Carboxymethyl Cellulose Binder Research Articles

Development of electrode architecture using Sb–rGO composite and CMC binder for high-performance sodium-ion battery anodes

Metallic antimony (Sb) is considered as a promising anode material for sodium-ion batteries (SIBs) owing to its high theoretical capacity (660 mAh/g) based on alloying/dealloying reactions with sodium ions. The main issues of Sb, however, are its large volume expansion upon cycling. In this study, we synthesized Sb-reduced graphene oxide (rGO) composite material by reduction of Sb2O3 nanoparticles. We confirmed that ~ 5 nm sized Sb nanoparticles are well distributed onto the rGO sheets, and Sb–rGO composite electrodes showed higher capacity and better cycling performance compared to bare Sb nanoplatelets. This improvement is attributed to increased electrical conductivity owing to incorporation of rGO, which also acts as a buffer against volume expansion of Sb particles during electrochemical reactions. The moderate rate performance of Sb–rGO composite materials was further improved by electrode formulation modification using a carboxymethylcellulose (CMC) binder. An electrode architecture containing Sb–rGO composite material with CMC binder achieved a high capacity (~ 400 mAh g−1) at a high rate (~ 30 C).

Si@S‐doped C anode with high cycling stability using PVA‐g‐PAA water soluble binder for lithium‐ion batteries

ABSTRACTThe nanostructured Si@S‐doped C (Si/C) hybrid is synthesized via a mild hydrothermal process of glucose and the simultaneous polymerization of 3,4‐ethylenedioxythiophene and poly(sodium‐4‐styrene sulfonate) on the surface of nano‐Si powders, then followed by a calcination process. A new water soluble polymer of poly(vinyl alcohol) (PVA) grafted with poly(acrylic acid) (PAA) is synthesized via a free‐radical polymerization of acrylic acid (AA) in a 1:1 weight ratio in PVA water solution. The Si/C anode using PVA‐g‐PAA binder, exhibits improved lithium storage properties and cycling stability than that of the parallel electrode with carboxymethyl cellulose binder, which exhibits an initial coulombic efficiency (82.0%), even a reversible capacity of 487 mAh g−1 after 300 cycles with 81.2% capacity retention at 0.4 A g−1. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48764.

Direct Observation of Carboxymethyl Cellulose and Styrene-Butadiene Rubber Binder Distribution in Practical Graphite Anodes for Li-Ion Batteries.

Despite the important role of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) binders in graphite electrodes for Li-ion batteries, the direct analysis of these binders remains challenging, particularly at very low concentrations as in practical graphite anodes. In this paper, we report the systematic investigation of the physiochemical behavior of the CMC and SBR binders and direct observations of their distributions in practical graphite electrodes. The key to this unprecedented capability is combining the advantages of several analytic techniques, including laser-ablation laser-induced break-down spectroscopy, time of flight secondary ion mass spectrometry, and a surface and interfacial cutting analysis system. By correlating the vertical distribution with the adsorption behaviors of the CMC, our study reveals that the CMC migration toward the surface during the drying process depends on the degree of cross-linked binder-graphite network generation, which is determined by the surface property of graphite and CMC materials. The suggested analytical techniques enable the independent tracing of CMC and SBR, disclosing the different vertical distribution of SBR from that of the CMC binder in our practical graphite anodes. This achievement provides additional opportunity to analyze the correlation between the binder distribution and mechanical properties of the electrodes.

Electrically Conductive Shell-Protective Layer Capping on the Silicon Surface as the Anode Material for High-Performance Lithium-Ion Batteries.

Rational design and construction of effective silicon (Si) electrode structures to relieve large volumetric changes that occur during the charge/discharge process remain significant challenges for the development of robust lithium-ion batteries (LIBs). Herein, we propose an electrically conductive poly[3-(potassium-4-butanoate)thiophene] (PPBT) capping layer on the Si surface (Si@PPBT) to serve as the active material and be used in conjunction with a common polymer binder as an approach to tackle issues emanating from volumetric changes. The PPBT protective shell layer provides the system with tolerance toward variations in active material volume during cycling, improves the dispersion of Si nanoparticles in the binder, enhances the electrolyte uptake rate, and provides a strong adhesion force between the Si/carbon additives/current collector, thereby helping to maintain electrode integrity during the charge/discharge process. The π-conjugated polythiophene backbone structure also allows the Si core to maintain electrical contact with carbon additives and/or polymer binder, enabling the formation of effective electrical transport bridges and stabilizing solid electrolyte interphase layer growth. The integrated Si@PPBT/carboxymethyl cellulose (CMC) anode exhibited high initial Coulombic efficiency (84.9%), enhanced rate capability performance, and long cycling stability with a reversible capacity of 1793 mA h g-1 after 200 cycles, 3.4 times higher than that of pristine Si anodes with the same CMC binder (528 mA h g-1). The results suggest that the Si@PPBT design presents a promising approach to promote the practical use of Si anodes in LIBs, which could be extended to other anode materials exhibiting large volume changes during lithiation/delithiation.

