Abstract The aerogel form of 0-5 wt.% of Li2O loaded NiFe2O4/SiO2 composite aerogel were successfully synthesized using the sol-gel process followed by the supercritical ethanol drying. The addition of small Li2O wt.% enhances the electrical conductivity of NiFe2O4/SiO2 composite aerogels. Based on the AC impedance analysis, the high conducting 5% Li2O + 95% [NiFe2O4/SiO2] composite aerogel with conductivity 2.1 × 10-11 S cm–1 was taken for the detailed analysis. We observed the maximum initial reversible discharge capacity of 930 mA h g-1, and it gradually fades to 370 mA h g-1 at 50th discharge. To elucidate the capacity-fading mechanism, the ex-situ X-ray Photoelectron Spectroscopy (XPS) technique is used to identify the chemical composition at different states of charge-discharge cycling. The capacity fading arises mainly from irreversible LixSiOy accumulation, which causes the loss of active lithium. Meanwhile, the metal to metal oxide conversion is partially reversible between Ni0 ↔ Ni2+, Fe0 ↔ Fe3+ during the subsequent cycles. To further support, the SEM images were taken for the respective electrodes, and the cell resistance and lithium diffusion coefficient (DLi+) was calculated from the electrochemical impedance spectroscopy (EIS) at the respective samples taken for ex-situ XPS analysis. The DLi+ gradually decreases from 1.8 × 10–13 cm2 s-1 to 9.6 × 10–14 cm2 s-1, and the cell resistance increases during the 1st to 10th discharge cycle. We conclude that the prolonged accumulation of irreversible LixSiOy phase will hinder the DLi+ in subsequent cycles, which leads to capacity-fading. The detailed results and electrochemical performance will be discussed.

中文翻译：

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锂离子电池用Li2O负载NiFe2O4/SiO2气凝胶负极的容量衰减机制：异位XPS分析

摘要 采用溶胶-凝胶法和超临界乙醇干燥法成功合成了 0-5 wt.% Li2O 负载的 NiFe2O4/SiO2 复合气凝胶。添加少量 Li2O wt.% 提高了 NiFe2O4/SiO2 复合气凝胶的电导率。基于交流阻抗分析，采用电导率为 2.1 × 10-11 S cm-1 的高导电率 5% Li2O + 95% [NiFe2O4/SiO2] 复合气凝胶进行详细分析。我们观察到最大初始可逆放电容量为 930 mAh g-1，并在第 50 次放电时逐渐衰减至 370 mAh g-1。为了阐明容量衰减机制，使用异位 X 射线光电子能谱 (XPS) 技术来识别不同充放电循环状态下的化学成分。容量衰减主要来自不可逆的 LixSiOy 积累，导致活性锂的损失。同时，在随后的循环中，金属到金属氧化物的转化在 Ni0 ↔ Ni2+、Fe0 ↔ Fe3+ 之间是部分可逆的。为了进一步支持，拍摄了各个电极的 SEM 图像，并从用于异位 XPS 分析的各个样品的电化学阻抗谱 (EIS) 计算了电池电阻和锂扩散系数 (DLi+)。DLi+ 从 1.8 × 10–13 cm2 s-1 逐渐降低到 9.6 × 10–14 cm2 s-1，并且在第 1 至第 10 次放电循环期间电池电阻增加。我们得出结论，不可逆 LixSiOy 相的长期积累将阻碍后续循环中的 DLi+，从而导致容量衰减。