In energy storage devices, energy is stored in different forms such as electromagnetic, electrochemical, chemical, potential, kinetic and thermal.25 In view of, power density, energy density, technical maturity and cyclability rechargeable batteries have been popularized.26 Among them, CMC has found wide range of applications as an electrolyte, binder for electrode in batteries and cells that have been discussed here in detail.
Traditionally, liquid electrolytes have been used in electrochemical applications because they are conductive even at low temperature. But they have certain drawbacks which make them unsuitable for electrochemical devices such as leakage, deterioration, instability and so on. 27 Moreover, they could react with electrode, lead to corrosion and decrease the life span of the device. 28 Additionally, boiling point of solvent restricts the temperature of the device, showing lower electrochemical firmness. 29 With the discovery of solid polymer electrolytes (SPEs) in 1975, 11 these were predicted as suitable substitute for liquid electrolytes due to their better conductivity as well as improved mechanical and thermal stability ( ). 29,30 From there on, SPEs are preferred due to their high elasticity, low self-discharge, no leakage, easy processibility and good compatibility with electrodes. 31 The only serious disadvantage of solid electrolyte is their crystallinity but it can be solved by using organic or inorganic acids/salts. 32 Nowadays, SPEs have gained considerable attention due to their potent applications in energy density batteries, electrochemical cells, electrochromic devices and fuel cells. 33 But natural polymer electrolytes are preferred over earlier synthetic polymers due to low cost, biocompatibility and availability. 28,34
The use of cellulose and its derivatives as solid polymer electrolyte (SPE) is noteworthy because these are predicting green future unlike toxic and harmful materials. One of the derivatives of cellulose is CMC which has been extensively used as solid electrolyte in batteries and cells. CMC, when combined with other biopolymers or salts, has been showing excellent conductivity with cost-effectiveness which makes it desirable as electrolyte in energy storage devices. CMC based blends reported as solid-state electrolytes are briefly summarized in next sections.
In order to use the synthetic polymers with poor processibility and low mechanical properties in electrochemistry, they are hybridized with other materials such as CMC.35 This could cause the collapse of polymer backbone during charge–discharge cycles resulting in their enhanced electrochemical power.36,37 For example, blend of polyethylene oxide (PEO) with CMC (30/70 wt%) was observed to exhibit reduced crystallinity as obvious by XRD. The blend was reported to exhibit 5.19 × 10−5 S cm−1 maximum electrical conductivity, minimum relaxation time and activation energy which make it a potent host matrix blend for SPE in energy storage devices.38 Research group of Karaca used CMC as coating material with two intercalated vanadium surfaces of polypyrrole oxide and pencil graphite. The capacitance properties like galvanostatic charge discharge, potential recycling and electrochemical impedance spectroscopy (EIS) methods of composites were compared with coating prepared without additives. The addition of vanadium had significantly enhanced the specific capacitance and CMC was an enhancer of cyclic properties of composite. The improved specific capacitance was the result of homogenous distribution and synergetic effect of two vanadium mixed surfaces. The capacitance value was studied in different solutions such as sulfuric acid (H2SO4), lithium sulfate (Li2SO4) and HBF4/TBABF4. Results of both symmetric and asymmetric capacitors result were compared; the charge–discharge of asymmetric capacitor with composite coating was leading. The capacitor showed high energy density 18 W h kg−1, high power density of 0.43 kW kg−1 at 0.5 A g−1 with potential range of 1.2 V of stable cycle life.39
The composites of CMC with other natural polymers are considered as state-of-the-art materials because of their low cost, high efficiency, environment friendliness and biodegradability. One of the polymers is kappa carrageenan (KC); an extractive mixture of sulfated polysaccharide from red algae. CMC and KC are hydrophilic polymers with anionic polysaccharide groups, have excellent water swelling ability due to their dissolution in water. Both are non-toxic, biocompatible, cost-effective, renewable and biodegradable polymers that have proved to be excellent materials for electrolyte system. CMC and KC blends with different molar ratios are reported as promising candidates for polymer applications in semiconductors as electrolyte systems. Further addition of ionic dopant and plasticizer can make these blends more worthwhile. Actually, the blending has caused an increase in the