Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (9 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2023)

The escalating global demand for lithium-ion batteries (LiBs), fueled by their integral role in achieving a sustainable, low-carbon future, is juxtaposed against pressing concerns over the supply chain of the cathode component. As one of the most resource-intensive elements of LiBs, the common cathode is characterized by its constitution of cobalt, nickel, and lithium. The supply chains for these critical materials are under threat due to geopolitical tensions, ethical issues, and economic uncertainties, thereby posing substantial risks to the scalability and sustainability of LiBs, and consequently, our climate ambitions.

This doctoral dissertation delves into an exploration of analytical methodologies aimed at discerning the inefficiency mechanisms inherent in promising emerging cathode materials — specifically, cation-disordered rock-salt transition-metal oxides and oxyfluorides (DRX). These materials offer a potential alternative to conventional cathode materials, owing to their capability to achieve high energy densities and to accommodate cost-effective, diverse transition-metal chemistries. The research begins with an in-depth analysis of a nickel-based DRX cathode. With the employment of advanced techniques, including 18O isotopic enrichment, differential electrochemical mass spectrometry (DEMS), and ex situ acid titration, the study disentangles the complex electron transfer processes within DRX, specifically the overlapping redox processes of transition-metal (TM) and oxygen. Through the establishment of a novel titration design strategy, the research not only resolves but also quantifies the intermixed redox capacities, overcoming the challenges encountered with other techniques.

The research proceeds to develop a two-step aqueous redox titration process, leveraging mass spectrometry to decouple oxygen and TM redox, specifically Mn3+/4+, in a Li-Mn-Ti-O DRX (LMTO). This approach provides deeper insights into the relationship between these redox contributions and voltage hysteresis. It uncovers that the hysteresis in LMTO cathodematerials arises not only due to an intrinsic charge-discharge voltage mismatch associated with oxygen redox but also from asymmetric Mn-redox overvoltages.

Finally, the study investigates the often overlooked aspect of in situ carbon dioxide (CO2) outgassing from LMTO cathodes in LiBs, a phenomenon typically attributed to side reactions at the cathode-electrolyte interface. Using the 13C isotopic enrichment and DEMS, the research highlights the pivotal role of electron-conducting carbon additives in electrolytedegradation mechanisms. Furthermore, it elucidates the unusual bimodal CO2 evolution caused by the oxidation of carbon black in the LMTO cathode.

This dissertation, in its entirety, aims to contribute to the development of sustainable and high-performing cathode materials, ultimately striving to address the impending challenges of raw material supply for LiBs. By revealing pathways for improvement in performance and stability, the research advances our understanding of the potential of these DRX materials in their practical applications. This work therefore paves the way towards the continued adoption and evolution of LiBs in various industries, most prominently in electrifying transportation, as we progress towards a sustainable and low-carbon future.

