Polysaccharides for sustainable energy storage - A review

The increasing amount of electric vehicles on our streets as well as the need to store surplus energy from renewable sources such as wind, solar and tidal parks, has brought small and large scale batteries into the focus of academic and industrial research. While there has been huge progress in performance and cost reduction in the past years, batteries and their components still face several environmental issues including safety, toxicity, recycling and sustainability. In this review, we address these challenges by showcasing the potential of polysaccharide-based compounds and materials used in batteries. This particularly involves their use as electrode binders, separators and gel/solid polymer electrolytes. The review contains a historical section on the different battery technologies, considerations about safety on batteries and requirements of polysaccharide components to be used in different types of battery technologies. The last sections cover opportunities for polysaccharides as well as obstacles that prevent their wider use in battery industry.

Li Alginate-Based Artificial SEI Layer for Stable Lithium Metal Anodes

Lithium metal anodes (LMAs) are critical for high-energy-density batteries such as Li-S and Li-O₂ batteries. The spontaneously formed solid electrolyte interface on LMAs is fragile, which may not accommodate the cyclic Li plating/stripping. This usually will result in a low coulombic efficiency (CE), short cycle life, and potential safety hazards induced by the uncontrollable growth of lithium dendrites. In this study, we fabricate a Li alginate-based artificial SEI (ASEI) layer that is chemically stable and allows easy Li ion transport on the surface of LMAs, thus enabling the stable operation of lithium metal anodes. Compared to bare LMAs, the ASEI layer-protected LMAs exhibit a more stable Li plating/stripping behavior and present effective dendrite suppression. The symmetric Li∥Li cells with the ASEI layer-protected LMAs can stably run for 850 and 350 h at current densities of 0.5 and 1 mA cm^-2, respectively. Additionally, the LiFePO₄∥Li full cell with the ASEI layer-protected LMA exhibits a capacity retention of about 94.0% coupled with a CE of 99.6% after 1000 cycles at 4 C. We believe that this study of engineering an ASEI brings a new and promising approach to the stabilization of LMAs for high-performance lithium metal batteries.

Metalophilic Gel Polymer Electrolyte for in Situ Tailoring Cathode/Electrolyte Interface of High-Nickel Oxide Cathodes in Quasi-Solid-State Li-Ion Batteries

High-Ni layered oxides are potential cathodes for high energy Li-ion batteries due to their large specific capacity advantage. However, the fast capacity fade by undesirable structural degradation in liquid electrolyte during long-term cycling is a stumbling block for the commercial application of high-Ni oxides. In this work, a functional gel polymer electrolyte, grafted with sodium alginate, is introduced to increase the stability of high-Ni oxide cathodes at the levels of both the particle and electrode. An in situ generated ion-conducting layer appears on the interface through the chemical interaction between transition-metal cations of the cathode and the metalophilic reticulum group in sodium alginate. Such a tailoring layer can not only enhance the interfacial compatibility on the cathode/electrolyte interface, reducing the interfacial resistance, but also inhibit the HF corrosion, suppressing the dissolution of transition-metal cations and harmful gradient distribution of components through the oxide cathode at the electrode level. Meanwhile, detrimental microcracks in oxide microspheres and between primary crystallites are impressively inhibited at the particle level. The high-Ni oxide cathode with the metalophilic gel polymer electrolyte shows excellent cycle stability with large initial capacity of 204.9 mA h g^-1 at a 1.0 C rate and high discharge capacity retention within 300 cycles at high temperature.

Enhancement of Power Output by using Alginate Immobilized Algae in Biophotovoltaic Devices

We report for the first time a photosynthetically active algae immobilized in alginate gel within a fuel cell design for generation of bioelectricity. The algal-alginate biofilm was utilized within a biophotovoltaics (BPV) device developed for direct bioelectricity generation from photosynthesis. A peak power output of 0.289 mWm-2 with an increase of 18% in power output compared to conventional suspension culture BPV device was observed. The increase in maximum power density was correlated to the maximum relative electron transport rate (rETRm). The semi-dry type of photosynthetically active biofilm proposed in this work may offer significantly improved performances in terms of fuel cell design, bioelectricity generation, oxygen production and CO2 reduction.

