# Coupled Biphasic NaMnO2 Cathode and Ti3C2 MXene Anode with Complementary Charge-Storage Kinetics for Aqueous and Non-aqueous Sodium-Ion Hybrid Energy Storage

## TL;DR

A new sodium-ion hybrid battery combines a NaMnO2 cathode and MXene anode to deliver high performance in both aqueous and non-aqueous systems.

## Contribution

The paper introduces a sodium-free hybrid system with complementary charge-storage mechanisms for enhanced energy and power density.

## Key findings

- The hybrid system achieves 90 W/kg energy density and 610 W/kg power density in aqueous electrolytes.
- In non-aqueous electrolytes, it reaches 360 W/kg energy density and 970 W/kg power density.
- The system retains 97% and 88% capacity after 1000 cycles in aqueous and non-aqueous electrolytes, respectively.

## Abstract

A metallic sodium-free
hybrid electrochemical system has been developed
by coupling a biphasic birnessite-type NaMnO2 cathode with
a multilayer Ti3C2T
x
MXene anode, exhibiting complementary and cooperative electrochemical
behavior. The orthorhombic/monoclinic NaMnO2 structure
enables stable Na+ intercalation/deintercalation, while
Ti3C2T
x
provides
fast, surface-driven pseudocapacitive charge storage with favorable
interfacial kinetics. This combination offers kinetic complementarity
between diffusion-controlled and surface-dominated processes, leading
to efficient charge balancing and enhanced rate performance. Assembled
coin cell devices exhibit outstanding rate capability and cycling
stability in both aqueous (Na2SO4) and non-aqueous
(NaPF6 in EC/DMC) electrolytes with a higher voltage window
for enhancing energy density. Energy and power densities reach 90
and 610 W/kg in the aqueous system, and 360 and 970 W/kg in the organic
one, with 97 and 88% capacity retention after 1000 cycles, respectively.
The demonstrated universality of this electrode pairing establishes
a versatile, safe, and sustainable strategy for high-performance sodium-ion
energy storage beyond metallic sodium systems.