Chitosan derived N-doped carbon coated SnO2 nanocomposite anodes for Na-ion batteries

Nitrogen doped hard carbons are synthesized from chitosan via hydrothermal carbonization (HTC) followed by further carbonization process at different temperatures (500, 750, 1000 °C). Those carbons are investigated as sodium ion battery anode materials. Latter, under HTC conditions, SnO2 nanoparticles are incorporated with carbon source to obtain SnO2/C composite. The influence of binders (carboxymethyl cellulose (CMC) and poly(vinylidene fluoride) (PVDF)) on the cyclic performance are investigated in which better cycling performances are achieved with PVDF. Indeed, electrochemical impedance spectroscopy test results reveal that the electrode prepared with PVDF has lower charge transfer resistance than that of CMC binder. Sodium ion diffusion coefficient values in the presence of CMC and PVDF are calculated from the Nyquist plot to be 4.35 × 10−11 and 3.06 × 10−10 cm2/s after 50 cycles, respectively.

In Situ Chemo-Mechanical Responses of Lithium Iron Phosphate Electrodes during Electrochemical Cycling

Rechargeable Li-ion batteries (LIBs) have been successfully commercialized for portable electronics in the last two decades. Although there has been a great interest to use LIBs in more demanding applications such as electric vehicles, adoption of LIBs has been hindered by capacity loss and poor performance. The current stage of the cathode performance is a limiting factor for the development of higher performance LIBs. Lithium intercalation induces considerable volumetric changes with associated stress generation in the electrode. Even small strain can cause particle fractures in brittle cathode materials. The formation of a fracture particles leads to the capacity fade and limits the lifetime of batteries. To investigate chemo-mechanical response of the cathodes, we previously calculated electrochemical stiffness changes cathodes by coordinating in situ stress and strain measurements1. The electrochemical stiffness response of lithium manganese oxide revealed that the underlying mechanisms governing stress and strain are intrinsically different. In this study, our objective is to evaluate chemo-mechanical responses of lithium iron phosphate (LFP) cathode. In situ stress measurements were carried out with the beam curvature method whereas digital image correlation (DIC) is utilized to measure in situ strain generation. Electrodes are constrained on the cantilever for stress measurement, whereas free-standing electrodes were fabricated for strain measurements. LFP electrodes were fabricated with a composition of 8:1:1 weight ratio of LFP, carboxymethyl cellulose binder and carbon black. Electrodes are cycled with cyclic voltammetry technique at different scan rates (between 10 and 250μV/s) in various electrolytes. Stress and strain derivatives are calculated with respect to applied potential. Derivatives present crucial information to probe potential-dependent surface stress evolutions and structural changes in the electrode. As expected, strain derivatives are well-correlated with the changes in the crystal structure during delithiation and lithiation. Interestingly, stress derivatives reveal that electrolyte solution has a role on the evolution of surface stress. Changes in stress and strain during electrochemical cycling reveal underlying mechanisms governing chemo-mechanical responses in the LFP electrode. References 1- Ö. Ö. Çapraz, K. L. Bassett, A. A. Gewirth, and N. R. Sottos, Adv. Energy Mater., 1601778–7 (2017). Acknowledgement This work was supported as part of the Center for Electrochemical Energy Science (CEES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.”

The Role of Surface Coatings on the Strain Evolution in Li-Ion Cathode Electrodes during Electrochemical Cycling

