0 Introduction
Through decades of development and application, energy storage batteries have expanded beyond their role as mere reserve power sources. They are now widely utilized across various fields, often serving as primary energy providers in scenarios such as solar street lighting, telecommunications backup power, and residential power supply.This trend necessitates increasingly stringent performance requirements for energy storage batteries.
The anode format for energy storage batteries—the earliest produced and most widely applied in China—primarily consists of lead powder, sulfuric acid, water, graphite, acetylene black, lignin, humic acid, barium sulfate, and other swelling agents blended in specific mass ratios. This represents the mature, traditional lead-acid battery anode paste formulation. Different additives exert varying effects on battery performance. Graphite alone can significantly increase plate porosity, affecting battery low-temperature performance and discharge capacity. However, as graphite content in the paste varies,
the plate appearance, battery capacity, low-temperature performance, and cycling performance all show distinct differences.
1. Experiment
Graphite was added to the negative electrode paste at mass fractions relative to lead powder of 0, 1%, 2‰, 3‰, 4‰, and 5%.Using the same batch of grids,13Ah negative plates with varying graphite contents were produced on the same production line. The strength, loose powder content,and free lead content of the negative plates with different graphite contents were compared. These 13Ah negative plates were formed in dedicated formation tanks at a current density of 0.2–0.5 A per gram of active material. Subsequently, these formed negative plates were assembled with positive plates from the same batch into 6-CNF-100 batteries. Comparative testing was conducted on battery discharge consistency, low-temperature performance, cycling performance, and plate appearance changes after 300 cycles.
2 Experimental Results and Discussion
2.1 Physicochemical Properties and Drop Strength of Negative Plates
Table1 shows that negative plates fabricated from lead paste with varying graphite contents exhibit no significant differences in w(Pb) and moisture content.However, their drop strength (5 forward and 5 reverse drops from a 1.5m height) demonstrates marked variations. As graphite content increases, the drop failure rate of the electrodes rises significantly. When graphite content ranged from 0 to 3%, the change in drop failure rate was relatively gradual. Graphite content exceeding 3% adversely affected plate strength, leading to increased scrap rates. Plates with 5% graphite exhibited a markedly elevated drop failure rate, indicating weaker bonding strength between lead pastes within the plate. Such plates demon strated a high scrap rate, resulting in significant waste of manufactur ing costs.
| Main physical and chemical properties of the negative electrode plate | ||||
| The content of graphite | w(Pb) | w(H,O) | Drop rate/ % | Photo after the drop |
| 0 | 3.5 | 0.22 | 0.35 | |
| 1 | 3.9 | 0.25 | 0.31 | |
| 2 | 3.3 | 0.30 | 0.39 | ① |
| 3 | 3.2 | 0.29 | 0.45 | ② |
| 4 | 3.9 | 0.21 | 0.88 | |
| 5 | 3.1 | 0.19 | 1.57 | ③ |
① ② ③
2.2 Appearance of plates
Under the condition of relative change in the amount of graphite added to the lead paste, the surface appearance of the negative plate after charging and forming is shown in Figure 1. From Figure 2, it can be seen that the surface of the plate with a graphite content of 3% is basically normal, and the surface of the plate with a graphite content of 4% shows a slight peeling phenomenon, while the surface of the plate with a graphite content of 5% shows a serious peeling phenomenon.
2.3 Charging capacity of batteries
The charging acceptance performance of batteries with different graphite content was tested according to the standard GB/T22473.1- 2021. As shown in Figure 3, the charging acceptance ability of the battery increased with the increase of graphite content. This is because graphite not only acts as a swelling agent to form crystal nuclei, but also forms a conductive network that can promote the in-depth progress of the charging reaction, so the charging acceptance ability of the battery is improved.