Two-Dimensional Electrolyte Design: Broadening the Horizons of Functional Electrolytes in Lithium Batteries.

ConspectusSince their commercialization in the 1990s, lithium-ion batteries (LIBs) have been increasingly used in applications such as portable electronics, electric vehicles, and large-scale energy storage. The increasing use of LIBs in modern society has necessitated superior-performance LIB development, including electrochemical reversibility, interfacial stability, efficient kinetics, environmental adaptability, and intrinsic safety, which is difficult to simultaneously achieve in commercialized electrolytes. Current electrolyte systems contain a solution with Li salts (e.g., LiPF6) and solvents (e.g., ethylene carbonate and dimethyl carbonate), in which the latter dissolves Li salts and strongly interacts with Li+ (lithiophilic feature). Only lithiophilic agents can be functionally modified (e.g., additives and solvents), altering the bulk and interfacial behaviors of Li+ solvates. However, such approaches alter pristine Li+ solvation and electrochemical processes, making it difficult to strike a balance between the electrochemical performance and other desired electrolyte functions. This common electrolyte design in lithiophilic solvents shows strong coupling among formulation, coordination, electrochemistry, and electrolyte function. The invention of lithiophobic cosolvents (e.g., multifluorinated ether and fluoroaromatic hydrocarbons) has expanded the electrolyte design space to lithiophilic (interacts with Li+) and lithiophobic (interacts with solvents but not with Li+) dimensions. Functional modifications switch to lithiophobic cosolvents, affording superior properties (carried by lithiophobic cosolvents) with little impact on primary Li+ solvation (dictated by lithiophilic solvents). This electrolyte engineering technique based on lithiophobic cosolvents is the 2D electrolyte (TDE) principle, which decouples formulation, coordination, electrochemistry, and function. The molecular-scale understanding of TDEs is expected to accelerate electrolyte innovations in next-generation LIBs.This Account provides insights into recent advancements in electrolytes for superior LIBs from the perspective of lithiophobic agents (i.e., lithiophobic additives and cosolvents), establishing a generalized TDE principle for functional electrolyte design. In bulk electrolytes, a microsolvating competition emerges because of cosolvent-induced dipole-dipole and ion-dipole interactions, forming a loose solvation shell and a kinetically favorable electrolyte. At the electrode/electrolyte interface, the lithiophobic cosolvent affords reliable passivation and efficient desolvation, with interfacial compatibility and electrochemical reversibility even under harsh conditions. Based on this unique coordination chemistry, functional electrolytes are formulated without significantly sacrificing their electrochemical performance. First, lithiophobic cosolvents are used to tune Li+-solvent affinity and anion mobility, promoting Li+ diffusion and electrochemical kinetics of the electrolyte to benefit high-rate and low-temperature applications. Second, the lithiophobic cosolvent undergoes less thermally induced decomposition and constructs a thermally stable interphase in TDEs, affording electrolytes with high-temperature adaptability and cycling stability. Third, the lithiophobic cosolvent modifies the local Li+-solvent-anion topography, controlling electrolyte electrochemical reversibility to afford numerous promising solvents that cannot be used in common electrolyte design. Finally, the lithiophobic cosolvent mitigates detrimental crosstalk between flame retardants and carbonate solvents, improving the intrinsic electrolyte safety without compromising electrochemical performance, which broadens the horizons of electrolyte design by optimizing versatile cosolvents and solvents, inspiring new ideas in liquid electrochemistry in other battery systems.

Passivating Lithiated Graphite via Targeted Repair of SEI to Inhibit Exothermic Reactions in Early-Stage of Thermal Runaway for Safer Lithium-Ion Batteries.

The self-exothermic in early stage of thermal runaway (TR) is blasting-fuse for Li-ion battery safety issues. The exothermic reaction between lithiated graphite (LiCx ) and electrolyte accounts for onset of this behavior. However, preventing the deleterious reaction still encounters hurdles. Here, we manage to inhibit this reaction by passivating LiCx in real time via targeted repair of SEI. It is shown that 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)cyclotrisiloxane (D3 F) can be triggered by LiCx to undergo ring-opening polymerization at elevated temperature, so as to targeted repair of fractured SEI. Due to the high thermal stability of polymerized D3 F, exothermic reaction between LiCx and electrolyte is inhibited. As a result, the self-exothermic and TR trigger temperatures of pouch cell are increased from 159.6 and 194.2 °C to 300.5 and 329.7 °C. This work opens up a new avenue for designing functional additives to block initial exothermal reaction and inhibit TR in early stage.

