热压烧结法制备新型NiTi-Si电极材料的结构演化和性能分析

通过选择不同烧结工艺,探索了热压烧结法制备NiTi-Si复合电极材料的结构演化及其对电性能的影响。结果表明,烧结过程的压缩率随热压烧结温度的升高而演化,可分为三个阶段:第一阶段未产生压缩变形,第二阶段由于Si的软化开始产生压缩变形,第三阶段NiTi也开始软化,压缩率显著增加。用X射线衍射(XRD)和扫描电子显微镜(SEM)分析每个阶段的相组成及微观结构,结果表明,热压烧结样品组成主要是Ni4Ti4Si7三元金属间化合物及部分Ni3Ti3O、NiTi与Si,复合物致密度也随着烧结温度的提高而改善。选取一组具代表性的NiTi-Si复合材料作为电极制备成纽扣电池,充放电曲线结果表明,电池在循环初期出现明显比容量衰减,但电池循环次数明显高于传统集电体Si电极材料。分析认为,Ni4Ti4Si7三元金属间化合物中的Si不参与电化学反应,但是该化合物有助于弛豫充放电过程中电极体积变化导致的应变。

Structural Evolution and Properties Analysis on a New Type NiTi-Si Anode Materials by Hot-Press Sintering

Si is considered as a quite promising anode electrode material for lithium ion batteries because of its high theoretical capacity.However,the large volume change of Si during the charge-discharge process may cause surface cracking and even pulverization of the electrode material.To solve this problem,NiTi alloys showing huge reversible strain were proposed to replace the conventional current collector,which may probably buffer the volume change of Si and thus improve the lifespan of the electrode.The NiTi-Si composite electrode material is synthesized by hotpressing sintering process at different temperatures.The microstructure and the electrical properties as a function of the sintering temperature are investigated.Results showed that a dramatically decrease of electrical capacity occurred after 1st cycle due to the major part of Si was presented in inactivate ternary intermetallic compounds Ni4Ti4Si7.However,compared to the Si electrodes with traditional current collector,the NiTi-Si composite electrodes have lar-ger cycle numbers,which may attributed to the buffering of the volume change by Ni4Ti4Si7.