Views: 5 Author: Site Editor Publish Time: 2022-01-22 Origin: Site
What is sodium carboxymethyl cellulose?
Sodium Carboxymethyl cellulose, (also called: Carboxymethyl cellulose sodium salt, Carboxymethyl cellulose, CMC, Carboxymethyl, CelluloseSodium, SodiumsaltofCaboxyMethylCellulose) is the world's most widely used types of fiber, dosage of maximum.
Cmc-na is a cellulose derivative with a polymerization degree of 100~2000 and a molecular weight of 242.16. White fibrous or granular powder. Odorless, tasteless, tasteless, hygroscopic, insoluble in organic solvents. This paper mainly to understand the application of sodium carboxymethyl cellulose in lithium ion battery details.
Progress in application of Sodium carboxymethyl cellulose CMC in lithium ion batteries
At present, polyvinylidene fluoride [pVDF, (CH: A CF:)] is widely used as binder in the production of lithium ion batteries. . PVDF is not only expensive, also need to use in the process of application of explosive, friendly to the environment of organic solvents, such as N methyl which the alkane ketone (NMp) and air humidity requirements for production process strictly, also easily with embedded metal lithium, lithium graphite secondary reaction, especially in the condition of high temperature, a spontaneous risk of thermal runaway. Sodium carboxymethyl cellulose (CMC), a water-soluble binder, is used as a substitute of pVDF for electrode materials, which can avoid the use of NMp, reduce costs and reduce environmental pollution. At the same time, the production process does not require environmental humidity, but also can improve the capacity of the battery, prolong the cycle life. In this paper, the role of CMC in the performance of lithium ion battery was reviewed, and the mechanism of CMC improving battery performance was summarized from the aspects of thermal stability, electrical conductivity and electrochemical characteristics.
1. Structure and performance of CMC
1) CMC structure
CMC is generally classified by different degree of substitution (Ds), and the product morphology and performance are greatly affected by Ds. LXie et al. studied THE CMC with Ds of different H pairs of Na. SEM analysis results showed that CMC-Li-1 (Ds = 1.00) presented granular structure, and CMC-Li-2 (Ds = 0.62) presented linear structure. The research of M. E et al proved that CMC. Styrene butadiene rubber (SBR) can inhibit the agglomeration of Li: O and stabilize the interface structure, which is beneficial to the electrochemical performance.
2) CMC performance
2.1 )Thermal stability
Z.j. Han et al. studied the thermal stability of different binders. The critical temperature of pVDF is about 4500C. When reaching 500℃, rapid decomposition occurs and the mass is reduced by about 70%. When the temperature reached 600℃, the mass was further reduced by 70%. When the temperature reached 300oC, the mass of CMC-Li was reduced by 70%. When the temperature reached 400℃, the mass of CMC-Li was reduced by 10%. CMCLi is more easily decomposed than pVDF at the end of battery life.
2.2 )The electrical conductivity
S. Chou et al. 's test results showed that the resistivity of CMCLI-1, CMC-Li-2 and pVDF were 0.3154 Mn·m and 0.2634 Mn, respectively. M and 20.0365 Mn·m, indicating that the resistivity of pVDF is higher than that of CMCLi, the conductivity of CMC-LI is better than that of pVDF, and the conductivity of CMCLI.1 is lower than that of CMCLI.2.
2.3) Electrochemical performance
F. M. Courtel et al. studied the cyclic voltammetry curves of poly-sulfonate (AQ) based electrodes when different binderswere used. Different binders have different oxidation and reduction reactions, so the peak potential is different. Among them, the oxidation potential of CMCLi is 2.15V, and the reduction potential is 2.55V. The oxidation potential and reduction potential of pVDF were 2.605 V and 1.950 V respectively. Compared with the cyclic voltammetry curves of the previous two times, the peak potential difference of the oxidation-reduction peak when CMCLi binder was used was smaller than that when pVDF was used, indicating that the reaction was less hindered and CMCLi binder was more conducive to the occurrence of the oxidation-reduction reaction.
