Highly conductive locust bean gum bio-electrolyte for superior long-life quasi-solid-state zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) are promising wearable electronic power sources. However, solid-state electrolytes with high ionic conductivities and long-term stabilities are still challenging to fabricate for high-performance ZIBs. Herein, locust bean gum (LBG) was used as a natural bio-polymer to prepare a free-standing quasi-solid-state ZnSO₄/MnSO₄ electrolyte. The as-obtained LBG electrolyte showed high ionic conductivity reaching 33.57 mS cm⁻¹ at room temperature. This value is so far the highest among the reported quasi-solid-state electrolytes. Besides, the as-obtained LBG electrolyte displayed excellent long-term stability toward a Zn anode. The application of the optimized LBG electrolyte in Zn–MnO₂ batteries achieved a high specific capacity reaching up to 339.4 mA h g⁻¹ at 0.15 A g⁻¹, a superior rate performance of 143.3 mA h g⁻¹ at 6 A g⁻¹, an excellent capacity retention of 100% over 3300 cycles and 93% over 4000 cycles combined with a wide working temperature range (0–40 °C) and good mechanical flexibility (capacity retention of 80.74% after 1000 bending cycles at a bending angle of 90°). In sum, the proposed ZIBs-based LBG electrolyte with high electrochemical performance looks promising for the future development of bio-compatible and environmentally friendly solid-state energy storage devices.

Locust bean gum was utilized to prepare a free-standing quasi-solid-state ZnSO₄/MnSO₄ electrolyte. Zinc-ion batteries with locust bean gum electrolyte achieved high energy density and superior lifetime.     

3D zinc@carbon fiber composite framework anode for aqueous Zn–MnO2 batteries

Rechargeable aqueous batteries are one of the most promising large-scale energy storage devices because of their environment-friendly properties and high safety advantages without using flammable and poisonous organic liquid electrolyte. In addition, rechargeable Zn–MnO₂ batteries have great potential due to their low-cost resources as well as high energy density. However, dendritic growth of the zinc anode hinders the exertion of cycling stability and rate capacity in an aqueous Zn–MnO₂ battery system. Here we use an electrochemical deposition method to in situ form a three-dimensional (3D) zinc anode on carbon fibers (CFs). This 3D Zn@CFs framework has lower charge transfer resistance with larger electroactive areas. Batteries based on the 3D zinc framework anode and α-MnO₂ nanowire cathode present enhanced rate capacity and long cycling stability, which is promising for utilization in other zinc anode based aqueous batteries as an effective way to solve dendrite formation.

Synthesis of a 3D Zn@CFs anode through constant voltage electrodeposition to realize a dendrite-free cycling performance in an aqueous Zn/MnO₂ battery.     

Enhanced storage behavior of quasi-solid-state aluminum–selenium battery

The current aluminum batteries with selenium positive electrodes have been suffering from dramatic capacity loss owing to the dissolution of Se₂Cl₂ products on the Se positive electrodes in the ionic liquid electrolyte. For addressing this critical issue and achieving better electrochemical performances of rechargeable aluminum–selenium batteries, here a gel-polymer electrolyte which has a stable and strongly integrated electrode/electrolyte interface was adopted. Quite intriguingly, such a gel-polymer electrolyte enables the solid-state aluminum–selenium battery to present a lower self-discharge and obvious discharging platforms. Meanwhile, the discharge capacity of the aluminum–selenium battery with a gel-polymer electrolyte is initially 386 mA h g⁻¹ (267 mA h g⁻¹ in ionic liquid electrolyte), which attenuates to 79 mA h g⁻¹ (32 mA h g⁻¹ in ionic liquid electrolyte) after 100 cycles at a current density of 200 mA g⁻¹. The results suggest that the employment of a gel-polymer electrolyte can provide an effective route to improve the performance of aluminum–selenium batteries in the first few cycles.

A quasi-solid-state aluminum–selenium battery has been established using gel-polymer electrolyte between the Se positive electrode and Al negative electrode which increasing the utilization of the active materials.     

