镍电极在充放电过程中的XRD原位观测

In situ study on nickel electrode by XRD in the process of charge and discharge

Ｎｉ（ＯＨ）２在不同的充放电条件下会发生多种晶型转变，这些变化与ＭＨ－Ｎｉ电池的性能有关。尤其是过充或大电流充电时生成的γ－ＮｉＯＯＨ可造成镍电极膨胀、开裂甚至失效，严重影响镍氢电池使用寿命。由于γ－ＮｉＯＯＨ不稳定，易自放电，常规研究方法很难定量考察充电过程中生成γ－ＮｉＯＯＨ的准确数量。Ｘ射线衍射原位测量技术可有效地在充放电过程中对氢氧化镍正极结构变化进行观测。本文采用该实验技术对氢氧化镍正极活性物质结构变化进行了动态研究。研究表明Ｎｉ（ＯＨ）２晶格缺陷和晶体结构无序化导致Ｘ射线衍射（ＸＲＤ）谱线宽化，具有ＸＲＤ谱线宽化特别是（１０１）谱线宽化特征的镍正极有较高的电化学活性。添加ＺｎＯ可抑制充电时生成γ－ＮｉＯＯＨ的数量，并运用ＸＲＤ定量分析γ－ＮｉＯＯＨ含量的方法计算了此时镍电极在充电状态下γ／（γ＋β）的比值为１４．２％。

Nickel hydroxide has multiple phase transformations under different charge conditions.All these changes have affected on the performance of battery.Especially γ NiOOH formed in overcharge or at high charge rate results in swelling of nickel electrode and leads to fracture.As a result the cyclic life of Ni MH battery is greatly deceased.It is difficult for γ NiOOH to be precisely quantified by the method of regulated X ray diffraction because of its characteristics of destabilization and self discharge.Therefore,in this paper the technology of in situ measurement using X ray diffraction was introduced to study the structure of active mass in nickel electrode during cycling.The results show that there is a close relationship between the broading of X ray diffraction for line and defects in crystal structure.Nickel electrodes with broading of XRD lines especially for(101)exhibit a high electrochemical activity.ZnO added to nickel electrode can effectively prohibit the formation of γ NiOOH and the ratio of γ/(γ+β)in a charged NiOOH electrode was given by 14.2% by the method of quantifying the amount of γ NiOOH in X ray diffraction.