Enhanced sodium ion conductivity in Na3VS4 by P-doping

All-solid-state sodium-ion batteries are promising candidates for renewable energy storage applications, owing to their high safety, high energy density, and the abundant resources of sodium. The critical factor for an all-solid-state battery is having a sodium solid electrolyte that has high Na ion conductivity at room temperature and outstanding thermal stability, low flammability, and long battery lifespan. Herein, a new Na ion solid-state electrolyte, Na₃VS₄, is prepared by a solid state reaction. It shows conductivity of ∼1.16 × 10⁻⁸ to 1.46 × 10⁻⁶ S cm⁻¹ from 25 to 100 °C. The sodium ion conductivity was enhanced to ∼1.49 × 10⁻⁷ to 1.20 × 10⁻⁵ S cm⁻¹ through P substitution for V in the composition Na₃P_0.1V_0.9S₄. Such sodium ion conduction enhancement could be attributed to P substitution for V leading to a wider Na migration path and the generation of sodium vacancies.

A new sodium ion conductor Na₃VS₄ was prepared and its conductivity improved by substitution of V with P.     

High voltage,solvent-free solid polymer electrolyte based on a star-comb PDLLA–PEG copolymer for lithium ion batteries

In this work, a novel star-comb copolymer based on poly(d,l-lactide) (PDLLA) macromonomer and poly(ethylene glycol)methyl ether methacrylate (PEGMA) was prepared, and the electrochemical properties were studied, with the aim of using it as a solid polymer electrolyte in lithium ion batteries. The six-arm vinyl functionalized PDLLA macromonomer was synthesized by a ring-opening polymerization (ROP) of d,l-lactide and subsequently an acylation of the hydroxy end-groups. A series of free-standing solid polymer electrolyte membranes from different ratios of PDLLA, PEGMA and LiTFSI were prepared through solvent-free free radical polymerization under UV radiation. The chemical structure of the obtained polymers was confirmed by ¹H NMR and FTIR. The as-prepared six-arm star-comb solid polymer electrolytes (PDLLA-SPEs) exhibit good thermal stability with T_d^5%s of ∼270 °C and low T_gs of −48 to −34 °C. The electrochemical characterization shows that the PDLLA-SPEs possess a wide electrochemical window up to 5.1 V with an optimal ionic conductivity of 9.7 × 10⁻⁵ S cm⁻¹ at 60 °C at an EO/Li⁺ ratio of 16 : 1. Furthermore, the all-solid-state LiFePO₄/Li cells display extraordinary cycling and rate performances at 60 °C by curing the PDLLA-SPEs directly on the cathode. These superior properties of the six-arm star-comb PDLLA-SPE make it a promising candidate solid electrolyte for lithium batteries.

In this work, a novel star-comb copolymer based on PDLLA macromonomer and PEGMA was prepared, and the electrochemical properties were studied, with the aim of using it as a solid polymer electrolyte in lithium ion batteries.     

High ionic conductivity of multivalent cation doped Li6PS5Cl solid electrolytes synthesized by mechanical milling

The performances of next generation all-solid-state batteries might be improved by using multi-valent cation doped Li₆PS₅Cl solid electrolytes. This study provided solid electrolytes at room temperature using planetary ball milling without heat treatment. Li₆PS₅Cl was doped with a variety of multivalent cations, where an electrolyte comprising 98% Li₆PS₅Cl with 2% YCl₃ doping exhibited an ionic conductivity (13 mS cm⁻¹) five times higher than pure Li₆PS₅Cl (2.6 mS cm⁻¹) at 50 °C. However, this difference in ionic conductivity at room temperature was slight. No peak shifts were observed, including in the synchrotron XRD measurements, and the electron diffraction patterns of the nano-crystallites (ca. 10–30 nm) detected using TEM exhibited neither peak shifts nor new peaks. The doping element remained at the grain boundary, likely lowering the grain boundary resistance. These results are expected to offer insights for the development of other lithium-ion conductors for use in all-solid-state batteries.

The performances of next generation all-solid-state batteries might be improved by using multi-valent cation doped Li₆PS₅Cl solid electrolytes.     

