Lithium Ion Battery Built-in Micro Sensor Preparation And Performance Study

Lithium-ion battery is a very complex energy storage system involving multi-field coupled electrochemical and physical processes.As lithium-ion batteries are widely used in portable devices,electric vehicles,aerospace and other fields,their safety issues are becoming more and more prominent.In order to monitor,evaluate and control battery safety,this thesis develops and designs a micro sensor inside the battery to realize real-time monitoring of the internal temperature and pressure of the battery.The implantation of the sensor has almost no negative impact on the electrical performance of the battery.The specific research contents are as follows:First,to place the sensor inside the battery,a flexible printed circuit（FPC）-based anode current collector was designed and fabricated in this work.Integrate the micro sensor on the sensing circuit of the FPC negative current collector,and use Polyimide glue to protect the sensor.Further,the negative electrode material is coated on the negative electrode current collector integrated with the micro sensor,and the lithium battery with the internal pressure/temperature sensor is assembled with the diaphragm and the positive electrode stack.The FPC current collector integrates the sensor and the negative electrode of the battery,which avoids the increase of the contact distance between the positive and negative electrodes caused by the traditional direct insertion sensor,which leads to the degradation of the battery capacity and rate performance.Secondly,on the basis of the FPC negative current collector,the built-in pressure and temperature sensors of the battery based on the DF9-16 piezoelectric patch sensing unit and the PT1000 thermal resistance patch sensing unit were prepared respectively.Performance was characterized and analyzed.Through the free fall of the weight to hit the sensor,the voltage signal generated by the DF9-16 pressure sensor has a linear relationship with the mass of the weight and the height of the free fall.CV tests show that the implantation of the DF9-16 pressure sensor does not cause electrochemical side reactions inside the battery.The battery with the internal integrated DF9-16 pressure sensor is charged and discharged with a current of 0.5 C/0.5 C for 20 cycles,and the discharge capacity retention rate is close to 90%.Between 0 and 120℃,the temperature has a good linear relationship with the resistance of the PT1000 temperature sensor.After the battery is short-circuited,the PT1000 temperature sensor can monitor the temperature status inside the battery in real time.The PT1000 temperature sensor array can monitor and locate the temperature in real time.The CV test shows that the implantation of the PT1000 temperature sensor array does not cause electrochemical side reactions inside the battery.The battery has a discharge capacity retention rate of89% after 20 cycles of charge and discharge at a current of 0.5 C/0.5 C.The capacity retention rate of the battery is close to 90% when discharged at a high current of 2 C,which fully proves that the implantation of the PT1000 temperature sensor array has little negative effect on the electrochemical performance of the battery.Finally,a combined pressure/temperature sensor based on PVDF-TrFE piezoelectric and pyroelectric films was integrated inside the battery,and the sensor performance and the electrochemical performance of the battery were characterized and analyzed.The built-in sensor of the battery based on the PVDF-TrFE film can simultaneously monitor the pressure and temperature changes inside the battery.The PVDF-TrFE thin-film sensor integrated inside the battery generates-1.9,-2.4,-4.8,and-8.2 m V piezoelectric pulse signals when the battery is subjected to a force of 4 N,6 N,8 N,and 10 N,respectively.When the battery is bulging,the PVDF-TrFE thin film sensor integrated inside the battery generates a-3.5 m V piezoelectric pulse signal.When the temperature suddenly increased（1.3℃）,the PVDF-TrFE thin film sensor generated a 125 μV pyroelectric pulse voltage signal.When the temperature increased by 285℃,the PVDF-TrFE thin film sensor generated a 2.25 m V pyroelectric pulse signal.Further,the response signals of piezoelectric and pyroelectric can be screened by oscilloscope and peak splitting software,and the pressure and temperature signals can be separated.After 100 cycles at 0.5 C/0.5 C,the battery with the PVDF-TrFE thin film sensor integrated inside showed a discharge capacity retention rate of 85.24%.The discharge capacity retention rates of the batteries at 0.5,1,and 2 C were 100%,97.32%,and 90.6%,respectively,relative to the discharge capacity at 0.2 C.The electrochemical performance of the battery with the PVDF-TrFE thin film sensor integrated inside is close to that of ordinary lithium batteries,indicating that the PVDF-TrFE thin film sensor can not only monitor the internal pressure and temperature changes in real time,but also the implantation of the sensor has negligible impact on the battery.