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.
Carbohydrate Polymers 265 (2021) 118063 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Review Polysaccharides for sustainable energy storage – A review Werner Schlemmer a, Julian Selinger a, b, Mathias Andreas Hobisch a, Stefan Spirk a, * a b Institute of Bioproducts and Paper Technology, Graz University of Technology, 8010, Graz, Austria Department of Bioproducts and Biosystems, Aalto University, P O Box 16300, 00076, Aalto, Finland A R T I C L E I N F O A B S T R A C T Keywords: Battery Polysaccharides Cellulose Alginate Chitosan Nanocellulose Binder Separator 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 Scope of the review This review aims at summarizing the use of polysaccharides in en ergy storage systems Central to this review is to focus on energy storage elements, i.e., active material, separator, binders The intention of the review is not to list all types of materials but to focus on requirements of the respective energy storage component and why polysaccharides can be versatile candidates in the development of such components We also discuss limitations of polysaccharides in this area as well as obstacles that prevent them from wider use in energy storage systems In the end of the review, the challenges and opportunities for polysaccharides in battery systems will be highlighted and discussed Introduction We are facing a global crisis as the use of fossil fuels has been emitting huge quantities of greenhouse gases such as CO2 and methane to the atmosphere The increasing concentration of these compounds into the atmosphere led to global warming at unprecedented rate in the history of mankind During the lifetime of Carbohydrate Polymers (September 1981 until now), the CO2 content in the atmosphere increased from 340 to 419 ppm (NOAA, 2021) As a consequence, policy makers in Europe and in other parts of the world aim at limiting these emissions to reduce global warming (European-Commission, 2020a, 2020b) A core element of this policy is to change the energy supply from fossil based towards green sources such as solar, wind and tidal energy Some countries have made remarkable efforts in this respect, e.g., Ger many shut down a high number of coal fueled plants and massively invested in wind and solar energy, which accounted for 42.1 % of overall energy production in 2019 (Fraunhofer-ISE, 2021) Similarly, the Nordic countries have been aiming at converting their energy supply to more sustainable sources, thereby curbing CO2 emissions A major challenge of renewable energy, however, originates from fluctuations in energy production, caused by weather conditions and seasonal changes In Abbreviations: AA, agar-agar; ANF, aramid nanofiber; BC, bacterial cellulose; CA, cellulose acetate; CaAlg, calcium alginate; CG, carrageenan; ChNF, chitosan nanofibrils; CMC, carboxymethyl cellulose; CMCh, carboxymethyl chitosan; CN-CMCh, cyanoethyl carboxymethyl chitosan; CNF, cellulose nanofibrils; CNC, cellulose nanocrystals; EC, ethyl cellulose; GA, gum arabic; GM, galactomannan; GG, guar gum; GPE, gel polymer electrolyte; HEC, hydroxyethyl cellulose; HNT, halloysite nanotube; HPC, hydroxypropyl cellulose; LIB, lithium ion battery; LPC, lignosulfonate–polyamide-epichlorohydrin complex; LTO, lithium titanate, Li4Ti5O12; LNMO, lithium nickel manganese oxide; m-CA, modified cellulose acetate; NaAlg, sodium alginate; PBI, poly(oxyphenylene benzimidazole); PE, polyethylene; PET, poly ethylene terephthalate; PMMA, poly(methyl methacrylate); PP, polypropylene; PPS, polypropylene sulfide; PPy, polypyrrol; PSA, polysulfonamide; PSS, polystyrene sulfonate; PVDF, polyvinylidene fluoride; PVDF-HFP, polyvinylidene fluoride-co-hexafluoropropylene; SBR, styrene-butadiene rubber; SPE, solid polymer electro lytes; TG, tara gum; TEMPO, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl; TOCN, TEMPO oxidized cellulose nanofibrils; XG, xanthan gum * Corresponding author E-mail address: stefan.spirk@tugraz.at (S Spirk) https://doi.org/10.1016/j.carbpol.2021.118063 Received 11 March 2021; Received in revised form April 2021; Accepted April 2021 Available online 20 April 2021 0144-8617/© 2021 The Author(s) Published by Elsevier Ltd This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) W Schlemmer et al Carbohydrate Polymers 265 (2021) 118063 addition, the energy is often produced at locations which are not in close spatial proximity to the end users Moreover, energy is produced at times when the supply exceeds the demand These challenges lead to signifi cant instabilities in the grid, requiring back-up plants to ensure the power supply The most promising solution to this problem lies in the installation of large-scale storage facilities, which can release the energy when it is needed Different approaches exist that rely on storage in the form of mechanical (e.g., flywheels), potential (hydropower, com pressed air storage) or chemical energy (e.g batteries, hydrogen) All of these technologies enable storage capacity ranging from two-digit MWh (flywheels) to GWh (hydropower) (Mongird et al., 2019) Lithium ion batteries (LIBs) have been proven to be an integral part of stationary storage with the largest battery being the Hornsdale Facility in Australia (100 MW h) However, there are several challenges with battery com ponents They mostly rely on depletable sources, their recycling is challenging and resources are not regionally available, causing a high CO2 footprint These issues have to be seen in the context of a steadily increasing share of electric vehicles, boosting the demand particularly for LIBs, accompanied with a rapid decline in costs which will probably soon cross the 100 $/kWh threshold In this review, the emphasis is put on energy storage components based on polysaccharides, comprising separators, electrolytes, and binders We highlight the specific advantages which polysaccharides can offer for each application Only batteries are covered, while super capacitors as well as electrode materials from biomass and lignin are not investigated in this review; here we refer to other reviews for further reading (Liedel, 2020; Nirmale, Kale, & Varma, 2017; Yu, Li, Chen, Wu, & Peng, 2019) The principle of batteries in combination with a his torical evolution of technology will be explained in brief in the following section dioxide (cathode) and uses sulfuric acid as electrolyte The acid reacts with both electrodes to form lead sulfate causing an electron flow from one electrode to the other, which are both reversible processes, enabling recharging of the battery Interestingly, the design of the lead-acid battery has not significantly changed since its invention In some ap plications, such as in car batteries, they are still in use The dry cell technology was the next step towards new application areas of batteries The basic concept is a paste-like electrolyte, that contains a small amount of moisture to allow for current flow As the electrolyte is a paste, these cells can be oriented in any direction as there is nothing that could potentially spill off Portable applications were realized, such as the zinc carbon battery (1.5 V) It is made of a zinc casing that serves at the same time as anode and a manganese(IV) oxide cathode which is connected to a conductive carbon rod Commonly