| Lithium-ion batteries(LIBs),which are new type of clean and efficient energy,have been widely used in 3C products.With the popularization of LIBs market applications,higher requirements are put forward for its safety and stability,so the all-solid-state batteries(ASSBs)appears.The perovskite-type solid electrolyte Li0.24La0.587 Ti O3(LLTO),which has a wide operating temperature and high total ionic conductivity,is of great research value.However,compared with organic electrolyte,its ionic conductivity needs to be further improved,which is the key to determine whether it can be applied.In this paper,pure LLTO,B-site(Al,Sn,Ta or W)doped LLTO and A&B-site(Ca&Ta or Ba&Ta)co-doped LLTO prepared by solid-state reaction method are the main research objects.XRD,SEM,Raman spectroscopy and XPS were used to characterize the phase,relative density,micromorphology and microstructure of specimens above.The electrochemical performance of LLTO electrolyte pellets were characterized,and the relationship between structure and electrochemical performance was established.Pure LLTO electrolyte pellets were prepared,and the preparation process parameters,micromorphology and electrochemical performance test methods were determined,which provided an experimental basis for doped specimens.The relative density of pure LLTO is up to 96.2%.It is proved that La-rich/poor layer structure exists in pure LLTO.Total conductivity is as high as 1.52 × 10–4S·cm–1,and the activation energy is 0.39 e V.Al or W(with small radii)doped LLTO were studied.XRD,SEM and electrochemical impedance spectroscopy were used to study the microstructure and electrochemical performance with doping amount as a variable.It is found that Al has the effect of stabilizing the LLTO cubic phase and is beneficial to the densification.In contrast,the relative density of W-doped LLTO is very low,only about 90%.However,no matter the Al or W doped specimens,the electrochemical performance is poor,and the total conductivity of them are only about 10–6–10–5 S·cm–1.The phase,structure and electrochemical properties of Sn and Ta(with a large radii)doped LLTO solid electrolyte as function of doping amount were studied and the corresponding relationship was established.It was found that Sn or Ta-doped LLTO sintered at 1350 oC for 12 h had high density(96.2%–97.9%)and high conductivity.The total conductivity of LLTTa0.04 O and LLTSn0.02 O were 4.09 × 10–4S·cm–1 and 2.98 × 10–4S·cm–1,compared with pure specimens,the total conductivity of the doped specimens has more than doubled.In addition,Sn or Ta doping can significantly reduce the activation energy,where the activation energy of LLTTa0.04 O is as low as 0.31 e V.The relationship between the structure and the total conductivity of the B-site doped LLTO was established.It was found that element with a larger radii doping can expand the Li+ transmission channel,improving the conductivity of LLTO.In contrast,element with a small radii doping is not conducive to the improvement of LLTO conductivity.Moreover,the increase in relative density,the decrease in the A-site ordering and the increase in the vacancy concentration of Li+ can effectively improve the total conductivity of LLTO.The phase and electrochemical properties of Ca&Ta co-doping and Ba and Ta double doping LLTO solid electrolytes were studied.Although the density of both is improved,Ba with a larger radius blocks the transport of Li ions,while Ca with a smaller radius reduces the transport channel of Li,so neither can further improve the total conductivity of LLTO. |
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