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Yang, Zhenzhen

Publications and source records attributed to Yang, Zhenzhen.

At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Positive Role of Fluorine Impurity in Recovered LiNi 0.6 Co 0.2 Mn 0.2 O 2 Cathode Materials

Lithium-ion battery (LIB) recycling is considered as an important component to enable industry sustainability. A massive number of LIBs in portable electronics, electric vehicles, and grid storage will eventually end up as wastes, leading to serious economic and environmental problems. Hence, tremendous efforts have been made to improve the hydrometallurgical recycling process because it is the most promising option for handling end-of-life LIBs owing to its wide applicability, low cost, and high productivity. Despite these advantages, some extra elements (Al, Fe, C, F, and so forth) remain as impurities in the removal process and are retained in the solution, which is a great challenge to obtain high-quality cathode materials. In this work, the impacts caused by fluorine impurity on the LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) cathode are intensively investigated via hydrometallurgical coprecipitation for the first time. Our results show that up to 1 at. % fluorine impurity brings a positive influence on the recovered material due to a higher Ni 2+ ratio on the surface of cathode particles. In addition, the presence of fluoride ions during coprecipitation could lead to the formation of holes in cathode particles, which improves the rate capability and cyclability dramatically. Compared to the virgin material, the capacity of the NCM622 material with 0.2 at. % fluorine impurity is boosted by ~8% (167.7 mA h/g) with a remarkable capacity retention of 98.0% after 100 cycles at 0.33 C. Besides, the cathode with 0.2 at. % fluorine impurity shows a far better rate performance, especially at high rates (~7% increased at 5 C) than that of virgin. Furthermore, these results convince that a low concentration of fluorine impurity is desirable in the hydrometallurgical recycling process. More importantly, this study offers implications in the design of high-performance NCM622 cathode materials via coprecipitation production with ion doping in the near future.

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DOE OSTI2021

An Environmentally Benign Electrolyte for High Energy Lithium Metal Batteries

In this work, a hybrid electrolyte comprising a high content of H 2 O for a lithium metal cell is reported. At high LiFSI salt concentration, the N-methyl-N-propyl-piperidinium bis(fluorosulfonyl) imide (PMpipFSI) electrolyte can tolerate up to 1 M H2O addition without sacrificing its redox stability on both lithium nickel manganese cobalt oxide (NMC) cathode and lithium metal anode. Molecular dynamics simulations revealed the underpinned mechanism that, at high salt concentrations, H 2 O molecules are embedded in the Li + , PMpip + , and FSI - bulk as a structural material with a strong solvation with Li + and are orderly distributed at the surface of both electrodes. This electrolyte eliminates the critical moisture controls required for the state-of-the-art (SOA) carbonate/LiPF 6 electrolyte, electrode, separator and cell assembly, thus significantly reducing the cost of the mass production of the batteries.

molecular dynamics simulation↗
DOE OSTI2021

Effect of cathode on crosstalk in Si-based lithium-ion cells

Crosstalk between the cathode and the anode in Li-ion batteries has a great impact on performance, safety and cycle lifetime. However, a systematic investigation of crosstalk behavior in silicon (Si)-based cells with various cathode materials has not been reported. We investigated the crosstalk behavior of a Si anode coupled with one of the following cathodes—LiCoO 2 (LCO), LiNi 0.5 Mn 0.3 Co 0.2 (NMC532), and LiFePO 4 (LFP)—in a full cell. For each electrochemical couple, we compared electrolyte decomposition products, solid electrolyte interphase (SEI) chemistry, and degradation mechanisms during cycling. From a very early stage of cycling, each couple showed different crosstalk behavior; different electrolyte decomposition products and SEI chemistry on the Si anodes were seen. Specifically, the formation and growth mechanism of Si SEI differ depending on cathode materials. For the LFP system, the Si SEI rich in LiF and inorganic species, which is stable and robust. It forms at an early stage of cycle. As a result, the SEI of Si from the LFP system well tolerates SEI breakage due to mechanical changes of Si and suppresses Li loss, resulting in stable cycle life.

