Search

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

In a novel two-stage crosslinking binder system, the chemical switch controlled crosslinking between PAA and PEI not only facilitates the lamination process but also leads to covalent crosslinking and much improved cycling performance.

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.

Biological nitrogen fixation is a fundamental process sustaining all life on earth. In the soil,Alphaproteobacteria, Betaproteobacteria, andCyanobacteriaare traditionally considered the major groups of nitrogen fixation population. This conventional knowledge has been accumulated by numerous PCR amplicon surveys for nitrogenase genes. However, this prevalent view appears to be inconsistent with results of recent PCR-free meta-omics investigations. Here, we show the global distribution and diversity of terrestrial diazotrophic microbiome, updated by fully leveraging the planetary collections of soil metagenomes along with recently expanded culture collections. After extensive analysis of 1,445 soil metagenomic samples, we proved that the previously-undervaluedAnaeromyxobacteraceaeandGeobacteraceaewithinDeltaproteobacteriaare ubiquitous and predominant groups of diazotrophic microbiome in the soils, spanning a broad spectrum of environments, with different geographic origins and land usage types, including aerobic (croplands, grasslands) and anaerobic ones (paddy soils, sediments). Our results delineate a revised scheme of soil nitrogen fixation, which is inclusive of both conventional diazotrophs and the so far undervaluedDeltaproteobacteria.

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...

The use of solid polymer electrolytes has previously proven to be an effective approach to address the lithium polysulfide dissolution and high electrode interfacial impedance of Li–S batteries via an in situ polymerization process. However, the conventional in situ synthesis employs a cationic ring-opening polymerization (CROP) of 1,3-dioxolane (DOL) catalyzed by a strong Lewis acid. New polymerization chemistry that is more compatible with Li–S chemistry needs to be developed to mitigate the disadvantages associated with the CROP process. Herein we report a new approach to in situ polymerize a set of new episulfide monomers in solution with LiTFSI salt via an anionic ring-opening polymerization (AROP). This new polymer system takes advantage of the inherent cell chemistry present in the Li–S cell through the nucleophilic lithium sulfides which are generated during the initial discharge cycle and act as the initiator for the polymerization. Their presence was shown to initiate the monomer solvents through AROP with no need for additional catalysts, rather than the more commonly utilized cationic systems which require an external Lewis acid catalyst. This work offers an important pathway toward in situ polymer electrolytes for Li–S batteries and offers a new avenue of exploration for polymer electrolyte synthesis.

Owing to their high specific capacity and suitably low operating potential, silicon-based anodes are an attractive alternative to graphite in next-generation lithium-ion batteries. However, silicon anodes suffer from low initial coulombic efficiency and fast capacity decay, limiting their widespread application. Pre-lithiation strategies are highly appealing to compensate for irreversible active lithium loss and to boost the cell energy density. In this work, we maximize the cell energy density by direct pre-lithiation of the NMC (LiNi0.5Mn0.3Co0.2O2) cathode to Li1+xNMCO2 without introducing inactive deadweight to either electrode. First, we demonstrate that Li1+xNMCO2 can be synthesized chemically, via reaction between NMC and lithium napthalide, and electrochemically. The NMC cathode is tolerant of a one-time over-lithiation up to 60 mA h gNMC−1, giving capacity retention on par with untreated NMC in half cell electrochemical cycling. Using synchrotron X-ray absorption spectroscopy (ex situ) and diffraction (in situ), we demonstrate that higher amounts of over-lithiation lead to local structure distortion – driven by transition metal reduction to Jahn–Teller active Mn3+ and Co2+ – as well as bulk structural hysteresis during over-lithiation and layer “buckling” that increases the amount of lithium extracted from the structure in the charged state. The Li1+xNMCO2 with low-to-moderate over-lithiation capacity (23, 46, and 70 mA h gNMC−1) is proven to be a highly effective dual-purpose lithium source and cathode material in full cell tests with a commercially relevant Si–graphite anode. These cells show higher capacity, superior cycle life, and improved coulombic efficiencies when compared to those with stoichiometric NMC cathodes. This study introduces a new and simple method to pre-lithiate layered transition metal oxide cathodes, opening up new possibilities for the development of high energy density lithium-ion batteries with next-generation anodes.

Redoxmers or redox-active organic materials, are one critical component for nonaqueous redox flow batteries (RFBs), which hold high promise in enabling the time domain of the grid. While tuning redox potentials of redoxmers is a very effective way to enhance energy densities of NRFBs, those improvements often accompany accelerated kinetics of the charged species, undermining stability and cycling performance. Herein, a strategy for designing redoxmers with simultaneous improvements in redox potential and stability is proposed. Specifically, the redoxmer 1,4-di

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.

