Revealing Nanoscale Solid-Solid Interfacial Phenomena for Long-Life and High-Energy All-Solid-State Batteries.

Enabling long cyclability of high-voltage oxide cathodes is a persistent challenge for all-solid-state batteries, largely because of their poor interfacial stabilities against sulfide solid electrolytes. While protective oxide coating layers such as LiNbO3 (LNO) have been proposed, its precise working mechanisms are still not fully understood. Existing literature attributes reductions in interfacial impedance growth to the coating's ability to prevent interfacial reactions. However, its true nature is more complex, with cathode interfacial reactions and electrolyte electrochemical decomposition occurring simultaneously, making it difficult to decouple each effect. Herein, we utilized various advanced characterization tools and first-principles calculations to probe the interfacial phenomenon between solid electrolyte Li6PS5Cl (LPSCl) and high-voltage cathode LiNi0.85Co0.1Al0.05O2 (NCA). We segregated the effects of spontaneous reaction between LPSCl and NCA at the interface and quantified the intrinsic electrochemical decomposition of LPSCl during cell cycling. Both experimental and computational results demonstrated improved thermodynamic stability between NCA and LPSCl after incorporation of the LNO coating. Additionally, we revealed the in situ passivation effect of LPSCl electrochemical decomposition. When combined, both these phenomena occurring at the first charge cycle result in a stabilized interface, enabling long cyclability of all-solid-state batteries.

Nucleation and Growth Mechanism of Lithium Metal Electroplating.

Understanding the mechanism of Li nucleation and growth is essential for providing long cycle life and safe lithium ion batteries or lithium metal batteries. However, no quantitative report on Li metal deposition is available, to the best of our knowledge. We propose a model for quantitatively understanding the Li nucleation and growth mechanism associated with the solid-electrolyte interphase (SEI) formation, which we name the Li-SEI model. The current transients at various overpotentials initiate the nucleation and growth of Li metal on bare Cu foil. The Li-SEI model considering a three-dimensional diffusion-controlled instantaneous process (J3D-DC) with the simultaneous reduction of electrolyte decomposition (JSEI) due to the SEI fracture is employed for investigating the Li nucleation and growth mechanism. The individual contributions of experimental and theoretical transient states, i.e., the fundamental kinetic values of diffusion coefficient (D), rate of nucleation (N0), and rate constant of electrolyte decomposition (kSEI), can be determined from the Li-SEI model. Interestingly, JSEI increases with time, indicating that the current contributing from the electrolyte decomposition increases with time due to the SEI fracture upon Li deposition. Meanwhile, the kSEI increases with overpotential, indicating the SEI fracture is more serious at higher overpotential or higher growth rate. The kSEI is smaller in the electrolyte with fluoroethylene carbonate (FEC) additive, indicating that FEC additive can significantly suppress the SEI fracture during Li metal deposition. This proposed model opens a new way to quantitatively understand the Li nucleation and growth mechanism and electrolyte decomposition on various substrates or in different electrolytes.

Designed Synergetic Effect of Electrolyte Additives to Improve Interfacial Chemistry of MCMB Electrode in Propylene Carbonate-Based Electrolyte for Enhanced Low and Room Temperature Performance.

The performance of lithium ion batteries rapidly falls at lower temperatures due to decreasing conductivity of electrolytes and solid electrolyte interphase (SEI) on graphite anode. Hence, it limits the practical use of lithium ion batteries at subzero temperatures and also affects the development of lithium ion batteries for widespread applications. The SEI formed on the graphite surface is very influential in determining the performance of the battery. Herein, a new electrolyte additive, 4-chloromethyl-1,3,2-dioxathiolane-2-oxide (CMDO), is prepared to improve the properties of commonly used electrolyte constituents-ethylene carbonate (EC), and fluoroethylene carbonate. The formation of an efficient passivation layer in propylene carbonate-based electrolyte for MCMB electrode was investigated. The addition of CMDO resulted in a much less irreversible capacity loss and induces thin SEI formation. However, the combination of the three additives played a key role to enhance reversible capacity of MCMB electrode at lower or ambient temperature. The electrochemical measurement analysis showed that the SEI formed from a mixture of the three additives gave better intercalation-deintercalation of lithium ions.

