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Open Access Publications from the University of California

Scholarly Works (9 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2020)

Solid-state batteries (SSBs) are considered to be the next-generation energy storage devices. By replacing the flammable organic liquid electrolyte in conventional Li-ion batteries (LIBs) with an inorganic solid-state electrolyte (SSE), SSBs hold the promise to offer increased energy density, power density and safety compared with LIBs. However, two critical bottlenecks remain in the development of SSBs towards commercialization: the development of SSEs with ionic conductivities rivaling those of conventional liquid electrolytes, and the stabilization of interfaces between SSB components, including the active material, SSE and conductive additives.

Over the past sixty years, extensive experimental efforts have been devoted to the search of solid materials with high ionic conductivities at room temperature, which have led to discoveries of numerous classes of superionic conductors (SICs) that were employed as SSEs in solid-state batteries. For interface stabilization, the use of coating has been demonstrated to be an effective strategy in mitigating parasitic interface reactions in SSBs. Despite these advances, the low throughput of experimental trial-and-error approaches has bottlenecked the speed of new materials discovery for SSB development. On the other hand, thanks to the recent advances in first-principles calculations, the ability to accurately compute material properties in silico combined with large material databases has provided a computational approach to high-throughput screening of materials with the target functionality, revolutionizing the material discovery process.

In this dissertation, I focus on leveraging first-principles techniques based on density functional theory (DFT) to search for new SSEs and coating materials for SSB applications. Chapter 1 introduces the concept of solid-state batteries and recent advances in the studies of SSEs and interface stability. Chapter 2 is devoted to a computational search for lithium oxide SICs for SSE development. In this chapter, I first revisited the ion-conduction mechanisms in lithium garnet and NASICON (sodium superionic conductor) structures, the two most used oxide SSEs, based on their Li diffusion networks. Three network features that are beneficial for superionic conduction were identified, i.e., a 3D ion diffusion network, short distances between occupied Li sites, and “homogenous local environments.” Then, I performed a high-throughput screening to identify new lithium oxide conductors with these beneficial features. At the end of this search, I proposed 7 candidates as promising lithium oxide SICs with room-temperature ionic conductivity of ~0.1 mS/cm or higher predicted by first-principles calculations. Furthermore, several new structural frameworks emerged, including spinel, oxy-argyrodite, sodalite, and LixM(SeO3)2, opening up exciting opportunities for lithium oxide SSE development.

Chapter 3 employs a computational framework to evaluate and screen materials for cathode coatings in SSBs, focusing on their phase stability, electrochemical and chemical stability, and ionic conductivity. From this tiered screening, polyanionic oxide coatings were identified to exhibit optimal properties, with LiH2PO4, LiTi2(PO4)3, and LiPO3 being particularly appealing candidates. Some lithium borates exhibiting excellent (electro)chemical stability at various interfaces were also highlighted. These results demonstrated the promise of using optimized polyanionic materials as cathode coatings for SSBs.

Finally, Chapter 4 summarizes the main findings of the dissertation and provides an outlook for the future directions of SSB development.

