sintering. Research results show that the relative density, ionic conductivity, and hardness of LLZTO are improved while electronic conductivity is reduced due to the formation of multiple complexions at grain boundary (GB). The SSE pellets also demonstrate improved wettability with Li metal, leading to stable galvanostatic Li plating/stripping cycling with low polarization, which allows for batter battery performance than pristine one. The concept of modifying SSE through the grain boundary complexion modification by thin ALD coating for enhancing the dendrite tolerance with better electrochemical properties of SSE may open a new direction for solid state battery research.

Optimized Lithium Ion Coordination via Chlorine Substitution to Enhance Ionic Conductivity of Garnet-Based Solid Electrolytes.

Garnet-type solid-state electrolytes attract abundant attentions due to the broad electrochemical window and remarkable thermal stability while their poor ionic conductivity obstructs their widespread application in all-solid-state batteries. Herein, the enhanced ionic conductivity of garnet-type solid electrolytes is achieved by partially substituting O2- sites with Cl- anions, which effectively reduce Li+ migration barriers while preserving the highly conductive cubic phase of garnet-type solid-state electrolytes. This substitution not only weakens the anchoring effect of anions on Li+ to widen the size of Li+ diffusion channel but also optimizes the occupancy of Li+ at different sites, resulting in a substantial reduction of the Li+ migration barrier and a notable improvement in ionic conductivity. Leveraging these advantageous properties, the developed Li6.35 La3 Zr1.4 Ta0.6 O11.85 -Cl0.15 (LLZTO-0.15Cl) electrolyte demonstrates high Li+ conductivity of 4.21×10-6 Scm-1 . When integrated with LiFePO4 (LFP) cathode and metallic lithium anode, the LLZTO-0.15Cl electrolyte enables the solid-state battery to operate for more than 100 cycles with a high capacity retention of 76.61% and superior Coulombic efficiency of 99.48%. This work shows a new strategy for modulating anionic framework to enhance the conductivity of garnet-type solid-state electrolytes.

Optimization of two-dimensional solid-state electrolyte–anode interface by integrating zinc into composite anode with dual-conductive phases

Solid-state electrolytes (SSEs) are a solution to safety issues related to flammable organic electrolytes for Li batteries. Insufficient contact between the anode and SSE results in high interface resistance, thus causing the batteries to exhibit high charging and discharging overpotentials. Recently, we reduced the overpotential of Li stripping and plating by introducing a high proportion of dual-conductive phases into a composite anode. The current study investigates the interface resistance and stability of a composite electrode modified with Zn and a lower proportion of dual-conductive phases. Zn-cation-adsorbed Prussian blue is synthesized as an intermediate component for a Zn-modified composite electrode (Li-FeZnNC). The Li-FeZnNC symmetric cell presents a lower interface resistance and overpotential compared with Li-FeNC (without Zn modification) and Li-symmetric cells. The Li-FeZnNC symmetric cell shows high electrochemical stability during Li stripping and plating at different current densities and high stability for 200 h. Full batteries with a Li-FeZnNC composite anode, garnet-type SSE, and LiFePO4 cathode show low charging and discharging overpotentials, a capacity of 152 mAh g−1, and high stability for 200 cycles.

Solid Interfaces for the Garnet Electrolytes.

Solid-state electrolytes (SSEs) have attracted extensive interests due to the advantages in developing secondary batteries with high energy density and outstanding safety. Possessing high ionic conductivity and the lowest reduction potential among the state-of-the-art SSEs, the garnet type SSE is one of the most promising candidates to achieve high performance solid-state lithium batteries (SSLBs). However, the elastic modulus of the garnet electrolyte leads to deteriorated interfacial contacts, and the increasing in electronic conduction at either anode/garnet interface or grain boundary results in Li dendrite growth. Here, recent developments of the solid interfaces for the garnet electrolytes, including the strategies of Li dendrite suppression and interfacial chemical/electrochemical/mechanical stabilizations are presented. A new viewpoint of the double edges of interfacial lithiophobicity is proposed, and the rational design of the interphases, as well as effective stacking methods of the garnet-based SSLBs are summarized. Moreover, practical roles of the garnet electrolyte in SSLB industry are also discussed. This work delivers insights into the solid interfaces for the garnet electrolytes, which provides not only the promotion of the garnet-based SSLBs, but also a comprehensive understanding of the interfacial stabilization for the whole SSE family.

