Inexpensive and green synthesis of multi-doped LiFePO4/C composites for lithium-ion batteries

Recent advances in the design of cathode materials for Li-ion batteries

The Li-ion battery (LIB) industry has rapidly developed and dominates the market of electric vehicles and portable electronic devices. Special attention is devoted to achieving higher power and energy densities, along with enhancing safety and reducing cost. Therefore, critical insights should be made on the understanding of the behavior of the components of LIBs under working conditions in order to direct future research and development. The present review discusses the literature on the properties and limitations of different cathode materials for LIBs, including layered transition metal oxides, spinels, and polyanionic positive electrode materials, with critical insights on the structural, thermal, and electrochemical changes that take place during cycling. Besides, the strategies and techniques capable of overcoming current limitations are highlighted.

Enhancement of Electrochemical Performance of LiFePO4@C by Ga Coating

LiFePO₄ (LFP) is one of the cathode materials widely used in lithium ion batteries at present, but its electronic conductivity is still unsatisfactory, which will affect its electrochemical performance. Ga-coated LiFePO₄@C (LFP@C) samples were prepared by a hydrothermal method and ultrasonic dispersion technology. Ga has good electrical conductivity and can rapidly conduct electrons within the LFP cathode material under the synergistic effect with C coating, thus improving the dynamic performance of the LFP cathode material. The experimental results show that LFP@C/Ga samples exhibit good electrochemical performance. Compared with the pristine LFP@C, the 1.0 wt % Ga-coated LFP@C cathode exhibits excellent discharge capacity and cycle stability. The former shows a discharge capacity of 152.6 mA h g^-1 at 1 C after 100 cycles and a discharge capacity retention rate of 98.77%, while pristine LFP@C shows only a discharge capacity of 114.5 mA h g^-1 and a capacity retention rate of 95.84% after 100 cycles at 1 C current density.

Stabilizing the structure of LiMn0.5Fe0.5PO4via the formation of concentration-gradient hollow spheres with Fe-rich surfaces

LiMn_xFe_1-xPO₄ (LMFP) has attracted extensive interest owing to its high safety and appropriate redox potential. Nevertheless, its poor electrochemical kinetics and structural instability, depending on its manganese content, are still limiting its further application. Herein, we realize a concentration-gradient LiMn_0.5Fe_0.5PO₄ hollow sphere cathode material with a carbon coating (HCG-LMFP/C) by a facile and controllable two-step solvothermal approach. On the one hand, the porous hollow architecture can sustain excellent structural stabilization against the volume changes that occur during repeated Li⁺ intercalation/deintercalation. On the other hand, the unique concentration-gradient structure with its Fe-rich surface can not only relieve interface deterioration and improve the ionic/electric conductivity due to the active nature of LiFePO₄, but also guarantees the chemical stability of the LMFP against electrolyte attack and remarkably reduces Mn dissolution, even at elevated temperature. Therefore, the obtained concentration-gradient HCG-LMFP/C cathode shows improved high-rate performance (111 and 78 mA h g^-1 at 20 and 60C rates, respectively) and excellent capacity retention (96% after 1000 cycles at the 10C rate) as well as outstanding temperature tolerance (over a temperature range from 40 °C to -10 °C). More importantly, the present gradient strategy opens up a new window for designing high-performance and stable olivine cathodes, which could also be compatible with many other energy-storage materials for various applications.