Facile Molten Vanadate-Assisted Surface Treatment Strategy for Li₂MnO₃ Activation of Li-Rich Cathode Materials

Abstract

Li-rich transition metal oxides (Li 1+X M 1−X O 2 ) are known as the next generation of cathode materials for lithium-ion batteries by reason of their high specific capacity. However, oxygen release and structural conversion in Li-rich layered oxides during the initial charge result in low initial Coulomb efficiency (ICE) and uninterrupted capacity attenuation. In this paper, we show a molten vanadate-assisted strategy at low temperature combined with washing treatment to regulate the amount of labile oxygen removed from the surface of Li-rich oxide (Li 1.25 Ni 0.126 Co 0.126 Mn 0.530 O 2 , LRMO). The pre-activation strategy leads to a considerable suppression of O 2 and CO 2 generation in the course of the first charge and noteworthily enables the structural stability of the LRMO during the charging/discharging process. Consequently, the molten vanadate-assisted strategy-treated LRMO material exhibits a high discharge capacity of 276 mA h g −1 and an enhanced ICE of 95.1% during the first cycling at 0.1C. This research establishes a fruitful approach to ameliorate the ICE and address the potential decline of the Li-rich cathode material.

Lithium Antievaporation-Loss Engineering via Sodium/Potassium Doping Enables Superior Electrochemical Performance of High-Nickel Li-Rich Layered Oxide Cathodes

“…The XPS spectra of Ni, Mn, Na, and K are also shown in Figure d–h. The Mn 2p band at 642.2 eV with a + 4 valence state was almost not influenced by the doping of Na and K whereas the presence of the peaks at 1072 and above 290 eV evidences the successful doping of Na and K, respectively, − as shown in Figures S6 and S7. The Ni 2p 3/2 peaks could be deconvoluted into two components of Ni 2+ and Ni 3+ and the O 1s peaks into three components of surface oxygen vacancies (SOVs), lattice oxygen (LO), and surface adsorbed oxide species (SO) from which their corresponding percentages could be estimated, , as shown in Figure f.…”

Inhibition of Adverse Phase Transition at 4.2 V via increasing Cobalt Content on Ni-Rich Layered Cathode Materials

“…If d E is linear with d √τ, then this applies to the equation In eq , τ is the relaxation time, 600 s; n is the amount of substance of active material; V m is the molar volume; Δ E s is the variation of voltage by impulse; and Δ E t is the variation of voltage in constant-current charging (or discharging). Figure a–d shows a linear relationship between d E and d √τ, so all four samples apply to eq …”

“…In eq 3, τ is the relaxation time, 600 s; n is the amount of substance of active material; V m is the molar volume; ΔE s is the variation of voltage by impulse; and ΔE t is the variation of voltage in constant-current charging (or discharging). Figure 9a−d shows a linear relationship between dE and d√τ, so all four samples apply to eq 33 33 The distribution of the diffusion coefficient of Li + describes the activity of Li + in the process of charge and discharge. First of all, the increase of cobalt content makes D Li + GITT increase significantly.…”

Modification Strategy for Constructing Li Gradient Combined with Spinel Phase Coating on Li-Rich Mn-Based Materials

“…Our research group adopted a simple vanadate heat treatment method to construct a lithium concentration gradient material which vastly enhanced the initial Coulombic efficiency and distinctly suppressed voltage attenuation. 22 In this work, we applied (NH 4 ) 2 SiF 6 to react with LLOs at 700 °C to form LiF and Li 2 SiO 3 on the surface of LLOs (Figure 1). As a result, the removing of Li 2 O from LLOs leads to the formation of Li and O vacancy on the surface of the material.…”

“…They demonstrated that the construction of a Li-poor phase can help remove the Li–O–Li bond on the surface and even replace Li–O–Li with Li–TM–Li, which immensely reduce the irreversible redox of anions and distinctly improved the initial Coulombic efficiency and cycling performance of LLOs. Our research group adopted a simple vanadate heat treatment method to construct a lithium concentration gradient material which vastly enhanced the initial Coulombic efficiency and distinctly suppressed voltage attenuation . In this work, we applied (NH 4 ) 2 SiF 6 to react with LLOs at 700 °C to form LiF and Li 2 SiO 3 on the surface of LLOs (Figure ).…”