Rechargeable Li-ion batteries (LIBs) have been successfully commercialized for portable electronics in the last two decades. Although there has been a great interest to use LIBs in more demanding applications such as electric vehicles, adoption of LIBs has been hindered by capacity loss and poor performance. The current stage of the cathode performance is a limiting factor for the development of higher performance LIBs. Cathode electrodes suffer from significant capacity fade with cycling due to continuous volumetric changes, unstable cathode-electrolyte interface and active material dissolution. Lithium intercalation induces considerable volumetric changes in the electrode and even small strain can cause particle fractures in brittle cathode materials. Surface modification of the cathode electrodes has been used to improve the capacity retention and cycling stability of the electrodes at higher charge/discharge rates by minimizing active material dissolution and stabilizing the electrode-electrolyte surface layer. Although various surface modification techniques were utilized to improve the performance of the electrodes, the underlying mechanism of surface modification has not been elucidated yet. In this work, we investigated the role of surface coatings on the strain generation in lithium manganese oxide (LMO) composite electrodes. Full-field strain measurements based on digital image correlation (DIC) is carried out to measure strain evolution in LMO electrodes1. Scalable electrolysis deposition method was performed to coat LMO particles with Au shell2. LMO composite electrodes were fabricated with a composition of 8:1:1 weight ratio of LMO, carboxymethyl cellulose binder and carbon black. Electrodes were cycled with cyclic voltammetry technique at different scan rates (between 10 and 100μV/s). As expected, composite electrodes expanded during delithiation when lithium is inserted into the electrode and contacted during lithiation when lithium is removed. Capacity was calculated to understand relationship between strain evolution with amount of lithium ions in the electrode at a given scan rate. Interestingly, The LMO electrode without coating undergoes larger strain generation at higher scan rates compared to LMO electrode with surface coatings. Volumetric expansion of LMO (without coating) electrode changes dramatically depending on scan rate whereas strain evolution in the gold-coated LMO electrode is primarily function of capacity, regardless of scan rate. The role of the surface coatings on the mechanical and electrochemical performance of the LMO electrodes will be discussed. References Ö. Ö. Çapraz, S. Rajput, S. White, and N. R. Sottos, Exp Mech, 15, 1182–11 (2018).J. L. Esbenshade, M. D. Fox, and A. A. Gewirth, J. Electrochem. Soc., 162 (1), A26 (2015). Acknowledgement This work was supported as part of the Center for Electrochemical Energy Science (CEES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.”

Enhanced Electrochemical Performance of Sb2O3 as an Anode for Lithium-Ion Batteries by a Stable Cross-Linked Binder

A binder plays an important role in lithium-ion batteries (LIBs), especially for the electrode materials which have large volume expansion during charge and discharge. In this work, we designed a cross-linked polymeric binder with an esterification reaction of Sodium Carboxymethyl Cellulose (CMC) and Fumaric Acid (FA), and successfully used it in an Sb2O3 anode for LIBs. Compared with conventional binder polyvinylidene fluoride (PVDF) and CMC, the new cross-linked binder improves the electrochemical stability of the Sb2O3 anode. Specifically, with CMC-FA binder, the battery could deliver ~611.4 mAh g−1 after 200 cycles under the current density of 0.2 A g−1, while with PVDF or CMC binder, the battery degraded to 265.1 and 322.3 mAh g−1, respectively. The improved cycling performance is mainly due to that the cross-linked CMC-FA network could not only efficiently improve the contact between Sb2O3 and conductive agent, but can also buffer the large volume charge of the electrode during repeated charge/discharge cycles.