25 ENERGY STORAGE↗
DOE OSTI2021

Chemical Interplay of Silicon and Graphite in a Composite Electrode in SEI Formation

In this study, we investigated the effect of the Si/graphite weight ratio in half-cells on the solid electrolyte interphase (SEI) layer's chemistry. The nominal concentrations of active materials were (wt % Si/wt % Gr) 15/73, 30/58, 60/28, and 80/0. The electrolyte in the cells consisted of either 1.2 M LiPF 6 in ethylene carbonate/ethyl methyl carbonate (3:7 by wt) or 1.2 M LiPF 6 in ethylene carbonate:ethyl methyl carbonate (3:7 by wt) + 10 wt % fluoroethylene carbonate. These coin cells were cycled five times at the C/10 rate. As expected, the addition of silicon to the electrode significantly increased the measured capacity. Examination of the aged composite material showed that the electrolyte influenced the concentration of chemical environments on the surface. Depth profiling revealed that these concentrations of surface environments changed with sputtering time. A statistics-of-mixtures model was used to deconvolute how silicon and graphite interacted during the formation of these species and how the interaction changed with depth.

25 ENERGY STORAGE↗
DOE OSTI2021

Graphitic Aza-Fused π-Conjugated Networks: Construction, Engineering, and Task-Specific Applications

2D π-conjugated networks linked by aza-fused units represent a pivotal category of graphitic materials with stacked nanosheet architectures. Extensive efforts have been directed at their fabrication and application since the discovery of covalent triazine frameworks (CTFs). Besides the triazine cores, tricycloquinazoline and hexaazatriphenylene linkages are further introduced to tailor the structures and properties. Diverse related materials have been developed rapidly, and a thorough outlook is necessitated to unveil the structure–property–application relationships across multiple subcategories, which is pivotal to guide the design and fabrication toward enhanced task-specific performance. Herein, the structure types and development of related materials including CTFs, covalent quinazoline networks, and hexaazatriphenylene networks, are introduced. Advanced synthetic strategies coupled with characterization techniques provide powerful tools to engineer the properties and tune the associated behaviors in corresponding applications. Case studies in the areas of gas adsorption, membrane-based separation, thermo-/electro-/photocatalysis, and energy storage are then addressed, focusing on the correlation between structure/property engineering and optimization of the corresponding performance, particularly the preferred features and strategies in each specific field. In the last section, the underlying challenges and opportunities in construction and application of this emerging and promising material category are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Revealing the Fast and Durable Na + Insertion Reactions in a Layered Na 3 Fe 3 (PO 4 ) 4 Anode for Aqueous Na-Ion Batteries

Aqueous sodium-ion batteries represent a promising approach for stationary energy storage; however, the lack of appropriate anode materials has substantially retarded their development. Herein, we demonstrated an iron-based phosphate material of Na 3 Fe 3 (PO 4 ) 4 as an inexpensive and efficacious anode alternative. While the Fe 3+ /Fe 2+ redox couple renders a two-Na-insertion reaction with desirable potentials, its unique layered structure further facilitates the Na-insertion kinetics and reversibility. Consequently, this electrode exhibits an appealing Na-insertion performance, with a reversible capacity of ~83 mAh g –1 , suitable anode potential of -0.4 V vs Ag/AgCl, excellent rate capability of 200 C, and outstanding cycling of 6000 cycles. Utilizing operando synchrotron X-ray diffraction and X-ray absorption spectroscopy, we revealed the structural evolution of the Na 3 Fe 3 (PO 4 ) 4 anode during the two-electron reaction, where the extremely small volume expansion (~3%) enables its fast-charging and long-cycling capability. Our work suggests new considerations of developing versatile iron phosphate compounds as appealing anode materials for energy storage in aqueous electrolytes.

25 ENERGY STORAGE↗
DOE OSTI2021

Comprehensive Insights into Nucleation, Autocatalytic Growth, and Stripping Efficiency for Lithium Plating in Full Cells

Synchrotron high-energy X-ray diffraction is used to enable nondestructive detection and quantification of heterogeneous lithium plating in working batteries. In this study a LiNi 0.5 Mn 0.3 Co 0.2 O 2 /graphite pouch cell was operated under 6C fast-charge rate for greater than 1200 cycles. The magnitude and spatial distribution of lithium plating, lithium stripping, and the effect of metallic lithium deposition on lithium intercalation into graphite were quantified. Fully intercalated graphite (LiC 6 ) was detected after discharge with a lateral distribution closely correlated with lithium plating, which can be used as a higher-sensitivity indicator for lithium plating. Over an extended cycle life, the overall metallic lithium concentration followed a sigmoidal curve indicating two-stage continuous nucleation and autocatalytic growth. The lithium stripping efficiency underwent an exponential decay as a function of cycle life as the buildup of metallic lithium hindered the efficient dissolution back into the electrolyte. The findings provide direct insights into the characteristics of lithium plating and stripping under realistic fast-charge conditions.

