Lithium-sulfur (Li-S) batteries have been regarded as the most promising candidates as the next-generation energy storage systems because of high theoretical capacities (Li: 3860 mAh g −1 and S: 1675 mAh g −1 ), low mass densities (Li: 0.534 g cm −3Lithium-sulfur (Li-S) batteries are strongly considered as next-generation energy storage systems because of their high energy density. However, the shuttling of lithium polysulfides (LiPS), sluggish reaction kinetics, and uncontrollable Li-dendrite growth severely degrade the electrochemical performance of Li-S batteries. Herein, a dual-functional flexible free-standing carbon nanofiber conductive framework in situ embedded with TiN-VN heterostructures (TiN-VN@CNFs) as an advanced host simultaneously for both the sulfur cathode (S/TiN-VN@CNFs) and the lithium anode (Li/TiN-VN@CNFs) is designed. As cathode host, the TiN-VN@CNFs can offer synergistic function of physical confinement, chemical anchoring, and superb electrocatalysis of LiPS redox reactions. Meanwhile, the well-designed host with excellent lithiophilic feature can realize homogeneous lithium deposition for suppressing dendrite growth. Combined with these merits, the full battery (denoted as S/TiN-VN@ CNFs || Li/TiN-VN@CNFs) exhibits remarkable electrochemical properties including high reversible capacity of 1110 mAh g −1 after 100 cycles at 0.2 C and ultralong cycle life over 600 cycles at 2 C. Even with a high sulfur loading of 5.6 mg cm −2 , the full cell can achieve a high areal capacity of 5.5 mAh cm −2 at 0.1 C. This work paves a new design from theoretical and experimental aspects for fabricating high-energy-density flexible Li-S full batteries.

We prepare a totally nonflammable phosphate-based electrolyte composed of 5 mol L-1 (M) Li bis(fluorosulfonyl) imide (LiFSI) in a trimethyl phosphate (TMP) solvent. The concentrated 5 M LiFSI/TMP electrolyte shows good compatibility with graphite and no Al corrosion. More attractively, such a concentrated electrolyte can effectively suppress the growth of Li dendrites in Li metal batteries because of a stable LiF-rich SEI layer. Therefore, this highly concentrated electrolyte is promising for safe Li batteries.

Rechargeable lithium (Li) metal batteries with conventional LiPF 6-carbonate electrolytes have been reported to fail quickly at charging current densities of about 1.0 mA cm-2 and above. In this work, we demonstrate the rapid charging capability of Li||LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) cells enabled by a dual-salt electrolyte of lithium bis(trifluoromethanefulfonyl)imide (LiTFSI) and

Constructing artificial solid‐electrolyte interphase (SEI) on the surface of Li metal is an effective approach to improve ionic conductivity of surface SEI and buffer Li dendrite growth of Li metal anode. However, constructing of homogenous ideal artificial SEI is still a great challenge. Here, a mixed lithium‐ion conductive Li2S/Li2Se (denoted as LSSe) protection layer, fabricated by a facile and inexpensive gas–solid reaction, is employed to construct stable surface SEI with high ionic conductivity. The Li2S/Li2Se‐protected Li metal (denoted as LSSe@Li) exhibits a stable dendrite‐free cycling behavior over 900 h with a high lithium stripping/plating capacity of 3 mAh cm−2 at 1.5 mA cm−2 in the symmetrical cell. Compared to bare Li anode, full batteries paired with LiFePO4, sulfur/carbon, and LiNi0.6Co0.2Mn0.2O2 cathodes all present better battery cycling and rate performance when LSSe@Li anode is used. Moreover, Li2Se exhibits a lower lithium‐ion migration energy barrier in comparison with Li2S which is proved by density functional theory calculation.

