水热法磷酸铁锂正极材料的应用性能研究

发布时间：2018-05-08 09:18

本文选题：水热法 + LiFePO_4　；参考：《河北工业大学》2015年硕士论文

【摘要】：目前商业化的磷酸铁锂(LFP)正极材料可由固相法和水热法制备。水热法LFP产品因其具有纯度高、晶体择向生长、颗粒细小均匀等特点成为高端产品。目前国内尚无水热法LFP产品供应。作为电极材料,需满足电化学性能和加工应用性能等多方面的要求。不同方法或工艺所得样品的理化指标不尽相同,这导致了材料在应用性能上的差异。本课题组已对水热法合成磷酸铁锂工艺进行了基础研究,尚需对样品的应用性能进行详细研究。探索了LFP/C的制浆性能。通过改变导电剂的含量和不同导电剂组合,考察浆料的固含量、表面电阻和面密度,得到最佳制浆配方。当Li FePO_4:PVDF:Super-P:KS-6=93.5:3.5:2:1时,浆料的稳定性和分散性能最好,涂覆出的极片的一致性最好。考察了水热法LFP对电解液酸度的敏感性并与固相法LFP进行了对比。将电解液放置于空气中10-30分钟以改变其中的水分和酸度。无论水热法或固相法的LFP,随电解液中酸度和水分的增加,电池的充电电压平台均有0.02-0.05V升高,但首次容量、倍率性能和循环性能在电解液酸度为59.2 ppm时出现最佳值。电解液酸度升至110.6 ppm时,两种材料的倍率性能均有所下降,相对于固相法LFP,水热法LFP对电解液中酸度更为敏感。考察了压实密度为2.15、2.25和2.30 g·cm-3时,水热法LFP材料的容量发挥。压实密度为2.25 g·cm-3时,电池放电容量最高,放电电压平台平滑,且平台较高。用26650型全电池对水热法LFP进行了测试,并与德国南方化学水热法产品(P2)、台湾长园固相法产品的电化学性能进行了对比。水热法的产品放电比容量分别为144.2(P2)、142.0 mAh·g-1(本实验室),高于固相法产品128.0 mAh·g-1的比容量。本实验水热合成的磷酸铁锂电池的倍率性能最好,其0.5 C、1 C、3 C和5 C的容量保持率分别为98.78%、97.25%、96.94%和96.64%,本实验室样品在高温存储后,其容量保持率和容量恢复率分别为96.23%和97.10%,内阻增长率较小,电压降为0.049V。在充放电100次循环后容量保持率仍为98.91%,500次后电池的容量保持率为97.61%,循环1000次后容量保持率也有93.97%。
[Abstract]:At present, commercial lithium-lithium phosphate (LFP) cathode materials can be prepared by solid phase method and hydrothermal method. Hydrothermal LFP products are high-end products due to their high purity, crystal selective growth and fine and uniform particle size. At present, there is no domestic supply of hydrothermal LFP products. As electrode material, it needs to meet the requirements of electrochemical performance and processing performance. The physical and chemical indexes of the samples obtained by different methods or processes are different, which leads to the difference in the application properties of the materials. The basic research on the hydrothermal synthesis of lithium iron phosphate has been carried out, and the application properties of the samples need to be studied in detail. The pulping properties of LFP/C were investigated. By changing the content of conductive agent and the combination of different conductive agents, the solid content, surface resistance and surface density of the slurry were investigated, and the optimum pulping formula was obtained. When Li FePO_4:PVDF:Super-P:KS-6=93.5:3.5:2:1 is used, the stability and dispersion property of the slurry is the best, and the consistency of the coated electrode is the best. The sensitivity of hydrothermal LFP to electrolyte acidity was investigated and compared with solid phase LFP. Place electrolyte in air for 10-30 minutes to change moisture and acidity. With the increase of acidity and moisture in the electrolyte, the charging voltage platform of the battery increases from 0.02-0.05V, but the initial capacity, rate performance and cycling performance of the battery are optimized when the acidity of the electrolyte is 59.2 ppm. When the acidity of the electrolyte increased to 110.6 ppm, the ratio properties of the two materials decreased. Compared with the solid phase method, the hydrothermal LFP was more sensitive to the acidity of the electrolyte. The capacity of hydrothermal LFP materials was investigated when the compaction densities were 2.15g / 2.25 and 2.30 g / cm-3. When the compaction density is 2.25 g cm-3, the discharge capacity of the battery is the highest, the discharge voltage platform is smooth and the platform is high. The LFP of hydrothermal process was tested with 26650 type full battery. The electrochemical properties of the products were compared with those of the chemical hydrothermal products of southern Germany and the products of Changyuan solid phase method in Taiwan. The specific discharge capacity of the hydrothermal method is 144.2 mAh / g ~ (-1), respectively. The specific capacity of the hydrothermal method is higher than that of the solid phase product (128.0 mAh g ~ (-1)). In this experiment, the hydrothermal synthesis of lithium iron phosphate battery has the best performance, its capacity retention rates of 0.5 C ~ (-1) C ~ (3) C and 5 C are 98.78 ~ 97.25 ~ 96.94% and 96.64%, respectively. The samples are stored at high temperature in our laboratory. The capacity retention rate and capacity recovery rate are 96.23% and 97.10, respectively. The growth rate of internal resistance is small, and the voltage drop is 0.049 V. After 1000 cycles, the capacity retention rate of the battery is 97.61, and the capacity retention rate of the battery is 93.97 after 1000 cycles.
【学位授予单位】：河北工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TM912

【相似文献】