Nanocellulose is used to prepare zinc ion flexible batteries

Compared with commonly used lithium-ion batteries of organic electrolytes, rechargeable batteries of water electrolytes are receiving increasing attention due to their low manufacturing cost and high safety. Metal zinc has high electrochemical stability in water electrolytes and can be used directly as the anode of zinc and zinc. Zinc can achieve two electrons participating in electrochemical reactions, with a higher theoretical specific capacitance (820 mAh g − 1 and 5855 mAh cm − 3) and a lower redox potential ( − 0.763 V vs standard hydrogen electrode). Zib has the advantages of safety, low cost, high energy density, etc., and is expected to become a high-efficiency energy storage device for the next generation of portable electronic devices.

1. Flexible electrode

The solid flexible aqueous solution ZIB was prepared CNF-based flexible gel electrolytes have high ionic conductivity. When the power density is 0.16 W g using zinc-grown graphite paper as the anode and nanopolyaniline- nanocellulose paper as the cathode. − 1, the energy density of this ZIB is 117.5 mWh g − 1. It also exhibits good cycle stability, with a capacitance retention rate of up to 84.7% over 1000 cycles.

More importantly, after 1,000 mechanical bending cycles, the specific capacity retention rate is still around 91%. As shown in FIG. 17a, Yi et al. use high-strength, lightweight, low-cost, and sustainable cellulose yarns as a solid flexible substrate for the cathode (polyaniline) and anode (metal zinc). When the power density is 0.16 kW kg - 1, the energy density of the fiber optic cell is 153.2 Wh kg - 1, and when the high power density is 6.5 kW kg - 1, the energy density remains at 61.1 Wh kg - 1. At the same time, the fiber cell has excellent cycle stability (91.9% for 1000 charge and discharge cycles) and high flexibility (97.5% for 1000 bending cycles).

2. Flexible electrolyte/diaphragm

Zhao et al. reported flexible BCNF/PVA composite hydrogel electrolytes (BPCEs) for flexible zinc-air batteries. By introducing BC microfibers , the mechanical properties of PVA films are improved. BPCE shows excellent toughness and mechanical strength thanks to the novel seepage bearing dual network. By adding 6 wt% BC, the elongation of the 6-BPCE film was doubled and the tensile strength was nine times higher. Compared with aqueous alkaline electrolytes, batteries using 6-BPCE membranes have higher stability and superior rechargeability. By designing dual network alkali-resistant hydrogel electrolytes, the team developed fibrous (500% stretchable) and flat (800% stretchable) zinc-air batteries. In dual network hydrogel electrolytes, sodium polyacrylate (PANa) chains contribute to the formation of soft domains. The hydroxyl neutralized carboxyl group and cellulose as potassium hydroxide stabilizers greatly improve the alkali resistance of the battery. The obtained fibrous zinc-air battery with super-extensibility has a high power density. Furthermore, after stretching to 500% of the original length, the power density increased slightly. A similar phenomenon occurs with flat zinc air batteries stretched 800%. Thanks to the advantages of high flexibility and alkali-resistant hydrogel electrolytes, these devices have slightly increased power density after stretching to 500% of the original length.

In summary, zinc anode using modified nanoporous nanocellulose- based composites helps maintain structure stability and reduce volume changes. Nanocellulose-based composite materials act as buffer layers to significantly inhibit hydrogen evolution and zinc corrosion. Nanocellulose-based composites used in zinc cathode materials can act as surface coatings to protect the cathode from structural degradation and dissolution. To integrate new functions in existing systems, further exploration and improvement are required from the perspective of polymer chemistry, so that the electrolyte has the ideal characteristics that meet practical applications. Further research on simplified machining techniques, novel cathodes and mechanisms will enable flexible high-performance ZIB.