The notorious lithium (Li) dendrites and the low Coulombic efficiency (CE) of Li anode are two major obstacles to the practical utilization of Li metal batteries (LMBs). Introducing a dendrite-suppressing additive into nonaqueous electrolytes is one of the facile and effective solutions to promote the commercialization of LMBs. Herein, Li difluorophosphate (LiPOF LiDFP) is used as an electrolyte additive to inhibit Li dendrite growth by forming a vigorous and stable solid electrolyte interphase film on metallic Li anode. Moreover, the Li CE can be largely improved from 84.6% of the conventional LiPF-based electrolyte to 95.2% by the addition of an optimal concentration of LiDFP at 0.15 M. The optimal LiDFP-containing electrolyte can allow the Li||Li symmetric cells to cycle stably for more than 500 and 200 h at 0.5 and 1.0 mA cm, respectively, much longer than the control electrolyte without LiDFP additive. Meanwhile, this LiDFP-containing electrolyte also plays an important role in enhancing the cycling stability of the Li||LiNiCoMnO cells with a moderately high mass loading of 9.7 mg cm. These results demonstrate that LiDFP has extensive application prospects as a dendrite-suppressing additive in advanced LMBs.

+ than that of Na/Na + , allowing KIBs to be potentially utilized in large-scale energy storage. [3-6] Importantly, the weaker Lewis acidity of K + which brings about smaller solvated ions as compared to Li + /Na + could improve diffusion through the electrolyte/electrode interface. [6] Moreover, selenium has emerged as an attractive candidate for KIB cathode thanks to its superior electronic conductivity (10 −3 S m −1) [7] and great electrochemical compatibility with carbonate-based electrolyte [8,9] together with its intrinsically high specific gravimetric capacity (675 mAh g −1) and volumetric capacity (3253 mAh cm −3). Therefore, the K-Se battery, in general, offers higher energy density compared to that based on conventional intercalation cathodes. [10,11] However, its full potential has yet to be unlocked, which is due to the unsatisfactory electrochemical performance arising from dissolution and migration of intermediate polyselenides and large volume expansion during charge/ discharge, which are the two typical problems challenging S-based batteries. [12-14] Since the K-Se battery is still at its early stage, there are only very few reports on the cathode development with limited capacity and cycle life ,[10,12,15] not to mention largely unknown electrochemical reaction mechanisms involved The potassium-selenium (K-Se) battery is considered as an alternative solution for stationary energy storage because of abundant resource of K. However, the detailed mechanism of the energy storage process is yet to be unraveled. Herein, the findings in probing the working mechanism of the K-ion storage in Se cathode are reported using both experimental and computational approaches. A flexible K-Se battery is prepared by employing the smallmolecule Se embedded in freestanding N-doped porous carbon nanofibers thin film (Se@NPCFs) as cathode. The reaction mechanisms are elucidated by identifying the existence of short-chain molecular Se encapsulated inside the microporous host, which transforms to K 2 Se by a two-step conversion reaction via an "all-solid-state" electrochemical process in the carbonate electrolyte system. Through the whole reaction, the generation of polyselenides (K 2 Se n , 3 ≤ n ≤ 8) is effectively suppressed by electrochemical reaction dominated by Se 2 molecules, thus significantly enhancing the utilization of Se and effecting the voltage platform of the K-Se battery. This work offers a practical pathway to optimize the K-Se battery performance through structure engineering and manipulation of selenium chemistry for the formation of selective species and reveal its internal reaction mechanism in the carbonate electrolyte. In-depth understanding on the fundamental mechanism of advanced battery materials is the prerequisite toward efficient material design aiming for property optimization. [1,2] Recently, many efforts have been devoted to developing high-performance K-ion batteries (KIBs) because of abundant potassium resource The ORCID identification number(s) for the author(s) of this article can be ...

