Peering into Batteries: Electrochemical Insight Through In Situ and Operando Methods over Multiple Length Scales

Abstract

Emerging new applications demand an expanded function of Li-ion batteries (LIB). However, many issues, including complex phase transitions of electroactive materials, the kinetics of ion transport, and electrode-electrolyte interfacial reactions, still limit the full realization of LIBs. To date, most interrogation approaches of batteries are static, and are unable to track mechanisms arising from dynamic battery (dis)charge behavior. To gain a meaningful insight into kinetic phenomena, both spatial and time dimensions must be considered over several orders of magnitude. This perspective discusses the application of in situ and operando methods over various length scales to gain an insight into dynamic electrochemical processes and failure mechanisms of energy storage systems for both insertion and conversion-type materials. We comment on future directions for gaining full insight into batteries through advanced in situ and operando characterizations to provide guidance for future innovation. In order to overcome the limitations of static and destructive characterizations of Li-ion battery materials and components, comprehensive investigation peering into batteries over various length and time scales is essential. In this regard, emerging in situ and operando characterization methodologies focusing on multiple size domains become a powerful approach to resolve current challenges and navigate future directions. This perspective provides a series of illustrative examples of in situ and operando characterizations over atomic, crystallite/particle, electrode, and battery system length scales with a focus on two electrode material classes: insertion and conversion materials. The operating principles, features, analysis methods, and information gained from each characterization method are discussed. Herein, we present the necessity and opportunity for in situ and operando characterization of electrochemical energy storage materials and systems. Further, we suggest future directions to gain the insight needed to tackle currently intractable issues on Li-ion battery application, failure, and emerging design concepts. In order to overcome the limitations of static and destructive characterizations of Li-ion battery materials and components, comprehensive investigation peering into batteries over various length and time scales is essential. In this regard, emerging in situ and operando characterization methodologies focusing on multiple size domains become a powerful approach to resolve current challenges and navigate future directions. This perspective provides a series of illustrative examples of in situ and operando characterizations over atomic, crystallite/particle, electrode, and battery system length scales with a focus on two electrode material classes: insertion and conversion materials. The operating principles, features, analysis methods, and information gained from each characterization method are discussed. Herein, we present the necessity and opportunity for in situ and operando characterization of electrochemical energy storage materials and systems. Further, we suggest future directions to gain the insight needed to tackle currently intractable issues on Li-ion battery application, failure, and emerging design concepts. Electrochemical energy storage systems, specifically batteries, have become a key component in our society. As demand increases for consumer electronics, electric vehicles, and integration of intermittent renewable energy sources, so does the need for high performing, reliable, and cost-effective battery systems to power the applications. Among a variety of rechargeable battery systems, the Li-ion battery technology (LIB) is dominant due to its long cycle life, high voltage, and high energy density.1Etacheri V. Marom R. Elazari R. Salitra G. Aurbach D. Challenges in the development of advanced Li-ion batteries: a review.Energy Environ. Sci. 2011; 4: 3243-3262Crossref Scopus (4681) Google Scholar Significant advances in LIBs have taken place since their commercial introduction in the 1990s;2Li J. Murphy E. Winnick J. Kohl P.A. Studies on the cycle life of commercial lithium ion batteries during rapid charge–discharge cycling.J. Power Sources. 