Applied Research On The Lithium Battery Materials In Polyanionic Cellulose Salt

In this paper, the group structure distribution of substituents of CMC-Na prepared by kneading method and slurry process in alternating glucose units(AGU) and molecular chain is analyzed by means of nuclear magnetism and chemical analysis. The number of long-chain in C6 of CMC-Na prepared by slurry process is more than that of CMC-Na prepared by kneading machine method. The elongation at break point of CMC-Na prepared by slurry process is around 12%, which is higher than that of CMC-Na prepared by kneading machine method, and the flexibility of molecular chain is better. By using CMC-Na prepared by slurry process as material, a new polyanionic cellulose lithium salt, namely carboxymethyl cellulose lithium is synthesized by two steps method. CMC-Na is acidized with 20% of the acid under 35 oC for two hours to obtain CMC-H, and the CMC-H is alkalized under 50 oC for two hours to obtain CMC-Li. The preparation technology is optimized and test method of CMC-Li is established. The characteristic of non-Newtonian fluid of CMC-Li is better than that of CMC-Na, and the thermal stability is similar to each other.Mixing the Polyethylene oxide(PEO) of 400,000 molecular weight as a co-solvent with the polyanionic cellulose salt prepared by slurry process in the pure water to obtain electrospinning solution, when voltage is 30 to 36 KV, spinning distance is 15 cm, concentration is 4%, speed is 1 to 4ml/h and the molecular weight of polyanionic cellulose salt is less than 100,000, the nano-fiber materials has the property of the smooth surface, smaller diameter(80 nm) and uniform distribution is obtained. The carbon quantum dot fluorescent material is coated by CMC-Na to obtain non-woven fabrics with the higher fluorescence intensity characteristic by means of electrospinning technique. CMC-Na microballoon prepared by electrostatic spraying technique has the property of better morphology and monodispersity. The hollow CMC-Na nanofiber is successfully synthesized by coaxial electrostatic spinning technology. The CMC-Li electrospinning solution and aluminum powder are electrospun by electrospinning technique to prepare Al/CMC-Li nano-composite fiber. The morphology of fiber material and dispersion of coated particles are characterized by means of scanning electron microscope(SEM) and transmission electron microscopy(TEM). Combing the excellent properties of nanofiber with the structure characteristics of polyanionic cellulose salt, the electrostatic spinning of polyanionic cellulose salt is implemented by electrospinning technique, which extends the application range of cellulose derivatives.The synthetic fabric consists of CMC-Li and lithium battery anode material of lithium iron phosphate(LiFePO4, LFP) is prepared by electrospinning technique, then synthetic fabric is carbonized and modified under high temperature to obtain a new modified electrode materials. The experimental model is established. The CMC-Li/LFP nano-filamentary composite material is pre-oxidized under 285 oC for 2 hours under the condition that the carbon content is 10% to 15%, and carbonized at 600 oC for 1 hour under the protection of nitrogen. Then CMC-Li is existed in the form of carbon nanofiber and Li+oxide salt, and completely mixed with LFP particles to obtain the new modified electrode materials with CNFs/LFP/Li+ salt(CLL). Based on the performance test of lithium battery using PVDF as binder, LFP and CLL as electrode material, the first charge and discharge specific capacity of CLL electrode material is reached 168 mAh g-1 and 161 mAh g-1, which is increased by 15.1% and 11.8% over that of unmodified LFP electrode material, respectively. After 200 charge-discharge circles under 0.1C, specific capacity is almost no loss. When discharge rate is increased from 0.1C, 0.2C to 5C, the specific capacity of battery is reached 120.5 mAh g-1. When discharge rate is decreased from 5C to 0.1C, the specific capacity of battery can be quickly returned to 167.5 mAh g-1. The reduction and oxidation peak of cyclic voltammetry(CV) is sharp and symmetric, and the minimum voltage difference between the two peaks is reached 0.25 V. All of these show that this method can effectively improve the conductivity of the anode materials, shorten the lithium ion diffusion path, reduce the degree of polarization and enhance the electrochemical performance.The mechanism model of emerging and embedding Li-ions in CMC-Li are established. It is the first time to apply the prepared CMC-Li including Li-ions as water soluble binder to the anode material LFP. The result shows that the first charge and discharge specific capacity of battery with CMC-Li as binder is reached 183.8 mAh g-1 and 179.5 mAh g-1, which increased by 22.2% and 27.5% over that of battery with PVDF as oil soluble binder, respectively. After 200 charging and discharging cycles, discharge specific capacity is reached 175 mAh g-1, and specific capacity loss is reached 3.31%. The charge and discharge specific capacity cycle performance with different rate from 0.1C to 5C is better, and the minimum difference value of CV test is reached 0.22 V. The property of EIS is better, which shows the better electrochemical performance.LFP is modified by CMC-Li with low molecular weight by means of electrospinning, and coated by nanofibers melting layer to form the modified electrode CLL. The performance test of Lithium battery composite electrode assembled by CMC-Li with high molecular weight as binder is established. Then process mechanisms is analyzed and explored of lithium battery performance. The morphology of composite electrode material particles is microballoon. The result shows that the morphology of composite electrode material particles with CMC-Li-6 as binder and CLL-3 as active material is microspheric, the infiltration of electrolyte is sufficient. The first charge and discharge capacity under 0.1C is reached 179.5 mAh g-1 and 176.8 mAh g-1. After 100 cycles, the specific capacity did not decrease but increase. The final charge and discharge specific capacity is reached 181.7 mAh g-1 and 180.6 mAh g-1, and the cycle efficiency has been close to 100%. When the rate is 5C, the charge and discharge specific capacity is reached 115 mAh g-1, the difference value between the CV peaks is 0.20 V, which shows the better electrochemical performance of battery.