Elucidation of the Sodium – Copper Extrusion Mechanism in CuCrS₂: A High Capacity, Long‐Life Anode Material for Sodium‐Ion Batteries

Abstract

The compound CuCrS2 with a quasi‐layered crystal structure was investigated as room temperature rechargeable sodium‐ion battery electrode. It exhibits excellent performance as anode material with a high reversible capacity of 424 mAh g−1 at 700 mA g−1 after 200 cycles and a capacity retention of 98.6 % compared to the third cycle. Results of ex‐situ X‐Ray diffraction experiments performed at different stages of the discharge process demonstrate that at the beginning of Na uptake, Cu+ cations are reduced to nanosized metallic Cu particles which are expelled from the host lattice. Simultaneously, Na is inserted into the host material leading to the formation of Na0.7Cu0.15CrS2 with significantly expanded interlayer space. Metallic Cu and Na0.7Cu0.15CrS2 coexist at this stage of discharge. Increasing the amount of Na per formula unit leads to successive conversion to X‐ray amorphous Cr, nanocrystalline Na2S and metallic Cu. The formation of highly disordered metallic Cr with domain sizes in the range of few nanometres is revealed by atomic pair distribution function analysis. During the charge process, the nanocrystalline Cu particles are retained and Na0.7Cu0.15CrS2 is at least partially reformed. The finely distributed Cu particles dramatically improve the long‐time stability as evidenced by comparison of the electrochemical behaviour of mere NaCuCrS2.

Superior Sodium Storage Properties in the Anode Material NiCr2S4 for Sodium‐Ion Batteries: An X‐ray Diffraction, Pair Distribution Function, and X‐ray Absorption Study Reveals a Conversion Mechanism via Nickel Extrusion

“…[ 41,42 ] On the other hand, some residual Ni 2+ ions may remain for charge compensation, i.e., Na 1− x Ni x /2 CrS 2 , comparable to findings for Na/CuCrS 2. [ 39 ] The results of the first cycle can be summarized as follows: i) during discharge Ni 2+ cations are removed from the host lattice and are simultaneously reduced, ii) Na + cations replace Ni 2+ in the vacancy layers and layer‐like int‐NaCrS 2 is generated, iii) during charge NiCr 2 S 4 crystallizes, reflections of elemental Ni disappear and tiny amounts of Na 1− x CrS 2 survive. The main differences after the 50th compared to the first cycle are: i) the intensity ratio of the (111) and (200) reflections of Ni is reversed after discharge indicating a change of morphology, ii) an increased reflection intensity at 1.92° 2θ demonstrates a larger amount of Na 1− x CrS 2 after charge, iii) reflections of NiCr 2 S 4 are broader after charge caused by domain size reduction.…”

“…Recently, we discovered the formation of crystalline Na 0.7 Cu 0.15 CrS 2 during the sodiation process in the pseudo‐layered compound CuCrS 2 via copper extrusion sodium insertion mechanism. [ 39 ] Hereby, nanosized Cu particles are expelled from a [CrS 2 ] host lattice dramatically enhancing the cycle stability of CuCrS 2 compared to mere NaCrS 2 . This discovery raised two indispensable questions: i) do other ternary layer‐like Cr sulfides exhibit comparable electrochemical properties and ii) can a transition metal extrusion from a pseudo‐layered host material be exploited to reversibly shuttle Na + cations with structural retention of the host lattice?…”

Understanding sodium storage properties of ultra-small Fe3S4 nanoparticles – a combined XRD, PDF, XAS and electrokinetic study

“…In contrast, the 1 st galvanostatic charge cycle and all subsequent GDC profiles do not exhibit well-resolved plateaus as often observed for conversion-based materials. 11,54,57 However, highly reversible electrochemical processes in the small potential window are evidenced by very similar GDC profiles after the 2 nd cycle applying 0.5 A g −1 (Fig. 3c) in contrast to the large potential window (Fig.…”

Sodium‐Ion Hybrid Battery Combining an Anion‐Intercalation Cathode with an Adsorption‐Type Anode for Enhanced Rate and Cycling Performance

“…Exploiting rechargeable battery technologies with enhanced performance as well as low cost and environmental friendliness has become a global and urgent demand since the explosive growth of portable electronic devices, electric vehicles as well as large‐scale energy storage . Meanwhile, the limited and uneven distribution of lithium resource has stimulated extensive investigations of energy storage devices based on other abundant metal ions, such as Na + , K + , Al 3+ ,, etc. Among them, sodium‐ion batteries (SIBs) have attracted increased attention owing to the merits of low potential (−2.71 V vs. standard hydrogen electrode (SHE)), high natural abundance, low cost, and similar electrochemical properties to lithium .…”

“…Consequently, attributed from the hybrid battery design, this SHB exhibits excellent rate capability and cycling performance with a reversible capacity of 80 mAh g À1 at 2 C over a voltage window of 0-3.8 V and capacity retention of 87 % after 1000 cycles at 10 C.Exploiting rechargeable battery technologies with enhanced performance as well as low cost and environmental friendliness has become a global and urgent demand since the explosive growth of portable electronic devices, electric vehicles as well as large-scale energy storage. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Meanwhile, the limited and uneven distribution of lithium resource has stimulated extensive investigations of energy storage devices based on other abundant metal ions, such as Na + , [12][13][14][15][16][17][18][19][20][21][22][23][24][25] K + , [26][27][28][29][30] Al 3 + , [31,32] etc. Among them, sodium-ion batteries (SIBs) have attracted increased attention owing to the merits of low potential (À2.71 V vs. standard hydrogen electrode (SHE)), high natural abundance, low cost, and similar electrochemical properties to lithium.…”