Recent findings demonstrate that cellulose, a highly abundant, versatile, sustainable, and inexpensive material, can be used in the preparation of very stable and flexible electrochemical energy ...storage devices with high energy and power densities by using electrodes with high mass loadings, composed of conducting composites with high surface areas and thin layers of electroactive material, as well as cellulose‐based current collectors and functional separators. Close attention should, however, be paid to the properties of the cellulose (e.g., porosity, pore distribution, pore‐size distribution, and crystallinity). The manufacturing of cellulose‐based electrodes and all‐cellulose devices is also well‐suited for large‐scale production since it can be made using straightforward filtration‐based techniques or paper‐making approaches, as well as utilizing various printing techniques. Herein, the recent development and possibilities associated with the use of cellulose are discussed, regarding the manufacturing of electrochemical energy storage devices comprising electrodes with high energy and power densities and lightweight current collectors and functional separators.
The recent progress of cellulose, as an appealing natural material that can outperform traditional synthetic materials, for use in energy‐storage devices is described. Cellulose can bring benefits in the fabrication and properties of energy‐storage materials and devices, eventually enabling significant improvements in electrochemical performance, mechanical flexibility, cost competitiveness, and form factors, which are difficult to achieve with conventional power source technologies.
The ongoing surge in demand for high‐performance energy storage systems inspires the relentless pursuit of advanced materials and structures. Components of energy storage systems are generally based ...on inorganic/metal compounds, carbonaceous substances, and petroleum‐derived hydrocarbon chemicals. These traditional materials, however, may have difficulties fulfilling the ever‐increasing requirements of energy storage systems. Recently, nanocellulose has garnered considerable attention as an exceptional 1D element due to its natural abundance, environmental friendliness, recyclability, structural uniqueness, facile modification, and dimensional stability. Recent advances and future outlooks of nanocellulose as a green material for energy storage systems are described, with a focus on its application in supercapacitors, lithium‐ion batteries (LIBs), and post‐LIBs. Nanocellulose is typically classified as cellulose nanofibril (CNF), cellulose nanocrystal (CNC), and bacterial cellulose (BC). The unusual 1D structure and chemical functionalities of nanocellulose bring unprecedented benefits to the fabrication and performance of energy storage materials and systems, which lie far beyond those achievable with conventional synthetic materials. It is believed that this progress report can stimulate research interests in nanocellulose as a promising material, eventually widening material horizons for the development of next‐generation energy storage systems, that will lead us closer to so‐called Battery‐of‐Things (BoT) era.
Recent advances and future outlook of nanocellulose for potential use in energy storage systems are described as a green material opportunity. The unusual 1D structure and chemical functionalities of nanocellulose bring unprecedented benefits in the fabrication and properties of energy storage materials and systems, which lie far beyond those achievable with traditional synthetic materials.
Conventional self‐charging systems are generally complicated and highly reliant on the availability of energy sources. Herein, a chemically self‐charging, flexible solid‐state zinc ion battery ...(ssZIB) based on a vanadium dioxide (VO2) cathode and a polyacrylamide‐chitin nanofiber (PAM‐ChNF) hydrogel electrolyte is developed. With a power density of 139.0 W kg‐1, the ssZIBs can deliver a high energy density of 231.9 Wh kg‐1. The superior electrochemical performance of the ssZIBs is attributed to the robust tunnel structure of the VO2 cathode and the entangled network of PAM‐ChNF electrolyte, which provide efficient pathways for ion diffusion. Impressively, the designed ssZIBs can be chemically self‐charged by the redox reaction between the cathode and oxygen in ambient conditions. After oxidation for 6 h in air, the ssZIBs manifest a high discharging capacity of 263.9 mAh g‐1 at 0.2 A g‐1, showing excellent self‐rechargeability. With the assistance of a small amount of acetic acid added to the hydrogel electrolyte, the galvanostatic discharging and chemical self‐charging cycles can reach 20. More importantly, such ssZIBs are able to operate well at chemical or/and galvanostatic charging hybrid modes, demonstrating superior reusability. This work brings a new prospect for designing flexible chemically self‐charging ssZIBs for portable self‐powered systems.
