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The last decade has witnessed the booming development of optical imaging in the second near-infrared (NIR-II, 1000-1700 nm) window for disease screening and image-guided surgical interventions, due to the merits of multi-color observations and high spatio-temporal resolution in deep tissue. Therefore, bright and multispectral NIR-II probes are required and play a key role. Here, we report the synthesis of a set of bright rare-earth based NIR-II downshifting nanoparticles (DSNPs) with hexagonal phase (β phase). As compared with the widely reported DSNPs (β-NaYF4@NaYF

Multiplexed imaging in the second near-infrared (NIR-II, 1000-1700 nm) window, with much reduced tissue scattering and autofluorescence background noises, could offer comprehensive information for studying biological processes and accurate diagnosis. A critical requirement for harvesting the full potential of multiplexing is to develop fluorescent probes with emission profiles specifically tuned at distinct excitations toward their target applications. However, the lack of versatile probes with separated signals in this NIR-II window hinders the potential of in vivo multiplexed imaging. In this study, we designed three types of Nd

Lithium-ion batteries (LIBs) are being used in locations and applications never imagined when they were first conceived. To enable this broad range of applications, it has become necessary for LIBs to be stable to an ever broader range of conditions, including temperature and energy. Unfortunately, while negative electrodes have received a great deal of focus in electrolyte development, stabilization of positive electrodes remains an elusive target. Here, we report a novel additive that shows the ability to protect positive electrodes against elevated temperatures and voltages. This additive can be used in small quantities, and its targeted behavior allows it to remain functional in complex electrolyte packages. This can prove an effective approach to targeting specific aspects of cell performance.

A hybrid electrolyte comprising a high content of H2O 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, H2O 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/LiPF6 electrolyte, electrode, separator and cell assembly, thus significantly reducing the cost of the mass production of the batteries.

Simply mixing several lithium salts in one electrolyte to obtain blended salt electrolytes has been demonstrated as a promising strategy to formulate advanced electrolytes for lithium metal batteries (LMBs) and lithium-ion batteries (LIBs). In this study, we report the use of dual-salt electrolytes containing lithium hexafluorophosphate (LiPF6) and lithium difluorophosphate (LiDFP) in ethylene carbonate/ethyl methyl carbonate (EC/EMC) mixture and tested them in layered high-nickel LIB cells. LiNi0.94Co0.06O2 was synthesized through a coprecipitation method and was used as a representative high-nickel cathode for the U.S. DOE realizing next-generation cathode (RNGC) deep dive program. The ionic conductivity of dual-salt electrolytes can be maintained by controlling the amount of LiDFP. Techniques including 1H Nuclear Magnetic Resonance (NMR), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-mass spectrometry (ICP-MS), and differential voltage analysis (DVA) were used to understand the improved performance. The multifaceted benefits of using the dual-salt electrolytes include (1) reduced transesterification, (2) formation of a stable cathode electrolyte interface, and (3) mitigation of cathode degradation at high voltages, especially stabilization of oxide particles during the H2 ↔ H3 transformation.

Considering the high energy consumption during processing, and the low compliance and adhesion of ceramic electrolytes, the integration of polymer into ceramic electrolytes provides a way to mitiga...

Molecular engineering of electrolyte structures has led to the successful application of trifluoropropylene carbonate (TFPC), a fluorinated derivative of propylene carbonate (PC), in next-generatio...

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 (NH3), 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-NH3) binders to their pristine states. The best-performing composition of 50% neutralization (PAA-50%NH3) provides comparable rheological response as a PAA-Li binder as well as much improved cycling performance. The half-cells using the PAA-50%NH3 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.

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 ∼5.7 M in acetonitrile at 25 °C. We show computationally and prove experimentally that the competition between two packing motifs, face-to-face π-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.

The thermal degradation of electrolytes containing lithium hexafluorophosphate (LiPF6) is a well-studied subject. However, practical application of the knowledge is difficult since the effects of t...

Nonaqueous electrolyte has become one of the technical barriers in enabling Li-ion battery comprising of a high voltage cathode and high capacity anode. In this work, we demonstrate a saturated piperidinum bis(fluorosulfonyl)imide ionic liquid (IL) with a LiFSI salt not only supports the redox reaction on the cathode at high voltages, but also shows exceptional kinetic stability on the lithiated anode as evidenced by its improved cycling performance in a NMC532/Si-graphite full cells cycled between 4.6 and 3.0 V. On the basis of the spectroscopic/microscopic analysis and molecular dynamics (MD) simulations, the superior performance of the cells is attributed to the formation of solid-electrolyte-interphase on both electrode as well as unique solvation structure where a deadlocked coordination network is established at the saturated state, which prevents transition metal dissolution into the electrolyte via a solvation process.

