Denis Y.W. Yu

Because the mass of lithium-air battery (LAB) changes due to oxygen reduction/evolution reactions (ORR/OER), weighing of the battery is an indispensable method for determining its actual energy density and analyzing the battery reactions. To this end, we have newly developed a weight monitoring system which can trace the semi-permanent weight change of air-batteries (∼11 g including a holder) with a precision of 7.87 μg. The system reveals the weight decrease of LAB in each cycle before finally losing its capacity. The in-situ weighing during battery operation also provides first-hand evidence of double layer capacitance and electrolyte evaporation of LABs. Specifically, the e−/O2 ratio during discharge is determined to be 1.954 ± 0.004 based on the weight increase of an LAB cell using tetraethylene glycol-based electrolyte at a current density of 100 μA cm−2, confirming the slightly lower e−/O2 ratio than the …

Dual-atom catalytic sites on conductive substrates offer a promising opportunity for accelerating the kinetics of multistep hydrogen and oxygen evolution reactions (HER and OER, respectively). Using MXenes as substrates is a promising strategy for depositing those dual-atom electrocatalysts, if the efficient surface anchoring strategy ensuring metal-substrate interactions and sufficient mass loading is established. We introduce a surface-modification strategy of MXene substrates by preadsorbing L-tryptophan molecules, which enabled attachment of dual-atom Co/Ni electrocatalyst at the surface of Ti3C2Tx by forming N–Co/Ni-O bonds, with mass loading reaching as high as 5.6 wt %. The electron delocalization resulting from terminated O atoms on MXene substrates, N atoms in L-tryptophan anchoring moieties, and catalytic metal atoms Co and Ni provides an optimal adsorption strength of intermediates and boosts …

This issue features summaries of four of the eight dissertations presented at Middleware 2005's 2nd International Middleware Doctoral Symposium. The March issue will feature the other four summaries.

Dual-ion batteries (DIBs), well-known for the high-rate capability of the graphite cathode, urgently need a suitable anode material to realize their high power density in practical applications. In that respect, Li4Ti5O12 (LTO), which can be cycled at high rates for thousands of cycles, can be a good candidate. However, a facile method to stabilize the graphite||LTO full cells is necessary. Herein, we introduce LiDFOB additive into the electrolyte of graphite||LTO cells, which drastically improves the cycling performance and reduces self-discharge of the DIBs. Specifically, by adding 1.0 wt% LiDFOB to 2 M LiPF6 in fluorinated ethyl methyl carbonate, graphite||LTO DIBs can maintain stable charge-discharge for over 8000 cycles at 20 C. Characterizations indicate that LiDFOB forms a robust LiF-rich solid electrolyte interphase (SEI) on the LTO anode to suppress side reactions such as electrolyte decomposition and gas …

Decorating single atoms of transition metals on MXenes to enhance the electrocatalytic properties of the resulting composites is a useful strategy for developing efficient electrocatalysts, and the mechanisms behind this enhancement are under intense scrutiny. Herein, we anchored Co single atoms onto several commonly used MXene substrates (V2CTx, Nb2CTx and Ti3C2Tx) and systematically studied the electrocatalytic behavior and the mechanisms of oxygen and hydrogen evolution reactions (OER and HER, respectively) of the resulting composites. Co@V2CTx composite displays an OER overpotential of 242 mV and an HER overpotential of 35 mV at 10 mA cm−2 in 1.0 M KOH electrolyte, which is much lower than for Co@Nb2CTx and Co@Ti3C2Tx, making it comparable to the commercial noble metal Pt/C and RuO2/C electrocatalysts. The experimental and theoretical results point out that the enhanced …

Air‐stable layered structured cathodes with high voltage and good cycling stability are highly desired for the practical application of Na‐ion batteries. Herein, we report a P2‐Na2/3Ni2/3Te1/3O2 cathode that is stable in ambient air with an average operating voltage of ~3.8 V, demonstrating excellent cycling stability with a capacity retention of more than 92.7% after 500 cycles at 20 mA g−1 and good rate capability with 91.9% capacity utilization at 500 mA g−1 with respect to capacity at 5 mA g−1 between 2.0 and 4.0 V. When the upper cutoff voltage is increased to 4.4 V, P2‐Na2/3Ni2/3Te1/3O2 delivers a reversible capacity of 71.9 mAh g−1 and retains 91.8% of the capacity after 100 cycles at 20 mA g−1. The charge compensation during charge/discharge is mainly due to the redox couple of Ni2+/Ni3+ in the host with a small amount of contribution from oxygen. The stable structure of the material …

