Atomic structure and migration dynamics of MoS2/LixMoS2 interface

Chen, Shulin; Wang, Liping; Shao, Ruiwen; Zou, Jian; Cai, Ruxiu; Lin, Jinhuang; Chen, Zhu; Zhang, Jingmin; Xu, Feng; Cao, Jian; Feng, Jicai; Qi, Junlei; Gao, Peng

doi:10.1016/j.nanoen.2018.03.076

Cited by 47 publications

(37 citation statements)

References 48 publications

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“…Due to an increasing projected reaction area during the phase boundary motion, the K ion diffusivity in CF x is estimated to be 2.2–2.5 × 10 –12 cm 2 s –1 , in Figure 3a and Table S1 in the Supporting Information, based on the equation D = d 2 /t , where D is ion diffusivity, d 2 is the projection area, and t is the diffusion time. [ 18 ]…”

Section: Figurementioning

confidence: 99%

Reaction Mechanism and Structural Evolution of Fluorographite Cathodes in Solid‐State K/Na/Li Batteries

et al. 2020

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Fluorographites (CFx) are ultrahigh‐energy‐density cathode materials for alkaline‐metal primary batteries. However, they are generally not rechargeable. To elucidate the reaction mechanism of CFx cathodes, in situ transmission electron microscopy characterizations and ab initio calculations are employed. It is found that it is a two‐phase mechanism upon K/Na/Li ion insertion; crystalline KF (crystalline NaF nanoparticles and amorphous LiF) is generated uniformly within the amorphous carbon matrix, retaining an unchanged volume during the discharge process. The diffusivity for K/Na/Li ion migration within the CFx is ≈2.2–2.5 × 10–12, 3.4–5.3 × 10–12 , and 1.8–2.5 × 10–11 cm2 s–1, respectively, which is comparable to the diffusivity of K/Na/Li ions in liquid‐state cells. Encouraged by the in situ transmission electron microscopy (TEM) results, a new rechargeable all‐solid‐state Li/CFx battery is further designed that shows a part of the reversible specific discharge capacity at the 2nd cycle. These findings demonstrate that a solid‐state electrolyte provides a different reaction process compared with a conventional liquid electrolyte, and enables CFx to be partly rechargeable in solid‐state Li batteries.

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Section: Figurementioning

confidence: 99%

Reaction Mechanism and Structural Evolution of Fluorographite Cathodes in Solid‐State K/Na/Li Batteries

et al. 2020

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“…Due to an increasing projected reaction area during the phase boundary motion, the K ion diffusivity in CF x is estimated to be ~232.9 nm 2 /s in Figure 2d, based on the equation D = d 2 /t, where D is ion diffusivity, d 2 is the projection area, and t is the diffusion time. 28 Sodiation of the CF x sample exhibits a similar two-phase response, as shown in Figure 2b, 3d-f, S4 and S6i-p, and Movie S3, S5. Observing the TEM and HAADF-STEM images, we conclude that the volume of CF x remains unchanged after sodiation (Figure 2e), and the SAED pattern ( Figure 3e) shows a two-phase reaction representing the transformation of CF x to NaF and C, which is in agreement with previous studies.…”

Section: Resultsmentioning

confidence: 63%

Reaction mechanism and structural evolution of fluorographite cathodes in Li/Na/K batteries

