Nanograin-boundary-driven anomalous pseudocapacitance in hierarchical Co3O4 nanorods for high-performance lithium-ion batteries
Avvaru V.S., Vincent M., Fernandez I.J., Hinder S.J., Rodriguez M.C., Etacheri V.
Article, Journal of Energy Storage, 2026, DOI Link
View abstract ⏷
Applications of secondary lithium-ion batteries are greatly hindered by their low energy (<300 Wh kg−1) and power density (<400 W kg−1) due to the use of low-capacity graphite anodes possessing sluggish Li-ion diffusion kinetics. Herein, we report a high energy (451 Wh kg−1) and power density (980 W kg−1) lithium-ion full-cell enabled by nanograin-boundary induced pseudocapacitance of hierarchical Co3O4 nanorods. This highly pseudocapacitive (∼81 %) anode exhibited high reversible capacity (1593 mAh g−1 @ 50 mA g−1), rate-performance (800 mAh g−1@ 30 A g−1), cycling stability (∼60 % after 1000 cycles @ 1 A g−1), coulombic efficiency (∼100 %) and ultrafast-charging (∼35 s @ 30 A g−1). These Li-ion storage performances are significantly better than the previously reported conversion type anodes. Li-ion full-cell composed of Co3O4 nanorod anode and LiNiMnCoO2 cathode demonstrated excellent stability (∼85 % after 200 cycles @ 1 A g−1). Mechanistic studies including in-situ XRD and EELS mapping illustrated unique Li-ion storage at nanograin boundaries. Outstanding performance of Co3O4 nanorods anode is credited to the synergy between conversion reaction and pseudocapacitive Li-ion storage at numerous Li2O/Co/Li1.47Co3O3.72 nanointerfaces. This strategy of nanograin-boundary induced pseudocapacitance can be extended for various transition metal-oxide anodes for next-generation high energy/ power density rechargeable batteries.
Visualizing Crystallization Dynamics and Transformation Pathways of Disordered Rocksalt Oxides During Thermally Activated Sol–Gel Synthesis
Cheng D., Kodalle T., Promi A.T., Halder A., Moral R.F., Grass M., Avvaru V.S., Kim H., Sutter-Fella C.M., Zheng H.
Article, Advanced Functional Materials, 2026, DOI Link
View abstract ⏷
Sol–gel synthesis is a wet-chemical processing route for fabricating functional materials with control over composition and microstructure at relatively low temperatures compared to conventional solid-state synthesis. While sol–gel process initiates with intermixed molecular precursors, the early-stage nucleation pathways are insufficiently understood. Here, the chemical and structural transformation of disordered rocksalt (DRX) Li1.2Mn0.4Ti0.4O2 (LMTO), a promising cathode material for lithium batteries, is studied by multiscale characterizations. In situ heating transmission electron microscopy (TEM) using a liquid cell visualizes and identifies crystallization pathways at the nanoscale. While some regions follow a classical multi-step transition through thermodynamically stable intermediates, others exhibit a kinetic shortcut via a localized amorphous matrix to directly form the DRX structure. Macroscale Fourier transform infrared spectroscopy corroborates the findings and reveals that transition metal ions are more strongly incorporated into the acetate-coordinated network than lithium. Although in situ heating TEM captures diverse local transformation pathways, in situ synchrotron X-ray diffraction indicates that the macroscopic transformation proceeds predominantly through spinel LMTO and lithium titanates toward DRX-LMTO. The findings uncover the spatiotemporal chemical and structural transformations in sol–gel derived DRX-LMTO materials, and call for fine-tuning of such sol–gel chemistries to manipulate the crystallization pathways and achieve target material homogeneity more efficiently.
Developing low-cost rechargeable batteries: beyond traditional layered oxide cathodes for Li-ion and beyond Li-ion batteries
Lohani H., Avvaru V.S., Jeong S., Kim H.
Article, Chemical Communications, 2026, DOI Link
View abstract ⏷
The rising demand for energy storage systems, driven by the rapid adoption of electric vehicles and the global shift toward renewable energy, necessitates continuous efforts to lower the cost of current lithium-ion batteries (LIBs) and enhance the sustainability of existing battery chemistries. This feature article examines the key challenges associated with Ni- and Co-containing LIB cathodes and compares advancements in cathode development for non-traditional Li-ion and beyond Li-ion chemistries. First, a review of earth-abundant element containing disordered rock-salt cathodes is presented, with a discussion of key strategies such as compositional tuning and carbon coating to improve their electrochemical performance. Hurdles in developing oxide-based cathodes for Na- and K-ion batteries are also highlighted, followed by an in-depth overview of polyanion and Prussian blue cathodes for Na- and K-ion systems. Overall, this article provides a systematic perspective on the design of earth-abundant, low-cost, and sustainable cathode materials for both LIB and beyond LIB technologies.
