Synthesis of Carboxymethyl Cellulose Lithium by Weak Acid

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Synthesis of carboxymethyl cellulose lithium by weak acid treatment and its application in high energy-density graphite anode for Li-ion batteries Hyunjung Park, Dongsoo Lee, and Taeseup Song Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b00851 • Publication Date (Web): 12 Jun 2018 Downloaded from http://pubs.acs.org on June 18, 2018

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Industrial & Engineering Chemistry Research

Synthesis of carboxymethyl cellulose lithium by weak acid treatment and its application in high energy-density graphite anode for Li-ion batteries

Hyunjung Park1,2, Dongsoo Lee2, and Taeseup Song2*

1

School of Chemical and Biomedical Engineering, Nanyang Technological University, 62

Nanyang Drive, Singapore 637459, Singapore. 2

Department of Energy Engineering, Hanyang University, Seoul 133-791, Korea

E-mail: [email protected]

Abstract Carboxymethyl cellulose lithium (CMC-Li) has recently been explored as a promising binder for Li-ion batteries because of enhanced Li+ ion flux. CMC-Li has been generally prepared by CMC acid form (CMC-H) as an intermediate product treated with a strong acid, which considerably causes a polymer degradation. Here we report a synthesis method of CMC-Li through a use of a weak acid (acetic acid) and its application in a high energy-density graphite anode. CMC-Li synthesized by acetic acid (CMC-Li (A)) exhibits enhanced physicochemical properties including an appropriate viscosity of ~3000 mPa·s at a shear rate of 10 s-1, good slurry stability, and strong adhesion force of 1.4 gf/mm compared to those of CMC-Li synthesized by hydrochloric acid. The high energy-density graphite anode prepared with CMC-Li (A) shows higher charge/discharge capacities and capacity retentions in various rates of 0.05-2C than those of the electrode prepared with CMC-Na that might be due to the enhanced Li+ ion flux upon cycling. 1

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1. Introduction Li-ion batteries (LIBs) have attracted great attention as an energy storage system in all kinds of portable electronics such as mobile phones, laptops, tablets, etc. There have been intensive studies to enhance battery performances by manipulating various factors including raw materials (negative/positive materials, conductive agents, binders, and electrolytes), cell design, packing, charging/discharging control strategy, and so on. As battery technology has been well-established and mature nowadays, a high degree of qualifications and standards are more required. In this regard, research in industrial scale become important for nextgeneration LIBs. Manufacturing processes of Li-ion batteries are as follow; 1) slurry preparation: mixing active materials, binders, and conductive agents in a specific ratio. 2) casting and drying: slurry coating on a current collector by a tape casting and drying a solvent at an elevated temperature in an oven. 3) calendaring: compressing electrodes for close packing. 4) cutting/slitting/punching: electrodes are cut or punched into a desired shape the same as a cell. 5) assembly: electrodes are wounded with separator and integrated into the housing1. Among those multiple procedures, a dispersion of solids including the active material and conducting agent in an appropriate solvent is a priority in that the slurry properties determine a homogeneity of thickness, mechanical strength, porosity of the electrode that are all directly relevant to cell performances. Especially, an appropriate rheological behavior and no sedimentation of the slurry should be achieved for a homogeneous coating of the slurry on the current collector in large-scale manufacturing, which is strongly governed by binders used. Binders as one of the major electrode components are essential for the slurry dispersibility and mechanical properties of the positive/negative electrode. Among various candidates explored for LIBs, polyvinylidene difluoride (PVDF) and carboxymethyl cellulose (CMC) are widely used in commercial batteries up to date. Particularly, the CMC is 2


