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LiAl5O8-coated Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials were synthesized by using the co-precipitation method along with a facile sol-gel coating process. Homogeneous and 3–5 nm thin LiAl5O8 film was formed on the LMNC surface. After the coating modification, discharge specific capacity, the initial Coulombic efficiency, and rate performance were improved to some extent. It was particularly important to note that the voltage decay of the battery after the charge and discharge cycle was well suppressed. Specifically, the 3 wt% LiAl5O8-coated electrode can deliver the initial discharge capacity of 243.5 mAh g−1 with a low irreversible capacity loss of 51.1 mAh g−1 and the initial Coulombic efficiency reached the maximum of 82.63% at 0.1 C rate. Although the 1 wt% LiAl5O8-coated electrode was cycled through 100 cycles at a rate of 0.5 C, the capacity retention rate was still up to 95.8%, while that of the LiAl5O8-free one was only 82.8%. The stable and thin LiAl5O8 coating layer protected the electrode structure from HF corrosion and other side reactions and reduced the oxygen loss (in the form of Li2O) by suppressing the initial activation of Li2MnO3.

The inorganic solid electrolytes Li6.25-xAl0.25La3Zr2-xTaxO12 (LALZT) with various Ta contents (x) are synthesized using conventional solid-state reaction method at 1200 ​°C for different holding times. The effect of holding time and Al/Ta co-doping on the crystal structure, microstructure and ionic conductivity of the LALZT solid electrolytes is discussed. The LALZT powder with a fine particle size and narrow particle distribution is prepared by the high-energy ball milling. Suitable Al/Ta doping stabilizes the cubic phase and enhances the ionic conductivity of the LALZT. The short holding time is 6 ​h due to the equal ionic conductivity for the LALZT samples sintered for 6 ​h or 10 ​h by the solid-state reaction method. The highest ionic conductivity can be obtained for the optimized composition of Li5.85Al0.25La3Zr1.6Ta0.4O12. The excellent ionic conductivity indicates that Al/Ta co-doped LALZT could be a promising electrolyte candidate for all-solid-state Li-ion batteries in practical application.

The electrochemical properties and microstructure of Li-rich cathode materials Li1.2Mn0.54Co0.13Ni0.13O2 synthesized in one-step were studied. The sample (s-g) was composed of single crystal particles (1–2 μm) with regular and smooth surface, and the particle size distribution was concentrated. Compared with the sample (cop) prepared by traditional coprecipitation method, the discharge specific capacity of sample s-g increased from 79.9 mAh g−1 to 114.5 mAh g−1 at 10C. After 100 cycles at the rate of 0.1C and 0.2C, the capacity retention rates of sample s-g were 99.48% and 105.36%, while those of sample cop were 66.23% and 71.55%, respectively. Homogeneous single crystal structure and good grain size control greatly released the capacity potential of Li-rich cathode materials and solved the problem of poor rate performance and fast capacity decay.