Self-Healing Lithium Dendrites through Spontaneous Passivating Layer Formation for Stable Solid-State Lithium-Metal Batteries
Jeong S., Kim C., Avvaru V.S., Teeter G., Ahn J., Yang G., Kim H.
Article, ACS nano, 2026, DOI Link
View abstract ⏷
All-solid-state lithium-metal batteries have attracted significant attention, owing to their high energy density and superior safety. However, lithium-metal penetration through the solid electrolyte, leading to short-circuiting, remains a critical failure mode that demands comprehensive mitigation strategies. Most existing strategies are effective only prior to the initiation of lithium-dendrite formation and fail once dendrites begin to propagate through the electrolyte. In this study, we propose a self-healing mechanism in which the penetrated lithium reacts with a self-healing agent to form a passivating layer along the particle boundaries. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was incorporated into a Li6PS5Cl solid electrolyte as the self-healing agent to suppress lithium-dendrite propagation even after dendrite formation initiated under high current densities. The self-healing induced by LiTFSI was verified through comprehensive experimental analyses and was further demonstrated in a full-cell configuration. Moreover, LiTFSI incorporation plays an important role in increasing the critical current density by reducing the overall electronic conductivity of the solid electrolyte and facilitating the formation of a robust LiF-containing solid-electrolyte interphase.
Electrostatic-Attraction-Driven Self-Assembled Graphene-Disordered Rocksalt Composite Cathode for Lithium-Ion Batteries
Avvaru V.S., Zuba M., Armstrong B.L., Wang S., Tran M.X., Rinkel B.L.D., Babbe F., Lohani H., Fu Y., Buyuker I.S., Battaglia V., Kahvecioglu O., Kostecki R., McCloskey B.D., Kim H.
Article, Advanced Functional Materials, 2026, DOI Link
View abstract ⏷
Disordered rocksalt cathodes hold promise for achieving high-capacity lithium-ion batteries while using low-cost, earth-abundant elements. However, their electrochemical performance remains critically limited by their poor electronic conductivity. Conventional strategies such as high-energy ball milling with excess carbon additives can improve conductivity but remain challenging to scale and often produce defects and increase surface area, thereby accelerating capacity degradation. Herein, we report an alternative approach of electrostatic-attraction-driven self-assembly to fabricate Li1.2Mn0.6Ti0.2O1.8F0.2 (LMTOF) particles uniformly wrapped with electronically conductive graphene sheets without associated materials degradation. The graphene-wrapped LMTOF demonstrates significantly improved cycling stability (89% capacity retention after 100 cycles) and superior rate capability compared with an LMTOF-carbon composite electrode fabricated using the conventional high-energy ball-milling process. Post-cycling analysis reveals reduced oxygen evolution, suppressed unwanted side reactions, and improved structural integrity for the graphene-LMTOF composite. This work highlights the advantages of solution-based carbon wrapping and offers a scalable strategy to prepare high-performance DRX cathodes for lithium-ion batteries.
High performance Mg-Li dual metal-ion batteries based on highly pseudocapacitive hierarchical TiO2-B nanosheet assembled spheres cathodes
Article, Nanotechnology, 2025, DOI Link
View abstract ⏷
Although Mg-Li dual metal-ion batteries are proposed as a superior system that unite safety of Mg-batteries and performance of Li-ion based systems, its practical implantation is limited due to the lack of reliable high-performance cathodes. Herein, we report a high-performance Mg-Li dual metal-ion battery system based on highly pseudocapacitive hierarchical TiO2-B nanosheet assembled spheres (NS) cathode. This 2D cathode displayed exceptional pseudocapacitance (a maximum of 93%) specific capacity (303 mAh g −1 at 25 mA g−1 ), rate performance (210 mAh g −1 at 1 A g−1 ), consistent cycling (retain ∼100% capacity for 3000 cycles at 1 A g−1 ), Coulombic efficiency (nearly 100%) and fast-charging (∼12.1 min). These properties are remarkably dominant to the existing Mg-Li dual metal-ion battery cathodes. Spectroscopic and microscopic mechanistic studies confirmed negligible structural changes during charge-discharge cycles of the TiO2-B nanosheet assembled spheres electrodes. Exceptional electrochemical properties of the 2D electrode is ascribed to remarkable pseudocapacitive Mg-Li dual metal-ion diffusion via the numerous nanointerfaces of TiO2-B caused by its hierarchical microstrucrure. Large surface area, nanosheet morphology, mesoporous structure and ultrathin nature also acted as secondary factors facilitating improved electrode-electrolyte contact. Demonstrated approach of pseudocapacitive type Mg-Li dual metal-ion intercalation through hierarchical nanointerfaces may be further utilized for the designing of numerous top-notch electrode materials for futuristic Mg-Li dual metal-ion batteries.
