Synthesis And Electrochemical Performance Of Li-rich Mn-based Cathodes Materials For Li-ion Batteries

Lithium-rich manganese-based oxide cathode has been one of the promising cathode candidates for the high-energy density lithium-ion batteries due to its advantages such as high specific capacity,low cost and non-toxic.However,many shortcomings including poor rate performance,severe voltage decay and capacity decay during cycling hindered the practical applications of lithium-rich manganese-based oxide cathodes.In this paper,the preparation and modification of the Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ cathode materials were conducted to improve their electrochemical performance as follows:Mo-doped Li_1.2(Mn_0.54Ni_0.13Co_0.13)_1-xMo_xO₂?x=0.006,0.01,0.03?cathode materials were prepared via a sol-gel method and in-situ electrochemically induced phase-transition.At the rate of 5 C,the specific capacity of Li_1.2Mn_0.538Ni_0.128Co_0.128Mo_0.006O₂ reaches 178mAh g^-1,and the capacity retention is 80%after 100 charge-discharge cycles,both of which are superior to that of the Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ cathode.Mo doping into the transition metal layer provides stable frame and expands the spacing of the layered structure,improving the lithium ion diffusion rate and enhancing the rate performance of the cathode.Surface-enriched Mo efficiently induces the phase-transition from the layered structure to a spinel or rock salt phase on the surface during the few charge-discharge cycles at initial and in-situ forms a uniform protective layer on the surface.The surface-stabilized structure prevents the further local spinel-like phase transformation inside the material,maintains the layered structure,and improves the cycle stability of the cathode.Moreover,Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ cathodes were prepared at various calcination temperature based on the co-precipitated precursors to investigate the effect of the temperature in the structure and electrochemical properties of the cathode.The lithium-rich manganese-based materials with uniform particles size,high crystallinity,and low degree of lithium-nickel mixed layered structure was obtained at a suitable temperature of 950?.The specific discharge capacity at a small rate of 0.1 C is 256.7mAh g^-1,and the specific discharge capacity at 1 C is 186.4 mAh g^-1,which is about72.6%of the specific capacity at 0.1 C.After 400 cycles the capacity retention rate is65.5%.Finally,the effect of the cutoff voltage in the voltage and capacity decay during the charge-discharge cycling was carefully investigated.The results show that the voltage and capacity decay was effectively suppressed when the charge cutoff was below 4.5 V.When the battery was charged and discharged at the voltage range was 2.0-4.5 V under 1 C,the capacity retention rate is 88.5%after 400 cycles,and the voltage decay value is 0.45 V.Its excellent cycle performance is attributed to the low charge cut-off voltage,which can inhibit the phase transition of the layered structure,Li⁺/Ni²⁺cation mixing,and the dissolution of transition metal manganese.