Lithium capacity fading mechanism

Arora P, White RE et al (1998) Capacity fade mechanisms and side reactions in lithium-ion batteries. J Electrochem Soc 145 3647-3667... 

To further improve the mechanical and electrical stability of silicon-based anodes, a hierarchical bottom-up approach (Fig. 15.12) was successfully utilized to develop a three-dimensional nanostructured silicon/carbon porous composite [89]. The existence of pores in the composite granules provides sufficient space to accommodate silicon expansion during lithium insertion. CVD deposition of silicon clusters (Fig. 15.12b) avoids formation of SiO thus reducing the first cycle, irreversible capacity. A high specific capacity of 1,950 mAh/g (C/20 rate) based on the total weight of the silicon/carbon composite was reported. In addition, the composite anodes had negligible capacity fade after 100 cycles at 1C rate and excellent rate capability (870 mAh/g at 8C rate). 

Peabody C, Arnold CB (2011) The role of mechanically induced separator creep in lithium-ion battery capacity fade. J Power Sources 196 8147-8153. doi 10.1016/j.jpowsour.2011.05.023... 

This mechanism does not require positive electrode weight loss, Jahn-Teller distortion," or lattice contraction. Consistent with this mechanism, analysis of C/LiMn204 cells cycled at 45°C found the majority (75%) of the immobilized lithium within the graphite negative electrode, the remainder (25%) was found within the positive electrode, implicating involvement of the negative electrode in spinel cell capacity fade. 

All the above mechanisms have some shortcomings. For example, voltage hysteresis and capacity fading cannot be convincingly explained. Therefore, the mechanism of lithium storage in micropores has gradually become accepted as the most reasonable and is currently widely accepted as a working model. 

Observations based on the alloy-type mechanism have shown that the reversible capacity of composite Sn oxides fades with cycling. In contrast, with the ionic-type mechanism, only slow capacity fading was observed with cycling. Using Li NMR (with LiCl solution as a reference), it was shown that the ionic nature of the inserted lithium is more than that for other negative electrode materials (Table 8.1). This indicates that ionic-type mechanisms may be possible. 

Apparently, the lithium oxide, by surrounding the tin particles, creates a sufficient amount of free volume to accommodate the mechanical stresses experienced by the metal during the alloy formation-decomposition process. This greatly improves the cycling performance albeit some capacity fade, due to the occurrence of tin particle aggregation, may stUl be observed over prolonged cycle tests. [31]. 

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