## 2 Experimental Method
### Test Electrical Performance  
#### 2.2.1 The Program Design of Cell Sample Test  
When accomplishing the electrical performance test of cells, internal resistance measurements are, in particular, very sensitive to electronic instrumentation and mechanical preparations; therefore, some precautions should be taken to produce consistent measurements throughout testing. A testing bench shown in Figure 1 is established; battery holders, cables or connectors are standard components of the battery management system. It is composed of a Battery Test System 4000 (BTS4000, NEWARE, Shenzhen, China) battery tester with eight independent channels, an intermediate machine, and a 64-bit host computer onto which a NEWARE BTS Software v7.5.6 and a MATLAB R2012a are installed. The battery tester is used to load the programmed current profiles on battery cells within a range of voltage of 0\(\sim\)10 V and a current of \(-\)6\(\sim\)6 A. The intermediate machine is mainly responsible for the network connection, receiving the control command from the host computer, controlling the lower battery cycler and uploading the real-time test data. The host computer is employed to control and monitor the cycler via Ethernet cables, as well as to store the voltage and current values acquired by sensors. Batteries, brackets, cables, or connectors, as shown in Figure 1, are standard components of the battery management system. The tested battery cells are Panasonic NCR18650 BE cylindrical cells (LiCoO\({}_{2}\) oxide) whose specifications mainly include the nominal capacity 3200 mAh, the operating voltage 3.7 V, the charging limit voltage 4.2 V, the discharge limit voltage 2.7 V and the maximum continuous discharging current 10 A. During the test, the battery current and the voltage values are recorded every second, while they are recorded every 10 ms during the PPC test. As for the vibrating table, 3 db/oct was applied in this experiment; the Switch-2 (SW-2) vibration controller and the MMF (Metra Mess- und Frequenztechnik in Radebeul e.K.) vibration accelerometer were also used. Based on the test bench, the detailed test steps about the electrical performance of cells are presented in Figure 2.  
Figure 1: Battery Test System 4000 (BTS4000) power battery testing bench.  
Figure 2: Schematic of electrical performance test process.  
In pre-test, from Figure 2, constant current and constant voltage (CC-CV) charge and CC-discharge are performed first in order to allow new cells to achieve a stable state of the performance; the test data will therefore be more accurate. Between the two steps, cells were allowed to stabilize during a rest period of 4 h [26]. It was identified within Ref. [21] that cells conditioned to 75% state of charge (SOC) displayed a greater tendency for electrical degradation; therefore, each cell was allocated a sample reference number, pre-conditioned to 75% SOC. In order to reduce the measurement uncertainty of capacity and DC resistance, the cells' characteristic values are used by the average of three measurement results.  
Post testing, if no significant mechanical damage or degradation (such as electrolyte leakage or external fatigue cracking) was observed on any of test samples after the vibration test, then the DC resistance, capacity, charge and discharge curve were measured at the environment temperature ranging from 25 \({}^{\circ}\)C \(\pm\) 3 \({}^{\circ}\)C.