Effect of Processing Conditions of 75Li2S-25P2S5 Solid Electrolyte on its DC Electrochemical Behavior

Effect of solid-electrolyte pellet density on failure of solid-state batteries

Despite the potentially higher energy density and improved safety of solid-state batteries (SSBs) relative to Li-ion batteries, failure due to Li-filament penetration of the solid electrolyte and subsequent short circuit remains a critical issue. Herein, we show that Li-filament growth is suppressed in solid-electrolyte pellets with a relative density beyond ~95%. Below this threshold value, however, the battery shorts more easily as the density increases due to faster Li-filament growth within the percolating pores in the pellet. The microstructural properties (e.g., pore size, connectivity, porosity, and tortuosity) of [Formula: see text] with various relative densities are quantified using focused ion beam-scanning electron microscopy tomography and permeability tests. Furthermore, modeling results provide details on the Li-filament growth inside pores ranging from 0.2 to 2 μm in size. Our findings improve the understanding of the failure modes of SSBs and provide guidelines for the design of dendrite-free SSBs.

Insight into Dendrites Issue in All Solid-State Batteries with Inorganic Electrolyte: Mechanism, Detection and Suppression Strategies

All solid-state batteries (ASSBs) are regarded as one of the promising next-generation energy storage devices due to their expected high energy density and capacity. However, failures due to unrestricted growth of lithium dendrites (LDs) have been a critical problem. Moreover, the understanding of dendrite growth inside solid-state electrolytes is limited. Since the dendrite process is a multi-physical field coupled process, including electrical, chemical, and mechanical factors, no definitive conclusion can summarize the root cause of LDs growth in ASSBs till now. Herein, the existing works on mechanism, identification, and solution strategies of LD in ASSBs with inorganic electrolyte are reviewed in detail. The primary triggers are thought to originate mainly at the interface and within the electrolyte, involving mechanical imperfections, inhomogeneous ion transport, inhomogeneous electronic structure, and poor interfacial contact. Finally, some of the representative works and present an outlook are comprehensively summarized, providing a basis and guidance for further research to realize efficient ASSBs for practical applications.

Disentangling Phase and Morphological Evolution During the Formation of the Lithium Superionic Conductor Li10 GeP2 S12

The structural and morphological changes of the Lithium superionic conductor Li₁₀ GeP₂ S₁₂ , prepared via a widely used ball milling-heating method over a comprehensive heat treatment range (50 - 700 °C), are investigated. Based on the phase composition, the formation process can be distinctly separated into four zones: Educt, Intermediary, Formation, and Decomposition zone. It is found that instead of Li₄ GeS₄ -Li₃ PS₄ binary crystallization process, diversified intermediate phases, including GeS₂ in different space groups, multiphasic lithium phosphosulfides (Li_x P_y S_z ), and cubic Li₇ Ge₃ PS₁₂ phase, are involved additionally during the formation and decomposition of Li₁₀ GeP₂ S₁₂ . Furthermore, the phase composition at temperatures around the transition temperatures of different formation zones shows a significant deviation. At 600 °C, Li₁₀ GeP₂ S₁₂ is fully crystalline, while the sample decomposed to complex phases at 650 °C with 30 wt.% impurities, including 20 wt.% amorphous phases. These findings over such a wide temperature range are first reported and may help provide previously lacking insights into the formation and crystallinity control of Li₁₀ GeP₂ S₁₂ .

Long-Life Lithium-Metal All-Solid-State Batteries and Stable Li Plating Enabled by In Situ Formation of Li3 PS4 in the SEI Layer