2001; 102: 294-301Crossref Scopus (193) Google Scholar however, new applications demand further advances in the technology placing new requirements on future generations of batteries. Batteries continue to be widely researched with numerous investigations published per year reflective of their importance. Ex situ measurements on components outside of the functional environment have been a standard approach for battery systems over multiple decades. However, these are often ultimately destructive techniques that risk distortion of the original chemical environment and do not capture kinetic phenomena. Recently, in situ characterization on a system in a functioning environment but inactive during the measurement and operando measurements during system operation have become more prevalent with the potential to yield unprecedented mechanistic insights. The appeal of these approaches is evidenced by a 350% increase in publications regarding “batteries and operando” techniques over the past 5 years (from Web of Science), yet these investigations comprise only ∼1% of the total battery publications in 2019. Comprehensive characterization of electrochemical energy storage systems requires investigation over multiple scales,3Abraham A. Housel L.M. Lininger C.N. Bock D.C. Jou J. Wang F. West A.C. Marschilok A.C. Takeuchi K.J. Takeuchi E.S. Investigating the complex chemistry of functional energy storage systems: the need for an integrative, multiscale (molecular to mesoscale) perspective.ACS Cent. Sci. 2016; 2: 380-387Crossref PubMed Scopus (35) Google Scholar where two aspects should be considered: a spatial dimension and a time dimension shown schematically in Figure 1. Observing materials over multiple length or spatial scales provides information on a series of size domains: atomic, crystallite/particle, electrode, and battery system level. The time dimension should be considered over many orders of magnitude ranging from sub-second electrochemical processes to years of functional lifetime. By coupling time and spatial resolutions, in situ and operando characterization over multiple sizes and time domains becomes a powerful approach, where many previously intractable issues causing battery degradation and failure can be directly detected and quantified, including spatially inhomogeneous phase transitions within materials, sluggish ion transport, significant interfacial side reactions, and observable energy loss through heat dissipation.4Bruck A.M. Wang L. Brady A.B. Lutz D.M. Hoff B.L. Li K. Stavinski N. Bock D.C. Takeuchi K.J. Takeuchi E.S. Marschilok A.C. 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At an atomic level, in situ transmission electron microscopy (TEM) has been deployed to gain insights on ion migration within materials. A variety of X-ray techniques have been widely applied as they provide both dynamic structural and morphological information15Finegan D.P. Quinn A. Wragg D.S. Colclasure A.M. Lu X. Tan C. Heenan T.M.M. Jervis R. Brett D.J.L. Das S. et al.Spatial dynamics of lithiation and lithium plating during high-rate operation of graphite electrodes.Energy Environ. Sci. 2020; 13: 2570-2584Crossref Google Scholar. X-ray diffraction (XRD) offers the ability to track atomic changes in electrode materials, allowing for an understanding of the material evolution and potential failure mechanisms. Energy-dispersive X-ray diffraction (EDXRD), where a high energy white beam is used as the sample is moved through the beam, has proven to be a successful approach used for the operando measurement of batteries within metal casings. Confocal XRD has recently been deployed offering improved peak resolution, but with longer measurement time.16Lin F. Liu Y. Yu X. Cheng L. Singer A. Shpyrko O.G. Xin H.L. Tamura N. Tian C. Weng T.-C. et al.Synchrotron X-ray analytical techniques for studying materials electrochemistry in rechargeable batteries.Chem. Rev. 2017; 117: 13123-13186Crossref PubMed Scopus (250) Google Scholar Neutron diffraction has also been effectively used to probe materials with a low-atomic number (such as Li) and distinguish between elements with similar X-ray scattering lengths.13Zhu H. Huang Y. Zhu H. Wang L. Lan S. Xia X. Liu Q. In situ probing multiple-scale structures of energy materials for Li-Ion batteries.Small Methods. 2020; 4: 1900223Crossref Scopus (17) Google Scholar,16Lin F. Liu Y. Yu X. Cheng L. Singer A. Shpyrko O.G. Xin H.L. Tamura N. Tian C. Weng T.