All-solid-state supercapacitors using a highly-conductive neutral gum electrolyte

Recently, the development of safe, stable, and long-life supercapacitors has attracted considerable interest driven by the fast-growth of flexible wearable devices. Herein, we report an MnO₂-based symmetric all-solid-state supercapacitor, using a neutral gum electrolyte that was prepared by embedding aqueous sodium sulfate solution in a biopolymer xanthan gum. Resulting from the high ion conductivity 1.12 S m⁻¹, good water retention, and high structure adaption of such gum electrolyte, the presently described supercapacitor showed high electrochemical performance with a specific capacitance of 347 F g⁻¹ at 1 A g⁻¹ and an energy density of 24 μW h cm⁻² The flexible supercapacitor possesses excellent reliability and achieves a retaining capacitance of 82% after 5000 cycles. In addition, the as-prepared supercapacitor demonstrated outstanding electrochemical stability at temperatures between −15 °C to 100 °C.

A highly-conductive neutral gum electrolyte was used for all-solid-state supercapacitors with outstanding electrochemical performance at temperatures between −15 °C to 100 °C.     

Enhanced ionic conductivity in halloysite nanotube-poly(vinylidene fluoride) electrolytes for solid-state lithium-ion batteries

Solid composite electrolytes have gained increased attention, thanks to the improved safety, the prolonged service life, and the effective suppression on the lithium dendrites. However, a low ionic conductivity (<10⁻⁵ S cm⁻¹) of solid composite electrolytes at room temperature needs to be greatly enhanced. In this work, we employ natural halloysite nanotubes (HNTs) and poly(vinylidene fluoride) (PVDF) to fabricate composite polymer electrolytes (CPEs). CPE-5 (HNTs 5 wt%) shows an ionic conductivity of ∼3.5 × 10⁻⁴ S cm⁻¹, which is ∼10 times higher than the CPE-0 (without the addition of HNTs) at 30 °C. The greatly increased ionic conductivity is attributed to the negatively-charged outer surface and a high specific surface area of HNTs, which facilitates the migration of Li⁺ in PVDF. To make a further illustration, a solid-state lithium-ion battery with CPE-5 electrolyte, LiMn₂O₄ cathode and Li metal anode was fabricated. An initial discharge capacity of ∼71.9 mA h g⁻¹ at 30 °C in 1C is obtained, and after 250 cycles, the capacity of 73.5 mA h g⁻¹ is still maintained. This study suggests that a composite polymer electrolyte with high conductivity can be realized by introducing natural HNTs, and can be potentially applied in solid-state lithium-ion batteries.

The special structure of HNTs and the further formation of amorphous PVDF contribute to the enhancement of the Li⁺ transfer.     

The synergistic effect of the PEO–PVA–PESf composite polymer electrolyte for all-solid-state lithium-ion batteries

Blending with poly(vinyl alcohol) (PVA) and poly(oxyphenylene sulfone) (PESf) has been investigated to improve the properties of a polymer electrolyte based on a poly(ethylene oxide) (PEO) matrix. The composite electrolyte shows a high ionic conductivity of 0.83 × 10⁻³ S cm⁻¹ at 60 °C due to the significant inhibition of crystallization caused by the synergistic effects of PVA and PESf. The symmetrical cell Li/CPE/Li is continuously operated for at least 200 hours at a current density of 0.1 mA cm⁻² without the enhancement in the polarization potential. In addition, the all-solid-state LiFePO₄/CPE/Li cells exhibit small hysteresis potential (about 0.10 V), good cycle stability and excellent reversible capacity (126 mA h g⁻¹ after 100 cycles).

PVA and PESf have synergistic effects for CPE, resulting in a wider electrochemical window, higher ionic conductivity and better cyclic performance.     

