面向金属离子电池研究的固体核磁共振和电子顺磁共振方法

Solid-State NMR and EPR Methods for Metal Ion Battery Research

电池,尤其是锂离子电池的快速发展极大改变了我们的生活。从移动电子设备到新能源汽车再到电网储能,电池应用于多个领域且目前在能量密度和功率密度方面难以被取代。电池技术的向前发展要求我们对其电化学反应机理有完整的认识,这需要来自不同领域研究人员的交叉碰撞。磁共振波谱技术包括核磁共振波谱(NMR)和电子顺磁共振波谱(EPR),前者适合于研究Li、Na、P、O等电池材料中常见的轻元素,后者适合于研究Co、Mn、Fe、V等电池材料中常见的过渡金属。加上它们具有对样品无损、对结晶度无要求、能够定量分析等优点,NMR和EPR在过去三十年的电池研究中不断进步,日益成为电池表征的重要角色。本文从磁共振方法的角度出发,首先概述了固体NMR和EPR中的主要相互作用及其哈密顿表达形式,接着概述了固体NMR和EPR常用的重要方法及其在金属离子电池研究领域的代表性应用。本文有助于让我们直观地了解磁共振技术本身在金属离子电池研究领域的重要价值,并有望为解决利用固体NMR和EPR进行电池研究的过程遇到的困难提供指导。

The rapid development of batteries,especially lithium-ion batteries,has dramatically changed our daily lives.From portable electronics to electric vehicles and smart grids,batteries are extensively used in many fields and are difficult to be replaced in terms of their excellent energy and power densities.The advancement of battery technology requires the thorough understanding of electrochemical reaction mechanisms,which strongly depends on the collaboration of researchers from different fields.Magnetic resonance spectroscopy includes the important techniques of nuclear magnetic resonance(NMR)and electron paramagnetic resonance(EPR),and the former is suitable for studying light elements commonly found in batteries including Li,Na,P and O,while the latter is suitable for studying heavier transition metals such as Co,Mn,Fe and V.In addition,NMR and EPR are capable of quantitatively analysis in a nondestructive manner regardless of sample crystallinity.Hence,NMR and EPR spectroscopies have allowed for significant research progress and have become increasingly important for battery research over the past three decades.Herein,we will provide our perspective of magnetic resonance methods and first summarize the main interactions and the Hamiltonian forms of solid-state NMR and EPR(dipole-dipole interaction,electric quadrupole interaction,chemical shift,and hyperfine interaction).Subsequently,we summarize the important and frequently-used methods of solid-state NMR and EPR spectroscopies and introduce their representative applications in metal ion battery research(mainly lithium-and sodium-ion batteries).Specifically,we introduce the basic principles and representative applications of(i)MQMAS(multiple-quantum magic angle spinning),(ii)pjMATPASS(MAT=magic-angle turning,PASS=phase-adjusted sideband separation,and pj=projection),(iii)WURSTCPMG(WURST=wide band uniform rate smooth truncation,CPMG=Carr-Purcell Meiboom-Gil),(iv)2D homonuclear correlation and exchange(2D EXSY),(v)2D homonuclear correlation based on dipole coupling(i.e.RFDR),(vi)perpendicular mode EPR,(vii)parallel mode EPR,(viii)in situ NMR,and(ix)in situ EPR.In addition,we briefly introduce representative applications of 2D heteronuclear correlation(i.e.CP-HETCOR),pulsed field gradient NMR,spin-lattice relaxation(SLR),spin alignment echo(SAE),DFT calculations,and dynamic nuclear polarization(DNP).Previous reviews regarding the application of magnetic resonance technology in battery research are almost all reported in terms of the classification of battery materials.In other words,they are written from the perspective of applications in cathode,anode,and electrolyte research.Herein,we summarize from the perspective of solid-state NMR and EPR methods,which may be beneficial for the readers to fully understand the value of these important technologies.We believe this review can serve as a guide to solve challenges related to using solid-state NMR and EPR spectroscopies in battery research.