Due to the strong electron-withdrawing fluorine groups, the aromatic ring of hexafluorobenzene (HFB) becomes more electron-deficient and strongly interacts with the lone-pair electrons of the mediu...

LiNi0.5Co0.2Mn0.3O2 (NCM523), as a cathode material for rechargeable lithium-ion batteries, has attracted considerable attention and been successfully commercialized for decades. NCM is also a promising electrocatalyst for the oxygen evolution reaction (OER), and the catalytic activity is highly correlated to its structure. In this paper, we successfully obtain NCM523 with three different structures: spinel NCM synthesized at low temperature (LT-NCM), disordered NCM (DO-NCM) with lithium deficiency obtained at high temperature, and layered hexagonal NCM at high temperature (HT-NCM). By introducing lithium deficiency to tune the valence state of transition metals in NCM from Ni2+ to Ni3+, DO-NCM exhibits the best catalytic activity with the lowest onset potential (∼1.48 V) and Tafel slope (∼85.6 mV dec-1), whereas HT-NCM exhibits the worst catalytic activity with the highest onset potential (∼1.63 V) and Tafel slope (∼241.8 mV dec-1).

We investigated the static reactions of highly delithiated Li(Ni1/3Mn1/3Co1/3)O2, Li(Ni0.5Mn0.3Co0.2)O2, Li(Ni0.6Mn0.2Co0.2)O2, and Li(Ni0.8Mn0.1Co0.1)O2 positive electrodes with 2,3-butanedione an...

Organic monolayers of epoxy-containing oligo(ethylene oxide)s were grafted to the surface of silicon nanoparticles via a hydrosilylation reaction. The surface functional groups suppressed the chemi...

In silicon-based lithium-ion batteries, polymeric binders play the crucial role of “gluing” the electrode matrix together, providing strong adhesion between the active silicon (Si) and conductive c...

Metallic Na electrodes are promising anodes for low-cost and high-energy density batteries due to their natural abundance and high specific capacity. Unfortunately, they are extremely reactive and ...

Although several principles have been recognized to fabricate a nominal “better” binder, there continues to be a lack of a rational design and synthesis approach that would meet the robust criteria required for silicon (Si) anodes. Herein, we report a synthetic polymer binder, i.e., catechol-functionalized chitosan cross-linked by glutaraldehyde (CS-CG+GA), that serves dual functionalities: (a) wetness-resistant adhesion capability via catechol grafting and (b) mechanical robustness via in situ formation of a three-dimensional (3D) network. A SiNP-based anode with a designed functional polymer network (CS-CG10%+6%GA) exhibits a capacity retention of 91.5% after 100 cycles (2144 ± 14 mAh/g). Properties that are traditionally considered to be advantageous, including stronger adhesion strength and higher mechanical robustness, do not always improve the binder performance. A clear relationship between these properties and ultimate electrochemical performance is established by assessing the rheological behavio...

Increasing the energy densities of Li-ion batteries necessitates operation of layered lithiated oxide cathodes at potentials exceeding 4 V vs Li/Li+. When continually exposed to such high potential...

An epoxy group was successfully attached to the surface of silicon nanoparticle (SiNPs) via a silanization reaction between silanol-enriched SiNPs and functional silanes. The epoxy-functionalized SiNPs showed a much improved cell performance compared with the pristine SiNPs because of the increased stability with electrolyte and the formation of a covalent bond between the epoxy group and the polyacrylic acid binder. Furthermore, the anode laminate made from epoxy-SiNPs showed much enhanced adhesion strength. Post-test analysis shed light on how the epoxy-functional group affects the physical and electrochemical properties of the SiNP anode.

Redox-active organic materials (ROMs) are becoming increasingly attractive for use in redox flow batteries as promising alternatives to traditional inorganic counterparts. However, the reported ROMs are often accompanied by challenges, including poor solubility and stability. Herein, we demonstrate that the commonly used diquat herbicides, with solubilities of >2 M in aqueous electrolytes, can be used as stable anolyte materials in organic flow batteries. When coupled with a ferrocene-derived catholyte, the flow cells with the diquat anolyte demonstrate long galvanic cycling with high capacity retention. Notably, the mechanistic underpinnings of this remarkable stability are attributed to the improved π-conjugation that originated from the near-planar molecular conformations of the spatially constrained 2,2′-bipyridyl rings, suggesting a viable structural engineering strategy for designing stable organic materials.