An ultrastable and kinetically favorable interface is constructed between sulfide-poly(ethylene oxide) (PEO) composite solid electrolytes (CSEs) and lithium metal, via in situ formation of a solid electrolyte interphase (SEI) layer containing Li₃ PS₄ . A specially designed sulfide, lithium polysulfidophosphate (LPS), can distribute uniformly in the PEO matrix via a simple stirring process because of its complete solubility in acetonitrile solvent, which is advantageous for creating a homogeneous SEI layer. The CSE/Li interface with high Li⁺ transportation capability is stabilized quickly through in situ formation of a Li₃ PS₄ /Li₂ S/LiF layer via the reaction between LPS and lithium metal to inhibit lithium dendrite growth. A Li/Li symmetric cell with the LPS-integrated CSE exhibits constant and small CSE/Li resistance of 10 Ω cm²  during cycling, delivering stable cycling for 3475 h at a current density of 0.2 mA cm^-2  and a high critical current density of 0.9 mA cm^-2  at 60 °C. Impressive electrochemical performance is also demonstrated for LiFePO₄ /CSE/Li all-solid-state batteries with capacity of 127.6 mAh g^-1  after 1000 cycles at 1 C.

Review on Interface and Interphase Issues in Sulfide Solid-State Electrolytes for All-Solid-State Li-Metal Batteries

All-solid-state batteries have emerged as promising alternatives to conventional Li-ion batteries owing to their higher energy density and safety, which stem from their use of inorganic solid-state electrolytes instead of flammable organic liquid electrolytes. Among various candidates, sulfide solid-state electrolytes are particularly promising for the development of high-energy all-solid-state Li metal batteries because of their high ionic conductivity and deformability. However, a significant challenge remains as their inherent instability in contact with electrodes forms unstable interfaces and interphases, leading to degradation of the battery performance. In this review article, we provide an overview of the key issues for the interfaces and interphases of sulfide solid-state electrolyte systems as well as recent progress in understanding such interface and interphase formation and potential solutions to stabilize them. In addition, we provide perspectives on future research directions in this field.

Lithium/Sulfide All-Solid-State Batteries using Sulfide Electrolytes

All-solid-state lithium batteries (ASSLBs) are considered as the next generation electrochemical energy storage devices because of their high safety and energy density, simple packaging, and wide operable temperature range. The critical component in ASSLBs is the solid-state electrolyte. Among all solid-state electrolytes, the sulfide electrolytes have the highest ionic conductivity and favorable interface compatibility with sulfur-based cathodes. The ionic conductivity of sulfide electrolytes is comparable with or even higher than that of the commercial organic liquid electrolytes. However, several critical challenges for sulfide electrolytes still remain to be solved, including their narrow electrochemical stability window, the unstable interface between the electrolyte and the electrodes, as well as lithium dendrite formation in the electrolytes. Herein, the emerging sulfide electrolytes and preparation methods are reviewed. In particular, the required properties of the sulfide electrolytes, such as the electrochemical stabilities of the electrolytes and the compatible electrode/electrolyte interfaces are highlighted. The opportunities for sulfide-based ASSLBs are also discussed.

Promises and Challenges of Next-Generation "Beyond Li-ion" Batteries for Electric Vehicles and Grid Decarbonization

The tremendous improvement in performance and cost of lithium-ion batteries (LIBs) have made them the technology of choice for electrical energy storage. While established battery chemistries and cell architectures for Li-ion batteries achieve good power and energy density, LIBs are unlikely to meet all the performance, cost, and scaling targets required for energy storage, in particular, in large-scale applications such as electrified transportation and grids. The demand to further reduce cost and/or increase energy density, as well as the growing concern related to natural resource needs for Li-ion have accelerated the investigation of so-called "beyond Li-ion" technologies. In this review, we will discuss the recent achievements, challenges, and opportunities of four important "beyond Li-ion" technologies: Na-ion batteries, K-ion batteries, all-solid-state batteries, and multivalent batteries. The fundamental science behind the challenges, and potential solutions toward the goals of a low-cost and/or high-energy-density future, are discussed in detail for each technology. While it is unlikely that any given new technology will fully replace Li-ion in the near future, "beyond Li-ion" technologies should be thought of as opportunities for energy storage to grow into mid/large-scale applications.