25 ENERGY STORAGE↗
DOE OSTI2021

Highly Perfluorinated Covalent Triazine Frameworks Derived from a Low-Temperature Ionothermal Approach Towards Enhanced CO 2 Electroreduction

Perfluorinated covalent triazine frameworks (F-CTFs) have shown unique features and attractive performance in separation and catalysis. However, state-of-art F-CTFs synthesized via the ZnCl 2 -promoted procedure have quite low fluorine contents due to C-F bond cleavage induced by chloride (a Lewis base) and the harsh conditions deployed (400-700 °C). Fabricating F-CTFs with high fluorine contents (> 30 wt%) remains challenging. Herein, we present a low-temperature ionothermal approach (275 °C) to prepare F-CTFs, which is achieved via polymerization of tetrafluoroterephthalonitrile (TFPN) over the Lewis superacids, e.g., zinc triflimide [Zn(NTf 2 ) 2 ] without side reactions. With low catalyst loading (equimolar), F-CTFs are afforded with high fluorine content (31 wt%), surface area up to 367 m 2 g -1 , and micropores around 1.1 nm. The highly hydrophobic F-CTF-1 exhibits good capability to boost electroreduction of CO 2 to CO, with faradaic efficiency of 95.7% at –0.8 V and high current density (–141 mA cm -2 ) surpassing most of the metal-free electrocatalysts.

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DOE OSTI2021

Building a spontaneously formed and self-healing protective layer with an F-rich electrochemically active organic molecule for ultra-stable Li metal batteries

Additives in the electrolyte act as engineers in Li metal batteries. Inspired by the superior cycle performance of organic materials in half cells, tetrafluoro-1,4-benzoquinone (TFBQ), the main structure of which has been widely applied as an organic cathode material, is utilized for the first time as an additive for Li metal protection. By chemical and electrochemical reactions between TFBQ and the Li metal surface, an F-rich interface layer is in situ formed on the Li metal surface during the charge and discharge process. From electrochemical tests and characterization, the powerful self-healing ability of the interface layer enabled by TFBQ is revealed, making an extremely stable Li metal anode. By using a lean electrolyte with 0.1 M TFBQ, the cycle life of Li|Li symmetric cells is increased at least 6 times compared to the control group. Moreover, impressive full cell performance was achieved. Ultra-stable Li–LFP cells showed a 0.026% average degradation for 600 cycles at 1C and Li–NMC622 cells showed a 36.8% higher capacity compared to the control group over 200 cycles at 0.5C, which are among the best results reported. Furthermore, this work efficiently and conveniently provides a new research direction to Li metal protection and Li metal batteries.

25 ENERGY STORAGE↗
DOE OSTI2021

A bifunctional zeolitic porous liquid with incompatible Lewis pairs for antagonistic cascade catalysis

The emergence of porous liquids (PLs) opened opportunities to form unique antagonistic systems capable of fulfilling cascade reactions promoted by incompatible active sites in one pot, which is a long-term challenging subject in catalysis. Herein, unique bifunctional type III PL-based systems were facilely fabricated via assembly of zeolite nanosheets with ionic liquids. Rational structural design afforded PLs that feature high zeolite concentration, stable dispersion after 2 years, abundant cavity distribution, and involvement of antagonistic groups (acid and base sites) in separated and active form via steric hindrance control and electronic repulsion regulation. These unique properties worked cooperatively to fulfill the cascade deacetalization-Knoevenagel/Aldol condensation in one pot with superior catalytic efficiency outperforming the traditional systems. The key to success lies in the formation of bifunctional composites, transformation of zeolite from heterogeneous to homogeneous via surface modification, as well as rapid mass transfer ensured by the rigid porous architecture.