Activation of Sodium Storage Sites in Prussian Blue Analogues via Surface Etching.

Sodium-ion battery technologies are known to suffer from kinetic problems associated with the solid-state diffusion of Na+ in intercalation electrodes, which results in suppressed specific capacity and degraded rate performance. Here, a controllable selective etching approach is developed for the synthesis of Prussian blue analogue (PBA) with enhanced sodium storage activity. On the basis of time-dependent experiments, a defect-induced morphological evolution mechanism from nanocube to nanoflower structure is proposed. Through in situ X-ray diffraction measurement and computational analysis, this unique structure is revealed to provide higher Na+ diffusion dynamics and negligible volume change during the sodiation/desodiation processes. As a sodium ion battery cathode, the PBA exhibits a discharge capacity of 90 mA h g-1, which is in good agreement with the complete low spin FeLS(C) redox reaction. It also demonstrates an outstanding rate capability of 71.0 mA h g-1 at 44.4 C, as well as an unprecedented cycling reversibility over 5000 times.

CuIn(S,Se)(2) thin films prepared from a novel thioacetic acid-based solution and their photovoltaic application.

Low-cost and high-yield preparation of CuInSe2 films is the bottleneck for promising CuInSe2-based thin film solar cells. Here, we developed a simple, safe and cost-effective method using thioacetic acid to fabricate the absorber films of CuIn(S,Se)2 (CISSe). Dissolution of Cu2O and In(OH)3 in thioacetic acid was attributed to the strong coordination ability of S. The adhesive precursor solution can be prepared without any heating, centrifugation and inert gas protection, superior to the previously reported methods. The precursor CISSe layer was easily deposited in air by spin coating to ensure low cost. Uniform and compact CISSe thin films with well-crystallized and pure-phased CISSe grains were obtained after one step annealing. The as-prepared CISSe thin films were successfully applied to solar cells and a energy conversion efficiency of 6.75% was achieved. This facile preparation provides a low-cost and easy method to fabricate Cu-based thin film solar cells.

4-Fluorobenzyl cyanide, a sterically-hindered solvent expediting interfacial kinetics in lithium-ion batteries.

The electrochemical performance of lithium-ion batteries (LIBs) is plagued by sluggish interfacial kinetics. Fortunately, the Li+ solvation structure bridges the bulk electrolyte and interfacial chemistry, providing a pathway for promoting electrochemical kinetics in LIBs. Herein, we improve the interfacial kinetics by tuning the Li+ coordination chemistry based on solvent molecular engineering. Specifically, 4-fluorobenzyl cyanide (FBCN), featuring steric hindrance and a weak Lewis basic center, is designed to construct a bulky coordination structure with Li+, weakening ion-dipole interaction (Li+-solvents) but promoting coulombic attraction (Li+-anions) at a normal Li salt concentration. This sterically-controlled solvation chemistry reduces the interfacial barrier and thus contributes to improved rate performance, as demonstrated practically in LiFePO4//graphite pouch cells. This study provides fresh insights into solvent steric control and coordination chemistry engineering, opening a new avenue for enhancing electrochemical kinetics in LIBs.

Direct lithium extraction from spent batteries for efficient lithium recycling.

The flourishing expansion of the lithium-ion batteries (LIBs) market has led to a surge in the demand for lithium resources. Developing efficient recycling technologies for imminent large-scale retired LIBs can significantly facilitate the sustainable utilization of lithium resources. Here, we successfully extract active lithium from spent LIBs through a simple, efficient, and low-energy-consumption chemical leaching process at room temperature, using a solution comprised of polycyclic aromatic hydrocarbons and ether solvents. The mechanism of lithium extraction is elucidated by clarifying the relationship between the redox potential and extraction efficiency. More importantly, the reclaimed active lithium is directly employed to fabricate LiFePO4 cathode with performance comparable to commercial materials. When implemented in 56 Ah prismatic cells, the cells deliver stable cycling properties with a capacity retention of ∼90% after 1200 cycles. Compared with the other strategies, this technical approach shows superior economic benefits and practical promise. It is anticipated that this method may redefine the recycling paradigm for retired LIBs and drive the sustainable development of industries.

1,3,5-Trifluorobenzene, an electrolyte additive with high thermal stability and superior film-forming properties for lithium-ion batteries.