Enhanced Performances for Solid-State Lithium-Ion Batteries with Llzo Thin Electrolyte and Silicon-Nanowires Electrode

In the past decades, due to an always more electrification and the research of a greener environment, Li-ion Batteries (LIB) have taken an important place in worldwide research. Solid-state batteries (SSBs) have the potential to revolutionize the energy storage industry, offering superior safety and energy density in comparison to traditional LIBs[1, 2]. Our research aims to enhance the performance and safety of solid-state batteries at ambient temperature by incorporating electrodes with high specific capacity with a lithium lanthanum zirconate (LLZO) solid electrolyte.The integration of SiNW electrodes into the solid-state battery architecture offers several advantages. SiNWs are known for their large surface area and superior electrical conductivity and offer a strong platform for efficient lithium-ion transport and cell energy density optimization, theoretically almost 10 times the capacity of graphite[3, 4]. Furthermore, LLZO solid electrolytes are a stable and non-flammable alternative to conventional liquid electrolytes[2, 5], significantly improving battery safety.The main objectives of this study are to investigate the combined effects of silicon nanowires (SiNWs) electrodes and LLZO solid electrolyte and to determine the optimal amount of liquid electrolytes to improve cell safety.In this work, an LLZO thin solid electrolyte tape has been manufactured by casting technique. Precise volumes of liquid electrolyte have been added to the LLZO tape to improve surface contact and ion conductivity. Furthermore, the study will provide a view of the relationship between the quantity of liquid electrolytes introduced and their impact on cell stability and safety.Preliminary results show the preparation of a mechanically stable LLZO tape with high ionic conductivity (>10-4 S cm-1) through an easy and up-scalable procedure. Improvements have been reported in the electrochemical performance of SiNW-LLZO solid-state batteries compared to the relative Li-ion liquid cell.In conclusion, here we developed a new thin solid electrolyte tape with high ionic conductivity, used in solid-state LIBs with silicon nanowires as anode material. Moreover, we standardized a procedure to optimize the use of organic liquid electrolytes as an additive, without omitting the volume or using any excess that could lead to safety issues. This optimization process can contribute to the development of solid-state batteries that are not only high-performance but also safe and reliable for various applications, including electric vehicles and portable electronics. References Wu, F., J. Maier, and Y. Yu, Guidelines and trends for next-generation rechargeable lithium and lithium-ion batteries. Chem Soc Rev, 2020. 49(5): p. 1569-1614.Wang, C., et al., Garnet-Type Solid-State Electrolytes: Materials, Interfaces, and Batteries. Chem Rev, 2020. 120(10): p. 4257-4300.Chan, C.K., et al., High-performance lithium battery anodes using silicon nanowires. Nat Nanotechnol, 2008. 3(1): p. 31-5.Kennedy, T., M. Brandon, and K.M. Ryan, Advances in the Application of Silicon and Germanium Nanowires for High-Performance Lithium-Ion Batteries. Adv Mater, 2016. 28(27): p. 5696-704.Xu, L., et al., Garnet Solid Electrolyte for Advanced All ‐Solid ‐State Li Batteries. Advanced Energy Materials, 2020. 11(2).

In Situ and Low-Cost Improvement of the Lithium Anode Interface in Garnet-Type Solid-State Electrolytes.

In recent years, the development of electric vehicles and environmental concerns have made necessary improvements in the energy density and safety of lithium-ion batteries. Therefore, the development of all-solid-state lithium-ion batteries (ASSLIBs) has become imperative. One advantage of ASSLIBs is their potential for downsizing with the use of lithium metal as the anode. However, in this study, a garnet-type solid electrolyte (Li6.75La3Zr1.75Ta0.25O12) was used, which has low reactivity with lithium metal. Thus, interface modification using CaCl2 was employed to form a Li-Ca-Cl composite anode. The interfacial resistance was remarkably reduced to 7 Ω cm2, and the symmetric cell exhibited stable cycling for 1200 h at room temperature and a current density of 0.1 mA cm-2. The voltage ranged from ±15 to ±16 mV. The full cell demonstrated a high initial discharge capacity of 149.2 mA h g-1 and a Coulombic efficiency of 98.0% while maintaining a discharge capacity retention of 91.3% after 100 cycles. These findings lay a solid foundation for future commercial applications as interface modification was achieved through a simple spin-coating process using low-cost CaCl2 (0.7 USD g-1).

Trigger of the Highly Resistive Layer Formation at the Cathode-Electrolyte Interface in All-Solid-State Lithium Batteries Using a Garnet-Type Lithium-Ion Conductor.

