Rechargeable Zinc-Electrolytic Manganese Dioxide (EMD) Battery with a Flexible Chitosan-Alkaline Electrolyte

Abstract

A high-performing flexible chitosan-based gel electrolyte with poly­(vinyl alcohol) (PVA) additive was prepared and swelled in varying concentrations of potassium hydroxide (KOH) solutions. A highest ionic conductivity of 457 mS/cm was recorded for the sample with a 2.1 swelling ratio, obtained by soaking in a 5 M KOH solution for 45 min. Stability test results demonstrated the prepared electrolyte to be strong and ductile along with stability under 50 °C and 2 V. Zn-EMD batteries were constructed with the prepared electrolyte using an optimized assembly technique employed to achieve good interfacial contact between the layers. Continuous charge–discharge tests were performed on the batteries at a current density of 0.1 A/g in specific limited and extended potential regions (low: 0.4–1.2 V and high: 0.4–1.6 V) to explore their performance and reversibility. Results indicated that the batteries cycled in the low region had higher capacity retention due to lower δ-MnO2 formations when compared to those in the high region cycling. To fully understand its performance capability, the battery was further tested extensively. Results indicated a good rate and initial bending performance of the battery with a maximum specific capacity of 310 mAh/g at 0.1 A/g. Additionally, the battery tested at 0.5 A/g showed an average specific capacity of 175 mAh/g over 300 cycles with a 96.5% Coulombic efficiency. Attaining energy densities between 150.4 and 252.4 Wh/kg (w.r.t. active cathode mass) is possible for these batteries, thus encouraging their use in varied applications. Utilizing chitosan gel electrolyte and limited voltage window testing, the prepared Zn-EMD alkaline batteries are among the first reported polymer-based alkaline electrolyte Zn rechargeable batteries with no cathode additives.

Flexible and Safe Additives‐Based Zinc‐Binder‐Free‐Hierarchical MnO2‐Solid Alkaline Polymer Battery for Potential Wearable Applications

“…Using this fabricated additives-based (MnO 2 +Co/Cu/Bi/ Bi+Cu) cathodes, cells were assembled and tested by using a previously developed {5}CP alkaline solid electrolyte (refer experimental section (1.2), Supporting Information) and zinc foil anode to examine their performance. [12] The cyclic voltammograms (CV) of the assembled Zn-MnO 2 cathodes with and without additives at a scan rate of 1 mV s −1 are shown in Figure 4c and Figure S4a-e in the Supporting Information. Two characteristic reduction peaks at 1.1 and 0.8 V corresponding to proton-insertion (Mn 4 + → Mn 3 + ) and the dissolution-precipitation reaction (Mn 3 + → Mn 2 + ) were observed for the pure MnO 2 cathode.…”

“…This was accomplished by adopting a limited voltage-window testing approach. [11,12] Though fair reversibility was achieved for flexible alkaline batteries; the restricted voltage window approach, limited electrical conductivity from the MnO 2 cathodes, and reduced active sites for reactions resulting from the presence of a binder and irreversible compound formations at cathodes have reduced the cathode material utilization, thus lowering the electrochemical performance of the cell (MnO 2 theoretical: 1-1.5 V; 617 mAh g −1 ). [12] Wielding the high theoretical performance of this chemistry, which stems from the active materials' ability to undergo a 2-electron (e-) step reaction, is paramount for use in applications.…”

“…[11,12] Though fair reversibility was achieved for flexible alkaline batteries; the restricted voltage window approach, limited electrical conductivity from the MnO 2 cathodes, and reduced active sites for reactions resulting from the presence of a binder and irreversible compound formations at cathodes have reduced the cathode material utilization, thus lowering the electrochemical performance of the cell (MnO 2 theoretical: 1-1.5 V; 617 mAh g −1 ). [12] Wielding the high theoretical performance of this chemistry, which stems from the active materials' ability to undergo a 2-electron (e-) step reaction, is paramount for use in applications. [10,[12][13][14][15] However, most times, only a single step discharge mechanism is obtained due to the electrochemical irreversibility of Mn x O y (Mn 2 O 3 , Mn 3 O 4 ) and ZnMn x O y (ZnMn 2 O 4 , ZnMn 3 O 7 ) precipitates resulting from the breakdown of MnO 2 and other side reactions during the second step (as shown in Equations section 2, Supporting Information).…”

“…[12] Wielding the high theoretical performance of this chemistry, which stems from the active materials' ability to undergo a 2-electron (e-) step reaction, is paramount for use in applications. [10,[12][13][14][15] However, most times, only a single step discharge mechanism is obtained due to the electrochemical irreversibility of Mn x O y (Mn 2 O 3 , Mn 3 O 4 ) and ZnMn x O y (ZnMn 2 O 4 , ZnMn 3 O 7 ) precipitates resulting from the breakdown of MnO 2 and other side reactions during the second step (as shown in Equations section 2, Supporting Information). [10,12,[15][16][17] These electrochemically inactive formations act as barriers on top of the active material leading to reduced active sites on the electrodes for further reactions to occur, thereby hampering reversibility and capacity.…”

“…[10,[12][13][14][15] However, most times, only a single step discharge mechanism is obtained due to the electrochemical irreversibility of Mn x O y (Mn 2 O 3 , Mn 3 O 4 ) and ZnMn x O y (ZnMn 2 O 4 , ZnMn 3 O 7 ) precipitates resulting from the breakdown of MnO 2 and other side reactions during the second step (as shown in Equations section 2, Supporting Information). [10,12,[15][16][17] These electrochemically inactive formations act as barriers on top of the active material leading to reduced active sites on the electrodes for further reactions to occur, thereby hampering reversibility and capacity. [15][16][17] Thus, it is necessary for large active area availability for better material utilization and reversibility even under two-step reduction to achieve better performance.…”