The introduction of 1,3,5-trifluorobenzene (F3B) as an additive for lithium-ion battery electrolytes can produce a LiF-rich solid electrolyte interface (SEI). Meanwhile, F3B has superior thermal stability compared with traditional fluorinated additives and is less likely to produce hydrogen fluoride to damage the cathode.

Revealing Surfactant Effect of Trifluoromethylbenzene in Medium-Concentrated PC Electrolyte for Advanced Lithium-Ion Batteries.

Despite wide-temperature tolerance and high-voltage compatibility, employing propylene carbonate (PC) as electrolyte in lithium-ion batteries (LIBs) is hampered by solvent co-intercalation and graphite exfoliation due to incompetent solvent-derived solid electrolyte interphase (SEI). Herein, trifluoromethylbenzene (PhCF3 ), featuring both specific adsorption and anion attraction, is utilized to regulate the interfacial behaviors and construct anion-induced SEI at low Li salts' concentration (<1 m). The adsorbed PhCF3 , showing surfactant effect on graphite surface, induces preferential accumulation and facilitated decomposition of bis(fluorosulfonyl)imide anions (FSI- ) based on the adsorption-attraction-reduction mechanism. As a result, PhCF3 successfully ameliorates graphite exfoliation-induced cell failure in PC-based electrolyte and enables the practical operation of NCM613/graphite pouch cell with high reversibility at 4.35 V (96% capacity retention over 300 cycles at 0.5 C). This work constructs stable anion-derived SEI at low concentration of Li salt by regulating anions-co-solvents interaction and electrode/electrolyte interfacial chemistries.

A "tug-of-war" effect tunes Li-ion transport and enhances the rate capability of lithium metal batteries.

"Solvent-in-salt" electrolytes (high-concentration electrolytes (HCEs)) and diluted high-concentration electrolytes (DHCEs) show great promise for reviving secondary lithium metal batteries (LMBs). However, the inherently sluggish Li+ transport of such electrolytes limits the high-rate capability of LMBs for practical conditions. Here, we discovered a "tug-of-war" effect in a multilayer solvation sheath that promoted the rate capability of LMBs; the pulling force of solvent-nonsolvent interactions competed with the compressive force of Li+-nonsolvent interactions. By elaborately manipulating the pulling and compressive effects, the interaction between Li+ and the solvent was weakened, leading to a loosened solvation sheath. Thereby, the developed electrolytes enabled a high Li+ transference number (0.65) and a Li (50 µm)‖NCM712 (4 mA h cm-2) full cell exhibited long-term cycling stability (160 cycles; 80% capacity retention) at a high rate of 0.33C (1.32 mA cm-2). Notably, Li (50 µm)‖LiFePO4 (LFP; 17.4 mg cm-2) cells with a designed electrolyte reached a capacity retention of 80% after 1450 cycles at a rate of 0.66C. An 6 Ah Li‖LFP pouch cell (over 250 W h kg-1) showed excellent cycling stability (130 cycles, 96% capacity retention) under practical conditions. This design concept for an electrolyte provides a promising path to build high-energy-density and high-rate LMBs.

Facile Replacement Reaction Enables Nano-Ag-Decorated Three-Dimensional Cu Foam as High-Rate Lithium Metal Anode.

In developing advanced lithium (Li) metal batteries with high-energy density, excellent cycle stability, and high-rate capability, it is imperative to resolve dendrite growth and volume expansion during repeated Li plating/stripping. 3D hosts featuring lithiophilic sites are expected to realize both spatial control and dendrite inhibition over Li nucleation. Herein, this work prepares silver (Ag) nanoparticle-decorated 3D copper (Cu) foam via a facile replacement reaction. The 3D host provides rigid skeleton to accommodate volume expansion during cycling. Ag nanoparticles show micro-structural affinity to guide efficient nucleation of Li, leading to reduced overpotential and enhanced electrochemical kinetics. As the result, under an ultrahigh current density of 10 mA cm-2, Cu@Ag foam/Li half cells demonstrate outstanding Coulombic efficiency (CE) of 97.2% more than 100 cycles. Also, Cu@Ag foam-Li symmetric cells sustain preeminent cycling over 900 h with a small voltage hysteresis of 32.8 mV at 3 mA cm-2. Moreover, the Cu@Ag foam-Li||LiFePO4 full cell demonstrates a high discharge capacity of 2.33 mAh cm-2 over 200 cycles with an excellent CE up to 99.9% at 0.6C under practical conditions (N/P = 1.3, 17.4 mg cm-2 LiFePO4). Notably, the full cell with LiFePO4 exhibits a higher areal capacity of 1 mAh cm-2 over 700 cycles under a high rate of 5C, corresponding to capacity retention up to 100% (N/P = 3, 17.4 mg cm-2 LiFePO4). This study provides a novel and simple strategy for constructing high-rate and long-life Li metal batteries.

