Engineering the interplanar spacing of K-birnessite for ultra-long cycle Zn-ion battery through “hydrothermal potassium insertion” strategy

Challenges and Perspectives for Doping Strategy for Manganese-Based Zinc-ion Battery Cathode

“…The layer-type structure of monoclinic birnessite phase was obtained following a hydrothermal reaction of 120 • C for 12 h with a large interlayer spacing (7.12 Å). Shi et al synthesized a cathode (K 0.29 MnO 2 •0.67H 2 O) with a larger interplanar spacing (7.4 Å) through a hydrothermal potassium insertion strategy [37]. Peng et al developed a Na + -incorporated layered δ-MnO 2 by subjecting K + -containing δ-MnO 2 to hydrothermal treatment using a 0.5 mol•L −1 Na 2 SO 4 solution at 180 • C for 3 h [38].…”

“…Wang's work revealed that the pre-intercalation of Bi 3+ into α-MnO 2 could effectively enlarge the lattice spacing and have a positive effect on the ion diffusion rates, resulting in a superior rate performance with a capacity retention of 150 mAh•g −1 at 5 A•g −1 [42]. K 0.29 MnO 2 •0.67H 2 O (KMO) with an interplanar spacing of 7.4 Å was synthesized via a simple hydrothermal strategy by Shi et al [37], as shown in Figure 6b, exhibiting high capacity (300 mAh•g −1 at 0.2 A•g −1 ) and an ultralong cycle performance (158 mAh•g −1 after 12,000 cycles at 2 A•g −1 ). According to the XRD pattern in Figure 6c, this work calculated that the interlayer spacing corresponding to the (001) plane increased from 6.8 Å to 7.4 Å according to Bragg's rule.…”

“…As shown in Figure 6e,f, KMO displayed a smaller overpotential and higher diffusion coefficient than MnO 2 dur-ing the discharge process, which indicated that the doping of K + indeed promoted ion diffusion kinetics. [37]; (e) GITT image of KMO and MnO2 electrodes [37]; (f) results of ion diffusion coefficients for KMO and MnO2 electrodes [37].…”

“…As revealed by the EIS spectrum (Figure 7c), Ti-doped MnO2 exhibited lower charge migration resistance, confirming that the unbalanced local electric field in the host structure could boost the mobility of ions/electrons. Furthermore, according to the DFT calcula- [74]; (b) structure schematic of KMO [37]; (c) XRD patterns of KMO and MnO 2 [37]; (d) calculation results of H + and Zn 2+ diffusion energy barriers for KMO and MnO 2 electrodes using DFT [37]; (e) GITT image of KMO and MnO 2 electrodes [37]; (f) results of ion diffusion coefficients for KMO and MnO 2 electrodes [37].…”

“…Figure 6. Enlarged interlayer spacing and faster ion diffusion kinetics: (a) XRD patterns of Vdoped MnO 2[74]; (b) structure schematic of KMO[37]; (c) XRD patterns of KMO and MnO 2[37]; (d) calculation results of H + and Zn 2+ diffusion energy barriers for KMO and MnO 2 electrodes using DFT[37]; (e) GITT image of KMO and MnO 2 electrodes[37]; (f) results of ion diffusion coefficients for KMO and MnO 2 electrodes[37].…”