Cu−Li batteries leveraging the two‐electron redox property of Cu can offer high energy density and low cost. However, Cu−Li batteries are plagued by limited solubility and a shuttle effect of Cu ions in traditional electrolytes, which leads to low energy density and poor cycling stability. In this work, we rationally design a solid‐state sandwich electrolyte for solid‐state Cu−Li batteries, in which a deep‐eutectic‐solvent gel with high Cu‐ion solubility is devised as a Cu‐ion reservoir while a ceramic Li1.4Al0.4Ti1.6(PO4)3 interlayer is used to block Cu‐ion crossover. Because of the high ionic conductivity (0.55 mS cm−1 at 25 °C), wide electrochemical window (>4.5 V vs. Li+/Li), and high Cu ion solubility of solid‐state sandwich electrolyte, a solid‐state Cu−Li battery demonstrates a high energy density of 1 485 Wh kgCu−1and long‐term cyclability with 97 % capacity retention over 120 cycles. The present study …

Recently, aqueous rechargeable zinc-ion batteries (AZIBs) have attracted much attention owing to their low cost and intrinsic safety. However, the reversibility of AZIBs is limited by dendrite growth on the Zn anode, which leads to low Coulombic efficiency and potential short circuit during cycling. Herein, we develop a new strategy using electrostatic shielding to enable a highly reversible Zn anode. Specifically, a cationic polymeric ionic liquid (PIL) coating layer with a strong positive charge evens out the charge distribution on the surface of the Zn electrode, enabling uniform stripping and deposition of Zn. As a result, a symmetric Zn–Zn cell can sustain stripping-plating for over 2000 h at 1 mA cm−2 with a capacity limit of 1 mAh cm−2, far exceeding the performance of bare Zn electrode. A highly reversible Zn stripping-plating on Cu substrate is also achieved with an average coulombic efficiency of 99.5% over 1100 …

Cu-Li battery with Cu metal cathode and Li metal anode is a candidate for next-generation energy storage system. While self-discharge of the battery can be suppressed with an anion exchange membrane, the voltage polarization depends strongly on the electrolyte. Specifically, when an electrolyte with 3áM LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) in dimethyl carbonate (DMC) is used, overpotential increases with cycling. In this work, we reveal why the voltage polarization changes, and reduce and stabilize it by replacing DMC solvent with a mixed solvent composed of dimethoxyethane (DME) and propylene carbonate (PC). The new electrolyte has higher ionic conductivity and stable solvation structure with more free TFSI− anions upon cycling, which also facilitates uniform plating of metal ions on the metal electrodes. These characteristics enable a stable Cu-Li battery with minimal change in …

Layered oxides based on manganese (Mn), rich in lithium (Li), and free of cobalt (Co) are the most promising cathode candidates used for lithium-ion batteries due to their high capacity, high voltage and low cost. These types of material can be written as xLi2MnO3·(1 − x) LiTMO2 (TM = Ni,Mn,etc.). Though, Li2MnO3 is known to have poor cycling stability and low capacity, which hinder its industrial application commercially. In this work, Li1.2Ni0.2Mn0.6O2 materials with different amounts of structural defects was successfully synthesized using powder metallurgy followed by different cooling processes in order to improve its electrochemical properties. Microstructural analyses and electrochemical measurements were carried out on the study samples synthesized by a combination of X-ray diffraction, transmission electron microscopy, and cyclic voltammetry. It is found that the disorder of the transition metal layer in Li …