A comparison study of MnO2 and Mn2O3 as zinc-ion battery cathodes: an experimental and computational investigation

The high specific capacity, low cost and environmental friendliness make manganese dioxide materials promising cathode materials for zinc-ion batteries (ZIBs). In order to understand the difference between the electrochemical behavior of manganese dioxide materials with different valence states, i.e., Mn(iii) and Mn(iv), we investigated and compared the electrochemical properties of pure MnO₂ and Mn₂O₃ as ZIB cathodes via a combined experimental and computational approach. The MnO₂ electrode showed a higher discharging capacity (270.4 mA h g⁻¹ at 0.1 A g⁻¹) and a superior rate performance (125.7 mA h g⁻¹ at 3 A g⁻¹) than the Mn₂O₃ electrode (188.2 mA h g⁻¹ at 0.1 A g⁻¹ and 87 mA h g⁻¹ at 3 A g⁻¹, respectively). The superior performance of the MnO₂ electrode was ascribed to its higher specific surface area, higher electronic conductivity and lower diffusion barrier of Zn²⁺ compared to the Mn₂O₃ electrode. This study provides a detailed picture of the diversity of manganese dioxide electrodes as ZIB cathodes.

MnO₂ and Mn₂O₃ cathodes for zinc ion batteries were experimentally and computationally explored.     

A PVA/LiCl/PEO interpenetrating composite electrolyte with a three-dimensional dual-network for all-solid-state flexible aluminum–air batteries

Aluminum–air batteries are promising electronic power sources because of their low cost and high energy density. However, traditional aluminum–air batteries are greatly restricted from being used in the field of flexible electronics due to the rigid battery structure, and the irreversible corrosion of the anode by the alkaline electrolyte, which greatly reduces the battery life. To address these issues, a three-dimensional dual-network interpenetrating structure PVA/LiCl/PEO composite gel polymer electrolyte (GPE) is proposed. The gel polymer electrolyte exhibits good flexibility and high ionic conductivity (σ = 6.51 × 10⁻³ S cm⁻¹) at room temperature. Meanwhile, benefiting from the high-performance GPE, an assembled aluminum–air coin cell shows a highest discharge voltage of 0.73 V and a peak power density (P_max) of 3.31 mW cm⁻². The Al specific capacity is as high as 735.2 mA h g⁻¹. A flexible aluminum–air battery assembled using the GPE also performed stably in flat, bent, and folded states. This paper provides a cost-effective and feasible way to fabricate a composite gel polymer electrolyte with high performance for use in flexible aluminum–air batteries, suitable for a variety of energy-related devices.

Problems relating to the leakage of alkaline liquid electrolyte, the evaporation of water, and flexibility in traditional aluminum–air batteries are solved in this study.     

Preparation and electrochemical performance of VO2(A) hollow spheres as a cathode for aqueous zinc ion batteries

Rechargeable aqueous zinc ion batteries (ZIBs), owing to their low-cost zinc metal, high safety and nontoxic aqueous electrolyte, have the potential to accelerate the development of large-scale energy storage applications. However, the desired development is significantly restricted by cathode materials, which are hampered by the intense charge repulsion of bivalent Zn²⁺. Herein, the as-prepared VO₂(A) hollow spheres via a feasible hydrothermal reaction exhibit superior zinc ion storage performance, large reversible capacity of 357 mA h g⁻¹ at 0.1 A g⁻¹, high rate capability of 165 mA h g⁻¹ at 10 A g⁻¹ and good cycling stability with a capacity retention of 76% over 500 cycles at 5 A g⁻¹. Our study not only provides the possibility of the practical application of ZIBs, but also brings a new prospect of designing high-performance cathode materials.

