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微型噴霧干燥機合成球形磷酸鐵鋰的研究

返回列表 瀏覽:182 日期:2021-03-22

磷酸鐵鋰具有熱穩定性好、充放電效率高、環境友好、價格便宜的特點,被認為是極有潛力的鋰離子電池,特別是動力鋰離子電池正極材料。目前,研究者們廣泛采用高溫固相法、液相法、共沉淀法、微波加熱等方法來合成磷酸鐵鋰,并通過碳包覆或摻雜等方式來提高材料的電導率以發問其電化學性能。噴霧干燥法是從料液中獲得超微干粉的一種較好的方法這種由液態經過霧化和干燥在瞬間直接變成粉體的過程,已經廣泛應用于食品、醫藥、電子和材料等一些與原材料顆粒大小密切相關的領域。與其他一些粉末生產相比較,噴霧干燥法具有如下一些優點︰

1.可以保證組分分布均勻,精確控制化學計量比,適合制備多組分的復合粉末;

2.保證粉末具有較高的純度和活性;

3.噴霧赤豆工序簡單,生產過程連續,產能大,生產效率高,有利于工業化生產;

4.噴霧干燥的顆粒大都呈規則的球形,有利于提高粉末的振實密度。

二、實驗用品

(一)器材

(1)噴霧干燥機

(2)球磨機。

(二)試劑

葡萄糖

(三)材料

磷酸鐵碳酸鋰。

三、LiFePO4/C材料合成。

具體工藝流程如下:

1.按化學計量比稱取正磷酸鐵和碳酸鋰,以葡萄糖為還原劑和碳添加劑,添加適量葡萄糖;

2.以去離子水為介質球磨1h,球磨轉速為120r/min;將球磨后的物料進行噴霧干燥﹔

3.將噴霧干燥后所得的粉末裝入瓷舟,置于高純氮氣保護的管式電爐中,于600~800度下

熱處理數小時;

4.冷卻至室溫,所得灰黑色粉末即為LiFePO4/C材料。

四、料液濃度的影響。

顆粒粒徑隨著料液固含量的降低而減小,當固含量降低到20%以下時,顆粒粒徑隨固含量的變化比較緩慢。固含量越低,越有利于合成顆粒細小的磷酸鐵鋰材料,這是因為料液濃度越高,其粘度也越高,在噴霧干燥過程中形成的霧滴也變大。這使得霧化后的液滴與氣體接觸的面積減小,干燥后形成的顆粒粒徑就變大。同時,高濃度的料液還容易導致顆粒團聚結塊現象的發生,其原因在于霧滴過大,尚末干燥就被高速離心霧化器甩到干燥塔內壁,導致顆粒結塊和沾壁,在固含量30%時這種現象比較明顯。

五、進料速度對粒度的影響

隨著進料速度的增大,顆粒粒徑逐漸變大。進料速度的增大引起霧滴的變大和霧滴數量的增加,霧滴在干燥前相互碰撞發生聚合,導致成核數量的減少,產品粒徑變大。

五、結果與分析

1.采用噴霧干燥-熱還原法合成了磷酸鐵鋰材料,噴霧干燥能有效抑制組分的偏析和顆粒的長大,保證物料實現很好的混合均勻度,有利于合成更純更細的磷酸鐵鋰正極材料;

⒉噴霧干燥過程對材料顆粒有較大的影響,低固含量,低進料速率有利小粒徑材料的合成;

3噴霧干燥所得到的材料形狀規則,顆粒細小且成球狀,對改善材料的電化學性能有很大意義。

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