    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2021)
    The reversibility of the redox processes plays a crucial role in the electrochemical performance of lithium-excess cation-disordered rocksalt (DRX) cathodes. Here, we report a comprehensive analysis of the redox reactions in a representative Ni-based DRX cathode. The aim of this work is to elucidate the roles of multiple cations and anions in the charge compensation mechanism that is ultimately linked to the electrochemical performance of Ni-based DRX cathode. The low-voltage reduction reaction results in the low energy efficiency and strong voltage hysteresis. Our data reveal that the Mo migration between octahedral and tetrahedral sites enhances the O reduction potential, thus offering a potential strategy to improve energy efficiency. This work highlights the important role that the high-valence transition metal plays in the redox chemistry and provides useful insights into the potential pathway to further address the challenges in Ni-based DRX systems.
      Cover page: Interplay between Cation and Anion Redox in Ni-Based Disordered Rocksalt Cathodes
      • Article
      • Peer Reviewed
      UC Santa Barbara Previously Published Works (2023)
      Lithium-excess, cation-disordered rocksalt (DRX) materials have been subject to intense scrutiny and development in recent years as potential cathode materials for Li-ion batteries. Despite their compositional flexibility and high initial capacity, they suffer from poorly understood parasitic degradation reactions at the cathode-electrolyte interface. These interfacial degradation reactions deteriorate both the DRX material and electrolyte, ultimately leading to capacity fade and voltage hysteresis during cycling. In this work, differential electrochemical mass spectrometry (DEMS) and titration mass spectrometry are combined to quantify the extent of bulk redox and surface degradation reactions for a set of Mn2+/4+-based DRX oxyfluorides during initial cycling with a high-voltage charging cutoff (4.8 V vs Li/Li+). Increasing the fluorine content from 7.5 to 33.75% is shown to diminish oxygen redox and suppresses high-voltage O2 evolution from the DRX surface. Additionally, electrolyte degradation processes resulting in the formation of both gaseous species and electrolyte-soluble protic species are observed. Subsequently, DEMS is paired with a fluoride-scavenging additive to demonstrate that increasing fluorine content leads to increased dissolution of fluorine from the DRX material into the electrolyte. Finally, a suite of ex situ spectroscopy techniques (X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectroscopy, and solid-state nuclear magnetic resonance spectroscopy) are employed to study the change in DRX composition during charging, revealing the dissolution of manganese and fluorine from the DRX material at high voltages. This work provides insight into the degradation processes occurring at the DRX-electrolyte interface and points toward potential routes of interfacial stabilization.
        Cover page: Tuning Bulk Redox and Altering Interfacial Reactivity in Highly Fluorinated Cation-Disordered Rocksalt CathodesCreative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2023)
        Pronounced voltage hysteresis in Li-excess cathode materials is commonly thought to be associated with oxygen redox. However, these materials often possess overlapping oxygen and transition-metal redox, whose contributions to hysteresis between charge and discharge are challenging to distinguish. In this work, a two-step aqueous redox titration is developed with the aid of mass spectrometry (MS) to quantify oxidized lattice oxygen and Mn3+ /4+ redox in a representative Li-excess cation-disordered rock salt—Li1.2Mn0.4Ti0.4O2 (LMTO). Two MS-countable gas molecules evolve from two separate titrant-analyte reactions, thereby allowing Mn and O redox capacities to be decoupled. The decoupled O and Mn redox coulombic efficiencies are close to 100% for the LMTO cathode, indicating high charge-compensation reversibility. As incremental Mn and O redox capacities are quantitatively decoupled, each redox voltage hysteresis is further evaluated. Overall, LMTO voltage hysteresis arises not only from an intrinsic charge-discharge voltage mismatch related to O redox, but also from asymmetric Mn-redox overvoltages. The results reveal that O and Mn redox both contribute substantially to voltage hysteresis. This work further shows the potential of designing new analytical workflows to experimentally quantify key properties, even in a disordered material having complex local coordination environments.
          Cover page: Quantitative Decoupling of Oxygen‐Redox and Manganese‐Redox Voltage Hysteresis in a Cation‐Disordered Rock Salt CathodeCreative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2023)
          Fast charging of most commercial lithium-ion batteries is limited due to fear of lithium plating on the graphite anode, which is difficult to detect and poses considerable safety risk. Here we demonstrate the power of simple, accessible and high-throughput cycling techniques to quantify irreversible Li plating spanning data from over 200 cells. We first observe the effects of energy density, charge rate, temperature and state of charge on lithium plating, use the results to refine a mature physics-based electrochemical model and provide an interpretable empirical equation for predicting the plating onset state of charge. We then explore the reversibility of lithium plating and its connection to electrolyte design for preventing irreversible Li accumulation. Finally, we design a method to quantify in situ Li plating for commercially relevant graphite|LiNi0.5Mn0.3Co0.2O2 (NMC) cells and compare with results from the experimentally convenient Li|graphite configuration. The hypotheses and abundant data herein were generated primarily with equipment universal to the battery researcher, encouraging further development of innovative testing methods and data processing that enable rapid battery engineering.