Sodium metal anodes are ideal candidates for advanced high energy density Na metal batteries. Nevertheless, the unstable solid electrolyte interphase (SEI), the uncontrollable dendrite growth, and low Coulombic efficiency during cycling have prevented their applications. Herein, a high‐performance Na anode is achieved by introduction of an ex situ artificial Na3P layer on the surface via a simple red phosphorus pretreatment method. The artificial SEI layer possesses high ionic conductivity and high Young's modulus, which regulates uniform deposition of ions and prevents the dendrite growth. Benefiting from these merits, the Na||Na cells with the protected layers demonstrate excellent electrochemical performance (780 h at 1.0 mA cm–2, 1.0 mAh cm–2). When assembled into a full battery with a Na3V2(PO4)3 cathode, the Na metal battery exhibits a long lifespan of 400 cycles at 15 C and a high rate capacity of ≈53.2 mAh g–1 at 30 C. In addition the red P pretreatment method can be applied to potassium metal anodes. Outstanding performance is also achieved in K||K cells with the formation of a KxPy protecting layer (550 h at 0.5 mA cm–2, 0.5 mAh cm–2). The artificial P‐derived protection approach can also be extended to solid‐state alkali metal batteries with high power density and energy density.

electrical energy storage than traditional lithium ion batteries. [14,15] However, the practical application of LMBs has been prevented due to the high chemical reactive between Li and organic electrolytes, forming an unstable solid electrolyte interphase (SEI) at the electrolyte/Li interface. The SEI is mechanically fragile that cannot accommodate the huge volume changes forming Li dendrites. The lithium dendrite growth leads to continuously consumed electrolytes and poor cycle life of LMBs. [16-18] Additionally, the SEI cracker causes locally enhanced Li ionic flux and nonuniform Li deposition, which triggers the continuous growth of dendrite and internal short circuits. There are three main approaches to get the stable SEI, namely, 1) building a high Li ionic conductivity SEI film ex situ on the Li metal surface, such as Li 2 S, [19] Li 2 Se, [20] LiF, [21] and Li 3 N; [22,23] 2) constituting SEI film in situ on the Li metal surface through regulating the composition of electrolytes and additives; [24-28] and 3) constructing a high mechanical strength SEI film ex situ on the Li metal surface. [29] Among these artificial SEI film, Li 3 N thin film coating has been demonstrated to suppress the lithium dendrite growth because of its high Li ionic conductivity(ionic conductivity: ≈10 −3 to 10 −4 S cm −1 at room temperature), [30,31] unique thermodynamic stability against Li metal [32,33] and high Young's modulus. [30] However, loosely connected Li 3 N small particles form porous artificial SEI layer that cannot hinder the penetration of corrosive electrolytes and tolerate the infinite volume change during the Li plating/stripping process. [34,35] Formation of compact and uniform Li 3 N contained passivation layer on Li metal is therefore highly desirable. Moreover, nitrogen-containing organic groups (CNC and N(C) 3 groups) have been demonstrated a strong interaction with Li, regulating lithium ions to be evenly distributed on the electrode surface. [36,37] One can expect that introduction nitrogen-containing organic groups into inorganic Li 3 N layer could combine the merits of both, improving lifespan of Li metal anode. Herein, we design a CNC and N(C) 3 groups-rich artificial SEI with Li 2 CN 2 phase and abundant high ionic conductive Li 3 N phase (denoted as N-organic/Li 3 N) via simple Lithium metal anodes are one of the most promising anodes in "next-generation" rechargeable batteries. However, continuous dendrite growth and interface instability of the anode have prevented practical applications. Constructing an artificial solid electrolyte interphase (SEI) is an effective way to solve these issues. Herein, an artificial organic/inorganic SEI layer (denoted as N-organic/Li 3 N) is designed, consisting of Li 2 CN 2 and Li 3 N phases, to achieve stable cycling of Li metal electrodes. Density functional theory (DFT) results reveal that the N-organic/Li 3 N layer with a high Li ionic conductivity can effectively facilitate the transport of Li ions across the electrode surface and lead to uniform Li ionic f...