This review provides a comprehensive overview about the “hidden champion” of lithium-ion battery technology – graphite.

Polymer-based electrolytes potentially enable enhanced safety and increased energy density of lithium-metal batteries employing high capacity, transition metal oxide–positive electrodes. Herein, we report the investigation of lithium-metal battery cells comprising Li[Ni0.6Mn0.2Co0.2]O2 as active material for the positive electrode and a poly(arylene ether sulfone)-based single-ion conductor as the electrolyte incorporating ethylene carbonate (EC) as selectively coordinating molecular transporter. The resulting lithium-metal battery cells provide very stable cycling for more than 300 cycles accompanied by excellent average Coulombic efficiency (99.95%) at an anodic cutoff potential of 4.2 V. To further increase the achievable energy density, the stepwise increase to 4.3 V and 4.4 V is herein investigated, highlighting that the polymer electrolyte offers comparable cycling stability, at least, as common liquid organic electrolytes. Moreover, the impact of temperature and the EC content on the rate capability is evaluated, showing that the cells with a higher EC content offer a capacity retention at 2C rate equal to 61% of the capacity recorded at 0.05 C at 60 °C.

Polymer electrolytes are considered potential key enablers for lithium-metal batteries due to their compatibility with the lithium-metal negative electrode. Herein, cross-linked self-standing single-ion conducting polymer electrolytes are obtained via a facile UV-initiated radical polymerization using pentaerythritol tetraacrylate as the cross-linker and lithium (3-methacryloyloxypropylsulfonyl)-(trifluoromethylsulfonyl)imide as the ionic functional group. Incorporating propylene carbonate as charge-transport supporting additive allowed for achieving single-ion conductivities of 0.21 mS cm −1 at 20 °C and 0.40 mS cm −1 at 40 °C, while maintaining a suitable electrochemical stability window for 4 V-class positive electrodes (cathodes). As a result, this single-ion polymer electrolyte featured good cycling stability and rate capability in Li||LiFePO 4 and Li||LiNi 0.6 Mn 0.2 Co 0.2 O 2 cells. These results render this polymer electrolyte as potential alternative to liquid electrolytes for high-energy lithium-metal batteries.

Manganese monoxide (MnO) currently has attracted increasing attention in aqueous zinc metal batteries (AZMBs) due to the high theoretical capacity, satisfactory output voltage, and low price. However, the development of a MnO cathode is still plagued by the low specific capacity arising from the sluggish reaction kinetics and rapid capacity decay induced by structural collapse. Herein, the oxygen-defect-rich MnO1–x integrated with a carbon nanofiber (MnO1–x @CNF) membrane is designed based on a facile electrospinning technique. In situ X-ray diffraction and ex situ X-ray photoelectronic spectroscopy results confirm the proton-dominated insertion electrochemistry during cycling. The theoretical calculation results revealed that the introduction of oxygen vacancies could effectively decrease the H+ diffusion energy barrier and thus promote H+ diffusion. In addition, CNFs could provide flexible and lightweight electron transport networks to ensure rapid electrode reaction kinetics. Consequently, the as-prepared MnO1–x @CNF cathode delivers a high specific capacity of 264 mAh g–1 at 0.1 A g–1 and an outstanding capacity retention after 2500 cycles at 2 A g–1. The high flexibility and light weight of the MnO1–x @CNF membrane may aid in future high-performance cathodes for wearable AZMBs.

Gel polymer-ceramic hybrid electrolytes (GHEs) have emerged as desirable candidates for preparing high energy density and excellent practicability gel batteries. However, the agglomeration of ceramic particles in polymer matrix leads to a decrease in cycling stability and low mechanical properties of GHEs. Here, we present a feasible method for improving the dispersity of Li0.24La0.59TiO3 (LLTO) nanorods in the polyvinylidenefluoride (PVDF)/poly(propylene carbonate) (PPC) co-blended matrix (K–LLTO/PVDF/PPC) by γ-(2,3-epoxypropoxy)propytrimethoxysilane (KH560) surface treatment. The as-prepared GHE with 10% K–LLTO filler (10% GHE) exhibits a high ionic conductivity (3.01 mS cm−1) and an appropriate lithium-ion transference number (0.55). The Li|10% GHE|Li symmetric cell shows an exceptional lithium stripping-plating lifetime of > 2000 h at 0.1 mA cm−2. The assembled LiFePO4 (LFP)|10% GHE|Li full cells show satisfactory cycling stability in the 2.5–4.2 V electrochemical window by recovering 84% of the initial capacity at 2 C over 500 cycles. The uniformly dispersed K–LLTO within the polymer matrix is ascribed to the formation of a bridge-linked network via Si–O–Ti bonds between KH560 and LLTO, and plenty of hydrogen bonds within the polymer matrix. This modification method provides a feasible strategy for fabricating GHEs with good repeatability, which may easily adapt to the high requirements of commercial production.

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.

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