Stabilizing High‐Voltage LiNi_0.5Mn_1.5O₄ Cathodes for High Energy Rechargeable Li Batteries by Coating With Organic Aromatic Acids and Their Li Salts

Abstract

z O 2 (NCA) cathode materials. [1,2] However, LFP suffers from low electric conductivity and relatively low discharge potential, [3] while the decreasing abundance, increased cost, and severe toxicity issues of cobalt and nickel raise a big question for the broad application of LCO/NCM/NCA-based Li batteries. [4] Surprisingly, commercialization of Cofree high-voltage cathode materials such as LiNi 0.5 Mn 1.5 O 4 (LNMO) with several outstanding properties, including 3D channels for high rate Li-ion diffusion, [5] high operating potential (≈4.7-4.8 V) with moderately high energy density (up to 650 Wh kg −1 ), [6,7] better thermal stability, [8] and relatively low cost, is comparatively behind and underrated. We believe that these outstanding inherent properties of high-voltage spinel LNMO cathodes can make them economical and promising for advanced LIB technologies. [9] Here, our primary aim was to address the two challenging issues of LNMO cathodes: limited cycle life and fast capacity degradation, especially at elevated temperatures. These critical issues typically originate from structural and chemical instability operating at higher potentials in Li batteries electrolyte solutions. During Li + intercalation/de-intercalation, Li-rich and Li-poor domains coexist, which leads to problems such as phase boundary dislocations, stress at grain boundaries, and pulverization of particles. [10] The gradual capacity drop during prolonged cycling is also associated with lattice parameter changes during LNMO's two-phase domains (Li-rich and Li-poor) formation and reduction in the octahedral MnO 6 distortion. [11] Moreover, Mn 2+ ions dissolution from the cathode's surface due to disproportionation reaction: 2Mn 3+ →Mn 4+ + Mn 2+ and Mn 3 O 4 -like phase formation during cycling further introduce structural instability/integrity associated with capacity drop. [12,13] In addition, thick poly(ethylene carbonate (EC))-rich cathode-electrolyte solutions interphase (CEI) formation while operating at the high potential in typical EC-based electrolyte solution causes high cells' impedance. [14] In addition, de-lithiated LNMO may catalyze electrolyte solution decomposition that induces self-discharge in the cells. [15,16] Furthermore, nickel Here, three types of surface coatings based on adsorption of organic aromatic acids or their Li salts are applied as functional coating substrates to engineer the surface properties of high voltage LiNi 0.5 Mn 1.5 O 4 (LNMO) spinel cathodes. The materials used as coating include 1,3,5-benzene-tricarboxylic acid (trimesic acid [TMA]), its Li-salt, and 1,4-benzene-dicarboxylic acid (terephthalic acid). The surface coating involves simple ethanol liquidphase mixing and low-temperature heat treatment under nitrogen flow. In typical comparative studies, TMA-coated (3-5%) LNMO cathodes deliver >90% capacity retention after 400 cycles with significantly improved rate performance in Li-coin cells at 30 °C compared to uncoated material with capacity retention of ≈40%. The cathode coating also prevents th...

Exploring the Capability of Framework Materials to Improve Cathodes’ Performance for High‐energy Lithium‐ion Batteries

“…This resistance was due to changes in lattice parameters during the formation of Li-rich and Li-poor domains in LNMO. [20] The LNMO cathodes stabilized well after applying a TMA-based coating. The experimental results showed smooth Li-ions diffusion through the artificial cathode/solution interphase (Figure 8f, g).…”

“…The predominant techniques employed for these objectives involve chemical coating or standard solidstate mixing methods. [20,33,[55][56][57][58]67] Detailed discussions related to each coating technique is mentioned in the upcoming sections.…”

“…A simple mixing of TMA with LNMO in ethanol and heat treatment under nitrogen flow was employed for this purpose. [20] TMA-coated LNMO cathodes show stable behavior in Li-cells at 30 °C with 90 % capacity retention (Figure 8a). However, initial cycles resemble uncoated cathodes with slightly lower capacity.…”

“…Their impressive energy density, long-term stability, and safety have yielded exceptional outcomes, validating their suitability as superior alternatives for high-performance LIBs. [17,[20][21][22][23][24][25][26][27][28][29][30][31][32][33] These transition metal oxides are promising materials for various applications due to their many redox-active sites and stable structures. However, their limitations prevent their wide-scale commercialization.…”

“…[55][56][57][58] Our review discusses functional strategies to introduce framework material-based engineering in cathode materials for high-performance LIBs. [20,33,[55][56][57][58]67] These modifications merge distinct precursors with beneficial synergistic effects between two or more metal components while retaining their wellinherited morphology and porosity. Insights into stabilizing the chemistry of framework materials will be instrumental in advancing next-generation LIBs.…”