Study of Sulfur-Based Electrodes By in Situ Characterization Techniques

The lithium-sulfur (Li/S) battery system is one of the most promising candidates to become the successor of the current Li-ion battery. However, the insufficient cycle life of the Li/S batteries needs to be resolved before envisioning their commercial use. Several phenomena are reported to be involved in the capacity fading of the Li/S cells upon cycling, among which important structural changes in the sulfur electrode. Hence the constant need for understanding of those mechanisms drives the use of innovative in situ characterization techniques. In the present study, operando acoustic emission (AE) technique and in-situ synchrotron X-ray tomography and diffraction are used to study the degradation mechanism of sulphur-based electrodes depending of their formulation. To date, AE technique has been used to characterize the degradation mechanisms (crack growth, friction, delamination, matrix cracking, corrosion, etc) of various materials subjected to a stress by mechanical, pressure or thermal means. In the present work, AE technique is used for the first time to monitor the mechanical degradation of sulfur electrodes depending on the nature of the binder (polyvinylidene difluoride ( PVdF) compared to carboxymethylcellulose (CMC)) and the geometry of the current collector (flat Al foil compared to 3D porous carbon paper (CP)). In all cases, AE signals are mainly detected during the 1st plateau of the 1st discharge, related to the initial dissolution of elemental sulfur into the electrolyte, causing a collapse of the electrode network. At the end of charge, the formation of micrometric sulfur on the surface of the electrode can be acoustically detected, in particular in the case of the CMC/Al formulation, where signals are also detected during subsequent cycles. This is believed to be a result of the good adhesion of CMC-based electrode to the current collector, which allows acoustic waves to propagate through the electrode to the AE sensor more easily. However, with CP current collector, no AE activity is detected upon charge, reflecting a lower mechanical stress attributed to a more homogeneous growth of the S particles in the electrode. It is also noted that inefficient electrode formulation/elaboration can be detected via AE, as AE signals are emitted at the end of the discharge when the cell polarizes more than usually observed. The use of CP as a current collector greatly improves the electrochemical performance of the cells, especially when combined with the better adhesion/cohesion strengths of CMC binder, reaching an initial capacity of 1180 mAh g-1 (~4.5 mAh cm-2) stabilizing around 860 mAh g-1 after 50 cycles. X-Ray computed tomography (XRCT) is certainly one of the most powerful analytical tools enabling non-destructive 3D imaging of objects with complex and porous morphologies such as S-based electrodes. Using appropriate image processing, segmentation and analysis procedures, quantitative parameters can be extracted such as the volume fraction, the size distribution, the connectivity and the geometrical tortuosity of the constitutive phases of the sulfur electrodes. A spatial resolution of a few tens of nm can be reached with a synchrotron X-ray source. This technique, coupled with in situ synchrotron X-ray diffraction, enables to follow in great details the evolution of the different species inside the tested Li/S batteries and get invaluable information on their degradation mechanisms. In the present study, in-situ synchrotron X-ray tomography and diffraction is used to investigate the structural changes upon cycling of sulfur electrodes integrating a poly-electrolyte binder (PEB) likely to confine the polysulfide chains and prevent sulfur loss over cycling. Its behaviour is compared to a classic CMC-binder based electrode.

Versatile Utilizations of Cellulose Nanofibers for High-Performance Silicon Anode in Lithium-Ion Batteries

Silicon is the most anticipated anode material in lithium-ion batteries due to its natural abundancy, low insertion voltage (<0.4 V vs. Li/Li+) and high specific capacity (<3579 mAh g-1). However, huge volume change (~ 300 %) during cycling which causes poor cycling stability and its insulating nature prohibit the practical use. In this research, cellulose nanofibers were utilized in various ways to enhance the performance of silicon nanoparticle anodes. As carbon sources, the ultrathin (~ 1.55 nm) cellulose nanofibers can provide an extensive conductive network to improve both the cycling stability and rate performance by mitigating the volume expansion of silicon and providing the efficient electron path. Furthermore, by using thicker (~ 30 nm) cellulose nanofibers as carbon sources, a porous conductive network can be achieved, which can provide both the efficient electron path and ion diffusion path. In addition, the void space generated by cellulose nanofibers became a buffer space which enhanced the cycling stability. Finally, as a binder additive, cellulose nanofiber can enhance the performance of carboxymethyl cellulose binder. It can act as both a filler and a binder to be utilized in an electrode composite, unlike the traditional reinforcing fillers. Therefore, the versatile, cheap and abundant cellulose nanofibers show great potential in lithium-ion batteries.

Hybrid humics/sodium carboxymethyl cellulose water-soluble binder for enhancing the electrochemical performance of a Li-ion battery cathode

A hybrid water-soluble humics-based binder (humics/sodium carboxymethyl cellulose (CMC)) was studied to enhance the electrochemical performance of a Li-ion battery cathode (LiFePO4) in this work. Molecular dynamics simulations of binder active fractions with related materials (LiFePO4 and Al) were performed to explore the binding mechanisms. Humics serve to connect the active material and provide a conducting bridge in the cathode. To improve the adhesion between the particles and current collector, CMC is added as an auxiliary fraction with a mass ratio of humics to CMC of 3:1. The scanning electron microscope results indicate that the morphology of the electrode with the hybrid humics/CMC binder is more uniform than that of electrodes with conventional polyvinylidene fluoride and CMC binders. The electrochemical performance and cycling stability of the cathode materials are obviously enhanced. The reversible specific capacity can reach 152.3 mAh g−1 at 0.5 °C after 100 cycles. The rate capability is greatly improved, with a specific capacity as high as 105 mAh g−1 at 8 °C. The humics/CMC composite can be regarded as a novel, environmentally friendly and high-efficiency binder for application in Li-ion batteries.

Carboxymethyl Cellulose Binder Greatly Stabilizes Porous Hollow Carbon Submicrospheres in Capacitive K-Ion Storage.

