## 3 Results and Discussion
### Mechanism of the Effect of Adding Carbon Black on the Negative Plate  
Based on the above research results, a model that can extend the service life of the battery by adding carbon black is proposed. This model can better explain the surface reaction of the battery negative plate when the batteries of e-bikes are charged and discharged in deep cycle duty under 100% DoD conditions. During charging, small lead sulfate crystals with high solubility can be reduced to lead. The large PbSO\({}_{4}\) crystals with poor solubility can hardly be reduced and recrystallized into larger lead sulfate particles on the surface of the negative plates [7; 32; 39]. As is well known, acetylene black and carbon black are small spherical structures. When acetylene black (Figure 7a) and carbon black (Figure 7b) are added as negative additives, point-to-point contact will be formed between  
Figure 6: Diagram of the relationship between water loss and the number of cycles. carbon particles and PbSO\({}_{4}\) particles and acetylene black particles may be independently dispersed on the negative plate to form conductive channels. For carbon black, the main factor influencing the conductive properties of carbon black is its structure, such as the degree of branching of carbon black. High-structure carbon black has a more developed chain structure than aggregates of low structural carbon black. It is possible that carbon black particles with high SSA are in contact with each other to form a continuous bead-like conductive network structure, while the low SSA carbon black forms a discontinuous chain structure due to the larger particle size. The less contact sides the carbon particles have between each other, the worse the charge transport and the electrical conductivity, so high SSA carbon black is more favorable for the diffusion of the electrolyte from the surface to the inside of the plate and the formation of small-sized lead sulfate crystals with high solubility [23; 40]. Therefore, the high SSA carbon black additive can better inhibit the growth of the lead sulfate crystal on the negative plate and prolong the cycle life of the battery. [PERSON] [41] proposed a model for the parallel mechanism of charge in which the electrochemical reaction process of the lead negative electrode occurs on both the surface of Pb and carbon black particles during the cycling of batteries under 100% DoD conditions. The electron migration diagram of Pb and carbon interface in negative plates is presented in Figure 7c. With the progress of the reaction, the PbSO\({}_{4}\) crystals grow continuously to form a rough and dense irreversible PbSO\({}_{4}\) layer on the surface of Pb and the barrier layer of PbSO\({}_{4}\) not only hinders the ion migration, but also amplifies the charge transfer resistance (R\({}_{1}\)) at the interface of Pb/H\({}_{2}\)SO\({}_{4}\)[15; 41]. However, the PbSO\({}_{4}\) barrier layer is not formed at the C/H\({}_{2}\)SO\({}_{4}\) interface because the mesopores of carbon material construct the channel of ion diffusion and migration, thus the resistance (R2) of ions passing through the C/H\({}_{2}\)SO\({}_{4}\) interface  
Figure 7: **(a,b)** Schematic diagram of acetylene black and carbon black on the negative plate under 100% DoD conditions, respectively. **(c)** Schematic diagram of ion migration through the Pb and carbon interfaces in the negative plate. (R\({}_{1}\) and I\({}_{\text{Pb}}\) are the resistance and current of ions passing through the interface of Pb/H\({}_{2}\)SO\({}_{4}\), respectively. R\({}_{2}\) and I\({}_{\text{C}}\) are the resistance and current of ions passing through the interface of C/H\({}_{2}\)SO\({}_{4}\), respectively.) is much smaller than that of R\({}_{1}\). Although CB1, CB2 and CB3 batteries have the same proportion of carbon black, CB3 batteries have carbon black that is evenly dispersed on the negative electrode surface compared to the other two types of batteries and its effect as an ion transport channel is greatly increased.