A flexible polyelectrolyte-based gel polymer electrolyte for high-performance all-solid-state supercapacitor application

A simple polymerization process assisted with UV light for preparing a novel flexible polyelectrolyte-based gel polymer electrolyte (PGPE) is reported. Due to the existence of charged groups in the polyelectrolyte matrix, the PGPE exhibits favorable mechanical strength and excellent ionic conductivity (66.8 mS cm⁻¹ at 25 °C). In addition, the all-solid-state supercapacitor fabricated with a PGPE membrane and activated carbon electrodes shows outstanding electrochemical performance. The specific capacitance of the PGPE supercapacitor is 64.92 F g⁻¹ at 1 A g⁻¹, and the device shows a maximum energy density of 13.26 W h kg⁻¹ and a maximum power density of 2.26 kW kg⁻¹. After 10 000 cycles at a current density of 2 A g⁻¹, the all-solid-state supercapacitor with PGPE reveals a capacitance retention of 94.63%. Furthermore, the specific capacitance and charge–discharge behaviors of the flexible PGPE device hardly change with the bending states.

A simple polymerization process assisted with UV light for preparing a novel flexible polyelectrolyte-based gel polymer electrolyte (PGPE) is reported.     

Insights into the spontaneous formation of hybrid PdOx/PEDOT films: electroless deposition and oxygen reduction activity

Hybrid palladium oxide/poly(3,4-ethylenedioxythiophene) (PdO_x/PEDOT) films were prepared through a spontaneous reaction between aqueous PdCl₄²⁻ ions and a nanostructured film of electropolymerized PEDOT. Spectroscopic and electrochemical characterization indicate the presence of mixed-valence Pd species as-deposited (19 ± 7 at% Pd⁰, 64 ± 3 at% Pd²⁺, and 18 ± 4 at% Pd⁴⁺ by X-ray photoelectron spectroscopy) and the formation of stable, electrochemically reversible Pd⁰/α-PdO_x active species in alkaline electrolyte and furthermore in the presence of oxygen. The elucidation of the Pd speciation as-deposited and in solution provides insight into the mechanism of electroless deposition in neutral aqueous conditions and the electrocatalytically active species during oxygen reduction in alkaline electrolyte. The PdO_x/PEDOT film catalyses 4e⁻ oxygen reduction (n = 3.97) in alkaline electrolyte at low overpotential (0.98 V vs. RHE, onset potential), with mass- and surface area-based specific activities competitive with, or superior to, commercial 20% Pt/C and state-of-the-art Pd- and PEDOT-based nanostructured catalysts. The high activity of the nanostructured hybrid PdO_x/PEDOT film is attributed to effective dispersion of accessible, stable Pd active sites in the PEDOT matrix.

Hybrid PdO_x/PEDOT films efficiently catalyse the direct 4e⁻ oxygen reduction reaction in alkaline electrolyte.     

Reducing interfacial resistance of a Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte/electrode interface by polymer interlayer protection

High interfacial resistance of an electrode/electrolyte interface is the most challenging barrier for the expanding application of all-solid-state lithium batteries (ASSLBs). To address this challenge, poly(propylene carbonate)-based solid polymer electrolytes (PPC-SPEs) were introduced as interlayers combined with a Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) solid state electrolyte (SSE), which successfully decreased the interfacial resistance of the SSE/electrolyte interface by suppressing the reduction reaction of Ge⁴⁺ against the Li metal, as well as producing intimate contact between the cathode and electrolyte. This work provides a systematic analysis of the interfacial resistance of the cathode/SSE, Li/SSE and the polymer/LAGP interfaces. As a consequence, the interfacial resistance of the Li/SSE interface decreased about 35%, and the interfacial resistance of the cathode/SSE interface decreased from 3.2 × 10⁴ to 543 Ω cm². With a PPC–LAGP–PPC sandwich structure composite electrolyte (PLSSCE), the all-solid-state LiFePO₄/Li cell showed a high capacity of 148.1 mA h g⁻¹ at 0.1C and a great cycle performance over 90 cycles.

Using PPC interlayers to protect the LAGP electrolyte and reduce the interfacial impedance between electrode and electrolyte.     