We evaluate hydrofluoroether (HFE) cosolvents with varying degrees of fluorination in the acetonitrile-based solvate electrolyte to determine the effect of the HFE structure on the electrochemical performance of the Li–S battery. Solvates or sparingly solvating electrolytes are an interesting electrolyte choice for the Li–S battery due to their low polysulfide solubility. The solvate electrolyte with a stoichiometric ratio of LiTFSI salt in acetonitrile, (MeCN)2–LiTFSI, exhibits limited polysulfide solubility due to the high concentration of LiTFSI. We demonstrate that the addition of highly fluorinated HFEs to the solvate yields better capacity retention compared to that of less fluorinated HFE cosolvents. Raman and NMR spectroscopy coupled with ab initio molecular dynamics simulations show that HFEs exhibiting a higher degree of fluorination coordinate to Li+ at the expense of MeCN coordination, resulting in higher free MeCN content in solution. However, the polysulfide solubility remains low, and no cr...

Redox-active organic materials (ROMs) have shown great promise for redox flow battery applications but generally encounter limited cycling efficiency and stability at relevant redox material concentrations in nonaqueous systems. Here we report a new heterocyclic organic anolyte molecule, 2,1,3-benzothiadiazole, that has high solubility, a low redox potential, and fast electrochemical kinetics. Coupling it with a benchmark catholyte ROM, the nonaqueous organic flow battery demonstrated significant improvement in cyclable redox material concentrations and cell efficiencies compared to the state-of-the-art nonaqueous systems. Especially, this system produced exceeding cyclability with relatively stable efficiencies and capacities at high ROM concentrations (>0.5 M), which is ascribed to the highly delocalized charge densities in the radical anions of 2,1,3-benzothiadiazole, leading to good chemical stability. This material development represents significant progress toward promising next-generation energy st...

Triethlylphosphite (TEP) and tris(2,2,2-trifluoroethyl) phosphite (TTFP) have been evaluated as electrolyte additives for high-voltage Li-ion battery cells using a Ni-rich layered cathode material LiNi0.5Co0.2Mn0.3O2 (NCM523) and the conventional carbonate electrolyte. The repeated charge/discharge cycling for cells containing 1 wt % of these additives was performed using an NCM523/graphite full cell operated at the voltage window from 3.0-4.6 V. During the initial charge process, these additives decompose on the cathode surface at a lower oxidation potential than the baseline electrolyte. Impedance spectroscopy and post-test analyses indicate the formation of protective coatings by both additives on the cathode surface that prevent oxidative breakdown of the electrolyte. However, only TTFP containing cells demonstrate the improved capacity retention and Coulombic efficiency. For TEP, the protective coating is also formed, but low Li(+) ion mobility through the interphase layer results in inferior performance. These observations are rationalized through the inhibition of electrocatalytic centers present on the cathode surface and the formation of organophosphate deposits isolating the cathode surface from the electrolyte. The difference between the two phosphites clearly originates in the different properties of the resulting phosphate coatings, which may be in Li(+) ion conductivity through such materials.

With the correlation between Li+ solvation and interphasial chemistry on anodes firmly established in Li-ion batteries, the effect of cation–solvent interaction has gone beyond bulk thermodynamic and transport properties and become an essential element that determines the reversibility of electrochemistry and kinetics of Li-ion intercalation chemistries. As of now, most studies are dedicated to the solvation of Li+, and the solvation of anions in carbonate-based electrolytes and its possible effect on the electrochemical stability of such electrolytes remains little understood. As a mirror effort to prior Li+ solvation studies, this work focuses on the interactions between carbonate-based solvents and two anions (hexafluorophosphate, PF6–, and tetrafluoroborate, BF4–) that are most frequently used in Li-ion batteries. The possible correlation between such interaction and the interphasial chemistry on cathode surface is also explored.

