Lithium uptake and release in lithium titanate (LTO) anode materials during a discharge and charge cycle is one of the fundamental processes of a lithium-ion battery (LIB), still not fully understood at the microscopic level. During the discharge cycle, LTO undergoes a phase transformation between Li₄Ti₅O₁₂ and Li₇Ti₅O₁₂ states within a cubic crystal lattice. To reveal the details of the microscopic mechanism, it is necessary to track the sequence of phase transformations at different discharge/charge states under operating conditions. Here, we use in situ Bragg coherent diffraction imaging (BCDI) and in situ X-ray diffraction (XRD) experiments to examine the lithium insertion-induced materials phase transformation within a single LTO particle and a bulk battery analogue, respectively. BCDI analysis from (111) Bragg peak shows the two-phase transformation manifesting as a distinct image phase modulation within a single LTO nanoparticle occurring in the middle of the discharge region then subsiding toward the end of the discharge cycle. We observe the biggest phase variation at the two-phase stage, indicating the formation of phase domains of 200 nm in size during the discharge process. We also observe a lattice contraction of >0.2% in a single LTO nanoparticle at the (400) Bragg peak measurement, larger than that in the corresponding bulk material. Our observation of this phase transformation at a single-particle level has implications for the understanding of the microscopic/mesoscale picture of the phase transformation in anode and cathode LIBs materials.

中文翻译：

---

成像锂离子电池钛酸锂阳极单颗粒的相变

钛酸锂（LTO）阳极材料在放电和充电周期中的锂吸收和释放是锂离子电池（LIB）的基本过程之一，在微观层面仍未完全了解。在放电周期中，LTO在立方晶格内经历Li ₄ Ti ₅ O ₁₂和Li ₇ Ti ₅ O ₁₂状态之间的相变。为了揭示微观机制的细节，有必要跟踪工作条件下不同放电/充电状态下的相变顺序。在这里，我们使用原位布拉格相干衍射成像（BCDI）和原位X射线衍射（XRD）实验分别检查了单个LTO颗粒和大容量电池类似物中锂插入引起的材料相变。从（111）布拉格峰进行的BCDI分析表明，两相转变表现为单个LTO纳米颗粒内的独特图像相位调制，该图像发生在放电区域的中部，然后逐渐向放电周期的末端沉降。我们在两相阶段观察到最大的相变，表明在放电过程中形成了大小为200 nm的相域。我们还观察到在（400）布拉格峰测量时，单个LTO纳米颗粒的晶格收缩大于0.2％，大于相应的块状材料中的晶格收缩。