used gel electrolytes in today’s dry cells contain a moist paste of ammonium or zinc chloride impregnated paper The paper serves as separator be tween the zinc anode and the manganese(IV) oxide cathode This type of cell has a significant market share (roughly 20 %) for portable batteries An even larger share of portable batteries is occupied by dry alkaline batteries In such batteries, zinc and carbon are used with potassium hydroxide as gel electrolyte and a separator, often made from cellulose The cell features a voltage of 1.4 V and is one of the most commonly used primary batteries with current market shares of roughly 50 % In the past two decades, battery development was boosted by several factors Portable electronics require high energy density while being rechargeable In addition, battery technology was boosted by massive investments in electric cars Lithium ion batteries are capable of delivering voltages of over V while having a high energy density Developed by G.N Lewis more than 100 years ago, it took several decades until LIBs became commercially exploitable, with significant efforts of Besenhard and later Goodenough (Besenhard & Eichinger, 1976; Eichinger & Besenhard, 1976; Mizush ima, Jones, Wiseman, & Goodenough, 1980) The first commercialized LIB was brought to the market by Sony in 1991 The main advantage of LIBs is that they operate at high voltages, requiring the use of electro lytes other than water, typically ethylene carbonate, propylene car bonate or diethyl carbonate In such electrolytes, the lithium species are dissolved (e.g LiPF6, LiBF4) Commercial electrode materials consist of layered oxides, spinels, polyanions (anode) and graphite (cathode) During operation of the battery the lithium ions move to the other electrode, where they intercalate into the electrode material (Fig 1) (Lu, Han, Li, Hua, & Ouyang, 2013) While LIBs have been used to power Batteries-a short historical survey The first battery was developed in the late 18th century when Luigi Galvani observed a phenomenon he later termed ‘animal electricity’ During the dissection of frog legs he realized that they twitched when the iron scalpel touched them (Galvani & Volta, 1791) However, his friend Alessandro Volta connected these observations to the metal sur faces of the scalpel rather than the frog legs and led the foundation for the invention of the voltaic pile-the first battery In such a battery, piled copper and zinc disks were assembled In order to avoid a short circuit, the metals were separated by cloth or cardboard, which were presoaked in an electrolyte solution to ensure conductivity (Dibner, 1964) The battery was fully functioning (stable supply of electricity, current, hardly any self-discharge) but had some disadvantages (electrolyte leakages, short battery lifetime) caused by the weight of the piles and parasitic reactions leading to hydrogen evolution during operation These issues were solved by the development of the Daniell cell, which had an operating voltage of 1.1 V This type of cell is based on a zinc anode, and a copper vessel, which was filled with a solution of copper sulfate Into the vessel, a porous, ceramic tray filled with sulfuric acid was placed which enabled an exchange of ions Therefore hydrogen evolution was suppressed and over time only conducting copper metal is deposited on the anode (Spencer, Bodner, & Rickard, 2010) The Daniell cell was a major accomplishment in battery technology and its impor tance can be seen in the unit of the electromotive force (Volt), since the operating voltage of the Daniell cell was roughly V (Hamer, 1965) Later on, different improvements such as the Bird cell (Bird, 1838), Gravity cell and the Poggendorf (Ayrton & Mather, 1911) cell were introduced, which we will not cover in more detail here It is noteworthy that the Gravity cell was widely used in British and American telegraph networks until the mid 1950s The next milestone in battery technology was the development of rechargeable batteries Until then, battery lifetime was limited by the amount of redox active compounds in the battery The lead-acid battery was a game changer in this respect It consists of lead (anode) and lead Fig Schematics of a lithium ion battery using LiCoO2 and graphite as electrode materials Reproduced from (Roy & Srivastava, 2015) with permission from The Royal Society of Chemistry W Schlemmer et al Carbohydrate Polymers 265 (2021) 118063 consumer electronics for the past 20 years, the increasing number of electrically powered vehicles is driving innovation in this area How ever, the past years showed that the current LIB technology features environmental drawbacks ranging from non-sustainable raw material supply (e.g., mining of lithium and cobalt) to challenging recycling Alternative, evolving battery technologies involve metals such as so dium and magnesium which are highly abundant and available in many places of the world Their operation is also safer than corresponding lithium ion batteries 2012) This practice would be acceptable if all experimental details are made available in scientific papers, however, precise details about the cell geometry are often not provided in publications This problem has been recognized for both supercapacitors and batteries (Freunberger, 2015; Gogotsi & Simon, 2011; Obrovac & Chevrier, 2014) but best practice publishing standards as recently proposed for solar cells are yet to be defined (Editorial, 2015) A material may show exceptional per formance when values are referenced to a single component, although the values might be biased In this respect, particularly the properties of nanomaterials such as graphene can be misleading, having a very low packing density, that allows for high electrolyte loading (which typically does have a Faradaic contribution) For a better comparability of device performance, for different fields of applications, energy and power density can be compared in a Ragone plot (Fig 2) Requirements for battery components Battery components must ensure a safe, economic and performance driven operation of the device Lately, the recycling, particularly of LIBs, has also become an issue which again is connected to the steady increase of electric vehicles on our streets Safety aspects are manifold and cover the cell chemistry, electrolytes, cell design, and separators Good articles covering these basic safety aspects are provided by Abada et al (2016) and Rezvanizaniani, Liu, Chen, and Lee (2014) Lately, car batteries that caught fire either after accidents or during charging sensitized the main public and policy makers in this respect as well The cell chemistry determines the energy density of the battery Mobile devices require a high energy density while stationary use works as well with systems having a lower energy density High energy density is related to higher chemical reactivity which increases the risk of un desired reactions in a battery Therefore, in commercial applications, the cell chemistry is usually optimized to ensure a safe operation rather than pushing the performance limits A prominent example is (high energy density) lithium cobalt oxide, which is subsequently replaced by other less reactive lithium species such as lithium iron phosphates to over come safety issues Electrolyte stability is another aspect that must be