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Understanding of the Irreversible Phase Transition and Zr-Doped Modification Strategy for a Nickel-Rich Cathode under a High Voltage
ACS Sustainable Chemistry & Engineering ( IF 7.1 ) Pub Date : 2022-03-11 , DOI: 10.1021/acssuschemeng.1c08633 Chen Wu 1 , Rong Li 1 , Ting Chen 1 , Tianzhao Hu 2 , Daqiang Wang 1 , Lang Qiu 1 , Benhe Zhong 1 , Zhenguo Wu 1 , Xiaodong Guo 1
ACS Sustainable Chemistry & Engineering ( IF 7.1 ) Pub Date : 2022-03-11 , DOI: 10.1021/acssuschemeng.1c08633 Chen Wu 1 , Rong Li 1 , Ting Chen 1 , Tianzhao Hu 2 , Daqiang Wang 1 , Lang Qiu 1 , Benhe Zhong 1 , Zhenguo Wu 1 , Xiaodong Guo 1
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Increasing the nickel content and broadening the voltage window are important means for LiNixCoyMn1–x–yO2 layered cathodes with low cost and high energy density, but these nickel-rich cathodes often suffer from structural instability and unsatisfactory cyclic performance. The systematic and detailed degradation mechanism especially under a high voltage is still unclear, which hinders the further development of nickel-rich cathodes. Our results show that due to the migration of high valence nickel ions to lithium sites, especially upon the deep removal of Li+ ions, the nickel-rich cathode undergoes an irreversible phase transformation from a layered structure to a spinel or even rock-salt phase. Such irreversible phase transitions within a wide voltage window would cause insufficient lithium utilization and voltage decay, finally deteriorating the electrochemical performance of nickel-rich cathodes. In a narrow voltage range of 3.0–4.3 V, the capacity retention of the Ni-rich cathode is 93.4%, and the voltage fading is only 40 mV after 250 cycles. However, the cathode only exhibits a capacity retention of 77.4% with a significant voltage decay over 180 mV, as the voltage range further extends to 3.0–4.6 V. Furthermore, various characterizations and electrochemical performances demonstrate that the strengthened metal–oxygen bonds in the transition layer can produce stable structures and suppress phase transitions, thereby displaying superior electrochemical performance in the widened voltage window. As a result, the cycling retention of a Zr-doped cathode reaches 84.5%, and the voltage decay is only 50 mV after 250 cycles at 3.0–4.6 V, which exhibits excellent long-term cycle performance. These insights provide guidance for understanding the electrochemical mechanism and the design of high-voltage cathode materials.
中文翻译：
了解高电压下富镍阴极的不可逆相变和 Zr 掺杂改性策略
提高镍含量和拓宽电压窗口是获得低成本、高能量密度的LiNi x Co y Mn 1- x - y O 2层状正极的重要手段，但这些富镍正极往往存在结构不稳定和循环性能不理想的问题. 系统和详细的降解机制，尤其是在高压下，目前还不清楚，这阻碍了富镍正极的进一步发展。我们的结果表明，由于高价镍离子迁移到锂位点，特别是在深度去除 Li +离子，富镍阴极经历了从层状结构到尖晶石甚至岩盐相的不可逆相变。这种在宽电压窗口内不可逆的相变会导致锂利用率不足和电压衰减，最终降低富镍正极的电化学性能。在3.0~4.3 V的窄电压范围内，富镍正极的容量保持率为93.4%，250次循环后电压衰减仅为40 mV。然而，随着电压范围进一步扩大到 3.0-4.6 V，正极仅表现出 77.4% 的容量保持率，电压衰减超过 180 mV。此外，各种表征和电化学性能表明，过渡层中强化的金属-氧键可以产生稳定的结构并抑制相变，从而在加宽的电压窗口中表现出优异的电化学性能。结果，Zr掺杂正极的循环保持率达到84.5%，在3.0-4.6 V下循环250次后电压衰减仅为50 mV，表现出优异的长期循环性能。这些见解为理解电化学机制和高压正极材料的设计提供了指导。表现出优异的长期循环性能。这些见解为理解电化学机制和高压正极材料的设计提供了指导。表现出优异的长期循环性能。这些见解为理解电化学机制和高压正极材料的设计提供了指导。
更新日期：2022-03-11
中文翻译：
了解高电压下富镍阴极的不可逆相变和 Zr 掺杂改性策略
提高镍含量和拓宽电压窗口是获得低成本、高能量密度的LiNi x Co y Mn 1- x - y O 2层状正极的重要手段，但这些富镍正极往往存在结构不稳定和循环性能不理想的问题. 系统和详细的降解机制，尤其是在高压下，目前还不清楚，这阻碍了富镍正极的进一步发展。我们的结果表明，由于高价镍离子迁移到锂位点，特别是在深度去除 Li +离子，富镍阴极经历了从层状结构到尖晶石甚至岩盐相的不可逆相变。这种在宽电压窗口内不可逆的相变会导致锂利用率不足和电压衰减，最终降低富镍正极的电化学性能。在3.0~4.3 V的窄电压范围内，富镍正极的容量保持率为93.4%，250次循环后电压衰减仅为40 mV。然而，随着电压范围进一步扩大到 3.0-4.6 V，正极仅表现出 77.4% 的容量保持率，电压衰减超过 180 mV。此外，各种表征和电化学性能表明，过渡层中强化的金属-氧键可以产生稳定的结构并抑制相变，从而在加宽的电压窗口中表现出优异的电化学性能。结果，Zr掺杂正极的循环保持率达到84.5%，在3.0-4.6 V下循环250次后电压衰减仅为50 mV，表现出优异的长期循环性能。这些见解为理解电化学机制和高压正极材料的设计提供了指导。表现出优异的长期循环性能。这些见解为理解电化学机制和高压正极材料的设计提供了指导。表现出优异的长期循环性能。这些见解为理解电化学机制和高压正极材料的设计提供了指导。
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