Multi‐Ions Electrolyte Enabled High Performance Voltage Tailorable Room‐Temperature Ca‐Metal Batteries

Abstract

Calcium metal batteries, as one of the promising alternatives beyond Li‐metal technology, is held back by the lack of suitable cathodes of considerable energy storage capability, and Ca anodes of long‐term stability and lower polarization potentials for Ca‐plating/stripping. Here, by recycling cellulose waste paper, feasible cathodes for Ca‐metal batteries of good high‐voltage and wide‐window‐voltage adaptability (0.005–4.9 V versus Ca/Ca2+), and impressive energy density (≈517.5 Wh kg−1 at 0.1 A g−1) are developed. Meanwhile, through tailorable Ca‐plating/stripping potentials (∆V ≈ 0.65 V) realized by a modified electrolyte of Li+, Ca2+, BF4−, and PF6− multi‐ions system, the proof‐of‐concept Ca‐metal batteries not only delivered enhanced storage capability (101 mAh g−1 versus 51 mAh g−1 at 0.1 A g−1 in the window voltage of 2.0–4.7 V) and cycling stability (≈77% capacity retention for 100 cycles), but also simultaneously show a high output average working voltage of ≈3.2 V. The work provides a hint that mixed metal deposition under multi‐ions electrolyte system may address the challenging issues faced by single alkali or alkaline‐earth metal batteries.

Current Status and Challenges of Calcium Metal Batteries

“…Similarly, Li/Ca hybrid SEIs, comprising of nanocrystals of LiH, Li 3 PO 4 , and a small amount of CaF 2 , were also verified to be applicable for lowering overpotentials and enhancing cycling stability, as well as tailoring deposition layer from dendritic crystal growth in Ca(BF 4 ) 2 electroyte to uniform planar growth in Ca(BF 4 ) 2 ‐LiPF 6 hybrid electrolyte, as shown in Figure . [ 61 ] These results demonstrate that plating/stripping reversibility of Ca‐metal and interface charge transfer kinetics of electrode–electrolyte can be properly tailored through rational engineering of electrolyte and interphase.…”

“…[76] Research of solvation properties of Ca 2þ also showed coordination number, distances, and species in solvation shell were highly relevant with concentrations. [77] Hence, through proper electrolyte and [45] Ca(BF 4 ) 2 0.45 M in EC/PC SS CaF 2 , hydroxide, carbonate 100 C, 0.05 mA cm À2 and 0.017 mAh cm À2 for 92 h, 0.05 V overpotential, negligible potential shift, 3.5 V anodic stability for Al [66] Ca(BF 4 ) 2 1 M in EC/PC Cu Unknown phase >1 V overpotential, observed Ca deposits, nearly inactive [71] Ca(BF 4 ) 2 1 M in EMI þ TFS Àa) Cu CaF 2 , CaS >1 V overpotential, observed Ca deposits, nearly inactive [72] Ca(BF 4 ) 2 1 M EC/DEC Ca CaF 2 >1 V overpotential, nearly inactive [61] Ca(PF 6 ) 2 1 M EC/DEC Ca CaF 2 >1 V overpotential, nearly inactive [59] Ca(ClO 4 ) 2 0.5 M in BL b) , or PC, or ACN Ca CaCl 2 , CaCO 3 , Ca(OH) 2 , >1 V overpotential at 5 mV s À1 , nearly inactive [67] Ca(ClO 4 ) 2 0.3 M in EC/PC SS Ca(OH) 2 75-100 C, >1 V overpotential at 0.5 mV s À1 , 0.004 mA stripping current, nearly inactive [66] Ca(TFSI) 2 0.1 M and 0.45 M in EC/PC Ca CaCO 3 25-100 C, charge transfer resistance >10 6 Ohm, inactive [83] Ca(TFS) 2 0.1 M in DMF c) SS -Corrosive [45] Ca(TFS) 2 0.05 M in DEME þ TFSA À , 0.1-0.3 M in TMP Ca -60 C, negligible capacity, inactive [55] Ca(BH 4 ) 2 1.5 M in THF Au CaH 2 1 mA cm À2 and 1 mAh cm À2 for 100 h, 0.1 V overpotential, negligible potential shift. <3 V anodic stability for Pt, 94-96% CE at 1 mA cm À2 [15] Ca[B(hfip) 4 ] 2 0.25 M in DME Pt, Ca CaF 2 0.1-0.5 mA cm À2 and 0.05-0.25 mAh cm À2 for 250 h, <0.06->0.5 V overpotential, little potential shift, 4.8 V anodic stability for Al, 80% CE at 80 mV s À1 [16] Ca[B(hfip) 4 ] 2 0.5 M in DME Au CaF 2 0.5 mA cm À2 and 1 mAh cm À2 for 72 h, 0.2 V overpotential, little potential shift, 4.1 V anodic stability for Al, 92% CE at 25 mV s À1 [17] Ca[B(hfip) 4 ] 2 0.25 M in DGM GC, Cu, Al, Pt CaF 2 1-8 mA cm À2 for 300 h, <0.1->0.5 V overpotential, 61-85% CE at 100 mV s À1 [53] a)…”

“…[ 58 ] Differently, a specially designed freestanding lattice‐expanded graphitic carbon fiber membrane cathode reversibly runs for almost 1900 cycles with 83% capacity retention and a high average discharge voltage of 3.16 V in CMBs. [ 59 ] By using an artificial hybrid solid electrolyte layer modified Ca as the anode, the carbon membrane cathode offered a high discharge voltage (>3.3 V) and a large capacity of ≈80 mAh g −1 at 200 mA g −1 and a high window voltage of 2.0–5.0 V. [ 60 ] Similarly, a voltage tailorable Ca‐metal battery with cellulose waste paper derived graphitic carbon as the cathode delivered a high working voltage of 3.2 V and reversible capacity of 101 mAh g −1 at 2.0–4.7 V. [ 61 ]…”

“…All the data are adapted from publications reported previously. [4,[10][11][12][13][14][15][16][17]41,43,44,[46][47][48][49][50][52][53][54]56,59,61,63,64,66,[79][80][81][82] polyanionic phosphates but also developing multicomponent high-voltage or Ca-rich large capacity cathodes such as Ni/Mnbased Li/Na-counterparts and defect/interface-engineered fast kinetics and cycling-stable cathodes. [31][32][33][34][35][36]…”

“…Although recent several reports presented plating and stripping signals and even Ca deposits, the large polarization overpotentials and severe kinetics hysteresis have not been improved for these calcium salts, with plating/stripping persisting on for only several cycles. [59,61,[71][72][73]…”