Interfacial materials design is critical in the development of all-solid-state lithium batteries. We must develop an electrode-electrolyte interface with low resistance and effectively utilize the energy stored in the battery system. Here, we investigated the highly resistive layer formation process at the interface of a layered cathode: LiCoO2, and a garnet-type solid-state electrolyte: Li6.4La3Zr1.4Ta0.6O12, during the cosintering process using in situ/ex situ high-temperature X-ray diffraction. The onset temperature of the reaction between a lithium-deficient LixCoO2 and Li6.4La3Zr1.4Ta0.6O12 is 60 °C, while a stoichiometric LiCoO2 does not show any reaction up to 900 °C. The chemical potential gap of lithium first triggers the lithium migration from the garnet phase to the LixCoO2 below 200 °C. The lithium-extracted garnet gradually decomposes around 200 °C and mostly disappears at 500 °C. Since the interdiffusion of the transition metal is not observed below 500 °C, the early-stage reaction product is the decomposed lithium-deficient garnet phase. Electrochemical impedance spectroscopy results showed that the highly resistive layer is formed even below 200 °C. The present work offers that the origin of the highly resistive layer formation is triggered by lithium migration at the solid-solid interface and decomposition of the lithium-deficient garnet phase. We must prevent spontaneous lithium migration at the cathode-electrolyte interface to avoid a highly resistive layer formation. Our results show that the lithium chemical potential gap should be the critical parameter for designing an ideal solid-solid interface for all-solid-state battery applications.

Low-Temperature In Situ Lithiation Construction of a Lithiophilic Particle-Selective Interlayer for Solid-State Lithium Metal Batteries.

Unexpected interface resistance and lithium dendrite puncture hinder the application of garnet-type solid-state electrolytes in high-energy-density systems. Different from the previous high-temperature (>180 °C) molten lithium that promotes the alloying reaction between the coating layer and Li to enhance the interface contact, herein, we introduce liquid-metal-like SbCl3 to construct a three-dimensional Li+ directional-selection interlayer by in situ low-temperature lithiation (80 °C). An interlayer with a more negative interface energy composed of SbLi3 and LiCl exhibits a superior affinity with Li and LGLZO, which reduces the interface resistance and suppresses the growth of Li dendrites by an insulated electron. The introduction of the SbCl3 modification layer into Li/Li symmetric cells enables charge/discharge at a current density of 6.0 mA cm-2 and operation for more than 1000 h under 2.0 mA cm-2 at room temperature. The full cells with the LiFePO4 cathode exhibit a high residual capacity of 144.8 mAh g-1 at 0.5 C after 1000 cycles and excellent cycling stability with a retention ratio of 94.7% at 1 C after 600 cycles. The low-temperature lithiation method based on an energy-saving perspective should be applied to other types of solid-state electrolyte modification strategies.

(Invited) Achieving High Areal Capacity and Extreme Critical Current Densities through Tailored Garnet Solid Electrolyte Structures

Garnet structured electrolytes are an exceptional candidate to substitute for organic liquid electrolytes owing to its high ionic conductivity and safety.[1] One of the main issues preventing the commercialization of this electrolyte is limited lithium plating capacity and lithium dendrite shorting.[2] To address this, we invented new single-phase mixed ion electron conducting (MIEC) garnet with comparable lithium-ion and electron conductivity at room temperature. We demonstrate that in a trilayer architecture, with a porous MIEC framework supporting a thin dense garnet solid electrolyte, the critical current density can be as high as 100 mA/cm2, with no dendrite-induced shorting at room temperature and without any stack pressure. The single-phase MIEC conductor spreads the potential uniformly across the material surface preventing dendrite propagation through the dense garnet solid electrolyte layer. Additionally, high lithium stripping capacity and impressive cycling stability were observed at commercial level current densities of well over 10 mA/cm2. The role of the porous MIEC garnet structure is elucidated using various electrochemical and electron microscopy techniques. Wang, C. et al. Garnet-Type Solid-State Electrolytes: Materials, Interfaces, and Batteries. Chem. Rev. 120, 4257–4300 (2020).Albertus, P., Babinec, S., Litzelman, S. & Newman, A. Status and challenges in enabling the lithium metal electrode for high-energy and low-cost rechargeable batteries. Nat. Energy 2017 31 3, 16–21 (2017).