VO₂(A) hollow spheres exhibit superior zinc ion storage performance, large reversible capacity of 357 mA h g⁻¹ at 0.1 A g⁻¹, and good cycling stability with a capacity retention of 76% over 500 cycles at 5 A g⁻¹     

A germanium and zinc chalcogenide as an anode for a high-capacity and long cycle life lithium battery

High-performance lithium ion batteries are ideal energy storage devices for both grid-scale and large-scale applications. Germanium, possessing a high theoretical capacity, is a promising anode material for lithium ion batteries, but still faces poor cyclability due to huge volume changes during the lithium alloying/dealloying process. Herein, we synthesized an amorphous germanium and zinc chalcogenide (GZC) with a hierarchically porous structure via a solvothermal reaction. As an anode material in a lithium ion battery, the GZC electrode exhibits a high reversible capacity of 747 mA h g⁻¹ after 350 cycles at a current density of 100 mA g⁻¹ and a stable capacity of 370 mA h g⁻¹ after 500 cycles at a current density of 1000 mA g⁻¹ along with 92% capacity retention. All of these outstanding electrochemical properties are attributed to the hierarchically porous structure of the electrode that has a large surface area, fast ion conductivity and superior structural stability, which buffers the volumetric variation during charge/discharge processes and also makes it easier for the electrolyte to soak in, affording more electrochemically active sites.

High-performance lithium ion batteries are ideal energy storage devices for both grid-scale and large-scale applications.     

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.     

Co9S8@carbon nanofiber as the high-performance anode for potassium-ion storage

Thanks to their intrinsic merits of low cost and natural abundance, potassium-ion batteries have drawn intense interest and are regarded as a possible replacement for lithium-ion batteries. The larger radius of potassium, however, provides slow mobility, which normally leads to sluggish diffusion of host materials and eventual expansion of volume, typically resulting in electrode failure. To address these issues, we design and synthesize an effective micro-structure with Co₉S₈ nanoparticles segregated in carbon fiber utilizing a concise electrospinning process. The anode delivers a high K⁺ storage capacity of 721 mA h g⁻¹ at 0.1 A g⁻¹ and a remarkable rate performance of 360 mA h g⁻¹ at a high current density of 3 A g⁻¹. A small charge-transfer resistance and a high pseudocapacitive contribution that benefit fast potassium ion migration are indicated by quantitative analysis. The outstanding electrochemical performance can be attributed to the distinct architecture design facilitating high active electrode–electrolyte area and fast kinetics as well as controlled volume expansion.

Co₉S₈@carbon nanofibers with boosted highly active electrode–electrolyte area, fast kinetics and controlled volume expansion show an excellent cycling and rate performance in potassium ion batteries.     

Designing conductive networks of hybrid carbon enables stable and long-lifespan cotton-fiber-based lithium–sulfur batteries

In modern society, flexible rechargeable batteries have become a burgeoning apodictic choice for wearable devices. Conventional lithium–sulfur batteries lack sufficient flexibility because their electrode materials are too rigid to bend. Along with the inherent high theoretical capacity of sulfur, lithium–sulfur batteries have some issues, such as dissolution and shuttle effect of polysulfides, which restricts their efficiency and practicability. Here, a flexible and “dead-weight”-free lithium–sulfur battery substrate with a three-dimensional structure was prepared by a simple strategy. With the cooperative assistance of carbon nanotubes and graphene attached to cotton fibers, the lithium–sulfur battery with 2.0 mg cm⁻² sulfur provided a high initial discharge capacity of 1098.7 mA h g⁻¹ at 1C, and the decay rate after 300 cycles was only 0.046% per cycle. The initial discharge capacity at 2C was 872.4 mA h g⁻¹ and the capacity was maintained 734.4 mA h g⁻¹ after 200 cycles with only a 0.079% per cycle decay rate.

A flexible, “dead weight”-free lithium–sulfur battery substrate was prepared, and batteries using these substrates showed great electrochemical performance.     

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).     

Dual-doped hierarchical porous carbon derived from biomass for advanced supercapacitors and lithium ion batteries

