RESUMO
K+/Cl- and K+/F- co-doped LiNi0.5Mn1.5O4 (LNMO) materials were successfully synthesized via a solid-state method. Structural characterization revealed that both K+/Cl- and K+/F- co-doping reduced the LixNi1-xO impurities and enlarged the lattice parameters compared to those of pure LNMO. Besides this, the K+/F- co-doping decreased the Mn3+ ion content, which could inhibit the Jahn-Teller distortion and was beneficial to the cycling performance. Furthermore, both the K+/Cl- and the K+/F- co-doping reduced the particle size and made the particles more uniform. The K+/Cl- co-doped particles possessed a similar octahedral structure to that of pure LNMO. In contrast, as the K+/F- co-doping amount increased, the crystal structure became a truncated octahedral shape. The Li+ diffusion coefficient calculated from the CV tests showed that both K+/Cl- and K+/F- co-doping facilitated Li+ diffusion in the LNMO. The impedance tests showed that the charge transfer resistances were reduced by the co-doping. These results indicated that both the K+/Cl- and the K+/F- co-doping stabilized the crystal structures, facilitated Li+ diffusion, modified the particle morphologies, and increased the electrochemical kinetics. Benefiting from the unique advantages of the co-doping, the K+/Cl- and K+/F- co-doped samples exhibited improved rate and cycling performances. The K+/Cl- co-doped Li0.97K0.03Ni0.5Mn1.5O3.97Cl0.03 (LNMO-KCl0.03) exhibited the best rate capability with discharge capacities of 116.1, 109.3, and 93.9 mAh g-1 at high C-rates of 5C, 7C, and 10C, respectively. Moreover, the K+/F- co-doped Li0.98K0.02Ni0.5Mn1.5O3.98F0.02 (LNMO-KF0.02) delivered excellent cycling stability, maintaining 85.8% of its initial discharge capacity after circulation for 500 cycles at 5C. Therefore, the K+/Cl- or K+/F- co-doping strategy proposed herein will play a significant role in the further construction of other high-voltage cathodes for high-energy LIBs.
RESUMO
INTRODUCTION: Despite high population immunity, pertussis remains one of the leading causes of vaccine-preventable deaths worldwide. The aim of this study was to determine the seroprevalence of IgG antibodies to pertussis toxin (PT) and diphtheria among the adult male population leaving or entering China. METHODOLOGY: Blood samples were obtained from 240 Chinese and 207 African healthy adults that were leaving and entering China, respectively. Serum IgG antibodies against PT (anti-PT IgG) and diphtheria were determined. RESULTS: The mean concentration of anti-PT IgG antibodies was 13.82 IU/mL and 18.11 IU/mL for the leaving and entering populations, respectively. None of the studied Chinese leaving China were seropositive for pertussis. Of the 240 subjects leaving China, 209 (87.1%) had anti-diphtheria antibody concentrations of ≥ 0.1 IU/mL and 31 (12.9%) had antibody concentrations between 0.01 and 0.099 IU/mL. Eleven (5.31%) of the studied Africans entering China had anti-PT IgG antibodies higher than 30 IU/mL and thus were considered seropositive for pertussis. Of the 207 Africans entering China, antibody concentrations of ≥ 0.1 IU/mL were found in 164 subjects (79.2%) while 43 (20.8%) had antibody concentrations between 0.01 and 0.099 IU/mL. CONCLUSIONS: Almost all Chinese adult men leaving China and most African men entering China have very low serum antibody levels of pertussis. Furthermore, the antibody level of diphtheria among these two populations was low among adults. A larger population study is needed to determine whether booster vaccinations against pertussis and diphtheria should be considered for adults in China and also for Africans entering China.