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DOE OSTI2021

Valence Effects of Fe Impurity for Recovered LiNi 0.6 Co 0.2 Mn 0.2 O 2 Cathode Materials

Iron impurities are generally included in the obtained leaching liquor solution during the hydrometallurgical recycling method of spent lithium-ion batteries (LIBs) due to the usage of iron in battery casings and machinery parts of recycling equipment, which would definitely affect the physical and electrochemical features of the recovered active materials. In this paper, the effects of iron impurity with different valence states (Fe 2+ and Fe 3+ ) and gradient concentrations (0.2, 1.0, and 5.0 at. %) for the obtained LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) cathodes are fully studied. It is found that Fe3+ impurity could easily lower the tap density and average size of NCM622 particles and even introduce some impurity phases in the NCM622 structure at high concentration (5.0 at. %), leading to much lower specific capacity, worse rate capability, and cycling performance of the Fe 3+ -based NCM622 cathode. On contrast, with certain concentrations of Fe 2+ impurity (0.2 and 1.0 at. %), the NCM622 cathode material exhibits comparable and much better electrochemical properties compared with the virgin NCM622 materials. Based on these results, the valence of Fe impurity should be considered and controlled as well as its concentration during the recycling process design for spent LIBs.

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DOE OSTI2021

From bulk to interface: electrochemical phenomena and mechanism studies in batteries via electrochemical quartz crystal microbalance

Understanding the bulk and interfacial behaviors during the operation of batteries (e.g., Li-ion, Na-ion, Li–O 2 batteries, etc.) is of great significance for the continuing improvement of the performance. Electrochemical quartz crystal microbalance (EQCM) is a powerful tool to this end, as it enables in situ investigation into various phenomena, including ion insertion/deinsertion within electrodes, solid nucleation from the electrolyte, interphasial formation/evolution and solid–liquid coordination. As such, EQCM analysis helps to decipher the underlying mechanisms both in the bulk and at the interface. This tutorial review will present the recent progress in mechanistic studies of batteries achieved by the EQCM technology. Here, the fundamentals and unique capability of EQCM are first discussed and compared with other techniques, and then the combination of EQCM with other in situ techniques is also covered. In addition, the recent studies utilizing EQCM technologies in revealing phenomena and mechanisms of various batteries are reviewed. Perspectives regarding the future application of EQCM in battery studies are given at the end.

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DOE OSTI2021

Ultrasound-driven fabrication of high-entropy alloy nanocatalysts promoted by alcoholic ionic liquids

High-entropy alloy nanoparticles (HEA-NPs) are highly underutilized in heterogeneous catalysis due to the absence of a reliable, sustainable, and facile synthetic method. Herein, we report a facile synthesis of HEA nanocatalysts realized via an ultrasound-driven wet chemistry method promoted by alcoholic ionic liquids (AILs). Owing to the intrinsic reducing ability of the hydroxyl group, AILs were synthesized and utilized as environmentally friendly alternatives to conventional reducing agents and volatile organic solvents in the synthetic process. Under high-intensity ultrasound irradiation, Au 3+ , Pd 2+ , Pt 2+ , Rh 3+ , and Ru 3+ ions were co-reduced and transformed into single-phase HEA (AuPdPtRhRu) nanocrystals without calcination. Characterization results reveal that the as-synthesized nanocrystals are composed of elements of Au, Pd, Pt, Rh, and Ru as expected. Compared to the monometallic counterparts such as Pd-NPs, the carbon-supported HEA nanocatalysts show superior catalytic performance for selective hydrogenation of phenol to cyclohexanone in terms of yield and selectivity. Our synthetic strategy provides an improved and facile methodology for the sustainable synthesis of multicomponent alloys for catalysis and other applications.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Engineering the Si Anode Interface via Particle Surface Modification: Embedded Organic Carbonates Lead to Enhanced Performance

Si nanoparticles (SiNPs) are recognized as a promising anode material for next-generation high-energy lithium-ion batteries. However, due to the more stringent requirements resulting from severe volume change, the solid-electrolyte interphase (SEI) on SiNPs plays a critical role in determining their cycling performance. Engineering the interface for higher stability has become an effective yet challenging approach to accommodate the deterioration of the silicon anode from the repeated lithiation/delithiation process. Herein, we report a novel approach of engineering a covalently bonded organic monolayer of ethylene carbonates onto the surface of the SiNPs that can help form a sturdy SEI. Finally, this molecule-level surface modification provides an effective approach to enable high-energy lithium-ion batteries with Si anodes.

