About

Thank you for visiting our group website! We are the Sustainable Materials and Energy Laboratory (SMEL) in the NanoEngineering department at UC San Diego. Our research group focuses on designing and understanding novel materials and chemical processes for energy and environmental applications. We are particularly interested in the following topics: (1) Energy storage and conversion materials and devices; (2) Batteries for extreme environments; (3) Next-generation battery recycling; (4) Porous materials for charge separation and storage. We are devoted to pushing the limit of scientific knowledge and creating social impact through teaching, research and outreach activities.

Research topics

• Materials science
• Chemistry
• Chemical engineering
• Organic chemistry
• Metallurgy
• Physical chemistry
• Nanotechnology
• Thermodynamics
• Composite material
• Inorganic chemistry
• Physics
• Chemical physics

Selected publications

• Synthesis of mugwort leaves-derived carbon quantum dots and their application in intracellular pH sensing and imaging

  SSRN Electronic Journal · 2026-01-01

  preprintOpen access
  PublisherDOI

• Incorporating Solvation Effects in Oxidative Stability Predictions of Battery Electrolytes

  The Journal of Physical Chemistry Letters · 2025-10-24

  article

  Accurately predicting the oxidative stability of battery electrolytes is crucial for improving our understanding of high-voltage behavior and rational design of next-generation systems employing novel chemistries. However, commonly applied strategies based on evaluation of orbital occupancies of isolated molecules within density functional theory techniques neglect many-body solvation and interfacial effects that govern the electro-thermodynamics in real systems. Here, we advance a computational methodology that integrates molecular dynamics sampling of local solvation environments with explicit vertical ionization potential (IP) calculations to account for such effects. Our approach allows for both statistical accounting of IP distributions as well as prediction of the oxidized species (e.g., solvent vs anion decomposition). Application of this method to a matrix of electrolytes based on common lithium salts and solvents yields more detailed conclusions that often disagree with those gained through conventional calculations. We also demonstrate that this methodology can capture variations in IP associated with increased salt concentrations as well as the speciation and stability next to electrified model interfaces. This work offers a comprehensive accounting of the microscopic factors and electronic structure considerations that stabilize molecules and their unique solvation environment in modern electrochemical systems.

  PublisherDOI

• Toward More Recyclable and Sustainable Lithium-Ion Batteries

  ACS Applied Energy Materials · 2025-10-04

  articleSenior authorCorresponding

  The rapid rise of electric vehicles has driven significant advancements in lithium-ion battery (LIB) technology. However, the pursuit of higher power, longer lifespan, and greater capacity has often overshadowed critical factors such as recyclability, material sustainability, and environmental impact. To ensure the long-term viability of LIBs, future developments must strike a balance between performance and sustainability. This review advocates for the design of next-generation battery components using abundant, environmentally friendly, and sustainable materials that minimize reliance on intensive mining and refining processes. Key innovations include metal-free electrodes, nonmetallic current collectors, solid-state electrolytes, biodegradable components, anode-free configurations, and water-soluble binders for electrode fabrication. We provide a comprehensive assessment of recent progress in these areas, discuss challenges for practical implementation, and outline future directions for advancing these technologies. By offering a forward-looking perspective on innovative battery materials and designs, this review provides valuable insights into the sustainable evolution of LIBs.

  PublisherDOI

• Tin Anode for High-Energy-Density Na-Ion Batteries

  Journal of The Electrochemical Society · 2025-10-01

  articleOpen accessSenior author

  Tin (Sn) is a promising anode material for sodium-ion batteries (SIBs) due to its high theoretical specific capacity (847 mAh g −1 ) and volumetric capacity (6238 mAh cm −3 ). In addition, Sn is a commodity and can be readily sourced. However, alloy anodes tend to suffer from a low initial Coulombic efficiency (ICE) and severe capacity loss due to extensive volume expansion (∼420% for Sn) during electrochemical cycling. In this work, commodity-sourced Sn is used (with an electrode active material composition of >99% Sn) to demonstrate how these traditional challenges can be overcome without major modifications. When paired with a NaCrO 2 (NCrO) cathode in a full cell, a high specific energy of 178 Wh kg −1 and volumetric energy density of 417 Wh L −1 can be achieved. This work highlights the opportunities for alloy materials such as Sn to enable high energy density SIBs.