This article deals with the estimation of parameters for the load-sharing parallel system when the underlying distribution of component lifetime is exponential Pareto. The appropriate iterative method is used to get the parameter estimators. And the asymptotic distribution of the proposed maximum likelihood estimator is presented. For the model simplified, the maximum likelihood and best asymptotic unbiased estimators of parameters are obtained. Moreover, the confidence intervals for the parameters are constructed using the parameter bootstrap technique. In the end, some appropriate simulation methods and an example are used to substantiate the proposed methods.

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...

Redoxmers are redox-active molecules that can store energy in electrolytes for redox flow batteries (RFBs), and their electrochemical properties are significantly affected by the choice of supporting electrolytes. Herein, we use 2,1,3-benzothiadiazole (BzNSN) as a model system to scrutinize the supporting electrolyte impact. By systemically varying the components of supporting salts, BzNSN not only shows substantial redox potential shifts but also exhibits varying electrochemical stabilities. Specifically, changing the size of cations can effectively alter the coordination between the supporting salt and BzNSN species. From Li+, Na+, K+, to NEt4+, the redox potential of BzNSN shifts negatively, from −1.63 V to −1.82 V vs. Ag/Ag+. Molecular dynamics and density functional theory simulations revealed that smaller cations, like Li+, are closer to the charged BzNSN when coordinated, implying stronger coordination, while larger cations, like K+ and NEt4+, are farther away. Interestingly, the large cation electrolytes also lead to much improved electrochemical stability, evidenced by the extraordinarily enhanced kinetic lifetime from electron paramagnetic resonance measurement. This study demonstrates the first example of tuning an anolyte redoxmer toward a concurrent improvement of lowered redox potentials AND enhanced calendar lives via solvation means, which is usually constrained by the thermodynamic–kinetic relation.

A fluorine-substituted ionic liquid based on a pyrrolidinium cation and a bis(fluorosulfonyl)imide anion was synthesized using a facile one-step reaction. The resulting ionic liquid is highly pure and when dissolved with LiFSI, the IL-based electrolyte showed good compatibility both in Li and graphite anodes, and superior voltage stability is demonstrated in a LiNi0.5Mn0.3Co0.2O2 cell.

Low-temperature electrolytes (LTEs) have been considered as one of the most challenging aspects for the wide adoption of lithium-ion batteries (LIBs) since the SOA electrolytes cannot sufficiently support the redox reactions at LT resulting in dramatic performance degradation. Although many attempts have been taken by employing various noncarbonate solvent electrolytes, there was a lack of fundamental understanding of the limiting factors for low-temperature operations (e.g., -20 to -40 °C). In this paper, the crucial role of the solid-electrolyte-interface (SEI) in LIB performance at low temperature using a butyronitrile (BN)-based electrolyte was demonstrated. These results suggested that an additive formed SEI with low resistance and low charge transfer dictates the LT performance in terms of capacity and cycle life, presenting a useful guideline in designing new electrolytes to address the LT issue.

In search for new classes of additives for high voltage NMC/graphite lithium-ion cells, the precursor additive bis(trimethylsilyl) malonate (bTMSM) is shown to be activated via a spontaneous reaction with LiPF6 and LiBF4 salts in carbonate-based electrolyte to form lithium tetrafluoro(malonato)phosphate (LiTFMP), and lithium difluoro(malonato)borate (LiDFMB), respectively. The reaction schemes and rates were studied via NMR spectroscopy and GCMS. The effects of LiTFMP and LiDFMB on high voltage electrochemical performance were then examined up to 4.5 V in Li[Ni0.4Mn0.4Co0.16]O2 (NMC442)/graphite and Li[Ni0.6Mn0.4Co0.0]O2 (NMC/640)/graphite pouch cells using aggressive voltage-hold cycling, long-term charge/discharge cycling, storage experiments, electrochemical impedance spectroscopy, and gas evolution measurements. While in situ converted additives suffer from gassing issues due to the presence of trimethylfluorosilane (TMSF) gas, a side product of the in situ reaction of bTMSM with LiPF6, the cycling and storage capability for the activated additives under study shows competitive performance and controlled impedance when compared to other well-known high voltage additives. Micro X-ray fluorescence spectroscopy (μXRF) confirmed that LiTFMP successfully minimizes the rate of transition metal deposition on the surface of graphite apparently by forming a protective agent at the cathode surface, hence allowing for improved cycling performance at high voltages.