Solid-State Electrolyte Design for Lithium Dendrite Suppression

All-solid-state Li metal batteries have attracted extensive attention due to their high safety and high energy density. However, Li dendrite growth in solid-state electrolytes (SSEs) still hinders their application. Current efforts mainly aim to reduce the interfacial resistance, neglecting the intrinsic dendrite-suppression capability of SSEs. Herein, the mechanism for the formation of Li dendrites is investigated, and Li-dendrite-free SSE criteria are reported. To achieve a high dendrite-suppression capability, SSEs should be thermodynamically stable with a high interface energy against Li, and they should have a low electronic conductivity and a high ionic conductivity. A cold-pressed Li₃ N-LiF composite is used to validate the Li-dendrite-free design criteria, where the highly ionic conductive Li₃ N reduces the Li plating/stripping overpotential, and LiF with high interface energy suppresses dendrites by enhancing the nucleation energy and suppressing the Li penetration into the SSEs. The Li₃ N-LiF layer coating on Li₃ PS₄ SSE achieves a record-high critical current of >6 mA cm^-2 even at a high capacity of 6.0 mAh cm^-2 . The Coulombic efficiency also reaches a record 99% in 150 cycles. The Li₃ N-LiF/Li₃ PS₄ SSE enables LiCoO₂ cathodes to achieve 101.6 mAh g^-1 for 50 cycles. The design principle opens a new opportunity to develop high-energy all-solid-state Li metal batteries.

New Concepts in Electrolytes

Over the past decades, Li-ion battery (LIB) has turned into one of the most important advances in the history of technology due to its extensive and in-depth impact on our life. Its omnipresence in all electric vehicles, consumer electronics and electric grids relies on the precisely tuned electrochemical dynamics and interactions among the electrolytes and the diversified anode and cathode chemistries therein. With consumers' demand for battery performance ever increasing, more and more stringent requirements are being imposed upon the established equilibria among these LIB components, and it became clear that the state-of-the-art electrolyte systems could no longer sustain the desired technological trajectory. Driven by such gap, researchers started to explore more unconventional electrolyte systems. From superconcentrated solvent-in-salt electrolytes to solid-state electrolytes, the current research realm of novel electrolyte systems has grown to unprecedented levels. In this review, we will avoid discussions on current state-of-the-art electrolytes but instead focus exclusively on unconventional electrolyte systems that represent new concepts.

Rapid and Tunable Assisted-Microwave Preparation of Glass and Glass-Ceramic Thiophosphate "Li7P3S11" Li-Ion Conductors

Glass and glass-ceramic samples of metastable lithium thiophosphates with compositions of 70Li₂S-30P₂S₅ and Li₇P₃S₁₁ were controllably prepared by using a rapid assisted-microwave procedure in under 30 min. The rapid preparation times and weak coupling of the evacuated silica ampules with microwave radiation ensure minimal reactivity of the reactants and the container. The microwave-prepared samples display comparable conductivity values with more conventionally prepared (melt quenched) glass and glass-ceramic samples, on the order of 0.1 and 1 mS cm^-1 at room temperature, respectively. Rietveld analysis of synchrotron X-ray diffraction data acquired with an internal standard quantitatively yields phase amounts of the glassy and amorphous components, establishing the tunable nature of the microwave preparation. X-ray photoelectron spectroscopy and Raman spectroscopy confirm the composition and the appropriate ratios of isolated and corner-sharing tetrahedra in these semicrystalline systems. Solid-state ⁷Li nuclear magnetic resonance (NMR) spectroscopy resolves the seven crystallographic Li sites in the crystalline compound into three main environments. The diffusion behavior of these Li environments as obtained from pulsed-field gradient NMR methods can be separated into one slow and one fast component. The rapid and tunable approach to the preparation of high quality "Li₇P₃S₁₁" samples presented here coupled with detailed structural and compositional analysis opens the door to new and promising metastable solid electrolytes.

