Thick-Film Cathode Based Solid-state Lithium Battery

The high energy density and high safety all-solid-state lithium batteries have catched focus of attention recently.Thick-film cathode based solid-state lithium battery combines the advantages of the all-solid-state thin film lithium battery and the bulk all-solid-state lithium battery.The convenient and efficient cast coating method is used to prepare the thick-film cathode,and magnetron sputtering and vacuum evaporation are used to prepare the ultra-thin electrolyte and anode.Thick-film cathode based solid-state lithium battery improves the low capacity of the all-solid-state thin film lithium battery,and the ultra-thin electrolyte and anode prepared by physical vapor deposition method overcome the shortcomings of excessively thick inorganic electrolyte layer and poor contact of interfaces in bulk all-solid-state lithium batteries.This work first optimizes the composition and surface structure of the thick-film cathode,then modifies the interface between the anode and electrolyte of thick-film cathode based solid-state lithium battery,finally proposes an organic-inorganic double-layer electrolyte composite structure to solve the interface stability problem between Polyethylene oxide（PEO）polymer electrolyte and high-voltage cathode.The specific research focuses are as follows:（1）Prepare four different compositions of thick-film cathode slurries and study the effect of each component on electrochemical performance.It was found that the thick-film cathode with a ratio of ferrous lithium phosphate（Li Fe PO₄,LFP）,carbon nanotubes（CNTs）,and solid polymer electrolyte（SPE）of 6:1:3 had the best electrochemical performance.At room temperature,its initial discharge capacity can reach 155 m Ah/g,and stable cycling for 100 cycles with 0.2 C.The addition of CNTs and SPE can form a continuous electron and ion conductive network in the cathode,making the thick-film cathode have excellent electrochemical performance in the all-solid-state battery.（2）Investigate the effect of active material loading on the electrochemical performance of all-solid-state batteries.Under low active material loading conditions,the utilization rate of the active material in cathode is above 90%.When the active material loading is greater than about 3.1 mg/cm²,due to the increase in ion transport distance inside the cathode,the active material far from the electrolyte side cannot participate in the electrochemical reaction in time,leading to a significant decrease in the utilization rate of the active material in the cathode.（3）During the cycling process,the all-solid-state thick-film lithium battery has a significant capacity decay due to the side reactions between the anode and electrolyte.Introducing a metal tin（Sn）buffer layer at the electrolyte-anode interface by magnetron sputtering methode to improves the cycling stability.At 60℃,the initial discharge capacity is 130 m Ah/g,and cycling more than 150 cycles with 0.2 C.The in-situ generated Li-Sn alloy between electrolyte and anode inhibits the occurrence of side reactions and induces the deposition of metallic lithium,thereby improving the long cycling performance of the battery.（4）The organic-inorganic double-layer electrolyte composite structure can solve the problem of irreversible capacity decay caused by Co⁴⁺and PEO between lithium cobaltate（Li Co O₂,LCO）cathode and SPE under high potential.The battery with double-layer electrolyte structure has an initial discharge capacity of 132 and 173 m Ah/g at the voltage range of 3.0-4.2 V and 3.0-4.5 V.After 100 cycles,the capacity retention rates are 90%and 87%,seperately.