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considered the most promising binder due to its water-soluble property, environmentally friendliness, the highest mechanical strength, and low cost2-4. Previous studies demonstrate that various cathodes and anodes prepared with the CMC show improved electrochemical performances that those of the PVDF5-7. Moreover, stiffer CMC binder constrain electrode deformation compared to more ductile PVDF binder, and thicker SEI layer are formed on the PVDF electrode that results in larger electrode expansion and irreversible deformation8. The CMC serves as a dispersant of active materials and/or conductive agents because of a swelling behavior of the CMC molecule driven by a repulsion force between carboxylate (COO-) in aqueous media, which is achieved only by using a small amount below 5 wt %2, 9. One of the interesting features of the CMC is different kinds of salt forms such as CMC-R (R = H, Li, Na, and K, etc.). Studies on an introduction of CMC-Li to Li-ion batteries as a binder have been conducted. According to the previous reports10-12, the electrodes prepared with the CMC-Li show better electrochemical performances such as higher Coulombic efficiency and charge/discharge capacities than those composed of the PVDF or the CMC-Na because of enhanced Li+ ion flux during charging/discharging. The similar result has been reported in lithium polyacrylate (Li-PAA) that prepared with PAA by cation exchange13. There are several synthetic methods for the CMC-Li. Among them, a general way is a two-step method as follows; 1) preparation of CMC-H from CMC-Na under strong acidic condition (hydrochloric acid (HCl)). 2) preparation of CMC-Li by cationic exchange with lithium sources such as lithium hydroxide (LiOH). Previous studies have demonstrated that the CMC-Li binder prepared in the way mentioned above acts as the efficient ion-conductive polymer with a suitable adhesiveness for the electrode11. However, treating CMC-Na with the strong acid is not desirable because it risks corrosion of processing equipment, raises a safety issue, and causes a degradation of the CMC and a breakage of the polymer chain in a certain extent that can potentially change its original physicochemical properties14-15. In the literature 3



of cellulose and cellulose derivatives by Emil Ott et all.,16 those phenomena are well explained. In brief, the acidic treatment of the CMC can mainly cause two kinds of reactions. First, hydrolytic degradation; this accompanies a scission of glucosidic chain bonds of the cellulose that results in differing in a molecular size and a degree of polymerization. Moreover, the degradation changes the crystallinity and decrease the viscosity as well as the strength of the CMC. Second, oxidative degradation; because of its polyhydric alcohol structure, cellulose can be easily oxidized especially in the acidity or basicity of the medium or in the presence of the oxidizing reagents. This oxidation cause attacks on carbon atoms and/or hydroxyl groups in the cellulose molecule, resulting in hydrolytic cleavage of the chain and/or a formation of carbonyl groups with/without ring cleavage. Hence, it remains challenging to synthesize CMC-Li in a more favorable way to minimize the polymer degradation. In this study, we report the synthesis of CMC-Li by treating the CMC-Na as a starting material with a weak acid such as acetic acid for the CMC-H and an application to a graphitebased anode for LIBs. Various physicochemical properties of the binder, the slurry, and the electrode with the CMC-Li synthesized by acetic acid (hereafter CMC-Li (A)) are investigated in comparison with CMC-Na as a reference and CMC-Li prepared with hydrochloric acid (designated as CMC-Li (H)) from the viewpoint of industrial qualifications. Finally, CMC-Li binders are introduced to the high energy density graphite anode, and electrochemical performances are evaluated through half-cell including charge/discharge capacity, cycle life, and rate capability. 2. Experimental 2.1 Preparation of CMC-H

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The acid forms of CMC-H were prepared by treating 5 g of CMC-Na (Sigma, Mw ~250,000, degree of substitution 1.2) with acid solutions HCl solution (DAEJUNG, concentration above 35 %) as a strong acid and an acetic acid (Sigma, > 99.8 %) as a weak acid in 150 mL of an ethanol/acid mixture (85:15, volume ratio) for 3 h at 35 °C. CMC-H mixtures were filtrated and washed with 500 mL of an ethanol/water mixture (85:15, volume ratio). Two kinds of CMC-H powders were dried at 80 °C in a vacuum oven, separately. 2.2 Preparation of CMC-Li CMC-Li (H) and CMC-Li (A) binders were synthesized by treating the above two kinds of pure CMC-H in 150 mL of an ethanol/water mixture (90:10, volume ratio) with 9.15 g of LiOH·H2O (Sigma, > 98 %) for 3 h at 50 °C. The reaction occurs at pH 11. After finishing the reaction, the pH of the mixture is neutralized to pH ~7 using acetic acid to eliminate residual hydroxide (OH-) in the samples. Finally, the pure CMC-Li was obtained by filtration them with 500 mL of an ethanol/water mixture (85:15, volume ratio) in several times and drying at 70 °C in a vacuum oven. 2.3 Preparation of high energy density graphite electrodes A graphite electrode with high energy density was prepared in an aqueous system. A synthetic graphite (SAMSUNG SDI) was used as the active material. Three types of CMC binders such as CMC-Na (reference), CMC-Li (H), and CMC-Li (A), and emulsified styrenebutadiene rubber (SBR, 40 wt % in D/I water) as binders were used. In detail, for one batch of a slurry, 19.5 g of graphite particles, 0.2 g of CMC powders, 0,75 g of SBR solution (a weight ratio of 97.5:1:1.5) were put into a 50 ml vial with 20 ml deionized water, and the mixture is thoroughly mixed using a Thicky mixer at 2000 rpm for 5 minutes. The asprepared slurry was cast onto a Cu current collector (7 µm thickness) using a doctor blade. Then the electrode was dried at 110 oC for 10 min in an oven. After drying, the mass loading level (L/L) of the electrode was 13.8 mg cm-2. To increase the packing density, the electrode 5



