Optimized 4‐V Spinel Cathode Material with High Energy Density for Li‐Ion Cells Operating at 60 °C

Abstract

Spinel cathodes comprising 16‐μm, AlPO4‐coated Li1.09Mn1.83Al0.08O4 with a high energy density of 1.2 W h cm‐3 are synthesized via a conventional solid‐state reaction using MnO2 and Li2CO3 at 770 °C for 10 h and using a solution‐based coating method in bulk scale (>20 kg). The cathodes are coated by aluminum phosphate at a thickness of <10 nm. The coated cathodes exhibit a first discharge capacity of 108 mA·h g‐1 and a coulombic efficiency of >99.8%, and their capacity retention is 78% after 200 cycles at a 0.5C rate in a Li‐ion cell under 60 °C. More importantly, a Li‐ion cell containing the coated cathode does not exhibit a swelling problem after 200 cycles at 60 °C. Transmission and scanning electron microscopy suggest that the uniformly distributed AlPO4 coating and the possible formation of a solid solution phase along the surface play key roles in enhancing the electrochemical performance of the LiMn2O4 spinel at 60 °C.

Surface Mn Oxidation State Controlled Spinel LiMn2O4 as a Cathode Material for High‐Energy Li‐Ion Batteries

“…[ 22 ] The X-ray diffraction patterns of the BLMO and CoLMO samples (the latter containing 5 wt% Li 1.15 Co 0.32 Mn 1.53 O 4 ), match those from the reference cubic spinel phase (Fd-3m, JCPDS 89-0118) with no impurities ( Figure S5, Supporting Information). [ 20 ] Recalling from Figure S4 (Supporting Information) that the Co atoms are evenly distributed across the surface of the secondary particles, cross-sectional EDX analysis was carried out to investigate the distribution of Co in their interior (Figure 2 d). Indeed, this would increase the concentration of smaller Mn 4+ relative to larger Mn 3+ ions ( r Mn 3+ = 0.645 Å, r Mn 4+ = 0.53 Å, coordination number = 6) and decrease the lattice parameter.…”

“…However, doping these materials brings about large reductions in capacity, [ 13 ] such that in practice, the capacities of commercial spinel materials for Li-ion batteries are only ≈70% of that available in theory, canceling this particular merit of LiMn 2 O 4 . [ 20 ] For example, Li 1.15 Co 0.32 Mn 1.53 O 4 , which was used in this paper Spinel lithium manganese oxide (LiMn 2 O 4 ) has attracted much attention as a promising cathode material for large-scale lithium ion batteries. Various metal oxide coatings such as Al 2 O 3 , [ 14 ] AlPO 4 , [ 15 ] SiO 2 , [ 16 ] SnO 2 , [ 17 ] MgO, [ 18 ] LiCoO 2 , [ 19 ] etc., have been studied in this context.…”

“…[ 20 ] For example, Li 1.15 Co 0.32 Mn 1.53 O 4 , which was used in this paper Spinel lithium manganese oxide (LiMn 2 O 4 ) has attracted much attention as a promising cathode material for large-scale lithium ion batteries. Cation-substituted spinel oxides such as Li 1+ x M n 2− x − y M y O 4 , fulfi ll these requirements; indeed, (1) they have the same spinel structure as stoichiometric LiMn 2 O 4 and form epitaxial layers (rather than segregated particles) on the bulk surface, thereby providing good coating coverage, (2) cation-substituted spinels with an average Mn oxidation state greater than 3.6 cycle well at elevated temperatures, and (3) they are electrochemically active therefore potentially good ionic conductors.…”

Hierarchical Surface Atomic Structure of a Manganese‐Based Spinel Cathode for Lithium‐Ion Batteries

“…However, the degree of doping cannot be increased more than a certain extent, because of the trade-off between the doping level and the gravimetric capacity. [15] Similarly, the surface of the active material cannot be fully covered by the metal-oxide coating. The coating coverage can be improved by increasing the amount of the coating material, but several disadvantages are observed as result, such as a reduction in capacity and an increase in ionic resistance.…”

“…These particles were then used to fabricate the two active materials evaluated in this study: 1) They were coated sequentially with Li 1. 15 Figure S1 in the Supporting Information). Assuming that the coating precursors were completely consumed in the reactions to form Li 1.…”