Tuning of Composition and Morphology of LiFePO4 Cathode for Applications in All Solid-State Lithium Metal Batteries

All solid-state rechargeable lithium metal batteries (SS-LMBs) are gaining more and more importance because of their higher safety and higher energy densities in comparison to their liquid-based counterparts. In spite of this potential, their low discharge capacities and poor rate performances limit them to be used as state-of-the-art SS-LMBs. This arise due to the low intrinsic ionic and electronic transport pathways within the solid components in the cathode during the fast charge/discharge processes. Therefore, it is necessary to have a cathode with good electron conducting channels to increase the active material utilization without blocking the movement of lithium ions. Since SS-LMBs require a different morphology and composition of the cathode, we selected LiFePO4 (LFP) as a prototype and, we have systematically studied the influence of the cathode composition by varying the contents of active material LFP, conductive additives (super C65 conductive carbon black and conductive graphite), ion conducting components (PEO and LiTFSI) in order to elucidate the best ion as well as electron conduction morphology in the cathode. In addition, a comparative study on different cathode slurry preparation methods was made, wherein ball milling was found to reduce the particle size and increase the homogeneity of LFP which further aids fast Li ion transport throughout the electrode. The SEM analysis of the resulting calendered electrode shows the formation of non-porous and crack-free structures with the presence of conductive graphite throughout the electrode. As a result, the optimum LFP cathode composition with solid polymer nanocomposite electrolyte (SPNE) delivered higher initial discharge capacities of 114 mAh g-1 at 0.2C rate at 30 ᴼC and 141 mAh g-1 at 1C rate at 70 ᴼC. When the current rate was increased to 2C, the electrode still delivered high discharge capacity of 82 mAh g-1 even after 500 cycle, which indicates that the optimum cathode formulation is one of the important parameters in building high rate and long cycle performing SS-LMBs.

Safe and Stable Lithium Metal Batteries Enabled by an Amide-Based Electrolyte

Highlights A novel amide-based nonflammable electrolyte is proposed. The formation mechanism and solvation chemistry are investigated by molecular dynamics simulations and density functional theory. An inorganic/organic-rich solid electrolyte interphase with an abundance of LiF, Li3N and Li–N–C is in situ formed, leading to spherical lithium deposition. The amide-based electrolyte can enable stable cycling performance at room temperature and 60 ℃. Abstract The formation of lithium dendrites and the safety hazards arising from flammable liquid electrolytes have seriously hindered the development of high-energy-density lithium metal batteries. Herein, an emerging amide-based electrolyte is proposed, containing LiTFSI and butyrolactam in different molar ratios. 1,1,2,2-Tetrafluoroethyl-2,2,3,3-tetrafluoropropylether and fluoroethylene carbonate are introduced into the amide-based electrolyte as counter solvent and additives. The well-designed amide-based electrolyte possesses nonflammability, high ionic conductivity, high thermal stability and electrochemical stability (> 4.7 V). Besides, an inorganic/organic-rich solid electrolyte interphase with an abundance of LiF, Li3N and Li–N–C is in situ formed, leading to spherical lithium deposition. The formation mechanism and solvation chemistry of amide-based electrolyte are further investigated by molecular dynamics simulations and density functional theory. When applied in Li metal batteries with LiFePO4 and LiMn2O4 cathode, the amide-based electrolyte can enable stable cycling performance at room temperature and 60 ℃. This study provides a new insight into the development of amide-based electrolytes for lithium metal batteries.

Effect of the supergravity on the formation and cycle life of non-aqueous lithium metal batteries

Extra-terrestrial explorations require electrochemical energy storage devices able to operate in gravity conditions different from those of planet earth. In this context, lithium (Li)-based batteries have not been fully investigated, especially cell formation and cycling performances under supergravity (i.e., gravity > 9.8 m s−2) conditions. To shed some light on these aspects, here, we investigate the behavior of non-aqueous Li metal cells under supergravity conditions. The physicochemical and electrochemical characterizations reveal that, distinctly from earth gravity conditions, smooth and dense Li metal depositions are obtained under supergravity during Li metal deposition on a Cu substrate. Moreover, supergravity allows the formation of an inorganic-rich solid electrolyte interphase (SEI) due to the strong interactions between Li+ and salt anions, which promote significant decomposition of the anions on the negative electrode surface. Tests in full Li metal pouch cell configuration (using LiNi0.8Co0.1Mn0.1O2-based positive electrode and LiFSI-based electrolyte solution) also demonstrate the favorable effect of the supergravity in terms of deposition morphology and SEI composition and ability to carry out 200 cycles at 2 C (400 mA g−1) rate with a capacity retention of 96%.