available space for chain mobility. Increase in ionic conductivity as a result of decrease in crystallinity has increased the potential of these blends in electrolytic system.40 Moreover, the primary host for the development of novel bio-based electrolytes based on the combination of carboxymethyl kappa-carrageenan and CMC was carboxymethyl kappa-carrageenan.41 The incorporation of CMC into carboxymethyl kappa-carrageenan was shown to be an effective method for enhancing material qualities such as conductivity. The highest ionic conductivity at room temperature was 2.41 ± 10−3 S cm−1 with 30 wt% of the salt. The increase in cross-linking between polymers chains and the doping salt resulted in enhanced conductivity.42 The excessiveness of charge carriers in the system of bio-based electrolytes also contributed to the conductivity. Using this electrolyte for the manufacturing of dye sensitized solar cells (DSSC) resulted in an efficiency of 0.13% under 100 mW cm−2 of light intensity.43 Weerasooriya et al., used CMC blend with hemicellulose, prepared with weight ratio of 2 : 3. The ionic conductivity and physiochemical properties were developed by using 1–5 wt% of lithium perchlorate (LiClO4) as doped salt. The highest tensile strength was obtained with 3 wt%, and ionic conductivity with 5 wt% of LiClO4. The 5 wt% loading of LiClO4 in films was considered outstanding for ionic conductance.44
The crosslinking of CMC with other carboxylic acids was investigated by different researchers. Pérez-Madrigal et al., have used CMC based pastes and hydrogels with supporting salts and citric acid as cross-linker in solid state electrolysis. The characteristics of these electrolytes were optimized with the capacitive response of poly(3,4-ethylenedioxythiophene) electrodes. The specific capacitance of optimized hydrogels was increased by 81.5 and 76.8 F g−1 by cyclic voltammetry (CV) and galvanostatic charge and discharge as compared to paste. These electrolytes have potential to be used in solid electrochemical supercapacitors.45 Badry et al., stated that CMC with different concentrations of acetic acid and constant concentration of glycerol as plasticizer is a perfect choice for solid state electrolyte. The prepared composite films were characterized; UV-vis showed that prepared material three optical band gaps have reduced due to increase in acetic acid amount up to 5 wt%, new absorption band around 1693 cm−1 due to CMC/acetic acid interactions were indicated by FTIR. In 1H NMR, the disappearance of carbonyl group in some samples, EIS showed highest ionic conductivity of 7.64 × 10−6 S cm−1 and thermal stability had been changed with varying acid concentrations and weight loss was observed in three stages of TGA curves.46
In an electrolyte system, ions for conduction can be provided by polymer–salt complex. Bio-based polymers with ammonium salts provide good number of ions because the later have been reported as good proton doner in polymer matrix. A group of Isa et al., has performed excellent work on the hydrogen ion conducting solid biopolymer electrolyte comprising CMC. When CMC was combined with propylene carbonate (PC) and ammonium chloride, prepared by solution casting method, the best conductance of (1.01 ± 0.03) × 10−2 S cm−1 was achieved by composite containing 8 wt% of PC whose addition make the inverse relation of free ions due to weaker protonation with ionic conductivity. The surge in density number of ions until addition of 12 wt% of PC was confirmed by ionic conductivity, hopping method of mobility and diffusion ( ). PC facilitated the dissociation of H+ from ammonium chloride which had improved the electrolyte performance. The optimized composite when utilized in solid-state ionic cell of hydrogen, the performance of cell was quite good with discharge of 9 mA and recharge capacity was up to 9 cycles. The maximum discharge capacity was 2.7 mA h for 20 minutes which indicated the stability of composite in electrochemical devices.40
Open in a separate windowIn another study by the same research group, NH4Br-doped CMC served as the polymer host in the biopolymer electrolyte (BE) system. Analysis of the BE system's ionic conduction has been carried out using EIS and the most conducting sample was found to contain 25% NH4Br. When different concentrations of plasticizer were introduced to the BE system, the ionic conductivity increased to 3.31 × 10−3 S cm−1. Proton batteries may be made using CMC based BE systems with high conductivities, according to linear sweep voltammetry (LSV) measurements. In comparison to previous studies that used polymer electrolytes in their solid-state batteries, these solid-state proton batteries produced higher open-circuit voltages (OCVs) of 1.36 and 1.48 V at room temperature and outperformed previous studies that used polymer electrolytes in their solid-state batteries.41 On the same ground, Yang et al., developed proton conducting BE by combining different NH4Br compositions (wt%) with biopolymer materials CMC. It has been revealed that the conducting material is mostly available proton (H+) in this study, as verified by FTIR and transference number measurement (TNM) analyses. The Zn + ZnSO4·7H2O/BE/MnO2 design of a rechargeable proton conducting BE battery generated an all-out open circuit potential (OCP) of 1.36 V at room temperature and demonstrated excellent rechargeability.42
