Mechanochemical synthesis of air-stable hexagonal Li4SnS4-based solid electrolytes containing LiI and Li3PS4

Sulfide solid electrolytes with high ionic conductivity and high air stability must be developed for manufacturing sulfide all-solid-state batteries. Li₁₀GeP₂S₁₂-type and argyrodite-type solid electrolytes exhibit a high ionic conductivity of ∼10⁻² S cm⁻¹ at room temperature, while emitting toxic H₂S gas when exposed to air. We focused on hexagonal Li₄SnS₄ prepared by mechanochemical treatment because it comprises air-stable SnS₄ tetrahedra and shows higher ionic conductivity than orthorhombic Li₄SnS₄ prepared by solid-phase synthesis. Herein, to enhance the ionic conductivity of hexagonal Li₄SnS₄, LiI was added to Li₄SnS₄ by mechanochemical treatment. The ionic conductivity of 0.43LiI·0.57Li₄SnS₄ increased by 3.6 times compared with that of Li₄SnS₄. XRD patterns of Li₄SnS₄ with LiI showed peak-shifting to lower angles, indicating that introduction of I⁻, which has a large ionic radius, expanded the Li conduction paths. Furthermore, Li₃PS₄, which is the most air-stable in the Li₂S–P₂S₅ system and has higher ionic conductivity than Li₄SnS₄, was added to the LiI–Li₄SnS₄ system. We found that 0.37LiI·0.25Li₃PS₄·0.38Li₄SnS₄ sintered at 200 °C showed the highest ionic conductivity of 5.5 × 10⁻⁴ S cm⁻¹ at 30 °C in the hexagonal Li₄SnS₄-based solid electrolytes. The rate performance of an all-solid-state battery using 0.37LiI·0.25Li₃PS₄·0.38Li₄SnS₄ heated at 200 °C was higher than those obtained using Li₄SnS₄ and 0.43LiI·0.57Li₄SnS₄. In addition, it exhibited similar air stability to Li₄SnS₄ by formation of LiI·3H₂O in air. Therefore, addition of LiI and Li₃PS₄ to hexagonal Li₄SnS₄ by mechanochemical treatment is an effective way to enhance ionic conductivity without decreasing the air stability of Li₄SnS₄.

Addition of LiI and Li₃PS₄ to hexagonal Li₄SnS₄ enhances ionic conductivity without decreasing the air stability of Li₄SnS₄.     

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.     

Li4SiO4 Doped-Li7P2S8I solid electrolytes with high lithium stability synthesised using liquid-phase shaking

In this study, mechanical milling and liquid-phase shaking are used to synthesise 3Li₂S·P₂S₅ LiI·xLi₄SiO₄ (Li₇P₂S₈I·xLi₄SiO₄) solid electrolytes. When mechanical milling is used, the electrolyte samples doped with 10 mol% of Li₄SiO₄ (Li₇P₂S₈I·10Li₄SiO₄) have the highest ionic conductivity at ∼25–130 °C. When liquid-phase shaking is used, they exhibit a relatively high conductivity of 0.85 mS cm⁻¹ at ∼20 °C, and low activation energy for conduction of 17 kJ mol⁻¹. A cyclic voltammogram shows that there are no redox peaks between −0.3 and +10 V, other than the main peaks near 0 V (v.s. Li/Li⁺), indicating a wide electrochemical window. The galvanostatic cycling test results demonstrate that the Li₇P₂S₈I·10Li₄SiO₄ has excellent long-term cycling stability in excess of 680 cycles (1370 h), indicating that it is highly compatible with Li. Thus, Li₇P₂S₈I solid electrolytes doped with Li₄SiO₄ are synthesised using the liquid-phase shaking method for the first time and achieve a high ionic conductivity of 0.85 mS cm⁻¹ at 25 °C. This work demonstrates the effects of Li₄SiO₄ doping, which can be used to improve the ionic conductivity and stability against Li anodes with Li₇P₂S₈I solid electrolytes.

The galvanostatic cycling test results demonstrate that the Li₇P₂S₈I·10Li₄SiO₄ has excellent long-term cycling stability in excess of 680 cycles (1370 h), indicating that it is highly compatible with Li anode.     