Aqueous solution-based synthesis approach for carbon-disordered rocksalt composite cathode development and its limitations
Avvaru V.S., Zuba M., Armstrong B.L., Wang S., Kim D.-M., Buyuker I.S., Siu C., Helms B.A., Kahvecioglu O., Kim H.
Article, Electrochimica Acta, 2025, DOI Link
View abstract ⏷
Disordered rocksalt cathodes exhibit high specific capacities and high energy density; however, their low electronic conductivity poses a great challenge. Herein, we explored an aqueous-solution-based synthesis route that involves controlling the surface charges of Li1.2Mn0.6Ti0.2O1.8F0.2 (LMTOF) to be anchored by a few-layer reduced graphene oxide (rGO) for the first time. The uniform rGO wrapping on the surface of the LMTOF particles is achieved by electrostatic attraction between the negatively charged rGO and positively charged LMTOF particles. Although the initial specific capacity of rGO-LMTOF composite increased by 58 % compared to the pristine LMTOF, the composite experienced a severe capacity fade over cycling. The synthesis process in an aqueous medium resulted in Li+/H+ exchange and TM dissolution as evidenced from inductively coupled plasmon analysis and X-ray diffraction analysis. Therefore, this work suggests the search for alternative media or conditions for the synthesis of carbon-disordered rock salt cathode composite.
Tin-Carbon Dual Buffer Layer to Suppress Lithium Dendrite Growth in All-Solid-State Batteries
Avvaru V.S., Ogunfunmi T., Jeong S., Diallo M.S., Watt J., Scott M.C., Kim H.
Article, ACS Nano, 2025, DOI Link
View abstract ⏷
All-solid-state lithium-metal batteries hold great promise because of their high energy density stemming from using an energy-dense lithium-metal anode. However, mitigating the dendritic lithium-metal growth, originating from heterogeneous lithium-metal deposition, is a priority to suppress short-circuit and extend cycle life. This study employs direct current (DC) magnetron sputter coating to deposit tin (Sn) and carbon (C) on a stainless steel (SUS) current collector to achieve uniform lithium-metal plating and improve cycling performance. In particular, we evaluated and compared two dual buffer layer designs, consisting of Sn and C: (1) a thin C layer is deposited on the Sn metal layer (SUS/Sn/C), and (2) the Sn metal layer is deposited on the thin C layer (SUS/C/Sn). This study demonstrated that the SUS/Sn/C buffer layer is more effective in suppressing lithium dendrite growth and improving cycling stability than the SUS/C/Sn buffer layer. The SUS/Sn/C buffer layer shows stable Li-plating/stripping cycling over 450 cycles without noticeable short-circuit. Ex situ and in situ characterization confirm the role of the SUS/Sn/C dual buffer layer: (i) the Sn metals result in a uniform lithium-metal deposition on the current collector and (ii) the carbon layer acts as a physical barrier to suppress the lithium dendrite growth toward the solid electrolyte because of its lithiophobic nature.
Alternative Solid-State Synthesis Route for Highly Fluorinated Disordered Rock-Salt Cathode Materials for High-Energy Lithium-Ion Batteries
Avvaru V.S., Li T., Lee G.-H., Byeon Y.-W., Koirala K.P., Marques O.J., Rinkel B.L.D., Fu Y., Milsted D., Jeong S., Szymanski N.J., Kunz M., Babbe F., Lee E., Battaglia V., McCloskey B.D., Weker J.N., Wang C., Yang W., Clement R.J., Kim H.
