Enhancing the Electrode Gravimetric Capacity of Li_1.2Mn_0.4Ti_0.4O₂ Cathode Using Interfacial Carbon Deposition and Carbon Nanotube-Mediated Electrical Percolation

Abstract

Mn-based cation-disordered rocksalt oxides (Mn-DRX) are emerging as promising cathode materials for next-generation Li-ion batteries due to their high specific capacities and cobalt- and nickel-free characteristic. However, to reach the usable capacity, solid-state synthesized Mn-DRX materials require activation via postsynthetic ball milling, typically incorporating more than 20 wt % conductive carbon that adversely reduces the electrode-level gravimetric capacity. To address this issue, we first deposit amorphous carbon on the surface of the Li1.2Mn0.4Ti0.4O2 (LMTO) particles to increase the electrical conductivity by 5 orders of magnitude. Although the cathode material gravimetric first charge capacity reaches 180 mAh/g, its highly irreversible behavior leads to a first discharge capacity of 70 mAh/g. Subsequently, to ensure a good electrical percolation network, the LMTO material is ball-milled with a multiwall carbon nanotube (CNT) to obtain a 78.7 wt % LMTO active material loading in the cathode electrode (LMTO-CNT). As a result, a 210 mAh/g cathode electrode gravimetric first charge and 165 mAh/g first discharge capacity values are obtained, compared to the respective capacity values of 222 and 155 mAh/g for the LMTO material ball-milled with 20 wt % SuperP C65 electrode (LMTO-SP). After 50 cycles, LMTO-CNT delivers a 121 mAh/g electrode gravimetric discharge capacity, largely outperforming the value of 44 mAh/g of LMTO-SP. Our study demonstrates that while ball milling is necessary to achieve a significant amount of capacity of LMTO, a careful selection of additives, such as CNT, effectively reduces the required carbon quantity to achieve a higher electrode gravimetric discharge capacity.

Direct Mapping of Fluorine in Cation Disordered Rocksalt Cathodes

“…With the advent of large-scale energy storage systems, such as electric vehicle batteries and smart power grids, the demand for high energy density, low-cost, and stable cathode materials is continually increasing. , A class of lithium excess disordered rocksalt (DRX) oxides has emerged as a promising cathode candidate for Li ion batteries (LIBs) due to a high specific energy density (∼1000 W-h/kg) and the capability to incorporate earth-abundant materials. − However, the high level of oxygen redox required to deliver a high capacity generally triggers oxygen loss from the Li-excess cathode materials, making them unusable in the long run. − To overcome this problem, fluorination of DRX oxides was proposed . Theoretically, the partial substitution of oxygen by fluorine can effectively decrease the average anion valance and increase the number of redox-active transition metals per formula unit .…”