A high performance Li-S battery with novel fluoroether-based electrolyte was reported. The fluorinated electrolyte prevents the polysulfide shuttling effect and improves the Coulombic efficiency and capacity retention of the Li-S battery. Reversible redox reaction of the sulfur electrode in the presence of fluoroether TTE was systematically investigated. Electrochemical tests and post-test analysis using HPLC, XPS, and SEM/EDS were performed to examine the electrode and the electrolyte after cycling. The results demonstrate that TTE as a cosolvent mitigates polysulfide dissolution and promotes conversion kinetics from polysulfides to Li2S/Li2S2. Furthermore, TTE participates in a redox reaction on both electrodes, forming a solid electrolyte interphase (SEI) which further prevents parasitic reactions and thus improves the utilization of the active material.

The successful development of Li-air batteries would significantly increase the possibility of extending the range of electric vehicles. There is much evidence that typical organic carbonate based electrolytes used in lithium ion batteries form lithium carbonates from reaction with oxygen reduction products during discharge in lithium-air cells so more stable electrolytes need to be found. This combined experimental and computational study of an electrolyte based on a tri(ethylene glycol)-substituted trimethylsilane (1NM3) provides evidence that the ethers are more stable toward oxygen reduction discharge species. X-ray photoelectron spectroscopy (XPS) and FTIR experiments show that only lithium oxides and no carbonates are formed when 1NM3 electrolyte is used. In contrast XPS shows that propylene carbonate (PC) in the same cell configuration decomposes to form lithium carbonates during discharge. Density functional calculations of probable decomposition reaction pathways involving solvated oxygen reducti...

One of the silicon-based electrolytes, tris(ethylene glycol)-substituted trimethylsilane (1NM3)–lithium bis(oxalate)borate (LiBOB), is studied as an electrolyte for the LiMn2O4 cathode and graphite anode cell. The solid electrolyte interface (SEI) characteristics and chemical components of both electrodes were investigated by X-ray photoelectron spectroscopy and X-ray diffraction. It was found that SEI components on the anode are similar to those using carbonate–LiBOB electrolyte, which consists of lithium oxalate, lithium borooxalate, and LixBOy. Moreover, we demonstrated that 1NM3–LiPF6 electrolyte, which lacks an SEI formation function, could not maintain the graphite structure during the electrochemical process. Therefore, it is evident that the 1NM3–LiBOB combination and its suitable SEI film formation capability are vital to the lithium ion battery with graphite as the anode.

Pentamethylcyclopentasiloxanes (D5H) with oligo(ethylene glycol) substituents, D5N3 and D5S3, and a short-chain siloxane derivative MD6N3M were synthesized by B(C6F5)3-catalyzed dehydrogenative coupling and by platinum-catalyzed hydrosilylation reactions. Conductivities were studied when doped with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). The oxygen-linked cyclic siloxane D5N3 exhibits higher conductivity than trimethylene-linked siloxane D5S3. The substituted linear oligmeric siloxane MD6N3M has a lower Tg than the D5 siloxanes, and showed much higher conductivity at the same Li+ concentration. The curvature of the plot of conductivity vs temperature dependence indicates a free volume mechanism of ion transport.

Network-type solid polymer electrolytes (NSPEs) were synthesized containing oligoethylene oxide chains, CH3(OCH2CH2)3(CH2)3−, within the network structures. Hydrosilylation reactions of precursors 1 and 2 (oligoethyleneoxy partially substituted pentamethylccyclopentasiloxanes (D5H)) with an α,ω-diallyloligo(ethylene glycol) were employed for the formation of the cross-linked networks. The conductivities of the network polymer/LiX complexes with variable EO/Li ratios were measured by impedance experiments. NSPE-2, with 36.0% cross-linking density, exhibited higher conductivity than NSPE-1, with 43.8%. The optimum conductivity (σ = 9.24 × 10-5 S/cm at 25 °C, 2.11 × 10-4 S/cm at 37 °C) was found for NSPE-2 with lithium bis(oxalato)borate (LiBOB). LiBOB-doped polymers exhibited higher conductivity than those doped with LiTFSI at the same salt concentration.

A novel cross-linked siloxane-based solid polymer network has been synthesized by the hydrosilylation of polymethylhydrosiloxane (PMHS) partly substituted with oligo(ethylene glycol) methyl ether side groups and a α,ω-diallyl poly(ethylene glycol) cross-linking reagent. The ionic conductivities of the networks doped with LiTFSI are high at ambient temperature (σ = 1.33 × 10-4 S cm-1 at the optimum LiTFSI concentration EO/Li+ = 20:1). The temperature dependence of the conductivity followed the VTF form, indicating that polymer segmental motion assists the ion transport in the solid networks.