Core-Shell-Structured Nanofibrous Membrane As Advanced Separator For Lithium-ion Battery

Separator,the core component of the Lithium ion batteries（LIBs）,has a great impact on the longevity and safety of the LIBs.The widely-used commerce separators have some deficiencies like bad thermal stability,electrolyte wettability and fading of the coated particles.Because of these disadvantages,the safe and efficient applications of the LIBs is limited.In this paper,the ceramic nanoparticles（SiO₂ or TiO₂）were encapsulated on the bacterial cellulose nanofibers via in-situ compositing method,and a high-performance nanofiber lithium ion battery separator with core-shell structure was prepared.The advantage of this nanofiber separator over commercialized separator Celgard 2325is mainly listed below:（1）The thermal stability of the BC/SiO₂ composite separator is better than Celgard 2325.After heating at 200℃for 3h,the size of BC/SiO₂composite separator was almost the same as before,while the Celgard2325 shrank into strip.The discharge capacity of the battery using BC/SiO₂ composite separator was 153 mAh g^-1 at 0.1C at 20℃,that was higher than the battery using the Celgard 2325.In addition,after 85cycles at 1C at 50℃,the BC/SiO₂ composite separator battery still retained a capacity of 90.7%,while the Celgard 2325 battery had only72.1%of its capacity.Consequently,the charge and discharge cycle performance of the BC/SiO₂ composite separator is better than that of the Celgard 2325 separator.（2）The electrolyte absorption rate of the BC/TiO₂ composite separator was 2.77 times that of the Celgard 2325 separator,and the contact angle for water and electrolyte of the BC/TiO₂ composite separator was much smaller than that of the Celgard 2325.So the wettability of BC/TiO₂ composite separator is better than the Celgard2325.After heating at 180℃for 1h,the size of BC/TiO₂ composite separator was almost the same as before,while the Celgard 2325 shrank into strip.Therefore,the thermal stability of the BC/TiO₂ composite separator is better.The discharge capacity of the BC/TiO₂ composite separator was 152.6 mAh g^-1 at 25℃and 0.1C,while that of the Celgard 2325 was only 148.3 mAh g^-1.In the rate charge-discharge test,the discharge capacity of BC/TiO₂ composite separator was higher than that of the Celgard 2325.Consequently,the charge-discharge cycle performance and the rate charge-discharge performance of the BC/TiO₂composite separator is better than of the Celgard 2325.