Design and Fabrication of an All‐Solid‐State Thin‐Film Li‐Ion Microbattery with Amorphous TiO 2 as the Anode

We have fabricated an all‐solid‐state thin film microbattery by using reactive radio frequency (RF) magnetron sputtering of the positive LiNi 1/3 Mn 1/3 Co 1/3 O 2 (LNMC) electrode at an elevated temperature, amorphous Li 3+ x PO 4− x N x (LiPON) electrolyte at room temperature, and in situ deposition of an amorphous titania (TiO 2 ) film below 200 °C. Electrochemical measurement of the TiO 2 half‐cell reveals a first discharge capacity of 102 μAh cm −2  μm −1 with 86 % capacity retention after 100 cycles. A capacity of 58 μAh cm −2  μm −1 from the LNMC thin film electrode can be achieved. The initial capacity of the TiO 2 /LiPON/LNMC full‐cell is as high as 52 μAh cm −2  μm −1 and 90 % capacity is retained after 400 cycles.