Red phosphorus (P) has attracted intense attention as promising anode material for high-energy density sodium-ion batteries (NIBs), owing to its high sodium storage theoretical capacity (2595 mAh g ). Nevertheless, natural insulating property and large volume variation of red P during cycling result in extremely low electrochemical activity, leading to poor electrochemical performance. Herein, the authors demonstrate a rational strategy to improve sodium storage performance of red P by confining nanosized amorphous red P into zeolitic imidazolate framework-8 (ZIF-8) -derived nitrogen-doped microporous carbon matrix (denoted as P@N-MPC). When used as anode for NIBs, the P@N-MPC composite displays a high reversible specific capacity of ≈600 mAh g at 0.15 A g and improved rate capacity (≈450 mAh g at 1 A g after 1000 cycles with an extremely low capacity fading rate of 0.02% per cycle). The superior sodium storage performance of the P@N-MPC is mainly attributed to the novel structure. The N-doped porous carbon with sub-1 nm micropore facilitates the rapid diffusion of organic electrolyte ions and improves the conductivity of the encapsulated red P. Furthermore, the porous carbon matrix can buffer the volume change of red P during repeat sodiation/desodiation process, keeping the structure intact after long cycle life.

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.

because of their high energy density and power density. [1][2][3] With expansion of the demand and applications, the price of lithium salt is increasing due to the limited lithium resources on earth, which prevents its application for large-scale application. Recently, Na-ion batteries (NIBs) and K-ion batteries (KIBs) have attracted increasing attention mainly because of the abundance of sodium and potassium in the Earth's crust. [4][5][6][7] Especially, the K + /K couple shows much lower redox potential (−2.93 V) in various carbonate-based electrolytes than that of the Na + /Na couple (−2.71 V), which offers widen electrochemical voltage windows and high energy density of full cell. [8] Thus, developing high-capacity and cost-effective rechargeable NIBs and KIBs is critical for both grid and transportation applications. Among different types of rechargeable batteries, room-temperature alkali metal-chalcogen batteries, such as sodium-sulfur (Na-S), potassium-sulfur (K-S), sodium-selenium (Na-Se), and potassium-selenium (K-Se) batteries, offer great potential because of their high energy density and low cost. [9][10][11][12][13] The inherent low electronic conductivity of S and soluble polysulfides shuttling in the ether-based electrolyte leads to the poor electrochemical performance of Na-S and K-S batteries. [10,11,14] Se possesses chemistry properties similar to sulfur (S) and has been considered to be an alternative cathode material for NIBs because of its high theoretical specific capacity (675 mA h g −1 ), high theoretical volumetric capacity (3253 mA h cm −3 ), and higher electronic conductivity (1 × 10 −3 S m −1 ) than that of S (5 × 10 −30 S m −1 ). [15][16][17] Among various metal-selenium batteries, including Li-Se, Na-Se, and K-Se batteries, Na-Se and K-Se batteries are especially attractive due to low material cost (rich abundance of Na and K in nature). Based on the reactions between Se and metal Li, Na or K: Se + 2M + + 2e − ↔ M 2 Se (M = Li, Na, K), these three Li-Se, Na-Se, and K-Se batteries possess the same theoretical specific capacity of 675 mA h g −1 . [17,18] The specific energy density of Na-Se batteries is smaller than that of Li-Se batteries but higher than that of K-Se batteries. [13,19,20] However, the Se cathode also suffers from short cycle life and low charging efficiency in NIBs Na-Se and K-Se batteries are attractive as a stationary energy storage system because of much abundant resources of Na and K in the Earth's crust. As the alloy-type Se has a severe pulverization issue, one critical challenge to develop advanced Na-Se and K-Se batteries is to explore a highly efficient and stable Se-based cathode. Herein, a flexible free-standing Se/carbon composite film is prepared by encapsulation of Se into a carbon nanotube (CNT) interwoven N,O dual-doped porous carbon nanosheet (Se@NOPC-CNT). The 3D interconnected CNT uniformly wrapped on the N,O dual-doped porous carbon skeletons improves the flexibility and offers an interconnected conductive pathway for rapid ionic/electronic transpo...

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.