Borate‐Based Surface Coating of Li‐Rich Mn‐Based Disordered Rocksalt Cathode Materials

Abstract

With this new turnaround in the midst of energy transition, there is a strong necessity to increase the viability of LIBs, which emphasizes the importance of the discovery and development of high-energy-density cathode materials based on sustainable and abundant metals. [1] Still, layered LiCoO 2 and hexagonal (R3m) Li(Ni, Mn, Co)O 2 cathode materials are currently the most widely used systems in electrical devices. [2] However, the high cost, limited resources, and toxicity of Co will limit its further development and application. [3] Thus, it becomes primordial to target cobalt-and nickel-free systems made from abundant metals.Li-rich disordered rocksalt (DRS) oxyfluorides based on manganese cathode materials with face-centered cubic-structure are one of the potential candidates for cathodes in LIBs. Manganese compounds based on this earth abundant and inexpensive 3d transition metal could potentially replace cobalt-containing cathode materials in certain applications. [4] So far, Mn-redox-based disordered materials have shown promising electrochemical performance but with considerable capacity fading during long-term cycling. [5] The capacity degradation is linked to structural instability, surface reconstruction associated with irreversible oxygen loss, and manganese dissolution into the carbonate-based electrolyte. [6] Especially, nanocrystalline DRS materials synthesized by ball-milling show a higher reactivity with electrolyte. In general, Li-rich DRS materials have been found to exhibit oxygen-redox and/or O 2 loss mainly at high voltage, which can accelerate side reactions with the electrolyte and surface layer growth. [7] All these irreversible processes, together with the low conductivity of the materials, are currently major obstacles to further development, and, eventually, commercialization.One possibility for further development is that interfacial reactions can be tuned by surface modification and/or coating. Thus, coating of the Mn-based DRS particles to improve stability and electrochemical properties may be vital for overcoming these limitations. Al 2 O 3 -coated materials have been reported with poor stability during the charge-discharge cycling. The exposed metal oxide can be partially converted to the corresponding fluoride material originating from HF, resulting from the electrolyte decomposition process. [8] Up to now, numerous previous studies have investigated performance enhancements Upon cycling, Li-rich Mn-based disordered rocksalt (DRS) oxyfluoride cathode materials undergo unwanted degradation processes, which are triggered by chemical side reactions or irreversible oxygen redox activity, especially at high voltages and in contact with the electrolyte. A surface coating can be an effective strategy to mitigate these parasitic reactions. However, oxyfluorides generally experience limited stability, which makes the application of coatings requiring high temperatures challenging. For this purpose, this study is dealing with the implementation of a chemically inert and Li ion conductin...

Ion-Exchanged Phosphomolybdic Acid Interfacial Modification Enhances the Electrochemical Performance of LiNi0.9Mn0.1O2

“…The ohmic internal resistance ( R s ) and CEI membrane resistance (fitted by parallel R f and CPE1) are reflected by the starting point and the arc of the high-frequency region in the Nyquist diagram. The charge transfer resistance in the electric double-layer region (fitted by the parallel of R ct and CPE2) is reflected by the low-frequency arc. , The dominant resistance comes from R ct compared to R s and R f , as shown in the fitting results of the Nyquist plots (Figure e). NM91 shows larger R ct values within 300 cycles than 91PMA-e2, confirming that the coating layer generated by PMA-e2 with the Keggin structure indeed promotes the charge transferability of the cathode.…”

Unravelling the Chemical and Structural Evolution of Mn and Ti in Disordered Rocksalt Oxyfluoride Cathode Materials Using Operando X-ray Absorption Spectroscopy

“…Also, the low-valent F – sets up the charge balance to favor the incorporation of Mn as Mn 2+ in the structure, allowing the Mn 4+ /Mn 2+ double-redox reaction. Particularly, previous studies showed that the composition Li 2 Mn 2/3 Ti 1/3 O 2 F (Ti33) with Ti 4+ and mixed Mn 2+/3+ in the initial state demonstrated better cycling stability. − After the initial charge, this composition can deliver a discharge capacity comparable to the Li-rich layered NMC (200–220 mAh/g) , and greater than the conventional LCO (170 mAh/g) . Furthermore, a capacity retention of 190 mAh/g (∼650 Wh/kg) after 100 cycles and 136 mAh/g (∼460 Wh/kg) after 200 cycles was obtained .…”

Modification Strategies and Challenges of High‐Performance Lithium‐Rich Manganese‐Based Cathode Materials

“…In addition to the aforementioned common coating methods, there are also other novel coating methods such as spinel nano‐coating, [ 57 ] borate coating, [ 58 ] lithium‐ion conductor coating, [ 59 ] etc., which have achieved certain results and can stabilize lithium‐rich cathode materials.…”