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Shi, Zhangxing

Publications and source records attributed to Shi, Zhangxing.

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Stable, Impermeable Hexacyanoferrate Anolyte for Nonaqueous Redox Flow Batteries

Redox-active molecules, or redoxmers, in nonaqueous redox flow batteries often suffer from membrane crossover and low electrochemical stability. Transforming inorganic polyionic redoxmers established for aqueous batteries into nonaqueous candidates is an attractive strategy to address these challenges. Here, in this study, we demonstrate such tailoring for hexacyanoferrate (HCF) by pairing the anions with tetra-n-butylammonium cation (TBA + ). TBA 3 HCF has good solubility in acetonitrile and >1 V lower redox potential vs the aqueous counterpart; thus, the familiar aqueous catholyte becomes a new nonaqueous anolyte. The lowering of redox potential correlates with replacement of water by acetonitrile in the solvation shell of HCF, which can be traced to H-bond formation between water and cyanide ligands. Symmetric flow cells indicate exceptional stability of HCF polyanions in nonaqueous electrolytes and Nafion membranes completely block HCF crossover in full cells. Ion pairing of metal complexes with organic counterions can be effective for developing promising redoxmers for nonaqueous flow batteries.

25 ENERGY STORAGE↗
DOE OSTI2024

Solvents and slurries comprising a poly(carboxylic acid) binder for silicon electrode manufacture

An silicon-containing electrode is formed by coating a silicon-containing slurry onto a conductive current collector. The slurry comprises a binder solution comprising a poly(carboxylic acid) binder dissolved in a mixed solvent system comprising an amide solvent of Formula I, as described herein, and a second solvent which can be water and/or an organic solvent. The binder preferably comprises poly(acrylic acid). The mixed solvent system comprises about 10 to about 99 vol % of the amide solvent of Formula I. The binder solution is utilized as a solvent for a slurry of silicon-containing particles for preparing the silicon-containing electrode. The slurries comprising the mixed solvent system have higher viscosity and are more stable than slurries containing the same concentrations of silicon particles, carbon particles, and binder in water as the sole solvent.

Zhang, Lu↗
DOE OSTI2022

Solvents and slurries comprising a poly(carboxylic acid) binder for silicon electrode manufacture

A binder solution for manufacturing silicon-based anodes useful for lithium-ion electrochemical cells is described herein. The binder solution comprises a poly(carboxylic acid) binder dissolved in a mixed solvent system comprising an amide solvent of Formula I, as described herein, and a second solvent which can be water and/or an organic solvent. The binder preferably comprises poly(acrylic acid). The mixed solvent system comprises about 10 to about 99 vol % of the amide solvent of Formula I. The binder solution is utilized as a solvent for a slurry of silicon-containing particles for preparing a silicon-containing electrode. The slurries made with the mixed solvent systems have higher viscosity and are more stable than slurries containing the same concentrations of silicon particle, carbon particles, and binder in water as the sole solvent.

Zhang, Lu↗
DOE OSTI2022

Binders for silicon electrodes in lithium-ion batteries

An electrode for a lithium-ion electrochemical cell comprises silicon particles and carbon particles coated on a conductive current collector. The silicon and carbon particles being bound to each other and to the current collector by a cross-linked binder formed from a combination of a poly(carboxylic acid) such as poly(acrylic acid) and a branched polyethyleneimine. A method of preparing the anode also is described.

Shi, Zhangxing↗
DOE OSTI2021

A chemical switch enabled autonomous two-stage crosslinking polymeric binder for high performance silicon anodes

Silicon (Si) is a promising high-capacity anode material for high-energy-density lithium-ion batteries. However, the drastic volumetric changes of Si upon lithiation/delithiation hinder the practical use of Si anodes. Although adhesive polymeric binders, such as poly(acrylic acid) (PAA), mitigate this issue, the cycling performance of the fabricated Si anodes is still far from meeting the criteria of practical applications. In this study, we present a novel polymeric binder system for Si anodes consisting of PAA, a chemical switch (ammonia, NH 3 ), and a crosslinker (branched polyethylenimine, PEI). The crosslinking between PAA and PEI is switched off in the slurry, which can then be turned on during electrode drying. Interestingly, the crosslinking reaction consists of two stages: ionic cross-linking (PAA-PEI-i) and covalent crosslinking (PAA-PEI-c) at a higher temperature (e.g., 130 °C). In half-cells, Si anodes fabricated using the PAA-PEI-c binder show a 67% increase in capacity retention compared to PAA anodes over 150 cycles at C/3 rate. The PAA-PEI-c binder also outperforms PAA in full cells. In addition, the chemical switch controlled crosslinking binder system also facilitates the slurry making process by avoiding early crosslinking. This system requires no additional steps compared to the conventional electrode lamination process, showing enormous potential for direct adoption in large-scale manufacturing.