Initiating a high-temperature zinc ion battery through a triazolium-based ionic liquid

Triazolium-based ionic liquids (T1, T2 and T3) with or without terminal hydroxyl groups were prepared via Cu(i) catalysed azide–alkyne click chemistry and their properties were investigated using various technologies. The hydroxyl groups obviously affected their physicochemical properties, where with a decrease in the number of hydroxyl groups, their stability and conductivity were enhanced. T1, T2 and T3 showed relatively high thermal stability, and their electrochemical stability windows (ESWs) were 4.76, 4.11 and 3.52 V, respectively. T1S-20 was obtained via the addition of zinc trifluoromethanesulfonic acid (Zn(CF₃SO₃)₂) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to T1, displaying conductivity and ESW values of 1.55 × 10⁻³ S cm⁻¹ and 6.36 V at 30 °C, respectively. Subsequently, a Zn/Li₃V₂(PO₄)₃ battery was assembled using T1S-20 as the electrolyte and its performances at 30 °C and 80 °C were investigated. The battery showed a capacity of 81 mA h g⁻¹ at 30 °C, and its capacity retention rate was 89% after 50 cycles. After increasing the temperature to 80 °C, its initial capacity increased to 111 mA h g⁻¹ with a capacity retention rate of 93.6% after 100 cycles, which was much higher than that of the aqueous electrolyte (WS-20)-based zinc ion battery (71.8%). Simultaneously, the T1S-20 electrolyte-based battery exhibited a good charge/discharge efficiency, and its Coulomb efficiency was 99%. Consequently, the T1S-20 electrolyte displayed a better performance in the Zn/Li₃V₂(PO₄)₃ battery than that with the aqueous electrolyte, especially at high temperature.

ZIB with T1S-20 electrolyte displays good charge/discharge performances and dendrite-free structure at high temperature, which is better than that with aqueous electrolyte (WS-20).     

Lithium-ion transport in inorganic active fillers used in PEO-based composite solid electrolyte sheets

In this study, we evaluated the properties exhibited by a composite solid electrolyte (CSE) prepared via tailoring the particle size of an active filler, Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO). The average particle size was reduced to 2.53 μm via ball milling and exhibited a specific surface area of 3.013 m² g⁻¹. Various CSEs were prepared by combining PEO and LLZTO/BM-LLZTO. The calculated lithium ionic conductivity of the BM-LLZTO CSE was 6.0 × 10⁻⁵ S cm⁻¹, which was higher than that exhibited by the LLZTO CSE (4.6 × 10⁻⁵ S cm⁻¹). This result was confirmed via⁷Li nuclear magnetic resonance (NMR) analysis, during which lithium-ion transport pathways varied as a function of the particle size. NMR analysis showed that when BM-LLZTO was used, the migration of Li ions through the interface occurred at a fast rate owing to the small size of the constituent particles. During the Li/CSEs/Li symmetric cell experiment, the BM-LLZTO CSE exhibited lower overvoltage characteristics than the LLZTO CSE. A comparison of the characteristics exhibited by the LFP/CSEs/Li cells confirmed that the cells using BM-LLZTO exhibited high discharge capacity, rate performance, and cycling stability irrespective of the CSE thickness.

A lithium ion transport mechanism according to particle size was demonstrated in a PEO-based composite solid electrolyte using inorganic active fillers.     

Effect of porous structural properties on lithium-ion and sodium-ion storage: illustrated by the example of a micro-mesoporous graphene1−x(MoS2)x anode

In this work, we synthesized micro-mesoporous graphene_1−x(MoS₂)_x with different compositional ratios via co-reduction of graphite oxide and exfoliated MoS₂ platelets. We systematically studied the performance of the micro-mesoporous graphene_1−x(MoS₂)_x as anodes in lithium-ion batteries and sodium-ion batteries. The results show that the specific surface areas of the composites decrease with introducing MoS₂. The irreversible capacitance, which is related to the formation of solid electrolyte interphases, also decreases. Besides specific surface area, we found that micropores can benefit the lithiation and sodiation. We demonstrated that a specific charge capacity of 1319.02 mA h g⁻¹ can be achieved at the 50th cycle for the graphene_½(MoS₂)_½ anode in lithium-ion batteries. Possible relationships between such a high specific capacity and the micro-mesoporous structure of the graphene_1−x(MoS₂)_x anode are discussed. This work may shed light on a general strategy for the structural design of electrode materials in lithium-ion batteries and sodium-ion batteries.

