Photo-enhanced All-solid-state Thin Film Lithium Batteries Based On Three-dimensional Molybdenum Oxide Thin Film Electrodes

All-solid-state thin film lithium batteries(TFBs)with the thickness of several micrometers are a typical class of power source for microelectronics.Their outstanding electrochemical properties,including high power density,ultralong cycle life,wide temperature range,high safety,and flexible configuration,are superior to those of the traditional lithium-ion batteries.Among the reported cathode materials for TFBs,some lithium-free transition metals oxides such as MoO₃and V₂O₅have been developed as the cathode materials for the first-generation TFBs,benefited from their high theoretical specific capacity.However,the inferior electrical conductivity and sluggish ionic diffusivity of these materials limit the thickness of cathode and the kinetics of charge transportation,resulting in unsatisfactory areal energy density and rate capability.Therefore,it is a great challenge to explore efficient strategies to optimize these electrodes.Aiming at this issue,research was carried out from two aspects in this thesis:Three-dimensional(3D)cathodes were constructed to increase the electrode/electrolyte interface and shorten the ion diffusion length.In this work,TFBs based on the 3D?-MoO₃nanowall array were successfully fabricated using the magnetron sputtering method.In comparison,the 3D-MoO₃based TFB significantly outperforms the 2D-MoO₃based TFB,exhibiting the large specific capacity(3D:280 m Ah g^-1at 50m A g^-1;2D:205 m Ah g^-1at50m A g^-1)and superior rate capability(3D:115 m Ah g^-1at 500m A g^-1;2D:85 m Ah g^-1at500m A g^-1).Based on above 3D-MoO₃based TFB,photo-assisted working mechanism was induced to promote the specific capacity and rate capability,which is a special working mode for energy storage system evolved from the integration of solar cells and energy storage devices.Given the similar thin-film configuration and matchable semiconductor-manufacturing process between the TFBs and solar cells,we attempted to modulate the electronic structure of?-MoO₃cathode by inducing photo illumination,which was also widely reported for the utilization in optoelectronic devices.In this work,a significantly promoted specific capacity of the 3D-MoO₃based TFB was achieved(from 155 to 225 m Ah g^-1at the current density of200 m Ah g^-1)under UV light illumination(380 nm).In addition,the charge/discharge rate was found to be dramatically increased via interaction with UV light.With the kinetic analysis and ex-situ characterization,it was revealed that ion diffusion ability and amounts of intercalated/de-intercalated lithium ions were promoted under illumination,demonstrating a new fast charging strategy.In conclusion,we report here that 3D configuration and illumination of a layered?-MoO₃cathode induces improved specific capacity and rate performance,benefiting from the optimized electrode/electrolyte interface and photo-modulated electronic structure of cathode material.These discoveries may lead to new fast rechargeable microbattery technologies for microelectronics.