Jingyi Zhu

Defect-Engineered Graphene for High-Energy- and High-Power-Density Supercapacitor Devices

Defects are often written off as performance limiters. Contrary to this notion, it is shown that controlling the defect configuration in graphene is critical to overcome a fundamental limitation posed by quantum capacitance and opens new channels for ion diffusion. Defect-engineered graphene flexible pouch capacitors with energy densities of 500% higher than the state-of-the-art supercapacitors are demonstrated.The development of high-energy and high-power density supercapacitors (SCs) is critical for enabling next-generation energy storage applications. Nanocarbons are excellent SC electrode materials due to their economic viability, high-surface area, and high stability. Although nanocarbons have high theoretical surface area and hence high double layer capacitance, the net amount of energy stored in nanocarbon-SCs is much below theoretical limits due to two inherent bottlenecks: i) their low quantum capacitance and ii) limited ion-accessible surface area. Here, we demonstrate that defects in graphene could be effectively used to mitigate these bottlenecks by drastically increasing the quantum capacitance and opening new channels to facilitate ion diffusion in otherwise closed interlayer spaces. Our results support the emergence of a new energy paradigm in SCs with 250% enhancement in double layer capacitance beyond the theoretical limit. Furthermore, we demonstrate prototype defect engineered bulk SC devices with energy densities 500% higher than state-of-the-art commercial SCs without compromising the power density.

Bacteria Absorption-Based Mn2P2O7-Carbon@Reduced Graphene Oxides for High-Performance Lithium-Ion Battery Anodes.

The development of freestanding flexible electrodes with high capacity and long cycle-life is a central issue for lithium-ion batteries (LIBs). Here, we use bacteria absorption of metallic Mn(2+) ions to in situ synthesize natural micro-yolk-shell-structure Mn2P2O7-carbon, followed by the use of vacuum filtration to obtain Mn2P2O7-carbon@reduced graphene oxides (RGO) papers for LIBs anodes. The Mn2P2O7 particles are completely encapsulated within the carbon film, which was obtained by carbonizing the bacterial wall. The resulting carbon microstructure reduces the electrode-electrolyte contact area, yielding high Coulombic efficiency. In addition, the yolk-shell structure with its internal void spaces is ideal for sustaining volume expansion of Mn2P2O7 during charge/discharge processes, and the carbon shells act as an ideal barrier, limiting most solid-electrolyte interphase formation on the surface of the carbon films (instead of forming on individual particles). Notably, the RGO films have high conductivity and robust mechanical flexibility. As a result of our combined strategies delineated in this article, our binder-free flexible anodes exhibit high capacities, long cycle-life, and excellent rate performance.

Roll-to-roll production of spray coated N-doped carbon nanotube electrodes for supercapacitors

Although carbon nanomaterials are being increasingly used in energy storage, there has been a lack of inexpensive, continuous, and scalable synthesis methods. Here, we present a scalable roll-to-roll (R2R) spray coating process for synthesizing randomly oriented multi-walled carbon nanotubes electrodes on Al foils. The coin and jellyroll type supercapacitors comprised such electrodes yield high power densities (∼700 mW/cm3) and energy densities (1 mW h/cm3) on par with Li-ion thin film batteries. These devices exhibit excellent cycle stability with no loss in performance over more than a thousand cycles. Our cost analysis shows that the R2R spray coating process can produce supercapacitors with 10 times the energy density of conventional activated carbon devices at ∼17% lower cost.

Influence of carbon nanomaterial defects on the formation of protein corona

In any physiological media, carbon nanomaterials (CNM) strongly interact with biomolecules leading to the formation of biocorona, which subsequently dictate the physiological response and the fate of CNMs. Defects in CNMs play an important role not only in material properties but also in the determination of how materials interact at the nano-bio interface. In this article, we probed the influence of defect-induced hydrophilicity on the biocorona formation using micro-Raman, photoluminescence, infrared spectroscopy, electrochemistry, and molecular dynamics simulations. Our results show that the interaction of proteins (albumin and fibrinogen) with CNMs is strongly influenced by charge-transfer between them, inducing protein unfolding which enhances conformational entropy and higher protein adsorption.