Polyethylene oxide film coating enhances lithium cycling efficiency of an anode-free lithium-metal battery.

The practical implementation of an anode-free lithium-metal battery with promising high capacity is hampered by dendrite formation and low coulombic efficiency. Most notably, these challenges stem from non-uniform lithium plating and unstable SEI layer formation on the bare copper electrode. Herein, we revealed the homogeneous deposition of lithium and effective suppression of dendrite formation using a copper electrode coated with a polyethylene oxide (PEO) film in an electrolyte comprising 1 M LiTFSI, DME/DOL (1/1, v/v) and 2 wt% LiNO3. More importantly, the PEO film coating promoted the formation of a thin and robust SEI layer film by hosting lithium and regulating the inevitable reaction of lithium with the electrolyte. The modified electrode exhibited stable cycling of lithium with an average coulombic efficiency of ∼100% over 200 cycles and low voltage hysteresis (∼30 mV) at a current density of 0.5 mA cm-2. Moreover, we tested the anode-free battery experimentally by integrating it with an LiFePO4 cathode into a full-cell configuration (Cu@PEO/LiFePO4). The new cell demonstrated stable cycling with an average coulombic efficiency of 98.6% and capacity retention of 30% in the 200th cycle at a rate of 0.2C. These impressive enhancements in cycle life and capacity retention result from the synergy of the PEO film coating, high electrode-electrolyte interface compatibility, stable polar oligomer formation from the reduction of 1,3-dioxolane and the generation of SEI-stabilizing nitrite and nitride upon lithium nitrate reduction. Our result opens up a new route to realize anode-free batteries by modifying the copper anode with PEO to achieve ever more demanding yet safe interfacial chemistry and control of dendrite formation.

Improved Interfacial Properties of MCMB Electrode by 1-(Trimethylsilyl)imidazole as New Electrolyte Additive To Suppress LiPF6 Decomposition.

Trace water content in the electrolyte causes the degradation of LiPF6, and the decomposed products further react with water to produce HF, which alters the surface of anode and cathode. As a result, the reaction of HF and the deposition of decomposed products on electrode surface cause significant capacity fading of cells. Avoiding these phenomena is crucial for lithium ion batteries. Considering the Lewis-base feature of the N-Si bond, 1-(trimethylsilyl)imidazole (1-TMSI) is proposed as a novel water scavenging electrolyte additive to suppress LiPF6 decomposition. The scavenging ability of 1-TMSI and beneficiary interfacial chemistry between the MCMB electrode and electrolyte are studied through a combination of experiments and density functional theory (DFT) calculations. NMR analysis indicated that LiPF6 decomposition by water was effectively suppressed in the presence of 0.2 vol % 1-TMSI. XPS surface analysis of MCMB electrode showed that the presence of 1-TMSI reduced deposition of ionic insulating products caused by LiPF6 decomposition. The results showed that the cells with 1-TMSI additive have better performance than the cell without 1-TMSI by facilitating the formation of solid-electrolyte interphase (SEI) layer with better ionic conductivity. It is hoped that the work can contribute to the understanding of SEI and the development of electrolyte additives for prolonged cycle life with improved performance.

An unexpected large capacity of ultrafine manganese oxide as a sodium-ion battery anode.

MnO2 is shown for the first time to be electrochemically active as a conversion anode for Na-ion batteries (NIBs). Space-confined ultrafine (UF)-MnO2, with an average crystal size of 4 nm, synthesized using a porous silicon dioxide templated hydrothermal process exhibits a high reversible sodiation capacity of 567 mA h g(-1), in contrast to the negligible activity shown by the aggregates of larger (14 nm) MnO2 nanocrystallites. The remarkably enhanced sodiation activity of the UF-MnO2 is attributable to its greatly reduced crystal size, which facilitates diffusion of Na ions, along with high surface energy arising from extensive heterogeneous interfacial bonding with the SiO2 surrounding. The UF-MnO2 anode exhibits an exceptional rate and cycle performance, exhibiting >70% capacity retention after 500 cycles. In operando synchrotron X-ray absorption near-edge structural analysis reveals combined charge-storage mechanisms involving conversion reaction between Mn(III) and Mn(II) oxides, Mn(III)-O1.5 + Na(+) + e(-)- ↔ 1/2Na2O + Mn(II)-O, and non-Mn-centered redox reactions. The finding suggests a new strategy for "activating" the potential electrochemical electrode materials that appear inactive in the bulk form.