Samsudin et al., also investigated CMC based BE systems containing NH4Br. FTIR spectroscopy revealed a putative coordination relationship between CMC and NH4Br, which was validated by the Grotthus mechanism. The BE sample containing 25% NH4Br had the maximum ionic conductivity at room temperature (1.12 × 104 S cm−1) and the least weight loss as evidenced by TGA. Ionic transference number of mobile ions determined by direct current polarization technique was 0.98, indicating that conducting species are ions (H+). The BE was electrochemically stable up to 1.42 ± 0.01 V, making it appropriate for proton batteries. Zn + ZnSO4·7H2O/BE sample/MnO2 rechargeable proton-conducting BE batteries were made. The proton battery had a starting cell potential of 1.52 V and a constant OCP of 1.36 V. It was recharged 10 times without losing cell potential.43
CMC based polymer nanocomposites serve as efficient electrolytes due to their monodispersity and reduced crystallinity. CMC extracted from kenaf bast fiber was reported to prepare BE system by mixing with an ionic liquid (1-butyl)trimethylammonium bis(trifluoromethylsulfonyl)imide, ammonium acetate and silica nanofiller. The amount of silica nanofiller influences the conductivity of films. The highest conductivity (8.63 × 10−3 S cm−1) and electrochemical stability (3.4 V) were observed with 1 wt% of silica.47 Gold nanoparticles produced from natural leaves extracts of Ricinus communis, Solanum nigrum and Morus nigra have also been reported for BE systems. Results showed that nanoparticles formed from Ricinus communis were more limiting with enhanced monodispersity. These particles were blended with CMC to form polymer nanocomposite. XRD showed decrease in crystallinity by addition of gold nanoparticles. FTIR confirmed the interaction of nanoparticles with the polymer which might facilitate the particles to transfer over the chain of polymer. These interactions were crucial for conduction behavior of electrolyte samples. Differential scanning calorimetry (DSC) showed that by addition of nanoparticles, thermal stability decrease and conduction enhanced in range of 9.86 × 10−12 to 4.12 × 10−9 S cm−1 at 353 K.48
Abutalib et al., reported the good optical, dielectric and electrical properties of CMC films grafted with polyvinyl alcohol (PVA) and graphene nanotubes. The optical energy band gap confirmed the optical characteristics of prepared polymer blends and dynamic behavior of ions of all samples were investigated by frequency dependence AC conductance. The nanocomposite films ionic conductivity increased by addition of graphene nanotubes concentration. The highest conductivity was observed 4.53 × 10−4 at 30 °C.49
Recently, an increase in the demand of lithium-ion batteries with improved energy density and long-lasting operation is due to their usage in portable electronic devices and large-scale batteries.50 There are two major types of Li-ion batteries, conventional Li-ion batteries and ASSLIB. In a conventional battery, liquid electrolyte has been used which could be highly flammable and of high energy density.51 ASSLIB has emerged as promising solution to conventional batteries because they use solid non-flammable electrolytes.52 This solid electrolyte can work as separator or it can be separately present in liquid electrolyte-based batteries. Thus, ASSLIB provides safety and stability along with durable nature.53 Among other binders and electrolytes, sodium Carboxymethyl Cellulose (Na-CMC) is a potential binder and electrolyte for solid state Li-ion batteries ( ).54
Open in a separate windowIn ASSLIB, there are different ways to upsurge the energy density of the batteries two of them are: (1) by improving the specific capacity of the cell, development of the high-energy density electrodes55 and (2) by improving the volumetric capacity of the cell, and designing a thick electrode with compact cell configuration.56 But, the use of thicker electrode causes the enhanced diffusion of Li-ion which causes resistance to the charge transport with degradation of electrochemical performance.57 Binders as major battery components, provide integrity with enhanced physiochemical properties to the electrodes ( ).58 Conventional CMC based aqueous binders are reliable, low cost, environment friendly and provides high energy density to the anodes of Li-ion batteries ( ).59,60 Yang et al., reported CMC with humic as a potential binder for lithium batteries for the enhancement of