Tuning the electronic structure of graphene through nitrogen doping: experiment and theory

Tuning the electronic properties of graphene by doping atoms into its lattice makes it more applicable for electronic devices. We present a study of nitrogen doped graphene samples grown using chemical vapor deposition with a variety of synthesis conditions. Soft X-ray absorption and emission spectroscopy, which are techniques sensitive to the unoccupied and occupied partial electronic density of states, respectively, were used to study the electronic structure of N-doped graphene. Complementary full-potential, all-electron density functional theory calculations of the measured spectra reveal the existence of graphitic, pyridinic and nitrilic-like sites in the samples studied. Although our study shows that the defect type is sensitively related to the synthesis conditions, the graphitic configuration is found to be the most dominant one in each system studied. The dependence of the defect type on the sample growth conditions and the corresponding shifts in the Fermi energy level from the Dirac point, result in n- or p-type material being obtained.

Impact absorption properties of carbon fiber reinforced bucky sponges

We describe the super compressible and highly recoverable response of bucky sponges as they are struck by a heavy flat-punch striker. The bucky sponges studied here are structurally stable, self-assembled mixtures of multiwalled carbon nanotubes (MWCNTs) and carbon fibers (CFs). We engineered the microstructure of the sponges by controlling their porosity using different CF contents. Their mechanical properties and energy dissipation characteristics during impact loading are presented as a function of their composition. The inclusion of CFs improves the impact force damping by up to 50% and the specific damping capacity by up to 7% compared to bucky sponges without CFs. The sponges also exhibit significantly better stress mitigation characteristics compared to vertically aligned CNT foams of similar densities. We show that delamination occurs at the MWCNT-CF interfaces during unloading, and it arises from the heterogeneous fibrous microstructure of the bucky sponges.

Simultaneous Suppression of the Dendrite Formation and Shuttle Effect in a Lithium-Sulfur Battery by Bilateral Solid Electrolyte Interface

Abstract Although the reversible and inexpensive energy storage characteristics of the lithium–sulfur (Li‐S) battery have made it a promising candidate for electrical energy storage, the dendrite growth (anode) and shuttle effect (cathode) hinder its practical application. Here, it is shown that new electrolytes for Li‐S batteries promote the simultaneous formation of bilateral solid electrolyte interfaces on the sulfur‐host cathode and lithium anode, thus effectively suppressing the shuttle effect and dendrite growth. These high‐capacity Li‐S batteries with new electrolytes exhibit a long‐term cycling stability, ultrafast‐charge/slow‐discharge rates, super‐low self‐discharge performance, and a capacity retention of 94.9% even after a 130 d long storage. Importantly, the long cycle stability of these industrial grade high‐capacity Li‐S pouch cells with new electrolytes will provide the basis for creating robust energy dense Li‐S batteries with an extensive life cycle.

A Versatile Carbon Nanotube-Based Scalable Approach for Improving Interfaces in Li-Ion Battery Electrodes

Resistive interfaces within the electrodes limit the energy and power densities of a battery, for example, a Li-ion battery (LIB). Typically, active materials are mixed with conductive additives in organic solvents to form a slurry, which is then coated on current collectors (e.g., bare or carbon-coated Al foils) to reduce the inherent resistance of the active material. Although many approaches using nanomaterials to either replace Al foils or improve conductivity within the active materials have been previously demonstrated, the resistance at the current collector active material interface (CCAMI), a key factor for enhancing the energy and power densities, remains unaddressed. We show that carbon nanotubes (CNTs), either directly grown or spray-coated on Al foils, are highly effective in reducing the CCAMI resistance of traditional LIB cathode materials (LiFePO4 or LFP and LiNi0.33Co0.33Mn0.33O2 or NMC). Moreover, the CNT coatings displace the need for currently used toxic organic solvents (e.g., N-methyl-2-pyrrolidone) by providing capillary channels, which improve the wetting of aqueous dispersions containing active materials. The vertically aligned CNT-coated electrodes exhibited energy densities as high as (1) ∼500 W h kg–1 at ∼170 W kg–1 for LFP and (2) ∼760 W h kg–1 at ∼570 W kg–1 for NMC. The LIBs with CCAMI-engineered electrodes withstood discharge rates as high as 600 mA g–1 for 500 cycles in the case of LFP, where commercial electrodes failed. The CNT-based CCAMI engineering approach is versatile with wide applicability to improve the performance of even textured active materials for both cathodes and anodes.