was pressed using a rolling press machine, and the thickness of the graphite film was decreased from 120 µm to 70 µm (not including the Cu current collector). Therefore, the final mass loading and the density of the high energy density graphite electrode were set at 13.8 mg cm-2 and 1.7 g cc-1, respectively. 2.3 Material characterizations Fourier-transform infrared spectroscopy (FT-IR) spectra on KBr pellets composed of CMC-Na, CMC-Li (H), and CMC-Li (A) were recorded by FTIR spectrometer (Nicolet 5700, ThermoElectron, US). X-ray diffraction (XRD) patterns were obtained by X-ray diffraction analyzer (Rigaku D/MAX RINT-2000) in the range of 10 o to 80 o at a scan rate of 3.0 o per min using CuKα X-ray source. X-ray photoelectron spectrometry (XPS, VG Microtech ESCA2000) was used for the elemental analysis. The mechanical properties of binder films were measured using universal testing machine, UTM (AGS-J, Shimadzu, Kyoto, Japan). The specimens were prepared by using ASTM D638-Type 5 cutter. The samples were elongated to obtain a stress-strain curve within a standard deviation of less than ± 10 %. The rheological behavior of the slurry was measured at 25 oC by using a rotational rheometer (MCR 501, Anton Paar, Germany) with a cone and plate geometry. The stress was applied on the slurry that contains a mass fraction of 50 % solids, and the relative viscosity was automatically calculated. To measure the adhesion strength between the copper current collector and graphite/CMC/SBR film, the peeling test was conducted by a UTM machine. In detail, the graphite electrode was cut by strip cutter. The size after cut is 25 × 50 mm and then attached to a glass plate (width: 25.4 mm, length: 50 mm). 2.4 Evaluation of electrochemical performances Before the evaluation, all the electrodes were dried at 145 oC for 4 h in a vacuum oven to thoroughly eliminate the moisture in the electrode. 2032 round type coin cells were fabricated using the graphite electrodes as a working electrode, lithium foil with a thickness 6


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of ~1.0 mm as a counter electrode, 0.5mL of 1.3 M LiPF6 in ethylene carbonate/diethyl ethylene carbonate (EC/DEC (3/7 vol %) with 5 wt % FEC, PANAX StarLyte) as an electrolyte, and a polypropylene (PP) film as a separator. All the cells were tested using a battery cycle tester (TOSCAT 3000, Toyo System, Tokyo, Japan). The 1C as the current density is 372 mA g-1 for the electrode based on the theoretical capacity of graphite (372 mAh g-1). The electrodes have a radius of 15 Φ and a mass loading levels of ~14 mg cm-2 that leads to ~8 mA as 1C for the electrochemical evaluations. As a test mode, a constant current mode was used down to 0.01V and then, it changed to a constant voltage mode at C/100 for discharge (lithiation). And a constant current mode was applied up to 1.4V for charge (delithiation). Each of one formation cycle at 0.05, 0.1, and 0.2C was performed.

3. Results and discussion 3.1 Binder characterization: CH2COONa CH2COONa

CH2COOH

CH2COOLi

CH2COOH

CH2COOLi

(1) (2)

Figure 1. Molecular structures and images of carboxymethylcellulose sodium (CMC-Na), carboxymethylcellulose (CMC-H), and carboxymethylcellulose lithium (CMC-Li).