considered, as its decomposition/degradation is more likely to take place at high voltages and elevated temperatures In addition, heat transport must be included in the design of the cells to avoid local hotspots in high energy density devices Among other issues, these hotspots can lead to separator failure as most of separators are made from polymeric materials When the separator melts, the cell undergoes a thermal runaway associated with severe fires This can be mitigated by the use of thermally stable separators A review on this aspect has been recently published (Yuan & Liu, 2020) Second only to safety, performance (e.g., energy density per volume/ mass, shelf-life, self-discharge, cycle life, device level) is of utmost importance for batteries (Nitta, Wu, Lee, & Yushin, 2015) Here, the cell chemistry determines the energy density and nominal voltage Another important aspect is shelf life, which however, again depends on battery chemistry, ranging from to years for Leclanche cells to approx years for alkaline batteries and up to ten years for LIBs Moreover, self-discharge, i.e the loss of battery capacity when not operated should be minimized The typical self-discharge rate for LIB is 2–3 % per month, while lead acid batteries feature about % loss within the same time In this context, temperature is an important factor, as elevated tempera tures typically accelerate undesired reactions, and promote self-discharge In addition, discharge rates, cycle life (number of char ge/discharge cycles until the capacity drops by 20 %) should be optimized The surface area of the electrodes is a crucial parameter, as the battery capacity, energy and power can be expressed as normalized values by weight or volume Often, such values are provided based on the mass of the electron conductor Although this is technically correct, it can be easily misleading as the true performance may be very different at the device level The correlation of performance metrics of electro chemical energy storage devices to the mass or volume of a certain “active” component has been become common for energy storage sys tems Often, the reported electrochemical performance parameters may represent just a part or even a negligible fraction of the total device mass or volume (Bruce, Freunberger, Hardwick, & Tarascon, 2012; Choi et al., Polysaccharide based components in batteries In the historical section, we already briefly described that poly saccharides have been crucial parts in batteries already from the very beginning of battery technology development However, research extended from a mere, electrically insulating barrier (separator) in the form of cloth or cardboard to different applications In the following, we will give a brief overview thereof 5.1 Binder The function of the binder is to prevent electrode swelling and me chanical damages as well as to protect the active material against the electrolyte, while enabling ion transport throughout the binder Particularly for high energy density devices such as LIBs, this of crucial importance so it is little surprising that significant efforts have been made to improve binder performance Here, mostly nanosized active electrode materials have been in the focus as any degradation will lead to drastic performance losses The challenge is that nanoparticles (e.g Si) undergo volume changes upon lithiation/delithiation in the range of 300 % and more As a consequence, the binder, which covers the nanoparticles, is exposed to mechanical stress (Fig 3) Cracking or stripping of the binder leads to increasing contact area of silicon and the electrolyte, causing increasing solid electrolyte interface (SEI) formation and electrode gravelling (i.e pulverization) Consequently, the nonconductive surface area increases which leads to a strong reduction in Fig Ragone plot illustrating the performances of specific power vs specific energy for different electrical energy-storage technologies Times shown in the plot are the discharge time, obtained by dividing the energy density by the power density Reprinted with permission from (Shao et al., 2018) Copyright (2018) American Chemical Society W Schlemmer et al Carbohydrate Polymers 265 (2021) 118063 Fig Schematic of the volume expansion of graphite (MCMB, mesocarbon microbeads), silicon, and silicon–MCMB graphite composite electrodes Reproduced from (Yim, Courtel, & Abu-Lebdeh, 2013) with permission from The Royal Society of Chemistry performance, with battery failure being the final stage Polyvinylidene fluoride (PVDF) is often used in commercial battery designs as it can be assembled in both anode and cathode materials Advantages of PVDF include high (electro-)chemical stability, and good adhesion to electrode materials and current collectors While these properties are important, rather poor mechanical flexibility of PVDF is unfavorable for a use as binder The advantage of many polysaccharides is that they readily form homogeneous films and layers onto different materials Moreover, many polysaccharides can be processed from aqueous solutions While envi ronmentally friendly, this also poses a risk during the drying as shrinkage may induce cracks in the binder or reduction of the interfacial contact areas by stripping However, the use of organic solvents during battery assembly can be avoided in case of aqueous polysaccharide systems, which is a benefit for the production A review on biopolymeric binders gives more details on these points (Bresser, Buchholz, Moretti, Varzi, & Passerini, 2018) In the past decades, polysaccharides have been proposed in binder formulation with carboxymethyl cellulose (CMC) as the most prominent example, which is even in commercial use Although one may think that CMC may form a ‘soft’ elastic layer on electrode materials to account for volume changes, this is actually not the case As known from paper making, where CMC can be used to improve paper strength, it is a rigid molecule Typically, CMC films not exceed 5–8 % elongation at break (Lestriez, Bahri, Sandu, Rou´e, & Guyomard, 2007) Consequently, the rigidity of the binder is only one important aspect in their performance This has been demonstrated by Li et al who compared pure CMC and styrene-butadiene-rubber (SBR-CMC) blends as binders One would argue that the more elastic SBR–CMC system should yield more stable performance, which was however not the case The stiffer CMC binder showed superior characteristics regarding all relevant electrochemical parameters – despite being more brittle (Li, Lewis, & Dahn, 2007) One reason was that CMC improves the processability of the electrode slurries as the encapsulation of silicon nanoparticles by CMC facilitates their dispersibility As many polysaccharides with carboxyl groups, the CMC can act as crosslinker in slurries, creating three-dimensional net works between particles and polymer suspensions Thereby, the inter action relies on the entanglements of the CMC macromolecules with the particles, which is further governed by its conformation (coiled vs extended), the degree of polymerization and the degree of substitution with carboxymethyl groups (Fig 4) It is known that high molar mass and a high extent of coiling favors crosslinking, which is beneficial for binders CMC based binders are capable of compensating for up to 400 % in volume change while