摘要
由于钠资源丰富,钠离子电池在大规模储能方面显示出巨大的潜力.随着近年来研究的深入,在正极材料中引入适量的阴离子氧化还原可以有效地提升钠离子电池的能量密度,同时减少高成本过渡金属元素如V、Co和Ni等的用量.有研究表明,材料循环过程中不可逆的氧损失以及Mn4+/Mn3+氧化还原的激活,导致了层状氧化物正极材料持续的电压衰减.本工作通过在Nax[Li,Ni,Mn]O2基钠离子电池正极材料中引入Ni3+作为Mn4+/Mn3+氧化还原屏障,利用Ni3+/Ni2+的氧化还原代替Mn4+/Mn3+的氧化还原,成功抑制了材料的电压衰减.电化学测试结果显示,改性材料在不损失容量的前提下,循环稳定性得到明显提升.X射线光电子能谱结果也验证了Ni3+的引入有利于维持材料多周循环后Mn价态的稳定.
Abstract
The storage of intermittent wind and solar electricity requires grid-level energy storage devices,and due to the abundance and wide distribution of Na resources,Na-ion batteries(NIBs)are much more cost-effective and have shown greater potential for large-scale energy storage than Li-ion batteries(LIBs).However,the lack of suitable cathode hinders the practical use of NIBs,so exploring suitable cathode materials that can maintain a balance between high energy density and cost-effectiveness is essential for NIBs.Ni-Mn based layered oxides are important cathode materials for NIBs,offering relatively high potential through the multi-electron redox reaction of Ni4+/Ni3+/Ni2+as well as the low-cost and non-toxic nature of Mn4+.P2-Na0.67[Ni0.33Mn0.67]O2 was the first reported Ni-Mn based Na-ion battery cathode with a high capacity of～160 mAh·g-1 in the voltage range of 2.0-4.5 V,while irreversible P2-O2 phase transition above 4.1 V makes poor capacity retention and limits their applications.Moreover,a dilemma has emerged in that a costly element(Ni)is used for sodium-ion batteries,which is supposed to be low-cost.With the intensive research in recent years,introducing an appropriate amount of anionic redox can effectively improve energy density while simultaneously reducing the amount of high-cost transition metals,such as V,Co,and Ni.However,because of irreversible oxygen loss and Mn4+/Mn3+redox activation,voltage decay is difficult to avoid for most of these anion-redox materials.In this research,we report a Li-substituted Nax[Ni,Mn]O2 cathode,the designed formula being Na0.85[Li0.2Ni0.15Mn0.65]O2.This material shows a unique combination of both cationic redox(Ni4+/Ni3+/Ni2+)and anionic redox(O2-/O2n-)during charge and discharge,showing a high capacity of～150 mAh·g-1(10 mA·g-1,1.5-4.5 V)with only 0.15 Ni.With an optimized voltage range,the material shows a capacity of～100 mAh·g-1 and stable cycling performance(80%of initial capacity after 100 cycles at 10 mA·g-1 within 2.5-4.25 V)and high-rate capability(the capacity of 500 mA·g-1 is 80%of 10 mA·g-1,2.5-4.25 V).Moreover,we demonstrate an effective way to suppress the voltage decay and Mn reduction through Ni3+as a redox barrier.Specifically,during the discharge process,the Mn4+/Mn3+reduction process was replaced by the Ni3+/Ni2+reduction process with higher redox potential in the layered oxides.In addition,the full Ni2+/Ni4+redox can compensate for the partial oxygen redox loss in the subsequent cycles.We believe that introducing the anion redox through Li substitution and the use of Ni3+as a redox barrier to suppress the voltage decay will provide a new way in the design of NIBs'cathode materials,with potential benefits such as higher energy density,lower cost,and longer cycle life.
基金项目
国家重点研发规划(2022YFB2402500)
国家自然科学基金(51725206)
国家自然科学基金(52122214)
国家自然科学基金(52072403)
国家自然科学基金(52002394)
中国科学院青年创新促进会(2020006)
北京市自然科学基金(2212022)
中国科协青年人才托举工程(2022QNRC001)
万方数据