Highly Crystallized Prussian Blue with Enhanced Kinetics for Highly Efficient Sodium Storage.

Prussian blue analogs (PBAs) featuring large interstitial voids and rigid structures are broadly recognized as promising cathode materials for sodium-ion batteries. Nevertheless, the conventionally prepared PBAs inevitably suffer from inferior crystallinity and lattice defects, leading to low specific capacity, poor rate capability, and unsatisfied long-term stability. As the Na+ migration within PBAs is directly dependent on the periodic lattice arrangement, it is of essential significance to improve the crystallinity of PBAs and hence ensure long-range lattice periodicity. Herein, a chemical inhibition strategy is developed to prepare a highly crystallized Prussian blue (Na2Fe4[Fe(CN)6]3), which displays an outstanding rate performance (78 mAh g-1 at 100 C) and long life-span properties (62% capacity retention after 2000 cycles) in sodium storage. Experimental results and kinetic analyses demonstrate the efficient electron transfer and smooth ion diffusion within the bulk phase of highly crystallized Prussian blue. Moreover, in situ X-ray diffraction and in situ Raman spectroscopy results demonstrate the robust crystalline framework and reversible phase transformation between cubic and rhombohedral within the charge-discharge process. This research provides an innovative way to optimize PBAs for advanced rechargeable batteries from the perspective of crystallinity.

Facile formation of tetragonal-Nb2O5 microspheres for high-rate and stable lithium storage with high areal capacity.

Niobium pentoxide (Nb2O5) has attracted great attention as an anode for lithium-ion battery, which is attributed to the high-rate and good stability performances. In this work, TT-, T-, M-, and H-Nb2O5 microspheres were synthesized by a facile one-step thermal oxidation method. Ion and electron transport properties of Nb2O5 with different phases were investigated by both electrochemical analyses and density functional theoretical calculations. Without nanostructuring and carbon modification, the tetragonal Nb2O5 (M-Nb2O5) displays preferable rate capability (121 mAh g-1 at 5 A g-1), enhanced reversible capacity (163 mAh g-1 at 0.2 A g-1) and better cycling stability (82.3% capacity retention after 1000 cycles) when compared with TT-, T-, and H-Nb2O5. Electrochemical analyses further reveal the diffusion-controlled Li+ intercalation kinetics and in-situ X-ray diffraction analysis indicates superior structural stability upon Li+ intercalation/deintercalation. Benefiting from the intrinsic fast ion/electron transport, a high areal capacity of 2.24 mAh cm-2 is obtained even at an ultrahigh mass loading of 22.51 mg cm-2. This work can promote the development of Nb2O5 materials for high areal capacity and stable lithium storage towards practical applications.

Ternary TiO2/SiOx@C nanocomposite derived from a novel titanium-silicon MOF for high-capacity and stable lithium storage.

A novel titanium-silicon MOF precursor was first designed and constructed via a facile solvothermal process. After subsequent pyrolysis, the derived ternary TiO2/SiOx@C nanocomposite exhibited superior lithium storage performances, which was attributed to their all-in-one architecture of synergistic components, including stable-cycling nanostructured TiO2, high-capacity SiOx and high-conductivity carbon matrix.

Formulation and characterization of a ten-peptide single-vial vaccine, EP-2101, designed to induce cytotoxic T-lymphocyte responses for cancer immunotherapy.