maintaining stable performance (Lestriez et al., 2007) However, the mode of interaction of CMC with the electrode surface is not merely physical This has been extensively studied for silicon nanoparticle-based electrodes Also covalent bonds are formed between the carboxyl groups of CMC and the nanoparticle surface, exhibiting forces which are one order of magnitude larger than caused by pure physisorption as shown by AFM (Maver, Znidarsic, & Gaberscek, 2011) For silicon nanoparticles, the tendency of surface Si− OH groups to un dergo condensation reactions strongly depends on the pH value ATR-IR spectroscopy and 13C solid state NMR spectroscopy demonstrated that the condensation reactions between the surface Si− OH groups could be modulated; at pH condensation was favored (Bridel, Azais, Morcrette, Tarascon, & Larcher, 2011; Hochgatterer et al., 2008; Mazouzi, Lestriez, Rou´e, & Guyomard, 2009) Several authors provide data on the influ ence of the pH value during processing, and in all cases slurries pro cessed at a pH value of performed better than those processed at pH (Tranchot, Idrissi, Thivel, & Roue, 2016) However, there are further conclusions from these results, namely that a defined silicon oxide/ hydroxide layer on the nanoparticles is crucial for the battery perfor mance (Delpuech et al., 2014) In the absence of such a defined layer, preparation of the slurry at pH did not improve performance Addi tionally, CMC features self-healing Upon intercalation, physical or W Schlemmer et al Carbohydrate Polymers 265 (2021) 118063 Fig Schematic illustration of the proposed interactions occurring between the carboxyl groups of CMC and Si particles Both H-bonds and ester bonds are established with the silanol (Si− OH) groups on the Si particle surface The volume expansion occurring upon lithiation causes the rupture of the bonds During the dealloying process, the Si particles shrink, but the ester bonds are not re-established On the other hand, the self-healing property of the weaker H-bonds permits the contact between the binder and the Si particles to be retained Reproduced from the Royal Society of Chemistry from Bresser, D., Buchholz, D., Moretti, A., Varzi, A., & Passerini, S., 2018, Energy & Environmental Science, 11, 3096− 3127 under a Creative Common License 3.0 covalent bonds between the carboxyl groups and the electrode material are cleaved However, new bonds accomplishing for the volume changes can be reformed commonly termed healing in this respect (Bridel, Azaïs, Morcrette, Tarascon, & Larcher, 2010) One may argue that the diffusion of Li+ ions is restricted by complexation with the carboxyl groups of the CMC, as a combination of coordination modes was observed It was, however, shown by NMR spectroscopy that the diffusion of Li+ was not compromised by CMC, showing Li-exchange rates in the nanosecond range (Casalegno et al., 2016) CMC may contribute also in another way to maintain battery per formance As the electrolyte degrades over time, a solid electrolyte interface (SEI) layer is formed As a consequence, pores are blocked, preventing the intercalation of lithium ions into the anode material (Mazouzi et al., 2012; Oumellal et al., 2011; Radvanyi et al., 2014) There is some evidence that CMC forms an artificial SEI layer on com posite electrodes, which is in contrast to PVDF based binder systems (Delpuech et al., 2014; Jeschull et al., 2016) This seems to be also promising for batteries having very high cell potentials (4 V), where CMC (and also alginate) exhibited superior binder performance compared to PVDF (Liang et al., 2021) CMC has been used in different setups and electrode configurations and a detailed electrochemical discussion would go beyond the scope of this review Apart from CMC, there is a decent amount of data available for other polysaccharides acting as binders In the following, we elab orate a few examples which are noteworthy either in terms of material or the binding mechanism to the electrode material An inexhaustive list of examples of electrode materials and poly saccharides as binders is depicted in Table For instance, alginates have been widely used as binders as they are capable of forming 3D networks upon crosslinking with divalent ions such as Ca2+ They have been used in conjunction with many electrode materials such as Li–S or silicon as binders and there are many cases known where they outperformed PVDF and even CMC-based binders (Bao, Zhang, Gan, Wang, & Lia, 2013; Zhang, Zhang et al., 2014) Particularly the crosslinking allows for an entrapment of the silicon nanoparticle electrode materials in the alginate network, while simul taneously increasing its mechanical strength Furthermore, the flexi bility of the alginate caused by its molecular structure may play an important role as well Alginate is a non-random copolymer consisting of two monosaccharides (D-mannuronic acid, and its C5 epimer L-gulur onic acid) that show different connectivity While the D-mannuronic acids are connected in a rigid β (1→4)-fashion, the α (1→4)-linkage of the L-guluronic acid moieties provides flexibility Consequently, volume changes upon lithium insertion can be easier compensated, while maintaining electrical and structural integrity of the electrode, yielding better battery performance Like CMC, alginates feature carboxyl groups and a similar self-healing mechanism was proposed (Fig 5) (Liu et al., 2014; Yoon, Oh, Jo, Lee, & Hwang, 2014) Recently, the mechanism of alginate-silicon anode interactions was further explored by in operando AFM measurements in the presence of electrolyte The authors showed that after immersion in the dimethyl carbonate electrolyte and operation for several hours the Young’s modulus was 56 times higher than those of PVDF (Lee et al., 2020) Crosslinking also improved the binder performance of other poly saccharides and battery chemistries For instance, chitosan was cross linked using glutaraldehyde, creating a 3D network, acting as binder for antimony anode materials in sodium batteries (Gao, Zhou, Jang, & W Schlemmer et al Carbohydrate Polymers 265 (2021) 118063 Table Polysaccharides used in binders in different battery technologies and electrode materials Polysaccharide Technology Electrode Reference Agarose LIB Zn-air LIB LIB Graphite Zn Si Graphite (Cuesta et al., 2015) (Masri & Mohamad, 2009) (Hwang et al., 2016) (Cuesta et al., 2015; Soeda, Matsui, Yamagata, & Ishikawa, 2013) (Feng, Xiong, Qian, & Yin, 2014) (Mitra, Veluri, Chakraborthy, & Petla, 2014) (Kumar et al., 2014) (Zhang, Ren et al., 2019) Alginate CdO CoFe2O4 CoFe2O4/rGO Dilithium terephtalate Fe2O3@C (hard C) Fe2O3 nanotubes LiMn2O4 LiNi1/3Co1/3Mn1/ 3O2 LTO MnO2 Si/graphite Si/pristine C Si/rGO Si-NP LIB Li-S SIB P P2-Na2/3MnO2 SnS Amylopectin Zn LIB TiO2 MnO2 Si Amylose LIB Si SIB Si P S Anthraquinone Graphite λ-Carrageenan CMC LIB LIB LTO MoO3 MoS2 nano-Sn/PPy NiFe2O4/rGO SnS nanorods Si SnS2 SIB Hard carbon CuO MoS2/ N-doped hard carbon Na3V2(PO4)2F3 Table (continued ) Polysaccharide Technology Electrode Reference SnS (Dogrusoz & Demir-Cakan, 2020) (Kumar, Krishnan, Samal, Mohanty, & Nayak, 2018) (Chai et al., 2013) (Gao et al., 2016) (Chen, Lee et al., 2016; Lee et al., 2018) (Cao et al., 2018; Zhao, Yim, Du, & Abu-Lebdeh, 2018) (Prasanna et al., 2019) (Kuenzel et al., 2020) (Chen et al., 2015; Feng et