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b-Axis Phase Boundary Movement Induced (020) Plane Cracking in LiFePO4.
ACS Applied Materials & Interfaces ( IF 8.3 ) Pub Date : 2020-08-07 , DOI: 10.1021/acsami.0c10838 Junjie Fu 1 , Kuan Wang 1 , Danmin Liu 1 , Zhenlu Zhang 2 , Manling Sui 1 , Pengfei Yan 1
ACS Applied Materials & Interfaces ( IF 8.3 ) Pub Date : 2020-08-07 , DOI: 10.1021/acsami.0c10838 Junjie Fu 1 , Kuan Wang 1 , Danmin Liu 1 , Zhenlu Zhang 2 , Manling Sui 1 , Pengfei Yan 1
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Phase boundary movement accomplishing reversible LiFePO4/FePO4 biphasic transition is a fundamental Li-ion intercalation/deintercalation mechanism for LiFePO4 cathode. Phase boundary energetically favors crack nucleation and propagation; thus, postmortem observation on cracks becomes a feasible approach to investigate the phase-transition behavior and the Li-ion diffusion mechanism. The previously observed (200) plane cracks facilitate the “domino” diffusion model. Herein, our microscopic observations reveal another type of cracks along the (020) planes in a commercial LiFePO4 cathode cycled at moderate rates (0.1C, 0.33C, and 1C). Such (020) plane cracks are more detrimental to electrochemical performance because they can cut off the Li-ion diffusion pathway, causing inactive segments of LiFePO4. The (020) plane cracks indicate the LiFePO4/FePO4 phase boundary is along the (020) plane and moving along the b-axis during battery operation, which is a typical bulk diffusion-limited Li-ion diffusion behavior. Our observations stress that large LiFePO4 primary particle (>200 nm) not only aggravates cracking degradation but also switches the Li-ion diffusion mode to a slow bulk diffusion mechanism, plunging the overall battery performance.
中文翻译：
LiFePO4中的b轴相边界移动引起（020）平面裂纹。
完成可逆LiFePO 4 / FePO 4双相转变的相界移动是LiFePO 4阴极的基本锂离子嵌入/脱嵌机制。相界在能量上有利于裂纹的形核和扩展。因此，事后观察裂纹成为研究相变行为和锂离子扩散机理的可行方法。先前观察到的（200）平面裂纹促进了“多米诺”扩散模型。在这里，我们的显微镜观察揭示了商用LiFePO 4中沿（020）平面的另一种类型的裂纹阴极以中等速率（0.1C，0.33C和1C）循环。这样的（020）平面裂纹对电化学性能更有害，因为它们会切断锂离子扩散途径，从而导致LiFePO 4的惰性链段。（020）平面裂纹表示LiFePO 4 / FePO 4相界沿电池运行期间的（020）平面并沿b轴移动，这是典型的体扩散受限的锂离子扩散行为。我们的观察结果强调，较大的LiFePO 4初级粒子（> 200 nm）不仅会加剧裂纹降解，还会将Li离子扩散模式切换为缓慢的整体扩散机制，从而降低了整体电池性能。
更新日期：2020-09-02
中文翻译：
LiFePO4中的b轴相边界移动引起（020）平面裂纹。
完成可逆LiFePO 4 / FePO 4双相转变的相界移动是LiFePO 4阴极的基本锂离子嵌入/脱嵌机制。相界在能量上有利于裂纹的形核和扩展。因此，事后观察裂纹成为研究相变行为和锂离子扩散机理的可行方法。先前观察到的（200）平面裂纹促进了“多米诺”扩散模型。在这里，我们的显微镜观察揭示了商用LiFePO 4中沿（020）平面的另一种类型的裂纹阴极以中等速率（0.1C，0.33C和1C）循环。这样的（020）平面裂纹对电化学性能更有害，因为它们会切断锂离子扩散途径，从而导致LiFePO 4的惰性链段。（020）平面裂纹表示LiFePO 4 / FePO 4相界沿电池运行期间的（020）平面并沿b轴移动，这是典型的体扩散受限的锂离子扩散行为。我们的观察结果强调，较大的LiFePO 4初级粒子（> 200 nm）不仅会加剧裂纹降解，还会将Li离子扩散模式切换为缓慢的整体扩散机制，从而降低了整体电池性能。
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