Argyrodite Solid Electrolyte with a Stable Interface and Superior Dendrite Suppression Capability Realized by ZnO Co-Doping

Despite the high ionic conductivity and good machinability, the application of sulfide solid electrolytes (SEs) is severely limited by the poor compatibility of oxide cathodes with Li metals. Herein, a ZnO co-doping strategy is proposed to enhance the chemical and electrochemical performance of sulfide SEs. Given the synergistic effect by incorporation of ZnO, the argyrodite electrolyte achieves superior interfacial stability and Li dendrite suppression capability. By in-depth ex situ analyses, the enhancement is ascribed to LiZn and Li₃OBr formed in the argyrodite/Li interface and a reduced electronic conductivity arising from the ZnO doping. In addition, O doping improves the air stability for argyrodite without degrading the ionic conductivity because of the compensation by Zn doping. Hence, all-solid-state batteries with ZnO-doped electrolytes achieve higher initial Coulombic efficiency and a larger specific capacity than those of the ZnO-free electrolyte. ZnO-doped sulfide SEs are promising to develop all-solid-state Li-metal batteries.

The Discharge Mechanism for Solid-State Lithium-Sulfur Batteries

The electrochemical discharge mechanism is reported for all-solid lithium sulfur batteries. Upon milling with carbon fibers, the solid electrolyte used within the cathode composite becomes electrochemically active. Analysis with Raman spectroscopy and XPS revealed the importance of bridging S-S bond formation and breaking in lithium polysulfidophosphates during electrochemical lithiation of the active solid electrolyte. Remarkably, when sulfur is introduced as an active material in the cathode composite, lithium polysulfides are formed as an intermediate product before full lithiation into lithium sulfide. The synthesis of materials based on bridging S-S bonds is an important avenue to the design of new cathodes for allsolid batteries.

Fluorinated solid electrolyte interphase enables highly reversible solid-state Li metal battery

Solid-state electrolytes (SSEs) are receiving great interest because their high mechanical strength and transference number could potentially suppress Li dendrites and their high electrochemical stability allows the use of high-voltage cathodes, which enhances the energy density and safety of batteries. However, the much lower critical current density and easier Li dendrite propagation in SSEs than in nonaqueous liquid electrolytes hindered their possible applications. Herein, we successfully suppressed Li dendrite growth in SSEs by in situ forming an LiF-rich solid electrolyte interphase (SEI) between the SSEs and the Li metal. The LiF-rich SEI successfully suppresses the penetration of Li dendrites into SSEs, while the low electronic conductivity and the intrinsic electrochemical stability of LiF block side reactions between the SSEs and Li. The LiF-rich SEI enhances the room temperature critical current density of Li₃PS₄ to a record-high value of >2 mA cm^-2. Moreover, the Li plating/stripping Coulombic efficiency was escalated from 88% of pristine Li₃PS₄ to more than 98% for LiF-coated Li₃PS₄. In situ formation of electronic insulating LiF-rich SEI provides an effective way to prevent Li dendrites in the SSEs, constituting a substantial leap toward the practical applications of next-generation high-energy solid-state Li metal batteries.

Interface-Engineered Li7 La3 Zr2 O12 -Based Garnet Solid Electrolytes with Suppressed Li-Dendrite Formation and Enhanced Electrochemical Performance

High grain-boundary resistance, Li-dendrite formation, and electrode/Li interfacial resistance are three major issues facing garnet-based solid electrolytes. Herein, interfacial architecture engineering by incorporating 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (BMP-TFSI) ionic liquid into a garnet oxide is proposed. The "soft" continuous BMP-TFSI coating with no added Li salt generates a conducting network facilitating Li⁺ transport and thus changes the ion conduction mode from point contacts to face contacts. The compacted microstructure suppresses Li-dendrite growth and shows good interfacial compatibility and interfacial wettability toward Li metal. Along with a broad electrochemical window larger than 5.5 V and an Li⁺ transference number that practically reaches unity, LiNi_0.8 Co_0.1 Mn_0.1 O₂ /Li and LiFePO₄ /Li solid-state batteries with the hybrid solid electrolyte exhibit superior cycling stability and low polarization, comparable to those with commercial liquid electrolytes, and excellent rate capability that is better than those of Li-salt-based ionic-liquid electrolytes.