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A difference in the general way of using hydrochloric acid as a strong acid (1) and our strategy is the use of acetic acid as a weak acid to convert the CMC-Na to the CMC-H for the synthesis of the CMC-Li based on equation (2). Their molecular structures and the images of as-prepared samples were shown in Figure 1. To investigate the effect of the acidic treatment on the CMC using the hydrochloric acid and the acetic acid, FT-IR spectra were obtained on as-prepared samples of CMC-Na (black line), CMC-H (H) (red line), and CMC-H (A) (blue line) as shown in Figure 2a. Bands at ~1050 cm-1 are ascribed to the ether group of cellulose found in all the CMC samples regardless of salt forms. Peaks at ~1630 and ~1418 cm-1 are attributed to the carboxylic and methyl functional groups, respectively. Peaks at 2923 cm-1 are originated from C–H stretching of methyl groups that are attached to carboxylic group. These IR spectra basically indicates all the samples possess the cellulose backbone with the carboxymethyl ether group. However, a noticeable difference between them is an appearance of absorption peaks at ~883 cm-1 and ~1733 cm-1 that represent hemiacetal bonds and/or aldehydic carbonyl groups (-CHO) typically observed in the oxidized CMC16-17. Especially, the peak intensity has a linear relationship with a degree of oxidative degradation of the original CMC according to previous studies on oxycellulose17-19. In this respect, the CMC-H (H) was more oxidized than that of the CMC-H (A) because of the stronger intensities of the peaks. Figure 2b shows XRD patterns of the three samples. The CMC-H (H) exhibits the much higher intensity of the broad peak in the 2θ range of 10–30o than those of the others. It has been known that the acid treatment can cleave glucosidic linkages in the cellulose chains, which results in a removal of amorphous region and/or a rearrangement of disordered region, and thus the intensity of the XRD peak increases without a substantial change in the structure confirmed by the previous reports16, 20. As a result, the XRD study confirms that the CMC-H (H) experiences a more severe degree of the chain rupture than that of the CMC-H (A) in comparison of the original CMC-Na. 8


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Figure 2 Binder characterization of CMC-Na, CMC-H (H), CMC-H (A), CMC-Li (H), and CMC-Li (A) binders. (a) FT-IR spectra. (b) XRD patterns. (c) and (d) XPS spectra. (e) Stressstrain curves. (f) Rheological behaviors of 0.7 wt % aqueous binder solutions.

To characterize the substitution of Li salt for Na salt in the final CMC binders, XPS spectra were obtained from three samples. As shown in Figure 2c, the CMC-H (H) and the CMC-H (A) do not exhibit Na 1s peaks in contrast to the CMC-Na sample that shows the Na peak at ~1071 eV. This confirms that the successful cation exchange of Na+ with H+ using both hydrochloric acid and acetic acid. After the lithiation process, the CMC-Li (H) and the CMC-Li (A) show Li 1s peaks at ~ 54.1 eV (Figure 2d). A shift to the lower binding energy (B.E) from ~ 55 eV (a reference of Li spectrum) was observed, and this could be a B.E change due to the bond with carboxylate ion (COO-). If polymer chain and/or structure are degraded under specific influences such as heat, light, chemicals like strong acid and alkalis, etc., physical properties of the binder can be changed. In this respect, a mechanical strength of the CMC-Na, CMC-Li (H), CMC-Li (A) was determined by the universal testing machine as shown in Figure 2e. Specimens for measuring were prepared using a dumbbell cutter (the inset). Stress-strain curves of three 9



samples demonstrate that a behavior of the CMC-Li (H) binder far deviates from behaviors of the CMC-Na and the CMC-Li (A). The CMC-Li (H) has the steepest slop when ~ 30 N stress was applied on the specimen that indicates it is the most brittle and has a lowest flexibility against deformation. Moreover, a rheological behavior of aqueous solutions with 0.7 wt% of CMC-Na, CMC-Li (H), and CMC-Li (A) was studied (Figure 2f). There is a noticeable difference that apparent viscosities of CMC-Li (H) and CMC-Li (A) are lower than that of CMC-Na. Particularly CMC-Li (H) has too lower viscosity and shows Newtonian behavior regardless of shear rates in the range of 1 - 1000 s-1. It is deduced from the results that the strong acidic treatment can severely cause changes in original physical and mechanical properties of the CMC-Na.

3.2 Slurry characterization: The graphite used in this work was characterized. Figure 3a shows a SEM image of graphite particles in the range of 10–20 µm. Figure 3b exhibits XRD patterns that confirms its high crystallinity and d-spacing of 3.3572 Å from (002) plane. Moreover, the surface area of the graphite was measured by the BET method. A calculated desorption value is ~3.58 m2/g.

Figure 3 (a) SEM image of graphite particles and (b) XRD patterns.

