Investigation of the potassium‐ion storage mechanism of nickel selenide materials and rational design of nickel selenide‐C yolk‐shell structure for enhancing electrochemical properties

Abstract

Metal selenide is contemplated as expeditious anode material for potassiumion batteries (KIBs). Here, nickel selenide (NiSe 2 -Ni 0.85 Se) was investigated as an anode material for KIBs. The NiSe x transformed into K 2 Se and K 2 Se 3 (K 2 Se x ) and reversibly returned to NiSe x after the discharge and charge processes (17NiSe 2 + 3Ni 0.85 Se + 38 K + + 38e À $ 19.55Ni + 10K 2 Se + 9K 2 Se 3 ). Furthermore, to enhance the electrochemical properties of nickel selenide, yolk-shell-structured nickel selenide and hollow carbon nanosphere composites, in which nickel selenides intensively existed in the core and were partially formed into nanocrystals in the shell, were produced by simple salt-infiltration and a post-treatment. NiSe x @C exhibited improved cycle and rate properties compared to bare NiSe x because of its structural merits that led to stable cycle performance and high electrochemical kinetics. NiSe x @C exhibited 373 mA h g À1 for the 100th cycle at 0.05 A g À1 and 234 mA h g À1 at 1.0 A g À1 .

Defects passivation and crystal growth promotion by solution-processed K doping strategy toward 16.02% efficiency Cu(In,Ga)(S,Se)2 solar cells

“…[19] The peaks at higher binding energy of 54.9 and 55.5 eV were assigned to the K 2 Se 3 phase. [37,38] This result demonstrated the existence of K-Se phase in the selenization process.…”

Controllable Double Gradient Bandgap Strategy Enables High Efficiency Solution‐Processed Kesterite Solar Cells

“…[42,43] The peaks at lower binding energies of 52.8 eV and 53.6 eV were assigned to the K 2 Se 3 phase, confirming the presence of the K─Se phase. [44] Figure 4h,i shows the XPS spectra of the Se Auger-K 2p region. For the K 2 S film, a shoulder peak on the Se Auger peak is observed at the low binding energy (292.6 and 249.8 eV) side, which is attributed to the K 2p response.…”

“…After the selenization temperature reaches 375 °C, the liquid K 2 Se 3 phase flows between grain boundary (Figure 5i), lowering the melting point and leading to rapid crystallization at lower temperatures. [44] Moreover, the flow of K 2 Se 3 liquid phase is accompanied by the supply of Se. Placing the K 2 S layer in the middle of the CZTSSe film facilitates the downward diffusion of the generated K 2 Se 3 to the rest of the film, which is the key reason why the film is able to form two layers of microcrystals when selenization time is 600 s. Meanwhile, the Cu 2 Se liquid phase also plays an obvious role in accelerating the crystallization process, and Cu 2 Se is usually formed in the preselenization period, Cu 2 S + Se → Cu 2 Se + S (g) this reaction occurs at 275 °C, but the presence of the Cu 2 Se phase can be detected at 225 °C when the film contains alkali metals, so we believe that this is another reason for the dominance of the K 2 S sample in the grain growth process.…”

Intrinsic carbon structure modification overcomes the challenge of potassium bond chemistry

“…[20][21][22][23][24] To date, various types of anode candidates have been developed and reported, which can be roughly divided into three categories according to the various energy storage mechanism, including an intercalationtype anode with a large interlayer spacing for K + insertion/ extraction (e.g., hard carbon, 25,26 graphite, 27 TiO 2 , 28 K 2 Ti 4 O 9 , 29 layered transition metal chalcogenides, [30][31][32] etc. ), a conversiontype anode with a reversible phase transition process and huge volume change (e.g., Co 3 O 4 , 33 Fe 2 O 3 , 34 CoS, 35 NiSe 2 , 36 FeSe 2 , 37 SnS 2 , 38 etc. ), and an alloying-type anode with a high specific capacity and more severe volume change than conversiontype 39 (e.g., Bi, 40 Sb, 41,42 P, 43 Sn, 44 etc.).…”

“…), a conversion-type anode with a reversible phase transition process and huge volume change ( e.g. , Co 3 O 4 , 33 Fe 2 O 3 , 34 CoS, 35 NiSe 2 , 36 FeSe 2 , 37 SnS 2 , 38 etc. ), and an alloying-type anode with a high specific capacity and more severe volume change than conversion-type 39 ( e.g.…”