Understanding the Li-ion storage mechanism in a carbon composited zinc sulfide electrode

Sulfide compounds are interesting conversion electrode materials for Li-ion batteries, due to their high theoretical capacity. However, they suffer from large volumetric changes and fast capacity fading. To overcome these issues, nanosized zinc sulfide (ZnS) modified with polyelectrolytes and graphene (ZnS-C/G) has been synthesized and investigated as an enhanced conversion-alloying anode material. In situ synchrotron X-ray diffraction and X-ray absorption spectroscopy are used to elucidate the Li storage process during the 1st cycle. In addition, the evolution of internal resistance and the corresponding solid electrolyte interphase (SEI) formation during the 1st cycle are discussed based on electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. The results reveal that the formation of lithiated products and the SEI layer at different voltages can influence Li+ diffusion into the electrode. Moreover, an artificial carbon layer can not only facilitate Li+ transport but also avoid the direct formation of the SEI layer on the surface of active particles. Compared to bare ZnS, the ZnS-C/G electrode shows outstanding rate capability and cycling capacity (571 mA h g−1 after 120 cycles at a specific current of 1.0 A g−1 with a retention rate of 94.4%). The high capacity at elevated current density is ascribed to the contribution of capacitive charge storage

Phosphoric acid and thermal treatments reveal the peculiar role of surface oxygen anions in lithium and manganese-rich layered oxides

The interplay between cationic and anionic redox activity during electrochemical cycling makes layered Li-rich oxides appealing cathodes for state-of-the-art lithium-ion batteries. However, it remains challenging as the origin of lattice oxygen activity is not yet fully understood. Here we report on the effects of a lithium-deficient layer in the near-surface region of Co-free Li-rich Li[Li0.2Ni0.2Mn0.6]O-2 (LLNMO) achieved via a phosphoric acid surface treatment. Our results show that oxidized On- (0 < n < 2) species are formed on the surface of H3PO4-treated LLNMO resulting from Li ion deficiency and lattice distortion. The metastable On- could be easily released from the oxygen surface lattice forming O-2 via thermal treatment, accompanied by a surface reconstruction and a layered-to-rock-salt/spinel transition. The presented results demonstrate that the surface lattice structure plays a critical role in the electrochemical performance of LLNMO. This information provides new insights into the oxygen redox in LLNMO and opens up an opportunity for Li-rich cathodes to achieve long cycle life toward a broad range of applications in electrical energy storage devices

Hybrid electrons in the trimerized GaV 4 O 8 .

International audienceMixed-valent transition-metal compounds display complex structural, electronic and magnetic properties, which often intricately coexist. Here, we report the new ternary oxide GaV 4 O 8 , a structural sibling of skyrmion-hosting lacunar spinels. GaV 4 O 8 ..

Understanding the Lithium Storage Mechanism in Core–Shell Fe2O3@CFe_{2}O_{3}@C Hollow Nanospheres Derived from Metal–Organic Frameworks: An In operando Synchrotron Radiation Diffraction and in operando X-ray Absorption Spectroscopy Study

In this work, a core−shell structure of an Fe2O3@C hollow nanosphere derived from metal−organic frameworks is used as an anode material for Li-ion batteries. This material delivers a reversible capacity of 928 mAh g−1 at 0.2 A g−1 in 1 M LiPF6 in ethylene carbonate/dimethyl carbonate = 1:1. Although 1 M lithium bis(trifluoromethane sulfonyl)imide is used as a conductive salt, it delivers only 644 mAh g−1 at 0.2 A g−1. In operando synchrotron radiation diffraction revealed that the intermediate phases LixFe2O3 (R3̅m, hexagonal) and LixFe2O3 (Fd3̅m, Li-lean) form and subsequently convert to LixFe2O3 (Fd3̅m, Li-rich), which finally transforms into Fe, Li2O, and LixFe2O3 (Fd3̅m, X phase). During the delithiation process, the material does not return to the initial Fe2O3 structure; instead, the partially delithiated Lix−1Fe2O3 (Fd3̅m, X phase) and an amorphous metallic Fe phase remain. The Fe K-edge transition and the formation of Fe are confirmed by the in operando X-ray absorption spectroscopy measurement. Furthermore, the resistive contributions of this material in the two types of Li-salts are evaluated by electrochemical impedance spectroscopy, which highlights a different type of solid electrolyte interphase induced by the salt. This work provides fundamental insights into understanding the lithium-ion storage mechanism in conversion-type electrodes