Functional Hybrid Materials Based on Manganese Dioxide and Lignin Activated by Ionic Liquids and Their Application in the Production of Lithium Ion Batteries

Kraft lignin (KL) was activated using selected ionic liquids (ILs). The activated form of the biopolymer, due to the presence of carbonyl groups, can be used in electrochemical tests. To increase the application potential of the system in electrochemistry, activated lignin forms were combined with manganese dioxide, and the most important physicochemical and morphological-microstructural properties of the novel, functional hybrid systems were determined using Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), scanning electron microscopy (SEM), zeta potential analysis, thermal stability (TGA/DTG) and porous structure analysis. An investigation was also made of the practical application of the hybrid materials in the production of lithium ion batteries. The capacity of the anode (MnO₂/activated lignin), working at a low current regime of 50 mA·g-1, was ca. 610 mAh·g-1, while a current of 1000 mA·g-1 resulted in a capacity of 570 mAh·g-1. Superior cyclic stability and rate capability indicate that this may be a promising electrode material for use in high-performance lithium ion batteries.

New eco-friendly low-cost binders for Li-ion anodes

In the production of commercial Li-ion batteries, the active materials slurries are generally prepared using polyvinylidene fluoride (PVdF) as binder because of its good adhesion properties and electrochemical stability. Unfortunately, there are some disadvantages related to the use of PVdF: the most important is the use of toxic and environmentally unfriendly solvents, such as N-methyl-pyrrolidone (NMP), and the second is the high costs. In the light of these considerations, it seemed straightforward to investigate the suitability of some water-soluble, inexpensive, and eco-friendly materials to test as alternative binders (sodium alginate, chitosan tragacanth gum, gelatin). The rheological properties of these materials have been investigated in addition to the electrochemical characterization. Furthermore, graphite electrodes with PVdF, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binders have been considered for sake of comparison. We found that some of these water-soluble binders, besides good electrochemical performances, showed a high adhesion to the current collector and a good electrochemical stability under the experimental conditions employed, which makes them interesting for the next generation of Li-ion batteries.

Sustainable and Superior Heat-Resistant Alginate Nonwoven Separator of LiNi0.5Mn1.5O4/Li Batteries Operated at 55 °C

High-voltage lithium-ion batteries have become a major research focus. As a major part of lithium batteries, the separator plays a critical role in the development of high-voltage lithium batteries. Herein, we demonstrated a sustainable and superior heat-resistant alginate nonwoven separator for high-voltage (5 V) lithium batteries. It was demonstrated that the resultant alginate nonwoven separator exhibited better mechanical property (37 MPa), superior thermal stability (up to 150 °C), and higher ionic conductivity (1.4 × 10^-3 S/cm) as compared to commercially available polyolefin (PP) separator. More impressively, the 5 V class LiNi_0.5Mn_1.5O₄ (LNMO)/Li cell with this alginate nonwoven separator delivered much better cycling stability (maintaining 79.6% of its initial discharge capacity) than that (69.3%) of PP separator after 200 cycles at an elevated temperature of 55 °C. In addition, the LiFePO₄/Li cell assembled with such alginate nonwoven separator could still charge and discharge normally even at an elevated temperature of 150 °C. The above-mentioned fascinating characteristics of alginate separator provide great probability for its application for high-voltage (5 V) lithium batteries at elevated temperatures.

Freestanding graphene/MnO2 cathodes for Li-ion batteries

Different polymorphs of MnO₂ (α-, β-, and γ-) were produced by microwave hydrothermal synthesis, and graphene oxide (GO) nanosheets were prepared by oxidation of graphite using a modified Hummers' method. Freestanding graphene/MnO₂ cathodes were manufactured through a vacuum filtration process. The structure of the graphene/MnO₂ nanocomposites was characterized using X-ray diffraction (XRD) and Raman spectroscopy. The surface and cross-sectional morphologies of freestanding cathodes were investigated by scanning electron microcopy (SEM). The charge-discharge profile of the cathodes was tested between 1.5 V and 4.5 V at a constant current of 0.1 mA cm^-2 using CR2016 coin cells. The initial specific capacity of graphene/α-, β-, and γ-MnO₂ freestanding cathodes was found to be 321 mAhg^-1, 198 mAhg^-1, and 251 mAhg^-1, respectively. Finally, the graphene/α-MnO₂ cathode displayed the best cycling performance due to the low charge transfer resistance and higher electrochemical reaction behavior. Graphene/α-MnO₂ freestanding cathodes exhibited a specific capacity of 229 mAhg^-1 after 200 cycles with 72% capacity retention.

Enhanced electrochemical performance of vanadium dioxide (B) nanoflowers with graphene nanoribbons support

Graphene nanoribbons support can improve significantly the electrochemical performance of monoclinic VO₂(B) cathode material for lithium-ion batteries.