  PublisherDOI

• Micron Size NaCrO ₂ Particles Enable High-Loading Dry-Processed Electrode for Sodium Ion Batteries

  ECS Meeting Abstracts · 2025-11-24

  article

  Dry-process fabrication using fibrillatable binder is emerging as a promising method to produce high-loading electrodes for energy storage applications, favored by its cost-efficiency and eco-friendliness. While previous studies have demonstrated the advantages of dry process over the traditional slurry method, there remains a gap in understanding how the particle size of active materials influence the mechanical and electrochemical performance of dry electrodes. In this study, four different particle size NaCrO 2 materials (Average size, S-NCO: 0.6 µm, M1-NCO 1.5 µm, M2-NCO: 4.4 µm, and L-NCO: 9.9 µm) were synthesized to investigate the effect of particle size on dry-processed high-loading electrodes. Our findings reveal that the larger micro-sized (> 4.4 µm) NCO dry films exhibit significantly improved tensile strength and electrochemical performance, primarily ascribed to the low film porosity, abundant inter-particle connection by the binder, comprehensive carbon coverage, and efficient percolation of conductive pathway. Notably, a full cell incorporated with a high loading (5.2 mAh/cm²) and high active material ratio (96.5 wt.%) L-NCO film electrode demonstrates promising cycling stability and rate capability. These results provide valuable insights regarding the design and fabrication of dry-processed electrode for future energy storage applications. Figure 1

  PublisherDOI

• Managing Impurities in Direct Battery Recycling: Advancing Separation and Purification for High-Quality Feedstocks

  ACS Energy Letters · 2025-12-12 · 3 citations

  articleSenior authorCorresponding

  Direct recycling offers a more sustainable and energy-efficient alternative to conventional metallurgical methods for treating end-of-life lithium-ion batteries (LIBs). However, the large-scale deployment of direct regeneration is limited by its low tolerance to impurities, making the production of high-purity feedstocks and impurity management essential for viability. Drawing on insights into how impurities affect cathode regeneration, this Perspective discusses current and emerging separation and purification technologies and delineates the remaining gap to the mass production of high-quality feedstocks. We propose integrated, high-efficiency approaches that elevate feedstock quality and broaden impurity control across the entire workflow, positioning impurity management in both preprocessing and regeneration as being essential to the economic and environmental performance of direct recycling. The result is a research roadmap to enable scalable, sustainable, and cost-effective battery recycling practices.

  PublisherDOI

• Solvent's Covert Role: Concerted Anion‐Solvent Co‐Intercalation Rewrites Voltage Rules for Dual‐Ion Batteries

  Angewandte Chemie International Edition · 2025-10-28 · 5 citations

  articleOpen accessCorresponding

  Anion intercalation into graphite cathodes governs dual-ion battery (DIB) performance but suffers from unexplained solvent-driven voltage shifts (>500 mV) and capacity variations (12-fold) across electrolyte solvents. Prevailing thermodynamic models overlook solvent involvement due to unresolved anion-solvent coupling dynamics. Using a spatially resolved operando Raman platform, we detect solvent-specific vibrational fingerprints and graphite G-band splitting at identical intercalation thresholds, confirming simultaneous anion-solvent insertion. This redefines solvents as active thermodynamic directors, revealing two hidden energetic contributions: 1) cation desolvation penalties governed by solvent donor number (DN) and 2) dielectric constant (ε)-modulated screening between anions and graphene layers. Integrating these into a revised Nernst model yields a DN-ε descriptor that quantitatively predicts intercalation voltages across solvents. We further demonstrate that salt-concentrated electrolytes disrupt this mechanism by depleting solvent activity, shifting pathways from co-intercalation to anion-dominant insertion. This work resolves long-standing DIB anomalies in anion-inserted graphite cathode reactions and establishes solvent properties as central levers for energy-dense DIBs.

  PublisherOA PDFDOI

• Rechargeable Aprotic Zinc–Oxygen Batteries with Reversible ZnO Formation on Cathodes

  Angewandte Chemie · 2025-11-11

  article

  Abstract Mastering the redox reactions of oxygen—a naturally abundant and high‐energy material—holds transformative potential to address the limitations in energy density, cost, and resource availability of current batteries. Despite their high energy density and cost‐effectiveness, conventional aqueous zinc–oxygen (Zn‐O 2 ) batteries were born with poor rechargeability. Critically, whether reversible oxygen electrochemistry can be established in aprotic Zn‐based electrolytes remains an open question. Herein, we show that ZnO, traditionally regarded as an insulating byproduct, can be harnessed as an exclusive and reversible cathode product, hence opening access to a rechargeable Zn‐O 2 battery chemistry. At the heart of this O 2 /ZnO redox is the combined use of high‐donicity aprotic electrolytes and Ru‐based catalysts, which enables selective oxygen reduction to form a chemically inert (toward electrolytes) but defect‐rich ZnO phase, whose oxygen vacancies promote low‐polarization Zn─O bond breaking upon recharge to release O 2 . The resulting reversibility of the oxygen cathode, coupled with stable Zn plating/stripping at the anode, ensures a prolonged cycle lifespan exceeding 1000 h for aprotic Zn‐O 2 cells. A semi‐solid pouch cell with an energy density of 120 Wh kg −1 is further achieved using a high utilization‐rate (40%) Zn anode. This work advances oxygen redox understanding and balances rechargeability with energy density in Zn batteries.