Zr- and Ce-doped Li6Y(BO3)3 electrolyte for all-solid-state lithium-ion battery

The ionic conductivity of Li₆Y(BO₃)₃ (LYBO) was enhanced by the substitution of tetravalent ions (Zr⁴⁺ and Ce⁴⁺) for Y³⁺ sites through the formation of vacancies at the Li sites, an increase in compact densification, and an increase in the Li⁺-ion conduction pathways in the LYBO phase. As a result, the ionic conductivity of Li_5.875Y_0.875Zr_0.1Ce_0.025(BO₃)₃ (ZC-LYBO) reached 1.7 × 10⁻⁵ S cm⁻¹ at 27 °C, which was about 5 orders of magnitude higher than that of undoped Li₆Y(BO₃)₃. ZC-LYBO possessed a large electrochemical window and was thermally stable after cosintering with a LiNi_1/3Mn_1/3Co_1/3O₂ (NMC) positive electrode. These characteristics facilitated good reversible capacities in all-solid-state batteries for both NMC positive electrodes and graphite negative electrodes via a simple cosintering process.

Ionic conductivity of Li₆Y(BO₃)₃ (LYBO) is enhanced by the substitution of tetravalent ions through an increase in the conduction pathways etc. Zr,Ce-doped LYBO can be used as an electrolyte for all-solid-state batteries via a cosintering process.     

Self-healing solid polymer electrolyte based on imine bonds for high safety and stable lithium metal batteries

Due to their low flammability, good dimensional stability and chemical stability, solid polymer electrolytes are currently attracting extensive interest for building lithium metal batteries. But severe safety issues such as cracks or breakage, resulting in short circuits will prevent their widespread application. Here, we report a new design of self-healing solid polymer electrolyte (ShSPE) based on imine bonds, fabricated from varying amounts of polyoxyethylenebis(amine) and terephthalaldehyde through a simple Schiff base reaction. Moreover, adding diglycidyl ether of bisphenol A improves the flexibility and high stretchability of the polymer electrolyte. The polymer networks exhibit good thermal stability and excellent self-healing characteristics. The ShSPE with the highest NH₂–PEG–NH₂ content (ShSPE-3) has an improved lithium ion transference number of 0.39, and exhibits an electrochemical stability up to 4.5 V vs. Li/Li⁺. ShSPE-3 shows the highest ionic conductivity of 1.67 × 10⁻⁴ S cm⁻¹ at 60 °C. Besides, the interfacial stability of ShSPE-3 is promoted and the electrolyte membrane exhibits good cycling performance with LiFePO₄, and the LiFePO₄/Li cell exhibits an initial discharge capacity of 141.3 mA h g ⁻¹. These results suggest that self-healing solid polymer electrolytes are promising candidates for high safety and stable lithium metal batteries.

A self-healing solid polymer electrolyte based on imine bonds is fabricated through a simple Schiff base reaction. The polymer electrolyte exhibit excellent self-healing characteristics and good electrochemical performance.     

High ion conductivity based on a polyurethane composite solid electrolyte for all-solid-state lithium batteries

Solid polymer electrolytes (SPE) are considered a key material in all-solid Li-ion batteries (SLIBs). However, the poor ion conductivity at room temperature limits its practical applications. In this work, a new composite polymer solid electrolyte based on polyurethane (PU)/LiTFSI–Al₂O₃–LiOH materials is proposed. By adding a few inert fillers (Al₂O₃) and active agents (LiOH) into the PU/LiTFSI system, the ion conductivity of the SPE reaches 2 × 10⁻³ S cm⁻¹ at room temperature. Exploiting LiFePO₄ (LFP)‖Li as electrodes, the PU-based composite lithium battery is prepared. The experimental result shows that the LFP|SPE|Li displays high specific discharge capacity. The first specific discharge capacities at 0.2C, 0.5C, 1C and 3C are 159.6, 126, 110 and 90.1 mA h g⁻¹ respectively, and the Coulomb efficiency is found to be stable in the region of 92–99% which also shows a desirable cyclic stability after 150 cycles.

Adding inert filler to reduce the coupling effect of functional groups to Li⁺ and modifying the functional groups to reduce the adsorption of Li⁺ can lead to high ionic conductivity.     

