Sodium-ion batteries are increasingly recognized as ideal for large-scale energy storage applications. Alluaudite Na 2+2 δ Fe 2− δ (SO 4 ) 3 has become one of the focused cathode materials in this field. However, previous studies employing aqueous-solution synthesis often overlooked the formation mechanism of the impurity phase. In this study, the nonequilibrium evolution mechanism between Na 2+2 δ Fe 2− δ (SO 4 ) 3 and impurities by adjusting ratios of the Na 2 SO 4 /FeSO 4 ·7H 2 O in the binary system is investigated. Then an optimal ratio of 0.765 with reduced impurity content is confirmed. Compared to the poor electrochemical performance of the Na 2.6 Fe 1.7 (SO 4 ) 3 (0.765) cathode, the optimized Na 2.6 Fe 1.7 (SO 4 ) 3 @CNTs (0.765@CNTs) cathode, with improved electronic and ionic conductivity, demonstrates an impressive discharge specific capacity of 93.8 mAh g −1 at 0.1 C and a high-rate capacity of 67.84 mAh g −1 at 20 C, maintaining capacity retention of 71.1% after 3000 cycles at 10 C. The Na 2.6 Fe 1.7 (SO 4 ) 3 @CNTs//HC full cell reaches an unprecedented working potential of 3.71 V at 0.1 C, and a remarkable mass-energy density exceeding 320 Wh kg −1 . This work not only provides comprehensive guidance for synthesizing high-voltage Na 2+2 δ Fe 2− δ (SO 4 ) 3 cathode materials with controllable impurity content but also lays the groundwork of sodium-ion batteries for large-scale energy storage applications.
Kailin Chi,Yuechen Zhai,Yao Wang,Xin Zhang,Fucheng Liang,Shibo Wang
The achievement of complete conversion of PbBr 2 films presents a significant challenge in the development of CsPbBr 3 films with consistent growth, comprehensive coverage, and controllable components. To address this challenge, introducing a porous structure in the planar PbBr 2 film is advantageous for facilitating the immersion of CsBr precursor, thereby reducing impurity phase formation and mitigating strain caused by the film volume expansion. In order to accomplish this, indium tribromide (InBr 3 ) was employed as an additive and the InBr 3 (DMF) 3 adduct was utilized to expedite the release of organic molecules in PbBr 2 (DMF), resulting in the transformation of planar PbBr 2 film into porous structures. The growth orientation of PbBr 2 crystals was altered by this transformation, effectively suppressing the generation of metallic Pb impurities in the film. Additionally, it not only optimizes the morphology of CsPbBr 3 film but also reduces impurity phase. As a result, the InBr 3 :CsPbBr 3 perovskite solar cell achieved an efficiency of 7.28 %. The majority of In 3+ ions were concentrated near the buried interface between SnO 2 and InBr 3 :CsPbBr 3 , leading to significant improvements in both non-radiative recombination defect states within the perovskite film and electron injection and collection capabilities within the device.
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