-C. et al.Synchrotron X-ray analytical techniques for studying materials electrochemistry in rechargeable batteries.Chem. Rev. 2017; 117: 13123-13186Crossref PubMed Scopus (250) Google Scholar Additionally, X-ray absorption spectroscopy (XAS) is becoming more widely deployed, as it is element specific and can provide oxidation state and local atomic environment information for the metal centers used in battery materials, and yet, does not require crystalline long-range order. This perspective aims to discuss in situ and operando techniques applied to lithium-ion type batteries in the context of case studies of two structural motifs, namely, insertion materials and conversion materials. Insertion materials are characterized by a reaction mechanism where mobile ions reversibly insert into the open space within a material’s crystal structure17Manthiram A. Electrode materials for rechargeable lithium batteries.JOM. 1997; 49: 43-46Crossref Scopus (22) Google Scholar allowing for facile ion diffusion. Insertion type materials can accommodate limited volume change due to the ion movement without material degradation over extended cycling; however, they have limited capacity as a result. Conversion materials offer much higher theoretical capacities and the prospect of higher energy density batteries, as these materials undergo chemical change allowing for multiple electron transfers per active center. However, conversion reactions are often complex and may suffer from material degradation and incomplete chemical reversibility over extended cycling.18Lu B. Lu F. Zou Y. Liu J. Rong B. Li Z. Dai F. Wu D. Lan G. In situ reduction of silver nanoparticles by chitosan-l-glutamic acid/hyaluronic acid: enhancing antimicrobial and wound-healing activity.Carbohydr. Polym. 2017; 173: 556-565Crossref PubMed Scopus (59) Google Scholar Both classes of materials, and each unique chemistry within these classes, offer different challenges for researchers. Owing to the different reaction mechanisms of the insertion and conversion materials, the mechanistic studies using in situ and operando techniques need to focus on structural and morphological changes at different length scales. Ultimately, the ways in which these systems are interrogated is a common factor among all battery research, and thus, this topic deserves analysis and discussion. Rather than being fully comprehensive, it is our aim here to introduce a series of illustrative examples on both ion insertion and conversion-type electrode materials characterized by in situ/operando TEM, XAS, XRD, EDXRD, and isothermal microcalorimetry (IMC). We elaborate on the merits, needs, and outlook of in situ/operando characterization over multiple length and time scales to provide an even greater insight on transport properties, mechanism, and design of both active materials and electrodes. Insertion materials have been widely used for practical LIBs since their introduction in the early 1990s.19Brédas J.-L. Buriak J.M. Caruso F. Choi K.-S. Korgel B.A. Palacín M.R. Persson K. Reichmanis E. Schüth F. Seshadri R. Ward M.D. An electrifying choice for the 2019 chemistry Nobel Prize: Goodenough, Whittingham, and Yoshino.Chem. Mater. 2019; 31: 8577-8581Crossref Scopus (12) Google Scholar Current commercial materials include transition metal oxides, such as lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), and lithium nickel manganese cobalt oxide (NMC, LiNixMnyCozO2), as well as lithium metal phosphates, such as lithium iron phosphate (LiFePO4). Insertion materials provide facile Li-ion diffusion, offering the advantage of high reversibility, but are limited in the number of ion/electron transfers per metal center, and thus, capacity. Thus, the search for higher capacity materials in this class continues. In this perspective, examples of two material types will be considered: NMC with a delivered capacity of ∼200 mAh/g20Tian C. Lin F. Doeff M.M. Electrochemical characteristics of layered transition metal oxide cathode materials for lithium ion batteries: surface, bulk behavior, and thermal properties.Acc. Chem. Res. 2018; 51: 89-96Crossref PubMed Scopus (122) Google Scholar depending on the composition and lithium vanadium oxide (LVO, LiV3O8) with a theoretical capacity of 362 mAh/g.21Depicciotto L. Adendorff K. Liles D. Thackeray M. Structural characterization of Li1+xV3O8 insertion electrodes by single-crystal X-ray diffraction.Solid State Ionics. 1993; 62: 297-307Crossref Scopus (170) Google Scholar, 22Sarkar S. Bhowmik A. Dixit Bharadwaj M. Mitra S. Phase transition, electrochemistry, and structural studies of high rate LixV3O8Cathode with nanoplate morphology.J. Electrochem. Soc. 2014; 161: A14-A22Crossref Scopus (29) Google Scholar, 23Wang Z.-K. Shu J. Zhu Q.-C. Cao B.-Y. Chen H. 