electrochemical performance. Both water soluble polymers acted as combined binder for charge–discharge and cathode preparation process. The binder forms stable interface layer of cathode with significant increase in electrical conductivity of electrode. After 100 cycles, the reversible capacity was observed which was higher than cathode with traditional binder. The cathode specific capacity was 105 mA h g−1 at 8 °C with discharge platform of 3.30 V.61 Jeong et al., reported that lithium incorporated hierarchically porous carbon monoliths (PCMs), a potential anode material in Li-ion batteries, were prepared with lithium salt of water-soluble CMC. The porous structure of carbon and homogeneity of lithium throughout the PCMs have enhanced the electrochemical properties of composites. PCMs have low initial irreversible capacity, stable life cycle at high current density and increase in resistance at the end of the discharge. Moreover, the galvanostatic intermittent titration technique indicated the high diffusion coefficient of prepared material at the end of the discharge.62 Karkar et al., compared polyacrylic acid (PAA) and CMC/citric acid as binders for silicon-based negative Li-ion battery electrodes and found later one as more effective. Concentration of binder affects the electrode slurry rheology, dry electrode shape, and physical characteristics. Electrochemical behavior of electrodes is a function of active mass loading (1 to 4.5 mg cm−2). Increasing the binder concentration from 4 to 12 wt% enhances 1st cycle efficiency due to its role as a pre-formed artificial solid electrolyte interphase layer. Increasing the binder concentration improves the cyclability of electrodes with active mass loading over 1 mg cm−2. CMC/citric acid is more effective at low concentration and PAA at high content, perhaps due to their molecular structures. For both binders, post-processing, called maturation improves electrochemical performance.63
Open in a separate windowCMC sourceBlends/composite materialSpecific capacitance (mA h g−1)Current density (mA g−1)Charge/discharge cyclesApplications in electrochemistryRefCommercial; Sigma-AldrichNa-CMC/SBR as binder4500.230• Carbon coated silicon/boron/graphite anode in Li-ion batteries 72 CommercialNa-CMC/SBR as binder222130• Modified elastomeric binder for silicon anode in Li-ion batteries 73 CommercialCMC as binder149.2200• CMC as cheap and green binder for LiNi1/3Mn1/3Co1/3O2 (NMC) as cathode material for Li-ion batteries 74 Synthetic CMC based on cotton celluloseCMC-Li binder180200• CMC-Li is cheaper, eco-friendly, biodegradable and safer binder for Li-ion batteries' electrodes 65 Commercial; Sigma-AldrichNa-CMC/SBR/acrylic acid hydrogels as binder157/1620.550• Physiochemical effect of CMC based binder for graphite anode in Li-ion batteries 71 Commercial; Sigma-AldrichCMC derived Li incorporated hierarchically porous carbon monoliths3123050• Pre-lithiated CMC derived porous carbon monoliths can act as an efficient material for high power anode 62 Open in a separate windowCotton is also used to make the water-based CMC binder with lithium (CMC-Li). CMC-Li can enhance the lithium content, boosting the diffusion efficiency and specific capacity. The CMC-Li battery preserved 98% of its original reversible capacity after 200 cycles at 176 mA h g−1, exceeding lithium iron phosphate (LiFePO4, LFP) predicted specific capacity. The batteries are electrochemically sound, pollution-free, and stable.64 Due to small loss and consistent performance, CMC-Li with high degree of substitution is preferred.65 Qiu et al., studied electrochemical characteristics of lithium iron phosphate and water-soluble binder cathodes, CMC-Na and CMC-Li. After 200 cycles, the CMC with lithium as binder enhanced LFP cathode cyclic ability by 96.7% at 175 mA h g−1 compared to poly(vinylidene difluoride) (PVdF). The LFP electrode with CMC-Li as the binder has the best capacity rate as compared to other binders. EIS studies demonstrate that CMC-Li has lower charge transfer resistance than CMC and PVdF alone.66 CMC-Li extracted from cotton after treatment with lithium ethoxide was reported to be used as lithium-replenishing binders in the negative electrode of batteries with water as a dispersant to assemble a battery. The batteries showed better results due to reduced resistance, improved impedance, cycle period with 2500 circles and increase in life span by 20% which could be attributed to lithium supplementation. By increasing the lithium content, batteries showed improved ion conduction rate and ion conductivity.67