Ding

Yang

Jiang

et al. 2020

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Fluorographites (CFx) are potential cathode materials for alkaline metal primary batteries with ultrahigh energy densities. To elucidate the reaction mechanism and structural evolution of CFx cathodes, we combine in situ transmission electron microscopy and ab initio calculations and discover a two-phase mechanism upon Li/Na/K ion insertion. Amorphous LiF (crystalline NaF and KF nanoparticles) are generated uniformly within the amorphous carbon matrix, which retains an unchanged volume during the discharge process. The diffusivity for K/Na/Li ion migration within the CFx is approximately 232.9 nm2/s, 479.7 nm2/s, and 2133.0 nm2/s, respectively, which is comparable to the diffusivity of Li/Na/K ions in liquid-state cells. During charging, amorphous LiF and crystal NaF decompose into alkali metal and F2. Our results reveal no substantial volume change and good ion diffusion kinetics, demonstrating the applicability of all-solid-state M/CFx (M = Li/Na/K) primary batteries. This new understanding may promote the design and development of better CFx-based batteries.While lithium ion batteries (LIBs) are widely applied in portable electronics and electric vehicles, cheaper, more advanced battery systems with higher energy and power densities, and improved safety performance remain in demand.1-5 Among the materials employed in cathode systems, conversion-type materials, such as halides, chalcogenides, and oxides, demonstrate high specific capacities, offering lithium-metal batteries with high energy densities.4,6,7 For example, fluorinated graphite (CFx, x = 1) cathodes exhibit a high theoretical energy density and power density of 3725 Wh kg-1 and 9313 Wh L-1, respectively 6, which can be used in Li primary cells. 8 The practical energy density in Li/CF1.0 cells reaches 2600 Wh kg-1, which is much higher than that in Li/I2, Li/SOCl2, Li/MnO2, Li/Ag2CrO4, and Li/CuS systems.9,10 CFx also delivers a discharge specific capacity of 1061 mAh/g (1439 Wh kg-1) with a discharge plateau of 2.4 V11,12 in a Na/CFx system, and 749 mAh g-1 (1869 Wh kg-1) with a discharge voltage plateau of 3.0 V in a K/CFx system13, which makes CFx applicable for multiple alkali ion batteries. Moreover, the irreversible conversion of CFx into LiF and carbon during discharge, due to the high dissociation energy of LiF (6.1 eV), means the decomposition of LiF by charging alone is not possible.9,10,12 Yazami et al. first demonstrated the reversible electrochemical reaction of CFx with lithium in F ion batteries with a reversible capacity of ~120 mAh g-1.14 Later, Liu et al. reported a reversible Na/CFx battery with a specific capacity of 786 mAh g-1.11 However, these batteries suffer from poor rate performance at low temperatures15, initial voltage delay during the discharge process8 and large heat generation at high discharge rates, which limit their application in harsh environments.9,16 Therefore, a detailed study of the reaction mechanisms is urgently required for the further optimization. Various studies have been conducted to understand these battery systems using different techniques.8,16-20 For example, in situ XRD results suggested a simultaneous formation of a CF(x-y)-Li+ intermediate phase and crystal LiF15,18, while other studies reported a formation of amorphous LiF followed by recrystallization to crystalline LiF.17,19 The crystalline LiF is generated in an orientation that relates to the absorption energy of the solvents on the LiF surface.16 The reversibility and reaction mechanism of CFx in Na/CFx batteries was studied using softX-ray absorption spectroscopy (SXAS) and nuclear magnetic resonance (NMR) techniques, which revealed reversible conversions between CFx and NaF.12 The liquid electrolyte was reported to act as an ion conductor and solution medium to dissolve and aggregate alkali fluoride crystals in a M–CFx (M = Li, Na, and K) system, resulting in large crystalline alkali fluorides.13 Despite intensive efforts focusing on the reaction mechanism, the structural evolution and reaction pathway of CFx in Li/Na/K batteries remains unclear. In this study, we use in situ transmission electron microscopy (TEM) with high spatial/temporal resolution to probe the phase transformation, intermediate phase, and volume change in real time (Figure 1a).21,22 We find that a two-phase reaction occurs during alkali ion intercalation, and the diffusivity of K/Na/Li ion intercalation in CFx is approximately 232.9 nm2/s, 479.7 nm2/s, and 2133.0 nm2/s, respectively. In situ electron diffraction patterns show the formation and even distribution of crystalline KF and NaF nanoparticles and amorphous LiF in the amorphous carbon matrix, leading to no volume change. Upon the insertion of K with a large ionic radius, the interlayer spacing of CF increases, and while only subtle changes are observed during Na/Li ion insertion, both are confirmed through density functional theory (DFT) calculations. Moreover, we find both amorphous LiF and crystalline NaF decompose into alkali metal and F2 during the charging process under vacuum. The results show no volume change and good ion diffusion kinetics during ion intercalation, suggesting that the all-solid-state M/CFx (M = Li/Na/K) primary batteries have broad applicability.

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“…Na + insertion induced the start of a two‐phase reaction, in which trigonal prismatic 2H MoS 2 gradually transformed into octahedral 1T‐NaMoS 2 . A boundary with 2 nm thickness was observed and propagated at ≈3–7 nm s −1 , which was much slower than that of lithiation (∼30–70 nm s −1 ) reported in previous studies (Figure ) . The Na + transport induced a large number of crystal defects in MoS 2 , which was accompanied by the fracture of the continuous layered structure into few nanosized domains (Figure e, f).…”

Section: Charge Storage In Sibs and Kibsmentioning

confidence: 99%

“…Hence, the preparation of ultrathin MoS 2 nanosheets might be an effective strategy to suppress the strain and improve the cycling stability of electrode materials. The atomic structure and dynamics of the reaction interface between the lithiated Li x MoS 2 and pristine MoS 2 have been investigated intensively using in situ TEM . The reaction interface was composed of a pristine 2H phase, a 1T phase, and a distorted 1T phase noted as 1T′ phase.…”

Section: Charge Storage In Libsmentioning

confidence: 99%

“… a) Experimental setup and, b) optical images of MoS 2 flakes during the lithiation and delithiation process (reproduced with permission, Copyright American Chemical Society, 2015). c) Fast Fourier space filtered image of the reaction interface between Li x MoS 2 and MoS 2 (reproduced with permission, Copyright Elsevier, 2018). d–g) Atomic‐scale visualization of lithiation of the MoS 2 nanosheet along the [001] direction (reproduced with permission, Copyright Elsevier, 2017).…”

Section: Charge Storage In Libsmentioning

confidence: 99%

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How does Molybdenum Disulfide Store Charge: A Minireview

et al. 2020

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MoS2 has attracted tremendous attention as a promising electrode material for rechargeable alkali metal ion (Li+, Na+, K+) batteries due to its high capacity and low cost. However, the practical application of MoS2 for energy storage has not been achieved yet, which is restricted by its intrinsic charge‐storage behavior. Debates still exist in this field although great efforts have been made to reveal alkali metal ion (Li+, Na+, K+) storage mechanism of MoS2. This Minireview aims to provide an analysis and summary of the related phase conversion, structure collapse, and loss of active material in a MoS2 electrode during the intercalation/extraction process of alkali metal ions. Hence, the fundamental understanding about the charge storage in MoS2 is of importance for the rational design of MoS2 electrodes with excellent electrochemical performance.

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Atomic structure and migration dynamics of MoS2/LixMoS2 interface

Cited by 47 publications

References 48 publications

Reaction Mechanism and Structural Evolution of Fluorographite Cathodes in Solid‐State K/Na/Li Batteries

Reaction Mechanism and Structural Evolution of Fluorographite Cathodes in Solid‐State K/Na/Li Batteries

Reaction mechanism and structural evolution of fluorographite cathodes in Li/Na/K batteries

How does Molybdenum Disulfide Store Charge: A Minireview

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