On account of the large radius of K-ions, the electrodes can suffer huge deformation during K-ion insertion and extraction processes. In our work, we unveil the impact of using carboxymethyl cellulose (CMC) instead of poly(vinylidene fluoride) (PVDF) as binders for K-ion storage. Our porous hollow carbon submicrosphere anodes using the CMC binder exhibit a reversible capacity of 208 mA h g-1 after 50 cycles at 50 mA g-1, and even at a high current density of 1 A g-1, they achieve a reversible capacity of 111 mA h g-1 over 3000 cycles with almost no decay, demonstrating remarkably improved reversibility and cycling stability than those using PVDF (18 mA h g-1 after 3000 cycles at 1 A g-1). It is showed that the CMC binder can result in higher adhesion force and better mechanical performance than the PVDF binder, which can restrain the crack during a potassiation/depotassiation process. According to the test of adhesion force, the hollow carbon submicrospheres using the CMC binder show above three times of average adhesion force than that using the PVDF binder. Furthermore, based on the rational design, our hollow carbon submicrospheres also exhibit 62.3% specific capacity contribution below 0.5 V vs K/K+ region, which is helpful to design the full cell with high energy density. We believe that our work will highlight the binder effect to improve the K-ion storage performance.

Study of sulfur-based electrodes by operando acoustic emission

The mechanical degradation upon cycling of sulfur-based electrodes is investigated by operando acoustic emission (AE). The AE response of S-based electrodes using two different binders, polyvinylidene difluoride (PVdF) and carboxymethylcellulose (CMC), as well as two different current collectors, usual aluminum foil and porous non-woven carbon paper (CP), are compared. In all cases, AE signals are mainly detected during the 1st plateau of the 1st discharge, related to the initial dissolution of elemental sulfur into the electrolyte, causing a collapse of the electrode network. At the end of charge, the formation of micrometric sulfur on the surface of the electrode can be acoustically detected, in particular in the case of the CMC/Al formulation, where signals are also detected during subsequent cycles. This is believed to be a result of the good adhesion of CMC-based electrode to the current collector, which allows acoustic waves to propagate through the electrode to the AE sensor more easily. However, with CP current collector, no AE activity is detected upon charge, reflecting a lower mechanical stress attributed to a more homogeneous growth of the S particles in the electrode. It is also noted that inefficient electrode formulation/elaboration can be detected via AE, as AE signals are emitted at the end of the discharge when the cell polarizes more than usually observed. The use of CP as a current collector greatly improves the electrochemical performance of the cells, especially when combined with the better adhesion/cohesion strengths of CMC binder, reaching an initial capacity of 1180 mAh g−1 (∼4.5 mAh cm−2) stabilizing around 860 mAh g−1 after 50 cycles.

Impact of Water-Based Binder on the Electrochemical Performance of P2-Na0.67Mn0.6Fe0.25Co0.15O2 Electrodes in Na-Ion Batteries

Aqueous binders are highly recommended in battery production for (i) reducing the costs and, (ii) increasing the safety due to the absence of an organic solvent. Unfortunately, the impact of water during the electrode formulation on sodiated phases is still unclear and deserves investigation. In this work, we used carboxymethylcellulose (Na-CMC) binder to prepare electrodes of a high energy density P2-layered oxide material, Na0.67Mn0.6Fe0.25Co0.15O2 (NaMFC). We investigated the effects of water-based electrode preparation on the electrochemical performance, by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and neutron diffraction. The water leads to degradation of the material limiting the reversible specific charge at 90 mAh·g−1 instead of 120 mAh·g−1 obtained with N-methyl pyrrolidone (NMP) solvent with polyvinylidene fluoride (PVDF) as binder. The protons exchanged in the structure, occurring during electrode preparation, are assumed to disrupt the Na ions extraction mechanism limiting the specific charge of such a material.

Novel Lignin-Derived Water-Soluble Binder for Micro Silicon Anode in Lithium-Ion Batteries

Micro silicon is considered as the most prospective anode material for large-scale application of lithium-ion batteries (LIBs) due to its low production cost and diverse accessibilities. However, micro silicon anodes coupled with conventional binders generally show poor performances in LIBs. Therefore, developing new binders with high performance for micro silicon anode in LIBs is highly desirable. In this work, we report the first lignin-derived water-soluble binder (lignin-graft-sodium polyacrylate, PAL–NaPAA) for the micro silicon anodes. The PAL–NaPAA binder is obtained via a free radical graft copolymerization, followed by an alkaline hydrolysis. The electrochemical performance of PAL–NaPAA is compared with commercial binder carboxymethyl cellulose (CMC) for micro silicon anodes. The electrode using the PAL–NaPAA binder retains a capacity of 1914 mAh g–1 after 100 cycles at a constant current density of 840 mA g–1, which is superior to that of the electrode using the CMC binder (1544 mAh g–1). Additi...

