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To increase the energy density of today’s lithium batteries, it is necessary to develop an anode with higher energy density than graphite or carbon/silicon composites. Hence, research on metallic lithium has gained a steadily increasing momentum. However, the severe safety issues and poor Coulombic efficiency of this highly reactive metal hinder its practical application in lithium-metal batteries (LMBs). Herein, the development of an artificial interphase is reported to enhance the reversibility of the lithium stripping/plating process and suppress the parasitic reactions with the liquid organic carbonate-based electrolyte. This artificial interphase is spontaneously formed by an alloying reaction-based coating, forming a stable inorganic/organic hybrid interphase. The accordingly modified lithium-metal electrodes provide substantially improved cycle life to symmetric Li||Li cells and high-energy Li||LiNi0.8Co0.1Mn0.1O2 cells. For these LMBs, 7 μm thick lithium-metal electrodes have been employed while applying a current density of 1.0 mA cm-2, thus highlighting the great potential of this tailored interphase.

Transitioning to solid-state batteries using polymer electrolytes results in inherently safer devices and can facilitate the use of sodium metal anodes enabling higher energy densities. In this work, solvent-free ternary polymer electrolytes based on cross-linked polyethylene oxide (PEO), sodium bis(fluorosulfonyl) imide (NaFSI) or sodium bis(trifluoromethanesulfonyl) imide (NaTFSI) and N-butyl-N-methyl-pyrrolidinium-based ionic liquids (ILs, Pyr$_{14}$FSI or Pyr$_{14}$TFSI) are developed. Synthesized polymer membranes are thoroughly characterized, verifying their good thermal and electrochemical stability, as well as a low glass transition and crystallinity, thus high segmental mobility of the polymer matrix. The latter results in good ionic conductivities around 1×10$^{−3}$ S cm$^{−1}$ at 20 °C. The polymer electrolytes are successfully employed in sodium-metal battery (SMB) cells operating at room temperature (RT) and using P2-Na$_{2/3}$Ni$_{1/3}$Mn$_{2/3}$O$_2$ layered oxide as cathode. The electrochemical performance strongly depends on the choice of anion in the conducting sodium salt and plasticizing IL. Furthermore, this solid-state SMB approach mitigates capacity fading drivers for the P2-Na$_{2/3}$Ni$_{1/3}$Mn$_{2/3}$O$_2$, resulting in high Coulombic efficiency (99.91 %) and high capacity retention (99 % after 100 cycles) with good specific capacity (140 mAh g$^{−1}$).

To tackle the poor chemical/electrochemical stability of Li

Lithium-metal batteries are anticipated to become the next-generation battery technology, allowing for substantially higher energy densities. To maximize the energy density, however, a “zero excess” of lithium in the cell is a must, e.g., by initially storing all electrochemically active lithium in the positive electrode.1 Nevertheless, this requires the fully reversible deposition of metallic lithium, i.e., a Coulombic efficiency of essentially 100%.2 Herein, the investigation of the lithium nucleation and plating/stripping from ionic liquid-based electrolytes composed of N-butyl-N-methyl pyrrolidinium bis(fluorosulfonyl)imide (PYR14FSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) on nickel current collectors is reported, involving a comprehensive set of electrochemical techniques coupled with operando and in situ atomic force microscopy and ex situ X-ray photoelectron spectroscopy. It was found that the morphology of the deposited lithium, the chemical composition of the interphase formed on the nickel current collector, and the reversibility of the lithium plating and stripping is highly dependent on the ratio of the ionic liquid and the lithium salt. Moreover, the addition of suitable film-forming additives allows for lower overpotentials and greater reversibility by tuning the interphase composition. The results are anticipated to contribute to the development of advanced electrolyte systems for “zero excess” lithium-metal batteries. (1) Nanda, S., Gupta, A., and Manthiram, A. Anode-Free Full Cells: A Pathway to High-Energy Density Lithium-Metal Batteries. Adv. Energy Mater. 2021, 11, 2000804. DOI: 10.1002/aenm.202000804 (2) Hobold, G.M., Lopez, J., Guo, R. et al. Moving beyond 99.9% Coulombic efficiency for lithium anodes in liquid electrolytes. Nat. Energy 2021, 6, 951–960. DOI: 10.1038/s41560-021-00910-w