On one side of a pristine polyethylene battery separator, a ceramic layer composed of aluminum oxide (Al2O3) powder, CMC, and styrene-butadiene rubber (SBR) mixed binder was effectively formed to create a coating separator made of ceramics for lithium batteries. In the preparation of separator, water as solvent was used with very little quantity of SBR–CMC combination as binder to improve the thermostability. The studies have shown that the ceramic-coated separator with SBR–CMC binder had excellent thermal stability, high fluid electrolyte absorption, and superior hydrophilicity. Tests of pouch cells with a ceramic-coated separator also demonstrate high cycle stability. The ceramic coating separator (CCS) membrane significantly improved thermal contraction, liquid electrolyte hydrophilicity, and electrolyte absorption. As the ceramic-coating layer increased on the CCS membrane, the absorption of electrolytes increased, and the thermal contraction was decreased. The punch cells constructed with ceramic-coated separators have superior cycling performance compared to those with polyethylene separators. Because just a minimal quantity of binder is required and the solvent is water, the CCS membrane is appropriate for use in secondary lithium batteries.68 Yeo et al., investigated the combination of rechargeable lithium-ion batteries with lumichrome cathodes and aqueous SBR-CMC binders. A 2S6P battery module was successfully made to power blue LEDs. Positive electrode lumichrome revealed no structural alterations compared to pristine powder. Large pouch cells had cathodic and anodic peaks with 2.58 and 2.26 V average potentials. Ethylene carbonate-dimethyl carbonate (EC-DMC) and triethylene glycol-dimethoxyethane (TEGDME) both have initial discharge capabilities of 142 mA h g−1. EC-DMC-injected pouch cells performed better than TEGDME-injected ones. This may be due to the decreased lithium-ion migration resistance at the electrode/electrolyte interphase and increased EC-DMC ionic conductivity. EC-DMC-injected pouch cells cycled more than TEGDME-injected ones. After 40 cycles, EC-DMC and TEGDME-injected cells retained 56.4% and 22.3% of their capacity. TEGMDE electrolyte decomposes and swells lithium metal negative electrodes. To enhance lumichrome active materials' electrochemical characteristics, novel electrolyte systems and negative electrode materials are being studied.69 Li et al., reported that CMC Oxa-Michael addition with sulfobetaine methacrylate (SBMA) resulted in zwitterionic modification because zwitterion segment can simultaneously provide quaternary ammonium and sulfonic group for electron and lithium-ion receptors. The limiting molar conductivity increased (61 S cm2 mol−1) and activation energy decreased (0.058 eV). This composite CMC/SBMA used as binder in graphite anode of lithium-ion batteries with discharge voltage plateau at 3.35 V and specific capacitance 140 mA h g−1. This binder had also been used in activated carbon electrode for supercapacitor with low diffusion parameter of 0.03, low internal resistance and high specific capacitance of 277.9 F g−1.70 Shin et al., increased the thickness of graphite anode which created a perfect cell of increased mass loading and density of the Li-ion battery. Increasing the duration of ionic migration route may reduce Li+ diffusivity. Using SBR as a binder, cross-linked poly acrylic acid–carboxymethyl cellulose hydrogels were generated to improve adhesion strength with diffusivity. Adhesion strength of electrode with electrolyte permeability were increased by 2.0 and 2.5 times, respectively, as compared to a standard CMC–SBR combination, leading to good electrochemical characteristics owing to improve interpolymeric and electrolyte properties. Retention capacity increased from 80 to 90% at 1 °C.71
Li-ion batteries are in demand because they are used in electrical vehicles, mobile devices and electrical products.75 But lithium is not an abundant metal like sodium and is expensive. Comparatively, sodium is abundant, low in cost, gaining researcher's interest to be used in sodium ion batteries. Anodes of these batteries include hard carbon,76 antimony,77 germanium,78 tin79 and tin-based materials.80 But only few of them can satisfy large capacity and good cyclability. To enhance the cyclability, anodes based on alloy of various kind of binders have been used like PAA,81 sodium polyacrylate,82 polyimide83 and CMC.84 CMC binder has better discharge capacity by showing small change in electrode volume during cycling ( ).76 For a non-aqueous sodium-ion battery, a hard-carbon negative electrode with sodium carboxymethyl cellulose (Na-CMC) binder exhibits higher repeatability and cyclability in NaPF6 propylene carbonate solution at ambient temperature when compared with another binder made of poly(vinylidene difluoride) (PVdF). Moreover, the effects of the monofluoroethylene carbonate (FEC) additive rely significantly on the combination of CMC and PVdF binders. Depending on the binders and FEC additive employed for the hard-carbon negative electrodes, surface studies indicate substantial changes in surface and contact resistance chemistry. In aprotic sodium cells, the hard-carbon electrode with CMC binder exhibited more cyclability than the electrode with PVdF binder. The FEC is required as an electrolyte addition in order to enhance the cyclability of the PVdF electrode.85
