Sawamura Miho, Kobayakawa Sho, Kikkawa Jun, Sharma Neeraj, Goonetilleke Damian, Rawal Aditya, Shimada Nanaka, Yamamoto Kentaro, Yamamoto Rina, Zhou Yingying, Uchimoto Yoshiharu, Nakanishi Koji, Mitsuhara Kei, Ohara Koji, Park Jiwon, Byon Hye Ryung, Koga Hiroaki, Okoshi Masaki, Ohta Toshiaki, Yabuuchi Naoaki
Department of Applied Chemistry, Tokyo Denki University, 5 Senju Asahi-cho, Adachi-ku, Tokyo 120-8551, Japan.
National Institute for Materials Science (NIMS), Namiki, Tsukuba, Ibaraki 305-0044, Japan.
ACS Cent Sci. 2020 Dec 23;6(12):2326-2338. doi: 10.1021/acscentsci.0c01200. Epub 2020 Dec 15.
Nanostructured LiMnO integrated with LiPO was successfully synthesized by the mechanical milling route and examined as a new series of positive electrode materials for rechargeable lithium batteries. Although uniform mixing at the atomic scale between LiMnO and LiPO was not anticipated because of the noncompatibility of crystal structures for both phases, our study reveals that phosphorus ions with excess lithium ions dissolve into nanosize crystalline LiMnO as first evidenced by elemental mapping using STEM-EELS combined with total X-ray scattering, solid-state NMR spectroscopy, and a theoretical study. The integrated phase features a low-crystallinity metastable phase with a unique nanostructure; the phosphorus ion located at the tetrahedral site shares faces with adjacent lithium ions at slightly distorted octahedral sites. This phase delivers a large reversible capacity of ∼320 mA h g as a high-energy positive electrode material in Li cells. The large reversible capacity originated from the contribution from the anionic redox of oxygen coupled with the cationic redox of Mn ions, as evidenced by soft XAS spectroscopy, and the superior reversibility of the anionic redox and the suppression of oxygen loss were also found by online electrochemical mass spectroscopy. The improved reversibility of the anionic redox originates from the presence of phosphorus ions associated with the suppression of oxygen dimerization, as supported by a theoretical study. From these results, the mechanistic foundations of nanostructured high-capacity positive electrode materials were established, and further chemical and physical optimization may lead to the development of next-generation electrochemical devices.
通过机械球磨法成功合成了与LiPO集成的纳米结构LiMnO，并将其作为一系列新型的可充电锂电池正极材料进行了研究。尽管由于两相晶体结构的不相容性，预计LiMnO和LiPO之间不会在原子尺度上均匀混合，但我们的研究表明，过量锂离子的磷离子会溶解到纳米尺寸的晶体LiMnO中，这首先通过结合STEM-EELS的元素映射、全X射线散射、固态NMR光谱以及理论研究得到证实。集成相具有低结晶度的亚稳相和独特的纳米结构；位于四面体位置的磷离子与相邻八面体位置稍有扭曲的锂离子共用面。作为锂电池中的高能量正极材料，该相具有约320 mA h g的大可逆容量。大的可逆容量源于氧的阴离子氧化还原与Mn离子的阳离子氧化还原的贡献，软XAS光谱证明了这一点，在线电化学质谱也发现了阴离子氧化还原的优异可逆性和氧损失的抑制。理论研究表明，阴离子氧化还原可逆性的提高源于与抑制氧二聚化相关的磷离子的存在。基于这些结果，建立了纳米结构高容量正极材料的机理基础，进一步的化学和物理优化可能会推动下一代电化学器件的发展。
