High Initial Reversible Capacity and Long Life of Ternary SnO_(2)-Co-carbon Nanocomposite Anodes for Lithium-Ion Batteries

The two major limitations in the application of SnO_2 for lithium?ion battery(LIB) anodes are the large volume variations of SnO_2 during repeated lithiation/delithiation processes and a large irreversible capacity loss during the first cycle, which can lead to a rapid capacity fade and unsatisfactory initial Coulombic e ciency(ICE). To overcome these limitations, we developed composites of ultrafine SnO_2 nanoparticles and in situ formed Co(CoSn) nanocrystals embedded in an N?doped carbon matrix using a Co?based metal–organic framework(ZIF?67). The formed Co additives and structural advantages of the carbon?confined SnO_2/Co nanocomposite e ectively inhibited Sn coarsening in the lithiated SnO_2 and mitigated its structural degradation while facilitating fast electronic transport and facile ionic di usion. As a result, the electrodes demonstrated high ICE (82.2%), outstanding rate capability(～ 800 mAh g^(-1) at a high current density of 5 A g^(-1)), and long?term cycling stability(～ 760 mAh g^(-1) after 400 cycles at a current density of 0.5 A g^(-1)). This study will be helpful in developing high?performance Si(Sn)?based oxide, Sn/Sb?based sulfide, or selenide electrodes for LIBs. In addition, some metal organic frameworks similar to ZIF?67 can also be used as composite templates.

Microstructure and performance of WC-Co-Cr coating with ultrafine/nanocrystalline structures

The WC-lOCo-4Cr composite powder was synthesized firstly. Then the composite powder was agglomerated to prepare thermal spraying feedstock. The ultrafine/nanostructured WC-lOCo-4Cr coating was prepared by high velocity oxygen fuel thermal spraying. The phase constitution, elemental distribution and microstructure of the coating were characterized by X-ray diffraction and transmission electron microscopy, respectively. The wear resistance and corrosion resistance of the prepared composite coating were tested. The results show that the main phases of the coating include WC, binding phase with partial amorphous structure, with a little WC and Co(Cr)coexisting. The distributions of Co and Cr elements from the phase boundary to the eutectic area then to Co zone were analyzed quantitatively. The mechanisms for the formation of the microstructure and effects of Cr on the performance of the composite coating are proposed.

Realizing Complete Solid-Solution Reaction to Achieve Temperature Independent LiFePO_(4) for High Rate and Low Temperature Li-Ion Batteries

The lithium iron phosphate battery(LiFePO4 or LFP)does not satisfactorily deliver the necessary high rates and low temperatures due to its low Li+diffusivity,which greatly limits its applications.The solid-solution reaction,compared with the traditional two-phase transition,needs less energy,and the lithium ion diffusivity is also higher,which makes breaking the barrier of LFP possible.However,the solid-solution reaction in LFP can only occur at high rates due to the lattice stress caused by the bulk elastic modulus.Herein,pomegranate-like LFP@C nanoclusters with ultrafine LFP@C subunits(8 nm)(PNCsLFP)were synthesized.Using in situ X-ray diffraction,we confirmed that PNCsLFP can achieve complete solid-solution reaction at the relatively low rate of 0.1C which breaks the limitation of low lithium ion diffusivity of the traditional LFP and frees the lithium ion diffusivity from temperature constraints,leading to almost the same lithium ion diffusivities at room temperature,0,−20,and−40℃.The complete solid-solution reaction at all rates breaks the shackles of limited lithium ion diffusivity on LFP and offers a promising solution for next-generation lithium ion batteries with high rate and low temperature applications.