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).     

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.     

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.     

Single-walled carbon nanotubes/lithium borohydride composites for hydrogen storage: role of in situ formed LiB(OH)4, Li2CO3 and LiBO2 by oxidation and nitrogen annealing

Lithium Borohydride (LiBH₄), from the family of complex hydrides has received much attention as a potential hydrogen storage material due to its high hydrogen energy densities in terms of weight (18.5 wt%) and volume (121 kg H₂ per mol). However, utilization of LiBH₄ as a hydrogen carrier in off- or on-board applications is hindered by its unfavorable thermodynamics and low stability in air. In this study, we have synthesized an air stable SWCNT@LiBH₄ composite using a facile ultrasonication assisted impregnation method followed by oxidation at 300 °C under ambient conditions (SWLiB-A). Further, part of the oxidized sample is treated at 500 °C under nitrogen atmosphere (SWLiB-N). Upon oxidation in air, the in situ formation of lithium borate hydroxide (LiB(OH)₄) and lithium carbonate (Li₂CO₃) on the surface of the composite (SWLiB@LiBH₄) is observed. But in the case of SWLiB-N, the surface hydroxyl groups [OH₄]⁻ completely vanished leaving porous LiBH₄ with SWCNT, LiBO₂ and Li₂CO₃ phases. Hydrogen adsorption/desorption experiments carried out at 100 °C under 5 bar H₂ pressure showed the highest hydrogen adsorption capacity of 4.0 wt% for SWLiB-A and 4.3 wt% for SWLiB-N composites in the desorption temperature range of 153–368 °C and 108–433 °C respectively. The observed storage capacity of SWLiB-A is due to the H⁺ and H⁻ coupling between in situ formed Li⁺[B(OH)₄]⁻, Li²⁺[CO₃]⁻ and Li⁺[BH₄]⁻. Whereas in SWLiB-N, the presence of positively charged Li and B atoms and LiBO₂ acts as a catalyst which resulted in reduced de-hydrogenation temperature (108 °C) as compared to bulk LiBH₄. Moreover, it is inferred that the formation of intermediate phases such as Li⁺[B(OH)₄]⁻, Li²⁺[CO₃]⁻ (SWLiB-A) and Li⁺[BO₂]⁻ (SWLiB-N) on the surface of the composites not only stabilizes the composite under ambient conditions but also resulted in enhanced de- and re-hydrogenation kinetics through catalytic effects. Further, these intermediates also act as a barrier for the loss of boron and lithium through diborane release from the composites upon dehydrogenation. Furthermore, the role of in situ formed intermediates such as LiB(OH)₄, Li₂CO₃ and LiBO₂ on the stability of the composite under ambient conditions and the hydrogen storage properties of the SWCNT@LiBH₄ composite are reported for the first time.

In situ formed Li⁺[B(OH)₄]⁻, Li²⁺[CO₃]⁻ & Li⁺[BO₂]⁻ on the surface of SWCNT@LiBH₄ not only stabilizes the composites in ambient conditions but also enhanced the de- and re-hydrogenation kinetics of the composites through catalytic effect.     

Low-temperature all-solid-state lithium-ion batteries based on a di-cross-linked starch solid electrolyte

The preparation of a low-temperature solid electrolyte is a challenge for the commercialization of the all-solid-state lithium-ion battery (ASSLIB). Here we report a starch-based solid electrolyte that displays phenomenal electrochemical properties below room temperature (RT). The starch host of the electrolyte is synthesized by two cross-linking reactions, which provide sufficient and orderly binding sites for the lithium salt to dissolve. At 25 °C, the solid electrolyte has exceptional ionic conductivity (σ, 3.10 × 10⁻⁴ S cm⁻¹), lithium-ion transfer number (t⁺, 0.82) and decomposition potential (dP, 4.91 V). At −20 °C, it still has outstanding σ (3.10 × 10⁻⁵ S cm⁻¹), t⁺ (0.72) and dP (5.50 V). The LiFePO₄ ASSLIB assembled with the electrolyte exhibits unique specific capacity and long cycling life below RT, and the LiNi_0.8Co_0.1Mn_0.1O₂ ASSLIB can operate at 4.3 V and 0 °C. This work provides a solution to solve the current challenges of ASSLIBs to widen their scope of applications.

