Layered O6/O3 Multi-Phase Composite Derived from the P2/O3 Nanocrystalline Composite for High-Performance Li-Rich Manganese-Based Cathode Material

Abstract

As a result of the redox reaction of lattice oxygen occurring at 4.5 V, the Li-rich manganese cathode material with an O3 configuration has a theoretically high discharge capacity (>250 mA h/g). However, it also suffers a structural transition from layered structure to spinel structure in the cycling process, leading to severe voltage decay and capacity fading. On contrary, the O6 type material obtained via ion exchange of P2 type material can effectively inhibit the phase transition and stabilize the layered structure. Hence, in this work, we design an O6/O3 multi-phase composite material after ion exchange of the P2/O3 nanocrystalline composite. Compared with the O3 type cathode, the as-obtained cathode composite exhibits a higher initial discharge capacity (≈265 mA h/g at 20 mA/g) and an excellent capacity retention (≈87% after 100 cycles). Moreover, the first cycle Coulombic efficiency increases by nearly 10%, and voltage attenuation is effectively inhibited. Our findings demonstrate that modulating the O6/O3 configuration is a practical and simple methodology to promote the electrochemical performance of lithium-rich layered materials.

Surface Miscible Structure Modulation of Li‐Rich Cathodes by Dual Gas Surface Treatment for Super High‐Temperature Electrochemical Performance

“…[ 1–5 ] Compared with olivine LiFePO 4 cathodes, spinel Li 2 MnO 4 cathode and traditional layered oxide cathode materials (LiTMO 2 , TM = Ni, Co, Mn), Li‐rich Mn‐based layer oxides ( x LiTMO 2 ·(1 − x )Li 2 MnO 3 , LRNCM) with high specific capacity (≧250 mAh g −1 ), high voltage (4.8 V), and low cost are becoming one of the key electrode materials for high‐energy‐density batteries. [ 6–9 ] The ultrahigh capacity is derived from the active reaction of oxygen at high voltage, including the reversible oxygen redox processes (O 2− to O n − , n < 2) and irreversible O 2 loss. The activity of oxygen at high voltage simultaneously triggers a series of fatal problems, such as poor rate capability, transition metal (TM) dissolution, and rapid voltage decay, which become huge obstacles to its practical application.…”

Research progress in cathode materials of secondary batteries with high specific energy based on anionic charge compensation mechanism