Lithium metal is considered as one of the most promising anode candidates for high-energy batteries [1-3]. However, safety concerns induced by the formation of Li dendrites largely hinder the practical application of lithium-metal batteries [4]. It is anticipated that the use of non-flammable inorganic solid-state electrolytes can resolve these safety issues [5], but solid ceramic electrolytes generally suffer from poor physical contact with the electrode and poor electro-/chemical stability at the electrolyte|electrode interface [6]. Herein, we report on a thin and flexible hybrid electrolyte composed of NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP), a polymer binder, and a small amount of an ionic liquid-based electrolyte. To reinforce the interfacial stability between LATP and Li, we coat an ultrathin polysiloxane-based single-ion conducting polymer (PSiO) on the Li metal surface via a simple dip-coating method. The implementation of PSiO-coated Li (PSiO@Li) in symmetric PSiO@Li||PSiO@Li cells enables a substantial extension of the cycle life, yielding >2,000 h of stable lithium stripping-plating. The full-cells comprising PSiO@Li as the negative electrode, LiNi0.88Co0.09Mn0.03O2 (NCM88) as the positive electrode active material, and the aforementioned hybrid electrolyte exhibit substantially enhanced rate capability at high dis-/charge rates above 0.5C and greatly prolonged cycle life at 1C. The superior performance achieved herein is mainly attributed to: (1) the prevented direct contact between LATP and Li, thus avoiding the reduction of LATP and the formation of mixed ion-electron conducting interphases; (2) the regulated Li+ flux at the electrode|electrolyte interface, ensuring homogeneous Li+ stripping-plating; and (3) the promoted intimate contact between PSiO and Li via the formation of Si−O−Li bonds. References [1] T. Li, X.-Q. Zhang, P. Shi, Q. Zhang, Joule, 3 (2019) 2647-2661. [2] B. Horstmann, J. Shi, R. Amine, M. Werres, X. He, H. Jia, F. Hausen, I. Cekic-Laskovic, S. Wiemers-Meyer, J. Lopez, D. Galvez-Aranda, F. Baakes, D. Bresser, C.-C. Su, Y. Xu, W. Xu, P. Jakes, R.-A. Eichel, E. Figgemeier, U. Krewer, J.M. Seminario, P.B. Balbuena, C. Wang, S. Passerini, Y. Shao-Horn, M. Winter, K. Amine, R. Kostecki, A. Latz, Energy Environ. Sci., 14 (2021) 5289-5314. [3] S. Wang, P. Xiong, J. Zhang, G. Wang, Energy Storage Materials, 29 (2020) 310-331. [4] Z. Yu, Y. Cui, Z. Bao, Cell Rep. Phy. Sci., 1 (2020) 100119. [5] S. Xin, Y. You, S. Wang, H.-C. Gao, Y.-X. Yin, Y.-G. Guo, ACS Energy Lett., 2 (2017) 1385-1394. [6] A. Banerjee, X. Wang, C. Fang, E.A. Wu, Y.S. Meng, Chem. Rev., 120 (2020) 6878-6933.

All-solid-state batteries (SSBs) are attracting widespread attention as next-generation energy storage devices, potentially offering increased power and energy densities and better safety than liquid electrolyte-based Li-ion batteries. Significant research efforts are currently underway to develop stable and high-performance bulk-type SSB cells by optimizing the cathode microstructure and composition, among others. Electronically conductive additives in the positive electrode may have a positive or negative impact on cyclability. Herein, it is shown that for high-loading (pelletized) SSB cells using both a size- and surface-tailored Ni-rich layered oxide cathode material and a lithium thiophosphate solid electrolyte, the cycling performance is best when low-surface-area carbon black is introduced.

In the recent years, all-solid-state batteries have attracted much attention as they are safer in terms of flammability compared to liquid electrolyte systems. There are polymer, oxidic, and sulfidic solid electrolytes with advantages and disadvantages. One major advantage of sulfidic electrolytes is their high ionic conductivity at room temperature which is even comparable with that of liquid electrolytes. Another feature is the possible usability of lithium anodes in this system which leads to very high energy density. One major challenge of the lithium metal anode is the formation and growth of lithium dendrites which results in short circuits. A lot of research is done to prevent dendrite growth but more research is needed to understand the actual dendrite growth mechanism [1]. In our work we analyzed the reasons for increase of overpotentials that is very likely related to lithium dendrite growth in symmetric lithium metal cells with solid electrolyte Li6PS5Cl. In a three-electrode set up, the interface of a lithium symmetric cell is analyzed during stripping and plating with electrochemical impedance spectroscopy. The changes of the resistance contributions are discussed in terms of possible major mechanisms that are involved in lithium dendrite growth. Furthermore, the plating behavior of lithium is investigated which gives insight into possible onset for lithium dendrite growth. Reference s : [1] Xin-Bing Cheng, Rui Zhang, Chen-Zi Zhao, and Qiang Zhang, Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review, Chem. Rev. 2017, 117, 10403−10473.