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Probing sources of capacity fade in LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622): an operando XRD study of Li/NMC622 batteries during extended cycling.J. Phys. Chem. C. 2020; 124 (LiNi0): 8119-8128Crossref Scopus (15) Google Scholar Although the cell cycled to 4.7 V delivered 20% higher capacity, it showed a higher capacity fade of 35% more capacity decrease compared with the 4.3 V charge by the 100th cycle. In the first two cycles, cells charged to 4.7 V had increased anisotropic lattice changes compared with the cells charged to 4.3 V. However, by the 100th cycle the microstrain was significantly elevated in the cell charged to 4.7 V. This elevated structural microstrain was identified as the main driver for the loss of capacity caused by particle disintegration supported by ex situ scanning electron microscopy (SEM). Microbeam XRD can quantitatively probe microstructure using an X-ray microprobe and enable the lattice parameters of a NMC111 electrode to be monitored during discharge with a resolution of 50 μm.16Lin F. Liu Y. Yu X. Cheng L. Singer A. Shpyrko O.G. Xin H.L. Tamura N. Tian C. Weng T.-C. et al.Synchrotron X-ray analytical techniques for studying materials electrochemistry in rechargeable batteries.Chem. Rev. 2017; 117: 13123-13186Crossref PubMed Scopus (250) Google Scholar Neutron diffraction studies and small-angle X-ray and neutron scattering studies have followed the lithiation of NMC cathodes to determine the phases involved at different rates.13Zhu H. Huang Y. Zhu H. Wang L. Lan S. Xia X. Liu Q. In situ probing multiple-scale structures of energy materials for Li-Ion batteries.Small Methods. 2020; 4: 1900223Crossref Scopus (17) Google Scholar As a complementary tool, studies using hard and soft XAS have revealed the redox mechanism of Li1.16Ni0.15Co0.19Mn0.50O2, the thermal stability of charged Li0.33Ni0.8Co0.15Al0.05O2 cathode material, and precise atomic distances in LiMn0.5Ni0.5O2 during (dis)charge.9Liu D. Shadike Z. Lin R. Qian K. Li H. Li K. Wang S. Yu Q. Liu M. Ganapathy S. et al.Review of recent development of in situ/operando characterization techniques for lithium battery research.Adv. Mater. 2019; 31: e1806620Crossref PubMed Scopus (214) Google Scholar,13Zhu H. Huang Y. Zhu H. Wang L. Lan S. Xia X. Liu Q. In situ probing multiple-scale structures of energy materials for Li-Ion batteries.Small Methods. 2020; 4: 1900223Crossref Scopus (17) Google Scholar,27Li J. Downie L.E. Ma L. Qiu W. Dahn J.R. 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Hartmann P. Sommer H. Brezesinski T. Janek J. Anisotropic lattice strain and mechanical degradation of high- and low-nickel NCM cathode materials for Li-Ion batteries.J. Phys. Chem. C. 2017; 121: 3286-3294Crossref Scopus (290) Google Scholar The XRD revealed that significant shrinkage of the c axis led to variations in bond character for NMC811 and could be responsible for the structural changes observed. The in situ light microscopy captured the large volume contraction upon charge and the resultant severe microcracking of the micron-scale particles for the NMC811 material, confirming the XRD results. The ability to interrogate the system during operation at both the atomic and particle scales allowed for a clear understanding of the differences between the Ni-poor and Ni-rich materials and the capacity-fade mechanisms. Consideration of the electrode and the working system demand understanding of the transport properties within the electrode structure. An interesting approach has exploited IMC to study the thermal effects of NMC type cathode materials while in working batteries. By isolating different heat flow sources from the total heat flow measured by the IMC, the heat flow originated from irreversible parasitic reactions could be resolved at various potential windows.27Li J. Downie L.E. Ma L. Qiu W. Dahn J.R. Study of the failure mechanisms of LiNi0.8Mn0.1Co0.1O2cathode material for lithium ion batteries.J. Electrochem. Soc. 2015; 162: A1401-A1408Crossref Scopus (290) Google Scholar,30Downie L.E. Dahn J.R. Determination of the voltage dependence of parasitic heat flow in lithium ion cells using isothermal microcalorimetry.J. Electrochem. Soc. 2014; 161: A1782-A1787Crossref Scopus (42) Google Scholar,31Glazier S.L. Nelson K.J. Allen J.P. Li J. Dahn J.R. 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Guidelines and trends for next-generation rechargeable lithium and lithium-ion batteries.Chem. Soc. Rev. 2020; 49: 1569-1614Crossref PubMed Google Scholar The reactions of these materials typically involve multiple electron transfers per active center, and therefore, can yield a much higher electrochemical capacity than insertion materials. However, the material changes such as large volume expansion induced by lithiation can impact cycle life and challenge a comprehensive understanding of the electrode reactions. The use of silicon as negative electrode material in lithium-based batteries holds a significant interest due to the ∼10-fold increase in capacity compared with the widely used graphite negative electrodes. As a result, this material has been studied for decades, toward the goal of implementation in batteries; yet, full adoption in commercial cells remains challengin