25 ENERGY STORAGE↗
DOE OSTI2021

Benchmark CO 2 separation achieved by highly fluorinated nanoporous molecular sieve membranes from nonporous precursor via in situ cross-linking

Molecular sieve membranes with rigid micropores and CO 2 -philic functionalities within the architectures are promising candidates in CO 2 separation. However, the development of ctieve approaches for their fabrication still remains a significant challenge. In this study, an in situ cross-linking strategy is developed for the preparation of nanoporous fluorinated moleffecular sieve membranes using commercially available dense and non-porous polystyrene (M PS ) as a precursor template. Based on the dehydrative Friedel-Crafts reactions with highly fluorinated benzylic alcohols, M PS membranes are cross-linked in situ upon exposure to Brønsted acid (CF 3 SO 3 H), affording fluorinated microporous polymeric membranes with surface areas up to 523 m 2 g –1 and the presence of micropores centered at 1.1–1.3 nm as well as ultra-micropores (~0.6 nm). The obtained modified membranes exhibit good ideal CO 2 permeability of 797 barrer and CO 2 /N 2 selectivity of 28.5. In addition, high fluorine content (up to 28.5 wt%) and good thermal stability made the cross-linked membranes promising candidates to produce fluorinated carbon molecular sieve membranes with improved textural properties, exhibiting surface areas up to 1020 m 2 g –1 and ultra-micropores of ~0.4 nm. These membranes achieve superior CO 2 /N 2 separation performances exceeding the Robeson upper bound limit (2008).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Doping-modulated strain control of bifunctional electrocatalysis for rechargeable zinc–air batteries

Changes in the local atomic arrangement in a crystal caused by lattice-mismatch-induced strain can efficiently regulate the performance of electrocatalysts for zinc–air batteries (ZABs) in many manners, mainly due to modulated electronic structure configurations that affect the adsorption energies for oxygen-intermediates formed during oxygen reduction and evolution reactions (ORR and OER). However, the application of strain engineering in electrocatalysis has been limited by the strain relaxation caused by structural instability such as dissolution and destruction, leading to insufficient durability towards the ORR/OER. In this work, we propose a doping strategy to modulate the phase transition and formation of self-supported cobalt fluoride–sulfide (CoFS) nanoporous films using a low amount of copper (Cu) as a dopant. This well-defined Cu–CoFS heterostructure overcomes the obstacle of structural instability. Our study of the proposed Cu–CoFS also helps establish the structure–property relationship of strained electrocatalysts by unraveling the role of local strain in regulating the electronic structure of the catalyst. As a proof-of-concept, the Cu–CoFS electrocatalyst with doping-modulated strain exhibited superior onset potentials of 0.91 V and 1.49 V for the ORR and OER, respectively, surpassing commercial Pt/C@RuO 2 and benchmarking non-platinum group metal (non-PGM) catalysts. ZABs with the Cu–CoFS catalyst delivered excellent charge/discharge cycling performance with an extremely low voltage gap of 0.5 V at a current density of 10 mA cm –2 and successively 0.93 V at a high current density of 100 mA cm –2 and afforded an outstanding peak power density of 255 mW cm –2 .

25 ENERGY STORAGE↗
DOE OSTI2021

CO 2 Chemisorption Behavior of Coordination-Derived Phenolate Sorbents

CO 2 chemisorption via C-O bond formation is an efficient methodology in carbon capture especially using phenolate-based ionic liquids (ILs) as the sorbents to afford carbonate products. However, most of the current IL systems involve alkylphosphonium cations, leading to side reactions via the ylide intermediate pathway. It is important to figure out the CO 2 chemisorption behavior of phenolate-derived sorbents using inactive and easily accessible cation counterparts without active protons. Herein, phenolate-based systems were constructed via coordination between alkali metal cations with crown ethers to avoid the participation of active protons in CO 2 chemisorption. Reaction pathway study revealed that CO 2 uptake could be achieved by O-C bond formation to afford carbonate. CO 2 uptake capacity and reaction enthalpy were significantly influenced by the coordination effect, alkali metal types, and alkyl groups on the benzene ring.

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