High-rate, high capacity ZrO2 coated Li[Li1/6Mn1/2Co1/6Ni1/6]O2 for lithium secondary batteries

Abstract

Recently, there have been many reports on efforts to improve the rate capability and discharge capacity of lithium secondary batteries in order to facilitate their use for hybrid electric vehicles and electric power tools. In the present work, we present a ZrO 2 -coated Li[Li 1/6 Mn 1/2 Co 1/6 Ni 1/6 ]O 2 . The bare Li[Li 1/6 Mn 1/2 Co 1/6 Ni 1/6 ]O 2 shows a high initial discharge capacity of 224 mAh g -1 at a 0.2 C rate. Owing to the stability of ZrO 2 , it was possible to enhance the rate capability and cyclability. After 1 wt% ZrO 2 coating, the ZrO 2 -coated Li[Li 1/6 Mn 1/2 Co 1/6 Ni 1/6 ]O 2 showed a high discharge capacity of 115 mAh g -1 after 50 cycles under a 6 C rate, whereas the bare Li[Li 1/6 Mn 1/2 Co 1/6 Ni 1/6 ]O 2 showed a discharge capacity of only 40 mAh g -1 and very poor cyclability under the same conditions. Based on results of XRD and EIS measurements, it was found that the ZrO 2 suppressed impedance growth at the interface between the electrodes and electrolyte and prevented collapse of the layered hexagonal structure.

Surface modification effects of [Li,La]TiO3 on the electrochemical performance of Li[Ni0.35Co0.3Mn0.35]O2 cathode material for lithium–ion batteries

“…The coated material annealed at 400°C showed the best capacity retention at all current states in the experiments, and the effects of the coating on the rate capability were manifested regardless of the annealing temperature. The enhanced cycle life performance due to surface modification is similar to results reported previously [12][13][14][15][16][17][18][19][20]. In the [Li,La]TiO 3 system, the composition, structure, and phase are significant factors when considering ionic and electronic conductivities [22][23][24][25].…”

“…All of the samples showed good layer hexagonal ordering, regardless of the [Li,La]TiO 3 content up to 5 wt%. Splitting of (018)/(110) is well known to indicate a high degree of crystallinity and good layered hexagonal ordering [16]. The absence of peaks corresponding to lithium lanthanum titanate in Fig.…”

“…This confirmed that a very small amount of the coating layer was present in the form of an amorphous oxide. The XRD patterns of coated particles are known to conform to the symmetry of the core materials irrespective of the coating material method because the coating material is present as a thin film, possibly as a mixed oxide formed by intercalation of the coating oxide with the core material [12,13,16,17,19,20]. Transmission electron microscopy (TEM) was used to investigate the surface shape of the pristine and surface-modified particles in detail.…”

“…The electrochemical properties for the electrode annealed at 700°C are likely due to enhanced diffusion of La and Ti element into the active material, which decreases the La and Ti contents on the surface, as shown by the XPS analysis. In general, a high frequency semicircle is related to a passivating surface film, a so called solid electrolyte interface, and an intermediate frequency semicircle is attributed to charge transfer resistance in the electrode/electrolyte interface [16]. In Fig.…”

“…A wide range of studies of layered cathode compositions has been reported [2][3][4][5][6][7][8][9][10][11], and surface modification of electrode materials for lithium batteries has been identified as a promising method for achieving improved electrochemical properties [12][13][14][15]. Studies of surface coating of cathode materials with various stable metal oxides or phosphates such as ZrO 2 [16], TiO 2 [17], MgO [18], AlPO 4 [19], and Co 3 (PO 4 ) 2 [20] have revealed that coating active materials is an effective approach for improving the electrochemical performance. The coating effect correlates highly with the coating material [17,20,21].…”