The all-solid-state lithium battery based on di-cross-linked starch electrolyte is applicable at low temperature.     

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.     

A facile and scalable process to synthesize flexible lithium ion conductive glass-ceramic fibers

Solid-state electrolytes have emerged as a promising alternative to existing liquid electrolytes for next-generation flexible Li metal batteries with enhanced safety and stability. Nevertheless, the brittleness and inferior room temperature conductivity are major obstacles for practical applications. Herein, for the first time, we have fabricated a flexible lithium ion conductive glass-ceramic fiber by using a melt-spun homogeneous NASICON-type structured Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) glass melt and annealed at 825 °C. The annealed samples exhibited a higher lithium ion conductivity than the air-quenched sample due to the presence of a well-crystallized crystal grain in the annealed sample. Meanwhile, the ionic conductivity has shown an inverse relationship with the diameter of annealed LAGP glass-ceramic fibers. The results revealed that the annealed glass-ceramic fiber, with a diameter of 10 μm, resulted in lithium ion conductivity of 8.8 × 10³ S cm⁻¹ at room temperature.

A flexible lithium ion conductive Li_1.5Al_0.5Ge_1.5(PO₄)₃ glass-ceramic fiber was prepared by melt-spun method.     

Crystal structure,magneto-structural correlation,thermal and electrical studies of an imidazolium halometallate molten salt: (trimim)[FeCl4]

A novel imidazolium halometallate molten salt with formula (trimim)[FeCl₄] (trimim: 1,2,3-trimethylimidazolium) was synthetized and studied with structural and physico-chemical characterization. Variable-temperature synchrotron X-ray powder diffraction (SXPD) from 100 to 400 K revealed two structural transitions at 200 and 300 K. Three different crystal structures were determined combining single crystal X-ray diffraction (SCXD), neutron powder diffraction (NPD), and SXPD. From 100 to 200 K, the compound exhibits a monoclinic crystal structure with space group P2₁/c. At 200 K, the former crystal system and space group are retained, but a disorder in the organic cations is introduced. Above 300 K, the structure transits to the orthorhombic space group Pbcn, retaining the crystallinity up to 400 K. The study of the thermal expansion process in this temperature range showed anisotropically evolving cell parameters with an axial negative thermal expansion. Such an induction occurs immediately after the crystal phase transition due to the translational and reorientational dynamic displacements of the imidazolium cation within the crystal building. Electrochemical impedance spectroscopy (EIS) demonstrated that this motion implies a high and stable solid-state ionic conduction (range from 4 × 10⁻⁶ S cm⁻¹ at room temperature to 5.5 × 10⁻⁵ S cm⁻¹ at 400 K). In addition, magnetization and heat capacity measurements proved the presence of a three-dimensional antiferromagnetic ordering below 3 K. The magnetic structure, determined by neutron powder diffraction, corresponds to ferromagnetic chains along the a-axis, which are antiferromagnetically coupled to the nearest neighboring chains through an intricate network of superexchange pathways, in agreement with the magnetometry measurements.

We present a novel halometallate molten salt based on imidazolium cation with two structural transitions from 100 to 400 K which has been studied by X-ray and neutron diffraction techniques. Furthermore, the magnetic structure at low temperature and the ionic conductivity is also described.     

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.     

A first-principles study on Si24 as an anode material for rechargeable batteries

Due to its intriguing geometry, possessing an open-channel structure, Si₂₄ demonstrates potential for storing and/or transporting Li/Na ions in rechargeable batteries. In this work, first-principles calculations were employed to investigate the phase stability and Li/Na storage and transport properties of the Si₂₄ anode to evaluate its electrochemical performance for batteries. The intercalation of Li and Na into the Si₂₄ structure could deliver a capacity of 159 mA h g⁻¹ (Li₄Si₂₄ and Na₄Si₂₄), and the average intercalation potentials were 0.17 V (vs. Li) and 0.34 V (vs. Na). Moreover, the volume change of Si₂₄ upon intercalation proved very small (0.09% for Li, 2.81% for Na), indicating its “zero-strain” properties with stable cycling performance. Li⁺ and Na⁺ can diffuse along the channels inside the Si₂₄ structure with barrier energies of 0.14 and 0.80 eV respectively, and the ionic conductivity of Li_2.66Si₂₄ was calculated to be as high as 1.03 × 10⁻¹ S cm⁻¹ at 300 K. Our calculations indicate that the fast Li-ionic conductivity properties make the Si₂₄ structure a novel anode material for both lithium and sodium ion batteries.