The robust tunnel structure of a vanadium dioxide cathode and the network of a polyacrylamide–chitin nanofiber hydrogel electrolyte provide efficient pathways for ion diffusion, lead to superior electrochemical performance for solid‐state zinc‐ion batteries. In addition, the flexible chemically self‐charging ssZIBs demonstrate excellent self‐rechargeability and superior reusability, which provide a facile route for portable self‐powered systems.
Despite the enormous potential of aqueous zinc (Zn)‐ion batteries as a cost‐competitive and safer power source, their practical applications have been plagued by the chemical/electrochemical ...instability of Zn anodes with aqueous electrolytes. Here, ionic liquid (IL) skinny gels are reported as a new class of water‐repellent ion‐conducting protective layers customized for Zn anodes. The IL skinny gel (thickness ≈500 nm), consisting of hydrophobic IL solvent, Zn salts, and thiol‐ene polymer compliant skeleton, prevents the access of water molecules to Zn anodes while allowing Zn2+ conduction for redox reactions. The IL‐gel‐skinned Zn anode enables sustainable Zn plating/stripping cyclability under 90% depth of discharge (DODZn) without suffering from water‐triggered interfacial parasitic reactions. Driven by these advantageous effects, a Zn‐ion full cell (IL‐gel‐skinned Zn‐anode||aqueous‐electrolyte‐containing MnO2 cathode) exhibits high charge/discharge cycling performance (capacity retention ≈95.7% after 600 cycles) that lies beyond those achievable with conventional aqueous Zn‐ion battery technologies.
Ionic liquid (IL) skinny gels are presented as a water‐repellent ion‐conducting protective layer customized for aqueous Zn‐ion battery anodes. The IL‐gel‐skinned Zn anode allows sustainable Zn plating/stripping behavior without water‐triggered interfacial parasitic reactions, thus enabling an aqueous Zn/MnO2 full cell to exhibit a high charge/discharge cycling performance (capacity retention ≈95.7% after 600 cycles).
The inability to guide the nucleation locations of electrochemically deposited Li has long been considered the main factor limiting the utilization of high‐energy‐density Li‐metal batteries. In this ...study, an electrical conductivity gradient interfacial host comprising 1D high conductivity copper nanowires and nanocellulose insulating layers is used in stable Li‐metal anodes. The conductivity gradient system guides the nucleation sites of Li‐metal to be directed during electrochemical plating. Additionally, the controlled parameter of the intermediate layer affects the highly stable Li‐metal plating. The electrochemical behavior is confirmed through experiments associated with the COMSOL Multiphysics simulation data. The distributed Li‐ion reaction flux resulting from the controlled electrical conductivity enables stable cycling for more than 250 cycles at 1 mA cm−2. The gradient system effectively suppresses dendrite growth even at a high current density of 5 mA cm−2 and ensures Li plating and stripping with ultra‐long‐term stability. To demonstrate the high‐energy‐density full‐cell application of the developed anode, it is paired with the LiNi0.8Co0.1Mn0.1O2 cathode. The cells demonstrate a high capacity retention of 90% with an extremely high Coulombic efficiency of 99.8% over 100 cycles. These results shed light on the formidable challenges involved in exploiting the engineering aspects of high‐energy‐density Li‐metal batteries.
An electrical conductivity gradient interfacial host composed of simply fabricated 1D high conductivity copper nanowires and nanocellulose insulating layers shows stable lithium metal plating/stripping during electrochemical reaction. The conductivity gradient offers to guide the nucleation of lithium metal deposition, resulting in a high capacity retention of 90% with an extremely high Coulombic efficiency of 99.8% over 100 cycles as a full‐cell test.