The increasing number of accidents relating to battery fire and explosion is raising people's attention towards safety of batteries. Abnormal battery operation can generate much heat and cause thermal runaway due to the exothermic reactions of the electrodes and electrolyte. Recently, dual‐ion battery (DIB) has gained many interests because of its low cost and high working voltage compared with traditional lithium‐ion battery (LIB). However, investigation on thermal stability of DIB is rare. In this paper, differential scanning calorimetry (DSC) was used to study the thermal stability of DIB using graphite as cathode with different states of charge (SOC) and with different amount of fluoroethylene carbonate as co‐solvent in the electrolyte. Then, the thermal stability of graphite cathode for DIB was compared with those of LiCoO2 and LiNi0.5Mn1.5O4 at their fully charged states. Specifically, charged DIB using graphite as …

High-Ni materials LiNiO2 or LiNi1-xMxO2 (x < 0.1), whose energy density is over 800 Wh kg−1 (discharge capacity >220 mAh g−1, average discharge voltage ∼3.8 V), are promising candidates as cathode for next-generation electric vehicle batteries. However, commercial applications of high-Ni cathodes have been hindered by their fast capacity fading with cycling. Herein, we synthesized a series of high-Ni materials (LiNiO2, LiNi0.95Co0.05O2 and LiNi0.9Co0.1O2) by adopting nanosheet hydroxide precursors. The obtained high-Ni materials with micro-spheres made up of nanorod grains can sustain the large volume deformation and eliminates cracking during charge-discharge. Owing to the hierarchical structure, our as-synthesized high-Ni cathodes exhibit excellent cycling stability up to 4.7 V and under high temperatures, and the corresponding full cells show superior long cycling stability suitable for practical …

Dual‐ion battery (DIB) is a promising energy storage system because it can provide high power. However, the stability and rate performance of the battery depend strongly on the type of salt and solvents in the electrolyte. Herein, the use of lithium bis(fluorosulfonyl)imide (LiFSI) is studied, which has better high‐temperature stability, as salt in the DIB and develop a 3 m LiFSI fluoroethylene carbonate/methyl 2,2,2‐trifluoroethyl carbonate (FEC/FEMC) = 3:7 electrolyte, which stabilizes graphite–lithium DIB with 94.1% capacity retention after 2000 cycles at 5C. The DIB also exhibits excellent rate performance with 100.4 mAh g−1 capacity at 30C, with a utilization of 96.3% compared to capacity at 2C. The outstanding electrochemical performance is attributed to the thin cathode electrolyte interface (CEI) layer and fast FSI− transport kinetics, confirmed by X‐ray photoelectron spectroscopy and activation energy …

Layered O3-type transition metal oxides are promising cathode candidates for high-energy-density Li-ion batteries. However, the structural instability at the highly delithiated state and low kinetics at the fully lithiated state are arduous challenges to overcome. Here, a facile approach is developed to make secondary particles of Ni-rich materials with nanosheet primary grains. Because the alignment of the primary grains reduces internal stress buildup within the particle during charge–discharge and provides straightforward paths for Li transport, the as-synthesized Ni-rich materials do not undergo cracking upon cycling with higher overall Li+ ion diffusion rates. Specifically, a LiNi0.75Co0.14Mn0.11O2 cathode with nanosheet grains delivers a high reversible capacity of 206 mAh g–1 and shows ultrahigh cycling stability, e.g., 98% capacity retention over 500 cycles in a full cell with a graphite anode.

Tin (Sn) is a common metal in our daily life. Recently, Sn and its alloys have received much interest as anode materials for lithium-ion batteries. Herein, we are the first to demonstrate a Sn–Li battery using Sn metal as the cathode and Li metal as the anode in a carbonate–ether based electrolyte. The Sn–Li battery uses electrochemical redox reactions of the two metal/metal cation pairs to store and release energy. With an anion exchange membrane as the separator, the battery can cycle at a current density of 0.2 mA cm−2 with an areal capacity limitation of 0.1 mA h cm−2 and a discharge voltage of about 2.8 V for more than 1500 cycles with an average Coulombic efficiency of about 99.5%. The discharge voltage plateau of the Sn–Li battery drops by only 0.05 V even when the current density is increased 5 times to 1 mA cm−2 (about a 10C rate), demonstrating its fast kinetics. Comparing batteries with Sn, Cu and …