CMC sourceBlends/composite materialCapacity (mA h g−1)Current density (mA g−1)Capacity retention (%)CyclesApplicationRefCommercial; Daicel, LtdCMC/poly (vinylidene difluoride) binder2502597100• CMC as binder for hard carbon negative electrode in sodium ion batteries 85 Commercial; Sigma-Aldrich Co. LtdCMC as binder4002520• Comparison of CMC binder with other kind of binders in sodium ion batteries 76 CommercialCMC as binder627.25073.4100• CuO nanosheets as anode with CMC binder showed satisfactory electrochemical performance 87 CommercialCMC/SBR as binder97200200• Spinel oxide-FeV2O4 with CMC/SBR binder used as conversion- based anode material in sodium ion batteries 86 Commercial; TCINa-CMC as binder6357360• BiFeO3-CMC electrode in sodium ion batteries 88 Open in a separate windowTransition metal oxides were also used as electrodes for sodium-ion batteries. FeV2O5 with eco-friendly and cost-effective binders of sodium carboxymethyl cellulose/styrene butadiene rubber has proved potential anode material for batteries. The transition metal oxide worked on the principle of pseudo-capacitive process and binders showed highly stable capacity of 97 mA h g−1 after 200 cycles. The higher stability might be due to the strong hydrogen bonding between carboxyl and hydroxyl groups which leads to superior binding with active material and current collector. By comparing the transition metal oxide capacitance with PVdF capacity, the later showed detachment of the electrode material from copper foil after 200 runs.86 Hydrothermally produced copper oxide (CuO) nanosheets were also evaluated as anodes of sodium-ion batteries. CuO nanosheets performed well as anodes due to their unique nanosheet structure. CuO nanosheets electrode with CMC binder demonstrated much better electrochemical performance than PVdF electrode. CuO nanosheet electrodes with CMC binder exhibited 627.2 mA h g−1 at 50 mA g−1. CuO nanosheet preserved 50.3% of its original capacity after 300 cycles at a current density of 2000 mA g−1. CuO nanosheets are attractive electrode materials because of their high reversible capacity, steady cycling performance, and excellent rate capability.87
Rechargeable zinc ion batteries are also a best alternative to the lithium-ion batteries in fulfilling the future energy storage demands. These batteries are of high capacity, low cost and highly abundant ( ).89 Recently, CMC composites have been used as binder for cathodes of zinc ion batteries which keep the cathode component intact during cycling. The effect of chemical structure of the conventional and green binders on the cyclability, performance and reaction of zinc ion batteries was investigated by Jaikrajang and coworkers. They concluded that sodium ion (Na+) in CMC structure plays a crucial role in battery reaction. These batteries have high ionic diffusivity and superior cyclic stability through 500 charge–discharge galvanostatic cycles.90 Similarly, Yang et al., investigated the influence of CMC as additive for zinc paste electrodes in alkaline zinc batteries. They concluded that an appropriate amount of CMC in alkali can inhibit the zinc dendrite growth with corrosion suppression.91 Li et al., designed CMC based electrolyte with high ionic conductivity 10.08 mS cm−1 and remarkable electron density and stability (97.35% after 2800 cycles). They highlighted the feasibility of moderately concentrated electrolyte to deal with the stability issue of aqueous soluble electrode material.92 Moreover, Mao et al., have introduced double-network structured electrolyte based on CMC and polyacrylamide to increase the electrostatic interaction between zinc ions (Zn2+) and carbonyl groups. This interaction has remarkably increased the stability and reversibility of zinc electrode. Flexible zinc ion batteries with this electrolyte possess 90.18% capacity retention over 500 cycles at 0.31 mA cm−2.93 Likewise, Dueramae et al., developed CMC and poly(N-isopropylacrylamide) based host polymer system in SPE of zinc ion batteries. They obtained high ionic conductivity (1.68 × 10−4 S cm−1) and greater stability during charge–discharge cyclic tests.94 Tangthuam et al., evaluated CMC/PVA based polyelectrolyte system as cation exchange separator in zinc iodine batteries. This system has also enhanced the ionic conductance and cyclic stability.95
