Uncovering the roles of oxygen vacancies in cation migration in lithium excess layered oxides

Qian, Danna; Xu, Bo; Chi, Miaofang; Meng, Ying Shirley

doi:10.1039/c4cp01799d

Cited by 249 publications

(276 citation statements)

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“…Through combined electron microscopy studies and theoretical calculations, Meng et al identified the most important structural origin for the performance degradation. [26][27][28][29] They found that due to the diffusion of the transition-metal (TM) ions to stable sites within the Li-rich intercalation planes (purple arrows in Figures 2a and b), a defective TM-rich spinel surface layer formed after cycling. Similar observations have been made by other research groups.…”

Section: Electrode Materialsmentioning

confidence: 99%

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Advanced analytical electron microscopy for lithium-ion batteries

Qian

et al. 2015

NPG Asia Mater

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Lithium-ion batteries are a leading candidate for electric vehicle and smart grid applications. However, further optimizations of the energy/power density, coulombic efficiency and cycle life are still needed, and this requires a thorough understanding of the dynamic evolution of each component and their synergistic behaviors during battery operation. With the capability of resolving the structure and chemistry at an atomic resolution, advanced analytical transmission electron microscopy (AEM) is an ideal technique for this task. The present review paper focuses on recent contributions of this important technique to the fundamental understanding of the electrochemical processes of battery materials. A detailed review of both static (ex situ) and real-time (in situ) studies will be given, and issues that still need to be addressed will be discussed. NPG Asia Materials (2015) 7, e193; doi:10.1038/am.2015.50; published online 26 June 2015 INTRODUCTIONTo implement the commercialization of lithium-ion batteries in electric vehicles and smart grid systems, further improvements are required, especially with respect to the energy/power density, coulombic efficiency and cycle life. These parameters primarily depend on the diffusion of lithium-metal ions, electron transport, structure and chemical dynamics of the electrode/electrolyte materials, among others. During electrochemical cycling, significant changes in the material structure and elemental distributions occur, including ion relocation, lattice expansion/contraction, phase transition and structure/surface reconstruction. These changes could substantially influence ion and electron transport and affect the performance of the entire battery system. Understanding the structure-property relationships for each component and their synergistic behaviors during electrochemical processes is, therefore, essential for the design of new battery materials and the optimization of existing systems.Although many analysis techniques (for example, X-ray diffraction, X-ray absorption spectroscopy, neutron diffraction, nuclear magnetic resonance and so on) have been employed for such studies, most of them can acquire only spatially averaged information. Nevertheless, the structural and chemical evolution of battery materials upon electrochemical cycling can often be linked to specific nanofeatures, such as defects, interfaces and surfaces. As a result, techniques based on analytical transmission electron microscopy (AEM) are ideal tools to study these issues. The capability of AEM to precisely probe the structural/chemical evolutions at an ultrahigh spatial resolution frequently provides insight that cannot be obtained directly using macroscopic characterization methods.

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Section: Electrode Materialsmentioning

confidence: 99%

“…26 (e) Spatially resolved EELS O-K edges from the surface to the bulk in the cycled Li-excess layered material. 29 All figures have been reproduced with permission. HAADF, high-angle annular dark field; STEM, scanning transmission electron microscopy.…”

Section: Electrode Materialsmentioning

confidence: 99%

Advanced analytical electron microscopy for lithium-ion batteries

Qian

et al. 2015

NPG Asia Mater

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“…27 More recently, there has been considerable discussion concerning the direct role of oxygen ions in the redox processes that occur in the lithium-rich LIB layered materials, [91][92][93] and the part they play in providing excess capacity beyond that estimated based on the redox-active transition metal ions. [94][95][96][97] Although the exact mechanisms that occur in the LIB electrode remain controversial, there is no reason to expect that similar mechanisms would not operate in NIBs for appropriate compositions and Li-substitution. Reaching high ionic and electronic conduction.-A good electrode material should be a good electronic and ionic conductor.…”

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confidence: 99%

Review—Manganese-Based P2-Type Transition Metal Oxides as Sodium-Ion Battery Cathode Materials

Clément

Bruce

Grey

2015

J. Electrochem. Soc.

412

388

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Sodium transition metal oxides (NaMO 2 ) with a P2 structure exhibit good Na + ion conductivity and are promising sodium-ion battery cathode materials. Manganese-based compounds have a high working potential vs. Na + /Na, and high capacity. Yet, the layered nature of these materials means that they are prone to structural rearrangements at high voltage/low Na contents, the phase transformations and Na + ion/vacancy ordering transitions resulting in capacity fade and poor reversibility. This review discusses the latest advances in the field and focuses mainly on recent work on Na y Mn 1-x M x O 2 (x, y ≤ 1, M = Ni, Mg, Li) compounds. We compare the different lithium and sodium transition metal layered oxides (P2, O3, etc.) and describe the structures and mechanisms observed on alkali (de)intercalation. The strategies used to enhance the electrochemical properties and stabilize the structural framework of sodium transition metal oxides are reviewed. We show how X-ray diffraction and 7 Li/ 23 Na solid-state Nuclear Magnetic Resonance can be combined to provide a detailed insight into the structural and electronic processes occurring upon electrochemical cycling of these materials. Why Are We Interested in Na-Ion Battery Cathodes?Together, the increasing demand for energy and the threat from Global Warming make electrical energy storage (EES) a world wide strategic priority. EES is expected to play a key role in the decarbonization of electric power sources. The two billion people worldwide not currently served by a reliable electricity supply are likely to be connected via local grids, for which EES is essential. While Li-ion batteries (LIBs) will play a role, a key challenge is to develop lower cost batteries that deliver safe, reliable storage with high cycle and calendar life. In this regard, Na-ion batteries (NIBs) are potentially important. NIBs operate in a similar fashion to LIBs, offering both advantages and disadvantages. Concerning the former, the ability to use Al instead of Cu as a current collector at the anode could substantially reduce cost. Na is also far more abundant in the Earth's crust than Li, and more widely distributed geographically. Regarding the disadvantages, the standard operating potential of Na metal is 300 mV more positive than Li metal. This generally translates into lower operating potentials for Na-ion systems, although the potential of a full cell depends on the difference in the chemical potentials of Na in the anode and cathode materials. There are considerable opportunities for scientists to develop new combinations of anode, electrolyte and cathode that are optimized for a variety of applications with different criteria such as high energy density, high power, and high operating potential. This has encouraged a rapid growth of interest in research into NIB components. Hard carbons show some promise as anodes, [1][2][3] but more must be done to improve performance. The cathode remains a major challenge and it is to this that we direct the current review. A comparative plot sho...