al., 2021; Kim, Cho, & Lee, 2020; Kim, Kim, Cho, Lee, & Lee, 2020) (Sun, Zhong, Jiao, Shao, & Zhang, 2014) (Zhong et al., 2017) (Wu et al., 2019; Yue, Zhang, & Zhong, 2014) (Zhong et al., 2014) (He, Wang, Zhong, Ding, & Zhang, 2015) (Jeong et al., 2014; Kwon et al., 2015) (Wang et al., 2013) (Cuesta et al., 2015) (Carvalho et al., 2018) (Yin et al., 2020) (Carvalho et al., 2016; Cuesta et al., 2015; Lee, Kim, & Oh, 2014) (Dufficy, Khan, & Fedkiw, 2015; Ling et al., 2015; Wang et al., 2021) (Kuruba et al., 2015) (Li et al., 2016; Liu et al., 2017; Lu et al., 2016) (Hu, Cai, Huang, Zhang, & Yu, 2019) (Cuesta et al., 2015) (Ling et al., 2015) (Li, Ling et al., 2015; Shaibani et al., 2020) (Xu et al., 2017) (Qi et al., 2019) (Bie, Yang, Nuli, & Wang, 2017) (Carvalho et al., 2016) (Wang, Wan, & Hong, 2020; Yoon et al., 2016) (Gendensuren, He, & Oh, 2020) (Zhao et al., 2019) (Bie, Yang, Nuli, & Wang, 2016; Hapuarachchi et al., 2020; Jin et al., 2021; Rohan et al., 2018; You et al., 2019) (Masri, Nazeri, Ng, & Mohamad, 2015) (Cuesta et al., 2015) (He, Zhong, Wang, & Zhang, 2017) (L´eonard & Job, 2019) (Chen et al., 2014) (Liu et al., 2017) SnS2 Chitosan LIB Graphite Sb Si Si/graphite (Li et al., 2019) CMCh (Veluri & Mitra, 2013) (Kim, De bruyn et al., 2019; Kong et al., 2015; Ryou, Hong, Winter, Lee, & Choi, 2013) (Soeda et al., 2013; Zhang, Deng et al., 2018) (He, Gendensuren, Kim, Lee, & Oh, 2020; Phanikumar et al., 2019; Toigo, Arbizzani, Pettinger, & Biso, 2020) (Li, Zhao, Wang, Ding, & Guan, 2012) (Gendensuren & Oh, 2018) (Liu et al., 2014) (Huang, Chen et al., 2019) (Kovalenko et al., 2011; Wu et al., 2017; Zhang, Zhang et al., 2014) (Bao et al., 2013; Luo et al., 2020) (Xiao et al., 2020) (Xu et al., 2019) (Dogrusoz & Demir-Cakan, 2020) (Ling et al., 2018) (Chang et al., 2020) (Ling et al., 2020; Murase et al., 2012) (Murase et al., 2012; Wen & Zhang, 2020) (Yoon et al., 2016) (Zhang, Lv et al., 2020) (Ling et al., 2017) (Xie et al., 2012) (Chang et al., 2019; Cuesta et al., 2015; Shin, Park, & Paik, 2017) (Carvalho et al., 2016; He et al., 2020) (Wang, Madhavi, & Lou, 2012) (Sen & Mitra, 2013; Volkov, Eliseeva, Tolstopjatova, & Kondratiev, 2020) (Chou et al., 2011) (Li et al., 2017) (Tripathi & Mitra, 2014) (You et al., 2019) (Zhong, Zhou, Yue, Tang, & Zhang, 2014) (Dahbi et al., 2014) (Fan, Yu, & Chen, 2017) (Pang et al., 2017) Li/S Si/hard carbon LNMO Li-S LIB LiFePO4 LNMO Si-NP CN-CMCh LIB SnS2 LiFePO4 β-Cyclodextrin LIB Si Galactomannan LIB LIB Li-S Graphite NMC LNMO LTO Si LIB Si/graphite Li-S Gellan gum LIB Si Gum arabic LIB LIB Graphite Si Li-S SIB LiS LIB Fe2O3 S Si Karaya gum Pectin LTO Si Si/graphite Starch Xanthan gum SIB LIB NVP Si Zn-air Zn LIB Graphite LiFePO4 LIB LiFePO4/LTO Si/graphene Li-S Goodenough, 2016) As for the alginates, the network was capable of accommodating volume changes upon sodium insertion/removal The same crosslinking strategy can also be applied for LIB and Si anode materials (Chen, Lee, Cho, Kim, & Lee, 2016) An interesting paper that compared different binders in one study (Zhao, Yang et al., 2018) W Schlemmer et al Carbohydrate Polymers 265 (2021) 118063 Fig (a) Molecular structure of alginate and Ca-mediated “egg-box’’ like cross-links in Ca-alginate (b) Expansion and self-healing mechanism of Ca-alginatecontaining silicon anodes during charge–discharge cycles Reproduced from (Yoon et al., 2014) with permission of the Royal Society of Chemistry Fig Voltammograms of cycle 1, (a) and (c), and cycle 5, (b) and (d), of the binder electrodes and bare Cu (c) and (d) show the SG/PVDF electrode for comparison purposes Reproduced from (Cuesta et al., 2015) with permission of Elsevier W Schlemmer et al Carbohydrate Polymers 265 (2021) 118063 ´n, Antun ˜ a, & was published by Cuesta et al (Cuesta, Ramos, Camea García, 2015) The direct comparison of the binders in the same testing setup is crucial to assess the true performance of the investigated ma terials (Fig 6) They used PVDF, CMC, alginate, gum arabic (GA), xan than gum (XG), guar gum (GG), agar-agar (AA) and carrageenan (CG) for graphitic electrodes in LIBs (Cuesta et al., 2015) All chosen binder systems were electrochemically and thermally stable under the employed experimental conditions Alginate, CMC, XG and GG binders (5 wt.% content) exhibited good to excellent electrochemical perfor mance in galvanostatic cycling experiments, which were superior to those of SG/PVDF electrodes with higher binder content (8 wt.%) The other systems had issues with adhesion on the electrode leading to worse performance Another interesting account deals with xanthan gum as binder for Si/ graphene electrodes in LIBs (Chen et al., 2014) They manufactured the nanocomposite using high-energy ball milling combined with thermal treatment Anodes prepared with XG binders exhibited a better cycling and rate performance compared to electrodes prepared using CMC as binder As mentioned above, the performance increase was caused by larger binder stiffness and the strong adhesion of the binder to the Si-based particles, accomplishing efficiently volume changes in the anode material A somehow unusual binder material is polymerized β-cyclodextrin This material possesses an inherent 3D network, which offers manifold coordination sites and hydrogen bonds to Si nanoparticles (Jeong et al., 2014) Also this binder featured self-healing as binder-Si nanoparticles interactions recovered during cycling, thereby maintaining good elec trode performance The cyclodextrin could be readily oxidized using H2O2 yielding a highly water soluble binder which showed promising results for sulfur composite cathodes (Wang, Yao, Monroe, Yang, & Nuli, 2013) were equivalent to conventional separators in their proof of concept in LiCoO2 based batteries Later on, a variety of nanopapers, i.e paper made from cellulose nanofibrils (either from lignocellulose or bacterial cellulose), were described as separators (Chun et al., 2012; Kim et al., 2013; Jiang, Yin, Yu, Zhong, & Zhang, 2015; Yu, Park, Jang, & Good enough, 2016) The nanofibrils in turn featured several intrinsic ad vantages as their high aspect ratio and high crystallinity contributed to mechanical and thermal stability As cellulose nanofibrils were amphi philic, they were able to accommodate a large variety of electrolytes In addition, the morphology and porosity of nanopapers could be fine-tuned depending on the precise electrolyte composition They can be produced as rather thin sheets and their flexibility allows them to be used as separators for bendable batteries This makes them perfect candidates for emerging technologies such as wearable electronics, active radio-frequency identification tags and bendable reading devices (Leijonmarck, Cornell, Lindbergh, & Wagberg, 2013) A common approach to fibrillate cellulosic pulps into CNF is TEMPO oxidation, which separates the fibrils by introduction of carboxyl groups The resulting materials are termed TEMPO-oxidized cellulose nanofibrils (TOCN) Depending on the pH value TOCN feature either Na+ or H+ as a counterion, which has an influence on its separator performance as porosity is affected by the change of the cation (Fig 7, Table 2) While cellulose nanofibrils have been widely employed in separators, the use of cellulose nanocrystals is more challenging One of the few examples involves