Stabilizing Nanosized Si Anodes with the Synergetic Usage of Atomic Layer Deposition and Electrolyte Additives for Li-Ion Batteries.

A substantial increase in charging capacity over long cycle periods was made possible by the formation of a flexible weblike network via the combination of Al2O3 atomic layer deposition (ALD) and the electrolyte additive vinylene carbonate (VC). Transmission electron microscopy shows that a weblike network forms after cycling when ALD and VC were used in combination that dramatically increases the cycle stability for the Si composite anode. The ALD-VC combination also showed reduced reactions with the lithium salt, forming a more stable solid electrolyte interface (SEI) absent of fluorinated silicon species, as evidenced by X-ray photoelectron spectroscopy. Although the bare Si composite anode showed only an improvement from a 56% to a 45% loss after 50 cycles, when VC was introduced, the ALD-coated Si anode showed an improvement from a 73% to a 11% capacity loss. Furthermore, the anode with the ALD coating and VC had a capacity of 630 mAh g(-1) after 200 cycles running at 200 mA g(-1), and the bare anode without VC showed a capacity of 400 mAh g(-1) after only 50 cycles. This approach can be extended to other Si systems, and the formation of this SEI is dependent on the thickness of the ALD that affects both capacity and stability.

Hierarchical copper-decorated nickel nanocatalysts supported on La2O3 for low-temperature steam reforming of ethanol.

Copper/nickel nanocatalysts with a unique morphology were prepared by thermal reduction of a perovskite LaNix Cu1-x O3 precursor (x=1, 0.9, and 0.7). During thermal reduction, copper was first reduced and reacted with lanthanum to form metastable Cu5 La and Cu13 La. When the thermal reduction temperature was increased, the perovskite decomposed to Ni and La2 O3 , CuLa alloys disappeared, and Cu deposits on Ni nanoparticles were generated, thereby forming Cu/Ni nanocatalysts with hierarchical structures. Nanosized nickel, decorated with copper and supported on La2 O3 , could be produced at 520-550 °C. The steam reforming of ethanol was used as a model reaction to demonstrate the catalytic capability of the materials formed. The hierarchical structure of the Cu/Ni/La2 O3 catalysts confers synergetic effects that greatly favor the dehydrogenation of ethanol and which break the C-C bond to produce a higher yield of hydrogen at a low reaction temperature, whereas La2 O3 provides the required stability during the reaction. The reaction at 290 °C achieved almost 100 % conversion with a hydrogen yield reaching 2.21 molH2 mol(-1) EtOH thus indicating that this special structural feature can achieve high activity for the SRE at low temperatures. The proposed synthesis of nanocatalysts appears to be a good way to generate oxide-supported hierarchically structured nanoparticles that can also be applied to other reactions catalyzed by a heterogeneous metal oxide system.

Controlled synthesis of CdSe quantum dots by a microwave-enhanced process: a green approach for mass production.

A method that does not employ hot-injection techniques has been developed for the size-tunable synthesis of high-quality CdSe quantum dots (QDs) with zinc blende structure. In this environmentally benign synthetic route, which uses less toxic precursors, solvents, and capping ligands, CdSe QDs that absorb visible light are obtained. The size of the as-prepared CdSe QDs and thus their optical properties can be manipulated by changing the microwave reaction conditions. The QDs were characterized by XRD, TEM, UV/Vis, FTIR, time-resolved fluorescence spectroscopy, and fluorescence spectrophotometry. In this approach, the reaction is conducted in open air and at a much lower temperature than in hot-injection techniques. The use of microwaves in this process allows for a highly reproducible and effective synthesis protocol that is fully adaptable for mass production and can be easily employed to synthesize a variety of semiconductor QDs with the desired properties. Possible applications of the CdSe QDs were assessed by deposition on TiO(2) films.