丁二酮肟沉淀分离-EDTA滴定法测定镍钴锰三元氢氧化物中镍

镍钴锰三元氢氧化物为制备锂离子电池正极材料镍钴锰酸锂的主要原料,Ni含量是其比较重要的质量指标。若直接采用EDTA滴定法测定镍钴锰三元氢氧化物中Ni含量,共存的Co和Mn会对测定结果存在干扰。试验首先将镍钴锰三元氢氧化物样品用盐酸溶解,在微氨性的溶液中,以丁二酮肟为沉淀剂,Ni²⁺与丁二酮肟生成红色沉淀并实现与Co²⁺、Mn²⁺的分离;再将沉淀溶解,用EDTA滴定法测定Ni²⁺,从而建立了丁二酮肟沉淀分离-EDTA滴定测定镍钴锰三元氢氧化物中Ni含量的方法。对实验条件进行优化,确定沉淀剂用量为理论用量的1.9倍,沉淀初始pH值为8~9,陈化时间为30min,陈化温度为80℃,沉淀洗涤次数为6次。通过对模拟样品溶液测定表明,样品中Mg、Fe、Cu、Zn、Cr、Cd等微量杂质元素对Ni测定的干扰可忽略。对NCM111型、NCM622型、NCM811型镍钴锰三元氢氧化物中的Ni进行准确度考察,测定结果的相对标准偏差(RSD,n=11)在0.29%~0.48%之间,测定值与电感耦合等离子体原子发射光谱法(ICP-AES)结合EDTA滴定法的结果相一致。对NCM523型、NCM811型镍钴锰三元氢氧化物的加标回收率在96.9%~102.5%之间。

Determination of nickel in nickel-cobalt-manganese composite hydroxide by EDTA titration after precipitation separation using dimethylglyoxime

Nickel-cobalt-manganese composite hydroxide is the main raw material for the preparation of lithium-ion battery anode material, i.e., LiNiCoMnO₂. The content of Ni is an important index for quality control. If Ni content in nickel-cobalt-manganese composite hydroxide was directly analyzed by EDTA titration, the coexisting Co and Mn would cause interference with the determination results.The nickel-cobalt-manganese composite hydroxide sample was dissolved with hydrochloric acid firstly. Then dimethylglyoxime was added as precipitant in a slightly ammoniacal solution. Ni²⁺ could react with dimethylglyoxime to form red precipitate, realizing the separation of Ni²⁺ from Co²⁺ and Mn²⁺. The precipitate was dissolved and the content of Ni²⁺ was determined by EDTA titration. Consequently, a determination method of Ni in nickel-cobalt-manganese composite hydroxide by EDTA titration after precipitation separation using dimethylglyoxime was established. The experimental conditions were optimized: the dosage of precipitant was 1.9 times of theoretical value; the initial pH for precipitation was 8-9; the aging time was 30min; the aging temperature was 80℃; the precipitate was washed for 6 times. The determination results of simulation sample solution indicated that the interference caused by trace impurity elements in sample (such as Mg, Fe, Cu, Zn, Cr and Cd) could be ignored. The accuracy tests of Ni were conducted using nickel-cobalt-manganese composite hydroxide samples including NCM111 type, NCM622 type and NCM811 type. The relative standard deviations (RSD, n=11) of determination results were between 0.29% and 0.48%. The found results were consistent with those obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES) combined with EDTA titration. The recoveries of NCM523 type and NCM811 type nickel-cobalt-manganese composite hydroxide were between 96.9% and 102.5%.