“…(c) Loal XRD patterns and SAED images of Li-rich materials prepared by various molten salts [28] , Copyright © 2014，Royal Society of Chemistry. (d) STEM image of Li-rich materials and diagram of the 3D Li + diffusion channel [29] , Copyright © 2023, John Wiley and Sons 3.3 氧排列次序调控 除了经典的O3型富锂层状氧化物以外，研究者们利用Li/Na离子交换策略来调控氧的排列次序和锂的局部 配位环境，探索并设计了一系列的亚稳态富锂正极如O2、T2、O6型及多相复合正极。其中，O2、T2和O6型 结构是由P2型的钠基前体交换而来的，而P3或O3型钠基母体能够转化为O3型结构 [30] 。P、O和T对应碱金属离 子的配位环境分别为三棱柱、八面体和四面体形，数字代表在一个单元中过渡金属层的数量。Cao等人 [31] 制备 了具有O2型结构的富锂层状正极，经100圈循环后，O2型正极展现出有限的电压损失，约为0.268 V, 而O3型 正极的电压损失高达0.681 V(图3(a), (b))，证明调控氧的排列次序有利于解决富锂正极面临的电压衰减问题。 Eum等人 [32] 结合高分辨透射电子显微镜表征和理论计算，阐明了O2型结构在充放电过程中能够实现几乎完全 可逆的过渡金属离子迁移(图3(c))。这是由于O2型结构中最终Li位点面共享阳离子之间具有强烈的排斥作用， 极大地阻碍了过渡金属离子迁移至最终Li位点，进一步促使过渡金属离子在充电过程中的反相迁移。Zuo等 A c c e p t e d https://engine.scichina.com/doi/10.1360/TB-2024-0457 人 [33] 设计了具有单层Li 2 MnO 3 超晶格结构的O2型富锂层状正极Li 1.25 Co 0.25 Mn 0.50 O 2 ，该正极在电流密度为10 mA g 1 、电压范围为2-4.8 V时展现出杰出的放电比容量，高达400 mAh g 1 。Luo等人 [34] 报道了一种拥有带帽 蜂窝超结构的O2型无钴富锂正极Li 1.1 [Ni 0.21 Mn 0.65 Al 0.04 ]O 2 ，经长循环测试展现出可忽略的电压衰减。这是因为 过渡金属离子部分占据了蜂窝结构中锂离子的正上方或正下方位点，有利于稳定富锂正极中的蜂窝型超结 构，从而抑制氧气释放和不可逆的相转变。Cao等人 [35] 对比了电化学和化学离子交换法所得的O2型富锂正 极，指出化学离子交换法能够作为一种有效的策略来制备优异的正极材料。Cao等人 [36] 为改善传统富锂材料的 容量和电压衰减问题，通过离子交换法从P2型的钠基前体Na 0.72 [Li 0.12 Ni 0.36 Mn 0.52 ]O 2 制备得到了一种T2型的富 锂层状正极材料Li 0.72 [Li 0.12 Ni 0.36 Mn 0.52 ]O 2 (图3(d))。原位XRD表征表明，在首次脱锂过程中富锂层状氧化物发 生了由T2至O2的相变，且在首次放电和后续的电化学过程中始终能够保持稳定的O2型结构，因此有利于实现 可逆的阳离子和阴离子氧化还原反应。此外， Cao等人 [37] 还设计了 O2/O3 型层状正极 Li 0.9 [Li 0.3 Mn 0.7 ]O 2 ( 图 3(e))，兼具了O3结构的高放电比容量与O2结构的优异结构稳定性，能够克服传统单相材料所面临的困境。 XRD图谱及精修结果显示，两相材料中O2和O3相的比例分别为81%和19%。Yang等人 [38] 合成了O6/O3两相复 合富锂氧化物，首圈放电比容量为265 mAh g 1 ，经100圈循环后电压降为0.349 V。在同样的测试条件下，O3 型富锂正极的放电比容量仅为265 mAh g 1 ，电压降高达0.455 V。上述一系列研究为实现高性能的富锂正极提 供了新的可能。 图3 (网络版彩色)富锂层状正极材料的氧排列次序调控. O3型(a)和O2型(b)富锂正极的充放电曲线 [31] , Copyright © 2021, American Chemical Society.…”

Fundamentals of Ion‐Exchange Synthesis and Its Implications in Layered Oxide Cathodes: Recent Advances and Perspective

“…and Li 5/6 Li 1/4 (Mn 0.675 Co 0.325 ) 3/4 O 2 materials, [38] which was carried out in an argon-filled tube furnace at 280 °C for 4 h. The Li 5/6 Li 1/4 (Mn 0.675 Co 0.1625 Ni 0.1625 ) 3/4 O x can also be synthesized by changing the atmosphere of the synthesis process to air, which can be completed at mild temperature of 280 °C for 4 h. [39] When using the ion-exchange method for the synthesis of Li 0.66 [Li 0.12 Ni 0.15 Mn 0.73 ]O 2 [37] and Li 2/3 [Li 2/9 Mn 7/9 ]O 2 [40] materials, the researchers further reduced the reaction time to 1 h, while maintaining a mild temperature of 280 °C in air during ion exchange. Yang et al [41] used the hydrothermal ion exchange to synthesize the Li-rich materials, in which the , [42] the reaction temperature was further reduced by solvothermal ion exchange at 120 °C for 24 h. Reducing synthetic temperature and time has always been an important part of production of materials. Chemical ion exchange enables the synthesis of materials at mild temperature and short time when compared to the traditional solid-state [12] Copyright 2021, Wiley-VCH GmbH.…”

“…P2-type Na X TMO 2 precursors can be converted not only to O2-type crystalline materials by Li + /Na + ion exchange, but also to various other crystalline structures such as O6 and T2 types. [15,52] Yang et al [41] designed a multiphase composite of xLi 5/6 Li 1/4 (Mn 0.6 Ni 0.2 ) 3/4 O 2−𝛿 −(1−x)Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 that combines O6/O3 double phases, which was synthesized via ion exchange from P2/O3 composite of Na-ion oxides. As shown in Figure 5a, the O6/O3-type composite materials reduce the loss of initial irreversible capacity from 89 mAh g −1 (pure O3-type) to 57 mAh g −1 (O6/O3-type).…”

“…b,c) Diffusion coefficient of Li + ions of O3 and 0.2O6-0.8O3 materials during b) chargeand c) discharge. Reproduced with permission [41]. Copyright 2022, American Chemical Society.…”