In Operando analysis of the charge storage mechanism in a conversion ZnCo2O4ZnCo_{2}O_{4} anode and the application in flexible Li-ion batteries

As a conversion-type electrode material, ZnCo2O4 (ZCO) is intensively researched due to its attractive high specific capacity. Much effort to study ZCO supported on a conductive matrix has been successful to overcome the inherent drawbacks of low conductivity and dramatic volume variation during the (de)lithiation process. Despite many reported studies, the lithiation storage mechanism in the ZCO electrode is not yet clearly elucidated. In this work, in operando synchrotron radiation diffraction and in operando X-ray absorption spectroscopy are used to study the lithium storage mechanism in the ZCO material. The initial conversion process of ZnCo2O4, involving multiple reactions based on intercalation, conversion and alloying is deeply elucidated. During the 1st lithiation intermediate phases such as LiCo2O3, CoO and ZnO are formed. On the other hand, upon delithiation, the conversion to ZnO and CoO (and not to the pristine ZnCo2O4) occurs. This is different from the previous conclusion, which claims that Co3O4 forms after the initial delithiation. Furthermore, a binder-free ZnCo2O4/carbon cloth composite electrode is also prepared, which exhibits higher rate performance and capacity retention, compared to the bare ZCO electrod

Co9S8@carbon\mathrm{Co_{9}S_{8}@carbon} yolk-shell nanocages as a high performance direct conversion anode material for sodium ion batteries

Cobalt sulfides based on conversion mechanisms are considered as promising anode materials for sodium-ion batteries due to their appropriate working voltage and high practical capacities. But the severe volume change and structure transformation make their cycle stability and rate capability unsatisfactory. In this study, metal-organic framework derived Co9S8@carbon yolk-shell nanocages (Co9S8@CYSNs) was prepared and its direct conversion mechanism was carefully demonstrated for the first time by various spectroscopic techniques and first-principles calculations. The unique hierarchical structure of Co9S8@CYSNs composed of Co9S8 nanoparticles dispersed in amorphous carbon matrix inside a rigid carbon shell was capable of accelerating the conversion reaction, shortening the Na+ diffusion distance and providing a fast electron transport channel. Benefiting from the accelerated electrochemical reactions and high activities of nanosized particles, the Co9S8@CYSNs exhibited a large discharge capacity of 549.4 mA h g-1 at 0.1 A g-1. In addition, a superior rate performance of 100 mA h g-1 at 10 A g-1 and excellent cycle stability with a very low capacity decay of 0.019% per cycle over 800 cycles at 10.0 A g-1 were achieved because of the confine effect of the carbon shell and improved charge transfer reactions of the electrode

Phosphoric acid and thermal treatments reveal the peculiar role of surface oxygen anions in lithium and manganese-rich layered oxides

The interplay between cationic and anionic redox activity during electrochemical cycling makes layered Li-rich oxides appealing cathodes for state-of-the-art lithium-ion batteries. However, it remains challenging as the origin of lattice oxygen activity is not yet fully understood. Here we report on the effects of a lithium-deficient layer in the near-surface region of Co-free Li-rich Li[Li$_{0.2}$Ni$_{0.2}$Mn$_{0.6}$]O$_2$ (LLNMO) achieved via a phosphoric acid surface treatment. Our results show that oxidized O$^{n−}$ (0 < n < 2) species are formed on the surface of H$_3$PO$_4$-treated LLNMO resulting from Li ion deficiency and lattice distortion. The metastable O$^{n−}$ could be easily released from the oxygen surface lattice forming O$_2$ via thermal treatment, accompanied by a surface reconstruction and a layered-to-rock-salt/spinel transition. The presented results demonstrate that the surface lattice structure plays a critical role in the electrochemical performance of LLNMO. This information provides new insights into the oxygen redox in LLNMO and opens up an opportunity for Li-rich cathodes to achieve long cycle life toward a broad range of applications in electrical energy storage devices