Article, Advanced Energy Materials, 2025, DOI Link
View abstract ⏷
Fluorination has been identified as a key element for enabling the stable cycling of earth-abundant manganese-based disordered rock salt (DRX) cathodes. However, fluorination in the DRX bulk remains a challenge for scalable solid-state synthesis. In this study, a tailored reaction pathway is proposed to synthesize a highly fluorinated DRX. It is demonstrated for the first time that the unconventional precursors, Li6MnO4, MnF2, and TiO2, can avoid the formation of Mn-based intermediates (such as Li2(Mn,Ti)O3, LiMnO2, and Mn3O4), which, once formed, persist until the synthesis temperature reaches close to or above that required for fluorine volatility. Therefore, this method can form a highly fluorinated DRX with a composition of Li1.23Mn0.40Ti0.37O2−yFy (y = 0.29–0.34) at a low temperature (800 °C) relative to that required for conventional DRX solid-state reactions (≥900 °C). Li1.23Mn0.40Ti0.37O2−yFy (y = 0.29–0.34) delivers a specific capacity above 300 mAh g−1 and a specific energy of 980 Wh kg−1 at 30 °C. Detailed characterization reveals that this DRX phase reversibly utilizes Mn2+/3+ redox in the low-voltage region and Mn3+/4+ redox in the middle-voltage range, whereas reversible oxygen redox is observed at high potentials.
Solvent Determines the Formation Pathway in Sol–Gel Synthesized Disordered Rock Salt Material for Lithium Ion Battery Application
Kodalle T., Fei Y., Grass M., Cheng D., Avvaru V.S., Halder A., Cruse K., Hau H.-M., Moral R.F., Babbe F., Kunz M., Kim H., Zheng H., Ceder G., Sutter-Fella C.M.
Article, Nano Letters, 2025, DOI Link
View abstract ⏷
The increasing demand for lithium-ion batteries with high capacity and cycling stability, in combination with the scarcity of cobalt and nickel, has led to significant efforts to develop new cathode materials based on earth-abundant transition metals. Mn- and Ti-based disordered rock salt (DRX) cathodes are promising candidates fulfilling these requirements. However, their large-scale fabrication can be energy- and time-intensive using traditional fabrication methods, e.g., solid-state synthesis. The present study showcases sol–gel synthesis as an alternative method with control over the crystallization pathway through solvent choice. Dimethylformamide (DMF) aids the homogenization of the transition metals during early crystallization stages and formation of Li2TiO3and LiMn2O4intermediates before the DRX phase is formed. In contrast, 2-methoxyethanol (2-ME) shows transition metal segregation and formation of an additional transition metal intermediate (Ti2MnO4) while not resulting in phase-pure DRX material after calcination. Coin cells prepared with DMF-material yield higher capacity and cycling stability compared with 2-ME material.
Mitigating Battery Cell Failure: Role of Ag-Nanoparticle Fillers in Solid Electrolyte Dendrite Suppression
Diallo M.S., Ogunfunmi T., Yang X., Oyakhire S.T., Avvaru V.S., Scott M.C., Tu Q.H., Ceder G.
Article, Advanced Energy Materials, 2025, DOI Link
View abstract ⏷
The development of solid-state batteries (SSBs) with lithium Li metal anodes holds significant promise for enhancing the energy density and safety of next-generation energy storage systems. However, their commercialization is hindered by challenges related to Li dendrite formation, which can lead to short circuits and battery failure. In this study, the role of Ag nanoparticles embedded within solid electrolytes (SE) is investigated in suppressing dendrite propagation. The results demonstrate that Ag nanoparticles effectively mitigate two key failure mechanisms: (1) dendrite growth within porous networks at low current densities and (2) stress intensification-induced SE fracture at higher current densities (12 mA cm−2). Ex situ characterization using focused-ion beam – scanning electron microscopy (FIB–SEM) and energy dispersive X-ray spectroscopy (EDS,) reveals that Ag nanoparticles migrate alongside advancing Li dendrites, promoting homogeneous dendrite growth and reducing the likelihood of localized stress concentrations. Additionally, the incorporation of Ag nanoparticles is shown to facilitate a more uniform Li distribution toward the anode side, which can potentially enable the use of higher charging rates in SSBs. This study provides a new perspective on Li dendrite suppression and presents new opportunities for enhancing the performance and safety of SSBs.
Transition Metal Oxide Nanomaterials for Sodium-Ion Batteries and Hybrid Capacitors
Book chapter, Materials for Energy Storage, 2024,
Ultrathin (15 nm) Carbon Sheets with Surface Oxygen Functionalization for Efficient Pseudocapacitive Na-ion Storage
Etacheri V., Maca R.R., Avvaru V.S., Hong C.N., Alazemi A., Pol V.G.
