The use process of forklift lithium battery is the process of charge and discharge cycle, the size of charge and discharge current, the choice of cut-off voltage of charge and discharge and the way of charge and discharge are also very important to the cycle life of forklift lithium battery. Blindly increasing the working current of the battery, increasing the cut-off voltage of charging and reducing the cut-off voltage of discharging will degrade the battery performance.

Different electrochemical systems of forklift lithium battery charge and discharge cut-off voltage is different. In the charging process of forklift lithium battery, where the cut-off voltage of charging is exceeded, overcharging is considered to occur. K.M aher etc will LiCoO2 battery charge cut-off voltage set in turn from 4.2 V to 4.9 V, and after the experiment of the electrode material for X-ray diffraction and Raman spectra experiment, shows that graphite anode and cobalt acid lithium anode structure change happened, by testing different charge cut-off voltage electrode entropy change curve of different SOC, also found that the structural changes in the electrode material. When the forklift lithium battery is overcharged, excess lithium ions from the positive electrode will deposit or embed on the negative electrode, and the deposited active lithium is easy to react with the solvent and release heat to increase the battery temperature. The positive electrode is thermally decomposed to give off oxygen, which makes the electrolyte easily decomposed and generates a large amount of heat [25]. Overdischarge occurs when the discharge voltage of a lithium battery is lower than the cut-off voltage. In the process of over discharge, lithium ions will be excessively released from the negative pole, and it will be difficult to embed the lithium ions next time they are charged. When yu zhongbao et al. [26] overdischarged the battery with MCMB as the negative electrode and LiCoO2 as the positive electrode to 0 V, the copper foil collector fluid was seriously corroded and the negative SEI film was destroyed. The SEI film formed again had poor performance, which increased the negative impedance and enhanced the polarization. The discharge capacity and charging and discharging efficiency are greatly reduced in the cycle after the battery is discharged.

The discharge of 18650 lithium ion battery at different rates was studied. The results show that the battery capacity attenuation increases with the increase of charge discharge ratio. The capacity of LiCoO2/ graphene lithium ion battery with high cycle rate has been seriously attenuated. Through analysis, it is concluded that the main reasons for the serious capacity attenuation are the change of anode material structure and the thickening of anode surface film, which lead to the decrease of Li+ quantity and the blocking of diffusion channel. In the case of large current discharge, ions need to be quickly embedded and released from the positive and negative poles, and the reaction speed is very fast. Tang zhiyuan et al. [28] thought through the experimental analysis that: because the battery needs to release a large amount of capacity in a short time when discharging with a large current, the electrode reaction is rapid and violent, and the discharge process of some lithium ions has ended before it is too late to disembed or pass through the anode material. In addition, the battery lugs may fuse under high current conditions, and equipment components may be damaged.