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100 results on '"Rajagopalan, Ranjusha"'

30. Turn “Waste” into Wealth: A Facile Reviving Strategy for Degraded Ni-Rich LiNi0.8Co0.1Mn0.1O2Cathodes

Author

Zhang, Shan, Feng, Ze, Rajagopalan, Ranjusha, Sun, Dan, Huang, Chenghuan, Tang, Yougen, Yan, Qunxuan, Ren, Yurong, and Wang, Haiyan

Abstract

Ni-rich layered cathodes have been regarded as one of the high-priority materials, but their commercial application was limited by the highly active surfaces, poor thermal stability, and irreversible phase transition. Furthermore, when they are stored in moist air, the particles can easily form an impurity layer of Li2CO3/LiOH. This inert substance hinders the transmission of lithium ions and electrons, leading to electrochemical performance deterioration. Herein, we report a simple method, namely, metaphosphate repair, which can successfully restore the degraded LiNi0.8Co0.1Mn0.1O2(NCM811) cathode materials and form an in situ multifunctional hybrid repaired layer of Li3PO4-YPO4-Y(PO3)3on the secondary particle. The repaired NCM811 delivers a discharge capacity of 171.7 mAh g–1after 100 cycles, which is much higher than those of pristine (147.6 mAh g–1) and stored degraded (116.2 mAh g–1) samples. Moreover, the restored sample could deliver a capacity retention of 92.3% after 100 cycles at 1C along with a better initial Coulombic efficiency (CE) of 88.4%. This study provides a facile strategy to revive degraded Ni-rich cathode materials and other similar layered oxide cathodes for advanced batteries.

Published
2022
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36. Dual-Element-Modified Single-Crystal LiNi0.6Co0.2Mn0.2O2as a Highly Stable Cathode for Lithium-Ion Batteries

Author

Feng, Ze, Zhang, Shan, Rajagopalan, Ranjusha, Huang, Xiaobing, Ren, Yurong, Sun, Dan, Wang, Haiyan, and Tang, Yougen

Abstract

Single-crystalline LiNi0.6Co0.2Mn0.2O2cathodes have received great attention due to their high discharge capacity and better electrochemical performance. However, the single-crystal materials are suffering from severe lattice distortion and electrode/electrolyte interface side reactions when cycling at high voltage. Herein, a unique single-crystal LiNi0.6Co0.2Mn0.2O2with Al and Zr doping in the bulk and a self-formed coating layer of Li2ZrO3in the surface has been constructed by a facile strategy. The optimized cathode material exhibits excellent structural stability and cycling performance at room/elevated temperatures after long-term cycling. Specifically, even after 100 cycles (1C, 3.0–4.4 V) at 50 °C, the capacity retention for the Al and Zr co-doped sample reaches 92.1%, which is much higher than those of the single Al-doped (85.4%), single Zr-doped (87.1%), and bare samples (76.3%). The characterization results and first-principles calculations reveal that the excellent electrochemical properties are attributed to the stable structure and interface, in which the Al and Zr co-doping hinders cation mixing and suppresses detrimental phase transformations to reduce internal stress and mitigate microcracks, and the coating layer of Li2ZrO3can protect the surface and suppress interfacial parasitic reactions. Overall, this work provides important insights into how to simultaneously build a stable bulk structure and interface for the single-crystal NCM cathode via a facile preparation process.

Published
2021
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37. A Three in One Strategy to Achieve Zirconium Doping, Boron Doping, and Interfacial Coating for Stable LiNi0.8Co0.1Mn0.1O2 Cathode.

Author

Feng, Ze, Rajagopalan, Ranjusha, Zhang, Shan, Sun, Dan, Tang, Yougen, Ren, Yu, and Wang, Haiyan

Subjects
*BORON, *ZIRCONIUM, *CATHODES, *ZIRCONIUM boride, *CRYSTAL surfaces, *DENSITY functional theory, *CALCINATION (Heat treatment)
Abstract

LiNi0.8Co0.1Mn0.1O2 cathodes suffer from severe bulk structural and interfacial degradation during battery operation. To address these issues, a three in one strategy using ZrB2 as the dopant is proposed for constructing a stable Ni‐rich cathode. In this strategy, Zr and B are doped into the bulk of LiNi0.8Co0.1Mn0.1O2, respectively, which is beneficial to stabilize the crystal structure and mitigate the microcracks. Meanwhile, during the high‐temperature calcination, some of the remaining Zr at the surface combined with the surface lithium source to form lithium zirconium coatings, which physically protect the surface and suppress the interfacial phase transition upon cycling. Thus, the 0.2 mol% ZrB2‐LiNi0.8Co0.1Mn0.1O2 cathode delivers a discharge capacity of 183.1 mAh g−1 after 100 cycles at 50 °C (1C, 3.0–4.3 V), with an outstanding capacity retention of 88.1%. The cycling stability improvement is more obvious when the cut‐off voltage increased to 4.4 V. Density functional theory confirms that the superior structural stability and excellent thermal stability are attributed to the higher exchange energy of Li/Ni exchange and the higher formation energy of oxygen vacancies by ZrB2 doping. The present work offers a three in one strategy to simultaneously stabilize the crystal structure and surface for the Ni‐rich cathode via a facile preparation process. [ABSTRACT FROM AUTHOR]

Published
2021
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41. Improved Reversibility of Fe3+/Fe4+ Redox Couple in Sodium Super Ion Conductor Type Na3Fe2(PO4)3 for Sodium‐Ion Batteries

Author

Rajagopalan, Ranjusha, primary, Chen, Bo, additional, Zhang, Zhicheng, additional, Wu, Xing‐Long, additional, Du, Yonghua, additional, Huang, Ying, additional, Li, Bing, additional, Zong, Yun, additional, Wang, Jie, additional, Nam, Gwang‐Hyeon, additional, Sindoro, Melinda, additional, Dou, Shi Xue, additional, Liu, Hua Kun, additional, and Zhang, Hua, additional

Published
2017
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50. Facile synthesis of a reduced graphene oxide wrapped porous NiCo2O4 composite with superior performance as an electrode material for supercapacitors.

Author

Al-Rubaye, Shaymaa, Rajagopalan, Ranjusha, Dou, Shi Xue, and Cheng, Zhenxiang

Abstract

Even though NiCo2O4 is considered to be one of the most promising materials for supercapacitor applications, its unsatisfactory rate performance and cycling stability, due to inherently low electrical conductivity, have limited its further growth as a supercapacitor electrode. The present study tries to profitably exploit reduced graphene oxide (rGO) nanosheets as a conducting unit to enhance the electronic conductivity, by a simple hydrothermal technique assisted by ammonia hydroxide, to improve the overall electrochemical performance of NiCo2O4 in supercapacitors. The as-prepared NiCo2O4–rGO nanocomposite consists of NiCo2O4 hexagons wrapped in conducting rGO sheets, which ensure a short ion diffusion distance, percolating electron conducting pathways, and stable structural integrity. Such a feasible design provides good synergism between the rGO and the NiCo2O4, resulting in better electrochemical performance. As a result, this nanocomposite displays impressive overall electrochemical performance, in aspects such as promising capacitance (1185 F g−1 at a current density of 2 A g−1) and remarkable cycling stability (98% capacitance retention after 10 000 charge–discharge cycles at 2 A g−1). This facile method could be beneficial for preparing similar materials that require high electronic conductivity. [ABSTRACT FROM AUTHOR]

Published
2017
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