Design, Preparation And Electrochemical Performance Of Advanced Anodes For Lithium-ion Batteries

Nowadays, the burgeoning developments of multi-functional electronic devices and electrical vehicles have stimulated increasing appetites for studies of lithium-ion batteries (LIBs) with higher performance. As for anode materials, commercial graphite cannot satisfy such demanding criteria of high energy-power density due to the low capacity and inferior rate ability. Amongst the next generation anodes, metal carbonates and Sn-based materials have attracted intensive attention owing to their-merits such as high capacity and low cost. However, it is a great challenge to realize both classes in practical application. One hand, different from the insertion/extraction mechanism, these materials are trapped in large volume expansion during charge-discharge process, which causes the deviation of structural integrity, rupture of SEI and cyclic instability. On the other hand, bulk structures induced by uncontrollable syntheses usually lead to inferior performance under fast rates.Herein, we present rational design and exploration of high-performed advanced anode materials from single-phase, hybrid structure and electrode architecture scope, which are all prepared through facile methods. From elaborative analyses on element, structure, synthetic mechanism and electrochemistry, we disclose the advantages of as-designed structures on Li-storage, thus proposing several general material and electrode structures for advanced LIBs anodes.Based on FeCO3 materials, a novel hollow micro/nano structure (FeCO3-HMS) has been prepared via classical Ostwald ripening, which overcomes the low performance of bulk phase FeCO3. FeCO3-HMS demonstrates a hollow structure consisted by numerous 1D nanofibers, together with void interiors and porous shells. 1D nanofibers and thin shells furnish shorter Li-ion diffusion path, while hollow void and porous structure largely alleviate structural expansion during charge-discharge. In consequence, FeCO3-HMS shows high capacity of over 1000 mAh g-1 at 50 mA g-1 and achieves capacity of 722 mAh g-1 with superior 200-cycle stability at 200 mA g-1In order to attain better rate performance, a 2D hybrid structure with ultrasmall Sn particles confined in N-rich carbon nanosheets (Sn@GCNS) has been rationally designed and prepared. During synthetic process, Sn nanoparticles are controlled down to 2 nm and confined into GCNS by in situ Sn growth and g-CsN4 soft-template, respectively. Ex situ AFM measurement verifies the robust structural integrity and the negligible thickness change during charge-discharge of Sn@GCNS, which overcomes the common cyclic instability induced by large volume expansion. Further, we introduces temperature-dependent method to control the doping content and found optimized doping content (13.28 wt.%), which also disclose the improvement on conductivity and Li-storage resulting from N-doping. Sn@GCNS reaches high capacity of 835 mAh g-1 at 0.2 A g-1, and remains excellent retention of 85% after 1000 cycle at 0.8 A g-1, indicating a favorable cyclic stability and rate capability.In order to obtain high-power LIBs anodes, we present a facile fabrication of orderly-packed electrode. We incorporate a materials scope design of large-area graphene (LG) composite, which leads to the desirable structure through universal doctor-blade method benefiting from the large contact area. Compared with the loosely-arranged electrode architecture of small-area graphene (SG), MnCO3-LG forms orderly-packed electrode with alternating layered arrangement owing to the large contact and facile orientation with current collector. Such orderly-packed electrode also facilitates continuous electron conductive matrix and effective ion transportation, rendering high electrochemical performance under high rate. As expected, capacity of MnCO3-LG electrode increases to high value of 1350 mAh g-1 owing to the rising valence of MnⅡ. Even under up-rated current of 10 A g-1, it still remains 420 mAh g-1. Stunningly, the capacity could reach as high as 1000 mAh g-1 without any retention for 1100 cycles. The MnCO3-LG orderly-packed electrode discloses the application of large-area graphene in LIBs, and represents simultaneous achievement of high capacity, high power and excellent stability.The presented hierarchically hollow micro/nano structure, ultrasmall particle embedded model and orderly packed electrode architecture can be regarded as general structure for the rational design of other new-type battery-anode. Meanwhile, their structural advantages can be extended to other realms, such as energy conversion and catalysis field.