            Cover page: High-throughput Li plating quantification for fast-charging battery designCreative Commons 'BY' version 4.0 license
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2021)
            High-entropy (HE) ceramics, by analogy with HE metallic alloys, are an emerging class of solid solutions composed of a large number of species. These materials offer the benefit of large compositional flexibility and can be used in a wide variety of applications, including thermoelectrics, catalysts, superionic conductors and battery electrodes. We show here that the HE concept can lead to very substantial improvements in performance in battery cathodes. Among lithium-ion cathodes, cation-disordered rocksalt (DRX)-type materials are an ideal platform within which to design HE materials because of their demonstrated chemical flexibility. By comparing a group of DRX cathodes containing two, four or six transition metal (TM) species, we show that short-range order systematically decreases, whereas energy density and rate capability systematically increase, as more TM cation species are mixed together, despite the total metal content remaining fixed. A DRX cathode with six TM species achieves 307 mAh g-1 (955 Wh kg-1) at a low rate (20 mA g-1), and retains more than 170 mAh g-1 when cycling at a high rate of 2,000 mA g-1. To facilitate further design in this HE DRX space, we also present a compatibility analysis of 23 different TM ions, and successfully synthesize a phase-pure HE DRX compound containing 12 TM species as a proof of concept.
              Cover page: Cation-disordered rocksalt-type high-entropy cathodes for Li-ion batteriesCreative Commons 'BY-NC-ND' version 4.0 license
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2024)
              Manganese-based materials have tremendous potential to become the next-generation lithium-ion cathode as they are Earth abundant, low cost and stable. Here we show how the mobility of manganese cations can be used to obtain a unique nanosized microstructure in large-particle-sized cathode materials with enhanced electrochemical properties. By combining atomic-resolution scanning transmission electron microscopy, four-dimensional scanning electron nanodiffraction and in situ X-ray diffraction, we show that when a partially delithiated, high-manganese-content, disordered rocksalt cathode is slightly heated, it forms a nanomosaic of partially ordered spinel domains of 3-7 nm in size, which impinge on each other at antiphase boundaries. The short coherence length of these domains removes the detrimental two-phase lithiation reaction present near 3 V in a regular spinel and turns it into a solid solution. This nanodomain structure enables good rate performance and delivers 200 mAh g-1 discharge capacity in a (partially) disordered material with an average primary particle size of ∼5 µm. The work not only expands the synthesis strategies available for developing high-performance Earth-abundant manganese-based cathodes but also offers structural insights into the ability to nanoengineer spinel-like phases.
                Cover page: Earth-abundant Li-ion cathode materials with nanoengineered microstructures.
                • Article
                • Peer Reviewed
                UC Santa Barbara Previously Published Works (2021)
                Conventional Li-ion cathode materials are dominated by well-ordered structures, in which Li and transition metals occupy distinct crystallographic sites. We show in this paper that profoundly new degrees of freedom for the optimization of electrochemical properties may be accessed if controllable cation disorder is introduced. In a class of high-capacity spinel-type cathode materials, we identify cation to anion ratio in synthesis as a key parameter for tuning the structure continuously from a well-ordered spinel, through a partially ordered spinel, to rocksalt. We find that the varying degree of cation disorder modifies the voltage profile, rate capability, and charge-compensation mechanism in a rational and predictable way. Our results indicate that spinel-type order is most beneficial for achieving high-rate performance as long as the cooperative 8a to 16c phase transition is suppressed, while more rocksalt-like disorder facilitates O redox, which can increase capacity. Our findings reveal an important tuning handle for achieving high energy and power in the vast space of partially ordered cathode materials.
                  Cover page: Realizing continuous cation order-to-disorder tuning in a class of high-energy spinel-type Li-ion cathodesCreative Commons 'BY-NC' version 4.0 license
                  • Article
                  • Peer Reviewed
                  UCLA Previously Published Works (2019)
                  Well-preserved mRNA in circulating tumor cells (CTCs) offers an ideal material for conducting molecular profiling of tumors, thereby providing a noninvasive diagnostic solution for guiding treatment intervention and monitoring disease progression. However, it is technically challenging to purify CTCs while retaining high-quality mRNA.Here, we demonstrate a covalent chemistry-based nanostructured silicon substrate ("Click Chip") for CTC purification that leverages bioorthogonal ligation-mediated CTC capture and disulfide cleavage-driven CTC release. This platform is ideal for CTC mRNA assays because of its efficient, specific, and rapid purification of pooled CTCs, enabling downstream molecular quantification using reverse transcription Droplet Digital polymerase chain reaction. Rearrangements of ALK/ROS1 were quantified using CTC mRNA and matched with those identified in biopsy specimens from 12 patients with late-stage non-small cell lung cancer. Moreover, CTC counts and copy numbers of ALK/ROS1 rearrangements could be used together for evaluating treatment responses and disease progression.
                    Cover page: Covalent chemistry on nanostructured substrates enables noninvasive quantification of gene rearrangements in circulating tumor cellsCreative Commons 'BY-NC' version 4.0 license
                    Top