MoN Supported on Graphene as a Bifunctional Interlayer for Advanced Li‐S Batteries

Abstract

drastically superior specific energy density. [1][2][3][4][5][6][7] However, the successful implementation of Li-S batteries is still hindered by many challenges. One of the largest problems facing the current Li-S battery is the rapid capacity decay and serious selfdischarge caused by the dissolution and migration of intermediate lithium polysulfides (LiPSs). [8][9][10][11][12][13][14][15] Significant efforts have been dedicated to the research of suitable approach to address polysulfide shuttling. As one of the strategies, inserting an interlayer between the separator and sulfur electrode is widely applied due to the minimal changes to existing applications. [16][17][18][19] Various materials such as metal oxides, sulfides, and metal-organic frameworks have been proposed as functional interlayer to trap LiPSs through chemisorption, and this strategy has been demonstrated to be effective to block the migration of polysulfide species. [20][21][22][23][24] The interlayer serves as both adsorbent and current collector, where polysulfides can be reduced to insoluble products. [25,26] While this helps block LiPSs and improve the sulfur utilization, the produced Li 2 S is hard to oxidize back to soluble LiPSs due to the intrinsically poor electrical and ionic conductivity. [27] The accumulation of Li 2 S not only leads to the loss of active materials but also passivates the interlayer and impairs the electrochemical performance because of the insufficient transport of Li ions especially for cathodes with high sulfur loading. [1,16,[27][28][29] There is thereby an urgent need but it is still a significant challenge to develop interlayers that can not only block LiPSs but also accelerate Li 2 S oxidation on interlayers.To achieve this, we propose several key factors to consider when developing a practical bifunctional interlayer: 1) the adsorption energies between interlayer and LiPSs/Li 2 S that provides a strong anchoring; 2) the Li ion diffusion barrier that ensures good Li ion mobility; 3) the electrical conductivity of interlayer materials that facilitates electron transport and electrochemical conversions. In this work, we introduce MoN as a suitable interlayer material for Li-S batteries. On the one hand, the surface Mo atoms with unoccupied orbitals act as Lewis acid sites, and thus, MoN can serve as a good adsorbent for LiPSs. [30,31] On the other hand, our theoretical calculation reveals an extremely low Li ion diffusion barrier on MoN Rational design of effective polysulfide barriers is highly important for highperformance lithium-sulfur (Li-S) batteries. A variety of adsorbents have been applied as interlayers to alleviate the shuttle effect. Nevertheless, the unsuccessful oxidation of Li 2 S on interlayers leads to loss of active materials and blocks Li ion transport. In this work, a MoN-based interlayer sandwiched between the C-S cathode and the separator is developed. Such an interlayer not only strongly binds lithium polysulfides via Mo-S bonding but also efficiently accelerates the decomposition of Li 2...

Electrospinning‐Based Strategies for Battery Materials

“…[ 58 ] Moreover, sulfur is low cost and environmentally benign. [ 59 ] However, several challenges hinder their applications including the poor electrical conductivity of sulfur and Li 2 S, high solubility of polysulfide and large volume change of 80%, [ 4c ] which lead to low rate capacity, poor Coulomb efficiency, and fast capacity degradation. [ 60 ] Due to the high electrical conductivity, porous structure, and excellent mechanical stability, porous carbon nanomaterials are widely chosen as sulfur hosts, which can enable fast electron transport, effective ion diffusion, good accommodation of volume change, and absorption of polysulfide.…”

Conductive FeOOH as Multifunctional Interlayer for Superior Lithium–Sulfur Batteries

“…After several cycles of CV, the EIS consist of two semicircles at high/middle frequency and a slop line at low frequency ( Figures S3 and S4, Supporting Information), presenting charge-transfer, adsorption, and diffusion processes. [8,33] Evidently, the resistance of charge transfer, adsorption, and diffusion of LiPSs in LSBs with FeOOH interlayer is obviously smaller, suggesting promoted redox conversion of intermediate LiPSs with conductive FeOOH.…”

“…In contrast, LSBs with FeOOH/PP separator display a lower potential barrier at 2.194 V, indicating lower solid-liquid conversion barrier catalyzed by FeOOH interlayer. [8,16,39] The catalytic redox conversion can be more clearly revealed by rate capability, which related to fast charge transfer and reversible multiphase conversion especially at high rates. [27] As depicted in Figure 7d, LSBs with FeOOH/PP separator exhibit reversible discharge capacity of 1294 (0.1 C), 1139 (0.2 C), 810 (0.5 C), 730 (1 C), and 449 (2 C) mAh g −1 .…”

“…These issues are rooting in poor electrical conductivity of charge/discharge products (e.g., S, Li 2 S 2 , and Li 2 S), considerable volumetric variation up to 80% during multistep phase transformation and severe intermediation lithium polysulfides (LiPSs) shuttle effect in ether‐based electrolyte. [ 3 ] To develop reliable LSBs, many strategies have been tried (the addition of multifunctional additives or binders; [ 4 ] designing sulfur‐conductive carbon/polymer composites; [ 5 ] separator modification [ 6–8 ] ) to suppress the shuttle of polysulfides.…”

The Development of Catalyst Materials for the Advanced Lithium–Sulfur Battery

“…The CV curve shows that Co4N nanoparticles can catalyze the conversion of Li2S6 to Li2S2 and Li2S, reducing the polarizability (Figure 5e). Da Tian and co-workers developed a separator material of MoN-G/PP [46]. Figure 5f shows the adsorption activation of Li 2 S on MoN.…”