In recent years, with the increasingly fierce market competition, in order to improve the price competitiveness of products, some manufacturers have changed the grid production process to continuous casting and rolling to reduce the production cost of batteries through large-scale automatic mass production. The continuous casting and rolling process is a major innovation in the traditional "gravity casting" grid manufacturing process, the main purpose is to produce thin grids with high efficiency and low cost to meet the needs of large-scale production such as automobile starting batteries. But what problems does the continuous casting and rolling process bring?

1. Structural strength and corrosion resistance issues, which are the core defects of the process

Metal fibers are cut off:

The drawnet process is similar to "stretching" a sheet of metal into a mesh structure. This process causes the metal grains and fibers inside the grid ribs (grid skeleton) to be cut off laterally in the direction of the force.

vs. Gravity Casting:

In gravity casting, the grid is a complete, molded monolith cast by mold, and its metal fibers are continuous and therefore have higher mechanical strength and structural integrity.

Consequence:

Low mechanical strength:

Continuous casting and rolling grids are more "brittle" than gravity-cast grids of the same thickness and are more prone to breaking or deformation due to stress during assembly, handling, or battery use.

Decreased corrosion resistance:

The severed metal fiber edges and grain boundaries become the preferred channels and starting points for corrosion. During the battery's charge and discharge cycle, the positive grid will be in a strong oxidation environment, and corrosion will accelerate along these weak points, eventually leading to premature grid breakage and battery failure. This is a key factor limiting its cycle life.

2. Limitations of geometry and current distribution

Uniform grid shape:

The drawnet process can only produce regular, uniform diamond or square grids. It cannot "freely design the geometry and rib thickness of different areas of the grid" according to electrochemical needs, as is the case with gravity casting.

Non-optimal current distribution:

In battery operation, the distribution of current on the grid is uneven, and the current density is greater at the edge and lug connections. Gravity cast grids can optimize current distribution and reduce internal resistance and hot spots through "variable section design" (e.g., thicker near the lug and slightly thinner away from it). The grid cannot do this, resulting in relatively high internal resistance and uneven current distribution, affecting high-current performance and overall efficiency.

3. Limitations of alloy materials

Rely on low-antimony or lead-calcium alloys:

The continuous casting and rolling process requires the alloy to have good ductility and plasticity for rolling and stretching. Therefore, it is often used with "lead-calcium alloys" or "low-antimony alloys". These alloys, while maintenance-free for batteries, also pose well-known problems:

l  The "antimony-free effect" of lead-calcium alloys: it is easy to lead to the passivation of the anode plate, and the deep cycle performance is poor.

l  Early capacity loss: Lead-calcium alloy grids are more prone to a barrier layer between the interface with the active material, leading to a rapid early decline in battery capacity.

High antimony alloys cannot be used: Traditional gravity casting can use alloys with higher antimony content (such as 4%-6%), which can enhance the mechanical strength and casting performance of the grid and reduce the PCL effect, but will lead to more gas separation and maintenance. The drawnet process cannot use high-antimony alloys because of its brittleness and unsuitable for rolling and stretching.

4. Restrictions on the type of battery applicable

Due to the above strength, corrosion resistance and deep cycle performance problems, continuous casting and rolling grids are mainly used in "starting, lighting, ignition (SLI)" batteries that do not require high cycle life, that is, automotive starting batteries.

In application scenarios requiring deep discharge and long cycle life, such as:

l  power batteries for electric tricycles, forklifts, etc

l  Solar wind energy storage system

l  Uninterruptible power supply (UPS) and communication backup power supply

Traditional gravity cast grids, especially tubular positive plates, remain preferred due to their superior durability and deep cycle performance unmatched by continuous casting and rolling grids.

Summary

The continuous casting and rolling grid production process is an efficient technology created to meet the needs of a large-scale, low-cost market. Its core flaw lies in sacrificing the structural integrity and corrosion resistance of the grid, thereby limiting the battery's cycle life and deep cycle performance. Therefore, it and the gravity casting/tubular grid process are a trade-off between "efficiency and performance":

l  For cheap and large automobile batteries, choose continuous casting and rolling technology.

l  For durable, deep-cycle industrial batteries, choose gravity-cast or tubular cathodes.

In the future, with the increasing requirements for battery life and reliability, as well as the growing demand in emerging fields such as energy storage, the continuous casting and rolling process may face more challenges, but its dominance in the SLI battery field is still difficult to shake in the short term.