Nanoscale Phase Separation, Cation Ordering, and Surface Chemistry in Pristine Li1.2Ni0.2Mn0.6O2for Li-Ion Batteries

Gu, Meng; Genç, Arda; Belharouak, Ilias; Wang, Dapeng; Amine, Khalil; Thevuthasan, Suntharampillai; Baer, Donald R.; Zhang, Ji Guang; Browning, Nigel D.; Li, Jun; Wang, Chongmin

doi:10.1021/cm4009392

Cited by 180 publications

(144 citation statements)

References 34 publications

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“…Boulineau et al 30 proposed that a surface Ni/Mn segregation, instead of the surface phase transformation, is the origin for the performance degradation. Moreover, Gu et al 31 suggested that the non-uniform TM distributions and the nanophase separation also influence the voltage evolution. Despite such a disagreement on the specific origin of the performance degradation, Wu et al recently identified the voltage range where the detrimental reactions occur.…”

Section: Electrode Materialsmentioning

confidence: 99%

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%

Advanced analytical electron microscopy for lithium-ion batteries

Qian

et al. 2015

NPG Asia Mater

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“…[ 37,38 ] Several transmission electron microscopy (TEM) studies revealed that Ni tends to segregate on certain surface facets in Li-Mn-rich (LMR) oxides which results in structural and chemical modifi cations of the surface layer. [ 18,[38][39][40] As aforementioned, such surface modifi cation can be expected to affect the performance of cathode materials. The fundamental understanding on the surface modifi cation layer, however, is largely nonexistent as systematic investigation on surface segregation has not been carried out.…”

Section: Introductionmentioning

confidence: 99%

Ni and Co Segregations on Selective Surface Facets and Rational Design of Layered Lithium Transition‐Metal Oxide Cathodes

Yan

Zheng

et al. 2016

Advanced Energy Materials

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103

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The chemical processes occurring on the surface of cathode materials during battery cycling play a crucial role in determining battery's performance. However, the understanding of such surface chemistry is far from clear due to the complexity of redox chemistry during battery charge/discharge. Through intensive aberration corrected STEM investigation on ten layered oxide cathode materials, two important findings on the pristine oxides are reported. First, Ni and Co show strong plane selectivity when building up their respective surface segregation layers (SSLs). Specifically, Ni‐SSL is exclusively developed on (200)m facet in Li–Mn‐rich oxides (monoclinic C2/m symmetry) and on (012)h facet in Mn–Ni equally rich oxides (hexagonal R‐3m symmetry), while Co‐SSL has a strong preference to (20−2)m plane with minimal Co‐SSL also developed on some other planes in Li–Mn‐rich cathodes. Structurally, Ni‐SSLs tend to form spinel‐like lattice while Co‐SSLs are in a rock‐salt‐like structure. Second, by increasing Ni concentration in these layered oxides, Ni and Co SSLs can be suppressed and even eliminated. The findings indicate that Ni and Co SSLs are tunable through controlling particle morphology and oxide composition, which opens up a new way for future rational design and synthesis of cathode materials.

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“…To deliver large discharge capacity, Li 1+x [Ni y Mn 1-y ] 1-x O 2 is charged to high potential (above 4.4 V) initially which accompanied with irreversibly release of Li + and O 2À (net loss of Li 2 O). The removal of Li 2 O also results in rearrangement of the transition metal ions on the surface and gradually in the crystal lattice, which leads to instability of surface and structure of the material [6,7]. Moreover, our previous studies showed that the capacity degradation is derived from drastic increase of the interfacial and charge transfer resistance of the cathode upon cycling [8].…”

Section: Introductionmentioning

confidence: 99%