No abstract

A 3D-printing technology and printed 3D lithium-ion batteries (3D-printed LIBs) based on LiMn 0.21 Fe 0.79 PO 4 @C (LMFP) nanocrystal cathodes are developed to achieve both ultrahigh rate and high capacity. Coin cells with 3D-printed cathodes show impressive electrochemical performance: a capacity of 108.45 mAh g −1 at 100 C and a reversible capacity of 150.21 mAh g −1 at 10 C after 1000 cycles. In combination with simulation using a pseudo 2D hidden Markov model and experimental data of 3D-printed and traditional electrodes, for the fi rst time deep insight into how to achieve the ultrahigh rate performance for a cathode with LMFP nanocrystals is obtained. It is estimated that the Li-ion diffusion in LMFP nanocrystal is not the rate-limitation step for the rate to 100 C, however, that the electrolyte diffusion factors, such as solution intrinsic diffusion coeffi cient, effi ciency porosity, and electrode thickness, will dominate ultrahigh rate performance of the cathode. Furthermore, the calculations indicate that the above factors play important roles in the equivalent diffusion coeffi cient with the electrode beyond a certain thickness, which determines the whole kinetic process in LIBs. This fundamental study should provide helpful guidance for future design of LIBs with superior electrochemical performance.

We synthesized a core-shell structure with graphene as the shell and nano-hollow γ-Fe2O3 as the core through a Kirkendall process at room temperature. When this hybrid is used as an anode material for lithium-ion batteries, it exhibits a remarkable electrochemical performance: a high reversible capacity of 1095, 833, and 551 mA h g(-1) at the current rates of 0.1 C, 1 C, and 2 C, respectively. When evaluated at 10 C, the capacity can still reach 504 mA h g(-1).

Specific capacity and cyclic performance are critically important for the electrode materials of rechargeable batteries. Herein, a capacity boost effect of Li- and Na-ion batteries was presented and clarified by nitrogen-doped graphene sheets. The reversible capacities progressively increased from 637.4 to 1050.4 mAh g (164.8% increase) in Li-ion cell tests from 20 to 185 cycles, and from 187.3 to 247.5 mAh g (132.1% increase) in Na-ion cell tests from 50 to 500 cycles. The mechanism of the capacity boost is proposed as an electrochemical induced cascading evolution of graphitic N to pyridinic and/or pyrrolic N, during which only these graphitic N adjacent pyridinic or pyrrolic structures can be taken precedence. The original and new generated pyridinic and pyrrolic N have strengthened binding energies to Li/Na atoms, thus increased the Li/Na coverage and delivered a progressive capacity boost with cycles until the entire favorable graphitic N transform into pyridinic and pyrrolic N.

Maghemite (γ-Fe2O3) nanocrystalline microspheres (MNMs) self-assembled with 52 nm nanocrystals bridged with FeOOH around grain boundaries were formed by solvothermal reaction and thermal oxidation. The unique architecture endows the MNMs with the lithium storage behavior of a hybrid battery-supercapacitor electrode: initial charge capacity of 1060 mAh g(-1) at the 100 mA g(-1) rate, stable cyclic capacity of 1077.9 mAh g(-1) at the same rate after 140 cycles, and rate capability of 538.8 mAh g(-1) at 2400 mA g(-1). This outstanding performance was attributed to the nanocrystal superiority, which shortens the Li(+) diffusion paths. The mechanism of this hybrid anode material was investigated with experimental measurements and structural analysis. The results indicate that at the first discharge, the MNM nanocrystal microsphere, whose structure can buffer the volume change that occurs during lithiation/delithiation, goes through four stages: Li(+) insertion in cation vacancies, spinel-to-rocksalt transformation, Li(+) intercalation of Li(1.75+x)Fe2O3 nanocrystals, and interfacial Li storage around nanocrystal boundaries. Only the latter two stages were reversible at and after the second charging/discharging cycle, exhibiting the hybrid behavior of a battery-supercapacitor with superior lithium storage.