Octahedral and truncated high-voltage spinel cathodes: the role of morphology and surface planes in electrochemical properties

Abstract

High-voltage spinel cathodes LiMn 1.5 Ni 0.5 O 4 are promising candidates for large-scale energy-storage applications such as electric vehicles. However, the widespread adoption of this high-voltage spinel cathode is hampered by severe capacity fade, particularly at elevated temperatures, resulting from aggressive formation of a thick solid-electrolyte interphase (SEI) layer through side reactions with the electrolyte at the high operating voltage, cationic ordering between Mn 4+ and Ni 2+ ions in the crystal lattice, and formation of a rock salt Li x Ni 1Àx O impurity phase. While these issues have been explored, the wide variation in physical and electrochemical properties with different synthesis methods is not fully understood. In this investigation, we present how the synthesis conditions of the co-precipitation method influence the microstructure and morphology through nucleation and growth of crystals in solution. The samples were prepared by two similar wet-chemical routes and were characterized by microscopy and electrochemical methods to determine the role of microstructure and morphology in the electrochemical performance. Various factors such as the degree of cation ordering between Mn 4+ and Ni 2+ , Mn 3+ content, Ni-Mn ratio in the sample, change in lattice parameter with the state of charge, and surface crystal planes were examined to develop a better understanding of the factors influencing the electrochemical performance. It is found that the surface crystal planes, the arrangement of lithium ions near the surface, and the lithium diffusion mechanism have a dominant effect on the capacity retention and rate performance.

Truncated octahedral LiNi0.5Mn1.5O4 cathode material for ultralong-life lithium-ion battery: Positive (100) surfaces in high-voltage spinel system

“…This embodies in the disputed results of both experimental data [26e30] and theoretical calculation [31e35]. Particularly, the results are also conflicted in high-voltage spinel LNMO system [28,30,32], because the surface behaviors with electrolyte at high operating voltage are affected by more factors like cation ordering, oxygen vacancies, size effect, and so on. Nevertheless, it is still a huge challenge to get LNMO with regular surface facets significantly improving the electrochemical performance.…”

Influence of Synthesis, Dopants and Cycling Conditions on the Cycling Stability of Doped LiNi0.5Mn1.5O4Spinels

“…Furthermore, the cycling stability and rate capability decrease when the octahedral spinel particles are truncated. 26 The results of the chemical analysis are listed in Table S1. XRD and FTIR spectrometry are performed to identify the structural differences between the four analyzed materials (s. Figure 2).…”

“…26,27 Furthermore the voltage profiles and the capacities are dependent on the synthesis temperature. [28][29][30] In this work we show the difference in the electrochemical behavior between Fe-, Ti-doped LNMO and Ru-, Ti-doped LNMO spinels.…”

Polyhedral ordered LiNi0.5Mn1.5O4 spinel with excellent electrochemical properties in extreme conditions

“…Doping with metal ions (Cr [15], Mg [16]) is another commonly used means for improving the cycle and rate performances of ordered LiNi 0.5 Mn 1.5 O 4 material, although it also cannot avoid the disadvantages of a complex synthesis process, increasing cost and/or reducing the discharge capacity. Recently, Manthiram [17,18] and co-workers have found that surface planes have an important effect on the electrochemical properties of ordered LiNi 0.5 Mn 1.5 O 4 cathode. Interestingly, our group [19] have also achieved a disordered LiNi 0.5 Mn 1.5 O 4 material with a good compatibility between energy/power density and cycle life without sacrificing any other properties through synthesizing a chamfered polyhedral structure.…”