Anionic Se‐Substitution toward High‐Performance CuS_1−xSe_x Nanosheet Cathode for Rechargeable Magnesium Batteries

Abstract

host materials, including metal oxides (V 2 O 5 , [2] VO x , [3] MnO 2 , [4] and MoO 3 [5] ), metal sulfides (Mo 6 S 8 , [6] MoS 2 , [7] Ti 2 S 4 , [8] α-Ag 2 S, [9] VS 4 , [10] and VS 2 [11] ), metal selenides (Mo 6 Se 8 , [12] TiSe 2 , [13] Cu 2 Se, [14] and Ni 0.75 Fe 0.25 Se 2 [15] ), have been proposed as possible cathode candidates. In particular, copper sulfide (CuS) has recently attracted great attention because of its unique properties of nontoxicity, eco-friendliness, low cost, and high theoretical specific capacity (560 mAh g −1 ). [16] Nevertheless, CuS cathode materials are still subject to a series of unsatisfactory performances related to reversible capacity, rate capability, and cycling stability caused by the serious polarization from divalent Mg 2+ . [17] Thus, the development of suitable host materials with fast reaction kinetics is highly desired but still challenging. To solve the aforementioned issues, many strategies have been proposed and brought considerable achievement in CuS cathode materials, including: i) increased ionic diffusion kinetics through elevating working temperature, [16] ii) enhanced Mg 2+ mobility by adjusting electrode-electrolyte interface, [18] and iii) shortened Mg 2+ diffusion length via constructing suitable nanoarchitectures. [19] However, the electron and solid-state Mg 2+ transport kinetics of the most reported CuS cathode materials are still unsatisfactory. It is therefore a great challenge to effectively design CuS cathode materials with high practical capacity and long cycling life, especially at high current densities. In our previous work, [19a] although the hierarchical CuS nanosheet showed good cycling performances for rMBs (135 mAh g −1 at 200 mA g −1 upon 200 cycles), its rate capability still needs to be further improved. Heavy heteroatom substitution in transition metal sulfides is expected as an efficient route to regulate their atomic structure for providing optimized configuration for Mg 2+ uptake. [20] In particular, the fractional anionic Se-substitution to S could enlarge the Mg 2+ diffusion path and reduce their interaction with the based lattice, thereby cutting down the ionic diffusion barrier and resulting much better kinetics. [21] Till now, despite the well-known Chevrel phase Mo 6 S 8−X Se X (X = 0, 1, 2), [12,21a,22] Se-substituted copper sulfide cathode materials for rMBs have been rarely reported.Herein, we develop an efficient synthesis strategy to prepare 2D anionic Se-substituted CuS 1−x Se x nanosheets with about Rechargeable magnesium batteries (rMBs) are promising as the most ideal further energy storage systems but lack competent cathode materials due to sluggish redox reaction kinetics. Herein, developed is an anionic Sesubstitution strategy to improve the rate capability and the cycling stability of 2D CuS 1−x Se x nanosheet cathodes through an efficient microwave-induced heating method. The optimized CuS 1−x Se x (X = 0.2) nanosheet cathode can exhibit high reversible capacity of 268.5 mAh g −1 at 20 mA g −1 and good cycli...

Challenges and Recent Progress on Key Materials for Rechargeable Magnesium Batteries

“…[ 15 ] For example, Cao's group used an effective microwave‐induced thermal method to achieve Se element substitution to synthesize 2D CuS 1− x Se x nanosheet cathodes. [ 100,101 ] When x = 0.2, through the reversible conversion reaction between CuS 1 ‐x Se x nanosheet and Mg, an excellent rate performance and impressive cycling stability were presented. Subsequently, both β‐Cu 2 Se and CuSe have been confirmed as a new conversion‐type Mg storage cathode material.…”

Designing Nanostructured Metal Chalcogenides as Cathode Materials for Rechargeable Magnesium Batteries

“…[11] Recently, the Mg battery research community has turned its attention toward metal chalcogenides as potential cathode materials (Figure 1b). [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] Up until 2017, research on metal chalcogenide cathodes has been primarily based on Mo 6 S 8 , which is widely used as the standard cathode material for evaluating new electrolyte systems and/or new cathode materials. A sudden change in trend is noticed when the number of publications reporting on other metal chalcogenides has increased significantly over the past 3 years.…”

“…[5,15,[33][34][35] Recent publications have also shown the benefits of nanostructuring of metal chalcogenides in improving battery performance as a consequence of increased surface area and shortened diffusion path for Mg 2+ ion in solid phase. [12,14,16,21] To our knowledge, however, no review has been done on the impact of nanostructure engineering of metal chalcogenide cathodes on RMB performance, prompting us to give a succinct review on the application of nanostructured metal chalcogenides for RMBs. This review, nevertheless, will also be beneficial to the development of advanced cathode materials for other emerging battery systems, such as sodium, calcium, and aluminum batteries, which are rapidly gaining much interest from the battery research community.…”

“…[53] In addition, the conversion cathode exhibits large voltage hysteresis observed between discharge and charge, which results in low energy efficiency. [53,54] The metal chalcogenides that have been experimentally attempted as conversion cathode for Mg batteries are CuS, [14,17,18,[23][24][25][26]34,[55][56][57][58] Ag 2 S and Ag 2 Se, [15,19,59] NiCo 2 Se 4 , [28] Cu 2−x Se, [13] CuSe, [60] Ni 0.85 Se, [61] CuS 1−x Se x , [16] CoS, [62] FeS 2, [63] Sb 2 Se 3 , [20] Bi 2 Se 3 , [20] CoSe 2 , [21] and Ni 0.75 Fe 0.25 Se 2.…”

“…In comparing the electrochemical properties of mixedanion CuS 1−x Se x with those of CuS, Wang et al have found that Se-substitution can lead to better Mg-ion storage performance by improving the conversion-type reaction kinetics. [16] This is because Se can enhance the net electronic conductivity and lower the Mg-ion migration barrier, which can accelerate the conversion reaction rates. For similar reasons, promising Mg-ion storage behavior was also observed when binary Cu 2−x Se phases were employed as cathodes.…”