Encouraging Voltage Stability upon Long Cycling of Li-Rich Mn-Based Cathode Materials by Ta–Mo Dual Doping

Abstract

The Li-rich and Mn-based material xLi2MnO3·(1–x)­LiMO2 (M = Ni, Co, and Mn) is regarded as one of the new generations of cathode materials for Li-ion batteries due to its high energy density, low cost, and less toxicity. However, there still exist some drawbacks such as its high initial irreversible capacity, capacity/voltage fading, poor rate capability, and so forth, which seriously limit its large-scale commercial applications. In this paper, the Ta–Mo codoped Li1.2Ni0.13Co0.13Mn0.54O2 with high energy density is prepared via a coprecipitation method, followed by a solid–state reaction. The synthetic mechanism and technology, the effect of charge–discharge methods, the bulk doping and the surface structure design on the structure, morphology, and electrochemical performances of the Li1.2Ni0.13Co0.13Mn0.54O2 cathode are systematically investigated. The results show that Ta5+ and Mo6+ mainly occupy the Li site and transition-metal site, respectively. Both the appropriate Ta and Ta–Mo doping are conductive to increase the Mn3+ concentration and suppress the generation of Li/Ni mixing and the oxygen defects. The Ta–Mo codoped cathode sample can deliver 243.2 mA h·g–1 at 1 C under 2.0–4.8 V, retaining 80% capacity retention after 240 cycles, and decay 1.584 mV per cycle in 250 cycles. The capacity retention can be still maintained to 80% after 410 cycles over 2.0–4.4 V, and the average voltage fading rate is 0.714 mV per cycle in 500 cycles. Compared with the pristine, the capacity and voltage fading of Ta–Mo codoped materials are effectively suppressed, which are mainly ascribed to the fact that the highly valence Ta5+ and Mo6+ that entered into the crystal lattice are favorable for maintaining the charge balance, and the strong bond energies of Ta–O and Mo–O can help to maintain the crystal structure and relieve the corrosion from the electrolyte during the charging/discharging process.

Interfacial Mn Vacancy for Li-Rich Mn-Based Oxide Cathodes

“…Besides, the M V @LMO realized the highest reversible capacity, showing the possibility of M V in elevating the reversibility of LMO. It is widely believed that the capacity fading of LMO at a low rate is closely related to the oxygen release and phase change from the layered to a spinel phase. , Herein, the phase change at around 3.2 V was restricted with the employment of M V (Figure e–g), therefore maintaining a high capacity and good cyclability in the M V -modified electrodes. , …”

“…It is widely believed that the capacity fading of LMO at a low rate is closely related to the oxygen release and phase change from the layered to a spinel phase. 26,27 Herein, the phase change at around 3.2 V was restricted with the employment of M V (Figure 3e−g), therefore maintaining a high capacity and good cyclability in the M V -modified electrodes. 28,29 The capacity fading of LMO always shows a large polarization at a high rate, which is ascribed to the slow kinetics of the Li 2 MnO 3 phase.…”

Blast injury of the finger caused by mobile battery explosion: A case report

“…The lithium-rich and manganese-based material is one of the new generations of cathode materials in lithium-ion batteries and is widely used because of its high energy density, low cost, and lesser toxicity [6] . Park et al conducted a risk assessment of hydrofluoric acid and lithium hydroxide, which can leak from lithium-ion batteries, and concluded that skin exposure to lithium hydroxide was deemed safe for humans because the quantity of lithium in a mobile battery is low [7] .…”

Boosting Electrochemical Performance of Lithium-Rich Manganese-Based Cathode Materials through a Dual Modification Strategy with Defect Designing and Interface Engineering

“…It has been shown that the reasons for the low initial Coulombic efficiency of LRMCs are the irreversible release of oxygen at a high voltage (>4.5 V), which will reduce the binding energy of transition metal ions (TMIs) with oxygen and induce the increase of cation mixing and large loss of irreversible capacity. , In addition, the release of oxygen during the first charge process can react with free Li + in the electrolyte to form Li 2 O, which irreversibly reduces the amount of Li + in the material. , Moreover, the capacity and voltage decay are mainly due to the migration of TMIs during the cycles, which leads to the transformation of the layered structure to the spinel phase. − Similarly, the reduction in the valence state of TMIs caused by the release of oxygen also causes a decrease in cell voltage and capacity. , Besides, the rate performance is related to the Li + diffusion kinetics and the interface charge transfer reaction in the crystal structure. The slower diffusion kinetics of Li + in Li 2 MnO 3 is the primary factor accounting for the inferior rate performance. , To circumvent these issues, various solutions including element doping, − surface coating, − and surface modification − have been proposed. The surface chemical treatment as an effective strategy to uniformly adjust the surface properties of the LRMCs for superior electrochemical performance has become a research hotspot currently.…”