Sodium/Lithium-Ion Transfer Reaction at the Interface between Low-Crystallized Carbon Nanosphere Electrodes and Organic Electrolytes.

Carbon nanosphere (CNS) electrodes are the candidate of sodium-ion battery (SIB) negative electrodes with small internal resistances due to their small particle sizes. Electrochemical properties of low-crystallized CNS electrodes in dilute and concentrated sodium bis(trifluoromethanesulfonyl) amide/ethylene carbonate + dimethyl carbonate (NaTFSA/EC + DMC) were first investigated. From the cyclic voltammograms, both lithium ion and sodium ion can reversibly insert into/from CNSs in all of the electrolytes used here. The cycling stability of CNSs in concentrated electrolytes was better than that in dilute electrolytes for the SIB system. The interfacial charge-transfer resistances at the interface between CNSs and organic electrolytes were evaluated using electrochemical impedance spectroscopy. In the Nyquist plots, the semicircles at the middle-frequency region were assigned to the parallel circuits of charge-transfer resistances and capacitances. The interfacial sodium-ion transfer resistances in concentrated organic electrolytes were much smaller than those in dilute electrolytes, and the rate capability of CNS electrodes in sodium salt-concentrated electrolytes might be better than in dilute electrolytes, suggesting that CNSs with concentrated electrolytes are the candidate of SIB negative electrode materials with high rate capability. The calculated activation energies of interfacial sodium-ion transfer were dependent on electrolyte compositions and similar to those of interfacial lithium-ion transfer.

Charge-Transfer Kinetics of the Solid-Electrolyte Interphase on Li4 Ti5 O12 Thin-Film Electrodes.

Invited for this month's cover are the groups of Shih-kang Lin at the National Cheng Kung University and Takeshi Abe at Kyoto University. The image shows how interfacial chemistry design can play a role in unlocking higher-energy-density and fast-charging Li4 Ti5 O12 -based lithium-ion batteries for electric vehicle applications. The Full Paper itself is available at 10.1002/cssc.202001086.

Charge-Transfer Kinetics of The Solid-Electrolyte Interphase on Li4 Ti5 O12 Thin-Film Electrodes.

Charge-transfer kinetics between electrodes and electrolytes critically determines the performance of lithium-ion batteries (LIBs). Lithium titanate defect spinel (Li4 Ti5 O12 , LTO) is a safe and durable anode material, but its relatively low energy density limits the range of applications. Utilizing the low potential region of LTO is a straightforward strategy for increasing energy density. However, the electrochemical characteristics of LTO at low potentials and the properties of the solid-electrolyte interphase (SEI) on LTO are not well understood. Here, we investigate the charge-transfer kinetics of the SEI formed between model LTO thin-film electrodes and organic electrolytes with distinct solvation ability using AC impedance spectroscopy whereas their stability was assessed by cyclic voltammetry of ferrocene. With the SEI film on LTO, the Li+ desolvation was rate-determining step but with larger activation energies, which showed a strong dependence on the solvation ability of electrolyte. The activation energies of desolvation for the fluoroethylene carbonate+dimethyl carbonate- and ethylene carbonate+diethyl carbonate-based systems increased from 35 and 55 to 44 and 67 kJ mol-1 , respectively, and that for the propylene carbonate-based system did not noticeably change at around 67 kJ mol-1 . In addition, the SEI passivation of LTO was much slower than that of graphite, and the rate also strongly depended on the solvation ability of the electrolyte. Understanding the surface properties of LTO at low potentials opens the door for high-energy-density LTO-based LIBs.

Acceptor-type hydroxide graphite intercalation compounds electrochemically formed in high ionic strength solutions.

The intercalation of hydroxide ions (OH-) into graphite formed graphite intercalation compounds (GICs) in high ionic strength solutions. GICs of solvated OH- anions with two water molecules (OH-·2H2O) in alkaline aqueous solutions and GICs of only OH- anions in a molten NaOH-KOH salt solution were electrochemically synthesized.

Strontium cobalt oxychlorides: enhanced electrocatalysts for oxygen reduction and evolution reactions.

Cobalt-based layered perovskite oxychlorides Sr2CoO3Cl and Sr3Co2O5Cl2 exhibit high oxygen electrocatalytic activity compared to conventional lanthanum cobalt-based perovskite oxides. The enhanced oxygen electrocatalytic activity can be attributed to the upshifted O p-band center relative to the Fermi level caused by the incorporation of chloride anion into oxygen sites.