Effective vaccines that mediate clinical responses in cancer patients may require generation of broadly specific cytotoxic T lymphocytes (CTL) directed against multiple epitopes and tumor-associated antigens (TAA). Pursuant to this goal we developed a synthetic peptide vaccine, EP-2101, composed of 10 synthetic peptide epitopes and formulated in Montanide ISA 51 adjuvant. Nine of the HLA-A*0201-restricted CTL epitopes were derived from five well-characterized TAA. The universal HLA-DR binding epitope PADRE was also included for T-cell help. Herein we describe studies on the formulation and characterization of the EP-2101 vaccine which supports generation of a sterile single-vial emulsion using standardized processes. The physicochemical properties of the peptides were highly disparate and as such, solubilization studies were required to identify a process which supported sterile filtration of the EP-2101 peptide mix. A homogenization-based formulation process with Montanide ISA 51 and 0.5 mg/ml of each peptide was developed to generate a water-in-oil emulsion. Physical studies indicated the vaccine emulsion to be stable, with little change in visual appearance, viscosity and water droplet size for at least three months. The physical stability of individual peptides in the vaccine emulsion was demonstrated using HPLC and immunogenicity of the vaccine formulation was confirmed in HLA-A*0201/K(b) transgenic mice where T-cell responses could be induced to all epitopes in EP-2101 following vaccination. Our study process is scalable for production of approximately 1.5 liters of potent experimental vaccine for preclinical animal toxicity and phase 1 clinical testing in patients with breast, colon or lung cancer.

Observation of an intermediate band in Sn-doped chalcopyrites with wide-spectrum solar response.

Nanostrcutured particles and polycrystalline thin films of Sn-doped chalcopyrite are synthesized by newly-developed methods. Surprisingly, Sn doping introduces a narrow partially filled intermediate band (IB) located ~1.7 eV (CuGaS(2)) and ~0.8 eV (CuInS(2)) above the valance band maximum in the forbidden band gap. Diffuse reflection spectra and photoluminescence spectra reveal extra absorption and emission spectra induced by the IBs, which are further supported by first-principle calculations. Wide spectrum solar response greatly enhances photocatalysis, photovoltaics, and photo-induced hydrogen production due to the intermediate band.

Phase-controlled synthesis of cobalt sulfides for lithium ion batteries.

The polyhedral CoS(2) with a narrow size distribution was synthesized by a facile solid-state assembly process in a sealed silica tube. The flux of potassium halide (KX; X = Cl, Br, I) plays a crucial role in the formation of polyhedrons and the size distribution. The S(2)(2-) groups in CoS(2) can be controllably withdrawn during heat treatment in air. The obtained phases and microstructures of CoS(2), Co(3)S(4), CoS, Co(9)S(8), and CoO depended on heating temperature and time. These cobalt materials, successfully used as the electrodes of lithium ion batteries, possessed good cycling stability in lithium ion batteries. The discharge capacities of 929.1 and 835.2 mAh g(-1) were obtained for CoS(2) and CoS respectively, and 76% and 71% of the capacities remained after 10 cycles. High capacities and good cycle performance make them promising candidates for lithium ion batteries. The approach combining solid-state assembly and heat treatment provides a simple and versatile way to prepare various metal chalcogeides for energy storage applications.

A decaepitope polypeptide primes for multiple CD8+ IFN-gamma and Th lymphocyte responses: evaluation of multiepitope polypeptides as a mode for vaccine delivery.

Proteins are generally regarded as ineffective immunogens for CTL responses. We synthesized a 100-mer decaepitope polypeptide and tested its capacity to induce multiple CD8(+) IFN-gamma and Th lymphocyte (HTL) responses in HLA transgenic mice. Following a single immunization in the absence of adjuvant, significant IFN-gamma in vitro recall responses were detected for all epitopes included in the construct (six A2.1-, three A11-restricted CTL epitopes, and one universal HTL epitope). Immunization with truncated forms of the decaepitope polypeptide was used to demonstrate that optimal immunogenicity was associated with a size of at least 30-40 residues (3-4 epitopes). Solubility analyses of the truncated constructs were used to identify a correlation between immunogenicity for IFN-gamma responses and the propensity of these constructs to form particulate aggregates. Although the decaepitope polypeptide and a pool of epitopes emulsified in IFA elicited similar levels of CD8(+) responses using fresh splenocytes, we found that the decaepitope polypeptide more effectively primed for in vitro recall CD8(+) T cell responses. Finally, immunogenicity comparisons were also made between the decaepitope polypeptide and a corresponding gene encoding the same polypeptide delivered by naked DNA immunization. Although naked DNA immunization induced somewhat greater direct ex vivo and in vitro recall responses 2 wk after a single immunization, only the polypeptide induced significant in vitro recall responses 6 wk following the priming immunization. These studies support further evaluation of multiepitope polypeptide vaccines for induction of CD8(+) IFN-gamma and HTL responses.