In contrast to noteworthy advancements in cathode active materials for lithium‐ion batteries, the development of cathode binders has been relatively slow. This issue is more serious for ...high‐mass‐loading cathodes, which are preferentially used as a facile approach to enable high‐energy‐density Li‐ion batteries. Here, amphiphilic bottlebrush polymers (BBPs) are designed as a new class of cathode binder material. Using poly (acrylic acid) (PAA) as a sidechain, BBPs are synthesized through ring‐opening metathesis polymerization. The BBPs are amphiphilic in nature owing to the hydrophilic PAA sidechains and hydrophobic polynorbornene (PNB) backbones. The PNB backbone allows process compatibility with nonaqueous solvent‐based commercial cathode fabrication, while the PAA sidechain provides strong adhesion between cathode active layers and metallic current collectors. Moreover, the PAA sidechain simultaneously chelates transition metal ions dissolved from cathode active materials (LiNi0.8Mn0.1Co0.1O2 (NCM811)) particles which are chosen as a model material. Driven by the well‐balanced amphiphilicity and bottlebrush‐based structural uniqueness of the BBP binder, the resulting NCM811 cathode exhibits uniform electron/ion conduction networks and dimensional stability. Notably, a high‐mass‐loading (27 mg cm−2, corresponding to 5.2 mAh cm−2) NCM811 cathode with stable cyclability is achieved with an extremely low content (1 wt%) of the BBP binder.
An amphiphilic bottlebrush polymer (BBP) is presented as a new cathode binder for high‐mass‐loading NCM811 cathodes. The BBP binder provides well‐developed electron/ion conduction pathways, strong adhesion between cathode layers and current collectors, and chelation of transition metal. The resulting NCM811 cathode exhibits high‐mass‐loading of 27 mg cm−2 (corresponding to 5.2 mAh cm−2) at a very low binder content (1 wt%).
Redox‐active organic electrode materials have garnered considerable interest as an emerging alternative to currently widespread inorganic‐(or metal)‐based counterparts in lithium‐ion batteries ...(LIBs). Practical use of these materials, however, has posed a challenge due to their electrically insulating nature, limited specific capacity, and poor electrochemical durability. Here, a new class of multiwalled‐carbon‐nanotube‐(MWCNT)‐cored, meso‐tetrakis(4‐carboxyphenyl)porphyrinato cobalt (CoTCPP) is demonstrated as a 1D nanohybrid (denoted as CC‐nanohybrid) strategy to develop an advanced LIB anode. CoTCPP, which is one of the metalloporphyrins having multielectron redox activities, shows strong noncovalent interactions with MWCNTs due to its conjugated π‐bonds, resulting in successful formation of the CC‐nanohybrids. The structural uniqueness of the CC‐nanohybrid facilitates electron transport and electrolyte accessibility, thereby improving their redox kinetics. Inspired by the 1D structure of the CC‐nanohybrid, all‐fibrous nanomat anode sheets are fabricated through concurrent electrospraying/electrospinning processes. The resulting nanomat anode sheets, driven by their 3D bicontinuous ion/electron conduction pathways, provide fast lithiation/delithiation kinetics, eventually realizing the well‐distinguishable lithiation behavior of CoTCPP. Notably, the nanomat anode sheets exhibit exceptional electrochemical performance (≈226 mAh gsheet
−1 and >1500 cycles at 5 C) and mechanical flexibility that lie far beyond those achievable with conventional LIB anode technologies.
Carbon‐nanotube‐cored cobalt porphyrin is presented as a 1D nanohybrid strategy for the development of an advanced lithium‐ion battery anode. The chemical/structural uniqueness of the nanohybrid contributes to the redox kinetics. Notably, all‐fibrous nanomat anode sheets based on the nanohybrid provide exceptional electrochemical performance (≈226 mAh gsheet
−1 and >1500 cycles at 5 C) and mechanical flexibility.
