Synthesis Of LiFePO₄ Lithium-ion Battery Cathode Materials By Microwave Heating And Its Modification

Higherandhigherrequirements forlithium ionbatteries areput forwardwiththequick developments of science and technology and due to the serious problems ofenergyand environment. LiFePO4 is becoming the hot issue as a cathode material forlithium ion batteries because of its stabilization, abundance, cheapness, security,environmental friendlyness and high theoretical capacity. However, its low electronconductivity and low lithium ion diffusion rate are the major obstacles affecting thepropertiesofLiFePO4.Theaimsofthepresentworkaretoincorporatethenewsourceof carbon and to dope with higher valence of ion to improve the electrochemicalproperties of LiFePO4. LiFePO4/C, LiFePO4/Ti4+ and LiFePO4/(C+Ti4+) compositecathode materials were synthesized using microwave heating. The microstructure andmorphologies of these composites were investigated by XRD, SEM and TEM. Thelithium ion batteries were assembled in an Ar-filled glove box. The electrochemicalperformanceswereevaluatedbygalvanostaticcharge-discharge.Carbon-coated LiFePO4 composite was synthesized using citric acid as carbonsource. The material with 10wt% carbon exhibited the best electrochemicalperformance. Its initial charge specific capacity is 141.63 mAh·g-1 at 0.1C. Thecapacitymaintained to be 134.33 mAh·g-1 after 10 cycles, with the capacityloss ratiobeing 5.16%. The initial charge specific capacity is 116.54 mAh·g-1 and 87.21mAh·g-1 at 0.3C and 1C, respectively. And the cycling behavior of the material isgoodundertheseconditions.LiFePO4/C composite using PAM as carbon source delivered a high initialspecific discharge capacityof 150.22 mAh·g-1 with 5wt% PAM at 0.1C. The capacitymaintained to be 104.71mAh·g-1 after 10 cycles. The capacityloss ratio is larger thanthat with citric acid as carbon source. The initial charge specific capacity is 95.15mAh·g-1 and 57.21 mAh·g-1 at 0.3C and 1C, and the cycling behavior of the materialisnotsogood.LiFePO4/Ti4+ composite showed a high initial specific discharge capacity of123.08 mAh·g-1 with 1mol% Ti4+ at 0.1C. The capacity maintained to be 116.63mAh·g-1 after 10 cycles. The initial charge specific capacity is 97.92 mAh·g-1 and59.38 mAh·g-1 at 0.3C and 1C, respectively, and the cycling behavior of the material isquitepoor.LiFePO4/(C+Ti4+) composite using citric acid and TiO2 delivered a high initialspecific discharge capacity of 138.52 mAh·g-1 with 5wt% citric acid and 1mol% Ti4+at 0.1C. The capacity maintained to be 129.42 mAh·g-1 after 10 cycles. The initialcharge specific capacity is 114.95 mAh·g-1 and 102.39 mAh·g-1 at 0.3C and 1C, andthecyclingbehaviorofthematerialisverygood.