Article, ChemElectroChem, 2024, DOI Link
View abstract ⏷
Disordered carbon is the state of the art anode material for Na-ion batteries due to their increased interlayer spacing and good electronic conductivity. However, its practical application is hindered by average specific capacity, poor rate performance, low coulombic efficiency and limited cycling stability. Herein, we report the superior pseudocapacitance enhanced Na-ion storage of in situ surface functionalized carbon nanosheets. Anodes composed of ultrathin (~15 nm) carbon nanosheets demonstrated excellent reversible specific capacity (375 mAh/g at 25 mA/g), rate performance (150 mAh/g at 2 A/g), long-term cycling performance (1000 cycles at 1 A/g) and coulombic efficiency (~100 %). Considerably higher pseudocapacitance (up to ~78 %) is also identified in this case compared to amorphous carbon particles. Spectroscopic and electrochemical studies proved Na-ion intercalation in to the disordered carbon and pseudocapacitive storage driven by oxygen-containing surface functional groups. Outstanding electrochemical performance is credited to the synergy between diffusion limited intercalation and pseudocapacitive surface Na-ion storage. The demonstrated synthetic method of in situ functionalized carbon nanosheets is inexpensive and scalable. The strategy of functional group and morphology induced pseudocapacitive Na-ion storage offer new prospects to design high-performance Na-ion battery electrodes.
Defect-driven ion storage on hexagonal boron nitride for fire-safe and high-performance lithium-ion batteries
Lei Y., Avvaru V.S., Ward Z., Liu H., Fujisawa K., Bepete G., Zhang N., Carreno A.F., Terrones H., Etacheri V., Terrones M.
Article, Chemical Engineering Journal, 2024, DOI Link
View abstract ⏷
The mass market adoption of electric vehicles has increased the risk of safety concerns, such as overheating and flammability. Rational design of fire-safe and high-capacity anodes with thermal tolerance, capable of fast-charging and long cycle-life, is crucial for the development of next generation Li-ion batteries operating under extreme conditions. Here we report a defect engineered hexagonal boron nitride (hBN) anode to mediate the safety dilemma. We demonstrate that the defects generated via cryomilling catalyze the reversible LiF formation and enable the pseudocapacitive type Li-ion storage on hBN. The non-flammability and excellent thermal tolerance of hBN allows high specific capacity (880 mAh/g @ 25 mA/g), rate performance (480 mAh/g @ 5 A/g) and stable cycling (5000 cycles) at 60 °C. The Li-ion full-cell with the defective hBN anode and the conventional cathode (LiNiMnCoO2) delivers significantly higher energy (400 Wh kg−1) and power density (1 kW kg−1) when compared to graphite/LiNiMnCoO2 full-cells (121 Wh kg−1 and 250 W kg−1). First-principles calculations confirm that nitrogen antisite (NBVN) defects are responsible for the electrochemical activation of otherwise inactive hBN. The strategy of defect-induced electrochemical activation opens up new avenues in the design of high-performance electrode materials for numerous secondary batteries.
Inverse Consequences of the SnO2 Protection Layers on Pt/C Catalysts in Proton-Exchange Membrane Fuel Cells
Byeon Y.-W., Mehrazi S., Stuhmeier B.M., Avvaru V.S., Kim D.-M., Helms B.A., Cheng L., Kim H.
Article, Energy and Fuels, 2024, DOI Link
View abstract ⏷
Proton-exchange membrane fuel cells (PEMFCs) are promising energy-conversion systems, offering an appealing blend of high energy efficiency and low environmental impact. However, carbon corrosion of PEMFCs is known to significantly degrade their performance, remaining a critical challenge to overcome. In this study, we applied a Nb-doped SnO2 (Nb-SnO2) nanoparticle coating on Pt/C catalysts as a protective layer, with the Sn/C ratio in the precursors varying from 0.25:1 to 2.0:1. Contradictory behaviors of the coated Pt/C catalysts were observed at different Sn/C ratios. The Sn/C = 1.0 sample exhibited improved electrochemically active surface area retention after 500 cycles of accelerated stress testing (AST) but with more significant polarization and resistance increase observed in the polarization curves. In addition, agglomeration of Nb-SnO2 particles was observed at a higher Sn/C ratio in the AST of a membrane electrode assembly, with less shrinkage of the total thickness of the Nb-SnO2-coated Pt/C electrode. We speculate that formation of Nb-SnO2 agglomerates occurs once the protective layer is broken down or the unprotected carbon surface is corroded and that these Nb-SnO2 agglomerates increase the tortuosity of the electron pathways and significantly increase the cell polarization.
Conductive carbon embedded beneath cathode active material for longevity of solid-state batteries
Byeon Y.-W., Yang S., Yang G., Kim D.-M., Avvaru V.S., Ogunfunmi T., Scott M., Helms B.A., Urban J., Kim H.