Stable Li Ion Batteries Anode By Inducing the Covalent Bond between Active Material and Binder By Esterification Reaction

Lithium ion batteries (LIBs) has been the main energy storage medium for portable electronics since the commercialization by Sony Corporation since 1991. Ever growing demand for large-scale energy storage devices such as electrical vehicles requires the high energy density and long cycle life LIBs that could not be attained by the currently used battery. Graphite is the most common anode material in commercial LIBs, but its specific capacity is relatively low (372 mAh g-1) with a poor rate capability, which does not meet the high demand for large-scale applications. Silicon (Si) is one of the most promising anode candidates due to its high theoretical specific capacity (3579 mAh g-1 for Li15Si4), relatively low discharge potential (~0.4V vs Li+/Li), and abundance in nature. However, Si goes through a dramatic volume change during cycling and thus undergoes a drastic structural deformation, which induces loss of electrical contact between Si and current collector, breakdown of solid electrolyte interphase (SEI) layer, and Si aggregation during cycling, eventually resulting in failure of cyclic performance. Although design a various nanostructure forms or introduction of secondary phase layers has been realized as a method to achieve high-performance Si anode, these methods require complex reactions such as hydrothermal or template-assisted synthesis and usually involve hazardous reagents like SiH4 or HF, which eventually result in cost and barrier to scale up. From the practical view, use of commercial Si is the most promising, where the commercial production of Si has been benefitted from the development in semi-conductor industry. Conventionally, battery is prepared by mixing active materials and binder with conducting agent in organic solvent to produce viscous slurry and blading onto copper current collector. Recently, the selection of binder has turned out to play critical role in the battery performance as maintaining the structural integrity of electrode film. It has been revealed that carboxylic acid or hydroxyl functional groups terminated binders which is commercially available, such as polyacrylic acid (PAA), carboxymethyl cellulose (CMC or Na-CMC) or alginate (Alg or Na-Alg) binder, can result in enhanced cycling performance utilizing the hydrogen bonding interactions with the native oxide on Si, compared to that of conventional PVDF binder which has no functional group and bonds weekly with Si through a week Van der Waals interaction. Nonetheless, due to the linear chain characteristic of these binders, susceptible sliding upon the continual volume change of Si results in the contact loss between binder and Si, which eventually results in the irreversible capacity failure. Herein, we propose a novel concept that can achieve stable Si anode by transitioning the bonding nature between binder and Si from hydrogen bond to mechanically robust covalent bond, which can effectively restrain any large movement of Si, and eventually prevent the destruction of the electrical network during cycling. Inducing the esterification reaction between binder and Si can be an efficient method to form a covalent bond between those two materials. (eq. (1)) R-COOH+HO-R’ -> R-COO-R’+ H2O -------- (1) To induce an esterification reaction between binder and Si, three crucial points have to be addressed. First, as carboxylate (–COO-) functional group terminated binder such as Na-CMC can hardly react with the hydroxyl functional group (-OH), PAA binder which is terminated with the carboxylic acid functional group (-COOH) has been selected in our system. Second, while commercially purchased Si has a –OH functional group by a partially hydrolyzed SiO2 layer covering the Si particles, its functional group density is insufficient for an esterification reaction to take place. Therefore, terminating –OH functional group at the surface of Si is crucial factor to increase the site to react with PAA binder. Third, due to kinetically sluggish characteristic of esterification reaction, proper usage of esterification catalyst is required. Experimental procedure is as follows; firstly, as-received Si was pretreated in piranha solution to terminate –OH. Then, –OH terminated Si was prepared into slurry by mixing with Super-P and PAA binder, casted onto copper foil, dried overnight and punched for a coin-type cell. To induce the esterification reaction, punched cell was dipped into sodium hypophosphite catalyst solution and then annealed in 180 °C for 1 h. Three counter groups are denoted as HB-Cell (punched cell with no annealing process), PE-Cell (annealed cell without usage of sodium hypophosphite), and FE-Cell (annealed cell with addition of sodium hypophosphite.) The fabricated FE-Cell exhibits superior cycle stability (2200 mAh g-1 at 100 cycles) compare to HB-Cell or PE-Cell, demonstrating the effect of covalent bond on obtaining the high-performance Si anode. Figure 1

HKUST-1, a Surface Metal-Organic Framework, As a Protective Back-End Coating Material for Si Anode

