Abstract Iron oxalate (FeC2O4), a promising anode material for lithium ion batteries (LIBs), is typically crystallized in orthorhombic-type phase. When the synthesis temperature rises, β-FeC2O4·H2O can transform into high-crystalline α-phase. At present, the detail evolution mechanism of crystal structure for two kinds of iron oxalate polymorphs is seldom studied. Through in-depth experiments, the tunable polymorph and morphology of iron oxalate can be obtained by controlling certain conditions. The oxalic acid complex ([Fe(C2O4) x]−2(x−1)), as unstable intermediate state, can change the reaction thermodynamics and kinetics, thus promoting the nucleation and growth of crystals. Higher temperature and longer reaction time would availably reinstitute stable hydrogen bonds and enhance the disordered state between successive stack layers, then resulting in various morphologies and phase-transition process. Due to short diffusion path and stable effective channels for Li+ ions, the mixed state of iron oxalate exhibits higher reversible capacity and more excellent cycling stability. Understanding the phase evolution mechanism of iron oxalate is critical to controllable synthesis, and ultimately, enhancing the performance of future LIBs.

中文翻译：

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作为锂离子电池负极材料的草酸铁纳米颗粒的可调多晶型和形态合成

摘要 草酸铁 (FeC2O4) 是一种很有前途的锂离子电池 (LIB) 负极材料，通常以正交型相结晶。当合成温度升高时，β-FeC2O4·H2O可转变为高晶α相。目前，对两种草酸铁多晶型物晶体结构的详细演化机制研究甚少。通过深入实验，通过控制一定的条件，可以获得可调节的草酸铁多晶型物和形貌。草酸络合物([Fe(C2O4) x]-2(x-1))作为不稳定的中间态，可以改变反应热力学和动力学，从而促进晶体的成核和生长。更高的温度和更长的反应时间将有效地重新建立稳定的氢键并增强连续堆叠层之间的无序状态，然后导致各种形态和相变过程。由于Li+离子的短扩散路径和稳定的有效通道，草酸铁的混合态表现出更高的可逆容量和更优异的循环稳定性。了解草酸铁的相演化机制对于可控合成至关重要，并最终提高未来 LIB 的性能。