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Figure 4 Rheological behaviors of (a) graphite/CMC-Na/SBR slurry, (b) graphite/CMC-Li (H)/SBR slurry, and (c) graphite/CMC-Li (A)/SBR slurry in terms of aging for 1/3/5 days.

For a mass production, especially the coating/casting process, a slurry is required to possess an appropriate viscosity in the range of 2000 – 10000 mPa·s at shear rates of 1 - 100 s-1 and no sedimentation. Figure 4a to c show rheological behaviors of three slurry samples prepared with the CMC-Na, the CMC-Li (H), and the CMC-Li (A) in terms of aging time for 5 days. It is desirable that the slurry has a shear thinning behavior during slurry mixing and coating processes in that the dispersed phase appear thick and viscous but tends to flow well with 11



minimum resistance. In this regard, the slurries prepared with the CMC-Na and the CMC-Li (A) have appropriate viscosities of ~3000 mPa·s at a shear rate of 10 s-1 and show the shear thinning behavior. In contrast, the viscosity of the slurry prepared with the CMC-Li (H) is still very low below ~2000 mPa·s in the shear rate range of 1 to 100 s-1, and the slurry shows a Newtonian behavior that means it is independent of shear rate and close to a liquid phase. It is worth noting that this low viscosity can cause problems in the coating process that results in uniformity of the thickness and the density of the electrode film.

Figure 5 Sedimentation test of (a) graphite/CMC-Na/SBR slurry, (b) graphite/CMC-Li (H)/SBR slurry, and (c) graphite/CMC-Li (A)/SBR slurry in terms of aging for 5 days. A phase separation between graphite particles and liquid phases is shown between a yellow line and a red line. Figure 5 shows a sedimentation test by aging for 5 days to investigate the slurry stability. There were no settlement and a separation between solid graphite particles and liquid phases in the samples prepared with the CMC-Na and the CMC-Li (A). This confirms that those two binders are enough to disperse the graphite particles can provide the good slurry stability in 12


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the aqueous medium. In contrast, the slurry prepared with the CMC-Li (H) exhibits settlement of graphite particles and the phase separation (from a yellow line to a red line). Despite the slurry instability and the sedimentation, it does not mean that the use of the CMC-Li (H) is not suitable as the binder for LIBs. The rheological behavior can be changed if the other active materials such as metal oxides, alloys, etc. and a larger amount of the binder are used in the slurry system. However, the result clearly confirms that the treatment of the CMC-Na with the strong acid can significantly affect dispensability and slurry stability.

3.3 Electrode characterization:

Figure 6 SEM top (left) and cross-view (right) images of graphite/CMC-Na/SBR electrodes with a mass loading level (mg cm-2) and a density (g cm-3) of (a) 9.7/1.6 and (b) 13.8/1.7. (c)

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graphite/CMC-Li (H)/SBR electrode and (d) graphite/CMC-Li (A)/SBR electrode with 13.8 mg cm-2 /1.7 g cm-3.

The CMC-Li binders were introduced to a high energy- density graphite electrode. The reason to choose the graphite as the active material is it has been used the most in the commercial LIBs. According to previous studies21-22, the high energy density graphite suffers from poor Li+ ion diffusivity because of a long pathway for Li+ ions from top to bottom of the thick electrode and a low electrode porosity. In this respect, the use of the CMC-Li binders for the thick and dense graphite anode can be an efficient strategy to improve Li+ ion flux and electrochemical properties. The current LIBs generally consist of the graphite anode with a loading level of ~9 mg cm-2, a density of ~1.6 g cm-3, and an electrode thickness of 50-60 µm23 that lead to a full cell capacity of ~3000 mAh g-1 especially for mobile phones (Figure 6a). With a significant development of the portable electronics, a demand for higher energy density LIBs has been increased. However, the electrode thickness increased to 80-90 µm, and the porosity decreased because of an applied higher pressure to closely pack the graphite particles by a roll press as shown in Figure 6b. The electrodes prepared with the CMC-Li (H) and the CMC-Li (A) are also shown in Figure 6c and d. There are no significant differences between samples (Figure 6c and d).

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Figure 7 Adhesion forces of graphite electrodes prepared with CMC-Na, CMC-Li (H), and CMC-Li (A) by a UTM peeling test.

