Unraveling the Mechanism of Cooperative Redox Chemistry in High‐Efficient Zn2+ Storage of Vanadium Oxide Cathode

Abstract The inferior capacity and cyclic durability of V2O5 caused by inadequate active sites and sluggish kinetics are the main problems to encumber the widespread industrial applications of vanadium‐zinc batteries (VZBs). Herein, a cooperative redox chemistry (CRC) as “electron carrier” is proposed to facilitate the electron‐transfer by capturing/providing electrons for the redox of V2O5. The increased oxygen vacancies in V2O5 provoked in situ by CRC offers numerous Zn2+ storage sites and ion‐diffusion paths and reduces the electrostatic interactions between vanadium‐based cathode and intercalated Zn2+, which enhance Zn2+ storage capability and structural stability. The feasibility of this strategy is fully verified by some CRCs. Noticeably, VZB with [Fe(CN)6]3−/[Fe(CN)6]4− as CRC displays conspicuous specific capacity (433.3 mAh g−1), ≈100% coulombic efficiency and superb cyclability (≈3500 cycles without capacity attenuation). Also, the mechanism and selection criteria of CRC are specifically unraveled in this work, which provides insightful perspectives for the development of high‐efficiency energy‐storage devices.


Preparation of V 2 O 5 cathode:
To prepare the V 2 O 5 electrode, the polyvinylidene fluoride (PVDF) was completely dissolved in 1-methyl-2-pyrrolidinone (NMP) solvent firstly.And then, the grinded mixed powder comprising commercial V 2 O 5 powder and acetylene black was added into the above solvent, followed by an agitation at room temperature for 4 hours.Subsequently, the formed slurry was uniformly coated on the carbon paper and dried at 60 °C overnight to obtain the V 2 O 5 electrode.As additional information, the weight ratio of V 2 O 5 powder, acetylene black and PVDF was 8:1:1, and the mass loading of V 2 O 5 electrode was 3.3 mg cm -2 , acquired by electronic scales (BT25S, 0.01 mg).

=
, ZSFeCN, ZSFe and ZSI electrolytes: 0.1 M K 4 Fe(CN) 6 •3H 2 O was dissolved in deionized water with magnetic stirring, followed by addition of 2 M ZnSO 4 •7H 2 O and agitation at room temperature until homogenized, which was denoted as ZSFeCN.And the ZSFe and ZSI electrolytes correspondingly with 0.1 M FeSO 4 and 0.1 M mAh g −1 ), E (Wh kg −1 ) and P (W kg −1 ) are the specific capacity, specific energy density and specific power density of cells correspondingly, Δt (h) is the discharging time, I (mA) is the specific discharging current in GCD measurements and m (mg) is the mass loading of electrode. of a and b are adjustable parameters, i is CV response current, v is scan rates, k 1 and k 2 are correspond separately to the proportionality coefficients of capacitive and diffusion-controlled contribution.

Figure S2 .
Figure S2.XRD pattern of the V 2 O 5 sample.

Figure S3 .
Figure S3.(a) SEM image, (b) high resolution SEM image of the V 2 O 5 sample.

Figure S4 .
Figure S4.SEM selected-area elemental mapping images of V 2 O 5 sample.

Figure S5 .
Figure S5.(a) TEM image (the corresponding SAED pattern is inset) and (b) high resolution

Figure S6 .
Figure S6.GCD curves of V 2 O 5 //Zn batteries with different content of FeCN-CRC additive at 0.1 A g −1 .

Figure S8 .
Figure S8.Water-based angle contact test of V 2 O 5 in ZS and ZSFeCN electrolytes

Figure S11 .
Figure S11.The comparison of b values between ZS and ZSFeCN.

Figure S14 .
Figure S14.The relationship between current density and scanning rate at 0.02 V versus

Figure S15 .
Figure S15.Comprehensive performance comparison of ZSFeCN with previously reported

Figure S16 .
Figure S16.Photographs of ZSFeCN pouch cells powering and an electronic stopwatch.

Figure S17 .
Figure S17.GCD curves of ZSI at various current densities.