Article, Journal of Materials Chemistry A, 2024, DOI Link
View abstract ⏷
A composite structure was developed for use in all-solid-state batteries that consists of a conductive 3D reduced graphene oxide framework embedded beneath cathode active material particles. This unique structure offers significant advantages when combined with a sulfide solid electrolyte as the heterogeneous distribution of the conductive carbon in the composite cathode ensures good contact between the carbon and cathode particles for facile electron transfer while a direct contact between the carbon and sulfide solid electrolyte is avoided or minimized. This approach assists in preventing or reducing unwanted irreversible faradaic reactions. As a result, the newly developed composite of cathode particles decorated on a 3D reduced graphene oxide framework delivers higher specific capacity with improved cycling stability compared with a typical composite cathode consisting of a homogenous mixture of the cathode active material, carbon nanofibers, and sulfide solid electrolyte.
High-Performance Mg−Li Hybrid Batteries Based on Pseudocapacitive Anatase Ti1-xCoxO2-y Nanosheet Cathodes
Article, ChemSusChem, 2022, DOI Link
View abstract ⏷
Despite the proposed safety, performance, and cost advantages, practical implementation of Mg−Li hybrid batteries is limited due to the unavailability of reliable cathodes compatible with the dual-ion system. Herein, a high-performance Mg−Li dual ion battery based upon cobalt-doped TiO2 cathode was developed. Extremely pseudocapacitance-type Ti1-xCoxO2-y nanosheets consist of an optimum 3.57 % Co-atoms. This defective cathode delivered exceptional pseudocapacitance (maximum of 93 %), specific capacities (386 mAh g−1 at 25 mA g−1), rate performance (191 mAh g−1 at 1 A g−1), cyclability (3000 cycles at 1 A g−1), and coulombic efficiency (≈100 %) and fast charging (≈11 min). This performance was superior to the TiO2-based Mg−Li dual-ion battery cathodes reported earlier. Mechanistic studies revealed dual-ion intercalation pseudocapacitance with negligible structural changes. Excellent electrochemical performance of the cation-doped TiO2 cathode was credited to the rapid pseudocapacitance-type Mg/Li-ion diffusion through the disorder generated by lattice distortions and oxygen vacancies. Ultrathin nature, large surface area, 2D morphology, and mesoporosity also contributed as secondary factors facilitating superior electrode-electrolyte interfacial kinetics. The demonstrated method of pseudocapacitance-type Mg−Li dual-ion intercalation by introducing lattice distortions/oxygen vacancies through selective doping can be utilized for the development of several other potential electrodes for high-performance Mg−Li dual-ion batteries.
Unusual pseudocapacitive lithium-ion storage on defective Co3O4nanosheets
Article, Nanotechnology, 2022, DOI Link
View abstract ⏷
Secondary lithium-ion batteries are restricted in large-scale applications including power grids and long driving electric vehicles owing to the low specific capacity of conventional intercalation anodes possessing sluggish Li-ion diffusion kinetics. Herein, we demonstrate an unusual pseudocapacitive lithium-ion storage on defective Co3O4 nanosheet anodes for high-performance rechargeable batteries. Cobalt-oxide nanosheets presented here composed of various defects including vacancies, dislocations and grain boundaries. Unique 2D holey microstructure enabled efficient charge transport as well as provided room for volume expansions associated with lithiation-delithiation process. These defective anodes exhibited outstanding pseudocapacitance (up to 87%), reversible capacities (1490 mAh g-1 @ 25 mA g-1), rate capability (592 mAh g-1 @ 30 A g-1), stable cycling (85% after 500 cycles @ 1 A g-1) and columbic efficiency (∼100%). Exceptional Li-ion storage phenomena in defective Co3O4 nanosheets is accredited to the pseudocapacitive nature of conversion reaction resulting from ultrafast Li-ion diffusion through various crystal defects. The demonstrated approach of defect-induced pseudocapacitance can also be protracted for various low-cost and/or eco-friendly transition metal-oxides for next-generation rechargeable batteries.
