J.X. Ma, S.H. Zheng,* L.P. Chi, Y. Liu, Y. Zhang, K. Wang, and Z.-S. Wu*

Advanced Materials, 2022, 34, 2205569.

DOI: 10.1002/adma.202205569 [PDF]

Rechargeable sodium ion micro-batteries (NIMBs) constructed using low-cost and abundant raw materialsinplanar configuration with both cathode and anode on the same[A1]substrate, hold promises for powering coplanar microelectronics, but are hindered by the low areal capacity owing to thin microelectrodes. Here,a prototype of planar and flexible 3D-printed NIMBs is demonstrated with three-dimensionally interconnected conductive thick microelectrodes for ultrahigh areal capacity and boosted rate capability.Rationally optimized 3D printable inkswith appropriate viscosities and high conductivityallowed the multi-layer printing of NIMB electrodes reaching a very high thickness of ~1200 μmwhile maintainingeffective ion and electron transfer pathways in them. Consequently, the 3D-printed NIMBs deliver superior areal capacity of 4.5 mAh cm^-2(2 mA cm^-2), outperforming the state-of-the-art printed micro-batteries. The NIMBs showed enhanced rate capability with 3.6 mAh cm^-2at 40 mA cm^-2and robust long-term cycle life up to 6000 cycles. Furthermore, the planar NIMB microelectrodes despite the large thickness exhibit decent mechanical flexibility under various bending conditions. This work opens a new avenuefor construction ofhigh-performance NIMBs with thick microelectrodescapable of poweringflexible microelectronics.