Improved Electrochemical Properties of LiMn2O4-Based Cathode Material Co-Modified by Mg-Doping and Octahedral Morphology

Abstract

In this work, the spinel LiMn2O4 cathode material was prepared by high-temperature solid-phase method and further optimized by co-modification strategy based on the Mg-doping and octahedral morphology. The octahedral LiMn1.95Mg0.05O4 sample belongs to the spinel cubic structure with the space group of Fd3m, and no other impurities are presented in the XRD patterns. The octahedral LiMn1.95Mg0.05O4 particles show narrow size distribution with regular morphology. When used as cathode material, the obtained LiMn1.95Mg0.05O4 octahedra shows excellent electrochemical properties. This material can exhibit high capacity retention of 96.8% with 100th discharge capacity of 111.6 mAh g−1 at 1.0 C. Moreover, the rate performance and high-temperature cycling stability of LiMn2O4 are effectively improved by the co-modification strategy based on Mg-doping and octahedral morphology. These results are mostly given to the fact that the addition of magnesium ions can suppress the Jahn–Teller effect and the octahedral morphology contributes to the Mn dissolution, which can improve the structural stability of LiMn2O4.

Screening LiMn2O4 Surface Modification Schemes under Theoretical Guidance

“…The small change in the initial discharge capacity again indicates that Mg is likely to be doped at both Li and Mn sites. After 200 cycles at 45 °C, the discharge capacity and Coulomb efficiency of all surface-doped samples are significantly higher than the bare sample, as shown in Figure b, which is also consistent with the experimental results in previous literature reports. , The cycling performance of the surface-doped LMO cathodes synthesized in this work is also comparable to previous studies. The same enhancement appears in the EIS spectra, as shown in Figure c.…”

“…Up to now, researchers have carried out a wide range of studies to mitigate Mn dissolution, including modulation of particle morphology, changing electrolyte components, coating, , and doping. , Since doping can affect the intrinsic stability of the material by regulating the interaction between atoms, we chose to study the effects of (surface) doping on Mn dissolution of the LMO cathode. Taking the 3.5+ nominal valence of Mn ions in the LMO cathode as the demarcation, the dopants that have been studied can be divided into two categories: (1) elements with 2+/3+ nominal valence such as Mg, Al, , Cu, Zn, and so forth. Researchers believe that these elements can reduce the proportion of Mn 3+ in the LMO cathode, thus reducing the deterioration of the LMO cathode properties due to the disproportionation reaction and the John–Teller effect. , (2) Elements with nominal valence higher than 3+ such as Ti, V, Cr, Nb, , and so forth.…”

First-Principles Simulations for the Surface Evolution and Mn Dissolution in the Fully Delithiated Spinel LiMn2O4

“…Therefore, to stabilize the interface, it is necessary to stabilize the surface oxygen to shut down the initial condition of Mn dissolution. By replacing the Mn atom with an element that interacts strongly with oxygen atoms, − the generation of surface oxygen vacancies can be suppressed. However, surface oxygen loss cannot be completely avoided with electrochemical cycling, so the electrolyte additives ,, (such as lithium bis­(oxalato)­borate (LiBOB)) and coating layers − would be useful supplements to further improve interfacial stability.…”

Enhancing Surface Chemical Stability of LiMn2O4 Cathode by Strontium Enrichment at Grain Boundaries

“…[1,11,12] It is essential to find an effective method to solve the abovementioned problems. Many ordinary methods can generally be divided into three groups: surface modification, [13][14][15] lattice substitution, [16][17][18][19][20] and morphology control. [21,22] For example, the lattice substitution method features a small amount of Mn is replaced by extraneous ions such as Al 3 + , [17] Mg 2 + , [16] Ni 2 + , [18] Sc 3 + [19] and P 5 + [20] so as to enhance crystal structural stability.…”

“…Many ordinary methods can generally be divided into three groups: surface modification, [13][14][15] lattice substitution, [16][17][18][19][20] and morphology control. [21,22] For example, the lattice substitution method features a small amount of Mn is replaced by extraneous ions such as Al 3 + , [17] Mg 2 + , [16] Ni 2 + , [18] Sc 3 + [19] and P 5 + [20] so as to enhance crystal structural stability. However, atom-doped LMO is still directly exposed to electrolyte, resulting in the generation of HF from electrolyte decomposition and dissolution of Mn 3 + in LMO, and leading to structural degradation.…”