Nowadays, designing heteroatom-doped porous carbons from inexpensive biomass raw materials is a very attractive topic. Herein, we propose a simple approach to prepare heteroatom-doped porous carbons by using nettle leaves as the precursor and KOH as the activating agent. The nettle leaf derived porous carbons possess high specific surface area (up to 1951 m² g⁻¹), large total pore volume (up to 1.374 cm³ g⁻¹), and high content of nitrogen and oxygen heteroatom doping (up to 17.85 at% combined). The obtained carbon as an electrode for symmetric supercapacitors with an ionic liquid electrolyte can offer a superior specific capacitance of 163 F g⁻¹ at 0.5 A g⁻¹ with a capacitance retention ratio as high as 67.5% at 100 A g⁻¹, and a low capacitance loss of 8% after 10 000 cycles. Besides, the as-built supercapacitor demonstrates a high specific energy of 50 W h kg⁻¹ at a specific power of 372 W kg⁻¹, and maintains 21 W h kg⁻¹ at the high power of 40 kW kg⁻¹. Moreover, the resultant carbon as a Li-ion battery anode delivers a high reversible capacity of 1262 mA h g⁻¹ at 0.1 A g⁻¹ and 730 mA h g⁻¹ at 0.5 A g⁻¹, and maintains a high capacity of 439 mA h g⁻¹ after 500 cycles at 1 A g⁻¹. These results demonstrate that the nettle leaf derived porous carbons offer great potential as electrodes for advanced supercapacitors and lithium ion batteries.

Nettle leaf derived nitrogen and oxygen dual-doped porous carbons exhibit great potential as anodes for high performance supercapacitors and lithium ion batteries.     

NaV6O15 microflowers as a stable cathode material for high-performance aqueous zinc-ion batteries

Reversible aqueous zinc-ion batteries (ZIBs) have great potential for large-scale energy storage owing to their low cost and safety. However, the lack of long-lifetime positive materials severely restricts the development of ZIBs. Herein, we report NaV₆O₁₅ microflowers as a cathode material for ZIBs with excellent electrochemical performance, including a high specific capacity of ∼300 mA h g⁻¹ at 100 mA g⁻¹ and 141 mA h g⁻¹ maintained after 2000 cycles at 5 A g⁻¹ with a capacity retention of ∼107%. The high diffusion coefficient and stable tunneled structure of NaV₆O₁₅ facilitate Zn²⁺ intercalation/extraction and long-term cycle stability.

NaV₆O₁₅ microflowers were synthesized as a stable cathode material for aqueous zinc ion batteries, which show a high specific capacity and excellent long-term cycling performance.     

Self-assembled hierarchical porous NiMn2O4 microspheres as high performance Li-ion battery anodes

Hierarchical structured porous NiMn₂O₄ microspheres assembled with nanorods are synthesized through a simple hydrothermal method followed by calcination in air. As anode materials for lithium ion batteries (LIBs), the NiMn₂O₄ microspheres exhibit a high specific capacity. The initial discharge capacity is 1126 mA h g⁻¹. After 1000 cycles, the NiMn₂O₄ demonstrates a reversible capacity of 900 mA h g⁻¹ at a current density of 500 mA g⁻¹. In particular, the porous NiMn₂O₄ microspheres still could deliver a remarkable discharge capacity of 490 mA h g⁻¹ even at a high current density of 2 A g⁻¹, indicating their potential application in Li-ion batteries. This excellent electrochemical performance is ascribed to the unique hierarchical porous structure which can provide sufficient contact for the transfer of Li⁺ ion and area for the volume change of the electrolyte leading to enhanced Li⁺ mobility.

Hierarchical structured porous NiMn₂O₄ microspheres assembled with nanorods are synthesized through a simple hydrothermal method followed by calcination in air.     

N doped carbon coated V2O5 nanobelt arrays growing on carbon cloth toward enhanced performance cathodes for lithium ion batteries

Highly flexible, binder-free cathodes for lithium ion batteries were fabricated by utilizing N doped carbon to coat V₂O₅ (V₂O₅@N-C) nanobelt arrays growing on carbon cloth. Such a robust architecture endows the electrode with effective ion diffusion and charge transport, resulting in high rate capability (135 mA h g⁻¹ at 10C) and excellent cycling performance (215 mA h g⁻¹ after 50 cycles at 0.5C).

Highly flexible, binder-free cathodes for lithium ion batteries were fabricated by utilizing N doped carbon to coat V₂O₅ (V₂O₅@N-C) nanobelt arrays growing on carbon cloth.     

