【摘要】：本文針對鋰電池正極材料的研究熱點及資源的循環(huán)利用,提出以黃磷副產(chǎn)物磷鐵為原料,采用水熱法將磷鐵溶解與磷酸鐵結(jié)晶一步完成的過程研究。本文方法實現(xiàn)了在水熱條件下將磷鐵的溶解與磷酸鐵的結(jié)晶在相同體系中一步完成,研究了反應(yīng)條件對產(chǎn)品磷酸鐵純度及電化學(xué)性能的影響。首先,以磷鐵、H_3PO_4、HNO_3為原料采用水熱法一步合成電池級磷酸鐵,并利用XRD、TG-DSC、SEM、FTIR、ICP-Ms以及電化學(xué)測試等手段表征產(chǎn)品的分子結(jié)構(gòu)、晶體結(jié)構(gòu)、形貌和電化學(xué)性能。研究了水熱反應(yīng)過程中硝酸濃度、反應(yīng)溫度、反應(yīng)時間及體系鐵濃度對產(chǎn)品中鐵含量及鐵磷比的影響,設(shè)計正交試驗優(yōu)化實驗條件,并對磷鐵一步反應(yīng)合成電池級磷酸鐵的反應(yīng)機理進行了初步的研究。其次,通過加入氫氟酸或超聲處理對水熱法制備的電池級磷酸鐵進行改性研究,研究了氫氟酸濃度、浸泡時間、超聲時間對磷酸鐵純度、結(jié)構(gòu)、形貌及電化學(xué)性能的影響。實驗結(jié)果表明:當(dāng)硝酸濃度為3.0mol/L、反應(yīng)溫度為110℃、體系鐵濃度為20g/L時反應(yīng)120min后,通過分析表征可知產(chǎn)品在純度、結(jié)構(gòu)等方面都符合市售電池級磷酸鐵的要求。同時以自制的FePO_4·2H_2O產(chǎn)品作為前驅(qū)體,采用高溫固相法制備的LiFePO_4/C具有良好的電化學(xué)性能,電池在0.1C下的首次放電容量為148.9 mAh/g,且通過EIS測試顯示電池電極電荷轉(zhuǎn)移電阻為48Ω。這是由于磷酸鐵產(chǎn)品中含有的鈦、釩、錳等微量金屬元素不僅有效利用了原料磷鐵中的雜質(zhì)金屬元素,而且對電池起到了一定的摻雜作用,改善了磷酸鐵鋰的電化學(xué)性能。對磷酸鐵的改性先采用濃度為4%的氫氟酸浸泡4h。并對氫氟酸處理前后磷酸鐵產(chǎn)品的結(jié)構(gòu)、形貌及電化學(xué)性能進行了分析對比。結(jié)果表明:氫氟酸處理后的產(chǎn)品在結(jié)構(gòu)上沒有發(fā)生改變,但產(chǎn)品形貌由團聚的層狀結(jié)構(gòu)分散為片狀,并且在片狀結(jié)構(gòu)上存在許多不同大小的微孔,這在一定程度上增大了磷酸鐵產(chǎn)品的比表面積。同時通過分析產(chǎn)品磷酸鐵形貌及電池性能的變化可知,將氫氟酸處理與超聲處理結(jié)合可有效縮短改性時間。
[Abstract]:Aiming at the research focus of cathode materials for lithium batteries and the recycling of resources, the process of dissolution of iron phosphate and crystallization of iron phosphate by hydrothermal method using yellow phosphorus by-product as raw material was put forward in this paper. In this paper, the dissolution of iron phosphate and the crystallization of iron phosphate in the same system were carried out in one step under hydrothermal conditions. The effects of reaction conditions on the purity and electrochemical properties of iron phosphate products were studied. First of all, the battery-grade ferric phosphate was synthesized by hydrothermal method using ferric phosphate, H3PO4 and HNOK3 as raw materials, and the molecular structure and crystal structure of the product were characterized by XRD,TG-DSC,SEM,FTIR,ICP-Ms and electrochemical tests. Morphology and electrochemical properties. The effects of nitric acid concentration, reaction temperature, reaction time and iron concentration of the system on the iron content and iron phosphorus ratio in the product during hydrothermal reaction were studied. The orthogonal test was designed to optimize the experimental conditions. The reaction mechanism of the one-step reaction of iron phosphate for the synthesis of battery-grade iron phosphate was studied. Secondly, the effects of hydrofluoric acid concentration, soaking time and ultrasonic time on the purity, structure, morphology and electrochemical properties of ferric phosphate prepared by hydrothermal method were studied by adding hydrofluoric acid or ultrasonic treatment. The experimental results show that when the concentration of nitric acid is 3.0 mol / L, the reaction temperature is 110 鈩，

本文編號：2374619