锂离子电池的明星材料磷酸铁锂:基本性能、优化改性及未来展望

LiFePO (LFP), an important member of the olivine-type lithium transition metal phosphate family, is currently regarded as one of the most successful commercialized cathode materials for lithium-ion batteries due to its prominent merits, including low cost, high safety, environmental friendliness, abundant resource, stable crystal structure, flat voltage profile, etc. However, its stable crystal structure leads to low electronic conductivity (10-10 S•cm) and lithium ions mobility (10-10 cm•s), which severely limit its electrochemical perfor-mance. In this regard, overcoming the intrinsic bottlenecks of material and elevating its reversible capacity as well as rate capability, have become one of the hot topics in the field of energy storage devices. On the one hand, continuous efforts devoted in fundamental researches have made us a more clear understanding over LFP and analogous materials, and provided a theoretical basis for further optimization and modification of LFP. On the other hand, the electrochemical performance of commercial production of LFP prepared via solid phase methods, the most commonly used ones at present, still has tremendous potential for enhancement. Consequently, improving the production process or developing new industrialized preparation technologies are of significant concern both in academic and in industry. In recent years, researchers have achieved fruitful results in the modification and optimization of LFP by adopting a variety of optimization strategies:Ⅰ. structural nanosizing; Ⅱ. coating with advanced carbon materials, Ⅲ. crystal orientation engineering; Ⅳ. in-situ carbon coating, Ⅴ. suppressing or eliminating defects, Ⅵ. ions doping and Ⅶ. quantum dots modification, etc. Indeed, achieving superior electrochemical performance of LFP-based composites requires affective combination of multiple methodologies, and it is unadvisable to expect to make breakthrough with a single approach. Moreover, for lithium ions migrate with single diffusion channels along the b-axis in LFP bulk phase, preparing LFP with (010) crystal planes preferred orientation is beneficial to shorten the transmission distance of lithium ions, thus increasing de-intercalation/intercalation sites and in turns enhancing reaction kinetics. In this respect, the crystal orientation engineering has been a crucial strategy for further improving the performances of LFP. Besides, with the deepening of the basic research of LFP, a series of significant progresses have been made in the dynamic processes, such as lithium ions delithiation/relithiation, transportation, reaction mechanism and material structure evolution. Based on the research exploring of crystal structure of olivine lithium iron phosphate (Pnma), this paper provides a systematical summary over the lithium ions diffusion in LFP crystal, the characteristic of (010) crystal plane and its influence on electrochemical performances, as well as a thorough review of the seven aspects. Furthermore, it also points out the research directions and perspectives of LFP in the near future, involving mechanism research and applied research.