Despite extensive studies on lithium‐metal batteries (LMBs) that have garnered considerable attention as a promising high‐energy‐density system beyond current state‐of‐the‐art lithium‐ion batteries, ...their application to flexible power sources is staggering due to the difficulty in simultaneously achieving electrochemical sustainability and mechanical deformability. To address this issue, herein, a new electrode architecture strategy based on conductive fibrous skeletons (CFS) is proposed. Lithium is impregnated into nickel/copper‐deposited conductive poly(ethylene terephthalate) nonwovens via electrochemical plating, resulting in self‐standing CFS–Li anodes. The CFS–Li anodes exhibit stable Li plating/stripping cyclability and mechanical deformability. To achieve high‐capacity flexible cathodes, over‐lithiated layered oxide (OLO) particles are compactly embedded in conductive heteronanomats (fibrous mixtures of multiwalled carbon nanotubes and functional polymer nanofibers). The conductive heteronanomats, as CFS of OLO cathodes, provide bicontinuous electron/ion conduction pathways without heavy metallic current collectors and chelate metal ions dissolved from OLO, thus improving the areal capacity, redox kinetics, and cycling retention. Driven by the attractive characteristics of the CFS–Li anodes and CFS–OLO cathodes, the resulting CFS–LMB full cells provide improvements in the cyclability, rate performance, and more notably, (cell‐based) gravimetric/volumetric energy density (506 Wh kgcell−1/765 Wh Lcell−1) along with the exceptional mechanical flexibility.
Conductive fibrous skeletons (CFS) are presented as a new electrode architecture strategy for ultrahigh‐energy‐density flexible lithium metal battery (LMB) full cells. The conductive poly(ethylene terephthalate) nonwoven and heteronanomat acts as CFS for Li metal anodes and over‐lithiated layered oxide cathodes, respectively. The resulting CFS–LMB full cell provides improvements in the electrochemical performance, mechanical flexibility, and (cell‐based) gravimetric/volumetric energy densities.
Porous crystalline materials such as covalent organic frameworks and metal–organic frameworks have garnered considerable attention as promising ion conducting media. However, most of them ...additionally incorporate lithium salts and/or solvents inside the pores of frameworks, thus failing to realize solid-state single lithium-ion conduction behavior. Herein, we demonstrate a lithium sulfonated covalent organic framework (denoted as TpPa-SO 3 Li) as a new class of solvent-free, single lithium-ion conductors. Benefiting from well-designed directional ion channels, a high number density of lithium-ions, and covalently tethered anion groups, TpPa-SO 3 Li exhibits an ionic conductivity of 2.7 × 10–5 S cm–1 with a lithium-ion transference number of 0.9 at room temperature and an activation energy of 0.18 eV without additionally incorporating lithium salts and organic solvents. Such unusual ion transport phenomena of TpPa-SO 3 Li allow reversible and stable lithium plating/stripping on lithium metal electrodes, demonstrating its potential use for lithium metal electrodes.
Although metastable crystal structures have received much attention owing to their utilization in various fields, their phase‐transition to a thermodynamic structure has attracted comparably little ...interest. In the case of nanoscale crystals, such an exothermic phase‐transition releases high energy within a confined surface area and reconstructs surface atomic arrangement in a short time. Thus, this high‐energy nanosurface may create novel crystal structures when some elements are supplied. In this work, the creation of a ruthenium carbide (RuCX, X < 1) phase on the surface of the Ru nanocrystal is discovered during phase‐transition from cubic‐close‐packed to hexagonal‐close‐packed structure. When the electrocatalytic hydrogen evolution reaction (HER) is tested in alkaline media, the RuCX exhibits a much lower overpotential and good stability relative to the counterpart Ru‐based catalysts and the state‐of‐the‐art Pt/C catalyst. Density functional theory calculations predict that the local heterogeneity of the outermost RuCX surface promotes the bifunctional HER mechanism by providing catalytic sites for both H adsorption and facile water dissociation.
Crystal phase‐transition of Ru/C from cubic‐close‐packing to hexagonal‐close‐packing creates a ruthenium carbide (RuCX, X < 1) nanosurface on Ru nanocrystal. The as‐created RuCX nanosurface presents a highly active and stable performance for the hydrogen evolution reaction (HER) in alkaline media. Density functional theory calculations predict the RuCX sites as bifunctional configurations for improving alkaline HER kinetics.