    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2022)
    Superionic lithium conductivity has only been discovered in a few classes of materials, mostly found in thiophosphates and rarely in oxides. Herein, we reveal that corner-sharing connectivity of the oxide crystal structure framework promotes superionic conductivity, which we rationalize from the distorted lithium environment and reduced interaction between lithium and non-lithium cations. By performing a high-throughput search for materials with this feature, we discover ten new oxide frameworks predicted to exhibit superionic conductivity-from which we experimentally demonstrate LiGa(SeO3)2 with a bulk ionic conductivity of 0.11 mS cm-1 and an activation energy of 0.17 eV. Our findings provide insight into the factors that govern fast lithium mobility in oxide materials and will accelerate the development of new oxide electrolytes for all-solid-state batteries.
      Cover page: Lithium superionic conductors with corner-sharing frameworks.Creative Commons 'BY-NC' version 4.0 license
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2019)
      Solid-state batteries are on the roadmap for commercialization as the next generation of batteries because of their potential for improved safety, power density, and energy density compared with conventional Li-ion batteries. However, the interfacial reactivity and resulting resistance between the cathode and solid-state electrolyte (SSE) lead to deterioration of cell performance. Although reduction of the cathode/SSE interfacial impedance can be achieved using cathode coatings, optimizing their compositions remains a challenge. In this work, we employ a computational framework to evaluate and screen Li-containing materials as cathode coatings, focusing on their phase stability, electrochemical and chemical stability, and ionic conductivity. From this tiered screening, polyanionic oxide coatings were identified as exhibiting optimal properties, with LiH2PO4, LiTi2(PO4)3, and LiPO3 being particularly appealing candidates. Some lithium borates exhibiting excellent (electro)chemical stability at various interfaces are also highlighted. These results highlight the promise of using optimized polyanionic materials as cathode coatings for solid-state batteries. The flammability of organic liquid electrolytes in Li-ion batteries is a serious safety risk. Solid-state batteries (SSBs) replace the liquid with an inorganic solid, dramatically improving the safety. Unfortunately, solid-solid contacts at the cathode/electrolyte interface are often unstable, leading to high interfacial impedance that grows during operation. Buffering this interface with another layer effectively improves stability; however, optimized buffer materials have not been found by previous research. This work develops and uses a computational framework to screen a wide range of chemistries for use as buffer layers between oxide cathodes and sulfide solid electrolytes and identifies the key factors such as Li content and oxygen bonding covalency that affect the stability of these materials. Many of these materials are polyanionic oxides that substantially outperform conventional oxide buffers. Our work provides guidance for material selection for the next-generation SSBs. Solid-state batteries are considered the next generation of batteries, but they still suffer from high interfacial resistance. One strategy to mitigate the problem is to use coating. We performed a computational screening to find promising cathode coating compositions. Polyanionic oxides are highlighted for good overall characteristics, and LiH2PO4, LiTi2(PO4)3, and LiPO3 are particularly appealing candidates. Furthermore, factors including oxygen bond covalency and Li content are identified to affect oxidation stability of polyanionic oxide coatings.
        Cover page: Computational Screening of Cathode Coatings for Solid-State Batteries
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2020)
        Solid-state batteries (SSBs) using a solid electrolyte show potential for providing improved safety as well as higher energy and power density compared with conventional Li-ion batteries. However, two critical bottlenecks remain: the development of solid electrolytes with ionic conductivities comparable to or higher than those of conventional liquid electrolytes and the creation of stable interfaces between SSB components, including the active material, solid electrolyte and conductive additives. Although the first goal has been achieved in several solid ionic conductors, the high impedance at various solid/solid interfaces remains a challenge. Recently, computational models based on ab initio calculations have successfully predicted the stability of solid electrolytes in various systems. In addition, a large amount of experimental data has been accumulated for different interfaces in SSBs. In this Review, we summarize the experimental findings for various classes of solid electrolytes and relate them to computational predictions, with the aim of providing a deeper understanding of the interfacial reactions and insight for the future design and engineering of interfaces in SSBs. We find that, in general, the electrochemical stability and interfacial reaction products can be captured with a small set of chemical and physical principles.
          Cover page: Understanding interface stability in solid-state batteries
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2021)
          The key component in lithium solid-state batteries (SSBs) is the solid electrolyte composed of lithium superionic conductors (SICs). Lithium oxide SICs offer improved electrochemical and chemical stability compared with sulfides, and their recent advancements have largely been achieved using materials in the garnet- and NASICON (sodium superionic conductor)- structured families. In this work, using the ion-conduction mechanisms in garnet and NASICON as inspiration, a common pattern of an “activated diffusion network” and three structural features that are beneficial for superionic conduction: a 3D percolation Li diffusion network, short distances between occupied Li sites, and the “homogeneity” of the transport path are identified. A high-throughput computational screening is performed to search for new lithium oxide SICs that share these features. From this search, seven candidates are proposed exhibiting high room-temperature ionic conductivity evaluated using ab initio molecular dynamics simulations. Their structural frameworks including spinel, oxy-argyrodite, sodalite, and LiM(SeO3)2 present new opportunities for enriching the structural families of lithium oxide SICs.
            Cover page: Lithium Oxide Superionic Conductors Inspired by Garnet and NASICON Structures
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2021)
            An amendment to this paper has been published and can be accessed via a link at the top of the paper.
              Cover page: Publisher Correction: Understanding interface stability in solid-state batteries
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2020)
              Low active material loading in the composite electrode of all-solid-state batteries (SSBs) is one of the main reasons for the low energy density in current SSBs. In this work, it is demonstrated with both modeling and experiments that in the regime of high cathode loading, the utilization of cathode material in the solid-state composite is highly dependent on the particle size ratio of the cathode to the solid-state conductor. The modeling, confirmed by experimental data, shows that higher cathode loading and therefore an increased energy density can be achieved by increasing the ratio of the cathode to conductor particle size. These results are consistent with ionic percolation being the limiting factor in cold-pressed solid-state cathode materials and provide specific guidelines on how to improve the energy density of composite cathodes for solid-state batteries. By reducing solid electrolyte particle size and increasing the cathode active material particle size, over 50 vol% cathode active material loading with high cathode utilization is able to be experimentally achieved, demonstrating that a commercially-relevant, energy-dense cathode composite is achievable through simple mixing and pressing method.
                Cover page: High Active Material Loading in All‐Solid‐State Battery Electrode via Particle Size Optimization
                • Article
                • Peer Reviewed
                UC Berkeley Previously Published Works (2020)
                The interfacial instability between a thiophosphate solid electrolyte and oxide cathodes results in rapid capacity fade and has driven the need for cathode coatings. In this work, the stability, evolution, and performance of uncoated, Li2ZrO3-coated, and Li3B11O18-coated LiNi0.5Co0.2Mn0.3O2 cathodes are compared using first-principles computations and electron microscopy characterization. Li3B11O18 is identified as a superior coating that exhibits excellent oxidation/chemical stability, leading to substantially improved performance over cells with Li2ZrO3-coated or uncoated cathodes. The chemical and structural origin of the different performance is interpreted using different microscopy techniques which enable the direct observation of the phase decomposition of the Li2ZrO3 coating. It is observed that Li is already extracted from the Li2ZrO3 in the first charge, leading to the formation of ZrO2 nanocrystallites with loss of protection of the cathode. After 50 cycles separated (Co, Ni)-sulfides and Mn-sulfides can be observed within the Li2ZrO3-coated material. This work illustrates the severity of the interfacial reactions between a thiophosphate electrolyte and oxide cathode and shows the importance of using coating materials that are absolutely stable at high voltage.
                  Cover page: Direct Visualization of the Interfacial Degradation of Cathode Coatings in Solid State Batteries: A Combined Experimental and Computational Study
                  • Article
                  • Peer Reviewed
                  UC Berkeley Previously Published Works (2019)
                  A key requirement for achieving high-energy density in solid-state batteries is highly efficient cycling of an alkali metal anode in a safe manner. Herein, we combine first-principles calculations and experimental characterizations to identify a protective hydrate coating for Na3SbS4 that leads to a passivating interface and greatly enhanced stability. The buried interface is characterized using post-operando synchrotron X-ray depth profiling. This finding identifies hydrates as promising for improving the metal/electrolyte interfacial stability and suggests a general strategy for interface design.
                    Cover page: Reactivity-Guided Interface Design in Na Metal Solid-State Batteries
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