Exploration of the modification of carbon-based substrate surfaces in aqueous rechargeable zinc ion batteries

The hydrophobic surfaces of carbon-based substrates lead to a huge interface impedance in aqueous rechargeable zinc ion batteries (ZIBs). Herein, we try to regulate the morphology and investigate the effects of polar groups on the substrate surface. With the treated substrate, the cyclic and rate performances of MnO₂ electrodes are improved by ∼42.5% and 97 mA h g⁻¹.

Oxygen-containing groups can be introduced to carbon paper surfaces by acidification. They improve the electrochemical performances and affect the charge-discharge behaviors of the MnO₂/CP cathode by reducing the interface resistance.     

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.     

Low cost bio-derived carbon-sprinkled manganese dioxide as an efficient sulfur host for lithium–sulfur batteries

Realization of the lithium-sulfur battery system is of major concern because a theoretical cell capacity of 1675 mA h g⁻¹ can be obtained at an average voltage of 2.1 V. The primary issues that hinder the practical applications of this system include its poor utilization of sulfur, limited cycle life and retarded rate performance. In the present study, hemp-derived carbon (C-hemp) is made into a composite with room temperature-synthesized MnO₂, which acts as a host for sulfur in the lithium-sulfur battery system. The composite material is characterized physico-chemically and electrochemically using various techniques. This composite exhibits better electrochemical performance as a sulfur carrier compared to pristine carbon. An initial specific capacity of 926 mA h g⁻¹ is obtained at 0.1 C for C-hemp/MnO₂-sulfur, which surpasses that of the C-hemp-sulfur sample. C-hemp provides a conductive matrix as well as porous sites for the accommodation of sulfur, while MnO₂ exhibits the ability to absorb polysulfide chemically. Thus, this composite is established as a potential cathode for lithium-sulfur batteries.

MnO₂-biomass (hemp) derived carbon composite is used as an effective cathode in Li–S cell. MnO₂ acted as polysulfide scuffolding in the composite enhancing Li–S cell performance. New carbon source (hemp-fibre) was utilised successfully in Li–S.     

Double-layer carbon protected CoS2 nanoparticles as an advanced anode for sodium-ion batteries

Cobalt disulfides with high theoretical capacity are regarded as appropriate anode materials for sodium ion batteries (SIBs), but their intrinsically low conductivity and large volume expansion lead to a poor electrochemical performance. In this work, graphitic carbon coated CoS₂ nanoparticles are encapsulated in bamboo-like carbon nanotubes by pyrolysis and sulfidation process. Graphitic carbon can improve the electrical conductivity and prevent the agglomeration of CoS₂ nanoparticles. Meanwhile, bamboo-like carbon nanotubes can serve as conductive skeleton frames to provide rapid and constant transport pathways for electrons and offer void space to buffer the volume change of CoS₂ nanoparticles. The advanced anode material exhibits a long-term capacity of 432.6 mA h g⁻¹ at 5 A g⁻¹ after 900 cycles and a rate capability of 419.6 mA h g⁻¹ even at 10 A g⁻¹ in the carbonate ester-based electrolyte. This avenue can be applicable for preparing other metal sulfide/carbon anode materials for sodium-ion batteries.

The outstanding electrochemical performance is ascribed to the novel structure design of CoS₂@GC@B-CNT.     

The study of zirconium vanadate as a cathode material for lithium ion batteries

The electrochemical properties of ZrV₂O₇ (ZVO) and ZVO@C were investigated in lithium ion batteries. The first charge (or discharge) specific capacity of ZVO and ZVO@C are 279 mA h g⁻¹, 392 mA h g⁻¹, 208 mA h g⁻¹ and 180 mA h g⁻¹ for 0%, 3%, 5% and 9% of carbon, respectively. The capacity retention rates (with 0% 3%, 5% and 9% carbon content) are 33.0%, 52.5%, 56.4% and 76.1% after ten cycles, respectively. The low inner resistance relates to the good contact of the electrode rather than the high content of carbon, and the specific capacity retention rate increases with the increase of the carbon content.

The carbon content in the electrode is not the only factor that determines the internal resistance. The high capacity of lithium ion batteries is related to high conductivity. The lattice is stable (expect for shrinkage) when Li ions insert into ZVO.