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...

A novel and facile polymer-assisted chemical solution method is successfully developed for the synthesis of LiNi0.5Co0.2Mn0.3O2 (NCM) with unique morphology and nanoparticle nature as cathodes for lithium-ion batteries. At calcination temperature up to 800 °C and 900 °C, NCM with hexagonal crystal structure of layered α-NaFeO2 ( R 3 ¯ m spacing group) is formed and a lower degree of Ni/Li cation mixing for sample heated at 900 °C is determined by XRD Rietveld refinement. SEM and TEM images reveal the uniform size distribution of nanoparticles. HRTEM confirms the single crystalline nature of particles with layered structure. XPS verifies the oxidation state of Co3+, Mn4+, Ni2+ and Ni3+. As compared with the sample prepared at 800 °C, the sample heated at 900 °C exhibits a higher initial discharge specific capacity of 189 mAh g−1 being charged to 4.5 V at a current rate of 0.05 C, and better cyclability at 4.3 V cutoff voltage at a current density of 1 C. This method has demonstrated easy tuning compositions and particle sizes of cathode materials.

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 ...

This paper mainly investigates a general load-sharing parallel system having two units. First, we construct some comparisons among a load standby system, a warm standby system, a hot standby system...

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...

Surface degradation of lithium-ion cathodes at high voltages represents a significant barrier to increasing the useable energy of conventional cathodes. Though much work has been focused on mitigating the detrimental effects of such phenomena, the complex and correlated mechanisms involved have made progress difficult. Herein, the effect of electrolyte identity on surface degradation is examined. LiNi0.5Mn0.3Co0.2O2 (NMC532)/Li4Ti5O12 (LTO) full cells were constructed using three different electrolytes: a baseline organic carbonate electrolyte, a baseline organic carbonate electrolyte with an oxidizable additive, and a fluorinated carbonate electrolyte. Each system was subjected to a 60 h potentiostatic hold at 3.05 V (4.6 V vs. Li+/Li) and subsequently deconstructed for characterization via transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). Molecular simulations were carried out on each distinct component of the three electrolytes in contact with crystal surfaces of an NMC532 particle. Results indicate an affinity for the additive-containing electrolyte to extract atomic oxygen from the cathode surface, whereas the fluorinated electrolyte components have negligible interactions. Hydrogen abstraction from the baseline electrolyte is facilitated by the NMC532 surface. TEM analysis of cathode surfaces, after the potentiostatic holds, revealed that the NMC532 particles cycled with the additive-containing electrolyte underwent significant surface degradation, including changes to local crystal structure in a region penetrating 20–40 nm from the surface; consistent with oxygen and lithium loss from the cathode material. However, the NMC532 in contact with the fluorinated electrolyte showed a disordered layer of just a few nm in thickness, similar to the depth of crystal disorder observed in pristine NMC532 primary particles. EELS data of the oxygen K-edge also indicated transition metal (TM) reduction, consistent with oxygen loss and changes in crystal structure extending into the cathode surface for each of the electrolytes surveyed. These surface reactions, including oxygen loss, are shown to correlate well with elevated oxidation currents and surface reconstructions of cathode particles.

We report 1-(dimethylamino) pyrrole (PyDMA) as an electrolyte additive for high voltage lithium ion batteries based on LiNi0.6Mn0.2Co0.2O2 (NMC622)//Graphite with an upper cutoff voltage of 4.4 V. Density Functional Theory (DFT) modeling indicates that the unique structure of PyDMA could be effective in preventing the hydrolysis of LiPF6 in a carbonate electrolyte, mitigating issues related to HF formation. The calculations also indicated that the additive would oxidize at lower potentials than typical electrolyte solvents, which could lead to protective films at the cathode surface. These expectations were tested using Nuclear Magnetic Resonance (NMR) and extensive electrochemical characterization. NMR studies confirmed the superb dehydrating capability of PyDMA, which successfully prevents HF formation even at high water content. Addition of 0.5 wt% PyDMA resulted in improved capacity retention in full-cells, and also in lower levels of transition metal dissolution from the cathode. Incremental capacity (dQ/dV) analysis indicates that benefits of PyDMA at low concentration (0.5-1 wt%) are associated with decreased rates of Li+-trapping reactions, and that higher concentrations of the additive can lead to isolation of cathode domains. Our study indicates that PyDMA could be a promising electrolyte additive for high voltage lithium ion batteries at a low concentration.