Si, the high-capacity anode for Li-ion battery (LIB), has intrinsic 300% volume changes limiting its commercial application. The volume change leads to particle pulverization that result in loss of electrical contacts. Various nanostructures are proposed to avoid the pulverization, but the commercialization is still a distant future. It has been known that the Al2O3 has demonstrated its ability to enhance electrochemical cycling performance. Recently, a comprehensive mechanistic role of the Al2O3 has been studied. By combining electrochemical and chemical agitation test, two novel mechanisms are proposed: Si agglomeration and a protective role of the Al2O3. LiPF6, the common Li salt of the LIB electrolyte, decomposes and form HF that etches the native oxide layer then form labile Si-H surface. Because of the labile Si-H surfaces, the Si particles agglomerate during the volume changes. The Si agglomeration has a detrimental effect on the cycling performance associated with the loss of electrical contacts. On the other hand, in the presence of the Al2O3, the Al2O3 consumes the HF, protecting the native oxide layer that resists the agglomeration. Thus, the Si particles with Al2O3 are better dispersed. The Al2O3 allows the better Si dispersion during electrochemical cycles, resulting in improved capacity retention. However, this study incorporated the Al2O3 via simple mixing. It is difficult to assume a homogeneous distribution of the additive. The homogeneous distribution of the additive will be crucial in effectively protecting the Si particles. To achieve such distribution of the additive, a back-end coatings are effective methods. The back-end coating methods involve applying coating on a prefabricated electrode surface. The back-end coating is typically done with atomic layered deposition (ALD) or molecular layered deposition (MLD). These techniques require high temperature, vacuum, and large-sized apparatus. To reduce the cost of the back-end coating, surface metal-organic frameworks (MOFs) are utilized in this work. The surface MOFs are a class of MOFs those have a self-limiting reaction and can be a coating layer on carboxylate surface. The surface of Si anode with carboxymethyl cellulose (CMC) binder can act as the substrate for the surface MOFs. Utilizing the carboxylate groups in CMC, a MOF can be coated at back-end of the electrode fabrication. Furthermore, the back-end coating with the surface MOF is done in room temperature, atmospheric condition, and requires only beakers, which significantly brings down the cost of the coating. Since the protective role can be achieved with various inorganic materials, HKUST-1 is chosen as a coating material. HKUST-1 is composed of 1,3,5-benzenetricarboxylate as an organic linker and Cu2+ ion as a metal cluster. Upon coating HKUST-1 on the Si anode, scanning electron microscopy, infrared, transmission electron microscopy, and energy dispersive X-ray spectroscopy are utilized to confirm the uniformity of HKUST-1 coating. The electrochemical performance as expected has improved with the HKUST-1 coating. Upon electrochemical cycling, X-ray photoelectron spectroscopy has been utilized to study the solid electrolyte interphase composition of the electrode. Compared to the ALD or MLD method, surface MOF achieves the goal of improving the Si anode performance with low cost. To the best of authors' knowledge, this work reports, for the first time, the utilization of the surface MOF on the Li-ion battery.