In this work, we systematically studied the effect of porous structural properties on performance of the micro-mesoporous graphene_1−x (MoS₂)_x as anodes in lithium-ion and sodium-ion batteries.     

Preparation and characterization of nanofibrous cellulose as solid polymer electrolyte for lithium-ion battery applications

A novel bacterial cellulose (BC)-based nanofiber material has been utilized as an ionic template for the battery system solid polymer electrolyte (SPE). The effect of drying techniques such as oven and freeze-drying on the gel-like material indicate differences in both visual and porous structures. The morphological structure of BC after oven and freeze-drying observed by field-emission scanning electron microscopy indicates that a more compact porous structure is found in freeze-dried BC than oven-dried BC. After the BC-based nanofiber immersion process into lithium hexafluorophosphate solution (1.0 M), the porous structure becomes a host for Li-ions, demonstrated by significant interactions between Li-ions from the salt and the C O groups of freeze-dried BC as shown in the infrared spectra. X-ray diffraction analysis of freeze-dried BC after immersion in electrolyte solution shows a lower degree of crystallinity, thus allowing an increase in Li-ion movement. As a result, freeze-dried BC has a better ionic conductivity of 2.71 × 10⁻² S cm⁻¹ than oven-dried BC, 6.00 × 10⁻³ S cm⁻¹. Freeze-dried BC as SPE also shows a larger electrochemical stability window around 3.5 V, reversible oxidation/reduction peaks at 3.29/3.64 V, and an initial capacity of 18 mAHr g⁻¹ at 0.2C. The high tensile strength of the freeze-dried BC membrane of 334 MPa with thermal stability up to 250 °C indicates the potential usage of freeze-dried BC as flexible SPE to dampen ionic leakage transfer.

Nanofibrous cellulose as solid polymer electrolyte for lithium-ion battery applications.     

Solid oxide fuel cell with a spin-coated yttria stabilized zirconia/gadolinia doped ceria bi-layer electrolyte

A thin yttria stabilized zirconia (YSZ)/gadolinia doped ceria (GDC) bi-layer membrane is fabricated through the slurry spin coating technique and used as an electrolyte of a solid oxide fuel cell with La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ as the cathode. The viscosity of the YSZ slurry is controlled by adding ethanol in the terpineol solvent, which shows a negligible effect on the thickness but a remarkable influence on the porosity of the YSZ film. The thickness of the YSZ layer increases with the YSZ content in the slurry. The YSZ films are pre-sintered at various temperatures, and the one sintered at 1200 °C has a moderate interaction with the GDC slurry, forming a 10 μm-thick YSZ/GDC bilayer with a low porosity and a low ohmic resistance. The corresponding single cell shows a maximum power density of 1480 mW cm⁻² at 750 °C.

Thin YSZ/GDC bi-layer electrolyte is prepared with the slurry spin coating method for SOFCs, and shows a P_max of 1480 mW cm⁻² at 750 °C.     

Role of polyvinylpyrrolidone in the electrochemical performance of Li2MnO3 cathode for lithium-ion batteries

While Li₂MnO₃ as an over-lithiated layered oxide (OLO) shows a significantly high reversible capacity of 250 mA h g⁻¹ in lithium-ion batteries (LIBs), it has critical issues of poor cycling performance and deteriorated high rate performance. In this study, modified OLO cathode materials for improved LIB performance were obtained by heating the as-prepared OLO at different temperatures (400, 500, and 600 °C) in the presence of polyvinylpyrrolidone (PVP) under an N₂ atmosphere. Compared to the as-prepared OLO, the OLO sample heated at 500 °C with PVP exhibited a high initial discharge capacity of 206 mA h g⁻¹ and high rate capability of 111 mA h g⁻¹ at 100 mA g⁻¹. The superior performance of the OLO sample heated at 500 °C with PVP is attributed to an improved electronic conductivity and Li⁺ ionic motion, resulting from the formation of the graphitic carbon structure and increased Mn³⁺ ratio during the decomposition of PVP.

