Lithium-ion batteries (LIBs) have transformed modern electronics and rapidly advancing electric vehicles (EVs) due to their high energy and power densities, cycle-life, and acceptable safety. However, the comprehensive commercialization of EVs necessitates the invention of LIBs with much enhanced and stable electrochemical performances, including higher energy/power density, cycle-life, and operational safety, but at a lower cost. Herein, we report a simple method for improving the high-voltage (up to 4.5 V) charge capability of LIBs by applying a Li+-ion-conducting artificial cathode–electrolyte interface (Li+-ACEI) on the state-of-the-art cathode, LiCoO2 (LCO). A superionic ceramic single Li+ ion conductor, lithium aluminum germanium phosphate (Li1.5Al0.5Ge1.5(PO4)3, LAGP), has been used as a novel Li+-ACEI. The application of Li+-ACEI on LCO involves a scalable and straightforward wet chemical process (sol–gel method). Cycling performance, including high voltage charge, of bare and LAGP-coated cathodes has been determined against the most energy-dense anode (lithium, Li metal) and state-of-the-art carbonate-based organic liquid electrolyte (OLE). The application of an LAGP-based Li+-ACEI on LCO displays many improvements: (i) reduced charge-transfer and interfacial resistance; (ii) higher discharge capacity (167.5 vs 155 mAh/g) at 0.2C; (iii) higher Coulombic efficiency (98.9 vs 97.8%) over 100 cycles; and (iv) higher rate capability (143 vs 80.1 mAh/g) at 4C. Structural and morphological characterizations have substantiated the improved electrochemical behavior of bare and Li+-ACEI LCO cathodes against the Li anode.

Lithium-ion batteries (LIBs) have continued achieving higher energy densities by utilizing various high-capacity, high-voltage cathode materials. However, they still show severe challenges regarding their reliability and electrolyte−cathode stability during operation especially at high-voltage charging that is needed to achieve higher energy density. Therefore, ensuring the stability of cathodes with electrolytes becomes much more critical for the safe and extended cycling of high-energy LIBs. Herein, we present a comprehensive investigation on maximizing cathode− electrolyte interfacial stability by employing a thin-film coating of various superionic single Li + ceramic conductors on the commonly used lithium cobalt oxide (LCO) cathode. In the present investigation, the lithium aluminum germanium phosphate (Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 ; LAGP) ceramic electrolyte is found to be the best LCO surface stabilizer among commonly known ceramic conductors. The investigation of different synthesis parameters, such as the coating thickness, sintering temperature and time, annealing atmosphere, and so on, has been accomplished. The optimized performance has been obtained with an LAGP coating of a thickness of 0.6 wt % (LAGP amount) annealed at 830 °C for 1 h in a pure oxygen atmosphere. When cycled in a voltage window of 3−4.3 V, 0.6 wt % LAGP on the LCO cell shows a discharge capacity of 180.87 and 163.91 mAh/g at 0.2 and 4C, respectively; in comparison, a pure LCO-based LIB shows 149.82 and 78.90 mAh/g at 0.2 and 4C. Furthermore, LAGP-coated LCO-based LIBs when compared to the pristine LCO-based LIBs show (i) remarkably better thermal stability, (ii) lower voltage polarizations during cycling, and (iii) an enabled higher voltage charge of up to 4.8 V.

An unprotected cathode of a lithium-ion battery (LIB) cell using lithium metal anode and organic carbonate liquid electrolyte undergoes a significant structural damage during cycling (Li+ intercalation/ deintercalation) process. Also, a bare cathode in contact with liquid electrolyte forms a resistive cathode electrolyte interface (CEI) layer. Both the cathode structure damage and CEI lead to rapid capacity fade [1]. Cathode surface modification has been used to reduce CEI formation and structural damage that in turn improves capacity retention, cycle life, energy density, power density, and safety of a LIB.Recently, the coating of the cathode with an intermediate layer (IL) which is transparent to Li+ conduction but impermeable to electrolyte solvent has been developed to minimize CEI formation and structural damage. IL based on Li+ insulating ceramics such as aluminum oxide (Al2O3), tin oxide (SnO2), and magnesium oxide (MgO) has been developed but to a limited success in mitigating the above cathode degradation. The limited success of Li+ insulating coating relates to limited thickness of coating because resistance of coating layer increases with thickness of IL.To overcome the challenges associated with Li+ insulating IL, recently, Li+ conducting IL (solid-state ceramic electrolytes) has been explored. Some of the most studied ceramic solid electrolytes include lithium niobate (LNO), lithium lanthanum zirconium oxide (LLZO), lithium aluminum titanium phosphate (LATP), etc. Though, LNO (σ = 10-5 mS.cm-1) and LLZO (σ = 10-4 mS.cm-1), LATP (σ = 10-4 mS.cm-1) are better Li+ conductor compared to complete Li+ insulating ILs [2] (Al2O3, MgO, SnO2) but still not adequate for high performance LIB.Lithium aluminum germanium phosphate (LAGP- Li1.5Al0.5Ge1.5(PO4)3 ) has one order higher Li+ conduction (σ = 10-3 S.cm-1) compared to LATP [3]. Thus, we present LIB performance improvement through application of LAGP as IL on lithium cobalt oxide cathode (LCO) (Fig. 1). Figure 1 shows rate capability of LAGP coated LCO vs. pristine LCO, LNO and LLZO coated cathode. We will present a sol-gel as an economical and scalable method to apply LAGP thin-film as IL on LCO. Also, impedance, and storage induced cell degradation will be presented.REFERENCES[1] Joshua P. Pender, Gaurav Jha, Duck Hyun Youn, Joshua M. Ziegler, Ilektra Andoni, Eric J. Choi, Adam Heller, Bruce S. Dunn, Paul S. Weiss, Reginald M. Penner, and C. Buddie Mullins, Electrode Degradation in Lithium-Ion Batteries, ACS Nano 2020, 14, 1243−1295[2] Jeffrey W. Fergus, Ceramic and polymeric solid electrolytes for lithium-ion batteries, Journal of Power Sources195 (2010) 4554–4569[3] B. Kumar, D. Thomas, and J. Kumar, Space-Charge-Mediated Superionic Transport in Lithium Ion Conducting Glass-Ceramics, Journal of The Electrochemical Society, 156(7) A506-A513 (2009)Figure 1. Rate capability test of LCO cathode with LAGP, LNO and LLZO coating. Cathode performance in a half-cell (Li/1MLiPF6/LCO with or without IL) set up. Figure 1