Highly Flexible Full Lithium Batteries with Self-Knitted α-MnO2 Fabric Foam

Flexible/bendable electronic equipment has attracted great interest recently, while the development is hindered by fabricating flexible/bendable power sources due to the lack of reliable materials that combine both electronically superior conductivity and mechanical flexibility. Here, a novel structure of manganese oxide, like fabric foam, was constructed, which was then cocooned with a carbon shell via chemical vapor deposition. Serving as a binder-free anode, the self-knitted MnO2@Carbon Foam (MCF) exhibits high specific capacitance (850-950 mAh/g), excellent cycling stability (1000 cycles), and good rate capability (60 C, 1 C = 1 A/g). Moreover, a flexible full lithium battery was designed based on an MCF anode and a LiCoO2/Al cathode, and the outstanding performance (energy density of 2451 Wh/kg at a power density of 4085 W/kg) demonstrates its promising potential of the practical applications.

Superior lithium storage performance using sequentially stacked MnO2/reduced graphene oxide composite electrodes

Hybrid nanostructures based on graphene and metal oxides hold great potential for use in high-performance electrode materials for next-generation lithium-ion batteries. Herein, a new strategy to fabricate sequentially stacked α-MnO2 /reduced graphene oxide composites driven by surface-charge-induced mutual electrostatic interactions is proposed. The resultant composite anode exhibits an excellent reversible charge/discharge capacity as high as 1100 mA h g(-1) without any traceable capacity fading, even after 100 cycles, which leads to a high rate capability electrode performance for lithium ion batteries. Thus, the proposed synthetic procedures guarantee a synergistic effect of multidimensional nanoscale media between one (metal oxide nanowire) and two dimensions (graphene sheet) for superior energy-storage electrodes.

Recent Advances in Nanocomposite Materials of Graphene Derivatives with Polysaccharides

This review article presents the recent advances in syntheses and applications of nanocomposites consisting of graphene derivatives with various polysaccharides. Graphene has recently attracted much interest in the materials field due to its unique 2D structure and outstanding properties. To follow, the physical and mechanical properties of graphene are then introduced. However it was observed that the synthesis of graphene-based nanocomposites had become one of the most important research frontiers in the application of graphene. Therefore, this review also summarizes the recent advances in the synthesis of graphene nanocomposites with polysaccharides, which are abundant in nature and are easily synthesized bio-based polymers. Polysaccharides can be classified in various ways such as cellulose, chitosan, starch, and alginates, each group with unique and different properties. Alginates are considered to be ideal for the preparation of nanocomposites with graphene derivatives due to their environmental-friendly potential. The characteristics of such nanocomposites are discussed here and are compared with regard to their mechanical properties and their various applications.

Nitrogen/carbon atomic ratio-dependent performances of nitrogen-doped carbon-coated metal oxide nanocrystals for anodes in lithium-ion batteries

We report the hydrothermal synthesis of the N-doped carbon-coated NiO nanocrystals (N-C-NiO NCs) with tunable N/C atomic ratios using the nitrogen-containing ionic liquids (ILs) as new carbon precursor, and the N-doped carbon layer composition-dependent performances of N-C-NiO NCs anode for lithium-ion batteries (LIBs). The results indicate that the N-doped carbon coating can significantly enhance the electronic conductivity, effectively avoid the problems of cracking or pulverization of the NiO, and prevent the aggregation of the active materials upon cycling. These properties make the synthesized material a promising anode material for LIBs. The N-C-NiO NCs with the N/C atomic ratio of 21.2% in the N-doped carbon layer show a high specific capacity of ∼710 mAh g(-1) at a current rate of 0.3 C (very closed to the theoretical capacity of 718 mAh g(-1) for NiO), a high rate capability (still able to deliver a discharge capacity of ∼430 mAh g(-1) at a current density of 10 C), and good capacity retention upon cycling (maintains at 710 mAh g(-1) at least up to the 50th cycle) compared with those of pristine NiO nanoparticles. Moreover, the electrochemical performances of the N-C-NiO NCs depend on the composition (N/C atomic ratios) in the N-doped carbon layer and are enhanced with increasing of the N/C ratios. Our approach offers an effective and convenient technique to improve the specific capacities and rate capabilities of highly insulating electrode materials for batteries and may also provide general and effective approach toward the synthesis of other metal oxides coated with N-doped carbon layer.

Solution synthesis of metal oxides for electrochemical energy storage applications

This article provides an overview of solution-based methods for the controllable synthesis of metal oxides and their applications for electrochemical energy storage. Typical solution synthesis strategies are summarized and the detailed chemical reactions are elaborated for several common nanostructured transition metal oxides and their composites. The merits and demerits of these synthesis methods and some important considerations are discussed in association with their electrochemical performance. We also propose the basic guideline for designing advanced nanostructure electrode materials, and the future research trend in the development of high power and energy density electrochemical energy storage devices.