Metal–metal battery bears great potential for next‐generation large‐scale energy storage system because of its simple manufacture process and low production cost. However, the cross‐over of metal cations from the cathode to the anode causes a loss in capacity and influences battery stability. Herein, a coating of poly (ionic liquid) (PIL) with poly(diallyldimethylammonium bis(trifluoromethanesulfonyl)imide) (PDADMA+TFSI−) on a commercial polypropylene (PP) separator serves as an anion exchange membrane for a 3.3 V copper–lithium battery. The PIL has a positively charged polymer backbone that can block the migration of copper ions, thus improving Coulombic efficiency, long‐term cycling stability and inhibiting self‐discharge of the battery. It can also facilitate the conduction of anions through the membrane and reduce polarization, especially for fast charging/discharging. Bruce‐Vincent method gives the …

Two sodium-rich transition metal (TM) oxides with the same spinel structure, Na2MoO4 and Na2WO4 have been investigated as cathode materials for Na-ion batteries for the first time. Although the oxidation state of TMs in the compounds are already at its highest value of 6+, both of them can be activated by anionic redox reaction during initial charge, as revealed by X-ray photoelectron spectroscopy, to give considerable reversible capacity between 1.2 and 4.7 V. In addition, ex-situ X-ray diffractometry (XRD) shows that both cathode materials undergo insignificant structural evolution during Na extraction/insertion, suggesting that the Mo-O4 and W-O4 tetrahedral framework are stable even when more than 1 Na is removed from the materials. Overall, Na2WO4 shows larger amount of Na extraction/insertion and better cycle stability than Na2MoO4. This is likely due to better structural integrity and better stability of …

Silicon monoxide (SiO) is a promising anode material for Li-ion batteries because of its high capacity. Though, its low first Coulombic efficiency (FCE) due to the formation of inactive Li–Si–O compounds during lithiation hinders its practical application. Herein, we report a facile pre-sodiation technique by annealing SiO with a small amount of Na2CO3 (≤ 5 wt%) under 850 °C, which improves FCE of pristine SiO from 61.4% to 86.0% without the use of lithium metal, solvent and disassembling and re-assembling of cells. Transmission electron microscopy, X-ray photoelectron spectroscopy, and nuclear magnetic resonance demonstrate that the incorporation of Na facilitates the disproportionation of SiO into crystalline Si and SiO2 through nucleophilic substitution, and reduces the reactivity of the oxygen atoms with lithium and thereby suppresses the irreversible capacity during initial lithiation. The pre-sodiation process …

Silicon (Si), which can give a high capacity, is a potential next-generation anode material for lithium-ion batteries (LIBs), though there is a growing concern over the safety of Si-based batteries with higher energy density, where the reaction between the electrolytes and the charged electrodes can cause thermal issues. In our study, we developed an electrolyte additive which effectively improves the thermal stability of Si electrodes. Specifically, addition of 5 wt % (3-aminopropyl)triethoxysilane (APTES) into a commercial carbonate-based electrolyte reduces the heat generation from the Si electrode significantly while not affecting its charge and discharge capacities. NMR and X-ray photoelectron spectroscopy characterizations suggest that APTES serves as a PF5/HF scavenger, stabilizing the electrolyte and suppressing its decomposition at a high temperature. At the same time, moisture in the electrolyte triggers the …

Silicon has been widely studied as a next-generation anode material for Li-ion batteries (LIB), as it has a high gravimetric capacity of up to 3570 mAh g− 1 and a low average discharge voltage of about 0.4 V vs. Li/Li+. One of the most significant challenges is to maintain reversibility of the electrode despite the large volume expansion of more than 280% from the Li-Si alloy reaction. In this chapter, we will focus on the mechanical issues that a Si anode undergoes during charge and discharge and discuss some of the recent developments to alleviate the problem. The chapter will begin with an introduction to the lithiation process and volume expansion of Si. Characterization(s), in particular on single particles and nanowires, gave us visual observations of how the expansion and contraction occur. In the final analysis, materials must be processed into electrodes for practical applications, thus the amount of thickness …