25 ENERGY STORAGE↗
DOE OSTI2021

TEMPO allegro: liquid catholyte redoxmers for nonaqueous redox flow batteries

Redoxmers are organic active molecules storing energy in redox flow batteries (RFBs). Liquid redoxmers represent an extreme scenario where maximum concentration may be achieved by minimizing supporting solvents, thus maximizing the energy density of RFBs. Herein, a series of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-based high potential (catholyte) liquid redoxmers, TEMPO-EG1, TEMPO-EG2, and TEMPO-EG3, were developed by incorporating polyethylene glycol (PEG) chains. Such modifications not only afford dramatic physical changes from solid to liquid and full miscibility in acetonitrile, but also impact the redox behavior. DFT calculations indicate that the incorporated PEG chains impact the charge distribution, which may account for the electrochemical changes. Importantly, compared to our previous liquid catholytes, the new redoxmers exhibit lower viscosity, which is desired for enhancing high concentration cycling performance. Furthermore, by using a hybrid flow cell, TEMPO-EG1 demonstrated more than 70% capacity retention over 100 cycles at 0.1 M and 66% capacity retention at 0.5 M, affording excellent cyclability at various concentrations. The study exemplifies how molecular engineering tuned the rheological properties of redoxmers, such as viscosity, to improve the high concentration cycling performance of RFBs, which may represent a promising avenue for a high energy density and low-cost flow battery system.

25 ENERGY STORAGE↗
DOE OSTI2020

Restorable Neutralization of Poly(acrylic acid) Binders toward Balanced Processing Properties and Cycling Performance for Silicon Anodes in Lithium-Ion Batteries

Neutralization of poly(acrylic acid) (PAA)-based binders using lithium hydroxide is a common strategy for fabricating silicon anode laminates, which improves rheological properties of slurries toward high-quality electrode laminates. However, the significantly increased basicity causes degradation of Si particles while the irreversible conversion of carboxylic acid groups to lithium carboxylates undermines the binding strength, collectively leading to adverse cycling performance of the fabricated Si anodes. Herein, a novel neutralization process for PAA binders is developed. A weak base, ammonia (NH 3 ), was discovered as a neutralizing agent that still promotes rheological response of binder solutions but results in a reduced pH increase. Interestingly, the resulting ammonium carboxylate groups may cleave during the drying process to restore the neutralized PAA (PAA-NH 3 ) binders to their pristine states. The best-performing composition of 50% neutralization (PAA-50%NH 3 ) provides comparable rheological response as a PAA-Li binder as well as much improved cycling performance. Additionally, the half-cells using the PAA-50%NH 3 binder can deliver 60% capacity retention over 100 cycles at C/3 rate, affording a 23.8% increase compared to PAA-Li half-cells. This restorable neutralization process of PAA binders represents an innovative strategy of mitigating issues from slurry processing of Si particles to achieve concurrent improvements in high-quality lamination and cycling performance.

25 ENERGY STORAGE↗
DOE OSTI2020

Competitive Pi-Stacking and H-Bond Piling Increase Solubility of Heterocyclic Redoxmers

Redoxmers are organic molecules that carry electric charge in flow batteries. In many instances, they consist of heteroaromatic moieties modified with appended groups to prevent stacking of the planar cores and increase solubility in liquid electrolytes. This higher solubility is desired as it potentially allows achieving greater energy density in the battery. However, the present synthetic strategies often yield bulky molecules with low molarity even when they are neat and still lower molarity in liquid solutions. Fortunately, there are exceptions to this rule. Here, we examine one well-studied redoxmer, 2,1,3-benzothiadiazole, which has solubility similar to 5.7 M in acetonitrile at 25 degrees C. We demonstrate computationally and prove experimentally that the competition between two packing motifs, face-to-face it-stacking and random N-H bond piling, introduces frustration that confounds nucleation in crowded solutions. Our findings and examples from related systems suggest a complementary strategy for the molecular design of redoxmers for high energy density redox flow cells.

25 ENERGY STORAGE↗