Thermally Treated Sodium Carboxymethyl Cellulose Binder for Si Alloy Anodes

Binder is a key component for enabling good cycle life of Si and Si-based negative electrode materials in Li-ion cells, despite comprising only 2-10 wt% of the electrode coating. In previous research, thermal carbonization of polymer binders, e.g. polyvinylidene fluoride (PVDF),1 cyclized polyacrylonitrile (PAN),2 and poly(amide imide),3 was shown to enhance the cycling performance of high energy density alloy anodes greatly. For instance, sintered Si electrodes with PVDF binder can maintain a reversible capacity of 1150 mA h g-1 over 500 cycles at 1C rate.1 Among various binders, sodium carboxymethyl cellulose (Na-CMC) has some favorable characteristics: abundance, low cost, high water solubility, good thickening properties, and a high carboxmethyl group content, which is responsible for surface binding interactions with Si.4,5 To our best knowledge, the effect of heat treatment on Na-CMC binder for Si-alloy containing anodes has not been explored yet.6 Here, electrodes were composed of 60 wt% Si alloy, 28 wt% graphite, 2 wt% carbon black (CB), and 10 wt% Na-CMC. Some of electrodes were sintered under Ar flow by heating up to 300 or 600 °C at a rate at 10 ºC/min, and then held at 300 or 600 °C for three hours. Figure 1(a) shows the TGA curve of Na-CMC polymer in the temperature range of 25-800 ºC under Ar gas. After being heated at 600 ºC in Ar, Na-CMC has a mass residue of 38.6 wt.%. The pyrolysis product consists of amorphous carbon (42 wt.%) and Na2CO3 (58 wt.%). The cycling capacity retention of Si-alloy/graphite electrodes with Na-CMC binder is shown in Figure 1(b). The unheated electrodes suffer from significant capacity fade, having only 78% capacity left after 100 cycles. The capacity retention is improved when the thermal treatment is applied. After heating at 300 ºC, the capacity retention after 100 cycles was improved to 87%. A significant improvement of capacity retention results when 600 ºC thermal treatment is applied: over 95% capacity is retained. The formation of Na2CO3 in a network of amorphous carbon contributes to this high capacity retention. Reference F. M. Hassan, V. Chabot, A. R. Elsayed, X. Xiao, and Z. Chen, Nano Lett., 14, 277–283 (2014).F. M. Hassan, R. Batmaz, J. Li, X. Wang, X. Xiao, A. Yu, and Z. Chen, Nat. Commun., 6, 8597 (2015).H. S. Yang, S. H. Kim, A. G. Kannan, S. K. Kim, C. Park, and D. W. Kim, Langmuir, 32, 3300–3307 (2016).U. S. Vogl, P. K. Das, A. Z. Weber, M. Winter, R. Kostecki, and S. F. Lux, Langmuir, 30, 10299–10307 (2014).C. C. Nguyen, T. Yoon, D. M. Seo, P. Guduru, and B. L. Lucht, ACS Appl. Mater. Interfaces, 8, 12211–12220 (2016).R. Petibon, V. L. Chevrier, C. P. Aiken, D. S. Hall, S. R. Hyatt, R. Shunmugasundaram, and J. R. Dahn, J. Electrochem. Soc., 163, A1146–A1156 (2016). Figure 1 (a)TGA curves of Na-CMC collected at a heating rate of 5 ºC/min under Ar gas. (b) Capacity retention of three V6/SFG6L/CB/Na-CMC electrodes: untreated, heated at 300 ºC in Ar, and heated at 600 ºC in Ar. Figure 1

Electrochemical Investigation of Natural Ore Molybdenite (MoS2) as a First-Hand Anode for Lithium Storages.

Considering serious pollution from the traditional chemical synthesis process, the resource-rich, clean, and first-hand electrode materials are greatly desired. Natural ore molybdenite (MoS2), as the low-cost, high-yield, and environmental-friendly natural source, is investigated as a first-hand anode material for lithium-ion batteries (LIBs). Compared with chemosynthetic pure MoS2, natural molybdenite provides an ordered ion diffusion channel more effectively owing to its excellent characteristics, containing well-crystalline, large lattice distance, and trance dopants. Even at a large current density of 2.0 A g-1, a natural molybdenite electrode employing a carboxymethyl cellulose binder displays an initial charge capacity of 1199 mA h g-1 with a capacity retention of 72% after 1000 cycles, much higher than those of the electrodes utilizing a poly(vinylidene fluoride) binder. These types of binders play a crucial role in stabilizing a microstructure demonstrated by ex situ scanning electron microscopy and in affecting pseudocapacitive contributions quantitatively determined by a series of kinetic exploration. Briefly, this work might open up a new avenue toward the use of natural molybdenite as a first-hand LIB anode in scalable applications and deepen our understanding on the fundamental effect of binders in the metal-sulfide.

Moving to Aqueous Binder: A Valid Approach to Achieving High-Rate Capability and Long-Term Durability for Sodium-Ion Battery.

Polyanionic Na3V2(PO4)2F3 with a NASICON‐type structure is heralded as a promising cathode material for sodium‐ion batteries due to its fast ionic conduction, high working voltage, and favorable structural stability. However, a number of challenging issues remain regarding its rate capability and cycle life, which must be addressed to enable greater application compatibility. Here, a facile and effective approach that can be used to overcome these disadvantages by introducing an aqueous carboxymethyl cellulose (CMC) binder is reported. The resulting conductive network serves to accelerate the diffusion of Na+ ions across the interface as well as in the bulk. The strong binding force of the CMC and stable solid permeable interface protect the electrode from degradation, leading to an excellent capacity of 75 mA h g−1 at an ultrahigh rate of 70 C (1 C = 128 mA g−1) and a long lifespan of 3500 cycles at 30 C while sustaining 79% of the initial capacity value. A full cell based on this electrode material delivers an impressive energy density as high as 216 W h kg−1, indicating the potential for application of this straightforward and cost‐effective route for the future development of advanced battery technologies.