With the widespread use of power tools, batteries lithium-ion batteries at high magnification using attention more and more. Rate characteristics of batteries, a battery research. Rate characteristics of batteries with a number of factors: (1) is negative electrode materials solid diffusion process, (2) is negative, the electrochemical process, (3) electrolyte system, migration and the ability to proliferation (4) E Battery strength. For a specific system, to understand the factors those influence the rate characteristics of the main reasons for the improved rate characteristics of its great importance. Vostro 1310 battery Vostro 1320 battery
Electrochemical simulation is an important means of various processes [1-6]. With the help of literature, using digital analysis to establish procedures for the specific battery system, numerical simulation reveals a different process to the impact of battery capacity.
1, mathematical model
1.1 Assumptions of the model and description of the equation
To facilitate the model, the following assumptions:
(1) collector with infinite conductivity;
(2) is a film negative electrode, the equation can be described Newman;
(3) documents the positive and negative is supposed to be central to the spread of the spherical particles according to Fick’s law;
(4) dilute solution of electrolyte in accordance with the theoretical description of the behavior;
(5) for the insulation system; Vostro 1400 battery Vostro 1500 battery
According to Bulter-Volumes and Fick’s law, describe the basic equations see [1].
1.2 The model parameters
The simulation in this way the battery is produced by rolling are extremely Shijiazhuang Bai LiCoO2 site is extremely negative Shanshan CMS, Zhangjiagang Guotai Huarong electrolyte 1M LiPF6/EC + DMC (1:1).
2 Results and discussion
Results 2.1 Model prediction and experimental
Figure 1 shows where different discharge rates the capacity of testing and comparing the results of the simulation. In the case of a low current volume changes (<2C), more slowly, in large current circumstances, the ability to change rapidly. In the case of low current experimental and simulation results match well, and the magnification of the case, and test data, test results over the simulation, which is due to: (a) if high current density, local areas of high concentration of electrolyte will be diluted theoretical assumptions about the need to make some changes, (2) for high current density, the battery may be the situation internal heat, resulting in the system is no longer an adiabatic system. But the overall test results are more compatible with the simulation shows that the numerical model and the parameters used with good adaptability. Vostro 1510 battery Vostro 1520 battery
2.2 The distribution of the concentration on the discharge capacity
Figure 2 shows the rate characteristics of different circumstances, the model of concentration over time within the battery. discharge end of the green line, where the image gradient of concentration. 3C and 4C in the battery to discharge when the behavior in time with the discharge of the electrolyte cathode near the collector close to the lithium ion concentration near 0, ie, in the case of the discharge rates high, then the solution phase was almost diffusion limited (migration) (in accordance with this model of the battery case, must be between 2C and 3C), because this part of the solution phase Li + concentration is very low, the active substance can not respond fully, leading to a reduced capacity to more post-3C quick. In addition, in the case of the discharge current, the battery will heat the whole, leading to the solution phase diffusion rate, so the actual concentration gradient lithium-ion batteries can be smaller than those calculated. apple MacBook 13-inch unibody battery apple MacBook 15-inch unibody battery
2.3 great piece on the distribution of current density in the discharge capacity
Figure 3 for the model of positive and negative pole on the chip distribution of current density. 3C discharge case shows, the solution phase near the cathode current collector part of the Li + is close to 0, leading to the discharge end portion of the cathode active material of the current density is also low and the outer casing over the current density. Depending on the results, the maximum current density is equivalent to 12C, the actual current density 4 times. 2C discharge in the case, the distribution of the product, the maximum current density is almost the 3C. If not, if it is 2C or 3C and discharge current density is relatively uniform. This shows that, with the rate of increase, especially after more than 2C, the current density distribution is very uneven, it is high current capacity decreases rapidly one reason. apple MacBook Air 13-inch battery
3 Conclusion
In this paper, the model with experimental data better, and can be used to predict changes in the capacity of the battery to the different lens, and reveals the various processes within the battery. According to the model reveals the results of testing the battery in case of high prevalence, the capacity has decreased mainly due to phase diffusion limited solution, resulting in some smart, can not be completely discharged positive active material caused. Vostro 1700 battery