cellulose nanocrystals (CNC) from Cladophora which have been subjected to a paper making process to give sheets with a thickness of 35 μm, an average pore size of about 20 nm, and a Young’s modulus of ca 5.9 GPa (Pan et al., 2016) Their good availability, solu tion processability and mesoporous structure (~20 nm average pore size) makes them promising as future separator materials (Zhou, Nyholm, Strømme, & Wang, 2019), suppressing the formation of lithium dendrites The described electrolyte contained M LiPF6 in ethylene carbonate; the separator was thermally stable up to 150 ◦ C and elec trochemically inert in a potential range between and V vs Li+/Li Similar results to those with Cladophora cellulose were described for mesoporous CNC separators produced by coassembly with tetramethyl orthosilicate from aqueous solutions with subsequent silica removal (Gonỗalves, Lizundia, Silva, Costa, & Lanceros-Mendez, 2019) How ever, challenges of CNC in separator applications were their high degree of brittleness when processed, causing the danger of pinholes Those and other problems in purely cellulosic separators might be overcome by blending with other components Composite membranes aim at increasing performance by combining different types of materials CNC for instance are promising materials but they have shortcomings when used without additives Examples include composites involving PVDF-co-hexafluoropropylene (PVDFHFP), a commonly used polymer in LIB separator technology (Kelley, Simonsen, & Ding, 2013) PVDF-HFP/CNC nanocomposite films exhibited improved Young’s modulus and tensile strength of the mem branes (Bolloli et al., 2016) Another approach to improve PVDF based separators is compounding with CMC One example includes the use of an Al2O3/ PVDF-HFP/CMC slurry that was deposited on a polyethylene (PE) substrate to form a separator which showed properties superior to a separator containing only PE (Deng et al., 2016) MFC/polysulfonamide composites were also suitable separator membranes for LIBs (LiCoO2, LiFePO4), working at temperatures up to 120 ◦ C (Xu, Kong, Liu, Wang et al., 2014) Similarly, cellulose/poly dopamine (CPD) membranes with a compact porous structure were re ported that exhibited superior mechanical strength and excellent thermal dimensional stability compared to commercial separators (Xu, Kong, Liu, Zhang et al., 2014) Lithium cobalt oxide/graphite cells with CPD separators showed a good cycling stability and rate capability compared to commercially available polypropylene and neat cellulose separators Another approach is to deposit a polymer on a commercial separator (e.g., polypropylene) This was accomplished with hydrox yethyl cellulose (HEC) aerogels deposited on commercial polypropylene 5.2 Separators Although the separator is not an electrochemically active component in a battery, its morphology as well as structural and physical properties have a large impact on battery performance as it provides a physical barrier between the anode and cathode materials (Lee, Yanilmaz, Top rakci, Fu, & Zhang, 2014) It must be permeable to ions during charge and discharge and chemically inert towards the electrolyte and the electrode materials even at extreme electrochemical conditions Sepa rators must be able to withstand elevated temperatures and/or corrosive environment while maintaining their mechanical properties The ideal separator features a high ionic conductivity and thus low internal resistance, which can be achieved when the electrolyte uptake of the separator is high For a comprehensive, general overview on separators the reader is referred to some review articles (Arora & Zhang, 2004; Lee, Yanilmaz et al., 2014) involving also cellulose materials (Fu & Zhong, 2019; Sheng, Tong, He, & Yang, 2017; Zhang et al., 2021; Zhang, Tian, Shen, Song, & Yao, 2019) Classical separators can be classified into microporous membranes, nonwovens, polymer electrolyte membranes and composite membranes Each of these systems has advantages and limitations and its usage de pends on the final application (Lee, Yanilmaz et al., 2014; Yang & Hou, 2012) Microporous membranes comprise the classic category for cellulose based separators and have been used already in the first Leclanche cells, and later in lead acid batteries and alkaline batteries They comprise conventional papers, paper composites, as well as nanopapers and membranes from nanocellulose and cellulose derivatives In 1996, Asahi Chemical Industries (Kuribayashi, 1996) described the usage of fines (0.5–50 μm) which were deposited on a regenerated microporous cel lulose film (pore sizes: 10–200 nm, thickness 39–85 μm) The membrane exhibited good mechanical strength when immersed in different elec trolytes (ethylene carbonate, propylene carbonate and γ-butyrolactone) The electrochemical properties determined by impedance spectroscopy W Schlemmer et al Carbohydrate Polymers 265 (2021) 118063 Fig SEM images of TOCN membranes before (TOCN-COO–Na+, a and c) and after protonation (TOCN-COOH, b and d), and STEM images of a TOCN single microfiber in trans mission mode at low (e) and high magnification (f) Among SEM images a–d, first and second rows correspond to the top and bottom sides of the membrane, respectively The black scale bars in the bottom right-hand corners corre spond to 400 μm, whereas white ones to 500 nm Reproduced from the American Chemical Soci ety from Kim, H., Guccini, V., Lu, H., SalazarAlvarez, G., Lindbergh, G., & Cornell, A., 2019, ACS Appl Energy Mater., 2, 1241–1250 under a Creative Commons license 3.0 based separators (Liao et al., 2016) The performance of the separator in a Li/LiFePO4 cell in terms of thermal stability, electrolyte uptake, ionic conductivity, cycling performance, was superior than the neat poly propylene A polyvinyl alcohol-CNF-Li composite membrane was man ufactured by the NIPS techniques and yielded a highly porous material (>60 %) with good ionic conductivity (ca 1.1 mS cm− 1) and remarkable electrolyte uptake (Liu, Shao, Wang, Lu, & Wang, 2016) Actually, the idea was to use CNF‒Li from mechanically treated Lyocell fibers for combining the properties of CMC-Li like separators with the advanta geous properties of nanofibers The electrolyte uptake of the separator was increased by CNF‒Li, promoting ion transport compared to com mercial membranes This concept was further improved by incorpora tion of ceramic particles (size 0.1–3 μm) Upon deposition of the CNF‒Li to a polyethylene terephthalate (PET) nonwoven, better results were obtained (Long, Wang, Zhang, Hu, & Wang, 2016) Electrospinning is a simple method to make non‒wovens with defined porosity and fiber diameter Consequently, a huge variety of separator systems is known from electrospinning with limited practical relevance as electrospinning still suffers from low throughput, making it an expensive method on large scale However, the described materials showed potential to be used and given the progress of electrospinning in the past years (e.g., parallelization, needle-less electrospinning, coaxial electrospinning (Huang et al., 2015)), it still could offer many oppor tunities for new materials in the future As for composite membranes, also for the electrospun substrates often mixtures of polymers were used For instance, PVDF/ Poly (methyl methacrylate) (PMMA)/cellulose ac etate (CA) composite nanofibrous mats have been manufactured in different ratios (100:0:0, 90:10:0, 90:5:5 and 90:0:10, all m:m:m) (Yvonne, Zhang, Zhang, Omollo, & Ncube, 2014) Pulp fibers, sodium alginate and silica have been reported to yield a heat-resistant and flame-retardant separator with good mechanical strength (Zhang, Yue et al., 2014) Further details and various other examples are listed in Table Another method to obtain nanofibrous mats is force spinning, which is based on centrifugal forces (Weng, Xu, Alcoutlabi, Mao, & Lozano, 2015) The advantages over electrospinning include higher throughput and easier operation conditions (Sarkar et al., 2010) However, litera ture on force spinning of polysaccharides in general is still limited and this is even more pronounced for separator applications (Alcoutlabi, Lee, & Zhang, 2015) Polymer electrolytes are very well-suited components in high energy density battery applications, as well as in electrochromic devices, dye sensitized solar cells and sensors Here, we will focus exclusively on battery applications although requirements for the other applications are usually not so different There are several types of polymer elec ˜ ez, trolytes as depicted in Fig (Boaretto, Meabe, Martinez-Iban Armand, & Zhang, 2020) Here, we will focus on gel and solid polymer electrolytes Polymer electrolytes enable ion conduction via local polymer chain relaxation Such relaxation, however, is more pronounced for amorphous polymers, W Schlemmer et al Carbohydrate Polymers 265 (2021) 118063 Table Overview on non-woven and composite separators involving polysaccharides Note that the last three examples contain chitin and its derivatives in contrast to the other, cellulose based systems ES: electrospinning; FS: force spinning; PI: phase inversion; PM: paper making; EISA: evaporation induced self assembly; VF: vacuum filtration; VIPS: vapor induced phase inversion, NIPS: nonsolvent induced phase inversion; CJS: centrifugal jet spinning, NIPS: nonsolvent induced phase inversion; CJA: centrifugal jet spinning, n.r.; not reported Meth Separator Material d [μm] P [%] EU [%] T [◦ C] Reference ES Cellulose 25 75 340 (Zhang et al., 2013) CA/PVDF 30 88 177 Cell./PVDF/ HFP CA/PVDF/ HFP CA/PVDF/ HNT PVDF/CA 27 65 280 n.r 66 355 30 86 311 n.r 99 323 ≥ 200 ≥ 150 ≥ 200 ≥ 200 ≥ 150 n.r PVDF/ PMMA/CA PVDF/TPP/ CA Cell./PAN n.r 94 315 n.r 58 90 301 21 n.r 205 Cell./PANAl2O3 m-CA 50 n.r 286 100 87 517 FS Cellulose 50 76 370 PI PVDF/HFP/ Cell PVDF/HFP/ Cell./C/TiO2 Al2O3/MFC n.r 51 170 50− 60 64 210 28 68 n.r Al2O3/MFC/ PVDF BC/ANF 28 56 n.r ~ 30 84 n.r CaAlg/Pulp 70 68 270 TOCN− Na+ 29 59 TOCN− H+ 34 62 LPC/CNF 100 72 ≥ 200 ≥ 200 161 ≥ 170 ≥ 250 ≥ 300 ≥ 220 ≥ 180 < 160 ≥ 160 ≥ 180 ≥ 180 ≥ 160 ≥ 180 150 ≥ 200 ≥ 200 ≥ 150 ≥ 350 ≥ 180 Table (continued ) Meth Separator Material d [μm] P [%] EU [%] T [◦ C] Reference PM C- ChNF 12 5.4 439 EISA ChNF ~ 25 60 252 CJS ChF 67 n.r n.r ≥ 170 ≥ 160 ≥ 200 (Zhang, Chen et al., 2019) (Zhang, Shen et al., 2017) (Kim et al., 2017) possessing a low Tg, i.e amorphous matrices are favored to accomplish for high ion conduction Conductivity in such systems is in the range of 10− 4S cm− which is below the required upper thresholds of most bat tery applications (approx 10− S cm− 1) Gel polymer electrolytes (GPE) are a subclass of polymer electrolytes In GPE, the presence of plasticizers restrict the crystallization of the macromolecule chains, thereby increasing ion mobility in crosslinked polymer matrices such as polyacrylonitrile, poly(vinylidene fluoride), poly(methyl methacrylate), and poly(ethylene oxide) derivatives In this context, polysaccharides offer a huge range of opportunities as they readily form gels that not feature a high degree of crystallinity There are a variety of strategies to adjust for the polysaccharide gel properties for GPE This involves crosslinking to form elastomeric structures, the introduction of flexible side chains (e.g poly(oxyethylene)), formation of composites as well as combinations thereof The crosslinking strategy was one of the first approaches published using polysaccharides The formation of elastomeric networks leads to extremely flexible structures with a low inherent tendency to crystallize, while providing sufficient ionic conductivity Schoenenberger, Le Nest and Gandini were the pioneers in this field as they published already in the 1990s an account on grafting oligoether on HEC followed by cross linking using urethane chemistry (Nest, Gandini, & Cheradame, 1988; Schoenenberger, Le Nest, & Gandini, 1995) The role of the HEC in that paper was to enhance the film formation – an important feature for processability – while the oligoethers side chains and crosslinked sites provided flexibility and sufficient relaxation to accomplish for ion conduction In the years to follow, several reports proposed cellulose esters and ethers as polymer electrolytes These polysaccharide materials involve hydroxypropyl cellulose (HPC), HEC (Regiani, De Oliveira Machado, LeNest, Gandini, & Pawlicka, 2001), CA (Abidin, Yahya, Hassan, & Ali, 2014; Ahmad et al., 2020; Chen, Shi et al., 2016; Kang et al., 2016; Lee et al., 2010), cellulose acetate butyrate (Liu, Li, Zuo, Liu, & Li, 2013; Pan et al., 2016), cyanoethylated cellulose/cyanoethylated HPC, methyl cellulose (Chinnam, Zhang, & Wunder, 2015; Li, Wang et al., 2015; Mantravadi, Chinnam, Dikin, & Wunder, 2016), ethyl cellulose (Para cha, Ray, & Easteal, 2012) and CMC (Regiani et al., 2001; Stojadinovic, Dushina, Trocoli, & La Mantia, 2014; Zhu et al., 2015) While intro duction of flexible side chains and plasticizers increases the amorphicity and the ionic conductivity, they can negatively impact the mechanical properties of the polymer electrolyte For instance, an HPC-PEO with lithium triflate as electrolyte and organic carbonates (ethylene carbon ate, propylene carbonate) as plasticizers, exhibited sufficient conduc tivity (ca 10− 3S cm− 1) at a plasticizer content around 50 % (Yue, McEwen, & Cowie, 2003) While conductivity was sufficient for that battery application, the mechanical properties were insufficient This was overcome by crosslinking using 1,6‒diisocyanatohexane which then allowed also to incorporate plasticizer contents up to 70 % In addition, the morphology of the gels (porous vs non‒porous) could be tuned by variation of the amount of the crosslinking agents Also pure cellulosic materials have been used for GPE, such as CNF (Willgert, Leijonmarck, Lindbergh, Malmstroem, & Johansson, 2014), MFC (Chiappone, Nair, Gerbaldi, Bongiovanni, & Zeno, 2013) and macroscale materials (Chiappone et al., 2011; Chiappone, Nair, Gerbaldi, Zeno, & Bongio vanni, 2014; Chiappone, Nair, Gerbaldi, Bongiovanni, & Zeno, 2015; Jafirin, Ahmad, & Ahmad, 2013; Liu, Liu et al., 2016; Nair et al., 2009; (Wang, Zhang, Shao, & Liu, 2019) (Zhang et al., 2013) (Huang et al., 2015) (Wang et al., 2019) (Yvonne et al., 2014) (Yvonne et al., 2014) (Chen, Qiu et al., 2020) (Jo et al., 2020) (Jo et al., 2020) (Chen et al., 2018) (Weng et al., 2015) (Li et al., 2020) (Li et al., 2020) (Huang, 2014) (Huang, 2014) (Yang et al., 2020) (Tan et al., 2020) (Kim, Guccini et al., 2019) (Kim, Guccini et al., 2019) (Zhang, Lan, Peng, Hu, & Zhao, 2020) (Zhu et al., 2020) (Zhang, Liu et al., 2018) (Zhang, Yue et al., 2014) (Gonỗalves et al., 