Systematic investigation of Si₂₄ for Li/Na ion batteries using first-principles methods.     

Facile metal-free reduction-based synthesis of pristine and cation-doped conductive mayenite

In the present study we synthesized conductive nanoscale [Ca₂₄Al₂₈O₆₄]⁴⁺(4e⁻) (hereafter denoted as C₁₂A₇:e⁻) material, and reduced graphene oxide (rGO) was produced, which was unexpected; graphene oxide was removed after melting the sample. The conductivity of C₁₂A₇:e⁻ composites synthesized at 1550 °C was 1.25 S cm⁻¹, and the electron concentration was 5.5 × 10¹⁹ cm⁻³. The estimated BET specific surface area of the highly conductive sample was 20 m² g⁻¹. Pristine C₁₂A₇:e⁻ electride was obtained by melting the composite powder, but the nano size of C₁₂A₇:e⁻ particles could not be preserved; the value of conductivity was ∼28 S cm⁻¹, electron concentration was ∼1.9 × 10²¹ cm⁻³, and mass density was 93%. For C₁₂A_7−xV_x:e⁻, where x = 0.25 to 1, the conductivity improved to a maximum value of 40 S cm⁻¹, and the electron density improved to ∼2.2 × 10²¹ cm⁻³; this enhancement in conductivity was also proposed by a theoretical study but lacked any associated experimental support.

A facile method to prepare pristine nanoscale mayenite electride is presented. The highest achieved conductivity of melted sample was ~28 S cm⁻¹, with 93% mass density.     

Highly enhanced electrical properties of lanthanum-silicate-oxide-based SOFC electrolytes with co-doped tin and bismuth in La9.33−xBixSi6−ySnyO26

Solid oxide fuel cells (SOFCs) are one of the most promising clean energy sources to be developed. However, the operating temperature of SOFCs is currently still very high, ranging between 1073 and 1273 K. Reducing the operating temperature of SOFCs to intermediate temperatures in between 773 and 1073 K without decreasing the conductivity value is a challenging research topic and has received much attention from researchers. The electrolyte is one of the components in SOFCs which has an important role in reducing the operating temperature of the SOFC compared to the other two fuel cell components, namely the anode and cathode. Therefore, an electrolyte that has high conductivity at moderate operating temperature is needed to obtain SOFC with medium operating temperature as well. La_9.33Si₆O₂₆ (LSO) is a potential electrolyte that has high conductivity at moderate operating temperatures when this material is modified by doping with metal ions. Here, we report a modification of the structure of the LSO by partial substitution of La with Bi³⁺ ions and Si with Sn⁴⁺, which forms La_9.33−xBi_xSi_6−ySn_yO₂₆ with x = 0.5, 1.0, 1.5, and y = 0.1, 0.3, 0.5, in order to obtain an electrolyte of LSO with high conductivity at moderate operating temperatures. The addition of Bi and Sn as dopants has increased the conductivity of the LSO. Our work indicated highly enhanced electrical properties of La_7.83Bi_1.5Si_5.7Sn_0.3O₂₆ at 873 K (1.84 × 10⁻² S cm⁻¹) with considerably low activation energy (E_a) of 0.80 eV comparing to pristine La_9.33Si₆O₂₆ (0.08 × 10⁻² S cm⁻¹).

Structure modification of La_9.33Si₆O₂₆ (LSO) as SOFC electrolyte via a bi-doping mechanism provides enhanced electrical properties of La_7.83Bi_1.5Si_5.7Sn_0.3O₂₆ at 873 K (1.84 × 10⁻² S cm⁻¹) with low activation energy of 0.80 eV compared to pristine LSO (0.08 × 10⁻² S cm⁻¹).     

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.