Wenbin Jin,Nan Liu,Fang Cheng,Zongqing Ma,Yongchang Liu,Pingzhan Si,Hongliang Ge
We report the C substitution effects in MgB 2 bulks on the lattice parameters, FWHM, and critical current density ( J c ) as a function of doping level. It is shown that using carbon-coated boron powder can effectively control the grain growth of MgB 2 during the whole sintering process. Accompanied by the rapid cooling process, the final average grain size can be restrained within merely 50 nm, and the J c value of the sample can be significantly improved at high field. On top of that, adding Cu is also considered a key factor in improving the current carrying property of the graphene-doped sample throughout the whole field, which can be attributed to the formation of the MgCu 2 alloy phase.
Faqiang Shi,Limeng Liu,Zhaoping Hou,Guihong Geng,Yujin Wang
Tantalum carbide ceramics with an overall composition of TaC 0.6 were prepared by hot pressing at 1700 °C for 1 h under 30 MPa pressure with fcc TaC and bcc Ta powder as starting materials. Effects of adding 0–30 mol% Cu on densification, phase formation, microstructural evolution , mechanical properties and electrical conductivity of the obtained composite ceramics were investigated. Full density could be reached at 20 mol% Cu addition and above. Reactions between TaC and Ta resulted in the final phases of hexagonal Ta 2 C and rhombohedral ζ-Ta 4 C 3-x . Plate-shaped ζ laminate grew in both TaC and Ta 2 C and consequently had their sizes confined by the parental grains. Addition of 20–30 mol% Cu could significantly grow the intermediate Ta 2 C grains, hence controlling length of the ζ laminates precipitated in them to form bimodal microstructures consisting of large grains. The 20 mol% Cu composition had a better flexural strength (706 ± 46 MPa) and fracture toughness (9.2 ± 1.7 MPa m 1/2 ). Electrical resistivity at room temperature of the composites decreased with Cu content from 1.03 μΩ m at 0 mol% addition to 0.12 μΩ m at 30 mol% Cu.
The low ionic conductivity of poly(ethylene oxide) (PEO)-based polymer electrolytes at room temperature and the undesired lithium-dendrite growth at Li|PEO interface impede their further application. Herein, a PEO polymer is regulated at the molecular level through a copper ion (Cu 2+ ) coordination effect with both PEO and Li salts to achieve a high Li + conductivity of 0.2 mS cm −1 and a transference number of 0.42 at 30 °C. Moreover, the Cu-coordinated PEO electrolyte is neither sticky nor hygroscopic because the hydrophilic oxygen groups in PEO are terminated by Cu ions. Furthermore, the in situ formed F/Li-rich inorganic layer induced by CuF 2 additive accelerates Li + transport kinetics and enables uniform Li + deposition during Li plating/stripping. As a result, the Cu 2+ -coordinated PEO electrolytes deliver a high critical current density of 1.5 mA cm −2 at 30 °C. An all-solid-state Li-LiNi 0.83 Co 0.12 Mn 0.05 O 2 (NCM83) battery with such a copper coordinated PEO electrolyte exhibits a long cycle life over 500 cycles with a capacity retention of 71% under 0.6 C at 30 °C. When the mass loading increases to a record high of 7 mg cm −2 , the Li-NCM83 cell delivers a high areal capacity of 1.07 mAh cm −2 under 0.1 C at 30 °C.
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