Rapid Li compensation toward highly conductive solid state electrolyte film

Garnet type solid-state electrolytes (SSEs) possess high stability against Li metal, intrinsic safety, and wide electrochemical window. To achieve the all-solid-state batteries (ASSBs) with high gravimetric/volumetric energy density and high power density, flat thin garnet SSEs with a high ionic conductivity of > 10−4 S/cm are required. However, the current fabrication processes are challengeable to maintain both the high ionic conductivity and the flat skeleton due to the severe Li loss during processing and the fragile nature of thin films. Herein, we introduce a rapid Li compensation (RLC) technique that combines the ultra-fast high-temperature sintering (UHS) technique with the tape casting process to produce highly ionic conductive, flat garnet SSE thin films. The freestanding Li6.4La3Zr1.4Ta0.6O12 (LLZTO) thin film with a thickness of 40 µm, fabricated using this technique, displays a surface roughness of 5 µm and a relative density of 95%. After a 10-seconds Li compensation, the compensated LLZTO film displays an ionic conductivity of 4.3 × 10−4 S/cm, 2 times higher than the non-compensated one. As a proof of concept, this RLC technique proposes a new strategy for the fabrication of high-performance ceramic thin films and also lays a solid foundation for the application of ASSBs.

Robust and Intimate Interface Enabled by Silicon Carbide as an Additive to Anodes for Lithium Metal Solid-State Batteries.

Garnet-type solid-state electrolytes are among the most reassuring candidates for the development of solid-state lithium metal batteries (SSLMB) because of their wide electrochemical stability window and chemical feasibility with lithium. However, issues such as poor physical contact with Li metal tend to limit their practical applications. These problems were addressed using β-SiC as an additive to the Li anode, resulting in improved wettability over Li6.75 La3 Zr1.75 Ta0.25 O12 (LLZTO) and establishing an improved interfacial contact. At the Li-SiC|LLZTO interface, intimacy was induced by a lithiophilic Li4 SiO4 phase, whereas robustness was attained through the hard SiC phase. The optimized Li-SiC|LLZTO|Li-SiC symmetric cell displayed a low interfacial impedance of 10 Ω cm2 and superior cycling stability at varying current densities up to 5800 h. Moreover, the modified interface could achieve a high critical current density of 4.6 mA cm-2 at room temperature and cycling stability of 1000 h at 3.5 mA cm-2 . The use of mechanically superior materials such as SiC as additives for the preparation of a composite anode may serve as a new strategy for robust garnet-based SSLMB.

In situ construction of a multifunctional interlayer for garnet-type electrolytes to suppress lithium dendrite formation in solid-state lithium batteries

Garnet-type solid-state electrolytes (SSEs) have great potential to be applied in all-solid-state lithium batteries (ASSLBs) due to their high ionic conductivity and excellent electrochemical stability with Li metal. However, the poor interface contact and the high electronic conductivity issues resulting in lithium dendrites growth remain challenging. Herein, we constructed a multifunctional interlayer LiF/Li-Ag alloy (LFA) in situ on the surface of garnet-type Li6.5La3Zr1.5Ta0.5O12 (LLZTO) to suppress Li dendrite growth. The matrix of the interlayer is a three-dimensional porous structure LiF and it is filled with Li-Ag alloy. The LiF blocks electron access to the LLZTO and the Li-Ag alloy ensures a good interface contact during cycling. The Li/LFA-LLZTO/Li symmetrical cells exhibit an ultralow interfacial resistance of 1.8 Ω cm2, a high critical current density of 1.1 mA cm−2 and outstanding galvanostatic cycling stability at 0.2 mA cm−2 for 2000 h. Moreover, the LiFePO4/LFA -LLZTO/Li full cell delivers a high discharge capacity of 155 mAh g−1 at 0.1 C with a capacity retention of 93% after 100 cycles.

Constructing a Superlithiophilic 3D Burr-Microsphere Interface on Garnet for High-Rate and Ultra-Stable Solid-State Li Batteries.

Garnet-type solid-state electrolyte (SSE) Li6.5 La3 Zr1.5 Ta0.5 O12 attracts great interest due to its high ion conductivity and wide electrochemical window. But the huge interfacial resistance, Li dendrite growth, and low critical current density (CCD) block the practical applications. Herein, a superlithiophilic 3D burr-microsphere (BM) interface layer composed of ionic conductor LiF-LaF3 is constructed in situ to achieve a high-rate and ultra-stable solid-state lithium metal battery. The 3D-BM interface layer with a large specific surface area shows a superlithiophilicity and its contact angle with molten Li is only 7° enabling the facile infiltration of molten Li. The assembled symmetrical cell reaches one of the highest CCD (2.7mA cm-2 ) at room temperature, an ultra-low interface impedance of 3 Ω cm2 , and a super-long cycling stability of 12000h at 0.1-1.5mA cm-2 without Li dendrite growth. The solid-state full cells with 3D-BM interface show outstanding cycling stability (LiFePO4 : 85.4%@900 cycles@1 C; LiNi0.8 Co0.1 Mn0.1 O2 :89%@200 cycles@0.5 C) and a high rate capacity (LiFePO4 :135.5mAh g-1 at 2 C). Moreover, the designed 3D-BM interface is quite stable after 90 days of storage in the air. This study offers a facile strategy to address the critical interface issues and accelerate the practical application of garnet-type SSE in high performance solid-state lithium metal batteries.