  PublisherDOI

• Stable Cycling of Sodium All-Solid-State Batteries with High-Capacity Cathode Presodiation

  ECS Meeting Abstracts · 2025-11-24

  articleSenior author

  Sodium all-solid-state batteries (NaSSBs) with an alloy-type anode (e.g., Sn and Sb) offer superior capacity and energy density compared to hard carbon anode. However, the irreversible loss of Na + at the alloy anode during the initial cycle results in diminished capacity and stability, impairing full-cell performance. This study presents an easy-to-implement cathode presodiation strategy by employing a Na-rich material to address these challenges. Leveraging the high theoretical capacity and suitable voltage window, Na 2 S is chosen as the Na donor, which is activated by creating a mixed electron-ion conducting network, delivering a high capacity of 511.7 mAh g -1 . By adding a small amount (i.e., 3 wt.%) of Na 2 S to the cathode composite, a NaCrO 2 || Sn full cell demonstrated capacity improvement from 90.8 mAh g -1 to 118.2 mAh g -1 (based on cathode mass). The capacity-balanced full cell can thus cycle to more than 300 times with > 90% capacity retention. This work provides a practical solution to enhance the full-cell performance and advance the transformation from half-cell to full-cell applications of NaSSBs.

  PublisherDOI

• Accelerating Li+ transport kinetics through ion-selective separators for dendrite-free lithium metal anodes

  Journal of Power Sources · 2025-07-16 · 5 citations

  articleOpen access

  Uncontrollable lithium dendrites caused by the kinetic mismatch between the rapid Li + deposition and the sluggish Li + diffusion, exacerbating capacity degradation and safety risks in lithium metal batteries. The commercially available separator hardly regulates Li + migration due to its heterogeneous pores and inferior electrolyte affinity. Herein, a polypropylene separator modified by lithiophilic sulfonated aramid fibers is proposed to suppress lithium dendrites by accelerating Li + transport kinetics. Specifically, the sulfonate group in the functionalized separator displays superior Li + affinity and effective suppresses anion migration. This enhances the Li + transference number to 0.72, which is two times of the unmodified separator. Additionally, the functionalized separator achieves an increased ionic conductivity of 4.45 × 10 −4 S cm −1 and a high critical current density of 7.7 mA cm −2 . The improved Li + transport kinetics effectively alleviates Li + depletion near lithium electrodes caused by the rapid Li + deposition on electrodes, ultimately suppressing the growth of lithium dendrites. Consequently, the Li||Li cells with as-prepared separators show superior cycling performances for 6000 h, and the 1.2 Ah LiCoO 2 pouch cell remains a capacity of 1.13 Ah after 100 cycles. This work provides a novel paradigm to promote the practical implementation of high-safety lithium metal batteries. • An ion-selective separator (AF-SO 3 Li@PP) with a t Li + of 0.72 is designed. • The AF-SO 3 Li@PP mitigates lithium dendrites by accelerating Li + transport kinetics. • Li||AF-SO 3 Li@PP||Li symmetric cells achieve stable cycling for 6000 h. • The LiCoO 2 ||AF-SO 3 Li@PP|||Li battery retains 92.0 % capacity after 250 cycles. • The NCM-based battery shows a capacity retention of 99.6 % after 200 cycles.

  PublisherDOI

Recent grants

• GOALI: Understanding and Resolving the Compositional and Structural Defects in High-Energy Lithium-Ion Battery Cathodes

  NSF · $314k · 2018–2022

Frequent coauthors

• Guanglei Cui

  Qingdao Institute of Bioenergy and Bioprocess Technology

  65 shared

• Ying Shirley Meng

  48 shared

• John Holoubek

  43 shared

• Hongpeng Gao

  University of California, San Diego

  41 shared

• Ping Liu

  Xi'an University of Technology

  36 shared

• Xiaofan Du

  First Affiliated Hospital of Xi'an Jiaotong University

  33 shared

• Mingqian Li

  University of California System

  31 shared

• Yijie Yin

  University of California, San Diego

  31 shared

Labs

• Z.Chen LAB@NanoEngineeringPI

Awards & honors

• Student Science Talented Award (Tianjin University, 2007)
• Chinese Government Award for Outstanding Self-Financed PhD S…
• MRS Graduate Student Silver Award (2011)
• Department Outstanding Graduate Award (UCLA, 2012)