All-solid-state batteries (ASSBs) have attracted enormous attention as one of the critical future technologies for safe and high energy batteries. With the emergence of several highly conductive solid electrolytes in recent years, the bottleneck is no longer Li-ion diffusion within the electrolyte. Instead, many ASSBs are limited by their low Coulombic efficiency, poor power performance, and short cycling life due to the high resistance at the interfaces within ASSBs. Because of the diverse chemical/physical/mechanical properties of various solid components in ASSBs as well as the nature of solid-solid contact, many types of interfaces are present in ASSBs. These include loose physical contact, grain boundaries, and chemical and electrochemical reactions to name a few. All of these contribute to increasing resistance at the interface. Here, we present the distinctive features of the typical interfaces and interphases in ASSBs and summarize the recent work on identifying, probing, understanding, and engineering them. We highlight the complicated, but important, characteristics of interphases, namely the composition, distribution, and electronic and ionic properties of the cathode-electrolyte and electrolyte-anode interfaces; understanding these properties is the key to designing a stable interface. In addition, conformal coatings to prevent side reactions and their selection criteria are reviewed. We emphasize the significant role of the mechanical behavior of the interfaces as well as the mechanical properties of all ASSB components, especially when the soft Li metal anode is used under constant stack pressure. Finally, we provide full-scale (energy, spatial, and temporal) characterization methods to explore, diagnose, and understand the dynamic and buried interfaces and interphases. Thorough and in-depth understanding on the complex interfaces and interphases is essential to make a practical high-energy ASSB.

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Interfaces and Interphases in All-Solid-State Batteries with Inorganic Solid Electrolytes.

Solid state electrolyte systems boasting Li+ conductivity of >10 mS cm−1 at room temperature have opened the potential for developing a solid state battery with power and energy densities that are competitive with conventional liquid electrolyte systems. The primary focus of this review is twofold. First, differences in Li penetration resistance in solid state systems are discussed, and kinetic limitations of the solid state interface are highlighted. Second, technological challenges associated with processing such systems in relevant form factors are elucidated, and architectures needed for cell level devices in the context of product development are reviewed. Specific research vectors that provide high value to advancing solid state batteries are outlined and discussed.

Review—Practical Challenges Hindering the Development of Solid State Li Ion Batteries

DOI: 10.1002/aenm.202002689 lightweight, and compact and allow for versatile device geometries. They must also be scalable and offer high energy density to provide improved packing efficiency and longer device operation. Although both Ni–MH batteries and LIBs have been commercialized since the 1990s,[1] LIBs possess twice the gravimetric/volumetric energy density (250 Wh kg−1/700 Wh L−1 vs 170 Wh kg−1/350 Wh L−1),[2] higher battery voltage (3.7 V vs 1.2 V), and longer cycle life with lower self-discharge,[3] contributing tremendously to the proliferation of portable electronic devices (e.g., mobile phones, laptops, cameras, tablets) as well as emerging new technologies such as wearable electronic devices (e.g., smart watches and sport-related tracking devices). Their high gravimetric/ volumetric energy density,[2] excellent cycle life (thousands of cycles), and lack of the memory effect have positioned LIBs as state-of-the-art power sources and one of the greatest successes of modern electrochemistry, revolutionizing the way we acquire, process, transmit, and share information globally. Nevertheless, advances in battery energy density, safety, costs, and flexibility in shape and size are still needed to keep up with the rapidly growing demand for devices with even longer runtime as well as real-time data collection and transmission capabilities in addition to increasingly energy-demanding applications such as electric vehicles (EVs) and electricity grid storage. Even though LIBs were first commercialized in all electric vehicles (EVs) in 2010 and also emerged for grid application in the same time frame, the low energy density (≈250 Wh kg−1) and high average cost (≈$156 kWh−1 in 2019) of conventional LIBs do not meet the requirements for advanced EVs and grid-scale energy storage.[4–6] Specifically, the driving range per charge (miles), which is related to the energy density of each cell, and the cost are important parameters for EVs. For example, one 85 kWh battery pack in a Tesla Model S requires 7104 LIB cells, with an energy density of 265 Wh kg−1, providing an average range of 250 miles, which is ahead of the range of other EVs but still behind the target of 375 miles.[4] In grid-scale applications, LIBs can be used for various tasks: frequency regulation, peak shaving, load leveling, and large-scale integration of renewable energies, with specific properties generally required for each task. For frequency regulation, LIBs need to provide a fast response, high rate performance, and high-power capability, The introduction of new, safe, and reliable solid-electrolyte chemistries and technologies can potentially overcome the challenges facing their liquid counterparts while widening the breadth of possible applications. Through tech-historic evolution and rationally analyzing the transition from liquidbased Li-ion batteries (LIBs) to all-solid-state Li-metal batteries (ASSLBs), a roadmap for the development of a successful oxide and sulfide-based ASSLB focusing on interfacial challenges is introduced, while accounting for five parameters: energy density, power density, longterm stability, processing, and safety. First taking a strategic approach, this review dismantles the ASSLB into its three major components and discusses the most promising solid electrolytes and their most advantageous pairing options with oxide cathode materials and the Li metal anode. A thorough analysis of the chemical, electrochemical, and mechanical properties of the two most promising and investigated classes of inorganic solid electrolytes, namely oxides and sulfides, is presented. Next, the overriding challenges associated with the pairing of the solid electrolyte with oxide-based cathodes and a Li-metal anode, leading to limited performance for solid-state batteries are extensively addressed and possible strategies to mitigate these issues are presented. Finally, future perspectives, guidelines, and selective interface engineering strategies toward the resolution of these challenges are analyzed and discussed.

