Enhancing electrochemical performance and structural stability of LiNi0.5Mn1.5O4 cathode material for rechargeable lithium-ion batteries by boron doping

Abstract

LiNi0.5Mn1.5O4 cathode materials with a range of boron doping contents were successfully synthesized via an in situ solid-state method. The structures and grain morphologies were examined to elucidate the effect of boron doping on the electrochemical performance of LiNi0.5Mn1.5O4. Scanning electron microscopy images show that the particle sizes of boron-doped LiNi0.5-x/2BxMn1.5-x/2O4 samples increase compared with those of pure LiNi0.5Mn1.5O4. Characterization results confirm that boron doping could create more Mn3+ ions and increase the Mn3+ ions contents in LiNi0.5-x/2BxMn1.5-x/2O4 samples with increasing boron doping content. A greater number of Mn3+ ions could enhance the cationic disorder degree, thereby resulting in high electronic conductivities of LiNi0.5-x/2BxMn1.5-x/2O4 samples. Charge-discharge tests reveal that improvements in the electrochemical performance are achieved in LiNi0.5-x/2BxMn1.5-x/2O4 samples compared with that of pure LiNi0.5Mn1.5O4. The boron-doped LiNi0.495B0.01Mn1.495O4 (denoted as LNMO-B0.01) cathode exhibits an excellent cycling stability with a capacity retention of 83.3% after 500 cycles at 3 C. Moreover, it also displays an optimal rate capability with discharge capacities of 136.1, 135.7, 130.3, 126.2, 123.1, 114.5, 104.5, and 82.9 mA h g−1 at 0.2, 0.5, 1, 2, 3, 5, 7, and 10 C, respectively. The highest Li+ diffusion coefficient of LNMO-B0.01 determined from cyclic voltammetry tests indicates that an appropriate amount of boron doping could accelerate the Li+ diffusion in LNMO-B0.01. The lowest charge-transfer resistance obtained from the impedance spectra suggests that boron doping could promote kinetic charge transfer. As a result, this modification strategy can be utilized to enhance the electrochemical performance of LiNi0.5Mn1.5O4 material.