High-energy sodium-ion hybrid capacitors through nanograin-boundary-induced pseudocapacitance of Co3O4 nanorods
Article, Journal of Energy Chemistry, 2022, DOI Link
View abstract ⏷
Sodium-ion hybrid capacitors (SICs) have been proposed to bridge performance gaps between batteries and supercapacitors, and thus realize both high energy density and power density in a single configuration. Nevertheless, applications of SICs are severely restricted by their insufficient energy densities (<100 Wh/kg) resulted from the kinetics imbalance between cathodes and anodes. Herein, we report a nanograin-boundary-rich hierarchical Co3O4 nanorod anode composed of ∼20 nm nanocrystallites. Extreme pseudocapacitance (up to 72%@1.0 mV/s) is achieved through nanograin-boundary-induced pseudocapacitive-type Na+ storage process. Co3O4 nanorod anode delivers in this case highly reversible capacity (810 mAh/g@0.025 A/g), excellent rate capability (335 mAh/g@5.0 A/g), and improved cycle stability (100 cycles@1.0 A/g with negligible capacity degradation). The outstanding performance can be credited to the hierarchical morphology of Co3O4 nanorods and the well-designed nanograin-boundaries between nanocrystallites that avoid particle agglomeration, induce pseudocapacitive-type Na+ storage, and accommodate volume variation during sodiation-desodiation processes. Nitrogen-doping of the Co3O4 nanorods not only generates defects for extra surficial Na+ storage but also increases the electronic conductivity for efficient charge separation and lowers energy barrier for Na+ intercalation. Synergy of conventional reaction mechanism and pseudocapacitive-type Na+ storage enables high specific capacity, rapid Na+ diffusion, and improved structural stability of the Co3O4 nanorod electrode. The SIC integrating this highly pseudocapacitive anode and activated carbon cathode delivers exceptional energy density (175 Wh/kg@40 W/kg), power density (6632 W/kg@37 Wh/kg), cycle life (6000 cycles@1.0 A/g with a capacity retention of 81%), and coulombic efficiency (∼100%).
Extremely pseudocapacitive interface engineered CoO@3D-NRGO hybrid anodes for high energy/ power density and ultralong life lithium-ion batteries
Avvaru V.S., Fernandez I.J., Feng W., Hinder S.J., Rodriguez M.C., Etacheri V.
Article, Carbon, 2021, DOI Link
View abstract ⏷
Although secondary Li-ion batteries are widely used for electrochemical energy storage, low energy (100–300 Wh kg−1) and power density (250–400 W kg−1) are limiting their applications in several areas including long-range electric vehicles. Herein, we demonstrate high energy (400 Wh kg−1) and power density (1 kW kg−1) Li-ion batteries (considering the weight of both electrodes) based on extremely pseudocapacitive interface engineered CoO@3D-NRGO hybrid anodes. These values are 2.8 and 2.3-fold higher respectively compared to graphite‖LiNiMnCoO2 full-cells under similar experimental conditions. Three-dimensional anode architecture presented here composed of ultrafine CoO nanoparticles (∼10 nm) chemically bonded to nitrogen-doped reduced graphene-oxide. This hybrid anode demonstrated excellent pseudocapacitance (∼92%), specific capacity (1429 mAh g−1 @ 25 mA g−1), rate performance (906 mAh g−1 @ 5 A g−1), and cycling stability (990 mAh g−1 after 7500 cycles @ 5 A g−1). Outstanding electrochemical performance of CoO@3D-NRGO‖LiNiMnCoO2 full-cells is credited to the extreme pseudocapacitance of CoO@3D-NRGO anode resulting from Li2O/Co/NRGO nanointerfaces and Co–O–C bonds. The demonstrated strategy of interfacial engineering can also be extended for other environmental friendly/inexpensive transition metal oxide (Fe2O3, MnO2 etc.) anodes for high energy/power density and ultra-long-life Li-ion batteries.
Realization of High Energy Density Sodium-Ion Hybrid Capacitors through Interface Engineering of Pseudocapacitive 3D-CoO-NrGO Hybrid Anodes
Feng W., Avvaru V.S., Maca R.R., Hinder S.J., Rodriguez M.C., Etacheri V.
Article, ACS Applied Materials and Interfaces, 2021, DOI Link
View abstract ⏷
Sodium-ion hybrid capacitors (SHCs) have attracted great attention owing to the improved power density and cycling stability in comparison with sodium-ion batteries. Nevertheless, the energy density (<100 Wh·kg-1) is usually limited by low specific capacity anodes (<150 mAh·g-1) and "kinetics mismatch"between the electrodes. Hence, we report a high energy density (153 Wh·kg-1) SHC based on a highly pseudocapacitive interface-engineered 3D-CoO-NrGO anode. This high-performance anode (445 mAh·g-1 @0.025 A·g-1, 135 mAh·g-1 @5.0 A·g-1) consists of CoO (∼6 nm) nanoparticles chemically bonded to the NrGO network through Co-O-C bonds. Exceptional pseudocapacitive charge storage (up to ∼81%) and capacity retention (∼80% after 5000 cycles) are also identified for this SHC. Excellent performance of the 3D-CoO-NrGO anode and SHC is owing to the synergistic effect of the CoO conversion reaction and pseudocapacitive sodium-ion storage induced by numerous Na2O/Co/NrGO nanointerfaces. Co-O-C bonds and the 3D microstructure facilitating efficient strain relaxation and charge-transfer correspondingly are also identified as vital factors accountable for the excellent electrochemical performance. The interface-engineering strategy demonstrated provides opportunities to design high-performance transition metal oxide-based anodes for advanced SHCs.