Spontaneous In Situ Formation of Lithium Metal Nitride in the Interface of Garnet-Type Solid-State Electrolyte by Tuning of Molten Lithium.

All-solid-state lithium-ion batteries (ASSLIBs) have attracted much attention owing to their high energy density and safety and are known as the most promising next-generation LIBs. The biggest advantage of ASSLIBs is that it can use lithium metal as the anode without any safety concerns. This study used a high-conductivity garnet-type solid electrolyte (Li6.75La3Zr1.75Ta0.25O12, LLZTO) and Li-Ga-N composite anode synthesized by mixing melted Li with GaN. The interfacial resistance was reduced from 589 to 21 Ω cm2, the symmetry cell was stably cycled for 1000 h at a current density of 0.1 mA cm-2 at room temperature, and the voltage range only changed from ±30 to ±40 mV. The full cell of Li-Ga-N|LLZTO|LFP exhibited a high first-cycle discharge capacity of 152.2 mAh g-1 and Coulombic efficiency of 96.5% and still maintained a discharge capacity retention of 91.2% after 100 cycles. This study also demonstrated that Li-Ga-N had been shown as two layers. Li3N shows more inclined to be closer to the LLZTO side. This method can help researchers understand what interface improvements can occur to enhance the performance of all-solid-state batteries in the future.

Accelerated Discovery of Novel Garnet-Type Solid-State Electrolyte Candidates via Machine Learning.

All-solid-state batteries (ASSBs) have attracted considerable attention because of their higher energy density and stability than conventional lithium-ion batteries (LIBs). For the development of promising ASSBs, solid-state electrolytes (SSEs) are essential to achieve structural integrity. Thus, in this study, a machine-learning-based surrogate model was developed to search for ideal garnet-type SSE candidates. The well-known Li7La3Zr2O12 structure was used as a base material, and 73 chemical elements were substituted on La and Zr sites, leading to 5329 potential structures. First, the elasticity database and machine learning descriptors were adopted from previous studies. Subsequently, the machine-learning-based surrogate model was applied to predict the elastic properties of potential SSE materials, followed by first-principles calculations for validation. Furthermore, the active learning process demonstrated that it can effectively decrease prediction uncertainty. Finally, the ionic conductivity of the mechanically superior materials was predicted to suggest optimal SSE candidates. Then, ab initio molecular dynamics simulations are followed for confirmation of diffusion behavior for materials classified as superionic; 10 new tetragonal-phase garnet SSEs are verified with superior mechanical and ionic conductivity properties. We believe that the current model and the constructed database will become a cornerstone for the development of next-generation SSE materials.

An advanced 3D gel cathode with continuous ion and electron transport pathway for solid-state lithium batteries

Ta-doped Li7La3Zr2O12 (LLZTO) is known as a garnet-type solid-state electrolyte with high ionic conductivity and good stability against lithium metal anode, which is regarded as one of the most promising electrolytes for the commercialization of solid-state batteries (SSBs). However, the poor electron and ion transport among cathode active material particles, as well as the large interfacial impedance between LLZTO ceramic pellet and cathode, remain major issues for SSBs. In this work, we proposed a novel 3D gel cathode based on the “cation-π” interaction between the organic cations in ionic liquid (IL) and the large electron-rich π-system in single-walled carbon nanotubes (SWNTs). The designed gel cathode, which is composed of SWNTs, IL and LiFePO4 (LFP) without binder, possesses a good wettability with the LLZTO ceramic pellet and affords highly efficient conductive pathways for electrons and ions through the interface and entire cathode. As a consequence, the assembled SSBs with the gel cathode exhibit excellent long-term cycling stability with a high capacity retention of 91.74% after 700 cycles at 0.5C, and a high coulombic efficiency close to 100% can be achieved over the course of cycling at 25 °C.