The modified OLO cathode materials for improved LIB performance were obtained by heating the as-prepared OLO in the presence of polyvinylpyrrolidone (PVP) under an N₂ atmosphere.     

Novolac-based poly(1,2,3-triazolium)s with good ionic conductivity and enhanced CO2 permeation

Novolac-based poly(1,2,3-triazolium)s with 1,2,3-triazolium side groups spaced by oligo(ethylene glycol), a new kind of poly(ionic liquid) membrane, was prepared via the well-known Click chemistry (1,3-dipolar cycloaddition reaction). The thermal properties, ionic conductivity and gas permeation performance of these self-standing membranes were investigated. The obtained membranes exhibit glass transition temperatures ranging from −1 °C to −7.5 °C, and a temperature at 10% weight loss above 330 °C. These membranes have good ionic conductivity (σ_DC up to 5.1 × 10⁻⁷ S cm⁻¹ at 30 °C under anhydrous conditions) as compared with the reported 1,2,3-triazolium-based crosslinked polymers. And they could be potentially used for CO₂ separation as they exhibit enhanced CO₂ permeability up to 434.5 barrer at 4 atm pressure.

Novolac-based poly(1,2,3-triazoliums)s with 1,2,3-triazolium in the side groups spaced by oligo(ethylene glycol) show enhanced CO₂ permeability.     

Atomic thermodynamics and microkinetics of the reduction mechanism of electrolyte additives to facilitate the formation of solid electrolyte interphases in lithium-ion batteries

The formation of a solid electrolyte interphase (SEI) between the anode surface and the electrolyte of lithium-ion batteries (LIBs) has been considered to be the most important yet the least understood issue of LIBs. To further our understanding in this regard, the density functional theory (DFT) B3PW91/6-311++G(3df,3pd) together with the implicit solvent model and the transition state theory were used for the first time to comprehensively explore the electroreduction mechanism of a novel additive, 4-chloromethyl-1,3,2-dioxathiolane-2-oxide (CMDO), and a few other solvents and additives, such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and even ethylene sulfite (ES), for comparison. The one-electron reduction potential of Li⁺-coordinated compounds Li⁺(X) for forming decomposition precursors [c-Li⁺(X˙⁻)] decreases in the following sequence: CMDO (1.9–2.2 V vs. Li⁺/Li) ∼ ES(1.9 V) > FEC (0.7 V) > EC (0.47 V) > PC (0.45 V) > DMC (0.38 V); this implies that CMDO is reduced prior to other solvents or additives in the mixture. Although the ring opening of [c-Li⁺(CMDO˙⁻)] is the least kinetically favorable, as reflected by the highest energy barrier (E_a), i.e., CMDO (18.8–22.9 kcal mol⁻¹) ∼ ES (23.4) > FEC (16.2) > PC (12.5) > EC (11.2) > DMC (8.0), CMDO still shows the highest overall reaction rate constant (∼10⁵³ s⁻¹) for forming an open ring radical [o-Li⁺(CMDO˙)⁻]. In addition, the termination reaction of [o-Li⁺(CMDO˙)⁻] for forming LiCl is thermodynamically more favorable than that of Li₂SO₃ or organic disulfite (LiSO₃)₂-R, which supports the experimental observation that the halogen-containing LiF or LiCl additives are predominant over all other halogen-containing species in the SEI layer. Moreover, the hybrid model by including the second solvation shell of Li⁺via a supercluster [(CMDO)Li⁺(PC)₂](PC)₉ and the implicit solvent model (SMD) can result in a reduction potential (∼1.7 V) that is in excellent agreement with the experimental reduction peak.

The formation of a solid electrolyte interphase (SEI) between the anode surface and the electrolyte of lithium-ion batteries (LIBs) has been considered to be the most important yet the least understood issue of LIBs.     