2. Application effect and mechanism of CMC
1) Application effect
P.j. Suo et al. studied the electrochemical performance of Si/C composite materials when pVDF and CMC were used as binders, and found that the battery using CMC had a reversible specific capacity of 700mAh/g for the first time and still had 597mAh/g after 4O cycles, which was superior to the battery using pVDF. J.h. Lee et al. studied the influence of Ds of CMC on the stability of graphite suspension and believed that the liquid quality of suspension was determined by Ds. At low DS, CMC has strong hydrophobic properties, and can increase the reaction with graphite surface when water is used as media. CMC also has advantages in maintaining the stability of the cyclic properties of silicon - tin alloy anode materials. The NiO electrodes were prepared with different concentrations (0.1mouL, 0.3mol/L and 0.5mol/L) CMC and pVDF binder, and charged and discharged at 1.5-3.5V with a current of 0.1c. During the first cycle, the capacity of the pVDF binder cell was higher than that of the CMC binder cell. When the number of cycles reaches lO, the discharge capacity of pVDF binder decreases obviously. After 4JD cycles, the specific discharge capacities of 0.1movL, 0.3MOUL and 0.5MovLPVDF binders decreased to 250mAh/g, 157mAtv 'g and 102mAh/g, respectively: The discharge specific capacities of batteries with 0.1 moL/L, 0.3 moL/L and 0.5 moL/LCMC binder were kept at 698mAh/g, 555mAh/g and 550mAh/g, respectively.
CMC binder is used on LiTI0. : and SnO2 nanoparticles in industrial production. Using CMC as binder, LiFepO4 and Li4TI50l2 as positive and negative active materials, respectively, and using pYR14FS1 as flame retardant electrolyte, the battery was cycled 150 times at a current of 0.1c at 1.5v ~ 3.5V at temperature, and the positive specific capacitance was maintained at 140mAh/g. Among various metal salts in CMC, CMCLi introduces other metal ions, which can inhibit "exchange reaction (vii)" in electrolyte during circulation.
2) Mechanism of performance improvement
CMC Li binder can improve the electrochemical performance of AQ base electrode in lithium battery. M. E et al. -4 conducted a preliminary study on the mechanism and proposed a model of the distribution of CMC-Li in the AQ electrode. The good performance of CMCLi comes from the strong bonding effect of hydrogen bonds produced by an OH, which contributes to the efficient formation of mesh structures. The hydrophilic CMC-Li will not dissolve in the organic electrolyte, so it has a good stability in the battery, and has strong adhesion to the electrode structure, which makes the battery has a good stability. Cmc-li binder has good Li conductivity because there are a large number of functional groups on the molecular chain of CMC-Li. During discharge, there are two sources of effective substances acting with Li: (1) Li in the electrolyte; (2) Li on the molecular chain of CMC-Li near the effective center of the active substance.
The reaction of hydroxyl group and hydroxyl group in carboxymethyl CMC-Li binder will form covalent bond; Under the action of electric field force, U can transfer on the molecular chain or adjacent molecular chain, that is, the molecular chain structure will not be damaged; Eventually, Lj will bond to the AQ particle. This indicates that the application of CMCLi not only improves the transfer efficiency of Li, but also improves the utilization rate of AQ. The higher the content of cH: COOLi and 10Li in the molecular chain, the easier Li transfer. M. Arrmand et al. believed that organic compounds of -COOH or OH could react with 1 Li respectively and produce 1 C00Li or 1 0Li at low potential. In order to further explore the mechanism of CMCLi binder in electrode, CMC-Li-1 was used as active material and similar conclusions were obtained. Li reacts with one cH, COOH and one 0H from CMC Li and generates cH: COOLi and one 0 "respectively, as shown in equations (1) and (2)
As the number of cH, COOLi, and OLi increases, THE DS of CMC-Li increases. This shows that the organic layer composed mainly of AQ particle surface binder becomes more stable and easier to transfer Li. CMCLi is a conductive polymer that provides a transport route for Li to reach the surface of AQ particles. CMCLi binders have good electronic and ionic conductivity, which results in good electrochemical performance and long cycle life of CMCLi electrodes. J. S. Bridel et al. prepared the anode of lithium ion battery using silicon/carbon/polymer composite materials with different binders to study the influence of the interaction between silicon and polymer on the overall performance of the battery, and found that CMC had the best performance when used as binder. There is a strong hydrogen bond between silicon and CMC, which has self-healing ability and can adjust the increasing stress of the material during the cycling process to maintain the stability of the material structure. With CMC as binder, the capacity of silicon anode can be kept above 1000mAh/g in at least 100 cycles, and the coulomb efficiency is close to 99.9%.
As a binder, CMC material can be used in different types of electrode materials such as natural graphite, meso-phase carbon microspheres (MCMB), lithium titanate, tin based silicon based anode material and lithium iron phosphate anode material, which can improve the battery capacity, cycle stability and cycle life compared with pYDF. It is beneficial to the thermal stability, electrical conductivity and electrochemical properties of CMC materials. There are two main mechanisms for CMC to improve the performance of lithium ion batteries:
(1) The stable bonding performance of CMC creates a necessary prerequisite for obtaining stable battery performance;
(2) CMC has good electron and ion conductivity and can promote Li transfer