Solid-State Li–Metal Batteries: Challenges and Horizons of Oxide and Sulfide Solid Electrolytes and Their Interfaces

All-solid-state Li batteries (ASSBs) employing inorganic solid electrolytes offer improved safety and are exciting candidates for next-generation energy storage. Herein, we report a family of lithium mixed-metal chlorospinels, Li2InxSc0.666−xCl4 (0 ≤ x ≤ 0.666), with high ionic conductivity (up to 2.0 mS cm−1) owing to a highly disordered Li-ion distribution, and low electronic conductivity (4.7 × 10−10 S cm−1), which are implemented for high-performance ASSBs. Owing to the excellent interfacial stability of the SE against uncoated high-voltage cathode materials, ASSBs utilizing LiCoO2 or LiNi0.85Co0.1Mn0.05O2 exhibit superior rate capability and long-term cycling (up to 4.8 V versus Li+/Li) compared to state-of-the-art ASSBs. In particular, the ASSB with LiNi0.85Co0.1Mn0.05O2 exhibits a long life of >3,000 cycles with 80% capacity retention at room temperature. High cathode loadings are also demonstrated in ASSBs with stable capacity retention of >4 mAh cm−2 (~190 mAh g−1). Intensive research is underway to develop solid-state electrolytes for rechargeable batteries. Here the authors report a family of mixed-metal halospinel electrolytes that exhibits promising properties for high-performance solid-state batteries. 

High areal capacity, long cycle life 4 V ceramic all-solid-state Li-ion batteries enabled by chloride solid electrolytes

Large-scale industrial application of all-solid-state-batteries (ASSBs) is currently hindered by numerous problems. Regarding thiophosphate-based ASSBs, interfacial reactions with the solid electro...

The Working Principle of a Li2CO3/LiNbO3 Coating on NCM for Thiophosphate-Based All-Solid-State Batteries

Measures to improve the cycling performance and stability of bulk-type all-solid-state batteries (SSBs) are currently being developed with the goal of substituting conventional lithium-ion battery ...

Rational Design of Quasi-Zero-Strain NCM Cathode Materials for Minimizing Volume Change Effects in All-Solid-State Batteries


 Enabling simple three-electrode (3E) setups for solid-state battery cells is important for allowing investigation of individual electrodes to shed more light on interface charge transfer and reactions occurring in solid-state battery cells. Two different 3E setups are compared, and their practical value is evaluated. A miniaturized reference electrode (μ-RE) is developed from lithium-plated gold wires with a tungsten core providing a stable potential. Cells with Li6PS5Cl as solid electrolyte, Li1-xNi0.85Co0.10Mn0.05O2 (NCM851005) as cathode active material, and Li4Ti5O12/Li7Ti5O12 (LTO) or In/InLi as anode are investigated. The reference electrode provides a stable potential of 0 V vs. Li+/Li, hence allowing the precise measurement of single electrode potentials. The setup leaves the usual cell geometry essentially unchanged and causes only minor additional work during cell assembly, allowing widespread application. Evidence is provided that 3E setups are needed to evaluate the rate capability of active materials correctly and that two-electrode setups can massively underestimate the rate capability of electrodes. The impedance of full cells is systematically analyzed based on separate anode and cathode impedances.

https://iopscience.iop.org/article/10.1149/1945-7111/accb6f/pdf

Miniaturization of Reference Electrodes for Solid-State Lithium-Ion Batteries

Sulfide-based electrolytes and Ni-rich cathode materials (i.e., LiNixCoyMn1–x–yO2, x ≥ 0.8) are considered as promising materials for high-performance solid-state batteries. However, their poor chemical compatibility causes stability issues and fast capacity fading, particularly at high potentials. Here, we propose a coating concept inspired by the natural cathode–electrolyte interphase (CEI) formation to overcome the degradation at the solid electrolyte–cathode active material interface. An artificial CEI (coating) is derived from sulfide-based electrolytes prior to cell assembly by a dry-coating approach combined with a heat treatment. A proof-of-concept using Li3PS4 and Li6PS5Cl as precursors confirms the interfacial stability. Accordingly, the Li6PS5Cl-derived coating enables a capacity retention of 84% after 100 cycles (2.6–4.5 V vs Li+/Li). Overall, this work emphasizes the suitability and the (as yet unexploited) great potential of this coating concept to suppress interfacial degradation in sulfide-based composite cathodes. 

Formation of an Artificial Cathode–Electrolyte Interphase to Suppress Interfacial Degradation of Ni-Rich Cathode Active Material with Sulfide Electrolytes for Solid-State Batteries

Jonas Hertle

Papers

The Working Principle of a Li2CO3/LiNbO3 Coating on NCM for Thiophosphate-Based All-Solid-State Batteries

Rational Design of Quasi-Zero-Strain NCM Cathode Materials for Minimizing Volume Change Effects in All-Solid-State Batteries

Miniaturization of Reference Electrodes for Solid-State Lithium-Ion Batteries

Formation of an Artificial Cathode–Electrolyte Interphase to Suppress Interfacial Degradation of Ni-Rich Cathode Active Material with Sulfide Electrolytes for Solid-State Batteries