*Article* **A Hollow-Structured Manganese Oxide Cathode for Stable Zn-MnO2 Batteries**

**Xiaotong Guo 1, Jianming Li 2,\*, Xu Jin 2, Yehu Han 1, Yue Lin 3, Zhanwu Lei 4, Shiyang Wang 4, Lianjie Qin 1,\*, Shuhong Jiao 4 and Ruiguo Cao 4,\***


Received: 3 April 2018; Accepted: 27 April 2018; Published: 5 May 2018

**Abstract:** Aqueous rechargeable zinc-manganese dioxide (Zn-MnO2) batteries are considered as one of the most promising energy storage devices for large scale-energy storage systems due to their low cost, high safety, and environmental friendliness. However, only a few cathode materials have been demonstrated to achieve stable cycling for aqueous rechargeable Zn-MnO2 batteries. Here, we report a new material consisting of hollow MnO2 nanospheres, which can be used for aqueous Zn-MnO2 batteries. The hollow MnO2 nanospheres can achieve high specific capacity up to ~405 mAh g<sup>−</sup><sup>1</sup> at 0.5 C. More importantly, the hollow structure of birnessite-type MnO2 enables long-term cycling stability for the aqueous Zn-MnO2 batteries. The excellent performance of the hollow MnO2 nanospheres should be due to their unique structural properties that enable the easy intercalation of zinc ions.

**Keywords:** manganese oxide; hollow structure; multivalent intercalation; zinc ion batteries
