Improvement Thick Electrodes by Double-Layer Coating Technology

Related articles mentioned that thick electrode technology still has a lot of problems:

• The coating is easy to crack;
• Uneven pores;
• Uneven stress distribution;
• Poor infiltration performance;
• High interface impedance and so on.

In this paper, we will analyze the improvement of double-layer coating technology for thick electrodes. (i.e., we need to think about how the dual-layer coating can alleviate these problems through the different material combinations of the base layer and the surface layer).

Lithium battery dual-layer coating technology is a different technology from the conventional single-layer coating process, which optimizes the electrode performance by coating different characteristics of the paste in layers.

The core of double-layer coating lies in the layered design of coating slurry formula, by adjusting the formula ratio, material ratio to improve the battery cell performance, the current double-layer coating technology of the upper and lower layers of the same level of density settings, in order to achieve the normal capacity to play.

I. Double-layer coating to improve the uneven stress of thick electrodes

Due to the inconsistency of the solvent evaporation rate in single-layer coating, it leads to the stress difference between the surface and bottom layers; and the inconsistency of the surface and bottom layers in the natural state of the binder further aggravates the phenomenon of uneven stress.

The stress can be physically or chemically dispersed by double-layering different different layers of the material function.

For example, the bottom layer may be designed to be highly bonded and flexible to absorb and buffer the volume change of the active material during charging and discharging, while the surface layer may focus on ion transport and mechanical support to prevent crack extension. (i.e., higher binder content in the bottom layer and more conductive agent content in the top layer)

In this way, after drying, the bottom layer has enough binder to enhance the bonding with the collector, so that the electrode can better transfer the stress to the collector when subjected to external forces or volume changes during the charge/discharge process, avoiding stress concentration and electrode dislodgement due to insufficient bonding, thus improving the uneven distribution of stress.

II. Double-layer coating to improve the porosity uniformity problem

Due to the effect of inconsistent solvent evaporation rate and particle weight influence, often thick electrodes have uneven porosity problems.

This can be mitigated by using a layered coating of large and small particles to make it uniform. For example, the top layer uses large particle material and the bottom layer uses small particle material. The particle size active material layer can form a relatively large ion transmission channel with high porosity, which facilitates the rapid diffusion of lithium ions, enabling the electrolyte to penetrate more fully into the electrode interior and improving the porosity uniformity inside the electrode. The small particle size active material layer can increase the contact area with the fluid collector and improve the electron conduction efficiency, and at the same time, its stacking will also form some smaller pores, which complement the pores formed by the large particle size active material, making the electrode from the fluid collector to the surface of the pore size distribution more reasonable, thus improving the uneven distribution of porosity.

III. Double-layer coating to improve the interface impedance problem of thick electrode

The impedance increases and the conductivity decreases due to the increase in thickness of thick electrodes and longer electrolyte infiltration.

It can be designed through the synergistic design of high electronic conductive paths in the bottom layer and high ion-permeable structures in the surface layer.

Summarize: double-layer coating technology can be used to solve some practical problems through a combination of different ratios, a combination of different materials, and the way, whether directly or indirectly, are more than one, because more than one of the reasons leading to the deterioration of performance. Therefore, it is necessary to carry out the layered design in a dialectical way.