Blends/composite materialSpecific capacitance (mA h g−1)Current density (mA g−1)Charge/discharge cyclesIonic conductance (mS cm−2)Applications in electrochemistryRefCMC/PVA as polyelectrolyte—10300119.8• CMC/PVA based polyelectrolyte separator in zinc iodine batteries 95 CMC/cellulose acetate315200500—• CMC based green binders in zinc ion batteries 90 CMC and KOH as additive—100——• CMC as additive in zinc paste electrodes 91 Na-CMC as electrolyte—268.2280010.08• Na-CMC based moderately concentrated electrolyte 92 CMC/poly(N-isopropylacrylamide) based electrolyte—0.25–51501.68 × 10−4• Physiochemical effect of CMC based binder for graphite anode in zinc ion batteries 94 Open in a separate windowElectrochemical supercapacitors are observed as popular substitute of energy storage devices due to high power density, long life cycle and rapid charge and discharge rates.96,97 Recently, researchers are trying to explore low cost, green electrode materials for super capacitors.98 Natural polysaccharides like cellulose, starch and CMC have been considered promising candidates for electrode materials ( ).99 CMC has cellulose backbone, rich in oxygen content due to carbonyl and hydroxyl groups, provides rich carbon source for oxygen self-doping in electrode materials ( ).100 For example, polypyrrole/sodium carboxymethyl cellulose (PPy/CMC) nanospheres were produced by in situ oxidative polymerization of pyrrole with CMC as a polymerization template. The composite's size and shape were homogenous, with a diameter of around 100 nm. After adding CMC as a template, the hybrid electrode exhibited high cyclic stability, with 80% retention after 200 charge and discharge cycles.35
CMC sourceBlends/composite materialSpecific capacitance (F g−1)Current density (A g−1)CyclesVoltage (V)Applications in electrochemistryRefCommercial; Tianjing Yuanli Chemical Co., ChinaSodium carboxymethyl cellulose (Na-CMC)/polyaniline nanorods425.2511000−0.2 to 0.8• CMC/polyaniline nanorods are used in high performance redox supercapacitors 116 Commercial; Anli (Henan, China)Na-CMC aerogels152.60.5−0.1 to 0 in 6 M KOH solution• Na-CMC aerogel enhanced electrochemical performance supercapacitors 110 Commercial; Zhiyuan Chemical Reagent Co., LtdCMC/bacterial cellulose/citric acid based hierarchical composite porous carbon3500.510 000• Renewable biomass-derived carbon material and its application in supercapacitors 103 CommercialCMC based polypyrrole–vanadium oxide composite on graphite electrode in acetonitrile8005.310001 mA cm−2• CMC based composite applications in asymmetric supercapacitors 39 Commercial; Anli LLC (Henan, China)Na-CMC derived nitrogen doped carbon aerogels185.30.55000−1 to 0• Na-CMC derived aerogels can be used as electrodes in supercapacitors 101 Commercial; Sigma-AldrichPorous carbon pearls of CMC217110 000 at 30 A g−10 to 1• Porous CMC derived pearls as active material for double-layer capacitors 108 Open in a separate windowOpen in a separate windowCMC based carbon aerogels with nitrogen doping also exhibit the potential to be utilized as electrode in supercapacitors. These were prepared via multistep advanced approach comprising sol–gel, freeze drying, carbonization and base stimulation process with ferric trichloride (FeCl3), collagen as cross-linker and nitrogen source. These carbon aerogels showed porous, three dimensional and higher surface area with magnetic properties. As an electrode material, the aerogel displayed current density 0.5 A g−1 and specific capacitance 185.3 F g−1 in a 6 M KOH electrolyte. The retention of specific capacitance was 90.2% after charge and discharge cycle showing cycling stability.101
CMC intercalated reduced graphene oxide films are also gaining considerable attention in charge storage devices due to their flexible, wearable and bendable nature. Reduced graphene oxide usage is challenging due to its density stacked structure with poor wettability to the electrolyte. Addition of CMC in reduced graphene oxide has acted as activating agent. The composite films were reduced to improve the electrochemical properties due to the increase in assessable area for electrolytic ions. The polymer composite films showed drastic increase in capacitance after charging/discharging cycles owing to electro activation and pseudo capacitance as compared to reduced graphene oxide film alone.102 Shu et al., have employed hierarchical porous carbon materials prepared from composite material of CMC/bacterial cellulose/citric acid as an electrode in supercapacitors. The prepared material has excellent rate capability of 254 F g−1 at current density 15 A g−1, 96% capacitance retention of cyclic stability after 10 000 cycles tests with enhanced rate capability and high specific capacitance of 350 F g−1 with current density at 0.5 A g−1. In aqueous KOH electrolyte, the symmetric porous carbon electrode showed higher specific capacitance and electron density of 28 W h kg−1.103
Ali et al., have employed bidirectional approach by using CMC samples from two different sources, bamboo (BCMC) and oil palm empty fruit bunch (OCMC), prepared by simple incipient wetness impregnation method proceeded by calcination process and incorporation of manganese oxide (Mn2O3). The carbonization step has converted CMC into porous CMC and surface area in case of BCMC was more than OCMC. After incorporation of metal oxide, the crystalline size of both CMC has reduced. Comparatively, BCMC/Mn2O3 composite film comprised of higher electrochemical performance (31.98 mF cm−2) then OCMC/Mn2O3 (24.15 mF cm−2). However, both CMC showed fairly high cyclic stability after 1000 charge/discharge cycles.104
