一种新型富锂层状正极氧化物电极材料

论文

20

22

速递

Structure design enables stable anionic and cationic redox chemistry in a T2-type Li-excess layered oxide cathode

Xin Cao, Haifeng Li, Yu Qiao, Min Jia, Hirokazu Kitaura, Jianan Zhang, Ping He, Jordi Cabana, Haoshen Zhou

Science Bulletin, 2022, 67(4): 381–388

doi: 10.1016/j.scib.2021.11.014

01

中文导读

得益于阴离子氧化还原反应的引入, 富锂材料具有较高的输出容量而被认为是下一代高能量密度电池正极材料的选择之一. 然而氧相关的阴离子氧化还原反应的利用常常伴随着不可逆的晶格氧析出和严重的结构畸变. 此外, 由于复杂的阴阳离子氧化还原反应, 使得富锂材料的电荷补偿机理也需要进一步澄清. 本文报道了一种T2型Li_0.72[Li_0.12Ni_0.36Mn_0.52]O₂正极材料. 研究发现, 与其他典型的富锂层状正极不同, 其具有不同于传统富锂材料的四面体碱金属配位环境与ABB′A′氧堆垛顺序. 得益于其良好的结构稳定性和可逆的锂离子脱嵌过程, 层状T2型正极材料具有良好的电化学稳定性, 在较长的循环中具有较少的容量衰减和电压下降. 研究人员通过详细的光谱表征, 不仅标定了复杂的阴离子氧化还原行为, 而且预估了相应的阳离子/阴离子氧化还原反应对应的电化学容量, 这进一步阐明具有复杂氧化还原行为材料的电荷补偿机理.

 

02

图文速览

Figure 1 Synthesis, structural characterization, and electrochemical performance of T2-type LLNMO. (a) Schematic illustration of Li/Na ion exchange reaction from P2-typeNa-based precursor to T2-type Li-based LLNMO. (b) The XRD patterns of pristine T2-type LLNMO. The observed pattern, the calculated pattern, the difference between the two patterns and the corresponding Bragg positions are shown. The inset is a schematic illustration of the crystal structure of the LLNMO with ABB¢A¢ oxygenstacking along the [110] zone axis. (c) Typical charge–discharge profiles of LLNMO within the voltage window of 2.0 to 4.8 V at a current density of 10 mA/g in Li-half cells. The mole numbers of electron were converted to mole numbers of (de)intercalated Li⁺ during the initial two cycles. (d) Cycling performance of LLNMO between 2 and 4.8 V at the current density of 10 mA/g. The inset displays the normalized discharge profiles of LLNMO in the 1st, 10th, 20th and 50th cycles. 

Figure 2 Phase evolution and Li migration processes of T2-type LLNMO during cycling. (a) In-situ XRD patterns of LLNMO electrode during the initial twocycles. (b) ⁷Li solid state NMR spectra of T2-type LLNMO electrode samples of pristine state, initial charge to 4.8 V and initial discharge to 2 V.

Figure 3 Analysis of cationic states in T2-type LLNMO during the initial two cycles. (a) Mn and (b) Ni K-edge hard X-ray absorption spectra (XAS) of different samples (pristine, 1st charged 4.8 V, 1st discharged 3.0 V, 1st discharged 2.0 V and 2nd charged 4.8 V). The magnified rising edge region of (c) Mn and (d) Ni K-edge XAS labeled by the light orange rectangle. The corresponding 1st derivative plots of (e) Mn and (f) Ni K-edge XAS.

Figure 4 Analysis of O activity in T2-type LLNMO during the initial two cycles. (a) O 1s XPS spectra of T2-type LLNMO electrode at different states (pristine, 1st charged 4.8 V, 1^st discharged 3.0 V, 1^st discharged 2.0 V and 2nd charged 4.8 V). XPS patterns of (b) charged and (c) discharged T2-type LLNMO electrode with different etching time. (d) Operando differential electrochemical mass spectrometry (DEMS) of the rate of evolution of O₂ and CO₂ during cycling. (e) Results of acid titrations-gas chromatography mass spectrometry (AT-GCMS) of two electrodes harvested at the end of each of the first two charge processes. (f) Capacity contributions of oxygen redox (reversible oxygen behavior, O₂ evolution) and Ni/Mn-based redox reactions during the initial two cycles.

03

本文通讯作者

乔羽 教授 厦门大学化学化工学院, 主要研究领域为二次电池储能体系机理研究与材料研发、电化学原位光谱、电极/电解液表界反应机理研究.

周豪慎 教授 南京大学现代工程与应用科学学院, 长期从事能源材料、气体传感器、太阳能电池、超级电容器、二次电池、锂离子电池、锂空气电池、下一代储能器件等的研究和开发。