In situ Raman investigation of electrolyte solutions in the vicinity of graphite negative electrodes.

The structure of electrolyte solutions plays an important role in the lithium-ion intercalation reaction at graphite negative electrodes. The solvation structure of an electrolyte solution in bulk has been investigated previously. However, the structure of an electrolyte solution at the graphite negative electrode/electrolyte solution interface, where the lithium-ion intercalation reaction occurs is more important. In this study, the structure of electrolyte solutions in the vicinity of a graphite negative electrode was investigated using in situ Raman spectroscopy during the 1st reduction process in 1 mol dm-3 LiClO4/ethylene carbonate (EC) + diethyl carbonate (DEC) (1 : 1 volume ratio), 1 mol dm-3 LiCF3SO3/propylene carbonate (PC), and 1 mol dm-3 LiCF3SO3/PC + tetraethylene glycol dimethyl ether (tetraglyme) (20 : 1 volume ratio). As a result, in the electrolyte solutions in which the lithium-ion intercalation reaction can occur (LiClO4/EC + DEC and LiCF3SO3/PC + tetraglyme), the Raman spectra of free solvent molecules (EC or PC) and anions showed a positive vibrational frequency shift during the co-intercalation reaction, and these shifts returned to their original positions during the lithium-ion intercalation reaction. On the other hand, there is no vibrational frequency shift in LiCF3SO3/PC, an electrolyte in which the lithium-ion intercalation reaction cannot occur. Based on our results, the relationship between the Raman shift and the solid electrolyte interphase (SEI) formation process was discussed.

Enhanced resistance to oxidative decomposition of aqueous electrolytes for aqueous lithium-ion batteries.

An efficient electrolyte solution containing organic sulfonates for use in aqueous rechargeable lithium-ion batteries (ARLBs) is shown to provide a wide potential window and enable a high operating voltage for ARLBs.

Formation of "fuzzy" phases with high proton conductivities in the composites of polyphosphoric acid and metal oxide nanoparticles.

A high proton-conducting phase appears in the composites of zirconium- and titanium-oxide nanoparticles and polyphosphoric acid (HPO(3)). Metal oxide nanoparticles (ZrO(2) and TiO(2)) react with HPO(3) and form composite electrolytes containing pyrophosphates (ZrP(2)O(7) or TiP(2)O(7)) and shortened HPO(3) chains. The ZrO(2)-HPO(3) composite exhibits eleven times higher conductivity than sole HPO(3) at the maximum. A formed layer of shortened HPO(3) chains surrounding the pyrophosphates enhances the proton conductivities of the composite electrolytes and reduces the activation energies for the proton conductivities from 50 to 30 kJ mol(-1).

Role of local and electronic structural changes with partially anion substitution lithium manganese spinel oxides on their electrochemical properties: X-ray absorption spectroscopy study.

The electronic and local structures of partially anion-substituted lithium manganese spinel oxides as positive electrodes for lithium-ion batteries were investigated using X-ray absorption spectroscopy (XAS). LiMn(1.8)Li(0.1)Ni(0.1)O(4-η)F(η) (η = 0, 0.018, 0.036, 0.055, 0.073, 0.110, 0.180) were synthesized by the reaction between LiMn(1.8)Li(0.1)Ni(0.1)O(4) and NH(4)HF(2). The shift of the absorption edge energy in the XANES spectra represented the valence change of Mn ion with the substitution of the low valent cation as Li(+), Ni(2+), or F(-) anion. The local structural change at each compound with the amount of a Jahn-Teller Mn(3+) ion could be observed by EXAFS spectra. The discharge capacity of the tested electrode was in the order of LiMn(2)O(4) > LiMn(1.8)Li(0.1)Ni(0.1)O(4-η)F(η) (η = 0.036) > LiMn(1.8)Li(0.1)Ni(0.1)O(4) while the cycleability was in the order of LiMn(1.8)Li(0.1)Ni(0.1)O(4-η)F(η) (η = 0.036) ≈ LiMn(1.8)Li(0.1)Ni(0.1)O(4) > LiMn(2)O(4). It was clarified that LiMn(1.8)Li(0.1)Ni(0.1)O(4-η)F(η) has a good cycleability because of the anion doping effect and simultaneously shows acceptable rechargeable capacity because of the large amount of the Jahn-Teller Mn(3+) ions in the pristine material.