An antifouling nanohybrid membrane comprising of CMC, graphene oxide nanosheet and magnesium oxide (MgO) nanoparticles was synthesized for water treatment and as an electrode in supercapacitor applications. TEIS Nyquist plots revealed the supercapacitor and energy applications of hybrid material.105 After that, another hybrid nanomaterial containing yttrium oxide (Y2O3) with modified graphene oxide and CMC has been prepared to utilize it as electrode in supercapacitor. The electrochemical properties were inspected by CV, Tafel plot and EIS which showed nanomaterial as promising candidate for energy storage and supercapacitors applications.106
CMC based macrostructure in combination with graphene oxide showed the potential to be used as antifouling membrane for pollutant detection and as an electrode in supercapacitor applications. Impedance analysis of fabricated nanocomposite approved the movement of charges between electrolyte and electrode for the accomplishment of specific capacitance.107
BiFeO3-CMC electrode has excellent electrochemical performance in combination with fluoroethylene carbonate (FEC) as electrolytes. These electrodes delivered initial capacity values of 635 and 453 mA h g−1 in charge/discharge process in the electrolyte composition of 1 M NaPF6 in EC/DEC (1 : 1, v/v) with 2% FEC additive. The capacity retention of 73% with capacity value stabilized around 10th cycle after 60 cycles.88 Chang et al., have developed porous carbon pearls (PCPs) from concentrated solution of CMC followed by ice-templating and carbonization. The PCPs with pearly luster had well developed bi-model pore structure with total pore volume of 0.81 cm3 g−1, specific surface area 1338.6 m2 g−1. The PCPs electrode showed high super-capacitive performance in three-electrode system with maximum specific capacitance of 217 F g−1 at 1 A g−1 in aqueous KOH electrolyte, excellent cyclic stability (100%) after 10 000 cycles at 30 A g−1. To infer concrete super-capacitive potential, a symmetric capacitor device was equipped by utilizing a coin cell which showed specific capacitance of 37 F g−1, power density of 5.0 kW kg−1, energy density of 2.88 W h kg−1 and current density of 1 A g−1. Moreover, this device had superior capacitance retention 98.5% and cycling stability of 10 000 cycles at current density of 10 A g−1.108
Pyrolysis of CMC aerogels with potassium hydroxide (KOH) activation produces porous carbon aerogels. Activation affects the characteristics of carbon aerogels. After 3 hours of KOH activation, carbon aerogels had 428 m2 g−1 specific surface area (SSA).109 Due to its extremely porous and linked 3D nanostructures, activated carbon aerogel boosted supercapacitor electrochemical performance. Specific capacitance achieved 152.6 F g−1 at 0.5 A g−1 in KOH solution (6 M) between 1.0 and 0 V. As-prepared carbon aerogels absorbed 249.6 mg g−1 methylene blue and 245.3 mg g−1 malachite green. These carbon aerogels are a potential material for energy storage, catalysis, and sewage treatment due to their increased electrochemical performance and dye adsorption capabilities.110 Méndez-Morales et al., have prepared loaded thick electrode with the highest mass that is a possible structural solution for enhancing supercapacitor energy density. However, the slowest ion transport with sluggish charge kinetics generated by the improved electrode thickness continue to pose significant obstacles to the advancement of high-performance energy storage systems.111 The fabrication of cellulose carbon aerogel-based separator, anode and cathode provides a one in all biopolymer aerogel based asymmetric supercapacitor device ( ). Both cellulose and carbon aerogel, by virtue of their three dimensional hierarchical porous percolation network structure, provide electrolyte penetration-friendly continuous routes, hence enabling the fast movement of ions and electrons.112
Open in a separate windowSodium salt CMC as a carbon source and nickel sulfate as a nickel precursor, were treated by a sol–gel procedure, freeze-drying, and pyrolysis.113 The prepared carbon aerogel (CA)/NiO composites have a three-dimensional network structure, broad surface area, and outstanding magnetic characteristics. NiSO4 affects composites' electrochemical characteristics.114 The CA-1.0 composites demonstrate better specific capacity (81.67 mA h g−1 at 0.5 A g−1) in KOH electrolyte solution (6 M), based on the coupling of CA double-layer capacitance and NiO redox reaction. After 5000 charge–discharge cycles, the CA-1.0 electrode retains 94.5% of its capability. A simple and affordable approach for making carbon/NiO composites has excellent possibilities for enhanced energy storage systems.115