2019) (Wang et al., 2019) (Huang, Ji et al., 2019) (Yoo et al., 2020) (Wang et al., 2018) (Huang et al., 2020) (Kim, Mattinen et al., 2020) (Chen, Zuo et al., 2020) (Casas, Niederberger, & Lizundia, 2020) 10 W Schlemmer et al Carbohydrate Polymers 265 (2021) 118063 Fig Comparison and classification of electrolytes for rechargeable batteries Reproduced from (Boaretto et al., 2020) using a creative common license 4.0 Copyright (2020) the Electrochemical Society Reproduced by permission of IOP Publishing All rights reserved Navarra et al., 2015; Song et al., 2004), some exhibiting competitive electrochemical performance Apart from cellulose, also other polysaccharides have been investi gated for GPE applications but to a much lesser extent Here, mostly chitosan and its derivatives such as chitosan acetate, plasticized chitosan acetate, chitosan acetate containing electrolyte, and plasticized chitosan acetate-electrolyte complexes were manufactured into films by casting (Osman, Ibrahim, & Arof, 2000) Regardless of the procedure, the films were well suited for GPE applications in batteries For other poly saccharides such as pectin (Andrade, Raphael, & Pawlicka, 2009), acaia gum (Arora, Sharma, Kumar, & Kumar, 2018), guar gum (Zhang, Sudre et al., 2017), inulin (Gachuz et al., 2020), cationic starch (Lobregas & Camacho, 2019) or xanthan (Migliardini, Di Palma, Gaele, & Corbo, 2018), limited information is available, despite their potential for GPE applications performance related to the production costs is often not known to a sufficient extent As the research at such a TRL is often not anymore covered by basic research funds, participation of companies/industries in R&D&I activities is needed These commercial partners, from both raw material and battery side, however need to know about the expected costs and the performance on device level before investing into new technologies As it is difficult to predict these parameters, technologies are often not further pursued despite their technological potential – a typical chicken–or-the–egg dilemma However, it can be expected that environmental and sustainability aspects of batteries and their compo nents will become more and more important in the upcoming years, further driving research in this area At the moment, societal discussion is focused on the active electrode materials (e.g Li, Co) but it can be expected that other components such as fluorinated long-lived, envi ronmentally persistent separator and polymer electrolyte materials as well as binders will also become an issue for battery (component) pro ducers At the same time, this will be an excellent opportunity to replace these materials (at least partially) by polysaccharides In general, polysaccharides could be integral parts of many battery systems as they are abundant and offer huge structural diversity already in their natural form For some applications, e.g., polymer electrolytes, chemical modifications are required to adjust for the needs of the battery component Although polysaccharide chemistry is challenging, signifi cant improvements in terms of available chemical functionality, sub stitution patterns, and purity at reasonable cost have been accomplished in the past years Particularly the use of tailormade polysaccharide components for polymer electrolytes and binders offers a huge potential which is waiting to be investigated However, systematic approaches to study the influence of functional groups and side chains on battery component performance have not been reported so far Another opportunity for polysaccharides comes from the materials’ side The increasing commercialization efforts for nanocellulose and microfibrillated cellulose production may unravel their potential in battery components once processing has been optimized Here, concrete application examples for commercialization include the use of cellulose Challenges and opportunities for polysaccharides in batteries The previous chapter showed that polysaccharides have the potential to be used in basically all components of batteries such as separator, binder, polymer electrolyte and – not discussed in this review – pre cursors for carbonaceous electrode materials However, only a few materials are used in commercial applications, such as cellulose based materials in separators (paper, fines, cellulose acetate) and carbox ymethyl cellulose as component in SBR–CMC binder systems There are several obstacles that prevent the commercialization of other polysaccharide-based components in battery systems, i.e to translate new technologies from technology readiness levels (TRL) 2–4 to TRL 7–9 For many materials, translation from single cells into functioning devices is challenging, which is often neglected in scientific literature Also, the scale up of the material production often is an issue as it re quires pilot lines for battery production and – in some cases –from raw material side Such pilot line trials, however, are needed to estimate the production costs as well as to identify problems of the materials in terms of processability (e.g drying, viscosity, conductivity) Consequently, the 11 W Schlemmer et al Carbohydrate Polymers 265 (2021) 118063 nanofibrils in ultrathin separators, which could be 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lithium-ion batteries Carbohydrate Polymers, 234, Article 115907 Chen, W., Shi, L., Wang, Z., Zhu, J., Yang, H., Mao, X., et al (2016) Porous cellulose diacetate-SiO2 composite coating on polyethylene separator for high-performance lithium-ion battery Carbohydrate Polymers, 147, 517–524 Chen, Q., Zuo, X., Liang, H., Zhu, T., Zhong, Y., Liu, J., et al (2020) A heat-resistant poly (oxyphenylene benzimidazole)/Ethyl cellulose blended polymer membrane for highly safe lithium-ion batteries ACS Applied Materials & Interfaces, 12, 637–645 Chiappone, A., Nair, J R., Gerbaldi, C., Jabbour, L., Bongiovanni, R., Zeno, E., et al (2011) Microfibrillated cellulose as reinforcement for Li-ion battery polymer electrolytes with excellent mechanical stability Journal of Power Sources, 196, 10280–10288 Conclusion and outlook Since the invention of batteries by Volta in the 18th century, poly saccharides have been integral elements of energy storage systems Back then, there were hardly any alternatives to biobased materials in bat teries as organic chemistry was still in its infancy and synthetic polymers (as well as the concept’ polymer’) were not known at all With the rise of low-cost synthetic polymers, the use of polysaccharides in battery components has been compromised and currently only a few poly saccharide (materials) are commercially used However, there is a huge potential as shown in this review to develop new polysaccharide-based battery components due to their rich structural diversity and innu merous possibilities to alter the polysaccharide backbone Particularly, the field of polymer electrolytes is a still underexplored area, where synthetic polysaccharide chemists, composite engineers and electro chemists can work together to design more sustainable battery components CRediT authorship contribution statement Werner Schlemmer: Data curation, Investigation, Writing - review & editing Julian Selinger: Investigation, Data curation, Writing - re view & editing Mathias 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