| Lithium-ion batteries continue to improve their performance in terms of power characteristics,energy characteristics,cycle life and safety,making lithium-ion power batteries gradually replace power batteries such as lead-acid batteries and nickel-hydrogen batteries,and are widely used in electric vehicles.However,the charge and discharge performance,cycle life and safety of lithium-ion battery are sensitive to temperature,so maintaining the charge and discharge of lithium-ion battery in a suitable temperature environment is to ensure the normal,safe and efficient operation of the electric vehicle.Therefore,in view of the sensitivity of the comprehensive performance of lithium-ion batteries to temperature environment,it is necessary to design a battery pack/module thermal management system solution with high efficiency and fast response.Understanding the instantaneous thermal characteristics of lithium-ion batteries is a prerequisite for fast and precise control of the battery pack/module temperature environment.To effectively predict the instantaneous thermal characteristics of lithium-ion battery in actual work,it is necessary to study the heat generation,heat transfer and heat dissipation of lithium-ion batteries,and analyze the temperature distribution of the battery in the time domain and space domain.The existing research shows that the lithium ion power battery in the actual working process,due to the difference in internal structure and structure heat generation,the temperature field distribution of the battery surface is not uniform.For a battery module consisting of several lithium-ion battery cells,the influence of the non-uniformity of the surface temperature field distribution of the battery cells on the instantaneous thermal characteristics of the module battery under normal charging and discharging conditions can be studied.A reference to the system thermal management scheme for fast and precise control of module temperature.In this paper,a 18650 type ternary lithium battery for a certain type of vehicle is used as the research object.From the study of the thermal characteristics and heat generation law of the uneven surface temperature distribution of the lithium ion battery unit,the structure and heat generation of each heat generating part inside the battery are deeply understood.Characteristics and their relative positions,and establish a simulated physical model that can effectively predict the temperature field distribution inside and outside the battery;apply the obtained battery cell simulation model to the battery module,and convect the lithium ion battery modules in different arrangements.The temperature field under liquid cooling conditions was simulated to investigate the influence of the difference of heat source of the battery structure on the temperature field distribution and instantaneous thermal characteristics of the module battery.The main research content of this paper can be summarized as:1)Study the thermal characteristics and heat generation law of uneven surface temperature distribution of lithium ion batteries.Through the experiment of the surface temperature thermal characteristics of the battery,the distribution characteristics of the battery surface temperature field during the discharge process of the battery cell were investigated.It was found that the surface temperature of the battery in the continuous discharge process was in the axial direction,and the surface temperature of the cylinder > the surface temperature of the negative electrode > The surface temperature of the positive electrode;in the circumferential direction,the temperature on the side of the busbar side of the cylindrical surface is higher than the temperature on the other side.Then,this phenomenon is explained from three aspects: the internal structure of the battery cell,the heat generation and heat transfer characteristics of the internal structure of the battery;2)The actual physical model of the internal structure of the battery is obtained by disassembling the battery cell,and the heat source of the main heat generating parts inside the battery cell is independently considered by using the distributed parameter battery heat generation model,and the battery can be used for simulating the battery.A simulation model of the temperature field distribution of the outer surface of the battery during discharge.The results show that the simulation data fits well with the experimental test data,indicating that the simulated physical model and simulation method of the lithium-ion battery cell established in this paper can be used to simulate the surface temperature field distribution when the battery cell is discharged.3)Study the distribution characteristics of the temperature field of the module battery under no cooling conditions.In this paper,the distribution characteristics of the battery cell temperature field and the different battery structure layout schemes for the module battery without cooling are investigated.It is found that the aggregation effect of the battery makes the surface temperature of the module battery rise sharply compared with the battery cell,the temperature difference increases,and the temperature uniformity index decreases.The different structural arrangement of the battery is for the battery surface of the module battery under different discharge rates.The average temperature,maximum temperature difference,and temperature uniformity are all affected,and this characteristic may be amplified in a battery pack/module composed of multiple batteries.4)Study the instantaneous thermal characteristics of the module battery under liquid cooling.The module battery was thermally managed by providing a cooling plate at both ends of the battery.As a result,it was found that the liquid cooling scheme arrangement of the two ends of the lithium ion battery can better reduce the temperature of the battery surface of the module battery under high rate discharge.However,the unevenness of the surface temperature distribution of the battery is increased.Further study on the instantaneous thermal effects of the battery in a variety of cold plate inlet flow and cooling abrupt conditions,the results show that the module battery has ultimate cooling capacity and cooling hysteresis,and the maximum cooling flow and cooling hysteresis of the liquid cooling module are proposed.Time,this result provides reference data needed for feed forward control of a battery pack/module thermal management scheme with feed forward control.According to these studies,it is found that the simulation method and physical model used in the thermal state simulation of lithium ion power battery can accurately simulate the temperature field distribution of the outer surface during battery discharge,and apply the simulation method and model of single cell to the module battery.In the study of the instantaneous thermal characteristics during the discharge process,it was found that the aggregation effect of the battery,the different structural arrangement of the battery cells and the liquid cooling conditions have a great influence on the temperature rise,temperature difference and temperature uniformity of the module battery.Further research has found that the module battery has limited cooling capacity and cooling hysteresis under liquid cooling and cooling conditions.This transient thermal effect of the module battery can be used to guide the battery pack/module thermal management system with precise,efficient and fast response.The design of the program. |
PDF Full Text Request