Enhancement of alkaline conductivity and chemical stability of quaternized poly(2,6-dimethyl-1,4-phenylene oxide) alkaline electrolyte membrane by mild temperature benzyl bromination

A series of quaternized polyphenylene oxide (QPPO) based alkaline electrolyte membranes with different degrees of quaternization were synthesized via a benzyl bromination method at mild temperature (75 °C). Quite a high hydroxide conductivity under the reduced water uptake and swelling was exhibited by this method. When the degree of bromination measured from ¹H NMR analysis was 30%, the corresponding hydroxide ion conductivity was 0.021 S cm⁻¹. The chemical stability of the QPPO membranes was excellent, showing only 3% weight loss in 3 M NaOH solution during 1 month. The fuel cell performance test under H₂/O₂ exhibited the power density of 77 mW cm⁻² and the current density of 190 mA cm⁻² at 70 °C. Such excellent properties of QPPO membranes resulted from the achievement of the quaternization at the benzyl position, specifically.

A series of quaternized polyphenylene oxide (QPPO) based alkaline electrolyte membranes with different degrees of quaternization were synthesized via a benzyl bromination method at mild temperature (75 °C).     

Preparation of thin solid electrolyte by hot-pressing and diamond wire slicing

The thickness of a solid electrolyte influences the performance of all-solid-state batteries due to increased impedance with a thick electrolyte. Thin solid electrolytes are favourable to improve the performance of all-solid-state batteries due to the short Li ion diffusion path and small volume of the solid electrolytes. Therefore, the preparation of thin solid electrolyte is one of the key process techniques for development of all-solid-state batteries. In this study, thin Li_1.5Ge_1.5Al_0.5(PO₄)₃ solid electrolyte with a Na super ion conductor structure is prepared by diamond wire slicing. The Li_1.5Ge_1.5Al_0.5(PO₄)₃ solid electrolyte is prepared by melt-quenching followed by crystallization at 800 °C for 8 h, after which the crystallized Li_1.5Ge_1.5Al_0.5(PO₄)₃ rod is subjected to wire slicing. Thin Li_1.5Ge_1.5Al_0.5(PO₄)₃ with a thickness of 200 μm is obtained. The crystal structure and cross-sectional morphology are not affected by the slicing. The total Li conductivity of the thin Li_1.5Ge_1.5Al_0.5(PO₄)₃ and activation energy are 3.3 × 10⁻⁴ S cm⁻¹ and 0.32 eV, respectively. The thickness and total conductivity are comparable to those of Li_1.5Ge_1.5Al_0.5(PO₄)₃ prepared by the tape-casting method which needs several steps to prepare Li_1.5Ge_1.5Al_0.5(PO₄)₃ tape-sheet and high temperature and a long sintering process. The ionic transference number of the thin Li_1.5Ge_1.5Al_0.5(PO₄)₃ is 0.999. The diamond wire slicing is a useful method to prepare thin solid electrolytes.

The thickness of a solid electrolyte influences the performance of all-solid-state batteries due to increased impedance with a thick electrolyte.     

High-pressure synthesis and electrochemical properties of tetragonal LiMnO2

Tetragonal structured LiMnO₂ (t-LiMnO₂) samples were synthesized under pressures above 8 GPa and investigated as a positive electrode material for lithium-ion batteries. Rietveld analyses based on X-ray diffraction measurements indicated that t-LiMnO₂ belongs to a γ-LiFeO₂-type crystal structure with the I4₁/amd space group. The charge capacity during the initial cycle was 37 mA h g⁻¹ at 25 °C, but improved to 185 mA h g⁻¹ at 40 °C with an average voltage of 4.56 V vs. Li⁺/Li. This demonstrated the superiority of t-LiMnO₂ over other lithium manganese oxides in terms of energy density. The X-ray diffraction measurements and Raman spectroscopy of cycled t-LiMnO₂ indicated an irreversible transformation from the γ-LiFeO₂-type structure into a Li_xMn₂O₄ spinel structure by the displacement of 25% of the Mn ions to vacant octahedral sites through adjacent octahedral sites.

Tetragonal structured LiMnO₂ (t-LiMnO₂) samples were synthesized under pressures above 8 GPa and investigated as a positive electrode material for lithium-ion batteries.