Review on solid electrolytes for all-solid-state lithium-ion batteries

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.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/aenm.201800933

Sulfide Solid Electrolytes for Lithium Battery Applications

By breaking through the energy density limits step-by-step, the use of lithium cobalt oxide-based Li-ion batteries (LCO-based LIBs) has led to the unprecedented success of consumer electronics over the past 27 years. Recently, strong demands for the quick renewal of the properties of electronic products every so often have resulted in smarter, larger screened, more lightweight devices with longer standby times that have pushed the energy density of LCO-based LIBs nearly to their limit. As a result, with the aim of achieving a higher energy density and lifting the upper cut-off voltage of LCO above 4.45 V (vs. Li/Li+), the development of LCO-based all-solid-state lithium batteries (ASSLBs) with a Li metal anode and LCO-based full cells with high-performance anodes have become urgent scientific and technological requirements. This review summarizes the key challenges of synthesizing LCO-based LBs with a higher energy density from the perspectives of structure and interface stability, and gives an account of effective modification strategies in view of the electrodes, liquid electrolytes, binders, separators, solid electrolytes and LCO-based full cells. The improvement mechanisms of these modification strategies and the controversy over them are also analyzed critically. Moreover, some perspectives regarding the remaining challenges for LCO-based LBs towards a higher energy density and possible future research focuses are also presented.

Reviving lithium cobalt oxide-based lithium secondary batteries-toward a higher energy density

Sulfide solid electrolytes for all-solid-state lithium batteries: Structure, conductivity, stability and application

Oxygen substitution effects in Li10GeP2S12 solid electrolyte

Composite Sulfur Electrode Prepared by High-Temperature Mechanical Milling for use in an All-Solid-State Lithium–Sulfur Battery with a Li3.25Ge0.25P0.75S4 Electrolyte

Composite sulfur electrodes are prepared by prolonged mechanical milling (;300min) for use in all-solid-state lithium-sulfur batteries, and their structure and electrochemical properties are investigated. These batteries exhibit a high initial discharge capacity (>1500mAhg−1). Sulfur, acetylene black, and the solid electrolyte Li3.25Ge0.25P0.75S4 are mixed by planetary ball milling to form composites that contain amorphous phases of the starting materials, as well as a byproduct with a novel structural unit arising from the reaction between sulfur and the solid electrolyte. Batteries with a composite electrode/Li3.25Ge0.25P0.75S4/Li–In anode configuration exhibit a high initial discharge capacity (>1100mAhg−1). However, the capacity fades during cycling (~500mAhg−1 at the 30th cycle), possibly because of the increased resistance of the composite. Structural and compositional changes of the byproduct and the solid electrolyte itself during the battery reaction could contribute to the increase in resistance that cause the deterioration of cyclability. © The Electrochemical Society of Japan, All rights reserved.

Composite Sulfur Electrode for All-solid-state Lithium–sulfur Battery with Li2S–GeS2–P2S5-based Thio-LISICON Solid Electrolyte

Amorphous Li3PS4 films were synthesized by pulsed laser deposition (PLD) at room temperature using Li3PS4 targets with excess lithium and sulfur. Raman and X-ray photoemission spectroscopies indicated that the Li3PS4 film synthesized with a stoichiometric amount of Li3PS4 target contained lithium-deficient phases such as Li4P2S6, Li2−xS and sulfur due to composition deviation caused during the ablation process. The film synthesized with a 14% Li2S-excess target (Li3.42PS4.21) contained fewer impurities, and exhibited a higher ionic conductivity of 5.3 × 10−4 S/cm at 298 K than the lithium-deficient film (3.1 × 10−4 S/cm). The target composition is an important factor for the fabrication of highly conductive Li3PS4 films for electrolytes in thin-film batteries.

Effect of Excess Li2S on Electrochemical Properties of Amorphous Li3PS4 Films Synthesized by Pulsed Laser Deposition

Local crystalline structures of LiCoO2 nanothin film cathodes in a lithium ion battery have been spectroscopically elucidated through confocal Raman imaging analysis at high spatial resolution of several hundred nanometers. A significant difference in the crystalline structure is found between the nanometric thin films and bulk powders. Thermally induced local decomposition of LiCoO2 into an impurity phase on the films has also been revealed along with the mechanism of the temperature-triggered decomposition process. Moreover, frequency-based Raman imaging enables us to locally probe spatial separation between stoichiometric (LiCoO2) and non-stoichiometric (Li1-xCoO2, 0 < x < 1) crystal phases on the thin films. Such local crystalline analysis is a promising approach to provide new insights into the degradation mechanism of lithium-ion batteries, which would result in improving the performance of thin film-based lithium ion batteries.

https://www.jstage.jst.go.jp/article/analsci/33/7/33_853/_pdf

Kosuke Hara

Papers

Oxygen substitution effects in Li10GeP2S12 solid electrolyte

Composite Sulfur Electrode Prepared by High-Temperature Mechanical Milling for use in an All-Solid-State Lithium–Sulfur Battery with a Li3.25Ge0.25P0.75S4 Electrolyte

Composite Sulfur Electrode for All-solid-state Lithium–sulfur Battery with Li2S–GeS2–P2S5-based Thio-LISICON Solid Electrolyte

Effect of Excess Li2S on Electrochemical Properties of Amorphous Li3PS4 Films Synthesized by Pulsed Laser Deposition

Raman Imaging Analysis of Local Crystal Structures in LiCoO 2 Thin Films Calcined at Different Temperatures