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“…The O edge at this voltage resembles that of NiO phase (Figure 3b) with a lower pre-peak intensity and average energy position of 7.5 eV. The O/TM atomic ratio of 1.6 measured for the surface phases and averaged over several particles show that the surface is oxygen deficient as compared to pristine NCA (2). Also, a reduction in Ni valence, measured from Ni L3/L2 ratio is observed at the surface (Ni +2.4 ) as compared to pristine NCA (Ni +3 ).…”

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confidence: 91%

“…This is consistent with the earlier report which shows that the diffusion barrier for TM migration is reduced when initial configuration of TM octahedron is five coordinated (MO5, deficient in one O) instead of regular six coordinated (MO6). [2] Chemical analysis was done on these particles and indeed oxygen loss accompanied these surface phase transformations. A characteristic EELS feature of pristine NCA is the presence of O-pre-peak, 12.0 eV from the main O peak, which occurs due to a transition from O 1s to a hybridized state formed by O 2p and Ni 3d states.…”

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confidence: 99%

STEM/EELS Analysis of Li(Ni 0.8 Co 0.15 Al 0.05 )O 2 Held at High Voltages

Mukherjee

Pereira

et al. 2016

Microsc Microanal

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Ni rich Li(Ni0.8Co0.15Al0.05)O2 commonly known as NCA is being used commercially as Li-ion battery cathode material for its high discharge capacity.[1] The stability and related safety concerns at high voltage limit the use of NCA at 3.6V, where only 50% of Li can be extracted. Thus, only a part of theoretical capacity is achieved in this process. At high voltages (>4V), the layered structure of the bulk NCA does not change, however new surface phases are formed. To utilize the full potential of this material, high-voltage studies of surface phases, their chemical evolution and their mechanisms are needed. We present here the evolution of surface phases in NCA held at a constant voltage up to 4.75V.The surface phases of NCA were observed in a cold cathode field emission aberration corrected JEOL ARM STEM (at Lehigh University). The spatial resolution of the STEM system was 0.07 nm. EELS chemical analysis as well as HAADF STEM imaging were carried out using aberration corrected HITACHI HD2700C TEM and GATAN Enfina EELS spectrometer with an energy resolution of 0.5 eV. A HAADF STEM image of a NCA particle (held at 4.75V for 2 weeks) oriented along [010] zone axis of layered (R-3m) structure is shown in Figure 1. Atomic-resolution images from different regions of the particle were obtained revealing structural inhomogeneity with two different surface phases. The HAADF STEM image from region 1 (Figure 2a) shows that the bulk layered structure (R-3m) is maintained up to the surface, but almost 1/3 of transition metal (TM) ions (mostly Ni) have migrated to the Li layer as determined from the intensity profile (Figure 2b). In region 2 the surface is fully transformed to a rocksalt (RS) type (Fm-3m) phase (Figure 2c). The contrast between Li and TM layer is uniform and the spacing between them is ~ 0.23nm (d111 of Fm3m phase). The presence of two different phases within the same particle shows that the surface of NCA particles is highly inhomogeneous. Also, this large scale migration of TM ions (1/3 of TM moving to Li layer) from its original octahedral site to a tetrahedral Li site is accompanied by creation of oxygen vacancies. This is consistent with the earlier report which shows that the diffusion barrier for TM migration is reduced when initial configuration of TM octahedron is five coordinated (MO5, deficient in one O) instead of regular six coordinated (MO6).[2] Chemical analysis was done on these particles and indeed oxygen loss accompanied these surface phase transformations. A characteristic EELS feature of pristine NCA is the presence of O-pre-peak, 12.0 eV from the main O peak, which occurs due to a transition from O 1s to a hybridized state formed by O 2p and Ni 3d states. For NiO, the pre-peak is smaller and located 7.5 eV from the main O peak. This pre-peak is almost missing in the surface phases from sample held at 4.75V (Figure 3a). The O edge at this voltage resembles that of NiO phase (Figure 3b) with a lower pre-peak intensity and average energy position of 7.5 eV. The O/TM atomic ratio of 1.6 measu...

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Uncovering the roles of oxygen vacancies in cation migration in lithium excess layered oxides

Cited by 249 publications

References 23 publications

Advanced analytical electron microscopy for lithium-ion batteries

Advanced analytical electron microscopy for lithium-ion batteries

Review—Manganese-Based P2-Type Transition Metal Oxides as Sodium-Ion Battery Cathode Materials

STEM/EELS Analysis of Li(Ni 0.8 Co 0.15 Al 0.05 )O 2 Held at High Voltages

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