High-rate and ultralong-life Mg–Li hybrid batteries based on highly pseudocapacitive dual-phase TiO2 nanosheet cathodes
Article, Journal of Power Sources, 2021, DOI Link
View abstract ⏷
Although Mg–Li hybrid batteries are proposed as an alternative to Mg-batteries, the lack of dual-ion compatible cathodes are limiting their practical application. Herein, we report a high-rate and ultralong-life Mg–Li hybrid battery based on a dual-phase TiO2 cathode. Highly pseudocapacitive hierarchical two-dimensional TiO2 consists of anatase (60%) and bronze (40%) nanocrystallites forming interfaces due to crystal structure mismatch. This dual-phase hierarchical cathode exhibits excellent pseudocapacitance (up to 92%), specific capacities (235 mAh/g @ 25 mA/g), rate performance (120 mAh/g @ 1A/g) cycling stability (~87% after 3000 cycles @ 1A/g) and coulombic efficiency (~100%). These results are vastly superior to the previously reported values for TiO2 based Mg–Li hybrid battery cathodes. Only minimal structural changes are observed during the charge-discharge of two-dimensional TiO2 electrode. Outstanding electrochemical performance of dual-phase TiO2 nanosheet cathode is attributed to the superior pseudocapacitive Mg/Li-ion diffusion through nanointerfaces between anatase and bronze crystallites. While other structural features such as 2D-morphology, ultrathin nature, mesoporosity, and high surface area act as secondary factors. The demonstrated approach for efficient pseudocapacitive Mg/Li-ion intercalation enhanced by nanointerfaces can be further exploited in the development of other high performance electrodes for advanced Mg–Li hybrid batteries.
Low heat yielding electrospun phosphenanthrene oxide loaded polyacrylonitrile composite separators for safer high energy density lithium-ion batteries.
Yusuf A., Avvaru V.S., Dirican M., Changchun S., Wang D.-Y.
Article, Applied Materials Today, 2020, DOI Link
View abstract ⏷
Battery-induced fire scenarios are on the rise globally. The severity of battery fires is directly linked to the combustion behavior of battery components such as the separator and electrolyte which constitute the main combustible materials in the battery. To achieve safer batteries, components with a low combustibility must be employed in the new lithium-ion batteries. In this work, aiming to alleviate the battery separator's combustibility and preserve the electrochemical performance of lithium-ion batteries, we designed a novel low heat releasing composite separator by incorporating 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) into the polyacrylonitrile (PAN) matrix via electrospinning technique. Notably, the membranes containing DOPO remarkably exhibited a decreased peak heat release rate (pHRR) which was evidenced by a 33% and 49% decrease for PAN-15DOPO and PAN-20DOPO samples respectively, evaluated using a microscale-combustion calorimeter (MCC). Furthermore, compared to pristine PAN based cells having an initial discharge capacity of 117 mAhg−1 at a C-rate of 0.6C, the PAN-15DOPO based cells showed a superior initial discharge capacity of 131 mAhg−1 and a capacity retention of 83% at a C-rate of 0.6C after 100 cycles. This strategy of electrospinning PAN with DOPO, provides a feasible design for fabricating batteries with simultaneously improved electrochemical properties and safety.
Carbon-based integrated devices for efficient photo-energy conversion and storage
Book chapter, Carbon Based Nanomaterials for Advanced Thermal and Electrochemical Energy Storage and Conversion, 2019, DOI Link
View abstract ⏷
Increasing energy demand and depleting fossil fuel resources require exploration of sustainable energy resources and efficient storage of the generated energy. There have been numerous efforts to develop solar cells and batteries/capacitors for energy conversion and storage, respectively. Integration of energy conversion and storage components into a single device has been recently demonstrated as effective to increase the efficiency and reduce size/weight of the hybrid devices. Photo-rechargeable integrated energy storage devices are promising candidates for portable applications. As of now, efficiency of around 5% was obtained in a complete device with dye-sensitized solar cell and supercapacitor. Carbon nanostructures have already possessed a great place in the modern-day energy research mainly due to the immense possibility in realization of environmentally friendly, cost-effective, flexible devices that can efficiently convert and store energy. Application of various carbonaceous materials in integrated devices for efficient photo-energy conversion and storage are summarized in this chapter.