To study a mechanical property of the graphite electrodes prepared with three binder samples, an adhesion force between a graphite/CMC/SBR film and a copper current collector was measured by the UTM peeling test. From the viewpoint of an industrial manufacturing, the high adhesion force is preferable for calendaring and cutting/slitting/punching processes. As shown in Figure 7, the electrode prepared with CMC-Na has the adhesion force of ~1.89 gf/mm as a reference. However, the adhesion force of CMC-Li (H) is ~0.82 gf/mm lower than the half of the CMC-Na. The CMC-Li (A) shows also lower value of ~1.4 gf/mm, but it is more improved compare to that of CMC-Li (H).

3.4 Electrochemical evaluation: After the systematic studies on the binder, the slurry, and the electrode, high energy density graphite anodes were prepared to investigate the favorable effect of CMC-Li binders on the electrochemical performance. Figure 8 shows the electrochemical performances tested in a voltage window of 0.01–1.4 V vs. Li/Li+ (1C = 372 mA g-1). As shown in voltage profiles at 0.05 C (Figure 8a), graphite anodes composed of CMC-Na. CMC-Li (H), and CMC-Li (A) give Coulombic efficiencies of 87.7, 92.7, and 90.1 % and charge capacities (delithiation) of 318, 330, and 334 mAh g-1, respectively. The anodes prepared with the CMC-Li (H) and the CMC-Li (A) show improved the Coulombic efficiency and capacity compared to those of the CMC-Na. Figure 8b shows a cycle performance over 30 cycles at 0.5 C. Capacity retentions of three graphite anodes are 98, 96.6, and 97.4 %, respectively. There is no significant difference, but the anodes prepared with the CMC-Li (H) and (A) show slightly lower value than that of CMC-Na that might be correlated to the adhesion force and weaker strength between the graphite particles and the CMC-Li 15



binders. A noticeable change was observed in a rate capability at current densities from 0.05C to 2C (Figure 8c). The capacity retentions of the graphite anodes prepared with CMC-Li (H) and CMC-Li (A) are higher than that of the graphite anode composed with CMC-Na through all the regions. Particularly, the capacities at 2C are 264, 292, 296 mAh g-1, respectively. Table 1 shows a summary of the electrochemical performances. Based on the coin half-cell tests, the use of CMC-Li binders improves the electrochemical performances of the high energy density graphite anode than CMC-Na that could be owing to the enhanced Li+ ion kinetics in the electrode upon cycling.

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Figure 8 Electrochemical performances of high energy-density graphite anodes prepared with CMC-Na, CMC-Li (H), and CMC-Li (A) in a voltage window of 0.01–1.4 V vs. Li/Li+. The electrodes had the same mass loading level of 13.8 mg cm-2 and density of 1.7 g cm-3. (a) Voltage profiles at 0.05 C, (b) cyclability at 0.5 C over 30 cycles, and (c) rate capability in various current densities of 0.05–2 C.

Table 1 Summary of electrochemical performances of the graphite electrodes prepared with CMC-Na, CMC-Li (H), and CMC-Li (A).

4. Conclusions In summary, the synthesis of the CMC-Li was developed using the weak acid such as acetic acid as the alternative to the conventional method by the strong acid, hydrochloric acid. The effects of treating CMC-Na with acids were investigated by various characterizations on the physicochemical properties of binders, slurries, and electrodes, especially from the viewpoint of the industrial qualifications. It was revealed that the CMC-Li prepared with the hydrochloric acid cause the significant changes in the original binder properties the CMC-Na as the starting material. Particularly, the low viscosity and the phase separation between the graphite particles and the liquid phases are not suitable for the graphite-based slurry that can 17



potentially cause the inhomogeneity of the electrode film during casting in large-scale manufacturing. In contrast, the CMC-Li synthesized by the acetic acid shows the improved binder properties compared to the CMC-Li (H). The high energy-density graphite anode prepared with the CMC-Li (H) shows enhanced the electrochemical performances including charge/discharge capacities and the rate capability compared to those of the anode prepared with CMC-Na. As a result, the use of CMC-Li synthesized by the weak acid as the binder for LIBs can be an efficient way to prevent the polymer degradation of the CMC caused by the strong acid treatment as well as take advantage of the CMC-Li such as enhanced Li+ ion flux upon cycling.

Acknowledgment This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry, & Energy (MOTIE) of the Republic of Korea through the reseach on Li-ion batteries (No. 20168510050080), Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT (2016R1C1B2007299) and the research fund of Hanyang University(HY-2017).

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Synthesis of Carboxymethyl Cellulose Lithium by Weak Acid

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