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A lithium-rich manganese-based cathode material (LRMC) is currently considered as one of the most promising next-generation materials for lithium-ion batteries, which has received much attention, but the LRMC still faces some key scientific issues to break through, such as poor rate capacity, rapid voltage, capacity decay, and low first coulomb efficiency. In this work, homogeneous Li 2 ZrO 3 (LZO) was successfully coated on the surface of Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 (LRO) by molten salt-assisted sintering technology. Li 2 ZrO 3 has good chemical and electrochemical stability, which can effectively inhibit the side reaction between electrode materials and electrolytes and reduce the dissolution of transition metal ions. Thus, the as-prepared LRO@LZO composites are expected to improve the cycling performance. It can be found that the discharge specific capacity of LRO is 271 mAh g -1 at 0.1 C, and the capacity retention rate is still 93.7% after 100 cycles at 1 C. In addition, Li 2 ZrO 3 is an excellent lithium-ion conductor, which is prone to increasing the lithium-ion transfer rate and improving the rate capacity of LRO. Therefore, this study provides a new solution to improve the structure stability and electrochemical performance of LRMCs.

The poor electronic conductivity of Na 2 FeSiO 4 always limits its electrochemical reactivities and no effective solution has been found to date. Herein, the novel Ni-substituted Na 2 Fe 1- x Ni x SiO 4 @C nanospheres (50-100 nm) encapsulated with a 3D hierarchical porous skeleton (named as alveolation-like configuration) constructed using in situ carbon are first synthesized via a facile sol-gel method, and the effects of Ni substitution combined with the design of a unique carbon network on Na-storage properties are assessed systematically, focusing on alleviating the inherent defects of the Na 2 FeSiO 4 cathode material. A series of characterization technologies such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and so forth, coupled with the electrochemical measurements and first-principles calculations, are used to explore the structure, morphology and electrochemical behaviors of the as-prepared materials. The results show that the synergism between Ni substitution and the special alveolation-like configuration enables fast Na ions mobility (from 10 -14 to 10 -12 cm 2 s -1 ), reduces band gap energy (from 2.82 to 1.79 eV) and lowers Na-ion diffusion barriers, finally reciprocating the vigorous electrochemical kinetics of the electrode. Especially, the elaborately designed material-Na 2 Fe 0.97 Ni 0.03 SiO 4 @C-displays superior Na-storage properties of around 197.51 mA h g -1 (corresponding to 1.43 Na + intercalation) at 0.1 C within 1.5-4.5 V along with desirable capacity retention (84.44% after 100 cycles), and the rate capability is also markedly enhanced (a capacity of 133.62 mA h g -1 at 2 C). Such the effective methodology employed in this work opens a potential pathway to synthesize the silicate cathode material with excellent electrochemical properties.

Na 2 FeSiO 4 , as one of the promising cathode materials in sodium-ion batteries, has attracted great interests. However, studies on the kinetic behaviors of Na ions insertion/extraction in Na 2 FeSiO 4 composite electrode have been barely considered, until now. Importantly, the specific capacity and rate capability of Na 2 FeSiO 4 cathode materials are greatly correlated with the kinetics of Na + transfer in the host material. Herein, on the basis of the characterizations of microstructure and morphologies (i.e., Rietveld refinement, FESEM, HRTEM, etc.), the electrochemical kinetics of Na ions extraction in Na 2 FeSiO 4 /C electrode are first studied in detail via two electrochemical techniques (EIS and GITT), establishing the rate-controlling steps of Na + transport in Na 2 FeSiO 4 /C, evaluating series of kinetic parameters, as well as calculating the Na + diffusion coefficient at various state-of-desodiation. Changes of impedance response of Na 2 FeSiO 4 /C electrode depending on the different levels of desodiation show that a serial features of electrode process for Na ions migration have tremendous discrepancies, indicating that the kinetics of Na + extraction from Na 2 FeSiO 4 /C electrode are largely influenced by different electrode reaction processes. These results provide useful insight into the inner properties of Na 2 FeSiO 4 /C electrode, and it is significant to optimize the electrochemical performance of Na 2 FeSiO 4 /C. Moreover, two models of equivalent circuits are also constructed to simulate the electrode processes and describe the behaviors of Na ions transfer in Na 2 FeSiO 4 /C.